A 
TEXT-BOOK . 
medical physics 
FOR THE USE OF STUDENTS AND PRACTITIONERS 
OF MEDICINE. 
PROFESSOR OF CHEMISTRY' AND PHYSICS IN THE MEDICAL DEPARTMENT OF THE UNIVERSITY' OF NEW YORK, 
JOHN C. DRAPER, M.D., LL.D., 
AND OF NATURAL HISTORY' AND PHY'SIOLOGY' IN THE COLLEGE OF THE CITY OF NEW Y'ORK 
AUTHOR OF “A TEXT-BOOK ON ANATOMY, PHYSIOLOGY, AND HYGIENE J ” AND 
“ PRACTICAL LABORATORY COURSE ON MEDICAL CHEMISTRY.” 
WITH THREE HUNDRED AND SEVENTY-SEVEN ILLUSTRATIONS. 
PHILADELPHIA: 
LEA BEOTHEES & CO. 
1885. Entered according to Act of Congress in the year 1885, by 
LEA BROTHERS & CO., 
In the Office of the Librarian of Congress at Washington. All rights reserved. 
DOENAN, PRINTER. PREFACE. 
The fact that a knowledge of Physics is indispensable to a 
thorough understanding of Medicine has not yet been as fully 
realized in this country as in Europe, where the admirable 
works of Desplats and Gariel, of Robertson, and of numerous 
German writers, constitute a branch of educational literature 
to which we can show no parallel. A full appreciation of 
this, the author trusts, will be sufficient justification for placing 
111 book form the substance of his lectures on this depart- 
ment of science, delivered during many years at the Univer- 
®ity of the City of Yew York. 
Broadly speaking, this work aims to impart a knowledge 
of the relations existing between Physics and Medicine in 
their latest state of development, and to embody in the 
pursuit of this object whatever experience the author has 
gained during a long period of teaching this special branch 
°f applied science. In certain cases topics not strictly em- 
braced in the title have been included in the text—for ex 
ample, the directions for section-cutting and staining; and 
m other instances exceptionally full descriptions of apparatus VI 
PREFACE. 
have been given, notably of the microscope; but in view of 
the importance of these subjects, the course pursued will 
doubtless be approved. Attention may be called to the para- 
graph headings and italicized words, which suggest a system 
of questions facilitating a review of the text. 
In conclusion, the author will feel that his labor has not 
been in vain if the work should serve to call deserved 
attention to a subject hitherto slighted in the curriculum of 
medical education. 
JOHN C. DRAPER. 
Medical Department oe the 
University oe the City oe New York. 
June 1; 1885. CONTE N T S. 
PART I. 
MATTER. 
SBC TlO N I. 
PROPERTIES OF MATTER. 
INTRODUCTION. 
PAGE 
derivation of physics—Eolation to metaphysics—Eolation to mathematics— 
Eelation to chemistry—Eelation to mechanics—Medical physics—-Per- 
ception of ph3’sical phenomena—Divisions of physics—Matter defined 35-39 
CHAPTER I. 
Subdivisions of matter—Mechanical subdivision—-Particles—Minute living 
organisms—Subdivision by solution-—-Chemical subdivision—Atom and 
molecule defined—Origin of the idea of atoms—Cohesion—Effects of 
heat and pressure on matter—The molecules do not touch—Motion 
among molecules—Theory of the structure of matter—Delative sizes of 
molecules and interstices—Estimation of actual sizes of molecules and 
interstices—lmperfection of so-called vacua—Omnipresence of matter 39-45 
STRUCTURE OH CONSTITUTION OP MATTER. 
CHAPTER 11. 
CHAPTER 11. 
ULTIMATE COMPOSITION OF MATTER. 
Elements and compounds defined—Theory of the oneness of matter—Hy- 
drogen the original element—Nature of atoms . . . 46-53 CONTENTS. 
CHAPTER 111. 
GENERAL PROPERTIES OE MATTER. 
; PAGE 
Indestructibility and transmigration of matter—Extensibility and impene- 
trability—Gravity and weight—Centre of gravity—Stability of position 
in animals—The balance—Weights and weighing—Essentials in a good 
balance—Method of double weighing—Density or specific gravity—Mo- 
bility—lnertia—Porosity—Compressibility—Elasticity—Divisibility 54-63 
SECTION 11. 
SOLID MATTER. 
CHAPTER IV. 
CHAPTER IV. 
GENERAL CHARACTERS OF SOLIDS. 
The physical forms of matter—Chemical divisions of matter—Eorm is fixed 
—Resist compression—Extent of volume variation—Density—Hydro- 
static balance—Specific gravity by volumetric method—Nicholson’s hy- 
drometer—Specific gravity of powders—Specific gravity of bodies soluble 
in water—Bodies lighter than waters—Table of specific gravities—A 
divided solid does not reunite ...... 64-70 
CHAPTER V. 
CHAPTER V. 
Crystallized and amorphous—Hardness—Fragility—Malleability—Ductility 
—Tenacity—Elasticity—Contractility—Elasticity of compression—Elas- 
ticity of flexure—Elasticity of torsion—Pliancy—Opacity, transparency, 
color—Building materials—Hypothetical constitution of solids . 70-80 
SPECIAL PROPERTIES OF SOLIDS. 
SECTION 111. 
SECTION 111. 
LIQUID MATTER. 
. CHAPTER VI. 
GENERAL AND SPECIAL PROPERTIES OF LIQUIDS. 
Form not fixed—Resist compression—Compressibility—Elasticity—Porosity 
—Volume variations—Density or specific gravity—Table of specific 
gravities—Reunite behind a dividing solid—Hypothetical constitution— 
Liquidity and viscosity—Assume spheroidal state . . . 81-86 CONTENTS. 
IX 
CHAPTER VII. 
HYDROSTATICS. 
PAGE 
Hydrostatics defined., Pascal’s law—Hydrostatic bed—Hydrostatic test for 
steam boilers—Action of Pascal’s law in the body—Vertical downward 
pressure—Vertical upward pressure—Lateral pressure—Equilibrium of 
floating bodies—Stability of floating bodies—Hydrostatic test in infanti- 
cide—Evidence of death by drowning—Equilibrium of a liquid in com- 
municating vessels—Natural springs—Wells and sewage—Artesian wells 
—Equilibrium of two liquids of different densities—Pressure on bottom 
of a vessel—Heterogeneous liquids—Spirit level . . . 87-99 
CHAPTER VIII. 
CHAPTER VIII. 
Baume’s hydrometer—Urinometer—Lactometers, vinometers, salimeters— 
Densimeter—Alcoholometer of Guy Lussac—Alcohol in wine and beer— 
Post-mortem detection of alcohol ..... 100-104 
HYDROMETERS. 
CHAPTER IX. 
HYDRODYNAMICS. 
Definition—Theorem of Torricelli—Course of stream from lateral opening— 
Height of stream from vertical opening—Form and quantity of efflux— 
Influence of tubes on efflux—Action of elastic ajutages—Movement of 
liquids in tubes—Form of falling stream—Movement in inclined tubes— 
Hydraulic tourniquet—Velocity in open channels—Transporting power 
of flowing water—Shoals and sewage—Sewage and malaria—Formation 
of waves—Sea waves—Measurement of waves—Resistance of fluids to 
moving objects—Mechanics of circulation of the blood . . 105-115 
CHAPTER X. 
HYDRAULICS. 
Definition—Earliest devices for raising water—Pulley wells—Archimedes’s 
screw—The Persian wheel—The siphon—The flexible siphon—The in- 
termittent siphon—Pumps and valves—Lift pump—Force pump—Hy- 
draulic ram—Water wheels—The turbine—Centrifugal pump—Mate- 
rials for hydraulic engineering—Sewage in houses—Utilization of sewage 
—Marsh draining and malaria ...... 115-184 X 
CONTENTS, 
S E C TlO N IV. 
GASEOUS MATTER. 
CHAPTER XT. 
GENERAL AND SPECIAL PROPERTIES OE GASES. 
PAGE 
General observations regarding gases—Form not fixed—Gases have weight— 
Reunite behind dividing solid—Hypothetical constitution of gases— 
Yapors—Determination of density—Relation of density to combining 
equivalent in gases—Compressibility—Expansibility—Elastic force— 
Elasticity ........ 185-142 
CHAPTER XII. 
CHAPTER XII. 
PNEUMATIC APPARATUS. 
Generation of gases—Collection at pneumatic trough—Pouring—Faraday’s 
tube receiver—Gases arrange themselves according to density—Col- 
lecting gases by displacement—Washing and drying gases—The aspi- 
rator—Compression air-pump—Life and condensed air—Exhaustion 
air-pump—Life and rarefied air—Mercury pump—-Bunsen’s filter pump 
—Limit of vacuum—Vacua by chemical agents . . , 143-156 
CHAPTER XIII. 
General properties—Composition of air—Height of the atmosphere— 
Atmosphere presses downwards—Air presses in all directions—Action of 
THE ATMOSPHERE. 
lift-pumps explained—The pipette—The cupping-glass—lntroduction of 
air into the lungs—Gases and principle of Archimedes—Balloons—Re- 
cent balloon ascents—Balloon traffic—Resistance of air to moving body 
—Parachute—Rate of movement into a vacuum—Cannon reports and 
thunder ......... 156-172 
CHAPTER XIV. 
BAROMETRY. 
Galileo’s explanation—Torricelli’s experiment—Pascal’s experiment—Pres- 
sure of the atmosphere—Cistern barometer—Fortin’s barometer—Siphon 
barometer—Wheel barometer—Glycerine barometer—Errors in barome- 
tric reading—Barometric variations—Mean barometric heights—Cause 
of barometric variations—Barometric variations and the weather—Ba- 
rometer and the winds—Barometer and the death rate . 172-183 CONTENTS. 
XI 
CHAPTER XV. 
MEASUREMENT OF PRESSURES AND ALTITUDES. 
B , , _ paof, 
°J e s or Mariotte’s law—Open compression manometer—Closed compres- 
sion manometer—Exhaustion manometer—Equality manometer—Ex- 
haustion water-valve—Aneroids—Determination of altitude by aneroid 
or barometer—Error in barometric determination of altitude—The ba- 
rometer in mines—Pressure and solubility of gases—The windmill— 
Conveyance of germs by air ...... 183-193 
CHAPTER XVI. 
PHYSIOLOGICAL AND THERAPEUTICAL EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
Composition of blood—Hemoglobin —Divisions of physiological effects of 
pressure—Tension of oxygen or other gas respired—Diminution of pres- 
sure below one atmosphere—Mai des Montagues—Symptoms of Mai des 
Montagues—Theoretical explanations of Mai des Montagnes—Theory 
of M. Jourdanet—Balloon sickness—Bert’s rarefaction cylinders—Air 
m caves—Death from diminished air pressures—lncrease of pressure 
above one atmosphere—Respiration of pure oxygen—Physiological ac- 
tion of moderately condensed air—Action of oxygen under high tension 
Cxygen poisoning—Relation of animal tissues to oxygen—Death from 
increased pressure—Therapeutical effects of respiring oxygen—Thera- 
peutical uses of compressed air—Hygienic management of compressed 
air Impurities in compressed air—Effects of decompression—Nature 
and treatment of decompression accidents—Relation of barometric varia- 
tions to natural history—Bert’s resume of his results . . 193-215 
SECTION V. 
SECTION V. 
ULTRA-GASEOUS OR RADIANT MATTER. 
CHAPTER XVII. 
CHAPTER XVII. 
GENERAL AND SPECIAL PROPERTIES OF RADIANT MATTER. 
Idea of radiant matter descended from Faraday—Crooke’s argument for 
radiant matter—Crooke’s explanation of the kinetic theory of gases— 
Action of radiometer explained—Extent of mean free path of the mole- 
cules in radiant matter—Radiant matter exerts phosgenic action where 
it strikes—Proceeds in straight lines—lntercepted by solid matter casts 
a shadow—Radiant matter striking a solid produces change therein—It 
exerts mechanical action where it strikes—ls deflected by the magnet— 
Radiant matter produces heat when its motion is arrested—The molecule 
the true matter—The absolute vacuum tube .... 216-227 CONTENTS. 
PART 11. 
ENERGY. 
SE CTIO N I. 
POTENTIAL ENERGY ATTRACTION, 
CHAPTER I. 
PAGE 
Ideas regarding energy—Potential and kinetic energy—Transformation of 
energy—Conservation of energy—Degradation of energy—Dissipation 
of energy—Subdivisions of energy—ldeas regarding force . . 281-239 
ENERGY AND FORCE. 
CHAPTER 11. 
ATTRACTION. 
Molar attraction. Gravity—Molecular attraction—Adhesion of solid and 
solid—Cements—Soldering—Adhesion of solid and liquid—Drops and 
minims—Solution—Adhesion of solid and gas . . . 239-246 
SECTION 11. 
KINETIC ENERGY—MOTION. 
CHAPTER 111. 
GENERAL PHENOMENA OF MOTION. 
Motion and repose—Velocity—Trajectory" and law of movement—Kinds of 
movement—Newton’s three laws of motion .... 247-251 
CHAPTER IV. 
MEASUREMENT AND REPRESENTATION OF ENERGY. 
The unit of time—The unit of space—Units of weight and mass—Represen- 
tation of forces by lines—The parallelogram of forces—Momentum and 
measure of force—Work and unit of work—Measurement of energy 251-256 CONTENTS. 
CHAPTER V. 
PAGE 
ectilinear motion—Falling bodies—Sand-glass—Path of projectiles—Colli- 
sion—Impact and transmission of impulse—Reflection of rectilinear 
motion—Oscillating or reciprocating motion—The pendulum—The me- 
tronome—The balance wheel—Rotation—Molar motions typical of intra- 
molecular movements—Centrifugal and centripetal forces or motions— 
Applications of centrifugal force ..... 256-268 
VARIETIES OF MOLAR MOTION. 
SEC TION 111. 
MACHINES AND INSTRUMENTS. 
CHAPTER VI. 
CHAPTER VI. 
Relations of machines to force—The three orders of levers—Estimation of 
power in the action of levers—The wheel and axle—The inclined plane 
The wedge—Scalpels and their management—The screw—The pulley 
—Friction ........ 269-277 
SECTION I V. 
TRANSLATORY MOLECULAR MOTION, 
CHAPTER VII. 
MOLECULES OF TWO MEDIA, ONE SET MOVING. 
Varieties of molecular motion—Divisions of translatory molecular motion— 
Phenomena of capillarity—Circumstances influencing capillarity—Sur- 
face tension of liquids—Causes of capillarity—Laws of capillarity— 
Inclined surfaces and capillarity—Capillarity and floating bodies—Im- 
bibition and absorption—Filtration—-Draper’s steam exhaust for filtra- 
tion—Special filtration—Absorption of gases by solids—Disinfection by 
charcoal explained—Occlusion—Transpiration of liquids and gases . 278-290 
CHAPTER VIII. 
CHAPTER VIII. 
MOLECULES OF TWO MEDIA, BOTH SETS MOVING. 
Solution and mixture contrasted—Diffusion between liquids or solutions— 
Crystalloids and colloids—Amoeboid movements imitated—Diffusion be- 
tween gases—Absorption of gases by liquids .... 290-295 XIV 
CONTENTS. 
CHAPTER IX. 
PAGE 
Establishment of continuous flow in capillary tubes—The endosmometer— 
Osmosis—Dialysis—Applications of dialysis—Osmosis of gases through 
porous media—Hygienic importance of osmosis of gases—Osmosis of 
MOLECULES OF MANY MEDIA, A PORTION MOVING. 
gases through metals—Vitiation of air by stoves Capillarity and 
chemi5m......... 295-303 
CHAPTER X. 
PHYSIOLOGICAL APPLICATION OP TRANSLATORY MOLECULAR MOTION. 
Ascent of sap in trees—Absorption in animals—Harvey’s mechanical theory 
of circulation-—lnsufficiency of simple mechanical theory of circulation 
—Draper’s physico-chemical theory of circulation—The physics of respi- 
ration ......... 303-310 
SECTION V. 
ACOUSTICS. 
CHAPTER XL 
Definition and province of acoustics—Vibrations described—Relations of 
vibrations and undulations Transverse vibrations Longitudinal 
vibrations Circular or elliptical vibration Undulations and their 
graphic representation—Undulations in space—Undulations in tubes— 
Reflection of waves—lnterference of waves .... 311-319 
VIBRATIONS AND UNDULATIONS. 
CHAPTER XII. 
Noise and sound—Origin of sound—Sounds from inanimate nature—Propa- 
gation of sound—Manner of propagation of sound—Dissipation of 
sound—Conduction of sound—The stethoscope and auscultation—Velo- 
city of sound in gases—Velocity of sound in liquids—Velocity of sound 
GENERAL PROPERTIES OP SOUND. 
in solids—Reflection of sound from plane surfaces—Reflection of sound 
from curved surfaces—Refraction of sound—Polarization of sound . 819-335 
CHAPTER XIII. 
CHAPTER XIII. 
SONOROUS BODIES. 
Vibrating strings—Laws of transverse vibrations—Nodes and loops—Vibrat- 
ing rods—Vibrating plates and bells—Vibrating membranes—Vibrating 
columns of air—Reed instruments—Singing flames—Sympathetic vibra- 
tions—Sensitive flames—Production of abnormal sounds in the chest 335-345 CONTENTS. 
XV 
CHAPTER XIV 
SPECIAL PROPERTIES OF SOUND. 
pecial properties of sounds—lntensity of sounds—Diminution in intensity 
of sounds—lncrease in intensity of sounds—Reinforcement of sounds— 
Resonance and percussion—Interference of sound undulations—Pitch or 
tone Savart’s wheel—The siren—The graphic method—Limits of per- 
ception of vibrations—The octave—The gamut and chromatic scale— 
Musical notation—Number of vibrations to each tone—Harmonics, 
overtones—Quality or timbre—Wave-lengths of sounds in air . 346-360 
CHAPTER XV. 
Helmholtz’s resonators—Konig’s manomctric flames—Konig’s sound ana- 
lyzer Synthesis of sounds—Results of Helmholtz’s researches—Lis- 
sajou’s method—lllustration of Lissajou’s curves—Leon Scott’s phonau- 
tograph—Edison’s phonograph—Acoustic attraction and repulsion . 360-370 
ANALYSIS AND SYNTHESIS OF SOUNDS. 
CHAPTEE XVI. 
CHAPTER XVI. 
PHYSIOLOGICAL PRODUCTION AND PERCEPTION OP SOUND. 
oice in the lower creatures—The human voice—The larynx and sons:— 
The mouth and speech—Ventriloquism—Simple ear of lower creatures 
The ear in man—The external ear—The middle ear—The internal 
ear—The audiphone—The photophone .... 370-378 
SECTION VI. 
SECTION VI. 
OPTICS. 
CHAPTER XVII. 
CHAPTEE XVII. 
THEORIES AND SOURCES OF LIGHT. 
Optics and light defined—Theories of light—The ether—Vibrations in the 
ether, their rate—Sources of light—The sun—Energy of solar action, its 
cause—Stars, planets, and satellites—Comets—Atmospheric sources of 
light Phosphorescence Fluorescence—Calorescence—lncandescence 
and oxyhydrogen lights—Electric arc and light—Motion and light— 
Combustion or chemical action—lllumination by gas flames—Forms of 
gas burners—lllumination by flames from fluids—lllumination by flames 
from solids—Constitution of flame—Light and life . . . 379-398 XVI 
CONTENTS. 
CHAPTER XYIII. 
page 
Transparent and absorbent media—Propagation of light in homogeneous 
medium—Pay, pencil, and beam—Shadow and penumbra—lmages from 
small openings—"Velocity of light—Qualities of light—Photometers— 
The candle and other units—Relative intensities of different sources of 
light ......... 398-408 
TRANSMISSION, ABSORPTION, AND INTENSITY OP LIGHT. 
CHAPTER XIX. 
CHAPTER XIX. 
REFLECTION AND MIRRORS. 
Law of reflection from polished surfaces—Reflection from unpolished sur- 
faces—lntensity of reflected light—Mirrors and process for silvering 
them—lmages from plane mirrors—Virtual and real images—Multiple 
images from plane mirrors—Deviation by rotation of mirror—Applica- 
tions of plane mirrors—Spherical concave mirrors—Formation of images 
by spherical mirrors Spherical aberration and caustics—Parabolic 
mirrors Cylindrical mirrors, anamorphosis Application of curved 
mirrors ......... 408-422 
CHAPTER XX. 
REFRACTION AND PRISMS. 
Refraction illustrated—Refraction power of different media—Laws of single 
refraction Index of refraction Critical angle. Total reflection 
Atmospheric refraction and mirage—Media with parallel surfaces—The 
prism—Track of ray in prism. Angle of deviation—Minimum devia- 
tion—Reflecting prisms ...... 422-430 
CHAPTER XXI. 
CHAPTER XXI. 
COMPOSITION OF LIGHT. 
The prismatic spectrum—Normal dispersion—Abnormal dispersion—Spec- 
trum colors are simple, and of different refrangibility—The rainbow— 
Newton’s theory of composition of white light—Recomposition of white 
light—The achromatic prism—Heat in prismatic spectrum—Chemical 
action in prismatic spectrum—Maxima of energies in prismatic spectrum 
—Light, heat, and chemical action are modes of vibration . . 430-437 
CHAPTER XXII. 
CHROMATICS. 
Monochromatic light—Color of opaque bodies. Pigments—lridescence 
Color of transparent bodies—Colors of mixed powders—Mixtures of 
colored lights—Methods of mixing colored lights—Complementarv 
colors—The primary color sensations—Accidental color images—Color- 
blindness—Color and musical pitch . ... 437-445 CONTENTS. 
XVII 
CHAPTER XXIII. 
LENSES. 
. PAGE 
* nneties of lenses—Parts of spherical lenses—Forms of spherical lenses— 
Action of convex lenses explained—Action of concave lenses explained 
Principal and conjugate foci of convex lens—Action of convex lens 
on convergent rays—Determination of foci of lenses—Optical centre. 
Secondary axes—lmages formed hy convex lenses—lmages formed by 
concave lenses—Spherical aberration—The coma—Chromatic aberration 
—Achromatic lenses—Aberration by curvature of field—Depth of focus 
—Stops and diaphragms ...... 445-460 
CHAPTEE XXIY. 
CHAPTER XXIY. 
FORMATION OF IMAGES BY REFRACTION. 
The camera lucida—The camera ohscura—The magic lantern—The solar 
microscope—The oxyhydrogen lantern—Photo-electric lantern—The 
megascope ........ 460-466 
CHAPTER XXY. 
CHAPTEE XXY. 
Parts of the eye—The mechanical mechanism—The optical mechanism— 
The sclerotic and cornea—Crystalline lens—The humors of the eye— 
The iris—The second tunic or choroid—The third tunic or retina— 
Terms applied to optical mechanism—Accommodation—Normal action 
of optical mechanism—Abnormal action of optical mechanism—Specta- 
cles—Binocular vision—The stereoscope—Size and distance of objects 466-477 
THE EYE AND VISION. 
CHAPTEE XXYI. * 
THE MICROSCOPE AND THE TELESCOPE. 
The simple microscope—The compound microscope—Parts of modern micro- 
scope—Dry objectives—lmmersion objectives—Choosing and testing 
objectives—Eye-pieces—Tube and accessories—The body—The stage— 
Focussing apparatus—The stand or foot—lllumination—Simple axial 
illumination Diaphragms Condensed axial illumination Oblique 
illumination—Eeflected illumination—Polarized illumination—Sources 
of illumination—Augmentation of magnifying power—Measurement of 
magnifying power—Care of microscope—Care of the eyes—Errors in 
interpretation—Non-vital motion—Binocular and chemical microscopes 
—Fixation of images—Preparation of slides and covers—Preparation 
of objects—Hardening and section-cutting—Simple microtome—lnjec- 
tion—Staining—Chemical testing—Preservative medium—The micro- 
scope and disease germs—Telescope . . . . . 477-519 
B CONTENTS. 
CHAPTEE XXVII. 
PAGE 
Double refraction—-Ordinary and extraordinary ray—lnterference of light— 
Diffraction Diffraction spectra Plane polarization by reflection— 
Angle of polarization—Polarization by single refraction—Polarization 
by double refraction Polarizing instruments—Theory of polarized 
light—lnterference of polarized light—Depolarization—Action of thin 
films—Production of colored rings by polarized light—Detection of mole- 
cular change by polarized light—Elliptical and circular polarization— 
Theory of elliptical and circular polarization—Production of circularly 
polarized light—Production of elliptically polarized light—Production 
and theory of rotatory polarization—Coloration by rotatory polarization 
—Rotatory power of liquids—Saccharimeter .... 520-586 
DOUBLE REFRACTION, INTERFERENCE, DIFFRACTION, AND POLARIZATION. 
CHAPTEE XXYIII. 
CHAPTEE XXYIII. 
SPECTROSCOPE AND SPECTRUM ANALYSIS. 
The spectroscope—Parts of single prism spectroscope—Slit and collimator— 
Prism and telescope—Scale of collimator—Sources of light—Multiple 
prism spectroscope—Direct vision spectroscope—Grating spectroscope— 
Continuous spectra—Bright-lined spectra—Banded spectra—Nebular 
spectra—Gaseous absorbent spectra—Solar spectrum—Ultra-violet solar 
spectra—lnfra-red solar spectra—Wave-lengths of lines of spectra—Use 
of solar lines as a scale—Atmospheric spectrum lines—Planetary and 
stellar spectra—Absorbent spectra by colored liquids—Absorbent spectra 
by colorless liquids—Blood spectra—Spectra of bile and Pettenkoffer’s 
fluid—Spectra of wine and ale. Abnormal spectra . . . 536-550 
SECTION VII. 
HEAT. 
CHAPTER XXIX. 
THEORIES AND EFEECTS OF HEAT. 
Theories of heat—Sources of heat—Effect of heat on physical properties— 
Effect on composition—Expansion—Expansion of solids—Expansion of 
liquids—Maximum density—Expansion of gases—Winds—Effect on 
measures of time and quantity ...... 551-561 CONTENTS. 
XIX 
CHAPTER XXX. 
MEASUREMENT OF HEAT. 
_ PAGE 
anctoiio’s thermometer—Differential thermometer—Liquid thermometers 
Calibering the tube—Preparing and filling—Graduation of the ther- 
mometer—The scale—Medical thermometers—Registering thermometer 
Displacement of zero—Absolute zero—Remarkable temperatures— 
Pyrometers—Breguet’s thermometer—What thermometers measure 561-567 
SPECIFIC HEAT AND HEAT OF FORM. 
CHAPTER XXXI. 
CHAPTER XXXI. 
Heat required to warm a substance—The calorimeter—Determination of 
specific beat—Calorie and thermal unit—Fusion and solidification— 
ariation in fusion and solidification—Change of volume in fusing— 
Annealing—Latent heat—Latent heat and climate—Freezing mixtures 
—Crystallization ....... 567-573 
CHAPTER XXXII. 
CHAPTER XXXII. 
VAPORIZATION. 
Temperature of formation—Properties of vapors—Causes influencing vapor- 
ization—Evaporation in vacuo—Vaporization a cooling process—lce 
machines—Effect of vapors on climate—Vapors and furnace heat— 
Elastic force of vapors—High-pressure engines . . . 573-579 
CHAPTER XXXIII. 
CHAPTER XXXIII. 
Instantaneous condensability—Low-pressure engines—Pulse glass, cryo- 
phorus, and water-hammer—Fog. Cloud. Meteorology—Rain—Rain 
and miasm—Snow and hail—Distillation .... 579-584 
LIQUEFACTION. 
CHAPTER XXXIV. 
CHAPTER XXXIV. 
Hygrometry—Mason’s hygrometer—Method of taking dew-point—Dew- 
point and sensation of temperature—Moisture exhaled from the lungs— 
Moisture exhaled from the skin—Effect of exercise on insensible perspi- 
ration ......... 585—589 
HYGROMETRY. 
CHAPTER XXXV. 
CHAPTER XXXV. 
EBULLITION. 
Phenomena of ebullition—Variations in boiling point—lnfluence of reduced 
pressure—Elevation and boiling point—lnfluence of elevation of pres- 
sure—Papin’s digester—Spherical state—Effect of presence of salts— 
Application of heat in cooking . . . . . 590-595 XX 
CONTENTS. 
CHAPTER XXXVI. 
SJ U JL lUi1! XJ 'JVii T iiv/xivii . 
PAGE 
Metals the best conductors—Different metals conduct differently—Action of 
gauzes on flames—The Davy lamp—Gas furnaces—Structure of flame— 
Blowpipe flames—Conduction by textile fabrics. Liquids are poor con- 
ductors—Application in kerosene furnace—Convection of heat—lso- 
thermal lines—lsland and continental climate—Non-conduction of dew 
—Gases the worst conductors ...... 595-602 
CONDUCTION AND CONVECTION. 
CHAPTER XXXYII. 
RADIATION AND TRANSMISSION. 
Radiant heat passes in straight lines—Reflection of heat—lnfluence of sur- 
face and color—Emission of heat not superficial—Absorption of heat— 
Transmission of heat—Theory of exchanges of heat—Formation of dew 
—Application of radiant heat in cooking .... 602-606 
CHAPTER XXXVIII. 
CHAPTER XXXYIII. 
ANIMAL HEAT. 
Source of heat in the body—Cooling process—Hot and cold blooded animals 
—Effects of exposure to cold—Distribution of plants and animals—Loss 
of heat by the body ....... 607-613 
CHAPTER XXXIX. 
CHAPTER XXXIX. 
"VENTILATION AND METHODS OE "WARMING. 
Action of artificial lights—Action of respiration—Object of ventilation 
Removal of foul air—Yentilation of sick rooms—Warming of houses— 
The charcoal brazier Open fireplaces—The stove Steam-pipes in 
rooms—Hot-air furnaces—Steam furnaces—Supply of vapor—Weather 
strips—Joule’s mechanical equivalent of heat . . . 618-610 
SECTION VIII. 
SECTION VIII. 
ELECTRICITY. 
HISTORY. THEORIES. LAWS. 
CHAPTER XL. 
CHAPTER XL. 
First observation in friction electricity—Extended to other bodies—Con- 
ductors discovered—Du Faye’s theory—Franklin’s theory—Electric 
laws—Pyroelectricity—Electricity by pressure and cleavage . 620-624 CONTENTS. 
XXI 
CHAPTER XLL 
MACHINE AND EXPERIMENTAL ILLUSTRATIONS. 
, PAGE 
arts of electric machines—Cleaning and preparing the plate—The spark in 
air Ihe broken spark—Electric aura—Discharge in vacuo—Charging 
the body—Attraction and repulsion illustrated—Electric bells—Electric 
vane—Conduction illustrated—The electrophorus—Hydroelectric ma- 
rine ......... 624-631 
CHAPTER XLII. 
CHAPTER XLII. 
MEASUREMENT AND DISTRIBUTION. 
Electroscopes—Electrometers—The torsion electrometer—The charge is on 
the surface—Distribution depends on form—Action of points—Dissipa- 
tion of charge ........ 631-635 
CHAPTER XLIIL 
CHAPTER XLIII. 
INDUCTION. 
Induction described—Bound electricity—Attraction and repulsion explained 
Pail experiment—lnduction passes through glass—Specific inductive 
power—The Leyden vial—Dissected Leyden vial—Penetration of the 
charge. Residuum—Leyden batteries—Discharge through a card— 
Lichtenherg’s figures—Holtz machine—Condensers—Rate of passage— 
Duration of spark Mechanical effects—Physical effects—Chemical 
effects—Physiological effects ...... 635-646 
CHAPTER XLIV. 
CHAPTER XLIY. 
Lightning identical with machine electricity—Electric state of atmosphere 
—Variation in amount and character—Origin of atmospheric elec- 
tricity—Lightning—Thunder—Return shock—Lightning-rod—Aurora 
borealis ......... 647-651 
ATMOSPHERIC ELECTRICITY. 
SECTION IX. 
SECTION IX. 
DYNAMIC ELECTRICITY. 
CHAPTER XLV. 
Electrodynamics defined—First observations—Volta’s pile—Origin of voltaic 
electricity—The simple cell—The electric current—Electromotive force 
—Quantity and intensity—Enfeeblement and local action . . 652-656 
THE YOLTAIC CELL. XXII 
CONTENTS. 
CHAPTER XLYI. 
PAGE 
BATTERIES AND THEIR PHYSICAL EFFECTS. 
Single fluid batteries—Double fluid batteries—Care of batteries—Measure- 
ments of electricity—Methods of coupling—Dry piles—Faure’s accu- 
mulator—The spark—The arc—lgnition effects—Deflagration . 657-662 
CHAPTER XLVII. 
Decomposition of water—The voltameter—Decomposition of cupric sulphate 
—Decomposition of sodium chloride—Electrochemical theory—Polari- 
zation of electrodes—Electrometallurgy—Electroplating . . 662-667 
VOLTAIC DECOMPOSITIONS. 
CHAPTER XLYIII. 
CHAPTER XLYIII. 
THERMOELECTRICITY. 
Heat in obstructed conductors—Thermoelectric batteries—Thermoelectric 
series—Other batteries ....... 667-669 
SECTION X. 
SECTION X. 
, MAGNETISM. 
CHAPTER XLIX. 
CHAPTER XLIX. 
HISTORY. LAWS. DISTRIBUTION. 
Natural magnets—Artificial magnets—Compound magnets—Polarity law of 
attraction and repulsion—Magnetic distribution—Magnetic metals— 
Magnetic induction ....... 670-673 
CHAPTER L. 
METHODS OF MAGNETIZING. TERRESTRIAL MAGNETISM. 
Magnetizing by single touch—Magnetizing by separate touch—Magnetizing 
by double touch—Magnetizing by the earth’s action—The power of 
magnets—Mayer’s floating magnets—Medical application of magnets— 
The earth’s action directive—Declination—The compass—Astatic needle 
—Dipping needle ....... 673-678 CONTENTS. 
CHAPTER LI. 
ELECTROMAGNETISM. 
Oeisted s experiments—Galvanometers—Rheostats—The long compensator— 
heatstone’s bridge—Electromagnets—Electromagnetic motors Cost 
of magnetic motors—Electric bells and clocks—The Morse telegraph— 
dhe needle telegraph—Reactions of currents upon currents and mag- 
nets Solenoids—Why the compass needle points north Paramag- 
netism—Diamagnetism—Diamagnetic illustrations—Action of magnet 
on polarized light ....... 678-689 
CHAPTER LIE 
CHAPTER LIE 
FARADAIC OR INDUCED CURRENTS. 
Currents induced by magnets—Currents produced by electromagnets—ln- 
ductorium—Experiments with inductorium—Geissler’s tubes—The tele- 
phone—Dynamoelectric machines ..... 689-694 
SJECTI ON XI. 
ELECTROBIOLOGY. 
CHAPTER LIII. 
CHAPTER Dili. 
Electricity in plants—Electric fishes—Apparatus for investigating muscle 
currents—Muscle currents at rest—The frog galvanoscope—Active 
muscle currents—Nerve currents ..... 695-697 
ELECTROPHYSIOLOGY, 
CHAPTER LIY. 
CHAPTER LIY. 
General effects of electricity—Static electricity—Constant primary current— 
Galvanocautery Electrolysis Galvanopuncture—Nerve stimulation 
by constant current—lntermittent primary current—Alternating second- 
ary or Faradaic current—Faradization localized—Electrotonus—Appli- 
cation for resuscitation—Application in diagnosis . . . 698-715 
ELECTROTHERAPY. 
Index ....... . . 717 LIST OF ILLUSTRATIONS. 
FIG. 
PAGE 
1. Expansion by heat ........ 42 
2- Expansion by reduced pressure , . . . . .43 
3. Vortex-rings . . , . • . . . .51 
4. Vortex-ring, structure . . . . . . .53 
6. Chemical balance ........ 58 
6. Hydrostatic balance ........ 66 
7. Nicholson’s hydrometer . , . . . . .67 
8. Specific gravity flask . . . . . . . .68 
9- Specific gravity bottle . . . . . . .83 
10. Plateau’s experiment . . . . . . .86 
11- Equality of pressure in fluids . . . . . .87 
12. Hydraulic press ........ 87 
13. Cartesian diver ........ 92 
14. Equilibrium of a liquid in communicating vessels . . . .95 
15. Artesian well . . . . . . . . .97 
16. Equilibrium of fluids of different densities . . . . .97 
17. Spirit level ......... 99 
18. Baumd’s hydrometer ........ 100 
19. Forms of urinometers ....... 101 
20. The densimeter ........ 103 
21. Alcoholometer ........ 104 
22. Torricelli’s theorem ........ 105 
23. Stream from vertical opening ...... 106 
24. Vena contracta ........ 106 
25. Efflux in tubes ........ 107 
2G. Forms of falling water ....... 108 
27. Hydraulic tourniquet ....... 109 
28. Measurement of waves . . . . . . .113 
29. Resistance of fluids to moving objects ..... 114 
30. Raising water in wells, early method . . . . .117 
31. Archimedes’s screw ........ 118 
32. Persian wheel . . . . . . . 118 
33. The siphon . 119 
34. Retaining siphon . . * .120 
35. Glass siphon . . . . . Y . . . . . 120 
36. Intermittent siphon . . . \ . . ‘ . • 121 
37. Valves . . . . \ . / . . 121 XXVI 
LIST OF ILLUSTRATIONS. 
FIG. PAGE 
88. The lift-pump ........ 122 
39. The force-pump . . . . . ... . 122 
40. Decanting acids ........ 123 
41. Hydraulic ram ........ 124 
42. The turbine ......... 126 
43. Trap for sewer gas . . . . . ... . 130 
44. Sewage ventilation ........ 131 
45. Weighing gases ........ 137 
46. Reunite behind dividing agent ...... 138 
47. Compressibility of gas ....... 141 
48. Elastic force of gas ........ 141 
49. Decomposition flask ........ 143 
50. Pneumatic trough ........ 144 
51. Pouring gas . . . ... . 145 
52. Faraday’s tube receiver ....... 146 
53. Pouring gas through air ...... 146 
54. Weight of carbonic acid gas ...... 147 
55. Hydrogen poured upwards . . . . . . . 148 
56. Collection by displacement ....... 148 
57. Washing bottle ........ 149 
58. Aspirator ......... 149 
59. Compression air-pump ....... 150 
60. Condensing chamber ........ 151 
61. Exhaustion air-pump . . . . . . .162 
62. Mercury pump ........ 154 
68. Bunsen’s filter pump ........ 154 
64. Magdeburg hemispheres . . . . . . .160 
65. Air presses in all directions ....... 160 
66. Fountain in vacuo ........ 16l 
67. Pipette ......... 162 
68. Hand-glass and cupping-glass ...... 163 
69. Inspiration and expiration of air . . . . . 164 
70. Baroscope ......... 165 
71. Balloon ......... 167 
72. Resistance of air to moving body ...... 169 
73. The parachute ........ 170 
74. Water hammer ........ 17l 
75. Burst bladder ......... 17l 
76. Barometer ......... 173 
77. Action of barometer illustrated . . . . - . . 174 
78. Cistern barometer ........ 176 
79. Fortin’s barometer ........ 177 
80. Siphon barometer . . . . ... . .177 
81. Wheel barometer ........ 178 
82. Mariotte’s or Boyle’s law . . . . . . . 184 
83. Mariotte’s or Boyle’s law ....... 184 
84. Expansion with diminished pressure ..... 185 
85. Open compression manometer ...... 185 
86. Closed compression manometer ...... 186 FIG. 
PAGK 
87. Exhaustion manometer ....... 186 
88. Equality manometer . . , . . . .187 
89. Exhaustion water-valve .... ... 188 
90. Rarefaction cylinder ....... 199 
91. Dog poisoned by oxygen ....... 205 
9-. Aero-therapeutical establishment at Milan .... 208 
Action of radiometer ....... 220 
94. Dark space tube . . . . . . . .220 
95. Ruby tube ......... 221 
96. Course of radiant matter ....... 222 
97. Shadow tube ........ 223 
98. Railway tube ........ 224 
99. Action of magnet on low vacuum tube ..... 224 
100. Action of magnet on high vacuum tube ..... 225 
101. Radiant matter produces heat where it strikes .... 225 
102. Law-of movement . . . . . . . 249 
103. Representation of forces by lines . . . . . .253 
104. Parallelogram of forces ....... 253 
105. Sand-glass ......... 258 
106. Trajectory of projectiles ....... 259 
107. Impact and transmission of impulse ..... 260 
108. Collision balls . . . . . . . .260 
109. Impulse through water ....... 261 
i 10. Law of reflection of motion ...... 262 
Hi. Pendulum ......... 263 
112. Metronome ......... 264 
113. Rotation ......... 265 
114. Whirling table . . . . . . . .267 
115. Gyroscope ......... 267 
116. The lever ......... 270 
117. Lever of first class ........ 270 
118. Lever of second class ... . . . . . 270 
119. Lever of third class . . . . . . . 270 
120. Law of levers ........ 271 
121. Wheel and axle ....... 272 
122. Inclined plane ........ 272 
123. Screw ......... 274 
124. Pulley . . . • . . . . . .275 
125. Eriction ......... 277 
126. Capillary elevation ........ 279 
127. Capillary depression ....... 279 
128. Capillary action 279 
129. Capillarity between inclined plates ..... 283 
130. Filtration ......... 285 
131. Rapid filtration ........ 286 
132. Draper’s steam exhaust ....... 286 
133. Absorption of gases by solids ...... 287 
134. Dobereiner lamp ........ 289 
135. Solution illustrated ........ 291 
LIST OF ILLUSTRATIONS. LIST OF ILLUSTRATIONS. 
FIG. PAGE 
186. Diffusion illustrated ....... 292 
187. Diffusion between gases ....... 294 
138. Flow in capillary tube ....... 296 
189. Endosmometer ........ 296 
140. Dialysis ......... 298' 
141. Diffusion of gases through barriers ..... 300 
142. Motion in a capillary tube ....... 303 
148. Wood cells . . • . . . . . . . 304 
144. Vibration of straight springs ...... 312 
145. Transverse vibration ....... 313 
146. Molecular formation of waves ...... 315 
147. Graphic representation of velocity of oscillating body . . 340 
148. Sound undulations in tubes ...... 317 
149. Reflection of sound waves ....... 318 
150. Interference of waves ....... 319 
151. Vibration and sound ....... 320 
152. Intermittent beam of light develops sound .... 322 
153. Propagation of sound bell, in vacuo ..... 323 
154.1 
155. Movement of molecules in propagation of sound . . . 325 
156. J 
157. Stethoscope. ......... 328 
158. Sound in conjugate mirror ....... 333 
159. The sonometer ........ 3^6 
160. Nodes and loops ........ 337 
161. Tuning-fork ......... 333 
162. Chladni’s figures ........ 339 
163. Sounding tube ........ 341 
164. Vibrating column of air . . . . . _ 344 
165. Vibrating reed ........ 342 
166. Singing flame ....... 342 
167. Reinforcement of sound ....... 349 
168. Interference of sound waves ...... 354 
169. Savart’s wheel ........ 352 
170. The siren ......... 353 
171. Graphic method ........ 354 
172. Resonance box and fork . . . . . . _ 357 
173. Characters of waves . . . . . . 340 
174. Konig’s resonator ....... goj 
175. Gas-flame manometer ...... gg2 
176. Konig’s manometric flames ...... 352 
177. Fundamental note ....... ggg 
178. Octave of preceding . . . . ggg 
179. Fundamental note and octave ...... ggg 
180. Yowel O on c and c' ...... 304 
181. Analysis of sound ....... 334 
182. Lissajou’s method ....... 3gg 
183. Lissajou’s figures ....... ggg 
184. Blackburne’s pendulum ...... 337 LIST OF ILLUSTRATIONS. 
XXIX 
FIG. PAGE 
185. Edison’s phonograph ....... 368 
186. The ear . . . . . . . .374 
187. Student’s lamp ........ 395 
188. Gas from candle flame ....... 396 
189. Umbra ......... 400 
190. Penumbra ......... 401 
191. Image through pinhole ....... 401 
192. Velocity of light ........ 402 
193. Intensity of light ........ 404 
194. Bouguer’s photometer ....... 405 
195. Photometer ......... 406 
196. Illumination photometer ....... 406 
197. Bunsen’s photometer ....... 407 
198. Reflection ......... 409 
199. Image in plane mirror . . . . . . .410 
200. Parallel mirrors . . . . . . . .411 
201. Lateral inversion of image ....... 411 
202. Effect of rotating mirror ....... 412 
203. Measurement of small angles . . . . . .413 
204. The sextant ......... 414 
205. Focus of spherical concave mirror ...... 416 
206. Conjugate foci . . . . . . . .417 
207. Virtual focus . . . . . . . .417 
208. Real image .... . 418 
209. Spherical aberration ....... 419 
210. Parabolic mirror . 420 
211. Anamorphosis ........ 420 
212. Refraction ......... 423 
213. Refraction in tank ........ 423 
214. Law of refraction ........ 424 
215. Critical angle ........ 426 
216. Twilight ......... 426 
217. Refraction through parallel plate ...... 427 
218. The prism ......... 428 
219. Right angle prism ........ 430 
220. The spectrum ........ 431 
221. Dispersion and deviation ....... 432 
222. Primary how 438 
223. Recomposition of light ....... 434 
224. Achromatic prism 435 
2~5. Maxima and minima of energies in prismatic spectrum . . . 436 
226. Rotating disk . . . . .' . . .441 
227. Complementary colors .....•• 441 
28. Convex lens 446 
229. Forms of convex lens .....•• 446 
Convex lens dissected 447 
31- Structure of convex lens 448 
Focus of convex lens .....•• 449 
Conjugate foci ....•••• 450 XXX 
LIST OF ILLUSTRATIONS. 
FIG. PAGE 
284. Virtual focus of convex lens ...... 450 
235. Optical centre . . . . . . . .451 
236. Formation of image by convex lens ..... 452 
237. Virtual image by convex lens ...... 452 
238. Virtual image by concave lens ...... 453 
239. Spherical aberration ....... 453 
240. Crossed lens . . . . . . . . 454 
241. The coma . . . . . . . . . . 456 
242. Chromatic aberration ....... 456 
243. Achromatic lenses ........ 456 
244. Convex image . . . . . . . 457 
245. Depth of focus ........ 457 
246. Stops and diaphragms ....... 458 
247. Spherical aberration ........ 459 
248. Action of diaphragm ....... 459 
249. Camera lucida ........ 460 
250. Camera obscura . . . . . . . 461 
251. Magic lantern ........ 461 
252. Projection lantern ........ 464 
253. Diagram of a horizontal section of the eyeball .... 467 
254. Visual angle ........ 470 
256. Accommodation ........ 471 
256. Irradiation ......... 472 
257. The stereoscope ........ 476 
258. Compound microscope ....... 479 
259. Eelation of eye-piece and objective ..... 480 
260. Achromatic objective ...... 480 
261. Numerical aperture , . . . . _ 433 
262. Adjustment for cover ...... 435 
263. Test for objectives ........ 491 
264. Eye-piece ....... 492 
265. Erector .... . . . . . 494. 
266. The microscope •••••... 495 
267. Varying effects of illumination . qqq 
268. Illumination of opaque objects ..... sqq 
269. Microtome ........ 521 
270. Micrococci 525 
271. A. Bacterium termo, 4000 diameters. B, C, D. Bacterium lineola. 3000 
diameters ........ 52g 
272. A. Bacillus subtilis, 4000 diameters .... 57g 
273. Vibrio regula, 2000 diameters ..... 525 
274. A. Spirillum undula, 3000 diameters ; B. Spirillum voluntans, 2000 di- 
ameters ••..... 
275. Double refraction ...... 59Q 
276. Diffraction ....... 592 
277. Polarization ........ 524 
278. Nicol’s prism ...... 597 
279. Compressed glass and polarized light .... 530 
280. Circular polarization ..... 539 LIST OF ILLUSTRATIONS. 
XXXI 
FIG- PAGE 
281. Rotatory polarization ....... 534 
282. The polariscope ........ 535 
288. The spectroscope ........ 538 
284. Direct vision spectroscope ....... 540 
285. Solar and stellar spectra ....... 545 
286. Absorbent spectra of blood ....... 549 
28 <• Ice flowers ......... 554 
288. Expansion of liquid and gas ...... 555 
289. Expansion compound bar ....... 556 
290. Difference in expansion of liquids ...... 557 
Gridiron pendulum ........ 560 
Compensation strips ....... 560 
290. Mercurial pendulum . . . . . . . 560 
294. Sanctorio’s thermometer ....... 561 
295. Differential thermometer ....... 562 
296. Medical thermometer ....... 565 
297. Breguet’s thermometer ....... 567 
298. fce calorimeter ........ 568 
299. Properties of vapors ....... 574 
3po. Evaporation in vacuo . . . . . . .575 
391. Elastic force of vapors . . . . . . . 578 
2. Instantaneous condensation of steam ..... 580 
303. The pulse-glass ........ 581 
B°E Forms of clouds ........ 582 
390. Liebig’s condenser ........ 584 
96. Mason’s hygrometer ....... 586 
97. Taking dew-point ........ 586 
3°B- Ebullition . . . . . . . .590 
Reduced pressure. Reduced boiling point .... 591 
10. Culinary paradox ........ 591 
' Eapin’s digester ........ 593 
12. Spheroidal state . . . . . . . 593 
10. Metals conduct differently ....... 596 
1 Wire gauze and flame ....... 597 
Lhe Davy lamp ........ 597 
0- Blowpipe flame ........ 598 
• Liquids poor conductors ....... 599 
• Eissemination of heat by currents ...... 600 
'kesHe’s canister ........ 603 
32?" Vap°r §enerator ........ 619 
32?" ’^6c*;r*c Pendulum ........ 622 
• Electric machine ........ 625 
324 ®lectric spark . . . . . . . . 626 
Jr- Broken spark 627 
z Electric aura 627 
327 eclric chimes ........ 629 
’ Electric vane ........ 629 
3uq ec°ndary conductor ....... 630 
Electrophorus ........ 630 LIST OF ILLUSTRATIONS. 
FIG. PAGE 
330. Gold-leaf electroscope . . . . . . .631 
381. Torsion electrometer ....... 632 
332. Induction ......... 635 
333. Pail experiment ........ 637 
334. Leyden vial ......... 689 
335. Dissected Leyden vial ’ . . . . . . . 640 
336. Discharging rod. Perforated card ..... 641 
837. Lichtenberg’s figures ....... 642 
338. Holtz machine ........ 643 
339. Voltaic pile ......... 653 
340. Simple cell ......... 654 
841. Grenet battery . . . . . . . 657 
342. Colland’s gravity battery ....... 658 
343. Daniell’s cell ........ 658 
344. Grove’s cell ........ 658 
345. Arc between carbon points ....... 661 
346. Decomposition of water . . . . . . 663 
347. Sodium chloride decomposed ...... 664 
348. Thermopile ......... 668 
849. Straight and horseshoe magnet ...... 671 
350. Compound magnet ........ 671 
351. Magnetic induction . . . . . . . 673 
352. Magnetizing steel bars ....... 674 
353. Mayer’s floating magnets ....... 675 
354. Compass ......... 677 
355. Astatic combination . . . . . . .677 
356. Dipping needle ........ 677 
357. Oersted’s experiments ....... 678 
858. The galvanometer . . . . . . ' . 679 
359. Long compensator ........ 681 
360. Wheatstone’s bridge . . . . . . 682 
361. Electromagnet ........ 683 
362. The solenoid ........ 687 
363. Medical magnetoelectric machine ...... 690 
364. Inductonum ......... 692 
365. Galvanocautery ........ 700 
366. ' 
367. 
368. }- Platinum cautery wires 700 
369. | 
370. J 
371. Galvanomoxa ....... 700 
372. Galvanocaustic loops ....... 700 
373. Galvanocautery snare ....... 701 
374. Double battery ........ 702 
375. Electrodes ......... 706 
376. Knob and brush electrode ....... 705 
377. Points for application of electrodes . . . . .711 MEDICAL PHYSICS. 
PART I. 
MATTER AND ITS FORMS. SECTION 1. 
PROPERTIES OF MATTER. 
INTRODUCTION. 
Derivation of physics—Relation to metaphysics—Relation to mathematics—Rela- 
tion to chemistry—Relation to mechanics—Medical physics—Perception of 
physical phenomena—Divisions of physics—Matter defined. 
1. Derivation.—The word physics is derived from <j>img, nature. 
It is the science of nature, or natural philosophy. 
2. Relation to Metaphysics.—lt is that branch of knowledge 
which has for its subject all things which exist independently of 
the mind’s conception of them. It thus stands distinct from 
Metaphysics, or the science which has for its subject the ideas 
which exist in the mind only. 
3. Relation to Mathematics.—While many of the laws of 
physics may be discussed from a mathematical point of view, 
Mere is a broad difference between mathematics and physics. 
1° illustrate this we quote the words of Herschel in his essay 
‘On the Study of Natural Philosophy”—“A clever man, shut 
up alone, and allowed unlimited time, might reason out for 
himself all the truths of mathematics by proceeding from those 
simple notions of space and number, of which he cannot divest 
himself without ceasing to think. But he could never tell 
by any effort of reasoning what would become of a lump of 
sugar if immersed in water, or what impression would be pro- 
duced on his eye by mixing the colors yellow and blue.” The 
essential difference between the two sciences, therefore, is that 
Physics is a science of observation and experiment, while mathe- 
Matics may be evolved by the reasoning faculty alone. 
Physics is an inductive science evolving a general principle 
h°m special facts. 36 
PROPERTIES OF MATTER. 
Mathematics is a deductive science drawing a particular truth 
from a general principle. Mill says, mathematics is the most 
perfect type of the deductive method. 
4. Relation to Chemistry.—Physics deals with all the phenomena 
and modifications which bodies present, so long as they are not 
changed in composition. In this respect it is separated from 
chemistry, which treats, of the composition of bodies and the 
changes therein. 
5. Relation to Mechanics.—Mechanics is that division of physics 
which treats of the principles involved in the construction and 
action of machines. In consequence, we find the term animal 
mechanics frequently applied to the consideration of those 
functions of the body which resemble the actions of machines. 
6. Medical Physics discusses the laws and phenomena of 
physics, with which the physician should be acquainted, to 
understand the processes of life, and also those, a knowledge of 
which is necessary for the improvement of the hygienic condition 
of the community in which he lives. In evidence of the 
manifold and varied applications of physics in medicine, the fol- 
lowing examples are cited: 
1. The explanation of the function of respiration on the 
principles of pneumatics and diffusion of gases. 
2, The influence of latent heat in the maintenance of a fixed 
temperature in all hot-blooded animals. 
3. The dependence of the phenomena of circulation of the 
fluids of the body on the laws of hydrodynamics and hydraulics. 
4. The application of the principles of capillarity to the 
explanation of absorption and secretion. 
5. The explanation of the action of the locomotive system on 
the principles involved in levers, with the numerous forms of 
surgical apparatus dependent on levers and wedges. 
6. The elucidation of the action of the organs of vision and 
of hearing, by the laws of optics and acoustics. 
7. Last though not least, the relations of meteorology to 
animal heat, and to the appearance, advance, and retrogression 
of various diseases. 
Many other examples might be offered to show that physics 
rivals, if it does not surpass chemistry in the explanation of the 
phenomena of life. It is no exaggeration to say that there 
is not a tissue, organ, or function of the body, the proper com- 
prehension of which does not involve a knowledge of the laws 
of physics. _ We may wdth equal justice affirm that there is 
scarcely a principle of physics which is not applied in some form 
in the human body. The importance of the study of this 37 
department of science will, therefore, he self-evident to every 
true student and practitioner of medicine. 
The disregard which physicians in the United States have 
hitherto shown, for even a superficial knowledge of physics, 
18 unpardonable. This arises in part from the newness of the 
country, and the desire to make money quickly. It may he said 
that, outside of our great cities, very few practitioners of medi- 
cine have any conception of their true relations to the community 
ui which they live. They move in a narrow" groove, and their 
knowledge is founded almost exclusively on personal experience. 
The title, physician, has honorably escaped the odium, that 
has fallen on that of doctor. Every quack, or charlatan, calls 
Himself a doctor, and those who believe in him yield to his 
assumption. Hot so with the title of physician. The wmrd, by 
ltß derivation, means, one having a knowdedge of nature, and to 
6 physicians in the true sense of the term, we must extend our 
knowledge and influence beyond the mere empirical practice of 
tue healing art. 
The true physician is the man of science in the community in 
which he lives. He interests himself in the sanitary conditions 
°f his vicinity. He warns his people regarding the deadly 
germs that may exist in the water they drink, and in the air they 
breathe. He insists on the proper ventilation and w-arming of 
their public and private buildings. He shows them the impor- 
tance of careful removal of all offal and sewage from their 
houses, and how it should be done. He teaches them how 
to distinguish wdiolesome from uimholesome food, and how to 
Prepare it so as to present the highest nutritive value. As far 
as m his power lies, he off the approach of disease, and 
seeks to improve hygienic conditions, so that the power to resist 
disease may be as perfect as possible. To accomplish this work 
Properly, he must have knowledge, not only of the principles of 
physics connected with the functions of the interior of the 
eeonomy, but also of those which offer the most favorable con- 
ditions for the maintenance of health. 
INTRODUCTION. 
7- Perception of Physical Phenomena.—The phenomena per- 
muted by bodies generally affect one or more of our special 
senses directly, as when they are sonorous, warm, luminous, 
sometimes the changes can only be perceived indirectly, as, for 
example, wrhen a mass of soft iron becomes magnetic, the change 
\best detected by its altered relation to other masses of iron, 
which it now attracts; whereas it failed to do so before the 
diagnetism w7as developed. 
divisions of Physics.—The study of physics arranges itself 
Naturally under two divisions. The first of these deals with the 38 
PROPERTIES OF MATTER. 
things or objects acted upon. These are grouped together under 
the general head of matter. The second treats of energy, or the 
origin of the forces which act upon matter, and produce the 
varied phenomena which matter presents for our consideration 
and examination. 
Professor Tait says : “The fundamental notions which occur 
to us when we commence the study of physical science, are those 
of time and space. In relation to these, algebra has been called 
the science of pure time, and geometry of pure space.” The 
study of the special mixed science of space and time is called 
kinematics. 
Close upon our ideas of time and space follow those of matter, 
position, motion, force. Of these, position is a space relation or 
geometrical conception. Motion is change of position, which, 
since it varies in rate, implies the idea of time as well as space. 
They are both independent of our conceptions of matter and 
force, or rather of energy, which may be defined as the power of 
doing work, or, as Tait puts it, “of doing mischief; ” and which 
we may regard as the cause of force. 
“As silver and gold are different forms of matter, so sound, 
heat, light, etc., are now viewed as different forms of energy. It 
is this idea which enables us to coordinate the apparently diverse 
sciences which constitute physics. In its application we are ever 
obliged to be on our guard, in respect to the manner in which we 
treat the evidences afforded by our sensations. Take, for ex- 
ample, sound and light; until they affect certain special senses 
they are wave-motions. The sensation is as different from the 
cause, as the pain produced by a cudgel is different from its 
motion.” 
So intimate are the relations between matter and energy, that 
it is impossible to consider matter, without at the same time 
dealing with certain forms of energy, as attraction and motion, 
which are inseparable from and inherent in matter. We shall, 
therefore, as occasion arises, examine the leading features of 
these two forms of energy, as far as is necessary for the proper 
comprehension of the constitution and forms of matter, and 
reserve their more detailed study to the division of energy proper. 
9. Matter Defined.— The most concise definition of matter is that it 
is anything which may he perceived by one or more of our special 
senses as occupying space. Everything not so perceptible is called 
immaterial. We may, perhaps, best realize the difference 
between the terms material and immaterial by an example; so, 
while the body is material, the mind or the soul is immaterial; 
while the universe presents the material on its grandest scale, 
the creator and ruler becomes to us the noblest illustration of the 
immaterial. The pride which we feel in our accumulated knowl- STRUCTURE OR CONSTITUTION OF MATTER. 
39 
edge is humiliated, when we realize how incompetent our finite 
painds are to grasp the ideas presented by the universe and 
fis creator. We may, it is true, fathom the meaning of space, 
so long as it is confined to measurements which we can execute; 
but infinite space like that embraced by the universe surpasses 
°ur comprehension. Time may be realized while limited to 
small portions of the brief span comprised in a lifetime; but no 
human mind has ever compassed the idea of eternity, that 
endless time, before which even the grandest intellect stands 
humbled and appalled. So energy in its turn may be realized 
while it remains shackled within the control of our individual 
Physical powers, but we cannot frame the first conception of an 
energy? or a force wdiich is almighty, which governs the universe, 
Regulates the motions of planets and suns, and which many 
imagine may even have created matter. 
CHAPTER I. 
STRUCTURE OR CONSTITUTION OF MATTER. 
übdivisions of matter—Mechanical subdivision—Particles—Minute living organ- 
isms—Subdivision by solution—Chemical subdivision—Atom and molecule 
defined—Origin of the idea of atoms—Cohesion—Effects of heat and pressure 
°n matter—The molecules do not touch—Motion among molecules—Theory 
°f the structure of matter—Relative sizes of molecules and interstices—Esti- 
mated actual sizes of molecules and interstices—Imperfection of so-called 
vacua—Omnipresence of matter. 
To understand the changes which matter presents, and the 
huence of forces thereon, it is necessary to determine the struc- 
le or constitution of matter. By means of the following 
Aperiments and investigations, we shall arrive at a satisfactory 
°mtiou of this problem. 
10. Subdivision of Matter may be of three kinds, or degrees, 
ccording to the methods employed. These are; 1, Mechanical 
ol.eap8 prions kinds; 2, Solution either of a solid in a fluid, 
°* a solid or fluid in air; 3, Chemical processes. 
a Mechanical Subdivision.—lf we place a portion of chalk in 
P°rcelain mortar and pound it with the pestle, it breaks into 40 
PROPERTIES OF MATTER. 
fragments, which become smaller and smaller as the pounding 
or blows are continued, until finally the whole mass is reduced 
to a coarse powder. This process is known as pulverization. To 
reduce the coarse to a fine powder, the contents of the mortar 
are submitted to a grinding operation, by rubbing them in the 
mortar with the pestle. This is called trituration. Many other 
methods of mechanical subdivision will suggest themselves, but 
these answer our purpose for the present. 
12. Particles.—The fine powder produced by trituration, though 
it appears to be impalpable, if examined under the microscope 
with a sufficiently high power is seen to be made up of minute 
masses, which are called particles. A particle may, therefore, be 
defined as the minutest subdivision of matter attainable by mechanical 
means. In the case of mercury this subdivision may be carried 
on until the globules are less than the 20W0 °f an inch 
diameter, as in blue mass. The smallest single particle discov- 
erable by the normal unassisted human eye is generally stated 
to be about ToVo °f an inch in diameter. In this method of 
subdivision the particles retain all the physical properties pre- 
sented by the original mass, viz., the color, hardness, etc., being 
unaltered. 
13. Minute Living Organisms.—Though our senses can with 
difficulty appreciate the minuteness of the particles attainable 
by mechanical subdivision, yet these are rivalled and even ex- 
ceeded in smallness by innumerable living organisms. The red 
corpuscle or disks which are found in human blood, for ex- 
ample, are often of an inch in diameter and scarcely 
of an inch thick. One of the most minute of the animalcules 
is the monas crepisculum, or twilight monad. This little creature 
is carnivorous in its habits, its globular body is sometimes only 
leooQ °f an inch in diameter, yet it has distinct organs, made 
up of innumerable particles, and thereby shows us that small 
as are the particles attainable by mechanical subdivision, there 
are subdivisions which are infinitely more minute. 
14. Subdivision by Solution.—lf we take one-tenth of a grain 
of indigo and dissolve it in a little strong sulphuric acid, it will 
give a blue tint to five hundred ounces of water. Such a solu- 
tion contains less than one-millionth of a grain of coloring 
matter to th 6 drop of fluid. It is even estimated that in this 
case the particles of indigo are only o*o 000000 P of a 
cubic inch in size. 
When a grain of musk is exposed in a room it will give its 
characteristic odor to the air of the apartment for many months, STRUCTURE OR CONSTITUTION OF MATTER. 
yet at the close of that time it will have lost only a small frac- 
tion of its weight. 
In these examples of subdivision and diffusion of one material 
throughout another, we have in reality separated the ultimate 
particles of one substance from each other by introducing be- 
tween them one or more exceedingly minute particles of another 
substance. If the dissolving material is vastly greater in mass 
than that dissolved, we may even approach the smallest degree 
subdivision of which the dissolved body is capable, and still 
retain its properties. To this degree of subdivision the term 
>n°lecule is applied. 
15. Chemical Subdivision.—Taking a portion of the chalk pow- 
uer produced by mechanical subdivision (11), and pouring dilute 
1 fdrochloric acid upon it, a violent effervescence is produced, 
aud at last the chalk disappears. Testing the nature of the 
leaping gas, we find that it is carbonic acid gas, or carbon di- 
uxide, while the lime of the chalk remains in the solution 
ol’tned. In this case we have by chemical action torn the 
tolecule of chalk asunder and produced therefrom a molecule 
°t carbon dioxide and a molecule of calcium chloride. In the 
same manner, we may by suitable methods separate the carbon 
lQxide into the two bodies, carbon and oxygen. Here our 
power ceases for the present, but we have learned that the 
ioieeule of calcium carbonate forming the chalk was not the 
.ast stage of separation of which that body was capable. From 
we get free the gaseous carbonic acid, which in its turn was 
into carbon and oxygen, and since we cannot separate 
ber of these into simpler bodies we call them dements. With 
ese facts before us, we are prepared to understand what is 
eant by an atom and a molecule. 
all om Molecule Defined.—An atom is the smallest conceiv- 
e portion into which an elementary body can he divided, or the 
portion of an element that can enter into combination. 
, ' bile we may conceive of an atom of oxygen or of any other 
mentary body, modern chemistry teaches us that a single 
on m never exists in the free state; it is always combined with 
sue I?1' more atoms of the same, or of a different kind. The 
of +p* P free portion of oxygen must, therefore, consist 
mol lwo afoms of this body, and we speak of this as a 
c 6011 6 °xygen; we may consequently say that a molecule is 
posed of atoms, and, is the smallest portion of a substance capable 
£0 °\ seP°vate existence. The term molecule may he applied both 
ato e^entary an(l compound substances, while the idea of an 
171 is only applicable to elements. 42 
PROPERTIES OF MATTER. 
17. Origin of the Idea of Atoms.—The conception of the atom 
descends to ns from the ancient Greeks, though it probably 
originated in India, where doctrines similar to the centres of 
force of Boscovich have been subjects of discussion from very 
remote times. Among the early students of atoms was Leu- 
cippus. He adopted the theory of atoms because all arguments 
in favor of infinite divisibility necessarily ended in empty words, 
or in incomprehensible thoughts. 
18. Cohesion.—For the subdivision of matter we have seen 
that force is necessary. It is, therefore, evident that some op- 
posing force exists in matter by which its molecules are united, 
or bound together. To this the name of cohesion has been 
given. 
Let a small sheet of glass, three or four inches square, be sus- 
pended by threads and so adjusted that its surfaces are in a 
horizontal plane. Then let the lower surface of the glass be 
brought in contact with water. The glass and water immedi- 
ately attract each other, and a certain amount of force is re- 
quired to separate them. 
In this case we have apparently shown the attraction between 
glass and water; but if we examine the experiment more care- 
fully, we find that the lower surface of the glass is covered with 
a layer of the liquid. It is, therefore, evident that we have not 
separated the glass from the water, but we have torn the mole- 
cules of water asunder, and the force required to do this was 
the measure of their cohesion for each other. 
19. Effects of Heat and Pressure on Matter.—Seeing that all 
matter is composed of molecules, the inquiry naturally arises, 
What is the relation of these to each other as regards position ? 
Fig- l- 
Are they in contact, or are they at a dis- 
tance from each other ? An answer to this 
question is offered by the following experi- 
ment, delineated in Fig. 1. Let Abe a 
sphere of brass, two or three inches in 
diameter, made as true as possible, and sus- 
pended by a chain. To the sphere, A, a 
metallic ring, B, is adapted, which at ordi- 
nary temperatures permits the sphere to 
pass through it easily. On raising the tem- 
perature of the sphere by means of a spirit 
or a gas flame, and then attempting to pass 
it through the ring, we find that it will no 
Expansion by heat. 
longer do so. From this we conclude that the metallic sphere has 
increased in size under the influence of the rise in temperature. 
Allowing the mass to cool, it again passes through the ring without STRUCTURE OR CONSTITUTION OF M'ATTER. 
difficulty. It has therefore diminished in volume by the diminu- 
tion in temperature. In like manner, variations in pressure cause 
ynriation in volume. In illustration of this, take a tube one 
inch in diameter with a bulb, A, expanded 
0n one end. The tube and bulb are almost 
entirely filled with water, which confines a 
bubble of air in the upper part of the bulb or 
sphere. The lower part of the tube dips under 
the surface of the water in a vessel, B, and 
thus the fluid is suspended in the tube and 
oulb. Placing this instrument under a tall 
ft! O 
‘nr-pnmp hell, C, and proceeding to exhaust, the 
onbble of air dilates, and the fluid retreats into 
the tube, and vessel, B. Restoring the press- 
hi’e of the atmosphere, the bubble of air at A 
c°ntracts, and the fluid returns to its original 
position. 
Fig. 2. 
20. The Molecules do not Touch.—The only 
explanation of the phenomena presented in the 
Preceding article is that the air in the bulb has 
expanded and contracted, under the influence 
0 the variations in pressure. This it could 
Expansion by reduced 
pressure. 
do if the molecules were in contact with each other. We, 
orefore, arrive at a correct answer to the question propounded 
n the last article, and conclude that the molecules both in the 
°od and in the gas, cannot be in contact, hut are separated by 
Paces or intervals, called interstices. 
oht^: on among Molecules.—The expansion and contraction 
rained in the preceding experiments, show that the molecules 
■ e uiobile in the solid as well as in the- gas. Numerous 
stances of mobility among the molecules of solids suggest 
0e but none is of greater interest than those which 
4-nuhe case of periodide of mercury which has been recently 
To • 
b httle of this substance be placed in a test-tube and 
ated, its color changes to a bright yellow. After a few 
***** it vaporizes, and, recondensing higher up in the tube, 
ture >a e^ow sublimate. Under these conditions of ternpera- 
an t*lere i®s °f course, no moisture present on which to base 
tou Ration of what follows. If the yellow sublimate be 
fo a G(* any hard substance, it instantly turns red, owing 
selv learrangeuaent of the molecules of periodide among them- 
iii t,eß' ®ven without the act of touching, the sublimate will 
t0 a complete change of tint, passing from yellow 
rilliant red. Arsenious oxide also offers an example of 44 
PROPERTIES OF MATTER. 
the same fact, changing slowly from a glassy amorphous into 
an opaque crystalline form. 
Phenomena like these demonstrate that in solids, molecular 
movements are not only possible by virtue of external inter- 
ference, but they may also arise without any apparent initiating 
act. The most rational explanation of the changes in the per- 
iodide of mercury is, that even in the yellow state, molecular 
oscillations or vibrations are occurring, and the change to the 
red state is merely dependent on some slight change in the 
manner or character of these movements. 
If the idea of movement in connection with molecules be 
granted in the most solid bodies, we have an explanation of the 
manner in which the interstices (20) are maintained. For 
motion to exist, the molecule must have space in which to 
vibrate, hence the interstice. Increase the temperature, and 
the motion or vibration increasing, the interstitial spaces also 
increase, and the body expands. Diminish the temperature, 
the amplitude of motion of the molecule diminishes, the cohe- 
sive force draws the molecules together, the interstices diminish, 
and the body contracts. 
Collecting the experiments and arguments embraced from 
article 11, and condensing them, we have the following: 
22. Theory of the Structure of Matter.—l. All matter is com- 
posed of molecules made up of atoms. 
2. These molecules do not touch each other, hut are separated by 
spaces, called intermolecular interstices. 
3 The molecules forming a substance are never at rest, hut are oscil- 
lating or moving in various ways, with inconceivable rapidity. 
4. The molecules are drawn toward each other by a force called 
attraction or cohesion (18), which tends to diminish the size of the 
interstices. 
5. The molecular movements resist the attractive or cohesive force. 
These motions are increased by the action of heat, and the size of the 
interstices is consequently increased. According as the cohesive force 
or the motion predominates, so does the size of the body vary. 
23. Relative Sizes of Molecules and Interstices.—By the action 
of heat, one cubic inch of water may be made to yield a cubic 
foot of steam. In its vaporous state the water molecules have 
the same chemical composition as in the fluid condition; the 
difference is the result of the expansion which the interstices 
between the molecules have undergone. This, and innumera- 
ble other examples, show how great the size of the interstices 
must be, compared with that of the molecules. In the case of 
dilated hydrogen gas this excess in size of the interstices is STRUCTURE OR CONSTITUTION OF MATTER. 
45 
enormous; some have even compared their relations to that 
existing between the planets of our solar system and the dis- 
tances separating them. 
24. Estimated Actual Sizes of Molecules and Interstices.—Sir 
'' illiam Thomson estimates that in ordinary solids and liquids 
the average distance between contiguous molecules is less than 
the millionth of a millimetre. In an article by Mr. G. J. Stoney 
(‘Phil. Mag.,” series 4, vol. 36), on the “Internal Motions 
°t Gases Compared with Motions of Waves of Light,” the 
author estimates that there are not fewer than a unit—eighteen, 
(unit) 18, or 1,000000000000000060 molecules in each cubic 
of a gas at ordinary temperatures and pressures. 
Considering that a cubic millimetre is about one-twentieth of 
an inch square on each face, we gain a faint conception of the 
Marvellous minuteness of molecules. 
25. Imperfection of So-called Vacua.—Admitting that a cubic 
Millimetre of air or gas contains a (unit) 18 molecules, it is 
that the so-called barometric vacuum is sadly misnamed, 
he admirable exhaustion obtained by Crookes in the prepara- 
un of his radiometer tubes is equivalent to the almost incon- 
ueivable pressure of 10 000 o o °f an atmosphere, yet even at 
fus reduction of pressure a cubic millimetre still contains 
>6OOOOOOOOOOO molecules of gas. 
26. Omnipresence of Matter.—The imperfections of our best 
apua (25) show that is hardly possible to conceive of space as 
istuig without matter. In other words, matter is omnipresent. 
i ere anJ doubt of the truth of this, a glance at the stars 
OMd reassure us. Distant though they be from us and from 
w'ir °^er> there is no part of the heavens that is not studded 
1 h them. Increase in the power of telescopes only serves to 
\vb‘0 i our ast°mshed gaze innumerable stars and nebulae, 
u 10 1 before were invisible. The wave theory of light, too, 
f mandB the existence of the ether, or an exceedingly attenuated 
11 of matter existing throughout space, and in which light is 
Tira^ated by oscillations or vibrations of its molecules. 
T , , 1 more truth than he kenned, did Milton in his “ Paradise 
cause the Almighty to exclaim: 
“ I am who fill 
Infinitude, nor vacuous the space 
Though I myself retire ” 46 
PROPERTIES OF MATTER. 
CHAPTER 11. 
ULTIMATE COMPOSITION OF MATTER. 
Elements and compounds defined-—Theory of the oneness of matter—Hydrogen 
the original element—Nature of atoms. 
27. Elements and Compounds Defined.—ln examining chemical 
subdivision (15), we have seen that there is a limit to the 
subdivision of a body as regards its constituents. In the case 
of calcium carbonate, for example, we arrive finally at cal- 
cium, carbon, oxygen. These we cannot separate into other 
and simpler bodies; though it is possible that such a result 
may some day be accomplished. Many substances once thought 
to be undecomposable have since been separated; the same may 
happen in other cases; we may, therefore, say that: 
An element is a body which has not yet been decomposed, while : 
A compound is made up of two or more elements. 
28. Theory of the Oneness of Matter.—While the discussion of 
the composition of bodies and the changes therein belongs 
properly to chemistry, there is one view regarding the origin of 
elements which places this question within the domain of 
physics. 
The chemist claims the existence of some sixty-tive distinct 
elements, out of which all the objects on the globe are con- 
structed. These he believes “no kind of alchemy will trans- 
mute the one into the other.” In discussing this, Dr. Arnott 
says: 
“How sixty-tive kinds of matter should, by variously com- 
bining, form the endless diversity of things and appearances 
winch our globe presents is not without analogy. All the words, 
all the literature of the English tongue is formed out of twenty- 
four letters, and all the letters of the multitude of tongues on 
the face of the earth are not more in number than the chemical 
elements. Even more wonderful is the fact that all the words of 
the English, or any other language, may now be signalled along 
a telegraph wire by combinations of only two different signals, 
a long and a short one.” He might have added that the long 
signal, or dash, is itself a combination of short signals or dots. 
The human invention of written language indicating not only ULTIMATE COMPOSITION OF MATTER. 
47 
ah the objects on the globe, but also expressing the thoughts, 
and passions with which man is endowed, is, as we 
have seen, reducible to a system of dots variously arranged, 
there is, therefore, nothing unwarrantable in the conception 
that the various kinds of matter, the presence of which we ex- 
press by the proper arrangement of the same kind of dots in 
telegraphy, may be composed of one kind of elementary atom, 
aud our so-called elements are mere modifications of this. The 
ftonis we may say have their analogues in dots, molecules in 
etters, and substances in words. 
Ihe astrologers of the East not only evolved the idea of the 
toln, but their long-continued observations of the ceaseless 
thovements of the heavenly bodies led them to believe that in 
f9r\Same waT at°ms or molecules of matter were never at rest 
They even carried the similitude further, and taught that 
cne stars of the firmament were alike in appearance, so matter 
fir ma(^e up of 0116 kind of atom, and the differences in 
itterent kinds were merely the results of difference in the kind 
Motion to which the elemental atom was subjected. The 
Jfmental atom, moreover, constituted the original or universal 
ether. 
1 the Greek philosophers, Leucippus, of whom we have 
‘ leady spoken (17), held that the idea of the atom as the ele- 
ontary substance gave a foundation on which, by the aid of 
ernal motion, combination, and separation, all material phe- 
mena might be built, and their relations explained. The 
e°t of motion in all its variety upon matter is finally summed 
i§} h Heraclitus in the saying that “Life is motion.” “Nothing 
att mas movement-” It is to thoughts like these that we must 
St ri ,te the search by the alchemists for the “Philosopher’s 
tu^ne~, 
y the base metals into gold; by the latter, to renew their 
h and prolong life to a thousand years or more, 
m * Modern thinkers the eminent physicist and chemist 
the *lara’ was a leading upholder of the “Oneness of matter and 
jje P°Wer of motion and combination to produce diversity.” 
oreover, conceived the idea that the diversity in motion 
that basis of diversity in matter, or, in other words, 
an atoni constituted an element of a special kind, according 
rp,e rate or the peculiarity of its movements, 
the riL of the oneness of matter is of especial interest to 
in ti ySlciail, Billce it bears a close analogy to what he finds 
a*iimm Btructure of all living organisms. Tracing the higher 
devel veSetable structures back through their course of 
Posed^f fbeir first genesis, we find that they are com- 
the ,°b an(J that they originate from, cells. In their structure 
1 Semblance of these cells to each other is very close. 48 
PROPERTIES OF MATTER. 
Whether it be a nerve-cell in the brain, a muscle-cell, a cell of 
tendinous or cartilaginous tissue, or even of bone itself, in its 
first inception it consists of the same parts, viz., cell-wall, con- 
tents, nucleus, and nucleolus. From mere cells, the multiplicity 
of forms composing the organic world is evolved, Omnia ex ova 
being the motto on which nature seems to work out her plans. 
To the analogy here drawn exception might be taken, to the 
effect that these cells are, after all, essentially different. Though 
they resemble each other in that they are composed of the same 
parts, they are different in size and form. We never, it might 
be said, find muscle-cells producing a serous membrane, nor 
nerve-cells forming muscle. They therefore differ essentially 
from each other, just as iron differs from copper; indeed, they 
might be regarded as the analogues of the atoms of elements, 
each building up its own special form of structure, and none 
other. 
Admitting, for the moment, this apparent objection, let us 
trace the genesis of the tissues of any organism a step further 
back, and for our example take man himself. The first differ- 
entiation of a human being consists of the formation of an ovum 
in the ovary of the female. To all appearances, this is nothing 
more nor less than a simple cell, and not distinguishable from 
similar ova of innumerable other animals, we might even say of 
plants also. Brought in contact under suitable conditions with 
its proper spermatozoa, which seem to bear to the ovum the same 
relation that energy bears to matter, and furnished with a form- 
less material as food, changes begin. What was at first a simple 
cell, by the act of subdivision becomes an infinite number of cells. 
In the mass so produced, the embryo is outlined little by little. 
Tissue after tissue, each with its own peculiar cells, appears. 
Finally the perfect foetus is formed. The child is born, and we 
are in the presence of the most wonderful of all creations, mar- 
vellously complex in its structure, possessing absolute character- 
istics which separate it from all other creatures; and yet all this 
complexity of structure has arisen from a single simple cell. Cells 
of brain, muscle, tendon, cartilage, bone, all have originated from 
the same source. Ho two elementary bodies differ from each 
other more than brain differs from cartilage, yet brain and car- 
tilage have been evolved from the same original cell. Is it any 
greater wonder to imagine that as such divers tissues as those 
we have mentioned have all originated from one cell, our so- 
called elementary bodies may have also originated from one 
ultimate element? 
Pushing the analogy still further, we arrive, in the organic 
world, at that curious body called protoplasm, from which the 
cell itself is produced, and which forms the completed body of an 
amoeba and a moner. Whatever opinions we may hold regard- 49 
ULTIMATE COMPOSITION OF MATTER. 
ing differences among cells, none can exist concerning the uni- 
formity of protoplasm, from whatever source it may be obtained. 
A mere formless, jelly-like material, without visible organiza- 
tion, it may be conceived to be the analogue of that something 
which we conceive to be distributed throughout space. We 
may further imagine that as cells are differentiated from proto- 
plasm, so elementary atoms arise from an ultimate element, and 
as the cell once differentiated retains its special form and prop- 
erties, which cannot be changed or altered by any agency at 
our command, so elementary atoms, in like manner, when once 
differentiated resist all our attempts at modification by the 
means we at present possess. 
29. Hydrogen the Original Element ?—ln the “American Journal 
of Sciences and Arts,” 3d series, vol. xviii. p. 9(J, there is a 
report of a paper read by J. Norman Lockyer, before the Royal 
Society, on December 12,1878. It is entitled “On the Supposed 
Compound Nature of the So-called Elements.” In this paper 
he says: “There are many facts and many trains of thought 
suggested by solar and stellar physics, which point to the hy- 
pothesis that the elements themselves, or at all events, some of 
them are compound bodies.” The original element would 
appear to be hydrogen, for the spectrum analysis of the hottest 
stars shoves this gas to be present in enormous quantity, wfith 
very little else, while stars of lowrer temperature show a less 
proportion of hydrogen, but present other elements the variety 
or number of which increases as the temperature descends. In 
the stars of the highest temperature other elements have not 
been formed, or they have been dissociated into hydrogen. 
Observations by Prof. Piazzi Smyth, in another direction, tend 
to the same conclusion. In the “Observatory,” for October, 
1880, he states that in experiments with low temperature vacuum- 
tubes, after a prolonged passage of the electric spark, “Chlorine 
has been changed into hydrogen, and nitrogen though more 
slowly, seems to be going the same wTay. Is nitrogen after all 
not an element, but a compound? Is nitrogen merely a par- 
ticular form or state of hydrogen ?” 
These opinions show that the tendency of modern thought is 
toward the acceptance of a modification of the ancient doctrine 
°f the oneness of matter, and though it may not be a proven 
fact, we cannot deny that there are many phenomena which 
support the idea of the origin of other elements from hydrogen. 
30. Nature of Atoms.—On this subject, says Professor Tait, 
various opinions have been held. “Among these, the first is 
that of the perfectly hard atom. You meet with it not only 
loug before the time of Lucretius, but also in all subsequent 50 
PROPERTIES OF MATTER. 
time, even in the works of Newton himself. We find Newton 
speculating on this subject in his unsuccessful attempt to account 
for the extraordinary fact that the velocity of sound, as calcu- 
lated by him by strictly accurate mathematical processes, was 
found to he something like one-ninth too little. We find New- 
ton suggesting that possibly the particles of air maybe little, hard, 
spherical bodies, which, at the ordinary pressure of the atmos- 
phere, are at a distance from one another of somewhere about 
nine times the diameter of each; and he says sound then may 
be propagated instantaneously through these hard atoms or par- 
ticles of air, while it is propagated with the mathematically cal- 
culated velocity through the space between each pair. But, 
unfortunately for this explanation, it implies that sound should 
move faster in dense than in rare air at the same temperature. 
This is inconsistent with the results of direct measurement.” 
“It is obvious, that if there are such small infinitely hard 
particles as atoms, they must be in all bodies at a distance from 
one another, because, so far as experiment has guided us, there 
is no portion of matter whatever that is not capable of further 
compression by the application of sufficient pressure; and, of 
course, compression of a group of infinitely hard particles must 
presuppose that they have certain interstices between them, 
so that they are capable of being brought still nearer” (23 
and 24). 
“Another school of philosophers and experimenters, recoiling 
from the notion of the hard atom, took up the following idea. 
All that we know of atoms will be perfectly well accounted for 
if we dispense altogether with the notion of an atom—dispense 
with anything material in the ordinary sense of the word matter 
—but suppose merely a centre cf force, such as we are accustomed 
to in those mathematical fictions which we meet with in our 
text-books. Suppose, in place of an atom, a mere geometrical 
point, which can exert repulsive or attractive forces, or rather 
suppose such forces tending toward or from a certain point, 
but nothing at the point, except, in some unexplained way, 
mass. So far as external bodies are concerned, this will behave 
just as an atom would do. That explanation was taken up and 
developed to a great extent by Boscovich, and was, to a certain 
extent, adopted in later times even by Faraday. It is, as I have 
stated at the outset, a mathematical fiction, but it is often an ex- 
tremely convenient one for the purpose of enabling us to make 
certain matheraatico-physical investigations of what takes place 
in the interior of bodies in their various states of solids, liquids, 
and gases.” 
A third hypothesis is that of the vortex atom, recently sug- 
gested by Sir William Thomson. Of this, Professor Tait says: 
“The peculiar properties of vortex-motion were mathematically ULTIMATE COMPOSITION OF MATTER. 
51 
deduced for the first time by Helmholtz. It is necessary to give 
a brief sketch of his results in order that you may easily follow 
my explanation of Sir William Thomson’s suggestion, and I do 
so the more readily because it is, or, at all events, it appears to 
myself to he by far the most fruitful in consequences of all the 
suggestions that have hitherto been made as to the ultimate 
nature of matter. Especially does it give us a glimpse, at least, 
of an explanation of the extraordinary fact, that every atom of 
Rny one substance, wheresoever we find it, whether on the earth 
or in the sun, or in meteorites coming to us from cosmical 
spaces, or in the farthest distant stars or nebulae, possesses pre- 
cisely the same physical properties.” 
“As a preliminary illustration, I shall show the formation of 
a simple circular vortex-ring, exhibiting one or two of its more 
important properties.” 
Fig. 8. 
Vortex-rings. 
“The apparatus consists of a very homely arrangement, merely 
a wooden box with a large round hole made in one end of it, 
'vhile the opposite end has been removed and its place supplied 
a towel tightly stretched. In order to make the air which is 
be expelled from this box visible, we charge it first with 
amnioniacal gas, by sprinkling the bottom of the box with strong 
solution of ammonia. A certain quantity of amnioniacal gas 
has now been introduced into it, and we shall develop in addition 
a quantity of muriatic acid gas. This is done by putting into 
me box a dish containing common salt, over which I pour 
sulphuric acid of commerce. These two gases combine, and 
i°rm solid sal ammoniac, so that anything visible which escapes 
morn the box is simply particles of sal ammoniac, which are so 
Very small that they remain suspended by fluid-friction, like 
Buioke in the air. How notice the effect of a sudden blow 
aPplied to the end of the box opposite the hole. There you 
See a circular vortex-ring moving on its own account through the 
r°oni as if it were an independent solid.” 
“ I shall now try to show the effect of one vortex-ring upon 52 
PROPERTIES OF MATTER. 
another, just as I showed it here to Thomson, when he at once 
formed his theory. You notice that when two vortex-rings 
impinge upon one another, they behave like solid elastic rings. 
They vibrate vehemently after the shock, just as if they were 
solid rings of India-rubber. It is easy, as you see, to produce 
such vibration of a vortex-ring without any impact from another. 
All we have to do is to substitute an elliptical, or even a square 
hole, for the circular one we have hitherto employed.” 
“Now, the first vortex-ring which you saw sailing up through 
the class-room, contained precisely that particular portion of air, 
mixed with sal ammoniac powder, which had been sent out of 
the box by the blow. It was not merely sal ammoniac powder 
which was going through the air, but a certain definite portion 
of the smoky air, if we so may call it, from the inside of that 
box, which, in virtue of the vortex-motion which it had, became, 
as it were, a different substance from the surrounding air, and 
moved through it very much like a solid body.” 
“In fact, according to the result of Helmholtz’s researches, if 
the air were a perfect fluid, if there were no such thing as fluid- 
friction in air, that vortex-ring would have gone on moving for- 
ever. Hot only so, hut the portion of the fluid which contained 
the smoke; which was, as it were, marked by the smoke, would 
remain precisely the same set of particles of the fluid as it moved 
through the rest; so that those which were thus marked by the 
smoke were, by the fact of their rotation, distinguished or differ- 
entiated from all the rest of the particles of air in the room, and 
could not by any process, except an act of creative power, be 
made to unite with the fluid in the room.” 
“ That is a point which appears to me to be one of the most 
striking characteristics in the foundation of this suggestion of 
vortex-atoms. Granted that you have a perfect fluid, you could 
not produce a vortex-ring in it; nor, if a vortex-ring were there, 
could you destroy it? No process at our command could enable 
us to do either, because, in order to do it, fluid-friction is essen- 
tially requisite. Now, by the very definition of a perfect fluid, 
friction does not exist in it.” 
“Thus, if we adopt Sir William Thomson’s supposition, that 
the universe is filled with something which we have no right to 
call ordinary matter (though it must possess inertia), but which 
we may call a perfect fluid, then, if any portions of it have 
vortex-motion communicated to them, they will remain forever 
stamped with that vortex-motion; they cannot part with it; it 
will remain with them as a characteristic forever, or at least 
until the creative act which produced it shall take it away again. 
Thus this property of rotation may he the basis of all that to our senses 
appeals as matter.” 
“In such a vortex-ring (as you will easily understand by 53 
thinking how it came out of the round hole in the box), the 
motion of the particles of air is of this kind. Suppose it to be 
coming forward towards you, then every portion of the air on 
the inner side of the ring is moving forward, and every portion 
pn the outer side is moving backward, so that the whole is turn- 
ing round and round its linear circular core. The air all about 
it is in motion according to a very simple law, which, however, 
. could not explain without mathematics—except in the par- 
ticular case of that within the annulus, which is moving forward 
taster than the ring itself. I shall afford any of you who desire 
!t an opportunity of convincing yourselves of the fact. Each of 
you will find that, if he places his face in the path of one of 
these large air vortex-rings, there is no sensation whatever until 
the vortex-ring is almost close to him, and when it reaches him 
he feels a sudden blast of wind flowing through the centre of it, 
I bus this vortex-ring not only involves in itself rotating ele 
merits which are thereby distinguished altogether from the other 
elements of the fluid, but it also is associated necessarily with 
ULTIMATE COMPOSITION OF MATTER. 
ether movements through the non-differen- 
lated air, and especially a forward rapid 
current of air passing through its centre in 
he direction in which it is going. Helm- 
holtz showed that if vortex-filaments exist in 
f continuous medium of any kind, they must 
e ring-shaped—that is to say, endless—after 
any number of knottings or twistings, the 
ends must come together. All vortex-rings 
rrand, therefore, according to Sir William 
homson, all atoms of matter—must neces- 
sarily be endless—that is to say, must have 
Fig. 4. 
Yortex-ring, structure. 
~*r ends finally united together after any number of convolu- 
lQns or knots.” 
. ‘ Secondly, though this is really involved in what we have 
Jest seen, Helmholtz shows that such a ring is indivisible; you 
cannot cut it. Do what you like; bring the edge of the keenest 
-I euptoit as rapidly as you please, it cannot be cut; it sim- 
b .V moves away from or wriggles round the knife ; and, in this 
ese, it is literally an atom. It is a thing which cannot be cut; 
. that you cannot cut it; but that you cannot so much as get 
it so as to try to cut it.” 
te the extracts we have given above from Professor Tait’s 
orh °n “ Recent Advances in Physical Science,” we have only 
W’th 11° present the recent ideas regarding the nature of atoms, 
1 bout accepting them. Those who desire a more extensive 
cquaintance with this subject, and with the doctrine of the 
e erogeneity of matter, must consult Professor Tait’s work. 54 
PROPERTIES OF MATTER 
CHAPTER 111. 
GENERAL PROPERTIES OE MATTER. 
Indestructibility and transmigration of matter—Extensibility and impenetrability 
—Gravity and weight—Centre of gravity—Stability of position in animals— 
The balance—Weights and weighing—Essentials in a good balance—Method 
of double weighing—Density or specific gravity—Mobility—Inertia—Porosity 
—Compressibility—Elasticity—Divisibility. 
31. Indestructibility and Transmigration of Matter.—We cannot 
create, neither can we destroy matter. The dew which has 
covered the petals of flowers with glistening drops, disappears 
when the rays of the rising sun envelop it. The water that 
formed it seems to have been destroyed, but it still exists. It 
has only passed from visible water to invisible vapor. Though 
the eye cannot perceive it, there is no difficulty in proving its 
existence by other means, and forcing it to reassume its visible 
liquid state. 
The candle-flame by which we seek to extend the length of 
our days, offers even a better example of the indestructibility 
of matter. The wax or fat of which the candle is formed, is 
composed chiefly of carbon and hydrogen. In giving forth its 
light the flame slowly feeds upon the combustible substance, 
and as this wastes away, it appears to have been destroyed, but it 
has not. In the flame itself, through which we may rapidly pass 
the linger without feeling any resisting medium, there is solid 
matter. This we may easily show by causing a flame to impinge 
upon a cold surface, when at once it deposits soot or solid 
carbon. Even when the carbon has disappeared in the upper 
part of the flame, and only invisible products are present, we 
may, by passing these over melted potassium, recover the carbon 
in the same state as we found it in the flame. The carbon of the 
wax has not been destroyed, it has only changed its state so as 
no longer to be perceptible to certain senses. 
Living plants and animals give an admirable illustration of 
the indestructibility of matter, and also of its unceasing passage 
through varied forms. The processes of animal life result largely 
in the production of carbonic acid gas, which is eliminated in 
the invisible state from the lungs. It is identical with the gas 
thrown oft* in the combustion in a candle-flame. It has even been 
said, and not without reason, that we ourselves may be likened 55 
to flames. We are mere forms through which matter is passing. 
We consume food as the flame consumes fat, this in each case 
18 oxidized, producing a more or less transient form. The 
Product of the oxidation in both is the same, carbonic acid gas. 
io plants this gas, the refuse of the bodies of animals, is of the 
utmost importance. To them it is food and sustenance. They 
consume it with avidity. Out of it they construct their tissues, 
producing forms far more permanent than those of animals, 
opt to be consumed by animals and again pass through the 
circuit of nature. 
Matter, therefore, is not only indestructible, but certain kinds 
cu it are ceaselessly passing through living creatures. Even 
Ulan himself cannot claim as individual property the atoms 
which build up the organs of his body. They are not even the 
Property of collective humanity, but have passed innumerable 
times through animal and plant creations. What a humiliating 
jesson this elementary scientific fact teaches us. The very 
oodles in which we take so much pride, and which we care for 
80.tenderly, are merely passing forms of matter in which the 
Bpirit is clothed for a brief time. We die, and our corporeal 
puWcles escape us, never to be regained. 
■the ancient doctrine of transmigration we may reject when 
aPplied to the soul, about which we know nothing, but in the 
ease of matter it is indubitable. Indeed, we may say that suffi- 
hlent time being granted, it is as much a property of matter as 
Uidestructibility itself. 
GENERAL PROPERTIES OF MATTER 
32. Extensibility and Impenetrability.—The first of these is the 
property by which matter occupies a certain fixed portion of space. 
£y impenetrability we understand that two portions of matter cannot 
occupy the same portion of space at the same time. If we press a 
ottle mouth downwards under water, the fluid cannot enter 
ft® vessel, since it is occupied by air. For the water to gain 
the air must escape, as we see is the case when the 
ottle. is immersed mouth upwards, when the rate of egress of 
e air is exactly proportional to the rate of ingress of the 
uid. So, a]Boj when a nail is driven into wood, the iron forces 
xi e w°od to the right and left; the two bodies do not occupy 
le same space at the same time. Strictly speaking, the term 
should only be applied to molecules and atoms, 
some, extension and impenetrability are used as synonymous 
g has here been said applies equally in the case of 
'Called penetrating wounds, the term is not correctly used. 
c tissues of the body are as impenetrable as any other matter, and 
snt ]'-ord zs onty admissible with the understanding that there is 
U Jon of continuity of the tissue. 56 
PROPERTIES OF MATTER. 
33. Gravity and Weight.—Matter may be dealt with under 
three conditions : molar, molecular, and atomic. The two forces 
of attraction and motion, which are inherent to matter, may 
also be considered from three similar points of view. 
Atomic attractions and motions belong properly to the domain 
of chemist^. 
Molecular attractions and motions determine the solid, liquid, or 
other form of a body, and its relations to light, heat, and 
electricity. Their consideration belongs to physics. 
Molar attractions and motions are by many dismissed to the 
province of mechanics, but we have retained them within that 
of physics, of which mechanics may be regarded as a subdi- 
vision (5). 
Molar attraction when applied to the attraction of the earth 
for objects on its surface, is called gravity. The resistance re- 
quired to overcome this attraction is called weight, and is accepted 
as one of the properties of matter in general. For the determi- 
nation of the weight of bodies, the student is referred to article 
36, on the balance. 
34. Centre of Gravity may also be called the centre of weight 
or attraction. It is the point in a body about which all its parts 
exactly balance one another. If this point be supported, the 
whole body will remain at rest in any position in which it may 
be placed. For many purposes the whole weight of a body may 
be regarded as being concentrated at its centre of gravity. 
In bodies of regular geometrical forms, the centre of gravity 
coincides with the centre of form, and may be easily determined, 
provided they are of uniform density. In a circle or sphere, it 
is at the geometrical centre. In a cube, at the crossing of the 
diagonals. In a cylindrical rod or bar, such as may be mused for 
the beam of a balance, it is at the centre of its axis. 
The experimental determination of the centre of gravity of 
any irregular body, may be accomplished as follows : The body 
is first suspended by a string attached to one point, the line 
formed by the string is projected through the object. The point 
of attachment of the string is then changed, and the new line of 
suspension projected through the substance. The crossing 
of these two lines is the centre of gravity of the object. 
The stability of position of a body depends upon the relations of 
its centre of gravity to its base. The essential condition is that 
the centre of gravity must lie vertically within the area occupied 
by the base. A greater extent of base, other things beino- 
equal, gives greater stability. The more vertical the centre of 
gravity over the centre of base, the greater the stability. The 
less the altitude of the body, the greater the stability. 
The combination of all of these conditions gives the most GENERAL PROPERTIES OF MATTER. 
57 
complete stability. A serious deficiency in any one of them 
may make the body exceedingly unstable, as when we attempt 
to stand a pyramid upon its apex. Though the centre of gravity 
may then be vertically over the centre of the supporting base, 
the latter is so minute that the slightest movement throws the 
centre of gravity to one side, or the other, of the supporting 
surface, and the body falls. 
35. Stability of Position in Animals.—ln quadrupeds, stability of 
position in the standing attitude is very great since their base of 
support is large, being represented by the area enclosed by their 
four feet, when in contact with the ground, and the centre 
of gravity is almost vertically over its centre. So little effort is 
required to maintain the erect position in these creatures, that 
they may often be seen sleeping in that attitude. JSText in sta- 
bility to quadrupeds, come the kangaroos. These, though 
biped in appearance, actually use the tail as a third leg, and so 
increase their base of support. 
In bipeds like man, the base of support is so small that 
numerous trials are required before the power to keep the erect 
position is acquired. In the act of walking, by bending for- 
wards, the centre of gravity is thrown first over one foot, and 
then over the other, as is imitated in the toy called the tumbler. 
■According as the width of the pelvis is greater, the adjustment 
°f the centre of gravity to the position of the feet requires 
greater extent of motion. Hence, the lateral sway seen in the 
walk of woman compared with that of man. The same move- 
ment is for a like reason exaggerated to a still greater extent in 
waddling walk of the duck and goose. 
The necessity of a continual adjustment of the centre of 
gravity to the supporting base, compels us to seek in surround- 
|jig objects some standard, by which we may ourselves maintain 
uu vertical position. Vertigo and sickness often result when 
We are deprived of these standards of comparison. Hence, on 
rupboard, the continued departure of the objects in our vicinity 
°m the perpendicular line, destroying the ordinary means of 
c°mpai'isons, we suffer from sea-sickness. The discomforts of this 
°udition may often be avoided by lying flat on the back, and 
poping the eyes tightly closed. Sea-sickness is also in part due 
irregular pressure upon the internal organs produced by the 
10tion, especially is this the case with the brain. 
Tb ®a^ance-—Of balances there are numerous forms, 
(pi ? ordinary balance consists of a rod of metal called the beam, 
as 1S-|S^ be as nearly inflexible as possible. It is mounted 
pa. Ver of the first class, the fulcrum being a triangular prism 
i ssing through the beam, and so adjusted that it rests on one of PROPERTIES OF MATTER. 
its edges. This is commonly called the knife-edge or axis 
of support. 
The axis, in the finer kinds of balance, is supported on 
polished plates of agate to enable it to move with the least fric- 
tion possible. Immediately beneath the knife-edge a long 
Pig. 5. 
Chemical balance. 
needle is attached to the beam. It projects downwards, and by 
its oscillations over a graduated arc, enables us to measure with 
exactness the movements and position of the beam. 
From the extremities of the beam the pans are suspended. 
In the finer kinds the method adopted is by knife-edges attached 
to the beam ; on these agate surfaces rest which sustain the pans 
by means of slender wires of platinum. 
When in use, the object which is to be weighed is placed in 
one pan; by its attraction for the earth, the pan in which it 
is placed sinks. Weights of known value are then placed in the 
opposite pan until the attraction of the earth for the object 
is overcome, and the beam of the balance assumes the horizontal 
position, or is equipoised, as is shown by the point of the 
attached needle oscillating to equal extents on the opposite sides 
of the zero of its scale. 
37. Weights and Weighing.—The most convenient weights 
to be used in all medical or physiological investigations are 
the French. They possess the great advantage, first, of being 
decimal, and, second, they give the means of converting weight 
into volume, since the cubic centimetre of distilled water"at 4°&C. 
weighs exactly one gramme, which is the unit of weight. GENERAL PROPERTIES OF MATTER. 
59 
In addition to the usual weights to he placed in the pan 
pl the balance, there is a sliding weight, called the rider, which 
placed on the beam of the balance, and which may he moved 
bJ means of a sliding rod which passes through the right side of 
Ihe case of the instrument. The beam bears a graduation of ten 
Pai‘lß; according as the rider is placed on one or the other of 
these, it measures one or more tenths of its own weight, which is 
usually one milligramme. 
It is well always to use the same pan of the balance for the 
weights. The most convenient for the majority of persons 
uiU be the right-hand pan as one sits facing the balance. The 
sliding rod also is on this side. Substances to be weighed 
should never be placed directly in the pan of the balance, but a 
tew thin watch-glasses should be procured. These should be 
uumbered by diamond scratches on the glass, and the weight of 
each determined and recorded, or a counterpoise may be made 
or.each. Either of these devices will save loss of time in 
Weighing the watch-glass each time it is used. 
vv hen a weighing is to be executed, the balance should be 
psted by throwing it into action and seeing that the pointer 
'ifrat:eß efiually on each side of the zero of the scale. Any 
mange in the level of the base should be corrected by the 
screws and spirit-levels. The watch-glass should then be tested 
° see it has not lost any of its weight by accident. The sub- 
stance is then placed in the watch-glass, and if a counterpoise is 
used the weight is obtained at once. If only the weight of the 
Watch-glass is known, this is to be subtracted from the total 
u eight of the substance and the glass, when the weight of the 
alone is obtained. 
. lue weights should not be touched with the fingers, but the 
PUlcers m the weight-box should be used. To avoid error in 
fading the weights, they should be removed from the pan and 
Paced in their order of value, either on the base of the balance 
1 °u the table, and counted up in that position before they are 
in the weight-box. To the weight so obtained, the 
efitht indicated by the rider should be added if it has been used, 
tb *^rometric bodies, or substances that absorb moisture from 
U^r’ Bh°uld be placed in a watch-glass, the edges of which 
c e ground fine and fit closely, air tight, to a fiat ground-glass 
ver or £0 another watch-glass. The watch-glass and its 
should be placed in a hot-air box, and dried at 100° C. 
e] /°U 8 judged that the exposure has been sufficient, the 
aparn^er Bh°uld be opened, the watch-glass quickly covered and 
is ?uVe(* over sulphuric acid in the drying apparatus. It 
p,i uen to be weighed and the weight recorded. The watch- 
-18 then uncovered and again exposed in the oven, twenty 
Unites or so; it is then quickly recovered, cooled, and re- 60 
PROPERTIES OF MATTER. 
weighed. If the weight is the same as before, it is correct. 
If it has diminished, the operation of heating must be repeated 
until the substance ceases to lose weight. 
In a few cases where heat is inadmissible, the drying must be 
done over sulphuric acid, with or without a vacuum. Light 
test-tubes closed by rubber stoppers are used sometimes in place 
of watch-glasses with covers. 
38. Essentials in a Good Balance.—Ist. The distances from the 
edge of suspension of the beam, to the edges of support of the 
pans on each side, should be exactly equal. 
2d. When the pans are empty, the needle should point to the 
zero of its scale. The long axis of the beam is then in the hori- 
zontal position. 
3d. When the beam is horizontal, its centre of gravity (34) 
should be vertically beneath the knife-edge of the fulcrum. 
The sensitiveness of the balance, or its power to determine 
very small weights, or very small differences between two 
weights, depends upon three conditions: 
Ist. The longer the beam, the greater the delicacy of the 
balance, the length being measured between the points of sus- 
pension of the pans. 
2d. The weight of the beam should be as small as is con- 
sistent with rigidity. 
3d. The centre of gravity of the beam should be as near as 
possible to the edge of support and beneath it. 
A good physical or chemical balance, when charged with 1000 
grammes, or a kilogramme, in each pan, should indicate a dif- 
ference of less than YUW a gramme, or a milligramme, 
between the contents of its pans. 
39. Method of Double Weighing.—Though a balance is not 
quite accurate, it may nevertheless be used for the exact deter- 
mination of the weight of a substance by the above named 
device. The operation consists in putting the object in one pan, 
and then counterpoising it with shot and tinfoil in the opposite 
pan. The object is then removed from its pan and weights 
placed therein until the exact weight of the counterpoise is de- 
termined. This weight represents the weight of the object, 
since both it and the object have balanced the counterpoise, and 
are, therefore, equal. 
40. Density or Specific Gravity.—A cubic inch of lead is almost 
forty times as heavy as a cubic inch of cork. As a rule, solids are 
heavier than liquids. To this there are notable exceptions. 
Organic and organized bodies generally float on the standard 
liquid, water. The metals potassium, sodium, and lithium, are GENERAL PROPERTIES OF MATTER. 
61 
also lighter than water, lithium being hut little more than half 
as heavy as that fluid. Mercury, on the contrary, presents us 
|vith a liquid form, on which all rocks and nearly all metals float. 
Iron drifts on its surface as readily as wood does on the surface 
°f water. 
A very good definition of density or specific gravity is that it repre- 
sents the weight of a given volume of a body compared with that of an 
e<jual volume of some other substance, taken as a standard. In the 
case of solids and liquids, water is the standard. If to it the 
value 1 is given, then the specific gravity of platinum, which is 
ab°nt twenty-two times as heavy, becomes 22. In like manner, 
be unit of specific gravity for gases and vapors is either air or 
hydrogen, 
41. Mobility.—Mobility is that property of matter by virtue of which 
1 5 position may be changed. 
Motion and rest may be either absolute or relative. They are 
absolute when the change or fixity of the position of a body is 
eterred to ideal fixed points in space. They are relative when 
eterred to surrounding bodies. A passenger on a steamer may 
e relatively at rest as regards the boat and the objects thereon, 
.JA k*6 i§ a state of relative motion as regards the banks of 
le river. These, in their turn, may be relatively at rest as 
egards the earth itself, but in motion when considered in rela- 
tb°n °^ier planets and stars. For practical purposes we may, 
t crefore, say, that absolute rest and motion are unknown, we 
cal with rest and motion only in their relative state. 
*a- inertia,—By this we understand that matter cannot of itself 
nf)e its condition either of rest or motion. If at rest, it remains 
until some force acts upon it to produce movement. If in 
°tion, it continues to move until some force causes the move- 
meM to cease. 
When we release our grasp on any object it falls to the earth, 
sulf llloVement Is not by virtue of any inherent property of the 
stance, but because it is acted upon by the force of gravity, 
bo riae'hullet finally comes to rest, not by virtue of its own 
ea ~.erS’ on account of the resistance of the air and other 
I®es. If there were no such counteracting forces, it would 
ume to move forward at the same rate forever, 
see of inertia of motion are offered by a careless de- 
cee Aom a moving vehicle: our feet strike the ground and 
bofi nove’ while the movement of the upper part of the 
dei t continues, and we are thrown prostrate. The fearful acci- 
en»‘S .Always are due to this cause. The motion of the 
bine being suddenly checked, the cars continue their advance, 62 
PROPERTIES OF MATTER. 
and are shattered by the force with which they are driven into 
each other. 
The following simple experiments on inertia of rest are not 
without interest. If we place a card upon a goblet, and then 
rest a coin upon the card, we may, by a sudden fillip of the 
finger, cause the card to glide oft' the tumbler. The coin does 
not pass with it, but, detained by its inertia, drops into the 
vessel, drawn down by gravitation. Gentle pressure against a 
suspended sheet of glass will cause it to move, while if a pistol 
be fired at it from a sufficient distance the bullet passes through 
the glass without producing the slightest change of position in 
the latter. 
43. Porosity.—The interstices or spaces between the parts of 
a substance are of two kinds, Ist. Physical pores, which exist 
between the molecules, and are so minute that the molecular 
forces of attraction or repulsion act across them. 2d. Sensible 
yores, cells or cavities across which these forces cannot act, on 
account of their magnitude. The effects of temperature in 
causing variations in the size of bodies are possible by virtue of 
the existence of physical pores or interstices (19, 20). In or- 
ganic substances the sensible pores are of especial importance, 
since they permit the functions of absorption, exhalation, and 
circulation. 
The existence of sensible pores in organic bodies may be 
illustrated by placing them in a vessel of water under an air- 
pump bell. An apple or a potato thus treated yields up innu- 
merable bubbles of air or gas, which escape from the cells or 
pores of the fruit or tuber. If the weight of the object of the 
experiment be taken before and after exhaustion, the increase 
in weight will show the extent or volume of the pores, since it 
represents the quantity of water which has replaced the air con- 
tained in them. 
In sponge, and in pumice, the sensible pores are of consider- 
able size and easily visible. In metals, on the contrary, they 
are very minute. Gold, for example, was shown by the Flor- 
entine academicians to possess pores, in the following way: 
They were attempting to determine the compressibility of 
water. For this purpose the fluid had been enclosed in a 
sphere of gold, which was hermetically sealed. The sphere 
was then submitted to pressure; any change in shape they knew 
would be attended by diminution in its capacity. Their surprise 
may be imagined when, on applying the force, minute globules 
of water were seen to ooze from the metal, and cover its”surface 
with dewy drops. As is so often the case, the experiment, insti- 
tuted to determine one fact, resulted in the unexpected estab- 
lishment of another and totally different one. The same ex- GENERAL PROPERTIES OF MATTER. 
63 
periment has since been repeated with globes of other metals, 
and the existence of minute sensible pores demonstrated. 
Among the practical applications of sensible pores, we may 
Mention the process of filtration through felt, paper, charcoal, 
stone, so commonly employed for the purification of water. 
opening of seams in rocks, by introducing dry wedges of 
'v°od and then wetting them, when they expand with great 
J°rce, furnishes another example of the existence of pores. 
44. Compressibility is a direct consequence and demonstration 
°f porosity. 
The most compressible bodies are gases, some of which may 
oo forced to diminish to one hundredth of the bulk they present 
fd ordinary temperatures and pressures. To this there is, 
however, a limit in every case, for under sufficient pressure and 
foduction of temperature, gases assume the liquid state. 
Solids in many cases are compressible to a moderate extent. 
■t-is is best shown by organic substances, as wood and paper, 
ratals also, when submitted to the pressure of the die in coin- 
ln|v or when hammered, undergo an increase in specific gravity, 
hich can only be explained by the diminution in the size of 
oeir pores, and consequent diminution in volume. 
the case of liquids the compressibility is the least for small 
P1 assures, and was for a long time denied. It however exists, 
s Will be shown when we study the properties of this form of 
flatter. 
45. Elasticity is the property by which certain bodies reassume 
eir original volume or form, when the force that has produced 
lQnge is removed. 
leases and liquids are endowed with this property, as regards 
oiurne, to a remarkable degree. They may indeed be said to be 
)solutely elastic (168). Solids, as we have seen, are very gen- 
rally compressible, but a few, like ivory, possess a certain 
■jAgree of elasticity. The elasticity of solids is rather that of 
, riri than of volume, and belongs to the consideration of the 
1 r°perties of this special kind of matter (67). 
ti we have already dealt with in the examina- 
refer°^j^le structure °f matter (22), to which the reader is SECTION 11. 
SOLID MATTER. 
CHAPTER IY. 
GENERAL CHARACTERS OF SOLIDS. 
The physical forms of matter—Chemical divisions of matter—Form is fixed— 
Resist compression—Extent of volume variation—Density—Hydrostatic 
balance—Specific gravity by volumetric method—Nicholson’s hydrometer— 
Specific gravity of powders—Specific gravity of bodies soluble in water 
—Bodies lighter than water—Table of specific gravities—A divided solid 
does not reunite. 
47. The Physical Forms of Matter.—Physicists classify matter 
under three typical forms: Ist, Solid; 2d, Liquid; 3d, Gas. 
Some add a 4th, Radiant or ultra gaseous. 
It is to be understood that by proper means these forms may 
be transmuted one into another. The terms are applicable 
to each substance only under the ordinary conditions of tem- 
perature and pressure. 
The demarcations between these forms are not always clean 
cut. Certain liquids, for example, pass through an intermediate 
or pasty condition before they become solid; others are gela- 
tinous, others viscous. 
Intermediate between liquids and gases, we find a group 
of bodies called vapors, which closely resemble gases, except 
that they are easily convertible into liquids. In all probability 
there is a continued gradation, from the densest solid to the 
most rarefied form of gaseous matter. 
48. The Chemical Divisions of Matter.—These are three in 
number: Ist, Inorganic bodies; 2d, Organic; and, 3d, Organ- 
ized, A knowledge of the general characters of these groups 
is necessary for the proper comprehension of our subject. 
The inorganic group includes all the ordinary objects on 
the globe which have not been dependent upon life action in GENERAL CHARACTERS OF SOLIDS. 
65 
plants or animals for their production. Minerals of all kinds, 
ail(l ores, water, and air, are typical examples of this division. 
Certain bodies, as marble, chalk, graphite, have been produced 
through the intervention of life action, yet they are truly inor- 
ganic substances; others, on the contrary, like bituminous coal, 
taay be grouped with organic substances, since, on being distilled, 
they yield oily bodies which are organic in their nature. The 
|ype of visible structure among inorganic bodies is the crystal- 
une, many are non-crystalline or amorphous, while a few, like 
Wrought iron, are fibrous. 
Organic and organized bodies are all compounds of carbon, 
ko absolute is this fact that their study is often spoken of as the 
study of the carbon compounds. isText to carbon are present, 
hydrogen, oxygen and nitrogen, the order of frequency being the 
as that in which they are mentioned. All substances of 
hese groups are decomposed by a heat less than 1000° F. If 
heated in vessels to which air does not gain free access, a black 
Residue of charcoal or carbon is left, which may be entirely 
hnied away in a current of air. 
Organic differ from organized bodies in that they are gener- 
aily crystalline in structure. Though commonly the product of 
he action—e.g., sugar—many of them have been made in the 
by the union of the elements themselves, without 
16 intervention of any life action. Acetyline, for example, is 
produced by the passage of the electric arc between poles of 
Pure carbon in an atmosphere of pure hydrogen. From acety- 
hie alcohol may be made, and from alcohol fatty bodies which 
O j -I t/ * 1/ 
e truly organic in their nature. Every day adds to the list of 
bodies produced by purely chemical processes, and 
°nbtless the majority of these substances will in time be pre- 
pared artificially.' 
Organized bodies, on the contrary, have never yet been pro- 
need by process into which life action does not enter, and we 
lay safely say that they never will be. They airier from simple 
lganie bodies, in that their structure always shows the pres- 
Rce either of the cell or of the fibre. They are not crystalline, 
°ngh they may enclose crystals of organic or inorganic bodies. 
9. The Form of Solids is Fixed.—True solids have a perma- 
tP form. In this respect they differ essen- 
\vl • , rom liquids and gases, which take the form of the vessel in 
is 101 are placecl' In certain resinous bodies this quality 
it 0s^e®se(l only in a low degree, these substances slowly chang- 
*§ their form in the lapse of time. Among the true solids 
me show more or less of plasticity; for example, ice. It is 
e possession of this character which enables a glacier to follow” 
e curves and windings of the valley through which it descends. 66 
SOLID MATTER. 
Prof. Tyndall attributes the plasticity in this case to alternate 
fusions and freezings of the ice, to which he has given the 
name of regelation. 
50, Eesist Compression.—True solids resist any ordinary force 
of compression to which they may be subjected. While some 
possess this power to only a slight degree, others possess it to a 
remarkable extent. All at last, however, reach their limit of 
resistance. Some, like quartz and glass, are crushed, while 
others, as the metals, undergo an actual diminution in bulk. 
51. Extent of Volume Variations.—While changes of tempera- 
ture and of pressure produce variations in the volume of a solid, 
these are exceedingly minute, compared with similar changes 
in liquids and gases. Of this fact we have seen an example in 
the case of the experiment (19), in which very delicate means 
were required to determine the expansion of the mass of metal. 
52. Density of Solids.—To obtain the specific gravity of a solid, 
as urinary or biliary calculi or a urinary sediment, we must 
know its weight in air, and the weight of an equal volume of 
water. The first is then divided by the second, when the quotient is 
the specific gravity. 
The conditions under which the determinations of specific 
gravity are to be made vary as follows: 
1. Solids heavier than water and insoluble therein. 
2. Powders heavier than water and insoluble therein. 
3. Solids heavier than water and soluble therein. 
4. Solids lighter than water and insoluble therein. 
5. Solids lighter than water and soluble therein. 
By the -principle of Archimedes, a body immersed in water dis- 
places its own volume of that liquid, and at the same time loses 
a part of its weight equal to the same bulk of water. Our 
Fig. 6. 
object being to determine the weight of a volume 
of water equal to the bulk of the substance, we 
may, by applying the principle stated above, 
obtain it at once by weighing the body in water, 
when the loss of weight will be the weight of 
an equal volume of water. This is the ordinary 
process, and is called the method by the hydro- 
static balance. 
53. The Hydrostatic Balance.—The application 
of this process to the first condition given above is 
as follows : The object (D) is suspended by a fine 
Hydrostatic balance. 
fibre (C) to one arm (A) of a balance. Weights are placed in the 
opposite pan. The weight in air is thus obtained: A vessel 67 
GENERAL CHARACTERS OF SOLIDS. 
°f water (E) is then placed beneath the suspended object, and 
raised until the object is completely ‘ immersed in the fluid. 
The weight is again determined; it is the weight in water. The 
Weight in water being subtracted from the weight in air, we 
have the weight of a bulk of water equal to that of the object, 
for example: 
Weight in air 10 
Weight in water = 8 
Loss of weight in water 2is weight of equal bulk of water. 
Then by (52), 
Weight of equal bulk, water 2) 10 weight in air, 
5 specific gravity. 
54. Specific Gravity by Volumetric Method.—A second method 
for obtaining the specific gravity under the first condition is that by 
volume. It is well adapted to many medical purposes, and 
though not so accurate as the preceding, gives proximative 
results that are sufficient!}7 exact for ordinary use. 
The apparatus to be employed consists of a tube graduated to 
oubic centimetres. This is partially filled with distilled water, 
ouch division of the scale then represents one gramme of water. 
The solid to be examined may be either in mass or in small 
fragments. Its weight in air in’grammes is first obtained. It is 
then dropped into the liquid in the tube and all bubbles of air 
removed from its surface. The amount of water displaced is 
shown by the rise of the fluid on the scale. This is read off, and 
gives at once the weight in grammes of a volume 
of water equal to that of the substance. The 
Weight of the body in air and that of an equal 
volume of water being known, the specific 
gravity is obtained by the usual calculation. 
Fig. 7. 
55. Nicholson’s Hydrometer.—Another method 
tor the determination of specific gravity of solids, 
18 by means of Mcholson’s hydrometer. 
This instrument consists of a hollow metallic 
float A which bears a weight-pan above at B, and 
an°ther below at C. The apparatus is placed in 
floater, and weights added to the upper pan B to 
81nk the cylinder to a mark on its stem. Let this 
oe 120 grains. It is removed and a mass of the 
substance less than 120 grains in weight placed 
thereon. Weights are then added until the water 
jSTicholson’s 
hydrometer. 
touches the mark on the stem of the apparatus. Suppose 20 
grains have been added, this subtracted from 120 grains gives the 68 
SOLID MATTER. 
weight of the body as 100 grains, which is the weight of the body 
in air. The substance is now transferred to the lower pan C. The 
cylinder does not sink as deeply in the water as before. More 
weight must be placed in the upper pan to bring the mark to the 
level of the water. Suppose the weight now added to the upper 
pan is 50 grains, this represents the weight of the water displaced 
by the object. Then dividing 100, the weight in air, by 50, the 
weight of equal volume of water, we have the specific gravity. 
If the body is lighter than water, it is confined to the lower 
pan by a wire cage. 
56. Specific Gravity of Powders.—ln the second condition, of 
'powders heavier than water and insoluble therein, the method is as 
Pig. 8. 
follows: A specific gravity flask (A) with a wide 
mouth is to be used. The stopper is perforated 
and gives passage to a narrow tube which expands 
above into a larger one. A counterpoise for the 
flask should he made and kept in the opposite 
pan throughout the operation. The flask should 
always be tilled to a certain mark (B) when a liquid 
is used. The excess of fluid which rises into the 
upper tube above this point should be removed 
by blotting paper. The steps of the operation 
are as follows: 
Ist. The quantity of distilled water at 4° C. 
the counterpoised flask will hold when the per- 
forated stopper is in position and filled to the 
mark is determined. 
Specific gravity 
flask. 
2d. The flask is carefully dried, some of the dry powder 
is introduced, the stopper placed in position, and the weight of 
the powder introduced determined. 
3d. The weight of the water the flask will hold and the 
weight of the powder are added together. Let this be w. 
4th. The flask containing the powder is then half tilled with 
water, placed under an air-pump bell and exhausted. The en- 
trapped air is thus removed, the powder is allowed to settle, the 
flask is filled completely, the stopper introduced, excess of fluid 
above B removed, and the weight determined. Let this be v. 
The weight v is then subtracted from the weight w, the result 
represents the weight of the water the powder has displaced. 
The weight of the powder and the weight of an equal volume of 
water being known, the specific gravity is calculated as before. 
This method is employed in the determination of specific gravity 
of uric acid and other insoluble sediments. 
57. Specific Gravity of Bodies Soluble in Water.—To meet the third 
condition, in which the body is soluble in water, some other fluid, as 69 
GENERAL CHARACTERS OF SOLIDS. 
°T of turpentine, or naphtha, in which it is insoluble is substi- 
tuted. The correct specific gravity is then obtained by multi- 
plying the number found by the specific gravity of the fluid 
used in the experiment. All the preceding steps are conducted 
us before. 
58. Bodies Lighter than Water.—For the fourth condition, body 
lighter than water, hut insoluble, the steps are as follows: 
Ist. Ascertain weight of substance, is A. 
2d. Determine weight in water of a piece of lead heavy 
enough to sink it, is B. 
3d. Attach light body to the piece of lead and determine the 
conjoined weight in water, is C. 
4th. Deduct Cfrom B and add A, this is D. 
sth. Divide A by D, and the result is the specific gravity of A. 
The fifth condition, body lighter than water and soluble therein. 
4 he specific gravity flask is to be employed, and benzine substi- 
tuted for water. The steps are the same as before described for 
the flask operation. The weight of a bulk of water equal to 
that of the displaced benzine is obtained by the following equa- 
tion : As specific gravity of benzine is to the weight of benzine 
displaced, so is the specific gravity of water to the weight of 
volume of water equivalent to that of the body. 
Weight of substance and weight of equivalent volume of water 
being obtained, density is calculated as before. 
59. Table of Specific Gravities.—Specific gravity of solids as com- 
pared with distilled water at 4° G. 
Platinum, rolled 
22.069 
China porcelain 
2.385 
Platinum, cast 
Gold, stamped 
20.337 
Sevres porcelain 
2.146 
19.362 
Native sulphur 
2.033 
Gold, cast 
19.258 
Bone 
2.010 
Lead, cast 
11.352 
Ivory 
1.917 
Silver, cast 
10.474 
Anthracite 
1.800 
Bismuth, cast . 
9.822 
Compact coal . 
1.329 
Copper, drawn wire 
8.878 
Muscle 
1.085 
Copper, cast . 
8.788 
Amber 
1.078 
German silver. 
8.432 
Soft organs of body . 
1.050 
Brass 
8.383 
Brain 
1.040 
Steel, not hammered 
7.816 
Sodium 
0.970 
Iron, bar. 
7.788 ' 
Lung with air . 
0.940 
Iron, cast 
7.207 
Melting ice 
0.930 
Tin, cast. 
7.291 
Pat . 
0.920 
Zinc, cast 
6.861 
Solid ice . 
0.917 
Antimony, cast 
6.712 
Potassium 
0.865 
Iodine 
4.950 
Beech 
0.852 
Heavy-spar 
4.430 
Oak . 
0.845 
Diamonds. . 3.581-3.501 
Elm . 
0.800 
Plint glass 
3 329 
Yellow pine 
0.657 
Statuary marble 
2.837 
Lithium . 
0.585 
Aluminium 
2.680 
Common poplar 
0 389 
Bock crystal . 
St. Gobin glass 
2 653 
2.488 
Cork 
0.240 70 
SOLID MATTER, 
60. A Divided Solid does not Reunite.—If a gas or a liquid be 
divided by any object passing through it, it reunites im- 
mediately behind the dividing body. In solids this, as a rule, 
is not the case. There are, however, a few exceptions: India- 
rubber will reunite by its freshly cut surfaces. Some of the 
metals will also reunite behind a cutting tool if they are at the 
same time submitted to very great compression. 
CHAP TEE Y. 
SPECIAL PROPERTIES OE SOLIDS. 
Crystallized and amorphous—Hardness—Fragility—Malleability—Ductility—Te- 
nacity—Elasticity—Contractility—Elasticity of compression—Elasticity of 
flexure—Elasticity of torsion—Pliancy—Opacity, transparency, color—Build- 
ing materials—Hypothetical consitution of solids. 
61. Crystallizable and Amorphous.— The cohesive or attractive force 
by which the molecules of a solid are held in their place, is not always 
equal in all directions around each molecule, hut is greatest in certain 
positions, lines, or planes, as is the case with the poles of a magnet. 
When the molecules of such a body are free to move, they 
arrange themselves in relation to these lines or planes, and pro- 
duce more or less perfect forms called crystals. Substances 
which do not possess this property are called non-crystalline 
or amorphous. 
Crystallization of a solid may take place in two ways. Ist, 
From the fused or melted body, as in the case of bismuth. This 
is called crystallization in the dry way. 2d, From a solution of 
the substance in water or some other solvent liquid. This is 
called the moist way. 
Water in the act of solidification presents a beautiful example 
of crystallization. The moisture which on a cold day congeals 
on the pavement or on windows, presents varied forms, closely 
resembling the leaves and stems of ferns and other low varie- 
ties of vegetation. One can hardly give these frostings a pass- 
ing glance without suspecting that the outlines of inferior plants 
are determined by the simple act of the passage of water from 
the fluid to a more or less fixed condition of solidity. 
Under the microscope the formation of crystals of inorganic 
and organic bodies from their saturated solutions, presents SPECIAL PROPERTIES OF SOLIDS. 
71 
m°st interesting phenomena. We may in this way detect the 
presence of numerous substances on a very minute scale. As 
an of this method, we may cite the example of urea, 
an exceedingly soluble body with so great an avidity for water 
that it will absorb it from the air, and deliquesce or form a 
solution. If to a drop of such a solution, placed on a micro- 
scope slide, we add a drop of nitric acid, the nitrate of urea 
forms. This being but little soluble in water crystallizes out, 
and by the appearance of the peculiar table-like crystals, we 
are at once informed of the presence of urea in the liquid under 
examination. 
The satisfactory demonstration of the crystalline structure of 
f1 soliq soluble in water may be obtained by placing a portion of 
hm a saturated solution thereof. Under these conditions the 
dissolution takes place very slowly, and the crystals composing 
the body are dissected out from the mass. Under this method 
°1 operation alum may be made to exhibit its structure of regu- 
ar_ octahedrons. Experiments of this nature show that the 
resistance to solution is strongest along the crystalline planes. 
In like manner, if we attempt to split a crystalline body by 
rneans of a point or an edge, as we would split wood, we find 
that it yields with comparative ease along certain planes which 
give smooth surfaces of fracture, whereas it cannot be split, but 
°iiiy broken along other planes, the fracture showing rough in 
Place of smooth surfaces. This splitting along certain planes 
111 preference to others is called cleavage. It is exhibited in 
greater or less perfection by all inorganic and organic crystal- 
line bodies. 
In the examination of the deposits which appear both in 
wealthy and morbid urine, a knowledge of the crystalline forms 
presented by various normal and abnormal ingredients of this 
<X?niplex fluid are of the utmost importance for the purposes of 
diagnosis. A few moments spent in the careful microscopic 
®Xaniination of such sediments, and the detection of certain crys- 
a|nne forms, will at once throw a flood of light on what may 
otherwise be a very obscure and puzzling disease. 
Ihe detection of the presence of poisons also may be greatly 
aeilitated by a microscopic examination of the crystals obtained 
I°m the solutions administered, and sometimes even of the 
secretions and excretions of the body. For an admirable dis- 
cussion of this, the micro-chemistry of poisons, the student is 
referred to the excellent work of Frof. Theo. Gr. Worrnley, M.D. 
Mention has been incidentally made of the fact that certain 
eiganic bodies assume a crystalline form, while others do not. 
odies which are of the crystalline type, possess the property 
M passing with considerable facility through membranous struc- 
ures of various kinds. Those which do not crystallize, as, for 72 
SOLID MATTER. 
example, albumen, possess this property of permeating mem- 
branes to a far less degree. Hence arises the division of bodies 
into the two groups, crystalloids and colloids. This will be found 
discussed at greater length in the article on dialysis. 
62. Hardness is a relative property. By it we understand the 
resistance which one- body presents to being abraded, worn, or 
scratched by another. It is entirely independent of density. 
Pure gold, for example, is one of the heaviest metals, but it is 
very soft. The true cause of hardness appears to be the force 
with which the molecules resist any change in their polar or 
crystalline arrangement. 
For the purposes of the mineralogist, a scale of different 
degrees of hardness, known as Mohr’s scale, is used. It consists 
of the following ten substances, each member of the list being 
harder than that preceding it: 
1. Talc. 
6. Adularia feldspar. 
7. Eock-crystal. 
8. Prismatic topaz. 
9. Corundum. 
2. Eock-salt. 
3. Calc-spar. 
4. TTuor-spar. 
5. Apatite. 
10. Diamond. 
To test the hardness of a body, we determine which of these 
it will scratch, beginning with the hardest. If it is scratched 
by topaz, but scratches quartz or rock-crystal, we say its hard- 
ness is between 7 and 8. 
Alloys, as a rule, are harder than the metals composing them; 
therefore, in the mints gold and silver are alloyed with copper 
to give them sufficient hardness to resist the wear and tear of 
circulation. The resulting coin is far harder than either of the 
metals in the pure state. 
There is no relation between the hardness of a body and 
its power to resist compression. A blow which shivers hard 
glass is easily resisted by soft wood. Hardness is also often 
independent of the chemical composition of a body. Carbon, 
for example, in the form of the diamond is the hardest sub- 
stance known; in the form of graphite, on the contrary, it is so 
soft that it is easily cut by the thumb-nail, and it is even used 
as an antifriction or lubricator for the journals and axles of 
wheels. 
When certain bodies, like steel, are raised to a specified tem- 
perature and then suddenly chilled, they are endowed with 
exceeding hardness. This operation is called tempering. Upon 
it all our surgical and other cutting implements of steel depend 
for their power to retain their sharpness or edge. In the case 
of an alloy of copper and tin, called tamtam metal, sudden chill- SPECIAL PROPERTIES OF SOLIDS. 
73 
ing in water produces exactly the opposite effect, the alloy being 
soft when quickly, and very hard when slowly cooled. 
We have thus far considered the question of hardness in rela- 
tion to inorganic bodies alone. We have seen that the miner- 
alogist employs a scale of tolerable exactness to determine the 
relative hardness of the bodies with which he deals. It is sur- 
prising that, with this example before him, the physiologist and 
pathologist have not yet contrived a scale by which this factor 
Df the properties of the bodies they examine might be expressed 
with some approach to accuracy and fairness of comparison. 
While the hardness of enamel, dentine, bone, and horn, as in 
the finger-nail, may be expressed by Mohr’s table, that of various 
tissues and of tumors like cancer, falls outside of its limits. A 
table of hardness constructed on a scale prepared by a known 
mixture of resin, wax, and oil in ten different proportions, and 
used always at 32° F., or in a mixture of ice and water, would 
doubtless give results regarding the hardness of various tissues 
and tumors, which would be of considerable importance from a 
diagnostic point of view. 
63. Fragility.— Though allied to hardness, fragility is distinct there- 
from. It is true that, as a rule, very hard bodies are also brittle 
or fragile. The molecular conditions that produce hardness, 
also conduce to fragility. Sudden changes of temperature are 
Very apt to cause a substance to become fragile. Glass, for ex- 
ample, if suddenly chilled, as in the formation of Rupert’s drops, 
is marvellously brittle. The fracture of a portion of the tail of 
these tadpole-shaped objects, immediately causes the body to fly 
mto thousands of pieces. Even in the ordinary state glass is too 
brittle for common use, unless it has been reheated and very 
slowly cooled. Such an operation is called annealing. It often 
requires many days for its successful completion. If proper 
eare is taken in this operation, the glass may have its brittleness 
so reduced as to bear very rough usage. It may even be dropped 
from a height on to the floor, or submitted to the blows of a 
hammer. In this condition it is known as malleable glass. In 
Rs malleable state the glass differs hut little from a Rupert drop 
ln hardness, while the difference in fragility or brittleness is 
very great. 
Among organized bodies like bone, variations in fragility are 
frequently seen. In this case, however, the change is owing to 
alteration in chemical composition or proportion of the ingre- 
dients entering into the structure of the substance. 
64. Malleability is the property by which certain bodies may be 
beaten or rolled into exceedingly thin leaves. In these substances the 
molecules appear to have no particular lines of coherence, but 74 
SOLID MATTER. 
to suffer themselves to be pressed or forced out of their position 
in all directions with equal facility. In this respect they re- 
semble the particles of a liquid. 
Of all metals, gold is the most malleable. It may be beaten 
into leaves °f an inch thick. In this state of tenuity, 
the metal allows a bluish-green light to pass through it. Tin also- 
is quite malleable, and may be made into leaves the i-610 oth part 
of an inch thick. It is by virtue of this property of malleability 
that the coppersmith produces from flat sheets of copper, various 
hollow domestic utensils, as kettles, without a single seam or 
crack throughout their whole extent. 
Of the ordinary malleable metals two, viz., platinum and iron, 
possess the property of being welded, or united together at a 
white or red heat. By the discovery of this welding 'property in 
the case of platinum, a distinguished English chemist is said to 
have made an enormous fortune by his own hands. He bought 
platinum black and scrap metal, and raising it to a white heat 
submitted it to blows in a steel cylinder, and thus converted it 
into bars or ingots, thereby more than quadrupling its value. 
The welding property of gold at the ordinary temperature of the 
air is applied by the dentist in filling teeth. 
65. Ductility.—Allied to malleability, but differing therefrom, 
is that property possessed by some metals which enables us to draw 
them out into wires of marvellous fineness. 
A platinum wire only the ■3o^onth of an inch in diameter, was 
made by Hr. Wollaston in the following way : A wire of plati- 
num was placed in the interior of a silver cylinder; the compound 
bar was then drawn out in the usual way, until the limit of 
ductility was reached. The silver was then dissolved in nitric 
acid, when a platinum wire remained, which was about half the 
thickness of the thread of a spider’s web, and only distinctly 
visible when heated to redness in a flame. 
Hext to platinum, the order of ductility for the metals is 
silver, iron, copper, gold. Molten glass is also very ductile. 
Certain organic bodies rival and even surpass inorganic sub- 
stances in this respect. Sugar, for example, may, at certain 
temperatures, be drawn into threads far finer than the wires of 
many metals. 
Of all known bodies, that which possesses this property in 
the highest degree is the liquid silk from which the spicier spins 
its gossamer thread. Hear the extremity of the abdomen in 
these creatures, there are four to six nipples, each of which, in 
some species, is perforated by about a thousand minute holes. 
From these the adhesive fluid oozes to form the thread, which 
hardens on contact with the air. The final thread of the web,, SPECIAL PROPERTIES OF SOLIDS. 
fine as it is, therefore, contains innumerable minute threads 
which have issued from the apertures of the spinneret. 
66. Tenacity is defined by Ganot as “ the resistance which a 
b°dy offers to the total separation of its parts.” It differs according 
t° the manner of application of the force. In the ordinary sense 
is resistance to traction, or a pulling force. If applied to re- 
sistance to fracture, it is called relative; to resistance to crushing, 
>eactive; to resistance to lateral displacement, sheering; to resist- 
ance to twisting, torsional. 
Continued application of a force diminishes the tenacity of a 
wire; elevation of temperature has the same effect. Tenacity 
also varies with the form of the bar; it is greater in a cylinder 
man in a prism, and greater in a hollow than in a solid cylinder. 
the latter case it reaches its maximum, when the external 
lad ms is to the internal as 11 to 5. The tenacity of many 
bodies is greater in one direction than in another. Wood, for 
Sample, offers greater resistance with the grain than across it. 
Animal and vegetable structures offer numerous examples of 
me use of hollow cylinders to increase tenacity. The quills of 
ii oa^iers5 the bones of animals, and the stems of grain, are 
ah constructed on this plan. The fibre of the silk-worm has a 
cnacity equal to that of brass wire, and three or four times that 
°t a hemp fibre of equal diameter. Ligaments and tendons are 
Very tenacious. Catguts made of intestines of the sheep and 
£>° fit, also possess great tenacity. 
Ihe superiority, in this respect, of iron and steel over other 
substances is shown by the following table, in which the weight 
ln tons, supported by a rod one inch square in section, is given. 
Metals. 
Cast steel. 
45-60 tons. 
Silver . 
. 5 tons 
Wrought iron . 
25-30 “ 
Gold . 
. 4J “ 
Ca|f iron . 
6-13 “ 
Zinc 
. 2 “ 
Copper . 
9-26 “ 
Tin 
. U “ 
Platinum 
8 “ 
Lead 
. \ “ 
Woods. 
Teak 
7-9 J tons. 
Deal 
. 6 tons. 
Oak. 
4-9“ 11 
Beech . 
. 5 “ 
Ash. 
8 “ 
67. Elasticity, in general terms, may be defined as the propertg 
V virtue of which a body that has been changed by the action of force 
1 e9<nns its original form and size when the force is relaxed. In liquids 
na gases the term is applicable only to variations in volume; in 
k °hds it applies also to the position of the molecules. 
Loth hard and soft solids are endowed with elasticity. In the 
°rmer the extent of strain permissible within the limits of 76 
SOLID MATTER. 
elasticity is much less than in the latter. If the limit of elasticity 
is exceeded, a permanent set is produced, as, for example, when 
the ligaments of a joint are sprained. 
As was the case with tenacity, elasticity in solids presents 
itself under different aspects, viz.; Ist, of traction; 2d, of com- 
pression; Bd, of flexure or bending; 4th, of torsion or twisting. 
In ordinary parlance, elasticity of tension or traction is applied to 
bodies like India-rubber, which will undergo considerable elonga- 
tion without breaking. In such cases the return to the original 
length is only partial, and after they have been stretched a few 
times they show a permanent elongation. The true force of 
elasticity in solids in scientific signification, is not so much that 
property which permits extension as it is that which permits the 
displaced molecules to return to their original position. 
Among animal tissues, examples of elasticity of traction are 
offered by the yellow elastic tissue in the arteries and by the 
ligamentum nuchee. It is said that in the long neck of the 
giraffe, if the ligamentum nuchse be cut from its attachments to 
the vertebrae, it cannot again be stretched to its original length 
without rupture, so great is the force with which it has con- 
tracted upon itself. 
68. Contractility.—The power of contractility, whereby a muscle 
under the influence of nervous stimulus can increase or diminish its own 
length, is the highest development of elasticity of traction. The force 
with which a muscle contracts is not realized until we examine 
the manner in which it is attached to the bones upon which it 
acts. Invariably it works on the short arm of a lever, and, 
therefore, to produce results which appear to be feeble, very 
great contractile force must be developed. 
While acting under the control of the will, the contractions of 
a muscle are usually within the limits of its elasticity, occasion- 
ally, however, where supreme efforts hav6 been made the limit 
of elasticity is overpassed, and rupture takes place. This not 
unfrequently happens in the contractions attending certain spas- 
modic diseases, and also from the action of drugs like strychnia. 
Though docile and obedient to the nervous influence while a 
creature lives, the muscular tissue asserts itself after death, and 
makes its last and most prolonged effort of contraction, thereby 
producing the condition of the body called rigor mortis. This 
usually supervenes in from three to six hours after death, but it 
often comes on much sooner. ISTurses always bind the jaw and 
close the eyelids as soon as possible after death, experience 
having taught them that sometimes the rigor sets in in these 
parts within a few minutes. Brown-Sequard says that rigor 
mortis sometimes comes on before the heart has ceased to beat. 
In death on the battle-field, when a bullet has struck a vital 77 
SPECIAL PROPERTIES OF SOLIDS. 
part and death is almost instantaneous, rigor mortis occurs im- 
mediately. The hand grasps the rifle with a firmer grip than in 
We, and the last expression of fury, or of terror, that flitted over 
the face, is stamped on the marbled countenance of the dead 
soldier. 
Duration of rigor mortis depends largely on temperature 
among other causes. Sometimes it lasts only one or two 
hours. In winter it often endures for six or eight days; in 
very cold weather, even for two or three weeks, 
hhe slaughtering of animals for table use should always be so 
hianaged as to allow time for the rigor mortis to pass off. From 
an aesthetic point of view, it is not pleasant to dine off* a chicken 
We have just seen disporting itself on the lawn of our friend’s 
country seat. From an epicurean point of view, such flesh is 
always tough. 
69. Elasticity of Compression.—An admirable example of the 
elasticity of compression is offered by an ivory billiard ball. If such 
a ball be dropped from a height upon a smooth stone slab which 
has been smeared with black paint, the paint will form a spot 
°f considerable diameter upon the ball. Resting the ball on 
the surface of the slab, only a minute spot is formed. It is 
therefore evident that when the ball strikes the surface with 
ponsiderable force its particles are driven in, or, in other words, 
ff undergoes compression, otherwise the formation of the large 
spot is inexplicable. It is the instant return of the molecules 
ct ivory to their original position that causes the ball to rebound 
|rom the slab. This property is possessed in so high a degree 
hy ivory that long-continued use of balls made of this substance 
produces no appreciable change in their spherical shape. 
'lbis form of elasticity is exemplified in animals by the inter- 
vcrtebral substance. , 
. Elasticity of Flexure.— When a horizontal bar of metal or wood 
cs fixed, at one extremity, and a weight applied at the other, the rod 
flexes or bends. The moment it is released from the weight it 
springs back toward its first position, passes it, and after a 
greater or less number of oscillations, it comes to rest at its 
original position. This is what is meant by elasticity of flexure. 
R is of interest in connection with the phenomena of sound, as 
produced from tuning-forks and other acoustic apparatus. 
J-hese are to be the subject of study hereafter. This form of 
plasticity in metals is generally increased by chilling or harden- 
ing, and lessened by annealing. Some metals, as steel, possess 
ff in a high degree, in others it scarcely exists. It is of impor- 
tance in the construction of all forms of surgical apparatus in 78 
SOLID MATTER. 
which springs are used, as in the trusses for hernia and appli- 
ances for the correction of deformity. 
Among organic bodies, it is seen in the costal cartilages; 
wood, likewise, possesses elasticity of flexure in a high degree. It 
is also found in such substances as feathers, wool, and hair, and 
gives to them the elasticity which adapts them for use in the con- 
struction of pillows or cushions, and other articles of furniture. 
The elastic virtue in hair has rendered its use possible as a 
means for the commission of murder. Instances are on record 
in which very finely chopped hair has been mixed with food and 
administered to the victims of the poisoner. Under the con- 
tractions of the stomach the portions of hair, by alternately 
yielding and regaining their form by virtue of their elasticity, 
have worked their way into and become imbedded in the 
mucous and muscular coats of the organ, to such an extent as to 
become sources of local inflammation which has finally caused 
death. The obscurity of origin, and the natural characters of 
inflammation so produced, render the detection of the crime 
exceedingly difficult. 
71. Elasticity of Torsion is that 'property by which, when a suspended 
rod, wire, or fibre is fixed at the upper end and twisted at the lower, the 
free end returns immediately towards its original position when released 
from the twisting force. If a shot, or other heavy body, be at- 
tached to the lower end of the suspended wire, in untwisting, 
the wire passes beyond its original position, and then returns 
in the opposite direction. Thus a series of oscillations are pro- 
duced, An apparatus formed on this principle, and known as 
the balance of Coulomb, is used for the measurement of electric 
attraction and repulsion. 
Spiral springs involve elasticity of torsion in their action as 
well as other Idnds of elasticity. In certain kinds of plants, 
such spiral elastic springs are applied to the purposes of project- 
ing the seeds to a distance from the parent plant. The castor- 
oil plant can in this way throw its seeds to a distance of ten or 
fifteen feet. Elasticity of torsion is possessed in a high degree 
by wood and steel; scarcely at all by lead. 
72. Pliancy.—By this we mean the property of being suddenly bent 
and twisted without fracture, as in the making of cord from hemp 
or cotton. 
Organized bodies being commonly more or less fibrous in 
their structure, possess this property, which is very rarely found 
among minerals. 
Cotton, wool, flax, silk, hair, and all similar materials which 
are woven into cloth or fabrics, are exceedingly pliant. It may 
be said to be the chief cause of their value. SPECIAL PROPERTIES OF SOLIDS. 
79 
, Among minerals an exceptional example of pliancy is found 
m the substance called asbestos or amianthus. So flexible is 
asbestos that it has been woven into gloves, jackets, and other 
articles of clothing. Since amianthus resists the action of very 
high temperature, such articles of clothing are incombustible, 
fhe difficulty connected with their practical use, is that they 
are so heavy that if a fireman dressed in a suit of asbestos cloth 
happens to fall, it is almost impossible for him to rise again. 
73. Opacity, Transparency, Color, are important properties of 
solid as well as other forms of matter. The study of these is 
best accomplished in connection with the examination of the 
relations of light to such bodies. 
74. Building Materials.—These embody many of the proper- 
ties of solids which we have just examined. The occurrence of 
accidents whereby life may be destroyed or persons maimed, 
renders it desirable that the physician should have some knowl- 
edge regarding the changes to which these materials are liable. 
. Wood, and similar organic bodies, undergo a gradual change 
ln the nature of a slow oxidation, which Liebig has called 
er&nacausis. This destroys its fibrous and cellular character, 
and undermines its strength. The stability of wooden struct- 
ures is, therefore, of comparatively brief duration. 
In the construction of railways, the preservation of the wooden 
tics on which the rails are laid is of the utmost importance. 
Lxposed as they are to the action of weather, they are very 
prone to this destructive change. To prevent it the wood has 
been injected with various solutions, as chloride of zinc, carbolic 
ucid, tar, and others too numerous to mention. The best 
uiethod for injection seems to be to draw the solution into the 
xv°od by exhaustion, rather than to force it in by pressure. 
. Iron, now so commonly employed in construction of build- 
lngs and of railways, under the continued vibration and changes 
°f temperature to which it is submitted, occasionally loses its 
hbrous structure, and becomes highly crystalline and brittle. This 
change is especially seen in the axles of railway cars, and not 
in the rails themselves. Hence the serious acci- 
dents which occur from the breakage of axles and rails, especially 
during the winter weather when the ground is frozen and 
unyielding. 
The destructibility by fire of buildings constructed of iron is 
Wonderful. Columns and beams which appear to have un- 
finiited powers of resistance, yield in the most unexpected 
Uianner. This is largely due to the warping and the fracture 
which iron is apt to undergo, if water be thrown on it when it 
18 heated to a certain temperature. The expansibility of the 80 
SOLID MATTER. 
metal also being much greater than the stone and brick with 
which it is combined, produces innumerable cracks and fissures 
in the walls, and so undermines their strength. 
Of building materials not one equals well-made brick, in its 
power to resist the action of fire, and we may add of time. If 
the composition of bricks is of the right kind, they come out of 
the ordeal unharmed. Their edges even are unscathed. Water 
may be thrown on them when they are at any temperature, and 
they do not fissure. Stone of all kinds, on the contrary, is 
chipped, flaked, and cracked, both by the action of the fire, and 
also by the water thrown on it when heated. 
75. Hypothetical Constitution of Solids.—The best summary of 
our present knowledge of this subject is that given by Prof. 
Crookes. It is as follows : 
1. Solids are composed of discontinuous molecules separated 
from each other by a space which is relatively large—possibly 
enormous—in comparison with the molecule itself. 
2. These molecules, composed of atoms, are governed by cer- 
tain:-forces, viz., cohesion or attraction, and motion. 
8. Attraction appears to be independent of absolute tempera- 
ture; it increases as the distance between the molecules dimin- 
ishes; and were there no other counteracting force, the result 
would be a mass of molecules in actual contact with no move- 
ment whatever—a state of things beyond our conception—a 
state, too, which would probably result in the creation of some- 
thing which, according to our present views, would not be 
matter. 
4. The force of cohesion is counterbalanced by the motion, 
which is also an inherent property of individual molecules them- 
selves. These movements vary directly with the temperature, 
increasing and diminishing in amplitude, as the temperature 
rises and falls. 
5. In solids the force of attraction or cohesion is greater than 
that of repulsion. 
6. The molecules in solids do not travel from one place to 
another, but possess a fixity of position about their centre of 
oscillation. 
7. Matter, as we know it, has so high an absolute temperature, 
that the movements of the molecules are large in comparison 
with their diameter, for the mass must be able to bear a reduc- 
tion of temperature of nearly —3oo° C., before the amplitude 
of the molecular excursions would vanish. 
8. The solid state is, in reality, merely the effect upon our 
senses of the motion of the molecules among themselves. SECTION 111. 
LIQUID MATTER. 
CHAPTER VI. 
GENERAL AND SPECIAL PROPERTIES OF LIQUIDS. 
Form not fixed—Resist compression—Compressibility—Elasticity—Porosity— 
Volume variations—Density or specific gravity—Table of specific gravities— 
Reunite behind a dividing solid—Hypothetical constitution—Liquidity and 
viscosity—Assume spheroidal state. 
76. Form not Fixed.—Any liquid placed on a level surface 
spreads itself into a layer of greater or less tenuity, and, if the 
quantity is considerable, with no regularity of outline. The 
slightest tilt of the surface at once changes the outline and the 
thickness of the layer in different parts. Poured into a vessel 
°f auy shape, the liquid immediately adapts itself to the form 
pf the vessel. Liquids, therefore, differ essentially from solids 
111 that they do not have a fixed form. 
77. Resist Compression.—ln this respect liquids stand interme- 
diate between solids and gases, the fixity of position in the 
molecules in solids giving them a great advantage over the 
other forms of matter. 
78. Compressibility,—The experiments of the Florentine acade- 
micians, in which water oozed through the walls of a hollow globe 
°f gold, led them to the conclusion that this liquid was incom- 
pressible, and for a long time that opinion was accepted. In 
1761 the English physicist, Canton, found that when water was 
placed in an air-pump vacuum it expanded. The amount of 
expansion was 0.000044 of the volume employed. 
Id 1819 Perkins submitted water enclosed in suitable vessels 
to enormous pressures by lowering them to great depths in the 
ocean. The results of his experiments gave 0.000048 as the 
compression for each atmosphere of pressure. 82 
LIQUID MATTER. 
A few years later (Ersted, by an instrument called the 
piezometre, in which the pressure was obtained by a screw, 
found nearly the same results. The following table gives the 
values of compression per atmosphere obtained by M. Grassi, 
by means of the process of Regnault. The experiments were 
made at 0° C. 
1. Mercury . . 0.000003 
2. "Water . . . 0.000030 
3. Chloroform . . 0.00006 
4. Alcohol . . 0.00008 
5. Ether . . . 0.000111 
79. Elasticity.—A general definition of elasticity has been 
given in (45). In the case of solids this property exists in 
various forms, but in that of liquids, only in respect to volume. 
In solids the elasticity of compression is displayed within narrow 
limits, beyond which they are permanently compressible, as 
shown in the greater density given to many metals by hammer- 
ing and rolling (see specific gravity, 69). In liquids, on the 
contrary, the amount of compressibility is greater, water shrink- 
ing of its volume under the pressure of a column of that 
fluid one mile in depth. On removing the pressure, a fluid 
returns rigorously to its original volume. The elasticity of 
liquids, therefore, is absolute under all ranges of pressure to 
which we can submit them. 
In the case of solids, elasticity of compression was shown 
by the recoil of an ivory ball from the surface of a slab of 
stone (69). In the same way globules of mercury rebound from 
a hard surface. Molten antimony thrown on a table or floor 
gives an admirable illustration of the same property, bounding 
along, and leaving a dot of metal wherever it has touched. 
The elasticity, contractility, apd pliancy of the solid tissues 
of animals are largely owing to the presence of water. A dry 
muscle could not contract. Deprived of its water, the skin 
would lose all the physical properties which so eminently fit it 
for the purpose it serves. So important is water in the human 
economy, that no less than two-thirds of the whole weight of 
the body is made up of this ingredient. In an oyster 81 per 
cent, is water, and in certain jelly fish or acalephse, 99 per cent. 
80. Porosity.—Porosity in the case of solids has been discussed 
in (48). Though we cannot see pores, like the visible pores of a 
solid, in a liquid body, nevertheless some maintain their exist- 
ence. In support of this doctrine the following experiments 
are given : The mixture of a pint of alcohol with a pint of water 
does not produce two pints, but much less. Gases, also, in 
enormous quantity, may be forced into water by the aid of 
pressure without any discoverable increase in the bulk of the general and special properties of liquids. 
83 
fluid. In both these examples it is as perfectly proper to sup- 
pose that the molecules of the alcohol or of the gas may occupy 
the intermolecular spaces. There is, however, one curious 
instance in which that explanation is hardly admissible, and 
the idea of the presence of pores seems the correct explanation. 
If pure melted silver be exposed to air, as where a globule of 
that metal is kept in the fused state in a blowpipe-flame, it 
absorbs the oxygen of the air in considerable quantity (some 22 
times its own bulk). On cooling, the gas escapes just before the 
metal becomes solid, and while it is yet pasty, as it were. In 
consequence of this escape of the gas, the metal is dragged out 
from the interior of the globule, and the exterior is covered by 
mossy or arborescent masses of frosted silver. 
81. Volume Variations.—ln solids these are exceedingly minute 
(pi). In liquids they are much greater. The amount of expan- 
sion for a given rise of temperature is also greater at a high 
than at a low degree. As the liquid approaches its boiling 
point the rate of expansion becomes very irregular. Towards 
the freezing point a similar irregularity is noticed. For this 
reason liquids cannot be used in the construction of thermome- 
ters, except within ranges which are more or less distant from 
their boiling and freezing points. 
82. Density or Specific Gravity.—Liquids, like solids, show 
considerable variations in specific gravity, from dense mercury 
and sulphuric acid to light, limpid ether. In a 
general way, it may be said that liquids are lighter 
inaii solids, and heavier than gases. As we have 
seen, there are many exceptions to the first of these 
Propositions; if by solids minerals alone were 
meant, it would be much nearer the truth. 
. The most satisfactory method for the determina- 
,°n of the specific gravity of liquids is by the spe- 
cific gravity bottle, A. This is so constructed that 
it will hold a definite quantity of the liquid to be 
examined. The volume is accurately measured by 
ihe introduction of a stopper, B, provided with a 
capillary tube to give egress to any excess of fluid. 
Fig. 9. 
Specific gravity 
bottle. 
J-he weight of the bottle and stopper is first determined while 
is perfectly dry. The bottle is then filled with distilled water 
at 4° C. The stopper is introduced and all excess of water 
carefully removed by bibulous paper; it is then weighed. The 
Weight of the bottle subtracted from this gives the weight of 
water it contained. The water is then removed, and the bottle 
rinsed with the liquid to be examined; it is then filled there- 
with at 0° C., and again weighed. The weight of the bottle 84 
LIQUID MATTER. 
deducted from this gives the weight of the volume of liquid. The 
volumes of the water and the liquid being the same, it remains 
to divide the weight of the liquid by the weight of the water, 
when the quotient is the specific gravity of the fluid. 
water at 4° C. as unity. 
83.—Specific gravities of liquids at 0° C. compared with that of 
Mercury. 
13.598 
Distilled water at 4° C. . 
1.000 
Bromine . 
2.960 
Distilled water at 0° O. . 
0.999 
Sulphuric acid 
1.841 
Claret .... 
0.994 
Chloroform 
1.525 
Castor oil 
0.969 
Nitric acid 
1.420 
Cod-liver oil 
0.928 
Bisulphide of carbon 
1.293 
Olive oil 
0.915 
Glycerine 
1.260 
Sperm oil 
0.875 
Hydrochloric acid . 
1.240 
Oil of turpentine . 
0.870 
Blood 
1.060 
Oil of lemon 
0.852 
Milk 
1.032 
Kectified spirit 
0.838 
Urine 
1.030 
Petroleum . 
0.836 
Sea-water 
1.026 
Absolute alcohol . 
0.793 
~W ell-water, rarely 
Common ether 
0.720 
as high as 
1.005 
Ether, absolute . 
0.713 
84, Reunite behind a Dividing Solid.—This property is possessed 
in common by all liquids and gases. It may be said to be one 
of their distinguishing characteristics; solids, only in very rare 
instances and under extraordinary circumstances, exhibit it in a 
minor degree. 
Hypothetical Constitution of Liquids. 
85.—1st. Liquids are composed of molecules separated by 
interstices. 
2d. The molecules are composed of atoms, as in solids. 
3d. The force of cohesion is much less than in solids. 
4th. The molecular movements are far greater in extent than 
in solids. They are also more tumultuous in their character. 
sth. The forces of cohesion and repulsion are very nearly 
balanced. 
6th. The molecules have no fixity of position, as in solids, but 
they travel from place to place. 
7th. When heated to a sufficiently high temperature, the 
movements of the molecules become so excessive, and the con- 
sequent repulsions so great, that at last cohesion is destroyed, 
the molecules fly oft‘ into space with enormous velocities, and 
the gaseous state is assumed. 
86. Liquidity and Viscosity.—We have said that the forces of 
attraction or cohesion, and of repulsion, nearly balance each GENERAL and special properties of liquids. 
85 
other in liquids. In different liquids, however, there are very 
Afferent degrees of cohesion. In ether, naphtha, and alcohol, 
the cohesive force is weak; it is scarcely sufficient to enable us to 
blow bubbles, or if formed they are evanescent. On being 
agitated, such liquids are exceedingly mobile. Possessing the 
property of liquidity in the highest degree, the term limpid is 
used to indicate their character. 
I.n °ther liquids the mobility of the particles is hampered, and 
their movements are sluggish, the effects of agitation are quickly 
Josh Examples of this group are offered by syrup, glycerine, 
sulphuric acid, and oils. To these the term viscous is applied; 
some of them, as soapsuds and glycerine, may be blown into 
bubbles of considerable size, which are quite permanent in their 
character. Albumen and mucus also impart this property in a 
ugh degree to fluids. The froth on an eggnog, made by 
beating white of egg, is a familiar example. In the case of 
Uri»e, the mucus present imparts this property to such an extent 
that it becomes a serious impediment in the way of reading the 
specific gravity, the layer of bubbles on the surface of the fluid 
obscuring the scale and its figures. 
.he welding metals, as platinum, iron, potassium, sodium, in 
their passage from the solid to the liquid state also show this 
yiseous character. Other solids, on the contrary, like ice, pass 
instantly from solidity almost to the extreme of liquidity of 
which they are capable. 
ssmne Spheroidal State.—As vapor of water passes from 
he gaseous into the liquid condition, it first appears as minute 
spherical vesicles; these coalescing produce rain, which also 
closely approaches the spheroidal form. In like manner, water 
brown in small quantities on the top of a red-hot stove, instantly 
gathers itself up into small spheres which drift about on the sur- 
aee of the metal, supported on a cushion of steam which is 
termed on their under surface. 
Other examples of this tendency of liquids to assume the 
spheroidal state are afforded by mercury when in a state of very 
tyinute subdivision. Melted lead also, as it passes through the 
fuOVe a sh°t manufactory, assumes this figure in its descent 
brough the air, and finally comes to us as solid shot, as nearly 
spheroidal as it is possible for anything to be. 
. Ihe cause of the assumption of the spheroidal state by fluids 
18 directly owing to, and is indisputable evidence of. the nearly 
e(fual balance between the two forces of cohesion and repulsion, 
associated with mobility of the molecules of the fluid. Another 
admirable illustration of this fact is offered by Plateau’s experi- 
in which a quantity of olive oil, A, is suspended in a 86 
LIQUID MATTER. 
mixture of alcohol and water of the same specific gravity as the 
oil. Under these conditions the oil is freed from the influence 
Fig. 10. 
of terrestrial gravitation, and, though 
several inches in diameter, the mass 
assumes an almost perfect spherical 
shape in the midst of the supporting 
alcoholic medium. When it is caused 
to rotate on its axis as is shown in 
the figure, a ring often forms like 
that around Saturn, 
The approximately spherical form 
of the satellites, planets, and sun of 
our solar system, and also of the 
stars, is generally received as evi- 
dence that, in the course of their 
formation, they have at one time been 
in the liquid condition. In the case 
Plateau’s experiment. 
of our own earth, many facts tend to show that the interior is still 
either partially or wholly liquid, and the exterior solid crust 
only some fifty or one hundred miles thick. The tendency of 
fluids to assume the spheroidal state is, therefore, not only of 
interest in the study of small masses, but it has an importance 
and application that are only limited by the cosmos or universe 
itself. 
Since the molecules of a liquid are exceedingly mobile, the 
complete study of their special properties makes it necessary 
that we should examine them, both in a condition of rest and of 
motion. The study of liquids at rest is called Hydrostatics, that 
of liquids in motion Hydrodynamics, and the application of these 
Hydraulics. The importance of the study of these subjects is 
dependent on the fact that they furnish the means for determin- 
ing such physical properties of liquids as their specific gravity. 
They explain the causes of the circulation of the various fluids 
in the body. They treat of methods available for furnishing a 
copious supply of pure water and removal of liquid effete ma- 
terial or sewage. We shall, therefore, devote a chapter to each. HYDROSTATICS. 
87 
CHAPTER YII. 
HYDROSTATICS. 
Hydrostatics defined. Pascal’s law—Hydrostatic bed—Hydrostatic test for steam 
boilers—Action of Pascal’s law in the body—Vertical downward pressure— 
Vertical upward pressure—Lateral pressure—Equilibrium of floating bodies— 
Stability of floating bodies—Hydrostatic test in infanticide—Evidence of death 
by drowning—Equilibrium of a liquid in communicating vessels—Natural 
springs—Wells and sewage—Artesian wells—Equilibrium of two liquids ot 
different densities—Pressure on bottom of a vessel—Heterogenous liquids— 
Spirit level. 
88. Hydrostatics Defined. Pascal’s Law.—Hydrostatics is the 
science which treats of the conditions of equilibrium in liquids, and of 
their 'pressures, either on their own mass, or on the walls of the vessels 
containing them.. 
The law which underlies all the phenomena of hydrostatics is 
known as Pascal’s law. It may be briefly stated as follows: 
Since the molecules of a liquid are exceedingly mobile, a pressure ap- 
plied on one portion of an enclosed mass of fluid must be equally re- 
sisted, and equally transmitted in all directions. 
Pet a piston and cylinder, A, communicate with a hollow 
sphere, B, the walls of which are perforated by small tubes, 0, 
Fig. 11. 
Fig. 12. 
Equality of pressure in fluids, 
Hydraulic press. 
ending in jets. The sphere and cylinder being filled with water, 
a*id pressure applied to the piston, the water does not issue 
solely from the jets opposite the piston, but with about the same 88 
LIQUID MATTER. 
freedom and force from all the jets, regardless of their position, 
thus demonstrating the equal distribution of the pressure in 
all directions. 
This property of liquids gives us the explanation of the action 
of the hydraulic press, by which, from a moderate force, enor- 
mous pressures may be produced. It consists of a large cylinder, 
A, with a piston, the area of the cross section of which is 100 
square inches. The lower part of A communicates with a small 
cylinder and piston, B, the area of which is 1 square inch. If 
on the top of the small piston a weight of one pound be placed, 
every square inch of the large piston will suffer the same press- 
ure as that on the small piston. Being 100 times as large, the 
pressure will, therefore, be 100 times as great. 
89. The Hydrostatic Bed.—The hydrostatic or water bed for 
the sick, in its first form, consisted of a water-tight box of the 
size of an ordinary sofa, and some 18 inches deep. In the box 
about six inches of water were placed. A sheet of water-proof 
material was laid loosely on the surface of the water, and 
fastened to the sides of the box. A thin mattress was then laid 
on the waterproof cloth, and on this a folded blanket. The 
water bed differs from the ordinary bed, in that the pressure on 
the body of the person lying on it is equally distributed over all 
portions of its surface of contact. Local pressures are impos- 
sible. The circulation in the capillaries is not interfered with, 
and consequently the formation of bed-sores is prevented. 
In its recent form, the water-bed is a mattress, or large sack 
made of stout India-rubber, and filled with water. It is costly, 
and for this reason we have described the earlier form, which 
may be improvised, at a moderate expense, with the exercise of 
a little ingenuity. Water beds are of especial value in the treat- 
ment of fevers. They not only prevent the formation of bed- 
sores, but the relief from distress afforded during the early part 
of the attack, often prevents the disease from reaching a danger- 
ous stage. 
Since there is no necessity for changing the position to gain 
relief from pressure, as on ordinary beds, persons have some- 
times remained unmoved for so long a time, on a water bed, 
that a serious stiffness of the joints has resulted; this should be 
prevented by occasional passive motion. Proper care should 
also be taken that the water with which the bed is charged is 
not too cold, as the patient might, in some instances, suffer 
thereby, either from shock or from too great an abstraction of 
caloric from the body. Especially should attention be paid to 
this matter in the case of a person suffering from phthisis. In 
certain febrile diseases the cold would be advantageous. If the 
dew point is high, and the water in the bed very cool, the bed- HYDROSTATICS. 
89 
cling would necessarily become damp by condensation of moist- 
ure of the air, and complications like rheumatism be introduced. 
Though an admirable contrivance, the water bed requires a 
great amount of attention in its use, not more, however, than 
any intelligent, humane physician ought to be willing to give in 
the interest of his patient. 
90. Hydrostatic Test for Steam Boilers.—The law demands that 
from time to time all boilers for steam engines shall be sub- 
mitted to a test by pressure, to determine their safety and 
ability to resist the elastic force of steam. For this purpose 
water is placed in the apparatus, a force pump is attached, and 
all outlets are closed. Pressure is then brought to bear upon 
all parts of the boiler by throwing the pump into action. 
By this method weak points in the machine are detected, 
ft yields quietly, and leakage occurs wherever there is a flaw in 
its construction. There is no explosion as would be the case 
with steam or air; there is therefore no risk to life in applying 
the test. The pressure thus applied is often double that for 
which the boiler is warranted by the inspector. 
The difficulty with this test is that, by the great strain 
brought to bear, parts which would otherwise have resisted 
ordinary pressures for a long time are weakened, and conse- 
quently less able to bear strain afterwards. The test, moreover, 
does not entirely meet the requirements of the case; it applies 
a steady, continued strain. In actual use, on the contrary, the 
strain is a pulsating one. A throb is produced every time the 
stoam passes from the boiler into the cylinder. It is evident 
fbat in the latter ease the tendency to the loosening and wear- 
lag of the rivets and other parts of joints, must be much greater 
man in the former. 
91. Action of Pascal’s Law in the Body.—The examples are very 
uunierous, especially in diseased conditions. Among these we 
may mention the pain and interference with the action of the 
ueart attending effusion into the cavity of the pericardium; 
he torture suffered in the cavity of a joint when its unyielding 
myalls are distended by accumulation of synovia; the effects upon 
me brain of accumulation of arachnoidal fluid within the bony 
Walls of the cranium, or of effusion of blood therein. 
lue manner in which an aneurism, especially that called dis- 
secting, finds its way between tissues depends upon this princi- 
flli intolerable pain suffered when the bladder is over- 
hed with urine, arises from the same cause. So long as the 
hTine accumulates in the bladder and it distends, the inconve- 
hience may be borne. When the sac is full and the outlet 
c °sed, as in stricture of the urethra, the secretion of the fluid 90 
LIQUID MATTER. 
continuing, the pressure upon the walls of the organ becomes 
so great as to be unbearable, and rupture occasionally results. 
92. Vertical Downward Pressure.—Gravity produces internal 
pressures of different degrees in different parts of a liquid. 
The lower layers of the fluid contents of a vessel, evidently 
support a greater weight than those which are superficial. The 
pressures in different parts of a liquid depend on the following 
general laws: 
1. Pressure on any layer is proportional to Us depth. 
2. In unlike liquids the pressure at the same depth is proportional 
to their specific gravities. 
3. In a given horizontal layer the pressure is the same in all its 
parts. 
Examples of the action of these laws are offered in certain 
diseased conditions of the human economy. In accumulations 
of fluid in the thoracic and abdominal cavities, certain positions 
are more endurable than others, according as they cause the 
fluid to press upon certain organs. The pleuritic patient natur- 
ally lies in the position which relieves his lung as much as pos- 
sible from the pressure of the fluid accumulation. In dropsy, the 
fluid percolating between the spaces of the areolar tissue accu- 
mulates in the feet, and may cause but little discomfort. When 
it begins to rise into the legs the increasing pressure produces 
pain, and may even result in rupture of tbe skin. Change of 
position, by keeping the feet elevated, brings relief by reducing 
the height of the column of liquid which produces the pressure. 
In the construction of the piers for bridges, where men are 
sometimes obliged to work in caissons under the pressure of a 
column of water sixty or seventy feet in depth, they pass through 
an intermediate valve or chamber to reach the open air. Thus 
the evil consequences of a sudden passage from extraordinary 
to ordinary pressures are to a large extent avoided. 
In the estimation of the pressure at various depths, it is well 
to remember that the increase is very nearty one pound to the 
square inch for every two feet of depth. Hence it is that when 
a ship founders at sea, or a whale-boat is drawn to a great 
depth, the wood does not again rise to the surface. Every pore 
has become charged with the sea water, and its buoyancy is lost. 
In houses in which water is distributed throughout the build- 
ing, the usual boiler or receptacle for hot water in the vicinity 
of the kitchen range affords an example of the application of 
vertical pressure, and of Pascal’s law. The pressure on the 
walls of such a boiler is far greater than would be supposed. 
It is continually under a very heavy strain, since from it, tubes 
pass often through many stories to a height of sixty feet, or even 
more. The pressure on every square inch of the boiler is, there- HYDROSTATICS. 
91 
fore, equal to nearly 30 pounds. If, while under this strain, the 
water be allowed to boil strongly, or a stopcock be suddenly 
closed, the thin metal of which the apparatus is made sometimes 
yields, and serious consequences result from the outflow of scald- 
ing water. 
Where allowance is to be made for the actual weight of a 
niass of water, or of its volume, it may be estimated on the basis 
that one cubic foot of water weighs nearly 621 pounds, and measures 
nearly 6* gallons. 
93. Vertical Upward Pressure is a natural sequent of the pre- 
ceding. It is very evident, when we attempt to press the hand 
down in such a heavy fluid as mercury, or when we seek to 
pick up some object in water four or five feet in depth. The 
upward pressure of a liquid is called its buoyancy; it is propor- 
tional to the specific gravity of the fluid. An example of this 
is afforded in the greater buoyant power of sea water compared 
with fresh water, when we attempt to swim therein. The mano- 
meter and all similar instruments depend upon the sum of the 
upward pressures of the layers of fluid through which they pass, 
for their action. The forcing of the lung into the upper part 
°f the pleural cavity by effusion in the chest, is also dependent 
upon this upward pressure of fluids. 
The laws governing the upward pressure of fluids are the 
same as thoee for downward pressure. 
94. Lateral Pressure in Liquids.—ln the construction of water 
tanks in the upper stories of dwellings, the question of pressure 
mi the sides of the tank often becomes a matter of importance. 
Ihe general law for such pressure, is that it “is equal to the 
Weight of a column of liquid, which has this portion of the side for its 
base, and whose height is the vertical distance from the centre of gravity 
°f the portion to the surface of the liquid.” 
From the above law, it is evident that it is better to give such 
janks considerable area of bottom, and small altitude. There 
is then but little pressure on the sides, and the great area of 
base distributes the weight better over the beams of the floor. 
Where cemented walls of masonry are constructed to keep 
banks of soil in position, openings should always be left in the 
lower parts to allow for the escape of accumulations of water. 
this is not done, the soil being wetted by a heavy rain, loses 
As consistency, and acting like a fluid mass will overthrow the 
wall, which cannot alone resist the pressure. 
landslides, which are so often attended by terrible results, 
Specially when they occur along the banks of railway cuttings, 
are produced in a similar manner. The incumbent mass of 
earfh rests on a stratum formed of clay of a peculiar consistenc}7. 92 
LIQUID MATTER. 
When the latter becomes soft by the percolation of water, it loses 
its sustaining power, and being for practical purposes reduced 
to the condition of a liquid, permits the whole mass of earth to 
slide down, as it would sink in water. 
95. Equilibrium of Floating Bodies,—Two forces act on a float- 
ing body, viz., its gravity, which forces it downwards, and the 
buoyant power of the liquid, which presses it 
upwards. The conditions of equilibrium under 
these circumstances are: 
Fig. 13. 
Ist. The floating body must displace a volume of 
the liquid of equal weight. 
2d. The centre of gravity of the floating body 
must be in the same vertical line with that of the dis- 
placed fluid. 
The above principles, together with the effects 
of variation in the specific gravity of the float- 
ing object, are beautifully shown in the toy 
known as the Cartesian diver, Fig. 13, in which 
A is a cylindrical vessel filled with alcohol and 
water, in which a small glass figure containing 
air floats. The mouth of the vessel is closed by 
a sheet of India-rubber. When pressure is 
made on the rubber, the air in the upper part of 
the cylinder is compressed, the pressure is trans- 
mitted to the fluid, which is forced through an 
aperture into the interior of the figure. The 
Cartesian diver. 
specific gravity of the figure being increased, it sinks; release 
of pressure produces the opposite effect. 
A device somewhat similar to the preceding is found in the 
swimming bladder of fishes. By allowing a part of the air con- 
tained therein to escape, they increase their specific gravity and 
sink. By increasing the included air, the body becomes lighter 
and rises. These movements are thus accomplished with 
scarcely any muscular effort. 
96. Stability of Floating Bodies.—As the whole weight of a 
body is regarded as being lodged in its centre of gravity, so its 
whole flotation power may be regarded as being concentrated 
in its centre of buoyancy. The centre of buoyancy is the centre 
of gravity of the fluid displaced by the body. 
That a floating body shall be stable and maintain its proper 
position in the fluid, its centre of gravity must he exactly below 
its centre of buoyancy. In the stowing of a ship’s cargo this is 
carefully attended to, otherwise she will capsize. It has hap- 
pened that when salt, sugar, or other substances soluble in 
water, have been placed in the hold, and water has gained 
access to the interior of the vessel, the salt or sugar dissolving HYDROSTATICS. 
93 
in the water has been pumped out in the bilge-water. The trim 
of the vessel being thus destroyed, shipwreck has followed. 
97. Hydrostatic Test in Infanticide.—Advantage is taken of the 
principle of flotation, in what is called the hydrostatic test for 
the examination of supposed cases of infanticide and murder. 
The lungs of a foetus never having been inflated with air, have 
little or no power of flotation. If, on the contrary, the child has 
been born and has breathed, the lungs having been once dis- 
tended with air have considerable flotation power, of which 
they can only be partially deprived. 
In a post-mortem, under such circumstances, the hydrostatic 
test should never be neglected. Errors may, however, arise. 
The hepatized lung of an infant would have but slight flotation 
power. Putrefaction of the lung of a foetus fills it with gas, 
and gives it considerable flotation power. Both of these errors 
are, however, avoided by proper precautions. Regarding the 
supposed fallacies of the hydrostatic test, Woodman and Tidy 
in their “Toxicology” say: 
Ist, If we take care that the water is cool (not above 62° 
Fahrenheit); 2d, If we remember to cut the lungs into pieces, 
if the whole do not float; and, 3d, If we combine pressure with 
the floating, there is in reality no fallacy except the difficulty of 
distinguishing cases of artificial inflation from those of natural 
breathing. We suppose it must be conceded that it is not pos- 
sible to distinguish, by any certain tests, the differences between 
inngs naturally expanded by breathing, and those artificially ex- 
panded by breathing into them. Though, as a generally true 
statement, it may be said that lungs artificially inflated are almost 
■fire to be emphysematous in a far higher degree than is probable 
ln lungs of the newly born w7hich have not been so treated. 
The conditions of the lungs in the two cases are given by the 
same authorities, as follows: 
Lungs which have not breathed. 
Lungs which have breathed. 
1- Dark in color (black, blue, maroon, 
0r purple). They resemble liver. 
Air-vesicles not visible to naked 
eye. 
1. Light in color (rose-pink, paler 
pink, light red, or crimson). 
2. Air-vesicles distinctly visible to 
naked eye, or to lens of low power (say 
a two inch or common reading glass). 
B. They crepitate or crackle freely. 
3- Do not crepitate or crackle when 
squeezed or cut. 
4. Contain but little blood, therefore 
dtle escapes on section. 
u. This blood is not frothy, unless 
there is putrefaction. 
6- They sink in water, unless putrid, 
aud often even then. 
4. Contain a good deal of blood, which 
escapes freely on section. 
5. This blood is freely mixed with air, 
and therefore frothy. 
6. They float in water, or, at all 
events, the parts which have been ex- 
panded or have breathed. If fully ex- 
panded, they will even buoy up the 
heart. 
7. The air cannot be easily squeezed 
out. 
“ The bubbles of gas arising from 
putrefaction can be squeezed out. 94 
LIQUID MATTER. 
98. Evidence of Death by DrowningI.—The manner of death of 
a corpse found in water is often a question of importance, and 
is not always easily settled. Persons who are drowning, in their 
struggles expel a large part of the air from their lungs and other 
organs. They also swallow a considerable amount of water; 
the specific gravity of the body is thereby so much increased 
that it usually sinks. Persons, on the contrary, who have been 
killed, and then thrown into the water, not having expelled the 
air from their bodies, may float near the surface. 
If, therefore, a corpse in which there are no evidences of 
putrefaction, and in which death has only recently occurred is 
found floating, the presumption is that the person was murdered, 
and then cast into the water, though there may be no evidence 
of external violence. It is true that, after putrefaction sets in, 
the body of a drowned person comes to the surface. The cause, 
in this case, is the accumulation of gases from the putrefactive 
process. These have diminished the specific gravity of the 
body by increasing its bulk. In this case the sense of smell 
quickly shows the possible cause of flotation. We cannot tell 
from flotation alone whether death occurred before or after im- 
mersion in water. 
Allowance must, of course, be made in this matter for the 
difference between the flotation power of the fresh water of 
interior regions and the brackish or salt water of sea-coast 
towns. The specific gravity of the latter being often as high as 
1028, a corpse would float easily therein which would sink in 
the waters of an inland pond, lake, or river. 
Death by drowning may be produced by a very small quantity 
of water. The following case occurred in Hew York. A gentle- 
man was taking a face bath in a basin with about an inch of water 
in it; in some way he managed to drown himself, and was 
found with his face in the water. Whether it was a case of 
suicide or not, was a subject of question. Instances are not un- 
common, in which persons have been accidentally thrown with 
their faces down in soft mud, and have expired in that position 
by drowning. 
According to Woodman and Tidy: Pat people float the best. 
Women better than men. Pat young children and infants 
better than women. Bony, lean persons not at all. Sometimes 
bodies do not sink in sea-water. 
When weights are found attached to a corpse in the water, 
especial care should be taken to remark the manner in which 
they are attached, and the conditions of the parts, to determine 
whether it was possible for the person to have attached them 
before death. 
In spite of the great flotation power of decomposing corpse 
they frequently do not rise to the surface for a long time. In HYDROSTATICS. 
95 
such instances, they are either caught by some heavy object, or 
partly covered by mud or sand. In the latter case, it is said 
bodies have sometimes been detached from their moorings by 
firing cannon over the water. The shock of the discharge trans- 
mitted through the air to the water, jars the corpse, and so 
loosens it from its attachments. 
99. Equilibrium of a Liquid in Communicating Vessels.—If tubes 
and vessels of different forms all open into one another below, 
as in Fig. 14, A, B, C, D, and water be poured into the vase A, 
Fig. 14. 
Equilibrium of a liquid in communicating vessels. 
will stand at the same horizontal level in all the tubes, 
bmnce, in the supply of water to the houses of cities, all other 
things being equal, the water from the common reservoir will 
riBe to the same level in all. At positions very distant from the 
reservoir, and with a heavy drain at numerous points upon the 
supply passing along the main pipes, this will not be true. If 
the amount drawn oft’ is sufficient, there may he none at all at 
the distant points. The moment, however, the escape of the 
Water is stopped, the law reasserts itself, and the fluid rises to 
the same level in all parts of the system. 
100. Natural Springs.—These are formed when the level of 
me water in certain strata rises above the edge of the retaining 
eusin in which it is held. As in the preceding system of tubes, 
.ue lowest one would determine the possible height of the fluid 
111 the others, and the fluid would escape from it. So the lowest 
P°int in the edge of a natural basin permits the overflow of its 
contents, and a spring is formed. 
-I he same result is attained when wells are sunk into a 
s latum in which water is lodged or flowing. The water rises LIQUID MATTER. 
in the cavity of the well to the same height it has in the stratum. 
We may, therefore, regard wells as being in reality springs, 
when they tap an underground flowing stream, and the water 
is as good as that of a living spring. When, on the contrary, 
thej7 strike a stagnant basin of water, it, as a rule, is not as 
good as that obtained from the flowing stream. 
If the strata in which water is lodged, or through which it 
has passed, contain mineral substances, as salt or chloride of 
sodium, Epsom salt or sulphate of magnesia, and other sub- 
stances soluble in water, these are dissolved and constitute 
natural mineral waters. 
If the mineral water contains only purgative salts, it is called 
saline. 
If it contains these bodies, and is also freely charged with 
carbonic gas, it is called effervescent saline. 
If it contains iron compounds, it is called chalybeate, 
If it contains sulphuretted hydrogen, it is called hepatic. 
If it contains iodides, bromides, or arsenic, it is called alterative. 
101. Wells and Sewage.—Whenever wells are constructed in 
the vicinity of cesspools, if the level of the water in the well be 
lower than that in the cesspool, it will sooner or later be con- 
taminated with the noxious products of sewage, on the princi- 
ples laid down in the preceding articles. In the vicinity of 
cemeteries, also, the same thing has occurred, and persons who 
have used the water in either of these cases for the purpose of 
drinking, have suffered from typhoid fever and other diseases, 
the germs of which have been in this manner conveyed into 
their bodies. 
Where wells are dug in gardens, or in close vicinity to stables 
or barnyards, the greatest care should be taken that no surface 
water from either of these sources reaches them, either in 
heavy storms or by percolating through the soil. 
All water that falls on the earth must be more or less con- 
taminated with the organic matter with which it comes in con- 
tact on its surface. As it passes to greater depths, and is spread 
throughout seams in rocks, and layers of sand and gravel, the 
oxygen it obtains from the air in these strata oxidizes or destroys 
these organic impurities. The water from springs and wells 
that are deep in their origin, though they may contain mineral 
ingredients, are free from such dangerous organic substances as 
are found in superficial waters. When water from deep springs 
is not available, it is much better to use rain water, which has 
accumulated in cisterns, lined with hydraulic cement, than to 
use surface waters. 
102. Artesian Wells offer another illustration of the tendency 
of water to rise to its own level. In true artesian wells the 97 
HYDROSTATICS. 
boring F has penetrated a vein of fluid B enclosed in a porous 
stratum C between two layers of rock A or clay D, which 
are impermeable to water. The source of the supply is in hills 
often many miles distant, the accumulation there presses upon 
the vein of water enclosed in the porous stratum C. Tapping 
Fig. 15. 
Artesian well. 
this at any point, the fluid at once appears at the surface F, rising 
through the upper strata E. Sometimes it rises far above it, as 
is the case with the well at Grenelle, near Paris. This is 1800 
feet deep, and the pressure is so great that the water is forced 
UP a tube to an altitude of more than 100 
feet above the surface of the earth. 
These wells receive their name from 
-Artois, in France, where they are very 
|mmerous. They did not originate there, 
cut have been made from very remote 
hmes in China and Egypt. The water in 
such wells having passed over a great ex- 
tent of surface of sand, rock, or other ma- 
terial, is remarkably free from organic con- 
tamination. 
Fig. 16. 
103. Equilibrium in Communicating Vessels 
°f Two Liquids of Different Densities.—Let 
tw° tubes A and B be in communication 
}vhh each other by their lower parts. Pour 
into one of the tubes sufficient mercury to 
." if to the depth of a couple of inches, it 
rises to the same horizontal 
Equilibrium of fluids of 
different densities. 
evel in the opposite tube according to the principle in (99). Fill 
orie °f the tubes, A, with water. If it is long enough to carry 
a column 13.6 inches in vertical height, the pressure of this 98 
LIQUID MATTER. 
upon the mercury at the bottom will force the mercury up the 
opposite tube, B, and cause'it to rise about one inch above its 
former level. We have already seen (88) that the specific 
gravity of mercury is more than thirteen and a half times that 
of water, it therefore follows that: In communicating vessels, two 
liquids of different densities will he in equilibrium when their heights 
above the horizontal surface of contact are in the inverse ratio of their 
densities. 
104. Pressure on the Bottom of a Vessel is Independent of its 
Shape.—Let' a conical vessel be in communication by its bottom 
with a narrow tube bent so as to rise vertically alongside of the 
conical vessel. Fill the bend of the tube with mercury. Pour 
water into the conical vessel, the pressure of the water upon the 
mercury will cause it to rise to a certain height in the narrow 
tube. Remove the conical vessel and substitute in its place a 
tube the sides of which are parallel, or even form an inverted 
cone when it is placed in position. Filling this with water so 
as to have a column of the same height as in the first case, the 
mercury rises to the same height in the narrow tube, showing 
that it is submitted to the same pressure. 
In (91) we have spoken of the cause of pain in the bladder 
when the muscular coat is too much distended. We now see 
how the rise of the fluid in the ureters may suffice to produce 
this distention, since the pressure exerted in a liquid mass does 
not depend upon the quantity, but upon the height of the 
column of fluid producing the pressure. 
105. Heterogeneous Liquids Arrange Themselves in Order of 
Density.—lf petroleum, alcohol, saturated solution of caustic 
potash, and mercury be poured into a bottle, they will arrange 
themselves in the order given, the mercury being below. The 
lighter liquids, each according to its specific gravity, floats on the 
next denser one. 
An application of this principle is shown in the method of 
determining the amount of alcohol in wines by the carbonate of 
potash. In a graduated tube, a measured quantity of the wine 
is placed, dry carbonate of potash is added, this dissolves in the 
water of the wine, and the alcohol being separated floats on the 
surface of the carbonate of potash solution. It only remains to 
read off the depth of the layer of alcohol, and compare it with 
the quantity of wine employed. We have a very fair approxi- 
mation to the percentage of alcohol in the wine examined. 
The determination of the amount of cream in milk is arrived 
at in the same way. A tube, known as the cream tube, gradu- 
ated to 100 divisions, is filled with new milk. This "is set 
aside for 24 hours. The cream, as it separates, being lighter HYDROSTATICS. 
99 
than the milk, floats on its surface. Reading off the number of 
divisions on the scale occupied by the layer of cream, we have 
the percentage of that substance that the milk contained. 
In illustration of the property of liquids to arrange themselves 
according to density, Dr. Arnott relates, that “some negro 
servants, in the West Indies, were once detected stealing rum, 
hy the simple though ingenious trick of inserting the long neck 
°t a bottle full of water through the top aperture of the rum- 
cask. In such case the water falls out of the bottle into the 
cask, wdiile the lighter rum ascends in its stead.” It only re- 
clamed to remove the bottle now filled with rum in place of 
water. 
106. The Spirit Level depends for its action on the principle 
explained in the preceding article, the only difference being 
that a closed tube, A B, Fig. 17, in which a bubble of air can 
he entrapped is used. The air is thereby made to represent an 
exceedingly light liquid. It floats on the alcohol with which the 
rest of the tube is tilled. Though the tube A B appears to be 
straight, it is very slightly curved. When its ends are placed 
ci the same horizontal plane the central portion is the highest, 
1° this part the bubble of air will rise. 
Fig. 17. 
Spirit level. 
Spirit levels are attached to the base of the supporting 
column of a balance to secure for it the horizontal position. 
I hey should always be filled with alcohol to avoid the effects of 
freezing, and the tube should have two marks on its upper sur- 
iace, between which the bubble of air should rest when hori- 
z°ntality is attained. 100 
LIQUID MATTER. 
CHAPTER Y 111. 
HYDROMETERS. 
Baume’s hydrometer—Urinometer—Lactometers, vinometers, salimeters—Densi- 
meter—Alcoholometer of G-uy Lussac—Alcohol in wine and beer—Post-mor- 
tem detection of alcohol. 
Hydrometers are instruments for the determination of the 
specific gravity of liquids. They depend for their action upon 
the principles discussed in the preceding articles. In the form 
of Nicholson’s hydrometer, as we have seen (55), they may also 
be applied to the determination of the specific gravity of solids. 
107. Baume’s Hydrometer was the first of a series of instru- 
ments of its type. The principle of flotation involved (95) 
is that in fSTicholson’s hydrometer. It consists 
Fig. 18, 
of an elongated glass bulb or float, A, which 
terminates below 7 in a small bulb, B, containing 
mercury or shot as a ballast to keep the instru- 
ment erect when placed in fluid, and sink it to 
a proper depth. From the upper part of the float 
a light tube, C, projects, in which a scale is 
placed. 
This instrument, in its first form, is used by 
manufacturers for the examination of liquids 
heavier than water, as syrups, acids, and saline 
solutions. The graduation is conventional; it is 
made as follows: The apparatus being so con- 
structed and ballasted that it sinks in pure water 
nearly to the top of the stem, this point is marked 
as the zero of the scale. It is then placed in a 
solution of fifteen parts of rock salt to eighty- 
five of pure water. The line the solution makes 
Baume’s 
hydrometer. 
on the stem is then marked, and the value fifteen given to it. 
The distance between 0 and 15 is then divided into fifteen equal 
parts, and the scale so obtained is extended. 
For liquids of less density than water, the plan is as follows: 
A solution of salt, ten parts, and water, ninety, being made, the 
instrument is placed therein and the level marked. To this the 
value 0° is given; it falls near the bottom of the stem; The in- 
strument is then placed in distilled water, and the level on the 101 
scale again marked, the value 10° being attached. This dis- 
tance is then divided into ten parts, and the scale continued to 
the top of the stem. 
These instruments do not determine the specific gravity, yet 
they are very extensively used. The readings are always given 
as so many degrees Baume. 
HYDROMETERS. 
108. The TJrinometer is a reproduction of the first form of the 
preceding, the difference being that in place of an arbitrary 
scale, it has readings wdiich represent the specific gravity of the 
fluid under examination. The graduation is made as follows: 
The instrument is placed in pure water, it sinks nearly to the 
top. This is marked, and the value 0° or 1000 given to it. 
Solutions of salt and water of different specific gravities—e.g., 
1010, 1020 to 1060, are then prepared by means of the specific 
gravity bottle (82), and the instrument placed successively in 
these. The lines corresponding to the levels of the different 
solutions being marked, the intervening spaces are each divided 
into ten parts, and the scale so completed. To the figures 10, 
20, attached to the scale, 1000 is to be 
added, when the gravity compared with 
water as 1000 is obtained. They are for 
convenience graduated at 15° C., and should 
be read at that temperature. Various forms 
°t the instrument are represented at A, B, 
C, Pig. 19. 
The following rules for the examination and 
Use of this instrument are recommended to the 
student. 
' Pig. 19. 
Ist, Do not purchase an instrument with- 
out examining it with water to see if the 0° 
p, 
pt the scale is correct. If this is in error, 
is evident that as so little pains has been 
taken to have the initial point exact, no re- 
liance is to he placed on the rest of the 
graduation. It is true that the zero may he 
nght, and yet the rest of the scale incorrect. 
Any error of that description can only be de- 
termined by comparison with a standard in- 
strument, the accuracy of which has been 
assured by the specific gravity bottle. 
Forms of urinometers. 
2d. In pouring the liquid into the cylinder hold it obliquely, 
at an angle of about 45°. The fluid will then flow gently down 
the side of the cylinder, without forming a foam. The presence 
°f foam or of bubbles seriously interferes with the reading of 
the scale. It may be removed by a drop of ether, but it is better 
to avoid its formation. 102 
LIQUID MATTER. 
3d. Stand with the back to the window or other source ot 
light that the scale may be as brightly illuminated as possible, 
and also that the eyes may be protected from the light. 
4th, The urinometer having been placed in the liquid, and 
there being sufficient fluid to float it freely, the cylinder is then 
to be held by the top, between- the thumb and index finger. It 
should be held loosely, that it may hang perpendicularly like a 
plummet. By this device the tendency of the urinometer to 
become attached to the sides of the vessel will be lessened, and 
greater facility for correct reading attained. 
6th, The level of the fluid in the cylinder must be brought to 
the same level as the eye. The horizontal line is easily obtained 
with sufficient accuracy, by selecting some object or point on 
the opposite side of the room, at the same height from the floor 
as is the height of the eye of the reader. The level of the fluid 
is then brought to this line. 
6th. The fluid in the cylinder will be seen to rise as it ap- 
proaches its sides. The liquid, therefore, has a curved instead 
of a plane surface. To avoid the error caused thereby, the 
reading should always be made where the lower convexity of 
the curve cuts the scale of the urinometer. It is also well to 
form the habit of counting backwards, that is, in reading a 
gravity of 1017, for example, read from 1020° upwards, rather 
than from 1015° downwards. The value of this device will be 
quickly seen in practical working, 
7th. There is always a tendency to error from the urinometer 
hugging the sides of the cylinder. To avoid this at least three 
readings should be made, the urinometer being gently touched 
at its top between each reading to make it vibrate and break up 
any adhesions it may have formed to the wall of the cylinder. 
From the readings of specific gravity of urine by urinometers, 
the attempt has been made to calculate the quantity of solid matter 
therein. Tables for this purpose are given in various works, but 
they are only approximate, since the quantity of solid matter de- 
pends on the nature of the ingredient of the urine which is in 
excess. It, of course, requires a much larger quantity of an in- 
gredient of small specific gravity, than of one with a great 
gravity, to make a difference of a reading of one degree in the 
gravity of the whole mass of liquid. The only correct method 
for the determination of the actual quantity of solid residue is 
to evaporate a known weight or volume of the urine, or other 
liquid to dryness, and to weigh the resulting residue, with 
proper precautions for preventing the absorption of moisture 
during the cooling and weighing of the mass. 
109. Lactometers, Vinometers, Salimeters, are instruments on 
the same principle as Baume’s hydrometer. They do not give HYDROMETERS. 
103 
the specific gravity, but are intended to show whether or no 
water has been added to the fluid for which they are adjusted. 
rp l-i. ••• •• 
have little or no scientific value, especially in the case of 
the so-called lactometer, which is intended to detect the addi- 
tion of water to milk. An example will perhaps best illustrate 
the point in question. Suppose a rich specimen of milk be 
given, it records its richness on the lactometer scale. The cream 
now rises, and being removed or skimmed off, the gravity of the 
milk will be increased. By the addition of water the original 
gravity may be restored, but the lactometer fails to detect as an 
adulteration the water which has been added. 
Another very simple sophistication is to add to the milk, 
water in which some kind of innocuous salt has been dissolved, 
nntil it has the same gravity as that of unadulterated milk. 
Again, the lactometer is deceived. There is only one reliable 
way to ascertain the addition of water to such complex organic 
fluids as milk and wine, and that is by a quantitative analysis, 
m which the actual proportions of the water and of other leading 
ingredients are determined by weight. 
110. The Densimeter is a form of hydrometer intended for the 
determination of the specific gravity of small quantities of 
liquid. 
Rousseau’s densimeter, Fig. 20, consists of an ordinary hydro- 
meter, B, to the upper part of the stem of which, C, a little 
cylindrical vessel, A, is attached. This should 
nave a capacity of one cubic centimetre. When 
this vessel is empty, and the instrument is 
placed in distilled water, the level of the water 
crosses the 0° of the scale, which is at the 
bottom of the stem B. One cubic centimetre 
°t water is now introduced by a pipette into 
the cup at the top of the stem, when the in- 
strument sinks in the water, and the level on 
the stem is marked and the value 20° attached, 
.he space between 0° and 20° is then divided 
nito twenty parts, and the graduation continued 
t° the top of the scale. The stem being of uni- 
rorrn bore, each division represents one-twen- 
tieth of a gramme or 0.05. 
To obtain the specific gravity of a liquid, 
place the apparatus in distilled water. From 
Fig. 20. 
The densimeter. 
. Cubic centimetre pipette drop 1 cubic centimetre of the liquid 
lnt° the cup. Suppose the water cuts the scale at twenty and 
one-half divisions. Then 20.5 X .05 = 1.025, the specific 
gravity of the liquid, water being 1. 104 
LIQUID MATTER. 
111. The Alcoholometer of Guy Lussac is a hydrometer graduated 
to show the percentage of alcohol in spirits, or in mixtures of 
Fig. 21, 
alcohol and water. It is similar in form to 
Baume’s hydrometer, but differs therefrom in 
that the water-line or 0° is at the bottom instead 
of the top of the stem. The instrument is gradu- 
ated by placing it in successive mixtures of 
alcohol and water of strengths differing in pro- 
portion by 10 per cent, of alcohol, and "finally in 
absolute alcohol. The last is then marked 100 pe.. 
cent. The lines obtained from the other mixtures 
90, 80 to o°, receive their respective values. The 
spaces between each of these is divided into 10 
divisions, each of these subdivisions marks one per 
cent, of alcohol in the mixture. To the stem of 
the instrument another graduation representing 
specific gravities is very commonly attached. 
Alcoholometer. 
112. Determination of Alcohol in Wine and Beer. 
—The determination of the percentage of alcohol 
in wines, ales, and similar liquids, in which other 
substances are present, is as follows. A known quantity of the 
nuid must bo carefully distilled, until the whole of the alcohol 
has passed over. To the distillate sufficient distilled water is 
added to make its volume equal to the original volume of the 
wine other fluid under examination. "The percentage of 
alcohol is then determined by the alcoholometer, when the 
result represents the percentage in the original liquid. 
113. Post-mortem Determination of Alcohol.—ln cases of the 
death of children or of adults by alcohol poisoning, the method 
to be followed is similar to that detailed above. The contents of 
the organs, the finely chopped brain, or other tissue, with or 
without mixture with water, are to be distilled over the water- 
bath If alcohol is present, the percentage and quantity in the 
distillate may be determined by the alcoholometer. HYDRODYNAMICS. 
105 
CHAPTER IX. 
HYDRODYNAMICS. 
Definition—Theorem of Torricelli—Course of stream from lateral opening—Height 
of stream from vertical opening—Form and quantity of efflux—lnfluence of 
tubes on efflux—Action of elastic ajutages—Movement of liquids in tubes— 
Form of falling stream—Movement in inclined tubes—Hydraulic tourniquet 
—Velocity in open channels—Transporting power of flowing water—Shoals 
and sewage—Sewage and malaria—Formation of waves—Sea waves—Meas- 
urement of waves—Resistance of fluids to moving objects—Mechanics of 
circulation of the blood. 
114. Hydrodynamics Defined.—Hydrodynamics is that branch of 
physics which treats of the laws governing the motion of fluids. It 
examines into the manner and rate of escape of fluids from outlets. 
It determines the conditions and rate of movements in tubes and in open 
channels. 
115. Theorem of Torricelli.—The velocity of a 
molecule of a liquid escaping by an aperture in 
the walls of a vessel is the same as it would have 
it fell freely from a state of rest at the surface 
°f the liquid to the centre of the orifice. 
The rate of efflux depends, therefore, on the 
depth of the opening, A B, beneath the sur- 
face of the liquid, M IST. It is immaterial 
whether the orifice be in the bottom or in the 
Slde of the vessel. Difference in specific 
Fig. 22. 
gravity does not influence the rate. Water has the same velocity 
as mercury, provided the diameter of orifice and depth of fluid 
are the same. 
Torricelli’s theorem. 
116. Course of Stream from Lateral Opening.—The axis of the 
opening being horizontal, the course of the stream is, at the first 
morhent, also horizontal, but the attraction of gravity acting 
upon it immediately, the particles of fluid fall from the hori- 
zontal, and assume a curved line. 
The curves thus formed are parabolic, and, according as the 106 
LIQUID MATTER, 
pressure at the orifice is greater, so do the parabolas formed by 
the issuing streams vary. 
117. Height of Stream from Vertical Opening.—From the prin- 
ciples laid down in vertical upward pressure (93), a stream 
issuing from an orifice opening verti- 
cally upwards, as at A in Fig. 23, 
should rise to the level, M IST, of the 
fluid in the reservoir. This it does 
not do : Ist. It is beaten down by the 
falling drops, 2d. It is drawn down 
by gravity. 3d. It is resisted by the 
air. If the stream is slightly inclined 
to the vertical, as at B, a better 
result is obtained, but at the best it 
Fig. 28. 
Stream from vertical opening. 
only reaches about T9¥ of the theoretical height, friction of the 
air and gravity reducing it to this extent. Allowing for these 
reductions, the result sustains the theorem of Torricelli. 
118. Form and Quantity of Efflux.—According to theory, the 
amount of water discharged from a circular opening in the 
thin walls of a vessel should be expressed by the formula 
Ai/2(7A, in which A is the area of the opening, g the accelerating 
Fig. 24. 
force of gravity, and h the height of the liquid. 
Actual experiment gives a very different result. 
Of this, Ganot offers the following discussion : 
Let A B represent an opening in the wall of a 
vessel. Every particle above will attempt to pass 
out, and so exert pressure on those around it. 
Those issuing near A B press in the lines M M and 
JST H; those at the centre in the line RQ, and the 
intermediate ones in the lines PQ PQ; consequently 
the water in the space PQ P cannot escape. That 
Vena contracta. 
which does pass out takes the form of a truncated cone, or vena 
contracta, and not of a cylinder, until it has reached a distance 
from the orifice equal to the diameter of the same. The area of 
a transverse section of the stream at this point is 0,62, or 
about -f- that of the orifice. The actual quantity passing out is 
therefore, but five-eighths of what might have been expected 
from the diameter of the opening. 
119. Influence of Tubes on the Efflux.—lf a cylindrical tube, 
having a length two or three times its diameter, be made the 
channel of exit of the fluid, the efflux increases to 0.82 of 
, the theoretical quantity, A tube of proper proportions, and 
f n the form of a truncated cone with its base at the may 107 
be made to raise the efflux to 0.92. If the smaller end of the 
cone be adapted to the aperture, the increase is still greater, 
and very little below the theoretical quantity. To these tubes 
HYDRODYNAMICS. 
the name ajutage is given. When a 
cylindrical ajutage of the proportions 
stated above is used, the water on enter- 
lng it forms a vena contractu, A, in the 
same manner as in the air; it then ex- 
pands. A partial vacuum is thus formed 
ln the position indicated in Fig. 25. If 
a. vertical tube, B, is attached to the 
ajutage at this point, and its lower ex- 
tremity dips into a fluid, the latter will 
pise in the tube, thus demonstrating the 
existence of the vacuum. 
Upon the above principles, or slight 
Modifications thereof, various modern 
appliances, as Bunsen’s filter-pump, Gif- 
t'ard’s injector, and certain forms of 
Fig. 25. 
Efflux in tubes. 
atornizing apparatus, commonly used in medicine, depend tor 
their operation (177). 
120. Action of Elastic Ajutages.—If an elastic tube of rubber 
be adapted to an outlet in a vessel, the rate of efflux is the same 
as by a rigid tube having a diameter equal to that which the 
elastic tube assumes. If, on the contrary, the flow is by any 
device made intermittent the results are entirely different. The 
elastic tube now shows a notable increase in efflux over the 
I’igid one. The manner of discharge is also very different. 
While the jet from the rigid tube reproduces every impulse ot 
the original intermittent action, that from the elastic one shows 
great diminution therein, and if the ajutage tube be of sufficient 
length the pulsation completely disappears. 
These observations are of importance in the explanation of 
Ibe manner of flow of the blood in the arteries, the coats of 
which are highly elastic. 
121. Movement of Liquids in Tubes.—Though the mobility ot 
the molecules of liquids is great, it is not absolute. Hence arises 
a certain degree of friction among the molecules themselves, 
tffld also between the fluid molecutes and the walls of the tube. 
In the latter case it is much greater than in the former, as may 
be seen in the more rapid flow of the water down the central 
Mid deep portions of a river, compared with its rate near the 
banks or over shoals. 
Hydraulic friction, which is the term applied to the resistance 
which we have been examining, is independent of the material 108 
LIQUID MATTER. 
of which the tube is made. It is increased by roughening its 
walls. It depends chiefly on the character of the fluid, whether 
it be viscous or limpid. In this respect ice-cold water shows a 
slight degree of viscosity compared with that which is luke- 
warm. 
Prony gives the following as the formula for the mean velocity, 
in metres, of water in a cast-iron pipe: 
V = 26.8 -\/dp 
I 
I being the length, d the diameter, p the pressure, and v the 
velocity. 
122. Form of a Falling Stream.—From the lower end of the 
vena contractu a falling stream of water takes the form of a con- 
Fig- 2.6- 
tinuous cylinder for a short distance. The 
accelerating action of gravity soon causes it 
to break into drops. The stream now assumes 
the appearance shown at A, of alternate nodal 
and ventral segments. In the nodal segments, 
the drops are extended longitudinally; in the 
ventral, transversely to the course of the 
stream. 
As these segments have a fixed position, it 
follows that each drop in its descent passes 
through the phases shown at B. 
Under illumination by the condensed elec- 
trie spark of an induction coil, the drops 
appear to be stationary, and their forms can 
be studied to advantage. 
123. Movement in Inclined Tubes.—lf in place 
of falling freely in the air, as is the case in 
the preceding article, the stream is falling in 
a vertical tube, the action of gravity will tend 
to produce the same effect. The lower parts 
having a greater velocity than those above, 
and the stream assuming the nodal and 
Forms of falling water. 
ventral form, will, in its latter state, act as a piston in the 
interior of the tube. Thus a vacuum will tend to form above 
each ventral part. To meet this the pressure of the air will 
be called into play on the surface of the reservoir from which 
the pipe issues, and a great acceleration of the efflux will ensue. 
The energy of the action thus evoked is shown in the suction 
or noisy draught with which the last portions of water are HYDRODYNAMICS. 
109 
drawn out from a wash-basin or bath-tub, the exit pipe of which 
is long and perfectly free. 
The presentation we have given above of the case in a vertical 
tube, applies less and less as the tube leaves this position and 
inclines towards the horizontal. 
The principles which we have been discussing are of impor- 
tance in the construction of the waste-pipes or drains of houses. 
Their application will be found later on. See (149). 
124. Hydraulic Tourniquet.—Fig. 27 represents the instrument 
ln question. It consists of a pear-shaped vase, Y, tilled with 
water, and so mounted as to revolve freely on its vertical axis. 
Fig. 27. 
Hydraulic tourniquet. 
. From the smaller and lower end of the vessel, two tubes pro- 
ject horizontally, which are continuations of a diameter. rThe 
outer extremity of each of these is bent horizontally, at a right 
augle to the shaft, as is shown at A in the figure. 
The opening of the extremity of each tube being closed, the 
liquid in the vase exerts an equal pressure on all parts of the 
wall of the tube, and the instrument is at rest. When the end 
of a tube is opened, the pressure on that side is relieved. The 
lube is then forced backward by the pressure on its opposite 
sides in the direction of the dotted line, and a rotatory motion 
is produced. 110 
LIQUID MATTER. 
Under the pressure of a head of water the vase may be dis- 
missed, and the apparatus attached directly to the tube supply- 
ing the water. In this manner a very convenient form of 
power is obtained, the discussion of which belongs properly to 
hydraulics as applied in the turbine. 
125. Velocity in Open Channels.—We have already had occa- 
sion to refer to the effects of hydraulic friction, as shown in the 
greater rapidity of movement in the deep parts of a stream as 
compared with that in its shallows. Were it not for the resist- 
ance afforded friction, a river which originates in a source 
1000 feet above the level of its mouth would have the velocity 
of water issuing from the bottom of a lake 1000 feet deep, or a 
rate of nearly 170 miles an hour. 
By the double action of the friction of the molecules of water 
on each other and on the banks of the stream, the rate is ordi- 
narily from three to live miles per hour, and the inclination of 
the channels from three to five inches in the mile. 
126. Transporting Power of Flowing Water.—The transporting 
power of running water involves two conditions : Ist. The force, 
or actual pressure of the moving mass; 2d. Its buoyant power. 
Owing to the combination of these two causes, it is estimated 
that if the rate of flow of water be doubled, its power of trans- 
portation is increased sixty-four times. 
Evidence of the fearful power of water in rapid motion, is 
shown by the manner in which mountain streams wrench 
masses of rocks from their foundations and hurl them down 
their course, until, by striking against each other, they are so 
pulverized that only an impalpable powder remains, which, 
when it settles, is called silt. 
It is estimated that the Mississippi River carries to the Gulf 
of Mexico, annually, an amount of solid matter equal to a mass 
one square mile in area and about 270 feet deep. It is easy to 
see that under these circumstances the deposition of the matter 
transported by rivers becomes a question of importance, as re- 
gards the disposal of the sewage of the cities on their banks and 
at their mouths. 
127. Shoals and Sewage.—When the sewer system of Hew 
York was first Constructed, and for some years thereafter, the 
effete materials were immediately swept into deep water, and 
carried by strong currents to a distance from the city. Since 
that time, by the extension of piers, deposit of cinders, washings 
of filth from the city streets, and largely by the silt brought 
down by the Hudson in spring freshets, shoals or bars have 
been formed. These have seriously modified the direction and HYDRODYNAMICS. 
force of the currents in the waters of the river front. As a con- 
sequence, the sewer tilth no longer passes into the current of 
deep water, but is deposited in the slips between the docks. 
The seething mass of putrefaction that forms the water-bed in 
such localities, is at all times throwing off various effluvia, 
among which is sulphuretted hydrogen, which may be detected 
throughout the year by its odor. In the summer time, when 
the action is more energetic, it may be seen rising in millions 
of bubbles to the surface, and the odor then becomes almost 
intolerable in certain localities. 
128. Sewage and Malaria.—Of all the ordinary gases none is 
more dangerous or insidious in its action than sulphuretted 
hydrogen. It is one of the so-called cumulative poisons. It 
acts upon the blood discs, impairing, and even destroying their 
function as carriers of oxygen. It thus reduces the power of 
the system to resist disease, and lays it open to attacks which 
would otherwise have no effect. It even seems to be in some 
Way related to the development or presence of malarial poison, 
lor, in localities where deadly forms of malarial diseases prevail, 
sulphuretted hydrogen is almost always to be found in the air. 
The proper methods for the correction of these troubles in 
great seaports may be arranged under three heads, viz.; Ist. 
The removal of all garbage, horse-droppings, and other filth 
from the streets, and its sale as a fertilizer. Thus the largest 
part of the noxious organic matter would be prevented from 
gaming access to the sewers, slips, and harbor basin. 
2d. The extension of the sewers to the pier-heads, where they 
may discharge into deep water. The sewer itself should end in 
ari arm turned down at right angles, like the termination of the 
ordinary stopcocks used in houses. To this point the level of 
the sewer should not be below high water. The final opening 
°f the termination should be below lowest water mark. 
3d. All accumulations, banks, or bars, which interfere with 
the original water-course and free passage of sewage into the 
mam current, should be removed. This is a subject of hygienic 
Tmportance which should not be overlooked. It is scarcely a 
matter of wonderment that under the present management of 
spch affairs in the city of JSTew York, it has become a malarial 
c%. It cannot fail to be so until better disposition is made of 
fhe sewage and filth that are now permitted to accumulate on 
!ts river fronts. 
It needs no apology, in view of such grave matters as these, 
te urge upon physicians a better knowledge of physics, even to 
the proper understanding of the manner of flow and formation 
. currents in the harbors of the cities they inhabit. Yo one 
m a community has the same interest in the subject as its phy- 112 
LIQUID MATTER. 
sician. Ho one has better opportunities of seeing the conse- 
quences of neglect of proper precautions. If it is not his busi- 
ness to attend to such matters and show how they are to be met 
and remedied, to whom, in the name of common sense, does it 
belong?' His duty to the community demands at least, that he 
shall initiate the discussion of these questions. To do this he 
must have a sufficient knowledge of the subject to agitate it 
intelligently. 
129. Formation of Waves.—When a pebble is dropped into a 
pond of smooth water, it displaces a portion of the fluid lat- 
erally, and a circular elevation or wall of liquid is raised around 
the spot of impact. This elevation, following the laws of 
fluidity, gradually widens. The depressed portion where the 
pebble struck, pressed upon by the surrounding elevation, which 
causes upward pressure from below, returns to and rises above 
its original level. It thus, in its turn, becomes a source of dis- 
turbance, and acting like the impact of the pebble, produces a 
second circle of depression and elevation. This oscillation con- 
tinuing, alternate circles of elevations and depressions, or waves, 
are produced, each becoming wider and wider, until at last they 
reach the margin of the pond, where they may be either broken 
or reflected. 
To the eye it appears as though, in the expanding circles of 
waves, the water was itself following the course of the wave, 
but it is not so. If a chip of wood, or any other light body, 
floating on the water is observed, it will be seen that it has little 
or no outward motion. As the wave approaches, it gently rises; 
as the wave passes, it falls. 
Since the chip merely copies the movements of the molecules 
of the water on which it is resting, we thus learn that the latter 
have little or no movement in the horizontal plane, or in the 
longitudinal direction of the wave motion. They move, on the 
contrary, in a vertical plane, or transversely to the course of the 
water wave. As in the case of the undulations we may pass 
along a rope, which is fastened at one end, while it is moved up 
and down at the other; it is the form that advances in the track 
of the wave, not the substance. That is moving at right angles 
to the wave motion. 
By virtue of the friction between the molecules of water, the 
new waves reach a less and less altitude than their predecessors, 
until finally the disturbance ceases, and the surface of the water 
becomes as unruffled, and mirror-like, as when the stone first 
struck it. 
130. Sea Waves.—As flowing water develops friction against 
the banks of the channels in which it is passing, so currents in HYDRODYNAMICS. 
the air produce friction upon the surface of the water over which 
they move. The little gusts of wind that strike upon shaooth 
water cause the instant appearance of ripples on its surface. It 
the velocity of the wind is great, and its application persistent, 
the ripples in time become waves, and these increase in volume 
and breadth until finally the rolling mountains of the ocean are 
formed. 
The rate of motion of these ocean waves is dependent upon 
their volume. In waves of great magnitude, like those off the 
Cape of Good Hope, the velocity may be as great as thirty or 
forty miles an hour. 
The mobile surface of water permits the propagation of waves 
over immense distances. This, combined with their velocity, 
will often carry intelligence of storms to distant shores, by the 
heavy breakers that fall upon them when no wind is blowing. 
131. Measurement of Waves.—Waves on water may be meas- 
ured in two ways: Ist, wave length; and, 2d, wave height. In 
the diagram, the distance, A B, from the centre of one depres- 
sion to the centre of the next, is the wave length. The same 
Fig. 28. 
Measurement of waves. 
Pleasure may also be applied from the centre of one crest to the 
centre of the next, or from the middle of one wave to the middle 
°f the next. 
The wave height is measured by the line C H, drawn from 
the horizontal line connecting two depressions, and perpendicu- 
Jarly to it, to the top of a crest. Sometimes the total elevation 
18 divided into wave and trough, the former being above the 
ordinary sea level, the other below it, as shown by the dotted 
une. In that case, the wave height is one-half of CH, and the 
WaYe depression the other half. 
lu great waves at sea, the elevation of the water above the 
ordinary level is rarely more than fifteen feet, making the total 
leight, from bottom of trough to top of crest, thirty feet. 
132, Resistance of Fluids to Moving Objects.—Water, by its 
Partial viscosity, experiences resistance on the surfaces over 
■whicfi it is moving; so, on attempting to move a body through 
ater, resistance is in like manner developed. 114 
LIQUID MATTER. 
An experimental illustration is afforded of this fact, as repre- 
sented in the figure. Let A B be a tube 2 feet in length, and 
Fig. 29. 
closed by corks at each end; a Minie-bullet, C, 
is to be introduced. On quickly inverting the 
tube, the bullet falls immediately from one end 
to the other, in a small fraction of a second. On 
filling the tube with water instead of air, and 
repeating the experiment, it will be found 
that it now requires many seconds for the 
bullet to fall from end to end. 
Another fact is at the same time perceived. 
When the bullet is descending with its point 
downwards, its velocity is much greater than 
when the butt or blunt extremity is foremost. 
The resistance offered by liquids to the pas- 
sage of a moving object is, therefore, largely 
dependent on the form of the object, those 
which are pointed or wedge-shaped moving 
with the greater velocity. 
132 A. Mechanics of the Circulation of the 
Blood.—Various devices for the measurement 
of the pressure of the blood in the arteries, 
and the character of its movement in these 
Resistance of fluids to 
moving objects. 
vessels have been devised; among these may be mentioned: 
Ist. The hocmadynamomder of Poiseuille, which is simply a 
U-shaped manometer, one end of which is attached to the artery, 
while the liquid in the bend shows the pressure exerted bv the 
blood. 
2d. The kymographion of Pick, by which the inertia of the 
mercury in the preceding apparatus is avoided. It is a complex 
apparatus consisting of a hollow spring filled with alcohol, and 
terminating at one end in a system of levers which record by a 
point on a revolving cylinder; the other end is brought in com- 
munication with the bloodvessel to be examined. 
3d. The cardiograph of Marey, consisting of a tambour 
adapted to the exterior of the chest over the region of the heart; 
its indications are recorded by another tambour. 
The same method has been adapted to the examination of the 
action of the heart itself, by introducing into that organ a kind 
of catheter bearing a bag or tambour at its extremity, and com- 
municating with a registering tambour externally. 
4th. The hcemadromometer of Volkmann, for the measurement 
of the speed of the flow of the blood. The stromuhr of Ludwig, 
is an improvement upon this, and admits of more accurate re- 
sults. The hcematachometer of Yierordt, and the dromograph of HYDRAULICS. 
115 
Tortet, are other applications of the same principle for the same 
purpose, viz., measurement of current velocity. 
sth. The sphygmograph for recording arterial tension was 
originally devised by Yierordt, and improved by Marey. 
6th. The gas-sphygmoscope by which the impulses of the artery 
are communicated to a small chamber, through which gas is 
passed and then ignited. The variations in the form of the 
flame show the variations in the condition of the artery. 
7th. The sphygmophone, a modification of the preceding, in 
which the flame is burned inside of a tube so as to produce a 
singing flame. To this the pulsations of the artery impart a 
kind of beat readily perceived at a distance. 
For a more thorough explanation of these forms of apparatus 
the student is referred to modern works on physiology. 
CHAPTER X. 
HYDRAULICS. 
Definition—Earliest devices for raising water—Pulley wells—Archimedes’s screw 
—The Persian wheel—The siphon—The flexible siphon—The intermittent 
siphon—Pumps and valves—Lift pump—Force pump—Hydraulic ram— 
Water wheels—The turbine—Centrifugal pump—Materials for hydraulic en- 
gineering—Sewage in houses—Utilization of sewage—Marsh draining and 
malaria. 
. 133. Hydraulics Defined.—Hydraulics is the application of the prin- 
cvples of hydrostatics, hydrodynamics, and also of pneumatics, to the 
construction of apparatus for the collection, storage, and distribution 
°f water or other fluids. It also includes the utilization of water as a 
source of power. 
The difficulty of separating hydrodynamics from hydraulics 
has been seen in the discussion of the hydraulic tourniquet, and 
111 other instances. In like manner, the description of pumps 
certainly belongs to hydraulics, though their action is to be ex- 
Eaincd on the pneumatic principles involved in the pressure of 
. e air. In all cases where this difficulty of arranging subjects 
111 their proper positions has arisen, we have followed the course 
which seemed to present the most practical advantages and the 
greatest simplicitv. 
For convenience the study of hydraulics may be divided as 116 
LIQUID MATTER. 
follows: Ist, Apparatus without valves for raising water; 2d, 
Valvular apparatus for raising fluid; 3d, Development of power; 
4th, The conveyance of fluids. 
Apparatus without Valves for Raising Water. 
134. Earliest Devices for Raising Water.—Doubtless the first 
cup of our ancestors wTas the palm of the hand hollowed by the 
contraction of the muscles. Following on this, and in the order 
of development as it were, we can easily imagine that a leaf bent 
and hollowed like the palm of the hand came into use. Then 
any naturally hollow vegetable product, as the shell of the 
cocoanut, and coverings of various fruits, also sundry animal 
products, as the emptied eggs of large kinds of birds, and shells 
of mollusks. Vext came the fashioning of vessels of clay, 
first dried in the rays of the sun, and afterwards baked by the 
heat of a fire. 
For the raising of water from natural springs these devices 
sufficed. When the spring was surrounded by a low wall to 
protect it from being soiled by cattle, some little improvement 
was needed. Here we can see the origin of the dipper, made 
perhaps as we now so often find it, out of the half shell of a 
cocoanut, to which a forked stick is attached as a handle. In 
copying this in earthenware, what more natural, on account of 
the fragility of the material, than to substitute the curved 
handle we now find attached to our tea-pots and cups. 
From the earthenware vessel with its handle on the side, 
which could not be conveniently used for purposes of carrying 
quantities of water to a distance, the passage to an earthenware 
vessel, with a straight rod run through two holes near its upper 
part, was easy and natural. Vow the mass of water could be 
retained and carried in the vessel, though it was filled nearly to 
the top. The next improvement, whereby the balancing of the 
filled vessel was made more facile, was to substitute a curved 
stick, or piece of vine, for the straight rod, and a pail which 
might also be used as a pot for boiling over the fire was formed. 
In dry seasons, as the water in springs fell, the simple and 
obvious remedy was to follow it down by removing the earth 
from the bottom and so digging it out. In doing this, to prevent 
the soil from falling in, the wall which surrounded the spring 
was carried down, and so the first wells came into existence. 
The earthenware vessel described above, or one of wood hol- 
lowed out, perhaps by the action of fire, with its curved handle, 
and a long piece of some vine, gave easy access to the water. 
So the original of the “Old Oaken Bucket” came into 
existence. HYDRAULICS. 
117 
_ For the purposes of irrigation, where water was raised from 
nvers or wells for many hours in succession, it was necessary to 
relieve, as far as possible, the strain on the muscles produced by 
always throwing the chief work on one process, i. e., that of 
pulling the bucket up. This was accomplished by the invention 
of the lever arrangement depicted in the figure, and which, 
though it first came into use thousands of years ago, is still 
employed in nearly all parts of the world. It is doubtful if any 
Pig. 30. 
Raising water in wells, early method. 
human contrivance has held its ground for so long a time, or 
been so universally applied, as the one in question. 
135. Pulley Wells are another device by which, in place of 
pulling upwards, force is applied to pull downwards, and so 
advantage is taken of the weight of the body. It consists of a 
I’ope which passes over a grooved wheel, or pulley, in the top of 
the well house. To each end of the rope a bucket is attached. 
The buckets balancing each other, their weight is eliminated, 
an additional advantage to that of applying the force downwards 
histead of upwards. 
An early improvement in the use of the pulley was to substi- 
tute the axle and winch therefor. At first it was applied 
to a single bucket to reduce the effort required to raise it when 
tilled with water. Afterwards it was modified, a series of 
buckets being attached to an endless rope. These passing under 
a wheel in the water of the well were filled, and emptied as they 
surmounted the wheel above, which gave motion to the appa- 
ratus. This device is still in operation in harbors for the purpose 
°f dredging, or raising accumulations of soft mud. 
Iu place of a series of buckets, an endless chain is sometimes 
arranged with disks about a foot apart. This is passed through 
a tube. The disks fitting the tube as closely as possible, carry 
the water upwards when the chain is passed through the tube 
rapidly. This constitutes the chain pump, and is very useful 118 
LIQUID MATTER. 
where dirty water is to be raised, since it is not so apt to 
become clogged as an ordinary pump, or if it does, relieves 
itself by reversing the motion. For the chain and disks a rope 
of hair is sometimes substituted. 
136. Archimedes’s Screw is another ancient device well adapted 
to raising large quantities of water to a moderate height. It con- 
sists of a pipe, AB, open at both ends, and wound spirally around 
a cylinder, as is shown in the figure. As the cylinder is made to 
revolve by the winch C, the lower end of the pipe dips under 
the water, which is raised along the tube as up an inclined plane. 
The inclination of the shaft, or cylinder, to the horizon should 
not be more than 45°. The pipe should make about three or 
four turns on the shaft at an angle of about 60° to its axis. 
Fig. 31. 
Archimedes’s screw. 
This is perhaps the most economical device for raising water, 
both as to cost and waste of power. It is extensively used in 
Holland for purposes of draining, the motive power being a 
windmill. It is also used in France, the motive power being 
steam, and the pipe sometimes five or six feet in diameter. It is 
also well adapted to raising sewage, and might in that case be 
driven by a windmill 
Fig. 32. 
37. The Persian Wheel is a large wheel 
with paddles, A A, which dip into a stream, 
the water of which has sufficient rapidity 
to cause it to turn. The margin of the 
wheel also carries buckets, which fill be- 
low and discharge into a trough at the top 
of the wheel. The water of the stream is 
thus forced to raise itself. A modification 
of this arrangement is depicted in the 
figure. In this the spokes, 88, of the 
wheel are troughs or tubes curved in the 
Persian wheel. 
manner shown. When their extremities dip into the water, a 
portion of the fluid is taken up and carried to the axis, X, of 
the wheel, where it is discharged along a tube. 119 
HYDRAULICS. 
138. The Siphon .—Where an elevation intervenes between the 
source of water and the place where it is used, it may be passed 
over the hill by a siphon. The vertical height to which the fluid 
may be raised cannot be more than thirty-four feet above the 
level of the water source. 
The siphon consists of a bent tube, open at both ends, as is 
shown in the figure. The arm Bis longer than the arm A. 
The extremity A being placed in water, and the entire length 
of the tube filled therewith, the longer column of water in B 
tends to fall out of it; an exhausting action is thus produced in 
the curved portion of the tube. The air pressing on the surface 
of the water at A, forces it up into the tube, and as fast as it 
reaches the curve it turns into B, and passing down a continu- 
ous flow is established. 
The greater the length of the long arm, compared with that 
of the short arm, the more rapid is the flow through the siphon. 
The siphon offers an example of the 
association of hydraulics with pneumatics, 
lor the force brought into play is the pres- 
sure of the air, as we have stated. This is 
easily shown by the fact that a siphon ceases 
fo work if it is placed under an air-pump 
oell and a vacuum made therein. 
By this device the government school at 
West Point is supplied with water from the 
opposite side of one of the hills by which 
that station is encircled. When the height 
fo which the water is raised in the short 
fube approaches 30 feet, the tube is liable 
f° bo gradually filled at the curve with air 
derived from the water; when this hap- 
pens the siphon ceases to work. The air 
must then be pumped out of the bend, 
when the siphon again acts. 
Barge siphons like that described above 
Fro. 33. 
The siphon. 
are most easily filled or refilled, when necessary, by having a 
stopcock at each end, and another at the highest point of the 
pend. The operation of filling then consists in merely closing 
fhe cocks at the extremities, and pouring in water at the bend 
the tube is full. Then closing the cock at the bend, and 
opening those at the extremities the flow is established. Large 
siphons have also been used for carrying sewage over interven- 
1U,™elevati°ns, and for emptying ponds. 
, bor the purpose of retaining the fluid in a small siphon, so 
hat it may at all times be ready for use in a given liquid, both 
arras are sometimes made of the same length and turned up, as 
18 shown in Fig. 84 at A B. 120 
LIQUID MATTER. 
This form is very useful in removing the liquids covering 
precipitates, especially when a number of analyses are to be 
made. Siphons of glass are frequently used in the laboratory. 
Fig. 34. 
Fig. 35. 
Retaining siphon, 
Glass siphon. 
When the liquid to he decanted is corrosive, the finger cannot 
be used to close the end of the instrument, as may be done in 
the case of water. Under these circumstances the form repre- 
sented in Fig. 85 is employed, as follows: The end of the short 
arm, C, being placed in the fluid, the stopcock near the end of 
the long arm, A, is closed. The mouth being applied at D, the 
fluid is drawn over the bend, B, into the long arm. As soon as 
the fluid passes the line in the long arm at which it is on the 
same level as in the vessel, C, the siphon begins to draw. At 
this moment the mouth must be removed from I). Opening 
the stopcock at A, the fluid passes out, the discharge being under 
perfect control by the stopcock. 
139. Flexible Siphon.—All kinds of material may be used in 
the construction of siphons. In filling electric batteries with 
dilute sulphuric acid, which has been made up in quantity, a 
piece of India-rubber tube answers admirably. The tube being 
dipped into the liquid, it fills; then bringing the upper end 
close to the surface, and pinching it together in order to close 
it, a portion of the tube is drawn over the side of the vessel, and 
a siphon is formed. On removing the pressure of the fingers, 
a flow is established into one of the battery jars. When the 
jar is full enough, the flow is stopped by again compressing the 
sides at the free end. By this method, without spilling or 
waste, the liquid may all be siphoned into the battery jars. HYDRAULICS. 
121 
Where it is desired to establish a very slow flow, an ordinary 
cotton lamp-wiek may be used. In the case of acids and other 
corrosive liquids, threads of asbestos, or a 
bundle of very fine capillary glass tubes 
Fig. 36. 
may be formed into a siphon. 
140. The Intermittent Siphon, as is shown in 
the flgure, consists of a siphon, A, in which 
the short arm is curved and dips nearly to 
the bottom of a vessel, into which water is 
continually flowing. The long arm passes 
through the bottom. When the water rises 
to a suflicient height to fill the bend of the 
siphon, it is thrown into action, and the con- 
Intermittent siphon. 
tents of the vessel pass off. The siphon then empties itself, and 
cannot act again until the fluid rises to the bend. 
The intermittent springs which occur in nature, are often 
produced in this manner. 
Valvular Apparatus por Raising Water. 
141. Pumps and Valves.—These consist usually of a cylinder in 
which a piston moves, water or air tight. The direction in 
which the water is to flow is governed by valves, and according as 
these are arranged, we may have three kinds of pumps : Ist. The 
suction or lift-pump; 2d. The force-pump; 3d. The compound 
pump, which is both suction and force in its action. 
The forms of valves employed are represented in the figures. 
At A, we have the ordinary form, viz., a disk of metalworking 
on a hinge and covered with leather below to make it air tight, 
bhis is called a clack valve. B represents the conical valve, con- 
Fig. 37. 
Valves. 
structed as follows: To a conical opening a plug is fitted. The 
movements of the plug are limited and guided by a rod which 
passes from it through an opening in a metallic loop below. In 
a third form a disk of metal is pierced by a number of small 
b°les, a strip of oiled silk stretches across these above, and 
Using or falling by its own elasticity, as the exhausting or com- 
Pressing force is applied, opens or shuts the holes and a 
VerJ perfect valve. This is the form usually employed in air- 
pumps and similar pneumatic apparatus. 122 
LIQUID MATTER. 
142. The Lift-pump.—Like the, siphon, the lift-pump depends 
upon the pressure of the air for its action. It contains two 
Fig. 38. 
valves : One in the base of the cylinder, B, and one 
in the piston, C. Both of these valves open 
upwards. The piston being at the bottom of the 
cylinder and moved upwards, the valve in the pis- 
ton closes, that of the cylinder opens, and as the 
piston rises the pressure of the air forces the water 
upwards into the cylinder. Having reached the 
top of the cylinder, A, the motion of the piston is 
reversed; instantly the valve in the bottom of the 
cylinder closes, the fall of the fluid is thereby pre- 
vented. The valve in the piston then opens, 
allows the piston to descend, the charge of water 
in the cylinder passing through the opening in the 
piston. At the next upward stroke the water in 
the cylinder is lifted higher and Hows out of the 
spout at B, its top. At the same time the air 
pressure forces more water into the cylinder, 
The lift-pump. 
and thus the action is continued. 
By means of a pipe attached to the bottom of the cylinder 
the action of the pump may be applied to water at a considerable 
distance below its position. Theoretically, the height a pump 
of this kind can raise water is thirty-four feet; practically, it is 
limited to twenty-eight or thirty feet. 
143. The Eorce-pump.—ln this form the piston is solid, as is 
shown in the figure at AC. The pump end, B, is placed in the 
Fig. 89. 
Force-pump. 
fluid to be raised. The lower part of the cylinder, C, is pro- 
vided with a valve, B. From the side of the cylinder, and near ‘hydraulics. 
123 
its bottom, a tube, D, passes, this is likewise closed by a valve. 
As in the lift-pump, both valves open upwards. The piston 
being at the top of the cylinder, on making a downward stroke, 
the valve, B, of the cylinder closes, that of D opens, and water 
flows through it. On making the upward stroke, the reverse 
takes place. The cylinder valve B opens, that in the tube I) 
closes, and the water flows into the cylinder. 
Usually an air or condensing chamber is attached to the exit 
tube. Its function is, by the compressibility and elastic proper- 
ties of the air, to make the discharge of water continuous and 
relieve the machine from the shocks to which it would be 
submitted by the action of the piston on the slightly compres- 
sible water. The air chamber is virtually a gas spring, and 
serves the same purpose as any elastic spring. 
The action of the heart is conducted on the same principle as 
a simple force-pump. It does not exert any suction action on the 
veins, but merely receives the blood from them and forces it into 
the arteries of the lungs or of the body. 
_ In the third form of pump, the departure from that just con- 
sidered consists in removing it to a distance above the fluid 
instead of placing it therein, a pipe being attached to the lowrer 
part of the cylinder. On making an upward movement of the 
piston, water is forced up into the cylinder by the pressure of 
the air. This constitutes the lift action, and is limited to thirty- 
four feet, as in the ordinary pump. The down stroke of the 
Piston produces the force action as before described. The only 
hniit to this latter movement is the 
strength of the apparatus and the power 
available. 
Another device, for the special purpose 
°f forcing acids out of the carboys in 
which they are stored, has been recently 
introduced. It consists of a rubber cap 
0r stopper, A, which fits the mouth of the 
carboy air tight. Through this two tubes, 
B and C, pass. Tube C goes to the 
bottom of the vessel. Tube B merely 
passes through the stopper; it terminates 
above in a small force-pump by which air 
is forced through B into the upper part of 
me carboy. The elastic force of this con- 
densed air, acting on the surface of the 
Fig. 40. 
Decanting acids. 
in the carboy, forces the liquid through the tube C. By 
Bus contrivance, strong acids may be transferred without the 
escape of irritating fumes which so often attend the pouring of 
hquid from a carboy. 124 
LIQUID MATTEB. 
144. Hydraulic Ram.—When water is flowing freely from a 
stopcock, if we suddenly check its escape the pipe emits a sound 
as though it were struck. This sound originates in the mo- 
mentum of the water moving in the pipe, and depends directly 
on the weight and rate of movement. In place of allowing the 
shock of the moving water to spend itself upon the pipe, let 
relief be offered by a small opening made in its side. If the 
stopcock be then suddenly closed, a fine jet of water will be seen 
to spurt from the opening to the height of many feet, and the 
clack or noise will disappear or be greatly lessened. 
The hydraulic ram acts on the principle lust described. In it 
Pig. 41. 
the momentum of a column of water 
is applied to the raising of a portion 
of the column to a very great height, 
compared with that of the original 
source from which the water was 
derived. The machine consists of a 
tube, A C, two or three inches in 
diameter, and twenty or more feet 
in length, with a fall such as may be 
available, say three to ten or more 
feet. At A there is a metal valve, guided and controlled by a 
loop. The valve opens downwards. At B another valve gives 
access to the reservoir above, this opens upwards; D is the 
delivery tube. 
Hydraulic ram. 
When the water in the pipe C is at rest, the heavy metallic 
valve at A falls; through the opening thus made, the water in 
C passes, a flow is thus established, which soon becomes so 
strong that it raises the valve at A. The momentum of the 
column of water in the tube being thus suddenly checked, it 
relieves itself by passing into the pear-shaped chamber by 
raising the valve at B. The chamber is constructed to act like 
an air or condensing chamber. When the momentum of the 
column of water has been relieved by the passage of a portion 
into the condensing chamber, and the pressure on the valve B 
lessens, the return of the water is prevented by the closure of 
the valve B. The water in the tube C having come to rest, the 
valve A drops, the flow is reestablished, again checked, again 
there is escape through B. This action continuing, sufficient 
pressure is finally accumulated in the air vessel to raise the 
water forced into it to a vertical height of a hundred feet 
or more above the ram through the tube J). 
The hydraulic ram is especially adapted to supplying water 
to houses in the country. In old days the farmer built his 
house under the shelter of a hill to protect it from the blasts of 
winter. At the same time he assured himself of a supply of 
water, either from a spring or from a well. In these times, HYDRAULICS. 
125 
when the merchant has accumulated money, he rears a palatial 
mansion in the country. Extended view of the surrounding 
landscape, and free exposure to every summer zephyr, are the 
things he chiefly seeks. An ample supply of water throughout 
the house is also essential. To obtain this on the hill summit, 
he must either construct tanks in the top of the building in 
which large quantities of rain water may be stored, or resort to 
pumping water from sources below the level on which his house 
is built. 
Under these circumstances, if a sufficient flow of water is 
available, the hydraulic ram furnishes just what is needed. 
Once thrown into action, it works for months or even years 
without any attention. All that is necessary, is to protect it 
and its pipes from frost, by placing them deep in the ground. 
Sand or grit should also be prevented from gaining access 
to the interior, where it would wear the valves. 
When the supply of water is not sufficient to work the 
machine continuously, the ram may still be used by constructing 
a cistern into which the water may run. Thus, in the course of 
twenty-four hours a sufficient quantity may be accumulated to 
run the ram for a number of hours or long enough to furnish a 
sufficient supply for the needs of the establishment. Under 
these circumstances, the storage cistern should he broad and 
shallow, not deep. The tube conveying the water from it to the 
ram, should have considerable fall and length, to gain as much 
momentum as possible. The greater the momentum, the 
greater the proportion of water raised. There is, of course, a 
hmit to the shock the machine will stand, and the momentum 
must be kept within bounds. To reduce the hydraulic friction 
m the tube which conveys the water to the house, and which is 
pften at a considerable distance, it should have a bore at least one 
mch in diameter. 
Development of Power. 
to air, water is the essential of greatest importance to the 
support of life. We cannot exist for more than a few moments 
air. Deprived of water, life may he sustained for a few 
days. Without food, but with sufficient supply of water and 
air, we may live for many weeks. 
To secure a sufficient supply of this important fluid, not only 
;?r the absolute maintenance of life, but also for the preserva- 
tion of health, is a matter which commands the earnest atten- 
10n of physicians. Therefore, it is, that we have presented 
ut length all the ordinary devices for raising water, so that 
U may be available in sufficient quantity to secure the most 
perfect cleanliness. 126 
LIQUID MATTER. 
In cities, a liberal supply of water to each individual is of even 
greater importance than in the country. To meet this demand 
on the scale required, necessitates the exercise of considerable 
ingenuity. To raise a sufficient amount of water for the demands 
of a large community, means the expenditure of considerable 
power. This may always be obtained by the agency of steam, 
but if a sufficient flow of water is available, it is far more 
economical to press it into service as the source of power. 
The production of power from running water may be accom- 
plished either by water-wheels or by the turbine. 
145. Water-wheels. These are of three kinds: Ist. The 
undershot wheel, in which the paddles of the wheel merely dip 
into the water of the stream as it flows past. 2d. The breast 
wheel, in which the water meets the wheel less than half way up 
its height, and then by means of a curved trough is kept in con- 
tact with the paddles. In this form, movement is produced 
partly by the impact of the water against the buckets, and partly 
by its weight as it passes down the trough and carries the 
buckets before it. 3d. The overshot wheel; in this the paddles are 
shut in on the sides and converted into buckets. The water 
being delivered on the top of the wheel, the buckets fill, and the 
action is entirely the result of the gravity of the water. For a 
given quantity of fluid this form gives the maximum of effect. 
It is, however, only applicable when the fall of water is of suffi- 
cient height. The breast wheel answers best with small fall and 
large flow. 
By the use of one of these wheels, in a stream of water unfit 
for the purposes of domestic use, power may be generated 
whereby the water from springs at a distance may be raised. 
146. The Turbine is a modification of the hydraulic tourniquet 
or Barker’s mill (124). It consists of a drum closed at ton and 
bottom. The interior of the drum is 
divided into a series of curved channels, 
which radiate from its axis. The water 
is admitted through the axis, which is 
hollow, and passes into the channels; 
by its reaction, as it glances off the 
curved blades, the drum is caused to 
revolve. 
Fig. 42. 
Various modifications of the above 
have been introduced. In some the 
blades revolve in the drum and so 
The turbine. 
develop power. On a great scale, turbines are employed at 
Philadelphia for the purpose of raising the water used in that 
city. HYDRAULICS. 
127 
147. The Centrifugal Pump.—The mention of this apparatus 
has been deferred until now for the sake of brevity of descrip- 
tion, It is virtually a turbine reversed. By steam, or other 
power, the blades in the last described form of turbine are 
thrown into rapid revolution. Water is then admitted at the 
axis, it is caught by the revolving arms and hurled to the cir- 
cumference, where the centrifugal force developed is so great 
that the water may by suitable means he made to rise in large 
volume to a moderate height. 
This form of pump is admirably adapted to the purposes of 
drainage where the height to he surmounted is not very great. 
Liberal supply of water to ancient cities was largely effected 
by means of open canals. Ruins of these still exist in connec- 
tion with the gigantic cities of Assyria. Through their agency 
the hanging gardens of Babylon were supplied. Phoenicia, 
Jordan, and Egypt, also present innumerable ruins of canals, 
tanks, and aqueducts. So extensive were the aqueducts of 
ancient Rome, that they delivered a per capita supply of forty 
gallons a day to its enormous population. Some of these, and 
there were about twenty, were over forty miles in length. 
They pierced hills, and traversed valleys on lofty arches of 
brick, many of which are standing at the present day. 
It is worthy of remark that a large part of the supply ot 
water to Rome was consumed at the baths. The lack of mate- 
rial, other than earthenware, for the construction of pipes which 
pould resist the pressure of a sufficient head of water, prevented 
its general introduction into houses. Hence arose the immense 
public baths, which were one of the chief places of public 
resort of those days. It is true, that in the palaces of the 
Wealthy, water, and even fountains, were to be found in their 
courts, but nothing existed to be compared with the distribution 
throughout the lofty houses of our time. 
Though the present supply to Hew York City is 95,000,000 
gallons daily, which is about 80 gallons per capita, it is doubtful 
ff the actual consumption for purposes of cleanliness is equal to 
that of ancient Rome. So great is the quantity of water used 
|n Hew York for manufacturing purposes, and so little attention 
Paid to waste, that it is estimated that much less than one- 
half of the supply is actually used in domestic service. This 
would give less than forty gallons per capita, which, as stated 
above, was the Roman allowance. 
Conveying, Storing, and Distributing Water. 
148. Materials for Hydraulic Engineering.—The Roman aque- 
ducts were built almost entirely of brick and hydraulic cement. 128 
LIQUID MATTER. 
The perfect adaptation of these materials to the purpose to 
which they were applied, is demonstrated by the manner in 
which these water conduits have survived the ravages of time. 
Another advantage they present, in addition to that of imper- 
ishability, is that when hydraulic cement has once fairly set 
and hardened, it is as little acted upon by water as is brick 
itself. The water delivered by these aqueducts was, therefore, 
free from any impurity other than what it may have brought 
from the hills among which it was collected. 
Rot only was Rome great in its aqueducts, but its sewers 
also excelled those of modern times. Even at the present day 
hardly a sewer exists that can compare in size with the Cloaca 
Maxima, and not one surpasses it in workmanship. 
f i: jt 
The great advantage in the distribution of water possessed by 
modern engineers, is the adaptation of pipes, made of different 
metals, to this purpose. In ancient days there was little choice 
beyond tubes of earthenware cemented together, or rude wooden 
tubes made like boxes, or by boring stems of trees. These can 
only withstand moderate pressures. As the houses in those 
days were not very lofty, rarely being more than one story high, 
these simple contrivances sufficed for the circumstances under 
which they were employed. 
The immense tubes of cast-iron now used as the water mains 
of great cities, are one of the recent contributions of science to 
the comfort and health of communities. The spinning of lead 
pipes is also a modern device, while the lining of leaden pipe 
with pure tin is an operation, the age of which is practically 
limited to the last twenty-five years. 
Of the materials just mentioned, though iron is slowly acted 
on .by water, the resultant oxides are innocuous. Recent im- 
provements have, moreover, so reduced the price of small tubes 
of iron, that they are very generally driving out those of lead. 
The difficulty in the use of lead is its liability to cause con- 
tamination of water, by being slowly dissolved therein as a 
supercarbonate. 
When water is very pure, the liability to the introduction of 
poisonous lead compounds is much greater than when it is 
impure, or contains sulphates of lime, soda, potassa, etc. Rain 
water, by virtue of its freedom from the salts we have men- 
tioned, is far more liable to contamination than is spring or well 
water. The latter nearly always contains sulphates, which, uniting 
with the lead as soon as it is dissolved, form a coating of a per- 
fectly insoluble sulphate of lead on the interior of the pipe. An 
old lead pipe will, therefore, deliver a purer water than one which 
is new. Advantage has heretofore been taken of this fact, and 
where a pure water was -to be conveyed in lead tubes, they have 
been tilled with solutions of sulphates, or of soluble sulphides, HYDRAULICS. 
129 
and an insoluble lining of sulphate or of sulphide of lead 
formed. 
The liability of the coatings above mentioned to fissure and 
split under varying changes of temperature and expose the lead, 
has resulted in the introduction of a process, whereby at the 
time the lead pipe is spun a lining of tin is also spun in its 
interior. If properly constructed, no pipe equals this in freedom 
from contamination in the water it conveys. The difficulties 
are: Ist. The liability to use impure tin, in which case a voltaic 
circuit is established between the alloyed metals and the water, 
and so poisonous metallic salts are introduced into the liquid 
m the tube. 2d. The difficulty of making joints in which two 
metals shall not come in contact with the water and produce 
the same result as if the tin was impure. 
Of all substances that may be employed for the conveyance 
of water, glass is perhaps the best. Its brittleness has heretofore 
prevented its introduction. Perhaps, in the future, malleable 
glass, which is now only known as a curiosity of the laboratory, 
may find its practical application in the construction of water 
pipes. 
149. Sewage in Houses is one of the questions in hygiene 
which is now a subject of general inquiry. We cannot put it 
more clearly before the reader than by a brief account of the 
development of this important factor in the construction of 
nouses in Hew York. 
When the Croton water was first introduced into the city, the 
streets were not generally sewered. It was, therefore, the 
common practice to prepare a receptacle for the waste water 
nnd sewage from water-closets, by knocking a hole in the 
bottom of the old rain water cistern, or by constructing a 
cesspool in the cellar. Though the water-closets of those days 
might have traps, the pipes from the basins and sinks were gen- 
erally without them. Under these conditions, there were often 
two or three feet of putrefying filth in the cesspool, the noxious 
gases from which gained access, by the waste-pipes, to the bed- 
rooms in all parts of the house. 
In time, the sewer system of the city was completed, and the 
abolition of cesspools became general, much to the advantage of 
the health of the community. In scattered localities, however, 
these foci of disease still exist. 
I hough the sewers were a great improvement, they did not 
accomplish all that was possible, because of faulty construction. 
-*m many localities the descent was not a continuous gentle 
decline, but here and there parts were horizontal and even 
sbghtly raised. The consequence was the formation of pockets, 130 
LIQUID MATTER. 
which became foci of fermentation as bad as the old cess- 
pools. 
To avoid the passage of the odorous sewer gas into the house, 
every basin or other outlet was then carefully trapped in the 
manner shown in the figure. By this device, a portion of 
the water flowing out of the basin was retained in the bend 
Fig. 43. 
of the tube at A, and acting as a water valve 
prevented the access of sewer gas to the house. 
The pipe at B is the overflow. 
The difficulty with this simple trap was, that the 
waste-pipe being often of small diameter and of 
the same calibre as the trap, the water in passing 
down the descending portion of the waste-pipe, 
drew with it the last portions of fluid out of the 
trap (123), and thus, being emptied, it became 
useless. When a large quantity of water passed 
down the general waste, as when a bath was dis- 
Trap for sewer 
gas. 
charged, the exhaust in the pipe was often so great as to draw 
the water from all the traps in the house and leave it without 
protection from the access of sewer gas. 
When waste-pipes have been in use for some time they 
become coated in the interior with a deposit of organic matter, 
which, undergoing putrefaction, gives out a most intolerable 
stench. It is from the pipes in the house rather than from the 
sewer, that the most abominable of the so-called sewer emana- 
tions arise. The deposit in question is the curdy material which 
may always be seen on the sides of a bath after use, especially 
when soap has been freely employed. It consists of epithelium 
with oily and saline excretions removed from the surface of the 
body by rubbing it with water. 
Soap also offers its share of contribution, especially if there be 
any lime salts in the water, which is nearly always the case. 
The manner in which it acts is, that whereas soaps with potash 
and soda are soluble in wTater, that formed with lime is insoluble 
and produces the curdy material which always appears when 
soap is used in a hard or lime water. This, in place of passing 
down the waste to the sewer, adheres in quantity to the walls of 
the waste-pipe. When persons recovering from exanthematous, 
or other diseases, use the bath, the germs of these are also 
entrapped in the curd, and lie in wait for such time as may 
bring them release and set them free for further action. Doubt- 
less in the material in which they find themselves embedded, 
opportunity is offered for the development of contagion spores 
in innumerable hosts. 
The prevention of the formation of these accumulations in 
waste-pipes has been one of the problems of modern hydraulic 
science. It has been found that if a circulation of air can be HYDRAULICS. 
131 
kept up in the tubes, the deposit will dry, and peeling off 
pass into the sewer and be disposed of. To secure this ven- 
tilation the waste-pipes must have sufficient size, the smallest 
being at least two inches in diameter of bore. The larger 
tubes should have a bore of six inches. They should be made 
of iron pipe, the joints of which are carefully closed with 
lead. 
In the adjoining figure a simple plan is given of one of the 
best arrangements of waste-pipes to secure ventilation thereof. 
Fig. 44. 
Sewage ventilation. 
from the sewer the drain should rise gently until it approaches 
the house. Within a few feet of the foundation wall a trap 
should be formed. This will prevent any passage of gas from 132 
LIQUID MATTER. 
the sewer. Just as it leaves the trap, a branch, five inches in 
diameter, should pass vertically upwards and communicate with 
the external air as at A. On entering the house the main waste- 
pipe should pass at an incline along one of the side walls of the 
cellar to its chief connections with the house pipes and leaders 
from the roof. Being exposed throughout its whole length, any 
leak or imperfection may be at once detected and remedied; 
careless workmanship is also easily discovered. 
The slight difference in expense of this method, over that of 
laying earthenware pipes under the cellar floor, is not worthy of 
consideration, when compared with the increased security 
offered. So carelessly is work done by the workmen of our 
day that it is often found, after examination, that these hidden 
pipes have been partially plugged with various materials when 
they were laid. At other times, no attention is paid to the 
preservation of a continuous decline, but shallow pockets in 
which solid sewage accumulates, are formed at more than one 
position. In every case many and frequently all the joints are 
open, and without the first vestige of cement. What wonder, 
in the latter case, that the leakage from the waste-pipes suffices 
to keep the subsoil of the cellar damp with liquid sewage, 
and suited to the development or propagation of various dis- 
eases. 
At the most convenient position, which will generally be 
some twenty ,feet from the rear of the building, the waste-pipe 
should pass vertically upward, out through the roof, and to a 
height of five or six feet above the same. Here it should termi- 
nate in an elbow at B. In its wffiole length, from Ato B, the 
waste-pipe forms an air siphon, the short arm being at A, and 
the ascending portion forming the long arm. An upward 
draught is established in the long arm by virtue of its greater 
warmth, as is the case in a chimney-shaft. Its course is shown 
by the arrows. To maintain the draught, air enters through 
the short arm at A, and so the main drain-tube is freely venti- 
lated throughout its whole extent. 
With a free current of air in the main drain, the lateral pipes 
of communication with the basins and closets may be sufficiently 
ventilated to secure the drying and removal of the deposit, 
when water is not passing along them. At the same time, 
free communication by the vertical pipe with the external air, 
and its great diameter, prevent the establishment of exhaust 
of any consequence upon the traps, and they are not emptied. 
If with such an arrangement as this, the water-closets and traps 
are, from time to time, freely flushed out with a liberal supply of 
water, the chances for the development ot noxious gases and 
germs are reduced to the minimum. HYDRAULICS. 
133 
150. Utilization of Sewage.—Though the utilization of the 
organic matter in the sewage of great cities has received little 
or no attention in this country, various methods have been 
adopted in Europe. Among these, the simplest is the direct 
use of the sewage water for the purposes of irrigation. Many 
devices have also been suggested for the precipitation of the 
organic material from the immense mass of liquid in which it 
is suspended. Of these, the most satisfactory is that by the 
superphosphate of magnesia, which not only throws down the 
organic matter, but also adds to it the phosphate so necessary 
for the formation of a first-class fertilizer. 
The method by magnesian phosphate consists in collecting the 
sewage discharge of a day in an immense tank. As it flows 
in, it receives its small proportion of magnesian phosphate. It 
is allowed to stand a day or so for the precipitate to settle. 
Meanwhile the sewage is directed into another tank, and so 
none is lost. When the solid matter in the first tank has settled, 
the clear water is discharged, a new supply admitted, and a 
second deposit forms. After the deposits have gained sufficient 
depth, they are removed, dried, and packed for use. Doubts 
have, of late, been raised as to the wisdom of the use of these 
deposits on account of their liability to contain germs of dis- 
eases, and to favor their propagation. 
151. Marsh Draining and Malaria.—ln closing the subject of 
hydraulics it seems proper that a few lines should be devoted to 
the subject of the drainage of marshes, in connection with the 
development of malaria. 
Experience has shown that malarial poison is generally most 
troublesome in those years in which there has been a deficiency 
in the rainfall. The common explanation given of this, is that 
under these circumstances the water in marshes having fallen 
below its normal level, the black slime of organic matter form- 
ing their beds has been exposed to the strong heat of the sum- 
mer sun, and the malarial emanations thereby increased in 
quantity and intensity. Low water in the great rivers of the 
West is also followed by increase in and aggravation of malarial 
troubles. 
Development of malaria likewise occurs from the mere up- 
turning of earth which has been undisturbed for many years. 
Of this Southern Hew York has given evidence, in the five 
great waves of malaria that accompanied the construction of 
the Croton Aqueduct, the building of the Harlem, Hudson 
River, and Hew Haven railroads, and of the Fourth Avenue 
Tunnel. Even the mere ploughing of an old orchard is not 
without its effect. In the latter case, if the upturning is done 134 
LIQUID MATTER. 
late in the fall, and the earth exposed to winter frosts, there is 
much less probability of malarial emanations, than if the earth 
is turned late in the spring or during the summer. 
These facts show that when it is deemed proper to drain a 
marsh, arrangements should be made to carry the operation out 
as late as possible in the fall of the year, and still leave sufficient 
time to give the soil an upturning before it freezes. Thus, the 
winter air, charged as it is with ozone, may have an opportunity 
to come in contact with the material from which malarial 
emanations arise, and exert its destructive action upon it. 
In no case should a marsh he either drained or its bed ex- 
posed to the intense heat of the summer sun. SECTION IV. 
GASEOUS MATTER. 
CHAPTEK XI. 
GENERAL AND SPECIAL PROPERTIES OF GASES. 
General observations regarding gases—Form not fixed—Gases have weight—Re- 
unite behind dividing solid—Hypothetical constitution of gases—Yapors— 
Determination of density—Relation of density to combining equivalent in 
gases—Compressibility—Expansibility—Elastic force—Elasticity. 
152. General Observations Regarding- Gases.—As water was taken 
as the type for the examination of the properties of liquids, so 
air offers a type for the examination of the gaseous form of 
matter. The study of the physical, in contradistinction to 
the chemical properties of gases, is called 'pneumatics. It deals 
with the weight, pressure, elastic force, and similar properties 
of this form of matter. In illustration of the leading peculiari- 
ties of gases and their contrast with liquids, we place before the 
reader the following extracts from the work of Br. Arnott. 
“ While the ancients had that vague notion of air which 
made them apply to it, almost indifferently, the names of air, 
ether, spirit, breath, life, they never dreamt of making experi- 
ments upon it, with a view to prove its identity with grosser 
matter. And one of the most interesting parts of the history 
of man’s progress in knowledge is that which tells how the 
light gradually dawned upon this subject. Galileo was the first 
to conclude that air made a definite pressure upon things at the 
surface of the earth—as in forcing water into the exhausted 
barrel of a common pump; Torricelli and Pascal proved that 
this was caused by its weight, and even attempted to estimate 
the height of the aerial ocean ; Priestley, Black, Lavoisier, and 
others discovered that air or gas was of different kinds—that, 
for instance, one kind, called oxygen, could unite with a metal, 136 
GASEOUS MATTER. 
so as to increase its bulk and weight, and produce a com- 
pound of totally new qualities; and at last chemists analyzed 
the atmosphere itself, and proved it to be a mixture of two dis- 
tinct substances. The nature of gases has now been so thor- 
oughly investigated that they can be manufactured, measured, 
and operated upon as readily as the more palpable liquids and 
solids. 
“The suspicion being once excited that air is as much a 
material fluid as water, only less dense by reason of a greater 
separation and repulsion of the particles, it is easy to confirm 
the analogy by reference to familiar facts. Thus, as a leathern 
bag when opened out under the surface of water becomes full, 
and, if its mouth be then tied, cannot afterwards be pressed 
together; so a bladder, opened out in air and then closed, re- 
mains bulky and resisting, and forms what is called an air-pillow. 
The motion of a flat board is resisted in water; the motion of a 
fan is resisted in air. Masses of wood, sand, and pebbles are 
rolled along or floated by currents of water; chaff, feathers, 
and even rooted trees are swept away by currents of air. There 
are mills driven by water; and so there are mills driven by the 
wind. Oil set free under the surface of water, or placed there 
in a bladder, is buoyed up to the surface; hot air or hydrogen 
gas placed in a balloon, is buoyed up in the air. A tish moves 
itself by its fins and tail in water; a bird moves and directs itself 
by its wings and tail in the air; and as on emptying the water 
from a vessel in which a fish swims, the creature falls to the 
bottom, gasps a few moments, and dies; so, on exhausting the 
air from a vessel in which birds or butterflies are enclosed, their 
flapping wings are powerless to support them, and if the experi- 
ment be continued they soon die.” 
153. Form not Fixed.—As was the case with liquids, the form ot 
gases is not fixed, but is determined by that of the vessel con- 
taining them. They in this, and in many other respects, re- 
semble liquids, as we have seen above. A very good description 
of gases might be summed up in the statement that their char- 
acters and properties are merely great exaggerations of those of 
liquids. Solids afforded numerous special properties, in addition 
to the general characters which they possess in common with 
liquids. In gases, the variety of these that we can distinguish 
is greatly reduced. As we pass to rarer and rarer forms of 
matter, there is greater and greater simplicity of properties. 
As far, at least, as regards their physical characteristics, sub- 
stances chemically different approach nearer and nearer to each 
other. The properties which were general in solids and liquids, 
are the chief ones presented by gases, but they have become so GENERAL AND SPECIAL PROPERTIES OF GASES. 
137 
exaggerated that they in reality are the special properties of 
this form of matter, and as such we shall treat of them. 
154. Gases have Weight.—ln common with solids and liquids, 
and notwithstanding their exceeding levity, gases possess weight. 
Of this a demonstration is offered by direct experiment. In 
Fig. 45, A represents a flask with a capacity 
of one hundred cubic inches. The mouth 
is closed by a stopcock B. Attaching the 
flask to one arm of a balance, it is carefully 
counterpoised. It is then removed from the 
balance, and brought into connection with 
an air pump by the screw on the stopcock. 
As water might be pumped out of the flask, 
so the air is removed by the air-pump. 
When the exhaustion is complete, the flask 
is again attached to the arm of the balance, 
when it will be found to have lost weight. 
Adding sufficient weight to the lighter, or 
flask arm of the balance, until equipose is 
restored, it will be found that about thirty- 
one grains are required for that purpose. 
Fig. 45. 
weighing gases. 
One hundred cubic inches of air, therefore, weigh thirty-one 
grains. Comparing air with water, the latter is seven hundred 
and seventy-three times the heavier. Among themselves gases 
show a far greater variation in weight than either solids or 
liquids. 100 cubic inches of hydrogen, which is the lightest, 
weigh 2.14 grains, while 100 cubic inches of hydriodic acid gas 
weigh 146 grains, or a ratio extending from one to sixty-five. 
In the case of ether and mercury, relatively one of the lightest 
and the heaviest of liquids, the variation is from one to twenty. 
If we exclude mercury and confine it to non-metallic liquids, of 
which sulphuric acid is one of the heaviest, the proportion dimin- 
ishes to about one to a little more than two. In metals it is 
greater than in liquids, the difference between lithium and pla- 
tinum being one to thirty-seven. It is true that in the case of 
solids, the extent of variation might be increased by comparing 
cork, or other organic bodies, with platinum, hut that would 
hardly be correct, since such organic substances owe their light- 
ness chiefly to the air entrapped in their structure. 
Since gases possess weight, it follows that, like fluids, they 
e^ei't pressures within their own volume. The amount and 
character of these pressures we shall examine later on. 
. Reunite behind Dividing Agent.—Since all liquids are 
visible, there is no difficulty in the verification of this fact. The 
invisibility of air and the ordinary gases, renders it more diffi- 138 
GASEOUS MATTER. 
cult of demonstration. If, however, we subject to experiment 
some gas which is visible by virtue of its color, we then find 
that gases possess this property in a higher 
degree than liquids. In demonstration of 
this take a large bottle of colorless glass, A, 
place in it a beaker with some copper trim- 
mings, B, and on these pour two or three 
drachms of nitric acid; red fumes of tetroxide 
of nitrogen quickly fill the vessel. Then pass 
into it a rod, I), with a circular disk, C, 
attached to its extremity. Ho matter how 
quickly the disk is made to traverse across 
the jar, the red gas closes in behind it in- 
stantly, even though the disk is moved with 
the flat surface forward. How pass the disk 
through water in the same manner, flat sur- 
face forward, though the water closes behind 
Fig. 46. 
Reunite behind dividing 
agent. 
it there is a short distance where no water is present. We thus 
tind how much more perfect the property of reuniting is in a 
gas than in a liquid. 
Though we cannot see this movement of closure in air on 
account of its invisibility, it is very apparent when sufficient 
velocity is given to the dividing body. A rifle-shot, for example, 
in its passage emits a peculiar noise caused by the clashing 
together of the air in the track the shot has ploughed through 
that medium. Even so impalpable a body as lightning, in its 
passage through the atmosphere, gives evidence of the same 
fact; the thunder that attends it being produced by the violent 
closure of the air it has divided in its course. 
156. Hypothetical Constitution of Gases.—The Kinetic (mveu, to 
move) theory of Clausius, as stated by Crookes, is as follows: 
“In gases the molecules fly about in every conceivable 
direction with constant collision and enormous and constantly 
varying velocities, and their mean free path is sufficiently great 
to release them from the force of cohesion. Being free to move, 
the molecules exert pressure in all directions, and were it not 
for gravitation they would fly off into space. The gaseous state 
remains so long as the collisions continue to be almost infinite 
in number and of inconceivable irregularity. The state of 
gaseity, therefore, is preeminently a state dependent on colli- 
sions. A given space contains millions of millions of molecules 
in rapid movement in all directions, each molecule having 
millions of encounters in a second. In such a case the length 
of the mean free path of the molecules is exceedingly small, 
compared with the dimensions of the containing vessel, and the 
properties which constitute the ordinary gaseous state of matter 
which depend upon constant collisions are observed.” GENERAL AND SPECIAL PROPERTIES OF GASES. 
In solids, as we have seen, the cohesive or attractive force is 
in excess of the repellant; in liquids these two forces are nearly 
evenly balanced; in gases the repellant is enormously in excess 
of the attractive force, so that gases may be said to possess 
scarcely any cohesive force at all. 
157. Vapors.—Gases like hydrogen and oxygen were formerly 
thought to be permanently gaseous in their nature. No pressure 
or intensity of cold to which they could be submitted possessed 
the power of changing their state. Improvements in the methods 
of manipulation have, however, shown that the most refractory 
gases may be compelled to assume the liquid and even the solid 
form. The old division of this group of bodies into permanent 
gases and vapors, therefore, no longer actually exists; never- 
theless, the convenience attending its use is such that it will 
doubtless be retained for some time. 
A gas may, therefore, he defined as an aerial body which cannot be 
easily forced to assume the liquid state. 
A vapor, on the contrary, is an aerial body which may be easily made 
to assume the liquid state by moderate reduction of temperature or 
increase of pressure. 
Under these definitions, bodies like hydrogen, oxygen, car- 
bonic acid, are dealt with as gases, while steam is a vapor. 
As the temperature of a vapor approaches the point at which 
tends to assume the liquid state, it does not contract and 
expand regularly. At a certain distance from this point all 
vapors obey the laws of contraction and expansions for gases. 
™hen, therefore, their specific gravity or other important prop- 
erty is to be determined, it should be at a sufficient distance from 
their point of liquefaction to insure accuracy in the results. 
158. Determination of Density.—The method is essentially the 
same as that for the determination of density of liquids by the 
specific gravity bottle. The great variations which the volume 
°f a gas undergoes from slight causes, require a number of cor- 
rections to be made in carrying out the process as thus simply 
stated. By the method of Begnault some of these may be 
avoided. It may be briefly described as follows: Two globes of 
thin glass of the same size and about a gallon in capacity are 
taken. One of these is hermetically sealed, and suspended 
from one arm of the balance. It acts as a volume counterpoise 
to the other globe which is to be employed for experimentation, 
kince both globes will expand and contract at the same rate 
under variations of temperature and pressure, their changes 
Wl*l balance each other, and these sources of error are conse- 
gently eliminated from the operation. 
The experimental globe is filled with air or with the gas at 
Zer° centigrade, the melting point of ice. This is done by 140 
GASEOUS MATTER. 
placing it in a vessel of ice, then by means of a three-way cock 
it may be connected either with an air-pump or with vessels 
holding purified air or gas. 
The weight of the empty globe is first determined, the air 
having been removed by as perfect an exhaustion as possible. 
Air which has been purified by passing it through tubes con- 
taining suitable reagents and dried by tubes of sulphuric acid 
and chloride of calcium, is then passed into the empty globe 
until the interior and exterior pressures are equal. All exterior 
moisture is carefully removed, and it is then weighed. The 
increase represents the weight of air it contains at 0° C. and 
the then prevailing barometric pressure. 
Again the globe is placed in the ice and exhausted. The gas 
to be examined is introduced after proper purification and 
drying. To insure removal of the last traces of air, the globe 
is connected with the air-pump and the gas removed by exhaus- 
tion. In this manner the last traces of air are, as it were, 
washed out, and it is weighed. It is then refilled with the dried 
gas, removed from the ice bath, the exterior carefully dried, and 
weighed. The increase in weight represents the weight of the 
gas at 0° C. and the prevailing pressure. From these data the 
specific gravity of the gas may be computed in the same way as 
for solids and liquids. All results are reduced to the pressure 
of 760 millimetres, and temperature of 0° C. 
159, Relations of Density to Combining Equivalent in Gases.—The 
determination of the correct densities of gases and vapors is of 
the utmost importance on account of the close relationship 
existing between the specific gravities and the atomic or the 
molecular weights of these bodies. 
When a table of densities is constructed with hydrogen as its 
basis, this relationship is at once evident, as will be seen below, 
the figures either being identical or multiples of each other. 
The fact of this relationship of specific gravities and atomic 
weights, or combining equivalents to each other, has enabled 
chemists to make more accurate estimations of the combining 
equivalents of many elementary substances. 
Substance. 
Molecular 
formula. 
Molecular 
weight. 
Atomic 
weight. 
Sp. gr. 
H=l. 
Sp. gr. 
air=]. 
Hydrogen 
h2 
2 
1 
1 
.069 
Chlorine 
CIa 
71 
35.5 
35.5 
2.460 
Oxygen . 
o2 
32 
16 
16 
1.108 
Nitrogen 
28 
14 
14 
.970 
Steam 
H,0 
18 
9 
.625 
Ammonia gas. 
nh3 
17 
8.5 
.589 
Carbonic acid gas . 
co2 
44 
22 
1.524 
Alcohol vapor 
c2h6o 
' 46 
23 
1.593 
Air 
14.44 
1.000 
Ether vapor . 
C>i0b 
74 
37 
2 557 
Chloroform vapor . 
CHClj 
119.5(?) 
G0.5(?) 
4.181 GENERAL AND SPECIAL PROPERTIES OF GASES. 
141 
‘ 160. Compressibility.—Take an ordinary syringe, consisting of 
the cylinder or barrel A, in which the piston C moves without 
leakage. Close the outlet B with a plug of wax or 
a cork, or even with the finger. Between the piston 
C and the outlet B a column of air will then be 
enclosed. On applying pressure to the piston by 
its rod at I), this columrf of enclosed air will be 
with ease reduced in volume, as is the case with 
liquids; therefore, gases are compressible. They, 
however, differ in this; that whereas water, the type 
of fluids, shrinks one-twenty thousandth of its volume 
for an atmosphere of pressure, air diminishes to 
one-half. 
Fig. 47. 
161. Expansibility.—The wonderful compressibility 
of gases, of which evidence has been given in the 
last article, would naturally lead us to expect a 
parallel extent of expansion on diminution of pres- 
sure. That this is the case is shown by the experi- 
ment (In) 
The expansibility of gases is one of their leading 
Compressibility 
of gas. 
peculiarities. It may be said to be almost infinite, for a gas 
will fill a space of any size we offer it. 
162. Elastic Force of Gases is in reality another terra applied to 
expansibility. If a small rubber sack, A, be partly filled with 
a|r» its mouth tightly closed, and placed on the 
air-pump plate under a bell-jar, B, on exhausting 
the air from the bell the rubber bag expands 
until it occupies the space represented by the 
dotted line, and may even be made to appear to 
hll the entire jar. 
The rationale of the action is as follows: 
Accord! ng to the kinetic theory of gases (156), 
their molecules are flying about in all directions; 
they are, therefore, battering and pressing 
against the interior walls of the bag. So long 
as the pressure of the air is not removed, it 
counterbalances the pressure in the interior of 
tbe bag. The moment the exterior pressure on 
Fig. 48. 
Elastic force of gas. 
the sack is removed, the interior pressure becomes evident, and 
expansion is the result; this continues until the interior and 
exterior pressures are again in equilibrio. 
.An interesting illustration of expansion may be performed 
an egg. In the large end of an egg there is a bubble 
°* air. A small opening is made in the narrow end of the egg 
and it is stood in a wineglass under an air receiver. On 142 
GASEOUS MATTER, 
exhausting the receiver, the contents of the egg pass out into 
the wineglass, being expelled from the shell by the elastic force 
of the bubble of air at the wide end. Restoring the pressure of 
the air the contents of the egg are returned to its shell. 
This elastic force of gases, which is perhaps their most charac- 
teristic property, has caused them to pass under the name of 
elastic fluids, in contradistinction to ordinary fluids like water. 
It is not to be confounded with the elasticity which gases 
possess in common with liquids proper. 
163. Elasticity refers to the power of returning to original 
volume when the cause of disturbance is removed and the 
original conditions restored. Both gases and liquids possess 
this property in a marked degree. Indeed, it may be said 
to be absolute, and the direct consequence in both cases of the 
mobility of their molecules. 
The experimental demonstration of the elasticity of gases 
may be derived from the arrangement employed in article 160, 
for on removing the pressure on the piston it at once returns to 
its original position. In like manner, articles 161 and 162 both 
furnish evidence of this fact, though in a different way, the 
return to original volume in this case being produced by restora- 
tion of original pressure. 
Owing to the elasticity of gases pressure may be suddenly 
transmitted through them to considerable distances. An illus- 
tration of this fact may be shown by suddenly increasing the 
pressure in the gas-pipes of a building, as by blowing into them 
the lights are all immediately extinguished. A method of 
telegraphy founded on this property of the air, is now employed 
in the transmission of signals on ships. Its great advantage is 
its certainty, since it is less liable to get out of order than other 
methods of signalling. The tambours of Marey are also based 
on this property of air. PNEUMATIC APPARATUS. 
143 
CHAPTER XII. 
PNEUMATIC APPAEATUS. 
Generation of gases—Collection at pneumatic trough—Pouring—Faraday’s 
tube receiver—Gases arrange themselves according to density—Collecting 
gases by displacement—Washing and drying gases—The aspirator—Com- 
pression air-pump—Life and condensed air—Exhaustion air-pump—Life and 
rarefied air—Mercury pump—Bunsen’s filter pump—Limit of vacuum— 
Vacua by chemical agents. 
164. Generation of Gases.—The demonstration of many of the 
physical properties of gases requires that we should have at 
hand one lighter and one heavier than air. Bor the first, hydro- 
gen will answer; for the second, carbonic acid gas. As a rule, 
gases are generated either by the action of heat on certain sub- 
stances placed in glass retorts, or by the action of acids on 
suitable materials. In either case, the methods of collection, 
storage, and manipulation are the same. 
Bor ordinary purposes of experiment the simple apparatus 
shown in the figure may be used for the generation of hydro- 
gen or carbonic acid. It consists of a bottle, A, with a tolerably 
wide mouth, B, closed by a rubber or cork 
stopper, which fits air-tight; this is the de- 
composition bottle. Through the stopper a 
tube passes to the bottom of the bottle, and 
terminates above in a funnel-like expansion, 
This is called the supply tube, by it the 
acid is to be added as required. A second 
tube, D, bent in the manner shown, also 
pierces the stopper, through which it just 
passes. By it the gas escapes as fast as it is 
generated. It is, therefore, called the escape 
tube, and serves to convey the gas to the ap- 
paratus for collection. 
Bor the generation of carbonic acid gas, a 
tew fragments of Italian marble or of chalk 
ai’e placed in the bottle, enough water is 
Fig. 49. 
Decomposition flask. 
added to cover them, the stopper is then put in position, when 
the lower end of the supply tube should dip’under the surface 
tn the water. Sulphuric acid is then added, a little at a time, 
by the supply tube. As it reaches the water and comes in con- 144 
GASEOUS MATTER. 
tact with the marble, effervescence is produced, carbonic acid 
gas being evolved. It passes oft" by the escape tube. When 
the effervescence decreases in vigor, more of the acid is to be 
added by the supply tube. At the beginning of the operation, 
the bottle is filled with air, it therefore follows that if we de- 
sire to obtain the carbonic acid comparatively pure, enough must 
be allowed to pass off to expel all the air from the bottle. A 
quantity twice the capacity of the bottle will answer. 
If hydrogen is to be made, the apparatus is emptied, cleansed, 
and strips of zinc are substituted for the marble. The re- 
mainder of the operation is conducted in the same way as for 
carbonic acid gas. As hydrogen is lighter than air, it is neces- 
sary to use a larger quantity in the removal of the air from the 
bottle. About three or four times its volume are generally re- 
quired. Great care must also be taken not to allow a flame to 
come in contact with the mixture of air and hydrogen, as it 
escapes from the tube D, or an explosion attended by serious 
consequences may occur. 
165. The Pneumatic Trough.—The collection of gases may be 
conducted in three ways. Ist. By reception in an exhausted 
vessel, as described in the method for taking specific gravity. 
2d. By collection over a liquid. 3d. By displacement of air. 
For the second method the apparatus known as the pneumatic 
trough is required. It consists of a water-tight box, AA, 
Fig. 50. 
represented in section in Fig. 50. 
The side and half way across is oc- 
cupied by the shelf B, on which the 
bell-jar C stands. The remainder of 
the trough, W, is called the well. 
Sufficient water is poured into the 
trough to fill the well entirely, and 
also to cover the shelf to a depth of 
a couple of inches, 
When a gas is to be collected, ajar 
is filled with water in the well, it is 
then turned with the mouth down, 
and without allowing the mouth to 
pneumatic trough. 
rise above the water, it is placed on the shelf, as is shown in the 
figure. Thus arranged, the jar remains filled with water, and 
if it has been properly filled is free from air, except so far as 
any may he dissolved in the water. The cause of the suspen- 
sion of the water in the jar is, as we shall find hereafter, the 
pressure of the atmosphere upon the surface of the water in the 
tank. 
The collection of the gas from the generation vessel is now 
accomplished by merely passing' its escape tube, B, under the PNEUMATIC APPARATUS. 
145 
mouth of the bell-jar, as it rests on the shelf of the trough. 
The gas bubbles rising through the water accumulate in the 
jar without mingling with the air, and the operation is con- 
tinued until the jar is tilled. The delivery tube is then placed 
under the mouth of .a second jar, and the collection continued 
in the same manner. 
When the gas to be collected is very soluble in water, as for 
instance ammonia gas, mercury may be substituted for water. 
In this case, the apparatus must be much smaller and much 
stronger, on account of the great expense and weight of that 
liquid. The tube apparatus is very convenient for this purpose 
(167). 
166. Pouring Gases at the Trough. The pneumatic trough 
also enables us to manipulate gases in almost any manner that 
we may desire. Suppose that it is required to transfer a meas- 
ured portion of gas to another jar, the 
operation is conducted as shown in the 
figure at A. A small graduated bell is 
filled with water, and held in the posi- 
tion shown at A, with its mouth under 
the water in the trough. The large bell 
containing the supply of gas is then 
immersed completely and its mouth 
inclined under that of the small bell 
until the gas passes in bubbles from 
the larger to the smaller jar. This up- 
side down pouring through water is con- 
tinued until the line of the gas in the 
Fig. 51. 
Pouring gas. 
small bell coincides with the desired line of the scale marked 
thereon. 
If the gas is to be measured in a narrow bell, a funnel may 
be used to facilitate the filling of the tube, as it would be to 
assist in tilling it with fluid. The only difference is that in this 
case the operation is reversed or upside down, as is shown at B 
in the figure. 
167. Faraday’s Tube Receiver.—Gases may be experimented 
with on the small scale by the instrument known as the tube 
receiver of Faraday. It consists of a test-tube about ten inches 
m length and three-fourths of an inch in diameter. This is 
bent in the manner shown at AB in Fig 52. The whole 
length of the tube is filled with water. It is then suspended 
with the closed end upwards. The air pressing on the sur- 
face of the water in the open end A of the short arm, retains 
the fluid in position in the long arm B. Passing the delivery 
tube D of a gas generator into the short arm to the bend, as fast 146 
GASEOUS MATTER. 
as the gas is evolved the bubbles pass into the long arm and are 
collected at B, the displaced water dropping into C. 
The short arm of this arrangement may be used as an experi- 
mental vessel, while the long arm serves as a reservoir. The 
manipulation in this case consists in filling A 
completely full of water. The mouth of Ais 
Fig. 52. 
then closed with the thumb, and the apparatus 
so inclined as to till the short arm with the gas 
collected in the long arm. Uncovering the 
mouth of A, by removing the thumb, a piece 
of wood bearing a spark, or paper imbued with 
any liquid test, may be applied to the gas it 
contains. For a second examination the short 
arm is again tilled with water; the gas it contains 
is thus displaced. It is then closed by the thumb, 
and the apparatus inclined to fill A with a second 
charge of gas, to which some other test, as paper 
moistened with a lead salt, may be applied. 
Thus test after test may be applied, until the 
gaseous contents of the instrument are consumed. 
Many examples of this form of apparatus are 
Faraday’s tube 
receiver. 
offered in utensils or articles in common daily 
use, though in these cases it is generally 
water rather than gas that is stored. Among 
such examples we may mention the water tube of Mason’s 
hygrometer; the bottles for holding ink, gum, and for the water 
Fig. 58. 
supply of bird-cages. The supply 
tank of many lamps is also constructed 
on this plan. 
168. Gases Arrange Themselves Ac- 
cording to Density.—As is the case 
with liquids, gases show a tendency 
to arrange themselves according to 
their specific gravity, the lighter 
floating on the heavier. That this is 
the case is demonstrated by the ex- 
periment delineated in Fig. 63, in 
which A is a large jar filled with air, 
and B a small one containing car- 
bonic acid. Inclining the mouth of 
B over that of A, and manipulating 
the jar exactly as though water were 
Pouring gas through air. 
being poured from the smaller to the larger, the carbonic acid 
gas will flow’ from B into A. That this has really happened is 
readily proved by examining the contents of the jars with PNEUMATIC APPARATUS. 
147 
a candle-flame C, when it will be found that it is extinguished 
in A when it reaches a certain depth, and continues to burn in 
B. Since carbonic acid gas does not support combustion, it is 
shown that it has flowed from B into A on account of its weight, 
and has expelled the lighter air from the jar. 
Fig. 64 represents another form of the same experiment. 
A B is a trough six feet in length, with sides six inches high. 
Fig. 54. 
Weight of carbonic acid gas 
A row of candles is placed along the bottom about a foot apart. 
The trough is inclined with one end, A, resting on the floor 
and the other, B, supported on a stool. The candles being 
lighted, a large jar of carbonic acid, C, is poured into the trough 
at its upper end. The gas at once passes down the trough as 
water would do, putting out the flames in its course, and spread- 
ing on the floor extinguishes other flames that may be within its 
reach. 
This tendency of carbonic acid to collect in low places is at 
times the cause of loss of life. In mines, caves, and wells, it 
not unfrequently happens with disastrous results. In breweries 
also, where it is generated in large quantities during the process 
of fermentation, it often accumulates to such an extent in the 
vats that workmen have lost their lives by breathing its poison- 
ous fumes. 
If an attempt is made to repeat the experiment shown in 
P lg. 53 with hydrogen gas, it will be found that the vessel A 
does not contain a trace of that gas. To determine what has 
become of it, let the experiment be repeated with the vessels 
arranged as shown in Fig. 55, in which A is suspended mouth 
downwards, and B is brought alongside, in the position shown 
b.Y the dotted lines, and then gradually tilted to the horizontal. 
(hi examining A with a candle-flame C, an explosion will result, 
showing that the hydrogen has by its inferior specific gravity 
floated upwards into the jarA, and displaced the air with which 
it was filled. 
Iu these experiments the hydrogen and carbonic acid gas 
retain their positions for only a short time. By degrees either 148 
GASEOUS MATTER. 
of these gases intermingles with the air, by virtue of the process 
called diffusion. This we shall study hereafter in connection 
with other forces. 
Fig. 55. 
Fig. 56. 
Hydrogen poured upwards. 
Collection by displacement. 
169. Collection of Gases by Displacement.—The experiments we 
have described explain the third method by which gases may be 
collected. This is known as the method by displacement. If 
the gas is lighter than air, the jar in which it is to be collected 
is suspended in the manner shown at A, Fig, 56; the delivery 
tube i) is then passed to the upper part of the jar. The gas as 
it accumulates in the jar displaces the air, until finally it is com- 
pletely expelled. 
If the gas is heavier than air, the jar is then arranged as is 
shown at B, Fig, 56, with its mouth upwards, and the delivery 
tube I) passes to the bottom. The mouth of the jar may be 
closed by a sheet of glass or paper, C. 
The method by displacement is especially applicable to the 
collection of gases like ammonia or hydrochloric acid, which 
are very soluble in water. They cannot be obtained quite free 
from contamination with air, on account of the tendency to 
diffusion of which we have spoken; but they may be thus col- 
lected for purposes of examining or demonstrating their leading 
properties. 
170. Washing and Drying Gases.—The separation of gases from 
finely divided solid matter, or from fluid or aerial substances 
with which they may be contaminated, is accomplished by 
means of the washing bottle and drying tubes. 
The washing bottle consists of a wide-mouthed bottle, A. 
The mouth is closed by a cork, through this a tube, B, passes to_ 
the bottom of the bottle. It may be the continuation of the 
delivery tube of a gas generator, or it may be connected there- 
with by a piece of rubber tube. In the bottle A, water is 
placed, through this the gas is obliged to pass in bubbles, these 149 
PNEUMATIC APPARATUS, 
are submitted to the action of the water, and any dust-like 
particles, vaporous mist of acid, or other impurity is washed 
out. By the use of a suitable liquid in the washing bottle, any 
gas soluble in such liquid may be separated from one which is 
insoluble, and a purified gas obtained. 
In place of a bottle, a tube of the shape delineated at C may 
be used. It is called aIT tube. The bend of the tube is to be 
occupied by the liquid, when it is used for 
the purpose in question. In Fig. 57, the 
U tube and bottle are combined. Various 
modifications of this tube are employed. 
Among these we may mention Liebig’s 
carbonic acid bulbs and the ammonia tube. 
For the purpose of drying gases, the 
U tube is tilled with pumice which has 
been heated red hot to expel all moisture, 
and then soaked in sulphuric acid ; it is 
shown at C. Sometimes it is tilled with 
Fig. 57. 
Washing bottle. 
solid porous chloride of calcium. Either of these substances hqs 
an intense affinity for water, and will abstract it from gases as 
they pass over or through them. 
The proper conduction of these washing and drying opera- 
tions requires that the gas should pass slowly, otherwise the 
action is only partial. To secure complete action, a number of 
bottles or tubes should be employed, and the incomplete action 
of the first supplemented by that of others. 
-171. The Aspirator is an apparatus used for drawing air or 
other gases through systems of tubes or bottles, in which they 
may be submitted to the action of various reagents. It consists 
ot a large bottle, A, with a capacity of a gallon or more. It is 
to be tilled with water. On opening the stopcock at B, the water 
hows out into C. As the water passes out, 
air enters at the mouth of the bottle. The 
mouth is closed by the cork A, through 
which a tube passes. If this is brought in 
communication with a IT tube, as repre- 
sented at D, the air in its course will be 
drawn through D, and submitted to the ac- 
tion of any agents that may be placed therein. 
The aspirator is used in the examination 
°1 air. It is also of service in ultimate 
organic analysis, for the purpose of with- 
drawing the last traces of gas from the 
combustion tube and other marts of the an- 
Fig. 58. 
Aspirator, 
paratus. 
For its action this instrument depends upon the pressure ot 
ine air, which forces its way into the bottle as the water runs 150 
GASEOUS MATTER. 
out. If the train of tubes through which the air must pass to 
reach the aspirator bottle contain much liquid, it may he neces- 
sary to attach a vertical tube one or two feet in length to the 
stopcock B. A long column of water being thus called into 
action, the pressure will be increased and the resistance over- 
come. See (128). 
172. The Compression Air-pump.—lt is necessary for the ex- 
amination of the properties of air and other gases that we should 
describe the forms of pumps employed for purposes of com- 
pression and exhaustion. The compression pump resembles an 
ordinary force pump in its structure and action (148). In Fig. 
59, A is the solid piston moving in 
the cylinder AB. Below A, a lateral 
tube with a conical valve opening 
towards the cylinder gives ingress to 
air or other gas which is to be made 
the subject of experiment. At 0 there 
is another tube, also closed by a valve 
which opens outwards from the cylin- 
der, and gives egress to the gas when 
the piston is forced downwards. Each 
upward movement of the piston draws 
gas in through V, while the down- 
ward movement forces it out through 
Y'; the valves in each case preventing 
its return. 
The bell-jar is represented at B. It 
Fig. 59. 
Compression air-pnmp. 
is a cylinder of thick glass capable of resisting three or four 
atmospheres of pressure. The upper and lower edges of the 
cylinder are ground and fitted air-tight to plates of brass, E and 
F. Metallic rods, as shown at E and F, pass from one plate to 
the other. By the aid of the screw threads and nuts in which 
these terminate, the metallic plates are held firmly in position. 
There are many applications of compression which are of 
interest. Among these is the air-gun. In this apparatus air is 
compressed in a reservoir, from which it is allowed to escape 
suddenly into a gun-barrel charged with a bullet. The propel- 
ling force of some of these instruments almost rivals that of 
gunpowder. They make less report than firearms, and as there 
is no smoke or flash, their use is not as easily detected as that of 
an ordinary gun or pistol. 
Another application of the elastic force of compressed air is 
in the construction of the condensing chambers of force pumps, 
fire-engines, and hydraulic rams. The condensing chamber 
operates to convert the intermittent action of the pump into a 
continuous one. It consists of a stout metallic chamber, A. PNEUMATIC APPARATUS. 
151 
Through the top of this a metallic tube passes nearly to the 
bottom. By means of a tube, B, which opens into the bottom, 
water is admitted at each stroke of the pump. The return 
of the water from the chamber is prevented 
by a valve which is placed at the opening 
of this tube. Between the lower end of the 
tube C and the top of the chamber A, at- 
mospheric air is entrapped. At each stroke 
of the pump this air shrinks in volume, 
receiving the blow delivered by the pistom 
While the piston is making its return stroke, 
the compressed air exerts its elastic force and 
keeps a continuous stream flowing from the 
upper or open termination of the tube C. 
Fig. 60. 
173. Life and Condensed Air.—ln the air- 
bell of the compression pump we may study 
the effects of condensed air or other gas 
upon the respiratory function of small 
animals. The extensive use of the divina-hell 
Condensing chamber. 
and caisson in certain engineering operations, as the construction 
of the piers of bridges at great depths under water, the recovery 
of treasure or a valuable cargo from sunken ships, render the 
study of this subject a matter of importance. In certain diseases 
also the respiration of condensed air has proved to be a valuable 
remedial agent. 
Water-tight diving dresses are now substituted for the diving- 
bell. They possess the advantage of giving the diver greater 
mobility, and his movements may be extended over considerable 
areas. Great care must be taken, both in the case of the diving- 
bell and the diver’s dress, that no accident occurs to the tube by 
which air is supplied. A delay of two minutes in raising a man 
to the surface of the water, where accidents have occurred, has 
been attended by a fatal result. 
Successful attempts have been recently made to avoid the 
operation of pumping air to the diver. On making a descent 
he carries a cylinder of compressed with him; from 
this a supply of fresh gas is conveyed to the interior of the 
dress, which holds sufficient atmospheric air to dilute the 
oxygen. Means for absorbing the carbonic acid are also sup- 
plied. In this way a diver has been enabled to remain for 
a much longer time under water, and move over very considerable 
distances. 
It is said that the greatest depth to which one may descend in 
water is 160 feet. Tinder these circumstances the diver carries 
TOO pounds on his back and breast, and 25 pounds attached to 
the soles of his shoes. Though respiration under these condi- 152 
GASEOUS MATTER. 
tions is difficult, yet men have remained at this depth for 30 or 
40 minutes. In one instance an experienced diver remained at 
a depth of 80 fathoms for 75 minutes, but he died within nine 
hours from congestion of the lungs. 
The power of the muscles of the chest to compress the air in 
the lungs is quite limited. Very few persons can blow air 
through a tube, the extremity of which is two feet perpendicu- 
larly under water. This, as we shall see hereafter, is only equal 
to'a pressure of one pound to the square inch. By using the 
muscles of the mouth alone, a greater degree of compression 
may be exerted. 
174. The Exhaustion Air-pump depends upon the elastic force of 
the air for its action. 
Its parts are similar to those of the ordinary lift or suction- 
pump already described when treating of hydraulics. 
Let P represent a ground-glass plate some ten inches in 
diameter, on this a bell-jar, J, is placed. The mouth of the jar 
Fig. 61. 
Exhaustion air-pump. 
is also ground fine, so that with the plate it makes an air-tight 
joint. From the centre of the plate a brass tube passes to the 
bottom of the cylinder C. The cylinder must be accurately 
formed. The piston, of which R is the rod, should fit the 
cylinder perfectly air-tight. At the bottom of the cylinder at 
C, there is a valve, and also one in the piston B; both of these 
open upwards. 
By means of the handle R the piston is thrown into action. 
At each stroke air is removed from the jar by its own elastic 
force, which is brought into play the moment the pressure is 
reduced at any point in the jar. 
After a few strokes the force required to move the piston is 
very considerable. To relieve this, a valve, V, opening upwards 
is placed on the top of the cylinder; as each stroke of the 
piston is completed, this supporting the pressure of the air 
reduces greatly the amount of force required to work the pump. 153 
PNEUMATIC APPARATUS. 
In double cylinder air-pumps the pressure on one piston balances 
that on the other, and these valves are not needed. 
There are many modifications of the form we have described. 
In all, the gradual removal of the air from the jar by repeated 
strokes of the piston finally produces a more or less perfect 
emptiness in the jar. To this the term vacuum is applied. 
175. Life and Rarefied Air.—When a lighted candle is placed 
under the bell-jar of an air-pump, and exhaustion is made, it 
soon burns with a flickering light, and after a little the flame 
dies out. In like manner small animals, under the same cir- 
cumstances, suffer distress long before a vacuum is reached. 
Data have been obtained in the ascent of high mountains, 
which show that large animals as well as small suffer when the 
air is rarefied. At an elevation of 15,000 feet, where the air 
has about half the density it possesses at the level of the sea, 
respiration in men becomes more or less labored and difficult. 
At 16,000 feet of elevation, the hardiest mountaineers cannot 
walk ten yards without taking a rest, muscular action becoming 
almost impossible. In the vicinity of Quito it is found to be 
very difficult to make pack mules and horses advance above an 
altitude of 15,000 feet. They halt, tremble, and fall down. If 
rest is not allowed, they soon die. Travellers and even experi- 
enced guides frequently faint suddenly in the attempt to ascend 
lefty peaks. A mountain range over 15,000 feet in height is an 
effectual barrier between two nations. At double this height it 
is doubtful if any form of life exists, partly on account of the 
tenuity of the air and partly on account of the intense cold. 
The exhaustion action of the walls of the chest, like their 
compression action, is limited to about one pound to the square 
inch. By the muscles of the mouth alone some persons can 
exert a wonderful exhaustion action, raising water nearly 30 feet, 
while others cannot raise it higher than 5 or 6 feet even in a 
narrow glass tube. 
Though the forced respiratory act is limited to a pressure of 
°ne pound to the square inch, it is quite sufficient to draw 
various objects into the lungs. In persons who have been 
drowned, mud, sand, weeds, and other substances which have 
come into the vicinity of the mouth and nostrils are thus intro- 
duced into the lungs. Occasionally children are suffocated by 
having some object in the mouth at the time of taking a sudden 
violent inspiration. In this way marbles, thimbles, and pieces of 
candy have found their way into the bronchial tubes. Cases are 
also on record, in which comparatively heavy bodies like pins 
and needles have thus been carried into the air passages. 
176. The Mercury Pump is also known as SprengeTs air-pump. 
In this a column of mercury is used to produce a vacuum. The 154 
GASEOUS MATTER. 
principle adopted consists in converting the space to be ex- 
hausted into a Torricellian vacuum (198). A simple form of 
this may be described as follows. In Fig. 62, CII is a glass 
tube about three feet in length and open at both ends. It is 
connected above by rubber tubing with a funnel, A, containing 
mercury, and properly supported. By a clamp on the rubber 
tube below C, the rate of flow of mercury into the vertical tube 
may be regulated. Just below the rubber tube a branch com- 
municates with the flask R. The tube C D passes below into 
another flask B. In the side of this there is a spout. The end 
of the vertical tube passes below the level of this spout, and 
dips beneath the surface of the mercury contained in the flask. 
Fig. 62. 
Fig. 63. 
Mercury pump. 
Bunsen’s filter pump. 
On opening the clamp at C, the mercury runs down, and ex- 
haustion begins, the air passing from the flask R forms alternate 
columns of air and mercury in the tube CD. As fast as the 
mercury flows from B through the spout into TI, it is returned 
to the funnel A. As the exhaustion becomes more and more 155 
PNEUMATIC APPARATUS 
complete, the columns of air in the vertical tube become shorter 
and shorter, until at last they disappear, and the tube seems to 
be tilled with a continuous column of mercury throughout its 
whole extent. As this point is approached a clicking noise is 
emitted by the tube similar to that produced in the water 
hammer. Mercurial pumps of this description have been used 
for the preparation of Geissler tubes. To save time the first 
portions of air may be removed from the apparatus to be ex- 
hausted by means of an ordinary air-pump. 
177. Bunsen’s Filter Pump.—The process of filtration may be 
greatly aided by submitting the contents of the filter to the 
pressure of the air. Since it often happens that substances 
evolving fumes which would corrode the metallic parts of a 
pump are to be submitted to this operation, the apparatus repre- 
sented in Fig. 63 was devised by Bunsen to accomplish this 
result. 
It is essentially a Sprengel pump, in which a long column 
of water is substituted for the mercury. It consists of a glass 
tube of the shape shown at B A C. Water enters at B, and 
falling through A, passes down C, which is the top of a leaden 
or iron tube 35 or 40 feet in vertical height. As the wTater 
passes the narrow opening of the smaller tube D, it draws in 
the air from any apparatus with which that tube may be con- 
nected, and produces a vacuum therein. 
178. Limit of Vacuum.—Theoretically an absolute vacuum can- 
not be obtained by the ordinary air-pump, since no matter how 
many strokes the piston may make it only removes a part of 
the air remaining in the jar. Even an infinite number of strokes 
would still leave some air in the jar. Practically the production 
of the vacuum is soon brought to an end for the following 
reason. 
At each stroke of the piston and removal of air from the jar, 
the elastic force of the remaining air becomes less and less. 
Finally, it is reduced so low that it is not sufficient to raise the 
valves of the apparatus. All further exhaustion then ceases. 
To overcome this difficulty air-pumps have been constructed 
ln which the valves are worked by hand or by the movements 
of the piston, without calling the elastic force of the air into 
play. Examples of these are offered by the pumps of Babinet, 
Fianci, and Deleuil. By the latter it is said an exhaustion equal 
fo a millimetre of mercury may be attained. 
179. Vacuum by Chemical Agents.—To obtain a still more 
Perfect vacuum various chemical means are resorted to for 
the removal of the last remaining traces of gas, even in the 156 
GASEOUS MATTER. 
Torricellian vacuum of a mercury pump. In the method 
adopted by Dewar, a vacuum estimated at of a millimetre 
of mercury was obtained. This method consists in heating 
charcoal to redness in a vessel which had been exhausted by a 
mercury pump. Finkener accomplished a similar result by 
tilling the vessel with oxygen, exhausting this with the mercury 
pump, and then heating to redness copper which had been pre- 
viously placed in the vessel. By similar chemical means Crookes 
has obtained a vacuum which he estimated at tto o oth of a milli- 
metre. 
CHAPTER XIII. 
THE ATMOSPHERE. 
General properties—Composition of air—Height of the atmosphere—Atmosphere 
presses downwards^—Air presses in all directions—Action of lift-pumps 
explained—The pipette—The cupping-glass—lntroduction of air into the 
lungs—Gases and principle of Archimedes—Balloons—Recent balloon ascents 
—Balloon traffic—Resistance of air to moving body—Parachute—Rate of 
movement into a vacuum—Cannon reports and thunder. 
180. General Properties.—The atmosphere is the gaseous ocean 
covering the whole surface of the globe. It attends the earth 
in its motion of rotation, and would not change its relations to 
objects attached to its surface were it not for local disturbances 
chiefly the results of changes in temperature. To overcome 
these disturbances and reestablish an equilibrium, currents are 
produced which we call winds. 
Upon the atmosphere all plants and animals depend for their 
existence. They can only bear a deprivation of its supply for a 
brief period of time. The higher animals, as mammals, usually 
die in a few moments when deprived of air. 
In experiments made on dogs, it was found that they might 
be deprived of air for three minutes and fifty seconds, and yet 
recover when air was admitted to the lungs. If the access of 
air was cut off for four minutes and ten seconds, death was the 
result. In this case the turning point between life and death 
was limited to twenty seconds. As it is not probable that a man 
would survive under these circumstances longer than a dog, the 
time during which access of air may be prevented is limited to 
less than four minutes. THE ATMOSPHERE. 
157 
In cases of death which have occurred in diving-bells, the 
limit of time has fallen as low as two minutes. Invertebrate 
creatures, like mollusks, have been submitted to the action of 
the vacuum of an ordinary air-pump for many hours, and have 
not only survived, but have apparently come out from the ordeal 
unharmed. 
Of the atmosphere and its phenomena generally, we have the 
following graphic account by Dr. Buist, of Bombay : “Its upper 
surface cannot be nearer to us than fifty, and can scarcely be 
more remote than five hundred miles. It surrounds us on all 
sides, yet we see it not; it presses on us with a load of fifteen 
pounds on every square inch of surface of our bodies, or from 
seventy to one hundred tons on us in all, yet we do not so much 
as feel its weight. Softer than the softest down—more impal- 
pable than the finest gossamer—it leaves the cobweb undisturbed, 
and scarcely stirs the lightest flower that feeds on the dewT 
it supplies; yet it bears the fleets of nations on its wings around 
the world, and crushes the most refractory substances with 
its weight. When in motion its force is sufficient to level the 
most stately forests and buildings with the earth, to raise 
the waters of the ocean into ridges like mountains, and dash the 
strongest ships to pieces like toys. It warms and cools by turns 
the earth and the living creatures that inhabit it. It draws up 
vapors from the sea and land, retains them dissolved in itself or 
suspended in cisterns of clouds, and throws them down again as 
rain or dew when they are required. It bends the rays of the 
sun from their path to give us the twilight of evening and 
of dawn ; it disperses and refracts their various tints to beautify 
the approach and the retreat of the orb of day. But for the 
atmosphere, sunshine would burst on us and fail us at once, and 
at once remote us from midnight darkness to the blaze of noon. 
We should have no twilight to soften and beautify the landscape, 
no clouds to shade us from the scorching heat, but the bald 
earth as it revolved on its axis, would turn its tanned and 
weakened front to the full and unmitigated rays of the Lord 
of Light.” . 
181. Composition of Air.—Air is a mixture of gases. The chief 
of these are oxj-gen and nitrogen. Next in importance are 
vapor of water and carbonic acid gas. Many other gases are 
present in minute proportions or traces. Excluding these, its 
composition may be expressed as follows ; 
Nitrogen . .... 
. 78.49 
Oxygen ....... 
. 20.63 
H20 (vapor of water) .... 
0.84 
CO,2 (carbonic acid gas) .... 
0.04 
100.00 158 
GASEOUS MATTER. 
Aqueous vapor arises by evaporation from the earth’s surface 
and from collections of water, also from the exhalations of 
plants and animals. Carbonic acid gas is produced in the res- 
piration of animals and in all processes of combustion, decom- 
position, putrefaction, and fermentation. It has been estimated 
that in Paris the diurnal production of this gas amounts to one 
hundred millions of cubic feet, of which one-tenth is from the 
respiration of human beings and animals, the remainder arising 
chiefly from processes of combustion. Accumulation of car- 
bonic acid gas in the air is prevented by plants, which decom- 
pose it, and setting its oxygen free unite its carbon with water 
to form gum, with which they build up their tissue. 
From the table given above, we And that a certain small pro- 
portion of carbon dioxide is always present in the air. When 
air is expired from the lungs, it has lost from four to six per 
cent, of oxygen, and has gained in its stead from, three to five 
per cent, of carbonic acid gas. The presence of six to ten per 
cent, of this gas in air is fatal to life. In an atmosphere con- 
taining this proportion of carbonic anhydride a candle will burn. 
It is, therefore, evident that the candle test does not necessarily 
show that it is safe to descend into a pit or well where it will 
burn. It only indicates that descent is absolutely negatived 
where it does not burn. 
Although oxygen is necessary for the maintenance of life, it 
must be used in the diluted condition in which we find it in 
air. When breathed in the unmixed state, it stimulates the 
nervous system strongly and finally causes death. The experi- 
ments of Mr, Broughton showed that rabbits died in from six to 
twelve hours when kept in pure oxygen. Despite the noxious 
action of pure oxygen, animals will live in an atmosphere of 
that gas three times as long as they will live in an equal volume 
of atmospheric air. 
182. Height of the Atmosphere.—The facts which have been 
presented regarding the elastic force of air in common with all 
gases would lead us to expect that its molecules would fly off 
into space. That this is not the case is apparent from the fact 
that it does remain bound, as it were, to the surface of the earth. 
This apparent contradiction receives its explanation in the 
fact that as air expands its elastic force becomes less. More- 
over, as it ascends to higher regions the cold is more intense, 
this also diminishes the tendency to expansion, until finally it is 
reduced to so low a point Fiat it comes under the control of 
gravity, and an equilibrium being established expansion ceases, 
and an exterior limit or boundary between the atmosphere and 
space is established. 
Observations on the density of air and of phenomena of THE ATMOSPHERE. 
159 
refraction connected with twilight, show that the depth of the 
atmospheric ocean is probably from forty to sixty miles. The 
great mass of the air by weight is, of course, confined within a 
small fraction of that depth. In opposition to this estimate the 
objection is raised that meteorites are often seen to emit light 
when the}7 are still more than 200 miles above the earth’s sur- 
face. Since the luminosity, in this case, is the sequent of the 
action of the air, it follows that we must extend the outer limit 
to that distance. Recent observations on the twilight arc b}7 
Mr. Liais, at Rio Janeiro, also tend to place the outer limit of 
the atmosphere at a distance of about 200 miles. 
183. The Atmosphere Presses Downwards.—Turning to the de- 
scription of the air-pump (174), and repeating the experiment 
therein detailed, it will be found that after a few strokes of the 
pump it becomes almost impossible to separate the bell-jar from 
its plate. This is explained upon the following principles. It 
has been shown that air is heavy, 100 cubic inches weighing 
31 grains. In the last article, we have also seen that the depth 
of the aerial ocean is variously estimated at from forty to two 
hundred miles. Though it is true that the atmosphere by its 
expansion gradually becomes lighter as we leave the surface 
of the earth, yet a long distance must be traversed, nearly 4 
miles, before the weight of 100 cubic inches has even diminished 
to one-half that which it had at the surface. 
The air being heav}T and there being so great a column of it 
resting on the top of the jar, we can easily understand that this 
is the reason why the jar is so firmly pressed down upon the 
plate of the pump. If any doubt exists regarding this explana- 
tion, it onl}7 remains to allow the air to regain access to the in- 
terior of the jar. As it passes in, its pressure is brought to bear 
on the interior as well as the exterior, and at last equilibrium is 
established between the interior and exterior pressures, and the 
jar may be removed from the plate of the pump with the same 
ease as before the experiment began. 
A capital illustration of the downward pressure of air is 
offered by a toy, well known to boys as the sucker. It consists 
pi a circular piece of thick leather, which is soaked with water. 
Through the centre a strong string passes, which is prevented 
from slipping through by knots made on the lower side. The 
leather having been well applied to the surface of a stone or 
other flat object, and traction applied by the string, the stone is 
raised; the pressure of the air binding the stone tightly to the 
leather. 
184. Air Presses in all Directions.—The study of hydrostatics 
shows that water presses in all directions. The similarity which 160 
GASEOUS MATTER. 
we have seen to exist between liquids and gases, regarding their 
properties, would lead us to expect that air would also press in 
all directions, and equally in the same plane as is the case with 
water. The experimental demonstration that such is the fact 
may be made in a number of ways. Of these the most classic 
is by the Magdeburg hemispheres represented in Fig. 61. The 
arrangement consists of two hollow hemispheres of brass, the 
edges of which are accurately ground. When placed together 
a hollow sphere is formed, access to the interior of which is 
offered by the stopcock. The hollow sphere being attached to 
the air-pump plate and exhausted, the stopcock is then closed, 
and the apparatus removed from the pump. No matter in what 
direction traction is now applied to separate the two hemi- 
spheres, they are pressed together with equal firmness in all. 
It is, therefore, evident that air exerts pressure equally in all 
directions. 
Fig. 64. 
Fig. 65 
Magdeburg hemispheres. 
Air presses in all directions. 
The same result may be obtained in a more inexpensive 
manner, by the device illustrated in Fig. 65. Let Abe a small 
bell-jar, or a wine-glass. It is to be filled with water over the 
dish 0. The mouth is then to be closed by a sheet of card- 
board, care being taken that no air is entrapped between the 
card and the surface of the fluid. Thus prepared, the jar 
may be turned mouth down. The water nevertheless remains 
suspended in the jar by the pressure of the air on the sheet of 
card closing its mouth. The glass may then be inclined, at all 
angles, B, yet, so long as the card does not slip, the water is re- 
tained in situ by the pressure of the air. 
Nature offers numerous illustrations of the application of the 
pressure of the air. The movements of flies, and other insects, 
along the smooth ceiling of a room, are accomplished on this THE ATMOSPHEEE. 
161 
principle. The tree toad also depends upon pressure of the 
air on the suckers of his toes for his ability to move as easily 
on the under as on the upper side of a branch. It is the 
presence of numerous suckers on the under surface of the arms 
of cuttle-fishes, that gives that creature its fearful hold upon 
whatever it touches. The great joints of our bodies are also 
held together firmly by pressure of the air. The ligaments of 
many of them may be completely severed, yet it is as difficult 
to separate the bones from each other, as it would be to tear 
asunder two Magdeburg hemispheres of equal diameter. 
By calling the pressure of air into play, the infant draws 
its supply of milk from its mother’s breast, and, following the 
precepts of his infancy, adult man imbibes the consolation to.be 
found in a sherry cobbler through the medium of a straw and 
by grace of the pressure of the air. 
185. Action of a Lift-pump Explained.—The apparatus repre- 
sented in Fig. 66 is known as the experiment of the fountain in 
vacuo. It consists of a tall jar, A, through 
the lower part of which a tube passes. This 
is furnished with a stopcock at B, and ter- 
minates in a jet in the interior of the jar. The 
exterior termination of the tube bears a screw 
thread by which it is to be attached to the 
air-pump. Exhausting the jar and closing 
the stopcock, the apparatus is detached from 
the pump, and introduced vertically into a 
basin, C, containing water. Passing the ex- 
ternal extremity of the tube to the bottom of 
C, and opening the cock B, a tine stream of 
water rises from the jet and impinges forcibly 
against the top of the jar, where it turns and 
flowing down the sides accumulates at the 
Fig. 66. 
Fountain in vacuo. 
base. The cause of the formation of this fountain is evidently 
the pressure of air upon the surface of the water in C. The 
moment the cock is opened this pressure is brought into action, 
and the whole train of phenomena initiated. 
As in the preceding case, the pressure of air forces the water 
up into the vacuous space A, so when by a downward stroke 
°t the handle in a lift-pump we make a partial vacuum in the 
cylinder, the water, with which it is connected by the pipe, is 
forced up into the pipe by pressure of the air upon the surface 
°f the fluid in a well or cistern. 
186. Action of a Pipette.—For the transference of urinary sedi- 
ments to a microscope slide, and also for the transference and 
measurement of small quantities of liquid, the apparatus known 162 
GASEOUS MATTER. 
as a pipette is very useful and convenient. It consists of a glass 
tube, AB, of the form shown in Fig. 67. The upper part, A, 
is open the full diameter, the lower, B, is drawn down to a fine 
point or jet, and dips into the bottle C. The fluid may then, by 
Fig. 67. 
placing A in the mouth, be drawn into the 
pipette to a measured mark, the end closed 
by the huger, and the fluid transferred to 
another vessel. 
Suppose sediment in the bottle C to be 
removed to the capsule I). The mouth, A, 
of the pipette is closed with the finger, the 
extremity, B, is then passed down into the 
sediment. As Ais closed by the finger, the 
air in the pipette prevents the ingress of the 
fluid while the pipette is passed through it. 
The point of the pipette being advanced into 
the sediment, the pressure of the finger on 
the opening A is slightly relaxed, a little air 
escapes, and the pressure of the atmosphere 
on the surface of the liquid forces it and the 
sediment into the pipette. A sufficient quan- 
tity having passed into the pipette, the press- 
ure of the finger at A is restored, and the 
instrument is removed from the bottle. As 
it passes into the air, the pressure of the 
Pipette. 
atmosphere on the narrow column of fluid in the jet of the 
pipette retains the fluid and precipitate in position until it is 
held over the capsule D. The pressure of the Anger at A being 
then released, the air gains access to the tube above, and a por- 
tion of liquid and precipitate is forced out. 
The rate of flow from a pij)ette is regulated by inclining it 
more or less at an angle to the perpendicular. If it is held 
vertically, the flow is the most rapid. If held horizontally, it 
may be diminished to nothing. Between these all rates desired 
may be obtained. 
-187. The Cupping-glass.—The effect of the pressure of air on 
the tissues of the body may be shown by the apparatus known 
as the hand-glass. It consists of a glass vessel or receiver, of 
the shape represented at A, Fig. 68, open above and below. 
The lower mouth is five inches, and the upper two inches in 
diameter. The lower mouth, having its edges finely ground, 
makes an air-tight joint when placed upon the plate of the air- 
pump B. Closing the upper, or smaller opening, with the palm 
of the hand and exhausting, the pressure of the air is brought to 
bear upon its dorsal surface. As the exhaustion is continued, 
the muscular and other tissues are forced down between the 163 
THE ATMOSPHERE. 
metacarpal bones, the outlines of which may be easily traced on 
the back of the hand. At the same time the palmar surface is 
bulged downwards into the receiver. It becomes intensely con- 
gested with blood, and if the exhaustion 
is sufficiently perfect, and continued for a 
sufficient time, the smaller bloodvessels are 
ruptured and ecchymosis produced. 
Fig. 68. 
The cupping-glass acts on the same 
principle as the hand-glass. It is usually 
shaped like a low bell-jar C, and made 
either of metal or of glass. The rim around 
the opening should have sufficient thick- 
ness to prevent it cutting the skin when 
applied. 
Sometimes cups are exhausted by 
means of a small air syringe. When this 
is the case they are perforated above, and 
the opening closed by a stopcock when the 
exhaustion is completed. Generally the 
vacuum is produced by the condensa- 
tion of vapor of water. In this case the 
cups are without any perforation above. 
Ordinary tea or coffee cups with thick lips 
1 laud-glass aud cupping-glass. 
answer perfectly well. The method of application is as follows. 
A small torch is prepared by wrapping a few folds of old linen 
around a penhandle. This is dipped into alcohol, and lighted. 
A copious flame is thereby produced. The mouth of the cup 
is then held close to the surface to which it is to be applied, 
the torch is passed into the cup, and almost immediately with- 
drawn. At the moment of withdrawal, the mouth of the cup is 
turned down on the surface of the skin. If it does not adhere 
at once, the torch is again applied. 
The operation of the flame is to till the cup with steam of 
high tension. The air is thus expelled, and if the mouth of the 
cap is closed by the skin before the steam begins to condense, 
when it does condense a vacuum is produced in the cup. The 
application of the flame to the interior should be momentary, 
otherwise the cup will be heated, condensation of the steam 
Wlll be imperfect, and the surface to which it is applied may be 
scorched. It is well to moisten or bathe the surface of the skin 
oefore the application of the cups is commenced. It is thus 
softened, and better opportunity offered for forming an air-tight 
joint. 
When a wound is accompanied by injection of poison, as in 
the hite of a venomous serpent, a cupping-glass may be used to 
withdraw the noxious matter from the part. Since, under these 
conditions, rapidity of removal of the poison is all important, 164 
GASEOUS MATTER. 
the mouth may be at once applied, and the wound sucked until 
cups can be procured. The person who offers his services in 
such a case should be certain that there is no wound or abra- 
sion of the skin about his lips or buccal cavity. If there is he 
may lose his life in consequence, for though such poison may 
be swallowed with impunity, it destroys life if brought in con- 
tact with a raw surface or wound. 
188. Introduction of Air into the Lungs.—In all the mammalia 
or higher animals, pressure of the atmosphere is brought into 
action in the introduction of air into the larger air-passages. 
By means of the apparatus shown in Fig. 69 
we may illustrate the manner in which the 
first stage of inspiration and the last of expi- 
ration are accomplished. 
Let A B be a bell-jar perforated above, and 
dipping into a vessel of water, I). The walls 
of the jar may be imagined to represent the 
walls of the chest. The surface of the water 
in I) would represent the diaphragm, and 
by raising and lowering I) in a regular 
rhythmic manner, the action of the dia- 
phragm may be imitated, and the capacity 
of the interior of the jar A B increased and 
diminished. The aperture at A is to be 
closed by a cork, through which an open 
tube T passes, and terminates in the inte- 
rior of the jar in a rubber sack, or a bladder, 
shown at C, Carrying out the substitution of 
parts, the tube T represents the trachea, and 
the sack C the lung. The dotted line shows 
the form of the bag when D is raised, and 
the capacity of the chest or bell diminished. 
Fig. 69. 
Inspiration and expiration 
of air. 
Lowering L>, the capacity of A B is increased, the air flows 
in through T to L, exactly as when the diaphragm is lowered 
it flows through the trachea into the lungs, and the inspira- 
tory act is accomplished. Raising B, the capacity of A B is 
diminished, pressure is brought to bear on the bladder C, it 
contracts, its contents passing out through T. In like manner 
the expiratory act is accomplished. The diaphragm being pressed 
up by the contraction of the abdominal muscles, it bulges up- 
wards, the capacity of the thoracic cavity is diminished, the 
lung yields to the pressure, and the foul air is expelled through 
the trachea. 
In these movements the total amount of compression and 
rarefaction of the air is quite small, not amounting to more 
than half an inch of water each way. This may be proved by THE ATMOSPHERE. 
165 
breathing with the nostrils unobstructed, and with a tube one 
end of which is placed in the mouth while the other end is 
kept an inch or so under water. 
The average total capacity of the lungs in the adult male is 
335 cubic inches. The average amount of air introduced at 
each inspiration is 30 cubic inches, and there are about 18 res- 
pirations per minute. This gives 540 cubic inches per minute 
as the amount of air inspired and expired by these organs. 
189. Gases and Principle of Archimedes, —The experiment 
with the Magdeburg hemispheres demonstrated that air presses 
equally in all directions upon bodies placed therein, acting in 
this respect in the same manner as water. It is, therefore, evi- 
dent that the laws regarding the equilibrium of bodies in liquids 
are applicable to bodies in air, and they mast lose a 'portion of 
their lueight equal to that of the air they displace. 
That this really happens is demonstrated by the instrument 
called the baroscope, which is represented in Fig. 70. It consists 
Fin. 70. 
of an arm or lever AB, moving on the fulcrum F, To the 
extremity A, a sealed glass globe is attached which is filled 
with air. To the opposite extremity a counterpoise of lead, 
I>, is suspended. The two objects A and B are so adjusted that 
the air they balance each other when the lever A B is 
horizontal. 
Placing the arrangement under a large bell upon the air-pump 
plate, after a few movements of the piston, the globe A descends, 
showing that it is really the heavier of the two bodies. The 
only rational explanation that can be given of this is, that before 
the air was removed from the jar it buoyed up each body just as 
water would do. On removing the air, since the sphere was the 
larger mass, it suffered most from the loss of buoyant power of 
Baroscope. 166 
GASEOUS MATTER. 
the air, and that end of the lever consequently sank because it 
was the heavier. 
That the loss of weight in the globe, while in the air, is 
actually owing to the bulk of air it displaces, is readily shown 
by measuring the capacity of the globe, and adding the cor- 
responding weight to the counterpoise. Suppose the globe 
measures 100 cubic inches, adding 31 grains, which is the weight 
of this volume of air, to the leaden counterpoise, that side will 
be heavier in the air, but in the completely exhausted receiver 
of the air-pump it will exactly balance the globe, thus proving 
the point in question. 
In place of a globe containing air and its counterpoise, an 
ounce of cork may be attached to one arm, and an ounce of lead 
to the other arm of the baroscope. In the air-pump vacuum 
the cork will he the heavier. The indications of the baroscope 
show us the necessity, in exact scientific work, of either weighing 
bodies in vacuo, or of giving their weight reduced to what it 
would be in vacuo. 
190. Balloons depend upon the buoyant power of the air for 
their action. They are immense bags made of some light 
material, as silk, covered with a caoutchouc varnish. This is 
enclosed in a network of cord, from which a car of wickerwork 
is suspended. In the top of the balloon there is a valve to permit 
the escape of gas; this is managed by a cord which passes down 
to the car. 
The car carries a certain number of bags of sand; by means 
of these and the valve the balloon may be made to rise and fall 
at the will of the aeronaut. If he desires to pass to a lower 
stratum and avail himself of the direction of the wind of that 
region, he opens the valve and allows sufficient gas to escape to 
accomplish this purpose. The rise or fall is produced by a 
variation of a very few pounds in the weight of the machine. 
If he desires to ascend, he allows a portion of the sand ballast to 
escape. Thus the balloonist can pass to one or another stratum 
of air, and so obtain a certain amount of control over the 
course of his aerial car. 
A balloon 35 feet in diameter will hold about 22,000 cubic 
feet. The weight of this bulk of air is 1600 pounds, of hydrogen 
200 pounds, and of coal-gas about 640 pounds. Filled with 
hydrogen it would have a carrying capacity for material, car 
fixtures and load of 1400 pounds. Filled with coal-gas its 
carrying capacity would be less than 1000 pounds. Though the 
ascensional power of hydrogen is so much greater than that of 
coal-gas, the latter is used in preference, since it is much cheaper 
and has less tendency to leak or to pass through the material of 
which the balloon is made. The largest balloon that has been THE ATMOSPHERE. 
167 
constructed was nearly 100 feet in diameter, it had a capacity 
of 450,000 cubic feet; charged with hydrogen, it ascended with 
thirty-two persons to a height of 2000 feet. 
The first balloons were raised by means ot air rarefied by 
heat. From their discoverer they were called Montgolfiers. 
The first ascent was made bj one of these in June, 1783. Shortly 
after this, in December, 1783, hydrogen was used as being less 
dangerous. In 1814, when coal-gas was introduced or lighting 
cities, it was substituted for hydrogen in balloons. 
An ascent made by Gay-Lussac in 1804 is worthy ot mention 
on account of the scientific, and especially the physiological 
Fig. 71. 
Balloon. 
information obtained. The height reached was 23,000 feet; the 
barometer sank to 12.6 inches; the thermometer, 31° C. at the 
ground, sank to —9° C. The air was so dry that paper shrank 
and crumpled as if it had been held near a hot fire. Respira- 
tion was greatly accelerated, and the pulsations of the heart, 
which were normally 66, became 120. Such profound dis- 
turbances of the functions of the body lead us to wonder that 
no attempt has been made to utilize balloons as a remedial 
agent in the treatment of certain diseases. Certainly it would 
seem that captive balloons might be employed in great cities for 168 
GASEOUS MATTER, 
the purpose of raising patients suffering with various complaints 
to a sufficient height to give them a supply of pure air during 
a few hours of the day. 
191. Recent Balloon Ascents.—In September, 1861, Glaisher 
made an ascent of which the following is the record. Left the 
earth at 1 p.m., in 23 minutes reached an altitude of 15,750 feet; 
in 11 minutes after 21,000 feet, temperature —lo° C. At 1.52, 
the altitude was 29,000 feet; temperature —l6° C. The ob- 
server then fainted. The lowest proximate estimate of baro- 
metric height was 7 inches. This would correspond to an 
elevation of 36,000 feet. 
At 19,000 feet Glaisher had no difficulty in making obser- 
vations, though his companion panted for breath. At 29,000 
feet his eyesight failed; the sense of hearing and other faculties 
remained a little longer. Muscular power was entirely lost, and 
his companion was partly paralyzed by the intense cold. 
An ascent made by the balloon “Zenith,”*in April, 1875, re- 
sulted fatally to two of the occupants, the third barely escaping 
with his life. The object of the ascent was to determine the 
amount of carbonic anhydride and vapor of water at great 
elevations. The aeronauts were Tissandier, Sivel, and Croce- 
Spinelli. 
The rate of ascent w7as nine feet per second at the start, this 
slowly diminished. In 90 minutes an altitude of nearly 23,000 
feet was reached. The travellers had a supply of oxygen with 
them, by which they were enabled to maintain respiration. At 
this point some ballast was thrown out. The ascent became 
more rapid, and Tissandier fainted. The balloon then descended. 
On recovering, all being well, more ballast was thrown over, 
and, at the same time, Spinelli threw overboard the aspirator, 
weighing 80 pounds. In the sudden rise that followed Tissan- 
dier became unconscious, and remained so for an hour. When 
he regained his senses, he found the balloon rapidly descending, 
and very little ballast left. The other occupants of the car were 
both dead, their faces black and covered with blood which had 
escaped from the mouth and nose. 
The maximum height recorded by the instruments was over 
28,000 feet. It is probable that death was caused by suffoca- 
tion, the result of the second rapid transition to a very rarefied 
atmosphere which followed the casting out of the aspirator. 
On many previous occasions life had been lost on the earth’s 
surface. The deaths of Sivel and Croce-Spinelli were the first 
recorded in the uppermost regions of the air, and great were 
the honors paid by France to her martyrs in the cause of science. 
192. Balloon Traffic.—During the investment of Paris by the 
Prussians, in 1870, a regular balloon service was established. THE ATMOSPHERE. 
169 
These balloons were spherical, and contained about 70,000 feet 
of gas. They were started in the evening. In the four months, 
beginning with September 23, sixty-four left Paris, laden with 
161 passengers, and nine tons of despatches, containing about 
3,000,000 letters. Out of the total number, 57 reached their 
destination, 2 were lost at sea, and 5 were captured by the 
Prussians. By this means Jansen, the astronomer and physicist, 
escaped from the beleagured city, and taking his instruments 
with him made observations in the south of France on an 
eclipse of the sun. 
193. Resistance of Air to Moving Body.—ln (132) the resistance 
of water to the movement of bodies therein was discussed, and 
experimentally illustrated. In the same manner, though to a 
less'extent, air resists the passage of objects. This is shown by 
tne instrument known as tne guinea and 
feather tube, Fig. 72. It consists of a stout 
glass tube, three inches in diameter, four or 
five feet long, and hermetically sealed below. 
The upper part is closed air-tight by a brass 
cap, through which a brass tube provided 
with a stopcock passes. In the interior of 
the glass tube, a disk of brass and a disk of 
paper of equal size are placed. 
Fro. 7'2. 
When the apparatus is filled with air, and 
quickly inverted, the metal drops immedi- 
ately from one end of the tube to the other, 
while the paper slowly sinks, requiring at 
least ten times the time occupied by the 
metal to pass through the length of the tube. 
Attaching the tube to the air-pump, exhaust- 
lllg it, closing the stopcock A, removing the 
apparatus from the air-pump plate, and 
again quickly inverting it, the paper and the 
metal fall together from one end of the in- 
strument to the other. If the vacuum is 
good, there is no perceptible difference in 
their velocity. The paper moves as rapidly 
as though it were a mass of lead. Opening 
the stopcock, and admitting air, the paper 
comports itself in the normal manner, and 
sinks slowly. The natural explanation of 
Resistance of air to moving 
body. 
phenomena in question, is that air resists the passage ot 
objects, acting in this respect in the same manner as a fluid. 
W hen the rate of movement is rapid, as in the case of a rail- 
road train, the resistance of the air is then very evident, the 
hand readily perceiving it, and if the head be passed outside of 170 
GASEOUS MATTER. 
the car window, with the face turned in the direction of the 
motion, serious interference with the act of respiration is experi- 
enced. It is this resistance of air that chiefly puts a practical 
limit to the rapidity of movement of railway trains. It also 
quickly reduces the velocity of the rifle-hullet, and, in order to 
avoid it, the lightning flash is driven to a zigzag course. 
194. Parachute.—In the use of balloons accidents have at times 
occurred, either from the valve becoming fixed or from rents in 
the balloon. Under these circumstances the aeronaut is enabled 
to leave the machine by the apparatus 
in question. A parachute may be de- 
scribed as an immense umbrella some 
16 feet in diameter, and capable of 
being folded up in the same manner. 
In the top there is a small opening. 
Leaving the balloon the parachute 
expands, and descends slowly on 
account of the resistance of the air to 
the great area of surface it offers. 
The air being compressed in the 
hollow of the apparatus escapes 
through an opening in the top, thus 
the descent is regulated, and freed 
from the swaying motion it would 
otherwise have. 
Fig. 73. 
The parachute. 
195. Rate of Movement into a Vacuum.—The resistance of air 
to moving bodies shows that though very mobile its particles 
have a certain amount of viscosity, and require time for the 
execution of movements. It, therefore, follows, that as time is 
required by the molecules of air to get out of the way of a 
rapidly moving body, time must also be required for them to 
till in the space behind an object in rapid motion. When the 
velocity of the body is very great, as when a cannon-ball first 
leaves the mouth of a gun, there is an almost perfect vacuum 
for a certain distance behind the shot. The question arises, 
What is the rate at which air can flow into this vacuum? 
Many attempts have been made, and various methods adopted, 
for the solution of this problem. That which appears to offer 
the greatest probability of accuracy, places it at about 1280 feet 
per second, which is more rapid than the rate at which sound 
traverses the atmosphere under ordinary conditions. 
196. The Cannon Report and Thunder.—ln explanation of these 
phenomena, the following experiments are offered. At AB, THE ATMOSPHERE. 
171 
Fig. 74, the instrument known as the water hammer is repre- 
sented. It is made of glass, stout enough to resist the pressure 
of the air when a vacuum is made in its interior. The tubular 
portion B is somewhat more than half tilled with water. The 
space above this is vacuous or contains vapor 
of water, no air. Holding the instrument in 
the position represented, and giving it a rapid 
upward movement, which is suddenly changed 
to a downward one, the column of water either 
leaves the bottom of the tube or breaks into 
two portions. The upper mass, drawn down 
by gravity, falls on the bottom or lower por- 
tion, and striking it emits a clicking sound. 
To produce this result the vacuum must be 
very good, since the presence of even a small 
portion of air, by its elasticity, takes oft' the 
shock and prevents emission of sound. From 
this we learn that two fluids or a fluid and a 
solid striking against each other in a vacuum 
produce sound vibrations which pass from the 
fluid through the glass to the air, and so affect 
our sense of hearing. 
To 
In the experiment, Fig. 75, A B represents 
a glass, the upper mouth of which, A, has been 
closed air-tight by a portion of bladder or some 
membranous structure. Placing the instru- 
ment with its other mouth, B, on the plate of 
an air-pump, and proceeding to exhaust, the 
pressure of the atmosphere borne by the mem- 
Fig. 74. 
Water hammer. 
nrane at last becomes so great that it suddenly ruptures, and 
the column of air falling on the plate of the air-pump produces 
a sound almost equal to that of a pistol-shot. In this case, the 
noise has originated in the sudden impact 
°/ a gas on a solid, there being compara- 
tively little air intervening to interpose 
!ts elasticity. 
with these illustrations before us we 
can understand the origin of the sound 
emitted by a rifle-shot in its passage. Its 
velocity approaching a couple of thousand 
teet per second as it leaves the gun, a 
vacuum is of necessity formed behind it. 
Into this cylindrical track of vacuum the 
Ftg. 75. 
a}r rushes at the rate of over 1200 feet per second from all 
sides. The opposing columns meeting at the axis of the cylinder 
induce sound, just as it is produced in the water hammer when 
die two columns of water strike together in the vacuum. 
Burst bladder. 172 
GASEOUS MATTER. 
In the track of the lightning flash a vacuum is also produced. 
The reverberations of thunder which accompany lightning in 
its course are the clashing together of the walls of the vacuous 
O c 5 
track the lightning has cleaved through the atmosphere. Yerily 
no better evidence of the materiality of air can be offered than 
the fearful crash which attends the striking of lightning near by. 
CHAPTER XIY. 
BAROMETRY. 
Galileo’s explanation—Torricelli’s experiment—-Pascal’s experiment—Pressure of 
the atmosphere—Cistern barometer—Fortin’s barometer—Siphon barometer 
—Wheel barometer—Glycerine barometer—Errors in barometric reading— 
Barometric variations—Mean barometric heights—Cause of barometric 
variations—Barometric variations and the weather—Barometer and the winds 
—Barometer and the death rate. 
197. Galileo’s Explanation.—-The explanation of the principle 
upon which the barometer depends, is best attained by a brief 
review of the history of its discovery. About the year 1642, 
an attempt was made at Florence, in Italy, to raise water by 
means of a lift-pump to the upper stories of a palace which 
had been recently erected. Galileo, the leading philosopher of 
the day, was called in consultation by the Grand Duke, and 
after many experiments found that no matter how perfect the 
construction of the pump, water could not be raised thereby to 
a height greater than about thirty-four feet. 
In those days the cause of the rise of water in a pump was 
attributed to “ Nature’s horror of a vacuum.” This explanation 
had passed unchallenged for many centuries. Galileo gave it as 
his opinion, that the reason why a pump could not raise water 
higher than thirty-four feet was because that was the limit to 
which the pressure of air could force it, an explanation which 
had been suspected as far back as the days of Aristotle. 
198. Torricelli’s Experiment.—Torricelli, a pupil of Galileo’s, 
sought to prove his master’s explanation. He suggested that 
since air had been shown to have weight, the true reason why 
the water rose in the pump was because the air pressed on 
the surface of the water in the cistern, and so forced it up. BAROMETRY. 
173 
The reason, he added, why there was a limit to the height was, 
because when the air had forced up a column of fluid equal to 
its own weight, equilibrium was established, and no further rise 
was possible. 
In demonstration of this theory he proposed the following 
experiment. Substituting mercury for water, be argued that 
since it was thirteen and a half times as heavy as water, and a 
pump could raise water about 34 feet, therefore it should raise 
mercury about 30 inches. Finding that such was the case, he 
contrived the instrument we now know as the barometer, or 
measurer of the weight of air. 
is required. It should have a bore about 
one-quarter of an inch in diameter, and 
be thirty-four inches in length. One ex- 
tremity, A, should be hermetically sealed, 
and the other open. It should be chem- 
ically clean in the interior. It must be 
tilled with pure mercury, and every bub- 
ble or trace of air carefully removed. 
This may be done in the following man- 
ner, when the object is to offer a lecture- 
room illustration of the construction of 
the instrument. The tube is tilled to 
within half an inch of the open end, it 
is then closed by the finger, and inclined 
so that the large entrapped bubble of air 
passes to the other end. In its course 
ff licks up all the small bubbles that 
nave been caught between the mercury 
and the wall of the tube. The removal of 
the air may be facilitated by heating the 
tube; the bubbles of air are thus expanded. 
The tube Anally assumes the appearance 
°t a rod of polished steel. For the method 
°f filling the barometer for accurate scien- 
tific research, see (3d, 206), 
For the construction of the barometer, a tube, A, of stout glass 
Fig. 76. 
Barometer. 
All air having been removed, the tube is filled with mer- 
°nry. Jts open extremity is closed by the finger, and it is 
placed with its mouth downwards under the surface of mer- 
cury in a small basin or cistern, B. Removing the finger from 
the mouth of the tube, the mercury drops from the upper 
or sealed extremity, and after a few oscillations stands at a 
yertical height of about thirty inches above the level of that 
ln the basin. The empty space between the top of the mer- 
cury and the top of the tube is called the Torricellian vacuum. 
It was for long supposed to be a perfect vacuum, but is now GASEOUS MATTER. 
known to contain traces of vapor of mercury, together with 
moisture, and the last portions of air which cannot be removed. 
Any movement of a barometer thus constructed is attended 
by oscillations of the liquid in the tube. It often strikes the 
sealed end with such force as to cause fracture of the glass. To 
avoid this the tube should be held in an inclined position, the 
mercury then rises to the top and there remains. There is then 
no oscillation and liability to fracture is avoided. 
The manner of action of air in forcing mercury up the 
barometer tube, may be illustrated by the following experi- 
Fig. 77. 
ment. Let A B represent a jar three feet in 
height and four inches in diameter. Suffi- 
cient mercury is poured into it to make a 
layer half an inch deep at the bottom. Into 
this a tube, C, longer than the jar, and with 
both ends open, dips. The mercury is seen 
to stand at about the same level in the tube 
and in the jar. Let water be poured into 
the jar. It presses upon the surface of the 
mercury at A; as more water is added the 
mercury rises higher in the tube. In like 
manner, pressure of the air upon the surface 
of the mercury in the cistern of a barometer 
forces that liquid up its tube. 
199. Pascals Experiment.—Torricelli did 
not long survive his discovery. Shortly after 
his death, Pascal took the subject up, and 
completed the demonstration by two methods 
of procedure. 
Ist. He argued that if Torricelli’s explana- 
tion is correct, and the mercury is sus- 
pended in the barometer tube by the pres- 
sure of air, it follows, that if the instru- 
ment is carried up a mountain, and the 
Action of barometer 
illustrated. 
column of pressing air reduced in altitude, the mercury must 
fall in the tube, and stand at a much lower level. Under his 
direction the experiment was tried on the summit of the Puy 
de Dome, in Auvergne, when it was found that the level of the 
mercury was three inches lower than it was at the base of the 
mountain. 
Pascal’s experiment may be illustrated by placing a barom- 
eter under a tall air-pump jar. On exhausting the jar, and 
so reducing the pressure upon the mercury in the cistern, the 
same effect is produced as though the instrument was car- 
ried up a mountain, and the liquid falls in the tube. By 
pushing exhaustion to theAxtreme, the mercury in the tube BAROMETRY. 
175 
and that in the cistern may be made to occupy very nearly the 
same level. Restoring the pressure of air, the mercury again 
rises in the tube, and with restoration of the original pressure 
it regains its normal height of thirty inches above the level of 
that in the cistern. 
The second method of Pascal was to repeat Torricelli’s 
experiment with a variety of liquids. Using a tube fifty feet in 
length, and manipulating with it as a barometer, he found that 
when it was filled with water that liquid stood at an altitude of 
thirty-four feet, or thirteen and a half times as high as the 
column of mercury. Mercury being thirteen and a half times 
as heavy as water, it followed that the weight of the column of 
water was exactly equal to the weight of the column of mercury 
used in Torricelli’s experiment. Consequently the columns 
were in each case supported by the same force, and that could 
be none other than the pressure of the air. Experiments with 
wine and oil gave like results. 
200. Pressure of the Atmosphere.—lf we grant that the tube 
used in the construction of a mercurial barometer has a trans- 
verse area equal to one square inch, and the mercury stands at 
an altitude of thirty inches, it follows that the column is equal 
to thirty cubic inches of mercury. The weight of this mass of 
mercury is nearly fifteen pounds. Consequently since this 
balances a column of air of equal area, it is evident that the 
pressure of the atmosphere on a square inch of surface is equal to 
fifteen pounds. This is about one ton to the square foot. As the 
surface of an ordinary human body is about sixteen square feet, 
!t follows that the pressure thereon must be equal to sixteen tons. 
The only reason we are not crushed to earth by this fearful 
incubus of weio-ht is, that it acts on the interior as well as the 
exterior of the body, and so the exterior pressure is counter- 
balanced or neutralized. That this is realty the case is shown 
by the fact that when pressure on any part of the surface is 
Removed, as in the act of cupping, that portion is immediately 
forced outwards. 
When any gas, vapor, or fluid, bears upon a surface in such a 
manner as to exert a pressure of fifteen pounds on each square 
inch of the surface, it is said to exert a pressure of one atmosphere; 
that being, as we have seen, the weight with which the atmos- 
phere presses. If, for example, steam in a boiler is exerting 
a pressure of sixty pounds on every square inch, we say that the 
olastic force of the steam is equal to four atmospheres of pres- 
sure. According to the metric system atmospheric pressure 
at 0° C. and the level of the sea, is equal to a column ot 
mercury 760 millimetres in height, and the pressure on a square 
centimetre is 1.03296 kilogramme. 176 
GASEOUS MATTER. 
201. The Cistern Barometer.—Various forms have been given to 
the barometer. That usually employed, and the simplest in 
construction, is the cistern barometer, Fig. 78. It consists of a 
Fig. 78. 
Torricellian tube about thirty-four inches in length, 
which is firmly attached to an upright support. 
This is constructed that it may be hung by the 
top and a perpendicular position secured. 
In measuring the height of the column of 
mercury in the barometric tube, the point of de- 
parture for the measurement is the surface of the 
mercury in the lower cup or cistern. From this 
to the top of the mercury in the tube is the height 
of the column balancing the air pressure at the 
time of observation. It is, of course, understood 
that this measure is taken with the tube in a per- 
pendicular or vertical position. 
As the mercury in the barometer rises and falls 
in the tube, more or less of it passes into the 
cistern. The quantity in the cistern being, there- 
fore, variable, the zero of the scale of measure- 
ment is variable. To avoid this error, the cistern 
is made as wide as possible in its upper part 
that the variations in level may be reduced to 
as small a fraction of an inch as possible. It is 
this enlargement of the cistern that gives the 
name to this form of instrument. The cistern 
is not entirely closed in from the air, an opening 
is left in the top, in the position shown at a. 
Through this air has access to the surface of the 
mercury, and variations in its pressure are not 
interfered with. 
Comparing the altitude of the column of mer- 
cury with that of the air which it is balancing, the 
length of the former is exceedingly small com- 
pared with the latter. It is, therefore, necessary 
to read the barometric variations to very small 
Cistern 
barometer. 
fractions of an inch. Even in ordinary barometers the readings 
are to hundredths of an inch. To read minute quantities such 
as this with even an approach to accuracy, the device known as 
a vernier is employed. 
202. Fortin’s Barometer.—ln this the error of cistern level in 
the preceding form is eliminated, and the instrument is at the 
same time made more portable. The main difference is in the 
construction of the cistern. This is composed of a glass cylinder, 
A, the bottom of which is formed by a piece of leather, B. EAROMETRY. 
177 
Against the centre of this a wooden button, C, presses. The 
button is driven by a screw, the head of which is shown at 
D, By means of this screw and the flexible bottom of the cis- 
tern, any variation in level of the mercury may be corrected. 
Fig. 79. 
The scale in this form takes its departure 
from a point, P, which projects downwards 
into the cylinder from its cover, and which 
may be readily seen through its glass wall. 
When an observation is to be made, the 
screw-head is turned either up or down, as is 
required, until this point just touches the 
surface of the mercury. The level of the mer- 
cury in the cistern is then at the true zero of 
the scale, and correct readings may be made. 
The connection between the barometer- 
tube and the metallic top of the 
cistern is made by means of a 
disk of leather tied to each. 
Through the pores of this va- 
riations in atmospheric pres- 
sure are readily transmitted. 
When the instrument is to be 
transported, the adjustment 
screw at the bottom is to be 
turned until the mercury fills 
the cistern. The barometer 
may then be inclined without 
the mercury striking the top, 
it may be even turned upside- 
down—indeed, that is the safest 
position in which it can be 
carried. 
Fig. 80. 
203. The Siphon Barometer.— 
In this the tube is bent in the 
manner shown in Fig. 80. It 
consists of a long arm A, and 
a short arm B. The long arm 
Fortin’s barometer. 
Siphon barometer. 
and short arm are filled with mercury. The instrument is 
then placed as in the figure, when the mercury takes the posi- 
tion shown and in the proportions given. The end of the short 
arm is open, air thus gains access and its variations in pressure 
are made evident. Another form is known as Gay-Lussac’s, 
His improvement consisted in the introduction of the narrow 
V tube between the larger and smaller tube. The instrument 
was thus made portable. 
A support and scale accompany the instrument. When a 178 
GASEOUS MATTER. 
reading is to be made, the top of the mercury in the short arm 
is brought to coincide with the zero of the scale. The pointer 
of the vernier is then adjusted to the top of the mercury in the 
long arm and the vernier read off. 
204. The Wheel Barometer is another form of this instrument. 
It is not employed in scientific inquiry, but is in common use 
as a weather gauge in houses. It is 
a siphon barometer of the old form 
before Gay-Lussac’s modification was 
introduced. On the mercury in the 
short arm there is a float, as is shown 
in Fig. 81. From this a rack passes 
upwards, which works on a toothed 
pinion on the axis of the index. As 
the mercury rises and falls in the short 
arm, the float and its rack also alter- 
nately rise and fall, thus the movement 
of revolution is imparted to the index 
through its axis. 
Fig. 81. 
205, Glycerine Barometer.—Glycerine 
having about one-tenth the specific 
gravity of mercury, has been employed 
for the construction of a barometer, in 
which the movements on the scale may 
be of considerable magnitude. The 
vertical height of such an instrument 
should be about twenty-eight feet. 
The tube may be ordinary iron gas 
pipe a little over half an inch in 
diameter; it can thus be made to follow 
such irregularities of course as may 
be required. The upper termination 
should be a glass tube one inch in 
diameter, about five feet long, and 
hermetically sealed above. This is to 
be arranged in one of the upper stories 
of the building, the cistern being in 
the cellar. Every inch on the ordinary 
Wheel barometer. 
barometer scale is equivalent to about ten inches on the scale of 
this instrument. 
Glycerine vapor having very low tension at ordinary temper- 
atures of the air, there is very little backward pressure in the 
upper part of the tube. In this respect it presents great advan- 
tages over water in its adaptability to the purpose in question. 
The chief disadvantage is that it absorbs moisture from the air. 179 
BAROMETRY 
This may be avoided by covering the glycerine in the cistern 
with a layer of paraffine oil. 
206. Errors in Barometric Readings.—lst. Lack of purity 
in the mercury. The presence of any baser metal as lead, tin, 
zinc, by altering its specific gravity, will alter the height of the 
column of fluid required to counterpoise the weight of the air. 
The mercury should be purified both by distillation and by the 
action of dilute nitric acid in a shallow dish. 
2d. The mercury must be perfectly free from oxide or it will 
adhere to the sides of the glass, and the column will be too long 
or too short, according as it has last moved upwards or down- 
wards. 
3d. Every trace of air and moisture must be removed. This 
is best done by pouring a small quantity of mercury into the 
tube, and boiling it for some time, all air and moisture are thus 
driven off. When it has cooled to 100° C., or thereabouts, a 
second quantity of mercury warmed to this temperature is 
added. This is also boiled for some time; this process is con- 
tinued until the tube is filled with the fluid. 
4th. The tube should be sufficiently wide to allow perfect 
freedom of movement to the column of fluid ; about half an inch 
in bore will answer. The instrument should be gently tapped 
to free the fluid from adhering to the glass whenever a reading 
is made. 
sth. In tubes that are less than eight-tenths of an inch in 
bore, there is a certain error caused by capillarity. This error 
varies according as the last movement of the fluid was upwards 
or downwards. Tables for the correction of these may be ob- 
tained from special works on the subject. They may be avoided 
by the use of a tube with an i nterior diameter greater than that 
mentioned. 
In the siphon barometer of Gay-Lussac, the long and short 
arm being of the same diameter, the errors on the two sides 
nearly counterbalance each other. A slight error, however, 
still remains. In one arm the movement has been upwards, 
and in the other downwards; consequently the curve of the 
surface of the mercury in the two is not exactly the same. 
6th. Temperature, by expanding and contracting the volume 
°f mercury, changes its specific gravity. This is met by cor- 
recting all barometric readings to the fixed temperature of 
32° E. or 0° C. 
207. Barometric Variations.—These are of two kinds. Ist. 
-Regular or diurnal; and 2d. Irregular or accidental. 
The di urnal variations are best marked at the equator. They 
are produced by the rotation of the earth upon its axis, whereby 180 
GASEOUS MATTER. 
one portion of the atmosphere after another is heated by the 
rays of the sun. So regular are these variations in the tropics 
that the barometer serves the purpose of a clock. At four p.m. 
it is at its lowest; it then rises, reaching the maximum at ten 
p.m.; after that it sinks, reaching the minimum at four a.m.; it 
then rises again, and attains the second maximum at ten a.m. 
The accidental variations depend on seasons, winds, geo- 
graphical situation, contour, and other causes. They are void 
of regularity. 
From the equator towards the poles, barometric variations 
increase both in amount and irregularity. Rhythmic changes 
which are the rule in torrid regions, though they still exist in 
northern climes, are so masked by accidental variations that 
they are almost undiscoverable. At the equator ordinary varia- 
tions are within one-quarter of an inch. In the region of New 
York State the limit is increased to an inch and a half, and at 
25 degrees from the pole it reaches two and a half inches. 
208. Mean Barometric Height.—From what has been said 
above, it is evident that this must vary for each region. It is 
usually given for the day, month, and year. 
Mean daily height is obtained by adding together 24 hourly 
variations and dividing the same by 24. 
Mean monthly height, by adding together the above for a month, 
and dividing by the number of days in the month. It is greater 
in winter than in summer. 
Mean annual height, by adding together the preceding for one 
year, and dividing by 12. 
At the equator the mean annual height is 758 millimetres, or 
28.84 inches. Between latitudes 30° and 40°, it attains its maxi- 
mum of 768 millimetres, or 30.04 inches. North of this it di- 
minishes. At sea level the general mean is 761 millimetres, or 
29,96 inches. 
209. Cause of Barometric Variations.—Reviewing the account 
of barometric variations at the equator (207), it will be noticed 
that at the hours of the day when the thermometer is the 
highest, the barometer is the lowest, and vice versa. From this 
it is evident that the causes of these variations are rarefaction and 
condensation of the air by changes in temperature. Elevation 
of temperature producing expansion of air, its specific gravity 
diminishes; it consequently rises and overflowing the cooler 
portions in the upper regions there is less air by weight to 
press, and the barometer consequently falls. 
The air which has overflowed in upper regions of the atmos- 
phere being added to that already existing in the region to BAROMETRY. 
181 
which it passes, the increased weight causes a rise of the 
barometer in these localities. In this manner, gigantic aerial 
billows are originated in the uppermost regions of the atmos- 
phere, which, as they pass across continents and oceans, may 
be traced by the variations they produce in the barometer, and 
changes far out of sight prognosticated and their approach 
heralded. 
210. Barometric Variations and the Weather.—When the barom- 
eter stands at about 30 inches in Hew York, the weather is 
generally fine; if it rises above this, the certainty of fine weather 
increases; if it falls below, the probability of rainy weather is 
greater. The barometer is, therefore, capable of indicating ap- 
proaching changes, and for this reason, especially when in the 
form of the wheel barometer, is called a weather glass. 
It must not be forgotten that what the barometer really indi- 
cates is the changes in the weight of the air. Change which is 
attended by a rise in the barometer is generally productive of 
conditions which prevent the precipitation of moisture; change, 
on the contrary, which is attended by a lowering of the barom- 
eter is usually favorable to this precipitation. It by no means 
follows that because the barometer falls it will surely rain. 
The best that can be said is, that there is strong probability of 
rain. The final result is largely influenced by the direction of 
prevalent winds. Winds which come from over the surface of 
warm oceans are laden with moisture, and with a falling 
barometer present conditions most favorable for rain or snow. 
Winds, on the contrary, which come over extensive areas of 
land, are apt to be dry, especially if they have surmounted a 
fountain range. Whether the barometer be high or low, the 
general tendency of such win#s is to produce fine weather. If 
they are attended by a high barometer, the weather is almost 
sure to be fine. 
. 211. Barometer and the Winds.—As soon as an area of dimin- 
ished pressure is established in any locality, the air of regions 
m the vicinity will flow towards it, and currents will thus be 
established. These movements are called winds. The direction 
of a wind indicates the positions of places at which different 
atmospheric pressures are prevailing. A barometer, therefore, 
not only acts as a gauge of pressure of the atmosphere, but also 
as a wind gauge. 
Suppose a difference of one-tenth of an inch in pressure at 
tw°. observatories, one hundred miles apart. If a series of 
stations were established between these, and barometers ex- 182 
GASEOUS MATTER. 
amined at each, it would be found that their altitudes when 
mapped would form a curved Hue, extending from one observa- 
tory to the other. To this modern meteorologists have given 
the name of the barometric gradient. Air flows down this gradient, 
and thus wind is produced. If this gradient is moderate, a gentle 
breeze arises; if it is steep, the resultant wind is strong. 
From the above facts it is evident that but little information 
can be derived from observations made with a single barometer. 
Valuable results are onlj’ to be obtained by numerous points of 
observations extended over great areas. 
Many causes beside that of gradients intervene to modify the 
character and course of a wind. Among these are rotation of 
the earth, also the course of mountain ranges, rivers, and 
valleys. When we add the size and shape of areas of high and 
low pressure, we can form some conception of the difficulty of 
collating so many varying data, and making an intelligent fore- 
cast of winds and weather. 
A singular fact in connection with the influx of air towards a 
region of low pressure, is its tendency to assume a vertical or 
whirling motion. Even on a small scale this tendency exists, 
as we have all seen in the whirling wind with which, on the 
approach of a thunderstorm, particles of paper, shavings, and 
dust are often carried to considerable altitudes. On a great 
scale such whirling storms constitute the tornadoes, whirlwinds, 
hurricanes, and cyclones of the tropics. 
212. Barometer and the Deathßate.—The relations of barometric 
indications to diseases and the death rate have not yet received 
that attention from physicians which their importance demands. 
One of the leading hygienic factors is the proper maintenance 
of exhalation of vapor of water together with other gaseous or 
vaporous substances from the skin and mucous surface of the 
lungs. Anything which tends to lower the capacity of the air 
for moisture, or causes its dew-point and temperature to ap- 
proach, must in the nature of things interfere with the facility 
with which vaporization takes place from both skin and lungs. 
The action of these great excretory organs being interfered 
with, certain noxious products of the economy are not properly 
eliminated. They, therefore, either accumulate in the system 
and produce blood-poisoning, or the attempt is made to cast 
them out through some other channel. The organ which is 
thus forced into vicarious action, resents the imposition, and in- 
flammation is the consequence. 
"We have seen that a lowering of the mercury in the barometer 
is attended by a precipitation of moisture. The conditions of 
which we have just been speaking are, therefore, present; inter- MEASUREMENT OF PRESSURES AND ALTITUDES. 
183 
ference to a greater or less extent with the functions of the 
system must follow. To persons who are already enfeebled by 
protracted disease, or who are still struggling with some fearful 
inflammation, a sudden fall in the barometer may bring dis- 
astrous consequences. Had the physician been forewarned of 
an approaching change, he might have been able to meet it 
bj’ suitable remedies, and aided his patient to tide over the 
crisis. It, therefore, appears to be both wise and proper that 
more attention should be paid to this subject. If physicians 
would supply themselves with these instruments, and make even 
a passing study of their relations to disease, fewer mistakes in 
prognosis would be made, and many a one who otherwise 
passes away without warning, would be enabled to set his house 
in order. 
CHAPTEE XY. 
MEASUREMENT OE PRESSURES AND ALTITUDES. 
Boyle’s or Mariotte’s law—Open compression manometer—Closed compression 
manometer Exhaustion manometer—Equality manometer—Exhaustion 
water-valve—Aneroids—Determination of altitude by aneroid or barometer 
—Error in barometric determination of altitude—The barometer in mines— 
Pressure and solubility of gases—The Windmill—Conveyance of germs by air. 
213. Boyle’s or Mariotte’s Law.—We have seen that the ba- 
rometer is essentiall}7 an instrument for measurement ol pres- 
sure, but its indications are limited to one atmosphere, or about 
fifteen pounds to the square inch. It is often necessary that 
pressures surpassing this, sometimes even a hundred-fold, should 
be determined; for this purpose various kinds of manometers, 
as they are called, have been contrived. They depend upon a 
general law of the expansion and contraction of gases, or on 
the action of springs. 
Boyle’s or Mariotte’s law deals with the compressibility of 
gases. It was discovered by Boyle in 1662, and passes under 
his name in England. In 1679 it was discovered independently 
by Mariotte, and is known as his law on the Continent. We 
have seen (160) how the volume of this form of matter changes 184 
GASEOUS MATTER. 
under variations of pressure. To measure these changes, Boyle 
contrived the apparatus represented in Fig. 82. It consists of a 
Fig. 82. 
Fm. 83. 
stout tube about four feet in length, 
hermetically sealed at one end, open 
at the other. It is bent so that the 
closed extremity forms the short arm. 
When it is to be used sufficient 
mercury is poured into the bend to 
fill it to the zero of each scale. A 
column of air is thus confined be- 
tween the surface of the mercury 
in the short tube, and the closed ex- 
tremity of the tube. When more 
mercury is poured into the long arm, 
pressure is brought to bear upon the 
mercury in the bend, and so upon 
the short column of air. As the 
mercury in the long arm rises inch 
by inch, Fig. 88, shrinkage takes 
place in the length of the column of 
air in the short arm. At last when 
the column of mercury in the long 
tube A B has reached an altitude, 
A, of 30 inches above that in the 
Mariotte’s or Boyle’s law, 
short arm, the air in the latter is submitted to a pressure of one 
atmosphere, and will be found to have diminished to one-half 
its first volume, as at C. 
At the commencement of the experiment the column of air 
in the short arm was already under the pressure of the normal 
atmosphere; addition of an atmosphere of pressure exerted by 
the column of mercury increases it to a pressure of two at- 
mospheres. We, therefore, learn that by doubling the pressure 
on a gas it shrinks to half its volume. If the length of the 
long arm is sufficiently increased, and atmosphere after atmos- 
phere of pressure added, the shrinkage of the column of air 
continues at a fixed rate. With three atmospheres of pressure 
it is one-third; ten atmospheres, one-tenth of the original 
volume. This rate of contraction has been verified by Dulong 
and Petit up to twenty-seven atmospheres. 
From the account given, the law of the volume of gases may 
be briefly stated as follows : The temperature remaining unchanged, 
the volume of a stated quantity of a gas is inversely as the pressure. 
For pressures less than one atmosphere the law also holds 
good. Diminution of the pressure to one-half, the volume is 
doubled; to one-tenth, the volume is ten-fold, and so on. The 
experimental demonstration of this fact may be obtained by the MEASUREMENT OF PRESSURES AND ALTITUDES. 
185 
apparatus, Fig. 84. BCis a deep, wide glass 
tube with a funnel-like mouth above. The 
tube and funnel are filled with mercury to the 
line indicated in B, In the mercury of this 
deep pneumatic trough a tubular bell-jar, A, 
is immersed. In this tube bell a column of air 
of known length is enclosed. When the 
mercury is at the same level in the tube, and 
in the pneumatic cistern, the air in A is under 
a pressure of one atmosphere. If the tube is 
raised so that there is a difference of 15 inches 
between the level of the mercury in it and in 
the tube trough, the pressure on the air in the 
tube receiver will be reduced to one half, and 
the column of air will be double the length it 
had previously. 
Fig. 84. 
While the law of Boyle is sufficiently exact 
for all ordinary purposes, it is not absolutely 
true. Despretz found that when examined 
side by side in tubes exposed to exactly the 
same conditions, carbonic acid gas, sulphuretted 
hydrogen, ammonia, and cyanogen, were more 
Expansion with 
diminished pressure. 
compressible than air. Up to 15 atmospheres, hydrogen follows 
the law for air; beyond that it is less compressible. Even for 
air the law is not absolute, for Cailletet has ex- 
amined it up to 600 atmospheres of pressure, 
and finds that up to 80 atmospheres it has a 
maximum relative compressibility ; after that it 
becomes less compressible, the compressibility 
diminishing more rapidly than in the case of 
hydrogen. 
As a rule, all gases deviate from the law as 
they approach their point of liquefaction. The 
greater the distance from this point, the more 
closely do they follow the law. 
Fig. 85. 
214. Open Compression Manometer. —ln its 
simplest form this instrument consists of a 
bottle or reservoir, A,nearly tilled with mercury, 
mid tightly closed by a screw stopper. Through 
this the tube B passes. It is over 5 feet in 
length, open at both ends, and dips into the 
mercury, nearly touching the bottom of the 
bottle. A second tube, C, passes through the 
Open compression 
manometer. 
side of the bottle; this is to he connected with the boiler or 
other apparatus in which the gas or vapor is generated. Through 186 
GASEOUS MATTER. 
the tube C the gas exerts its elastic force upon the surface of the 
mercury in the bottle. The mercury is consequently pushed up 
the tube B, and continues to rise until the column of fluid 
balances the pressure exerted by the gas or vapor. The height 
of the column is then read off in inches of mercury, or it may 
be given in atmospheres or fractions thereof. It may also be 
expressed in pounds to the square inch. This form can only be 
used for moderate pressures, the great length of tube required for 
high pressures rendering it too inconvenient for practical use. 
215. Closed Compression Manometer.—A simple form of this 
instrument is represented in Fig. 86. It consists of a thick 
Fig. 86. 
glass tube of uniform diameter closed at one 
end and bent as at A, B, C. The bend is tilled 
with mercury. The space Ais tilled with air. 
The stopcock C is connected with the apparatus 
in which the pressure is generated. 
As the pressure in the generator, a steam 
boiler for example, increases, the column of air 
A diminishes. When, according to Boyle’s 
law, it has reached one-half its original length, 
the pressure is one atmosphere in addition to 
the air pressure, and so one to one-tenth for ten 
atmospheres, and one-hundredth for one hun- 
dred. Since the increase in pressure in the 
Closed compression 
manometer. 
boiler is partly counterpoised by the increasing weight in the 
column of mercury that attends its increase in height, the error 
that is thus introduced must be corrected. urns is 
a mere matter of calculation, and is best done in 
the preparation of the scale which is attached to the 
instrument, and by which its indications are ob- 
served. 
Fig. 87. 
216. Exhaustion Manometers.—For the measure- 
ment of perfection of a vacuum, any of the forms 
of barometer we have described will answer. In 
practice, however, it is found that the mercurial 
barometer is very inconvenient on account of its 
length and fragility. To avoid these objections the 
adjoining contrivance, or exhaustion gauge, is em- 
ployed. It consists of a tube closed at A, and 
open at E, The arm BD is tilled with mercury, 
all air and moisture being carefully expelled. The 
height of the apparatus is about eight or ten inches. 
The tube is attached to a scale, and both are en- 
Exhaustion 
manometer. 
closed in a stout glass cylinder fitted into a brass cap below by 
which it may be attached to an air-pump, vacuum pan, or other MEASUREMENT OF PRESSURES AND ALTITUDES. 
187 
apparatus, in which the perfection of the exhaustion is to he 
measured. 
The working of the instrument is as follows. The top of the 
column of mercury in A having an altitude of eight inches 
above the level of that fluid in D, when the exhaustion falls 
below eight inches of mercury in the barometer, the mercury 
at A begins to leave the top of the tube. The exhaustion being 
pushed it falls lower and lower, until when a perfect vacuum 
is approached it stands at very nearly the same level in both 
arms of the tube. If the gauge has been perfectly freed from 
air and moisture when the mercury was introduced, the level 
B will never fall exactly as low as that in D. If it does fall as 
low, or even lower, it shows that the construction of the instru- 
ment is not perfect. Intermediate pressures between 8 inches 
and a vacuum, are indicated by the difference between the levels 
of the mercury of the two arms. 
217. Equality Manometer.—lt often happens that in physio- 
logical inquiries it is necessary to know whether the contents of 
an air-chamber or bell are under the same 
pressure as the then prevailing atmospheric 
pressure. This is determined by a gauge of 
FIG 88. 
the form represented at ABC D. It is a 
tube open at both ends and bent in the manner 
shown. The extremity B is attached to the 
chamber or air-bell. The bend is filled to the 
height B C with mercury, water, or ether, ac- 
cording as greater delicacy is required. The 
mouth A offering free communication with 
the air, any increase in pressure in the jar 
over that of the air, will be shown by a rise 
of the fluid above B, an}? decrease by its fall. 
Equality manometer. 
218. Exhaustion Water-valve.—ln the preparation of solutions 
of ammoniacal and other gases, in water, and also in washing 
gases, it not unfrequently happens that partial vacua are suddenly 
formed in some part of the apparatus, and the contents of a 
washing bottle or the freshly formed solution is drawn into 
another part of the apparatus and lost. 
To illustrate this let A, Fig. 89, represent a flask in which 
ammonia gas is in process of generation from aqua ammonise. 
It is supplied with a safety tube B, which is open at both ends 
and dips below the surface of the liquid A. The gas, as it is 
generated, cannot escape up this tube, for its mouth is closed by 
liquid. It, therefore, passes by the tube Cto the bottom the 
three-necked bottle, and bubbles through the water I) contained 
therein. Any portions that escape solution in I), pass out 188 
GASEOUS MATTER. 
through the escape tube F into a second bottle, and so on 
through a train of half a dozen or more. Each of these bottles 
is provided with a safety tube E 
open at both ends, and dipping a 
short distance under the fluid it 
contains. 
Fig. 89. 
Let us suppose that from any 
cause the space above the water 
in the bottle D becomes ex- 
hausted, the tendency would be 
to draw water from the next bot- 
tle through F, and so injure the 
solution already formed. This, 
however, does not happen, for the 
moment the exhaustion reaches 
a certain point air rushes down 
the tube E, and any further in- 
crease of vacuum is prevented. 
Exhaustion water-valve. 
In like manner formation of a vacuum in the flask A is im- 
mediately checked by an ingress of air through its safety tube 
B, and loss of any part of the solution already formed in I> 
prevented. 
In the preparation of oxygen and protoxide of nitrogen for 
the purposes of respiration, careful purification of these gases 
by washing them with various solutions is indispensable. Each 
bottle in the series should be provided with safety tubes like 
those represented. 
219. Aneroids,—These are instruments for the measurement 
of pressure, and having an appearance similar to that of a watch 
with its graduated face and hands. They vary in size from that 
of a lady’s watch to that of an ordinary clock. They derive their 
name from«, without, and vqpk moisture, indicating the fact that 
liquid does not enter into their construction. They are of two 
kinds, the first for the measurement of pressures beyond that 
of the atmosphere, the other for those that are less; the latter 
is called the aneroid barometer. 
The aneroid barometer consists of a metallic drum, the heads 
of which are made of very thin corrugated metal. The interior 
of the drum is exhausted; the heads are consequently forced 
inwards by the pressure of the air on the outside. Any diminu- 
tion in this pressure causes the drum heads to recede from each 
other, partly by the elasticity of the corrugated metal, and partly 
by the action of a spring. Any increase of pressure, on the 
contrary, causes them to approach. By means of a delicate 
system of levers, these movements are multiplied and brought 
to act upon the hands, just as in a watch the movements of the 189 
MEASUREMENT OF PRESSURES AND ALTITUDES. 
main spring are by a series of wheels brought to bear upon its 
hands. 
Instruments of this description are constructed by Casella 
which possess marvellous delicacy. Their portability gives 
them a great advantage over the mercurial barometer. The 
only difficulty is, that the multiplying machinery is liable to 
get out of order; hence it is necessary to compare their indi- 
cations from time to time with those of a good barometer. 
Especially are they apt to give false indications when they 
have been submitted to sudden and unaccustomed changes of 
pressure. 
By reversing the construction of .the aneroid barometer, and 
admitting gas or vapor to the interior so that it may exert its 
elastic force therein, the instrument is converted into a gauge 
for measurement of compression or condensation. In this form 
it is now found attached to steam boilers, and may be said to 
be the ordinary steam-gauge. 
220. Determination of Altitude by Aneroid or Barometer.—The 
experiment of Pascal demonstrated not only the point of which 
he sought proof, viz., that air exerted pressure, but also, that the 
higher a barometer was taken above the surface of the earth the 
lower did its mercury stand. This fact offers a method by 
which the altitude of a mountain, and even of lesser elevations 
may be determined. 
In examining the extent to which the barometer might be 
used for this purpose, one of these instruments was carried from 
the level of the water in the Thames to the top of St. Paul’s 
Cathedral. The mercury fell nearly half an inch, the ascent 
being 450 feet. On the summit of Mt. Blanc the fall is fifteen 
inches the elevation being about 15,000 feet; from this it follows 
that one-half of the whole weight of our atmosphere is em- 
braced in a layer about three and one-half miles thick on the 
surface of the globe. 
In estimating the height of a mountain by barometer, observa- 
tions should be made at the base and the summit at the same 
time. Corrections must be made for the effects of tempera- 
ture on the two columns of mercury, and also for differences in 
gravity. 
By the use of the aneroid barometer for this purpose many 
of the errors which arise with the mercurial barometer may be 
avoided. The facility of conveyance is also an especial advantage 
which the aneroid enjoys. 
221. Errors in Barometric Determinations of Altitude.—These 
have amounted to as much as one-twenty-third of the whole 
height. Buhl man has shown that the cause of this error is that 190 
GASEOUS MATTER. 
the mean of the temperature at the two stations, as indicated by 
thermometers, was not the actual mean of temperature of the 
air between these stations. 
That thermometers do not give the true temperature of the 
air is owing to the fact that their indications are affected by 
radiations from the earth and from objects in their vicinity. In 
the management of meteorological observations more attention 
O # O 
should be paid to this fact. 
222. Barometer in Mines.—As ascent above the earth’s surface 
produces a fall in the barometer, so a descent beneath its sur- 
face produces an increase in the altitude of the mercurial 
column. Variations in the barometer in coal mines in which 
fire-damp or carburetted hydrogen escapes, are of especial value to 
the miner, since the}7 afford him the means of knowing whether 
this dangerous gas is escaping from the crevices in which it is 
confined. When the pressure of the air is high, carburetted 
hydrogen is forced back into the crannies in which it is gen- 
erated. When the pressure falls, it then by its elastic force 
presses its way out, escapes from its hiding places and becom- 
ing mingled with the air of the mine, forms therewith a dan- 
gerous explosive mixture. It also exerts a poisonous action on 
the systems of those who are obliged to breathe it, and is, 
therefore, doubly dangerous and objectionable. 
223. Pressure and Solubility of Gases.—Place a glass containing 
cool freshly drawn water under an air-pump bell and throw the 
pump into action. As the pressure diminishes, the water will 
become milky in appearance. This loss of transparency is pro- 
duced by the formation of myriads of minute bubbles of air or 
water gas, which the water held in solution at the ordinary 
pressure, but which it was unable to retain when the pressure 
fell. 
Reversing the above experiment and exposing water to a gas 
under pressure, it is found that it takes up a larger proportion 
of gas than at the ordinary atmospheric pressure. This fact 
lies at the basis of the explanation of the formation of all 
natural and artificial effervescing waters as well as of effervescing 
wines. As might be expected, the amount of gas a fluid will 
hold in solution is determined by Mariotte’s law. 
As an example of the facts in question, we find that at ordi- 
nary pressures and temperatures water will hold about its own 
bulk of carbonic acid gas in solution. If the gas is freely sup- 
plied at a pressure of, say, four atmospheres, and the solvent 
action of the water promoted by gentle agitation, the water will 
take up the same bulk of gas as before, but this gas will be 
denser than in the preceding case, and there will really be four MEASUREMENT OF PRESSURES AND ALTITUDES. 
191 
times as much in the water as when the solution was made at 
the ordinary atmospheric pressure. That this is the explana- 
tion is shown by relieving the water from pressure, when at 
once it surrenders its excess of dissolved gas, a violent effer- 
vescence being produced. 
It is worthy of mention that when the air dissolved in water 
is removed therefrom, by submitting it to the action of a vacuum, 
it assumes an insipidity similar to that of pure distilled water. 
When it has regained its original supply of gas, its flavor returns. 
This would seem to show that though oxygen is generally stated 
to be without effect on the sense of taste, there is something in 
connection with its action which enables us to detect its presence 
m the free state in water, or, we might better say, its absence. 
224. The Wind-mill.—As the force of moving water is applied 
as a motor in various kinds of water wheels, so that of wind is 
utilized in the wind-mill. This form of apparatus is extensively 
employed for purposes of drainage in Holland. It is also used 
ln mills for grinding grain. In the western regions of the 
United States it is applied for purposes of irrigation. To phy- 
sicians it is of interest in connection with its use as a motor 
for pumps or other hydraulic apparatus employed in raising 
water or removal of drainage and sewage. 
225. Conveyance of Germs by Air.—In closing this division of 
our subject, we desire to add a few words regarding the convey- 
ance of germs by the air. If pure distilled water is exposed 
tO. uir, after a while it is found to contain various forms of 
Microscopic beings, some of which belong to the plant and 
some to the animal kingdom. For long it wTas a matter of 
dispute as to whether these were produced by spontaneous genera- 
hon or were conveyed to the fluid by the air in the form of 
exceedingly minute germs or spores. It is clear that there is no 
bait way between the two theories. 
After innumerable experiments it is now generally admitted 
that tbe floating particles in air, which appear to us as the 
that dance in the sunbeam, are the medium by which these 
spores or germs are carried. It is true we may not be able to 
discover the germs themselves on account of their minuteness, 
but of their presence and existence there can be no doubt. If 
air is filtered, by passing it slowly through a long column of 
cotton in a glass tube, and then admitted to a flask containing 
Pore water, the appearance of vegetable and animal life is 
greatly hindered or entirely prevented. If, at the same time, a 
Jar m the immediate vicinity is supplied with air at the same 192 
GASEOUS MATTER. 
rate and in the same manner, but of which there is no filtration, 
organized beings appear in the usual way. 
If spores and germs capable of initiating constructive changes 
which result in the production of organized beings can be so 
small as to be undiscoverable even by the microscope; if, more- 
over, such germs are conveyed by the air, there is certainly 
nothing objectionable in the proposition that disease germs may 
both exist and be conveyed in the same manner. See Schizo- 
mycetes (601 A). It is scarcely a valid objection to such a 
theory, that disease germs may be supposed not to have any 
existence. There are many facts which show that they do exist, 
and that in some cases, at least, they are the agents of retro- 
grade or destructive metamorphosis, just as other germs are 
agents of constructive metamorphosis. 
Many diseases, and among them those known as malarial, are 
conveyed by winds to a distance from the place of genera- 
tion. Hot infrequently a fringe of certain trees will act as 
a complete barrier to the passage of such emanations. The 
most rational explanation of such a fact is that in passing among 
the leaves of the trees, the air has undergone a removal or 
destruction of the agent, spore or otherwise, which originates 
malarial trouble in the body. It is easy to imagine that in this 
case the spores are destroyed or paralyzed by the emanation of 
the plant to which they are exposed as they pass among its 
leaves. Absence of malarial disease in regions occupied by 
terebinthine or pine trees, would tend to show that the result 
is probably owing to the action of ozone. 
The destruction of germs attached to motes in the air may 
in other cases be very difficult of accomplishment. It has been 
found, in the management of disinfectant apparatus attached to 
quarantines, that a temperature of 212° F. or the boiling of 
water does not always destroy germ life. To insure this result, 
a temperature of 250° F. or even higher is requisite. This may 
be readily attained by means of an oven or by high pressure 
steam. In all cases of death by diseases in which there is any 
probability of conveyance by germs, the physician should see to 
it that all articles of clothing are destroyed or at least submitted 
to a temperature of 300° F. 
The dust which settles on the walls of rooms is often an 
unsuspected agent in the conveyance of disease germs. The 
passage of an affected person may have left them in the air. 
They have thus become attached to the floating motes and so to 
the walls. Here they may remain for a long time, until by some 
cause they become detached and, gaining entrance to a human 
body, initiate the peculiar train of symptoms which they are 
capable of producing. A thorough cleansing of the walls of 
rooms is the only safeguard against this source of infection. The 193 
EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
good that is accomplished by such cleansing is shown by the 
change in odor of a room after it has been thoroughly cleaned. 
With increase in the penetrative and magnifying power 
of microscopes, it is not improbable that light will be thrown on 
this question of the propagation of certain diseases by special 
spores or germs. In connection therewith, we may mention a 
device which offers some opportunity of entrapping these 
objects for examination. It consists of an aspirator (171) by 
which air is drawn through a tube which is loosely packed 
with fine gun-cotton. As is the case with ordinary cotton, this 
entraps the floating motes. To separate these from the gun- 
cotton, the latter is dissolved in ether, and a very dilute collodion 
formed; in this the motes sink and may be prepared for examina- 
tion under the microscope in the usual way. 
CHAPTEE XYI. 
PHYSIOLOGICAL AND THERAPEUTICAL EFFECTS OF 
VARIATIONS IN DENSITY OF AIR. 
Composition of blood—Haemoglobin—Divisions of physiological effects of pres- 
sure—Tension of oxygen or other gas respired—Diminution of pressure below 
one atmosphere—Mai des Montagnes—Symptoms of Mai des Montagnes— 
Theoretical explanations of Mai des Montagnes—Theory of M. Jourdanet— 
Balloon sickness—Bert’s rarefaction cylinders—Air in caves—Death from 
diminished air pressures—lncrease of pressure above one atmosphere—Res- 
piration of pure oxygen—Physiological action of moderately condensed air 
—Action of oxygen under high tension—Oxygen poisoning—Relation of 
animal tissues to oxygen—Death from increased pressure—Therapeutical 
effects of respiring oxygen—Therapeutical uses of compressed air—Hygienic 
management of compressed air—lmpurities in compressed air—Effects of de- 
compression—Nature and treatment of decompression accidents—Relation of 
barometric variations to natural history—Bert’s resume of his results. 
To place this important matter in as clear a light as possible 
it is necessary that we first examine briefly into certain characters 
°f the blood, the chief circulating fluid of the body. 
226. Composition of Blood.—ln all the higher animals blood 
consists essentially of two parts : Ist. A fluid portion called 
plasma, composed of water, albumen, fibrin, and other organic 194 
GASEOUS MATTER. 
bodies, together with various inorganic salts. 2d. Corpuscles 
or globules; these are of two kinds, white and red. White 
globules are the mother cells of the red corpuscles, and the 
latter are carriers of oxygen from the lungs to the system. It 
is with the latter that we are at present especially concerned; 
their composition, according to condition, is as follows. 
Wet Corpuscles. 
Water . 
56.5 
Solids . 
48.5 
100.0 
Dry Corpuscles. 
Haemoglobin . 
90.54 
Proteids. 
8.67 
Lecithin 
.54 
Cholesterin 
.25 
100.00 
227. Haemoglobin.—The chief constituent of red blood cells 
may be readily obtained therefrom by breaking up the cell wall 
either by alternate freezing and thawing, or by addition of chlo- 
roform or of bile salts. In some creatures it is crystalline and in 
others amorphous. According to Hoppe-Seyler, its composition 
in the dog is 
Carbon 
. 53.85 
Hydrogen . 
. 7.32 
Nitrogen . 
. 16.17 
Oxygen 
. 21,84 
Sulphur 
0.39 
Iron . 
. 0.43 
In addition there is about 8 or 4 per cent, of water of crystalliza- 
tion, Besides the ordinary elements in proteid bodies, haemo- 
globin contains iron, to which element doubtless its special 
properties are due. It is readily soluble in warm water, the 
solution having a bright arterial color. Even though very 
dilute this solution gives a characteristic spectrum, a part of 
the red and the greater portion of the blue being absorbed, and 
two strongly marked absorption bands appearing between the 
solar lines I) and E. 
When crystals or solutions of haemoglobin, prepared as above, 
are placed in the vacuum of the mercurial air-pump they give 
off' a definite proportion of oxygen gas, viz., 1.76 cubic centi- 
metre per gramme, or 1.34 under a pressure of one metre. 
This oxygen is entirely independent of that entering into the 
composition of the substance. It is loosely associated with it, 
and may be added to or dissociated therefrom at pleasure with- 
out injury. 
The associated oxygen of haemoglobin in solution may be 
separated by other means than the vacuum; among these are 
hydrogen, other gases, and various reducing agents as ammonium 
sulphide. EFFECTS OP VARIATIONS IN DENSITY OF AIR. 
195 
Haemoglobin which has lost its associated oxygen, loses its 
bright scarlet color, the crystals become darker and of a 
purple tint. They are also dichroic, the thin edges appearing 
green and the thicker parts purple. The solution shows a 
similar change of hue, passing from light scarlet to a purplish 
claret tint when examined in thick layers, but green when in 
thin. 
The spectrum of reduced haemoglobin is entirely different 
from that which contains oxygen. The two absorption bands ol 
the latter have disappeared, and in their place a single broader 
but fainter band has come into existence. The blue also suffers 
Jess absorption by reduced haemoglobin (650). 
When reduced haemoglobin is exposed to oxygen or to air 
containing oxygen, it immediately absorbs that gas, and if it is 
present in sufficient quantity takes up its full complement, one 
gramme of crystals associating to itself 1.34 c. cm. of oxygen. 
To haemoglobin which contains associated oxygen the name ot 
oxyhcemoglohin is given. When this has suffered a dissociation 
of its oxygen, it is called simple or reduced haemoglobin. 
The facts we have hereby acquired enable us to comprehend 
the role which the red corpuscles play as carriers of oxygen. 
Their function is accomplished by virtue of their haemoglobin. 
Tn the lungs they associate oxygen to themselves, and carrying 
!t into the innermost parts of the system, it is there dissociated 
by virtue of the looseness with which it is held. Thus altern- 
ately the corpuscles receive and surrender oxygen, and the de- 
mand for oxygen by the system is supplied. 
In a similar manner haemoglobin combines with carbonic acid. 
This case, however, differs essentially from that of oxygen, for 
with the latter scarcely any of the gas is held in the plasma, 
nearly all is in the haemoglobin. In the case of carbonic acid, 
°n the contrary, the plasma contains as large a per cent, as the 
corpuscles. 
228. Divisions of Physiological Effects of Pressures.—Under- 
standing the agency by which oxygen is conveyed into the in- 
terior of the body, we are prepared to examine the complex 
effects of variations of pressure upon this act with a fair degree 
°f intelligence, and with some prospect of arriving at a correct 
solution of the phenomena which present themselves. 
For sake of convenience the subject may be studied under 
two divisions: 
Ist. Diminution of pressure below one atmosphere. 
2d. Increase of pressure above one atmosphere. 
For the facts we are about to give, science is largely indebted 
to M. Paul Bert, from whose work on “Barometric Pressures” 
we have made the abstract presented in this chapter. The impor- 196 
GASEOUS MATTER. 
tance of this work, and the extent of the field it opens, cannot 
fail to be appreciated by all who give their attention thereto. 
229. Tension of Oxygen or Other Gas Respired.—The term ten- 
sion is frequently met in M. Bert’s work; its significance is both 
convenient and important. It combines two factors: Ist. The 
percentage of gas in the mixture; 2d. The pressure in atmos- 
pheres or fractions thereof. 
In air, the per cent, of oxygen being 20.6 and the pressure 
one atmosphere, the tension is 20.6. This is the standard or 
normal tension; from it we have various departures, for example, 
the percentage remaining the same, the pressure may increase. 
Percentage. Pressure. Tension. 
2 atmospheres .... 20.6 \ 2 = 41.2 
5 atmospheres . . . . 20.6 X 5 103.0 
In the latter case, a creature respiring normal air under a 
pressure of five atmospheres is virtually introducing into its 
lungs more oxygen than if it were respiring pure oxygen at a 
pressure of one atmosphere, e.g., 
Air, 5 atmospheres pressure. . 20.6 X 5 = 103 0 
Oxygen, 1 atmosphere pressure . 100.0 X 1 == 100.0 
Percentage. Pressure. Tension. 
In like manner, reduction of pressure reduces tension, for ex- 
ample, 
Percentage. Pressure, Tension. 
| atmosphere . • . . 20.6 X 2 = 10-3 
t atmosphere . . . . 20.6 X i = 4.1 
Diminution of Pressure Below One Atmosphere. 
230.—This may arise: Ist. By ascent of a lofty mountain; 
when symptoms constituting Mai des Montagues appear. 2d. 
By ascent in balloons to great heights. 3d. In exhausted re- 
ceivers. 4th. By a reduction of the percentage of oxygen in 
air; the tension may then fall far below the normal of 20.6, even 
though the pressure is more than one atmosphere. Reduction of 
tension in Ist, 2d, 3d, is accomplished by reduction in pressure; 
in 4th the same effect is produced by reduction of the percentage 
of oxygen. 
231. Mai des Montagnes.—Travellers generally sutler from this 
complaint at an altitude of 10,000 feet. They seldom reach 
17,000 feet without serious inconvenience. On the other hand EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
197 
Gay-Lussac, Glaisher, Burrall, and Bixie, suffered but little at 
an altitude of 23,000 feet. 
The causes of these differences are numerous. One fact seems 
fo be pretty well marked, and that is, that the peculiar physio- 
logical effects begin to appear about 1700 feet above the line of 
eternal snow. Though there are many exceptions to this, yet 
it may be said that the more elevated the line of snow, the 
higher can the traveller ascend without suffering from Mai des 
Montagnes. Much depends upon the condition of the person 
himself, great difference appearing in different ascents of the 
same mountain, though he is not conscious of any material 
difference in his condition. 
232. Symptoms of Mai des Montagues.—Digestion. Very little 
appetite, one-third or one-fourth the usual amount of food 
satisfies hunger. Thirst, distaste for food, and even for its sight 
and odor; insipidity of fluids, nausea, vomiting, are experienced 
by nearly all. Hot only are phlegm and bile thrown up, but 
also blood, and the irritability of the stomach is sometimes so 
great that not even a teaspoonful of water can be retained. 
Bscape of bile into the intestine during the paroxysms of vomit- 
ing brings on diarrhoea, which is aggravated by the intense cold 
and unavoidably wet feet. 
Respiration becomes short, frequent, difficult, and interrupted, 
fhe oppression in the chest is often attended by severe pain. 
J-his with exaggerated ' fatigue constitutes generally the first 
evidence of Mai des Montagues. Animals suffer equally with 
men. 
Circulation. Acceleration of the pulse, though not so frequently 
mentioned by authors as the respiratory and digestive symptoms, 
is nevertheless not less constant. The record is as high as 140 
and 150 beats for great altitudes. Acceleration of the pulse is 
not transitory, it continues throughout the sojourn at great 
elevations. Its force also diminishes, it becomes irregular, more 
compressible, and smaller. 
The venous system shows fulness of the vessels, congestion 
°f the skin, lips, conjunctiva. Suddenly these sometimes give 
Way to a death-like pallor, menacing syncope and complete loss 
°i consciousness. To this train of symptoms hemorrhages from 
nose, lungs, eyes, lips, ears, intestines, and kidney are occasionally 
added. 
Locomotion. One of the earliest signs is a sense of extreme 
weight in the lower extremities, a fatigue having no relation to 
the work done. The strongest and most experienced walkers 
can only take a few steps at a time. Hot only walking, but 
any form of exercise becomes almost impossible. 198 
GASEOUS MATTER. 
Innervation. Fearful headache, as though the head were bound 
in a fillet of steel; intellectual depression; buzzing in the ears; 
dulness of taste and smell; sometimes dimness of vision, som- 
nolence, and syncope. 
Aeronauts experience similar symptoms. The moral faculties 
suffer before the physical; memory is obscured; the manage- 
ment of the balloon.is forgotten ; the members fall asleep. At 
great altitudes insensibility often conies on suddenly. 
233. Theoretical Explanations of Mai des Montagnes.—Of these 
there are two groups; one presents so curious a list of absurdities 
that we quote it. The other deals with the mechanical, physical, 
and chemical effects which attend changes in barometric pres- 
sures. 
In the first category we may mention pestilential exhalations, 
electricity, deficiency of oxygen, fatigue, cold, diminution of the 
weight supported by the body, escape of gas from the blood, 
dilatation of intestinal gas, relaxation of the hip-joint (Hum- 
boldt), excess of carbonic acid. From these fanciful explana- 
tions, we turn to the 
234. Theory of M. Jourdanet, who reasoned that whatever 
might be the affinity of blood corpuscles for oxygen during 
respiration, it was evident that in air po-or in oxygen the 
amount of that gas taken up by the blood would be less. In 
the rarefied atmospheres of mountains there is less weight of 
oxygen in each inspiration, therefore the blood is not so rich in 
that gas as at the sea level. This poverty in oxygen is exactly 
the same as though the number of blood corpuscles was re- 
duced, and the consequences are also the same. An ascension 
of 10,000 feet gives a barometric deoxygenation of the blood, 
just as bloodletting gives a corpuscular deoxygenation, and 
when pushed to an extreme they are alike fatal. At moderate 
altitudes, like the great Mexican plateau, the difference in rich- 
ness in oxygen is not sufficient to attract attention under ordi- 
nary conditions; but when disease attacks the people of these 
plateaus, the physician quickly recognizes the fact that it 
is invariably of an anaemic type, the result of deficient supply 
of oxygen. 
235. Balloon Sickness presents the same symptoms as Mai des 
Montagnes. It comes on in aeronauts later than in those who 
ascend mountains, because the former reserve the force which 
the latter have spent in making the ascent. A similar lack of 
force results from a sleepless night, indigestion, or any indis- 
position. The tired man and the sick man are both subjects 
for Mai des Montagnes or balloon sickness. EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
199 
Croce-Spinelli and Sivel, in their first high ascent, observed 
that at an altitude where the mercury stood at 300 millimetres, 
they experienced more discomfort than when in Bert’s re- 
ceivers. This they attributed to the greater amount of muscu- 
lar exertion, to the great depression of temperature, and the 
length of their sojourn in the attenuated strata. Regarding 
inhalation of oxygen at great altitudes, they say “we direct 
special attention to the favorable effects of the respiration of 
oxygen under diminished pressure. Return of strength and 
appetite, diminution of headache, reestablishment of clear vision, 
and coolness of nerves.” All these phenomena they had already 
observed in Bert’s cylinders. 
236. Bert’s Rarefaction Cylinders.—For the apparatus by which 
he conducted his researches, M. Bert tells us he was indebted 
to M. Jourdanet. For diminished 
pressures the apparatus consisted of 
two large cylinders which communi- 
cated by a door. They were nearly 
seven feet in height and more than 
three feet in diameter. The exhaust- 
ing pump was driven by a Lenoir 
gas engine. A pressure of 250 milli- 
metres could be obtained in twenty 
minutes. 
Tig. 90. 
In this apparatus Bert verified the 
symptoms which have been given 
as mountain sickness and balloon 
sickness. It was shown that they 
priginated in a deficiency of oxygen 
in the blood, caused by its dimin- 
ished tension in the air respired. Re- 
garding balloon sickness, he says : 
“At half an atmosphere of pressure 
everything must be doubled to secure 
Rarefaction cylinder. 
the same introduction of oxygen as at the level of the sea. 
only must the respiratory movements be increased in force 
an(t rapidity, but the heart beats must be doubled in force 
aud intensity. This is clearly impossible, consequently the per- 
centage of oxygen in the blood diminishes, on this there fol- 
lows diminished activity of the respiratory muscles; the ampli- 
tude of the inspiratory act becomes less and less. The same 
happens with the beating of the heart. The pulsations may 
.e more frequent, but the force of its action is greatly dimin- 
ished. In like manner the functions of every organ are inter- 
tered with.” 200 
GASEOUS MATTER. 
237. Air in Caves.—lt sometimes happens that in caves and 
mines in which sulphides are present, the oxygen of the air 
uniting with the sulphur in the pyrites undergoes a gradual re- 
moval, and the composition of the air becomes seriously altered. 
As an example of this the following analysis of the air of a 
deep cave near St. Maurice is given: 
Nitrogen ...... 
Oxygen ....... 
. 15.83 
Carbonic anhydride .... 
1 99 
In this case, the tension of the oxygen is about 15 compared 
with that of air at 21. It is equivalent to an elevation of 
6500 feet, and not unfrequently produces symptoms similar to 
those of Mai des Montagues. It is recorded that in a copper 
mine near Cam-Brea the oxygen tension is only 14.5. 
238. Death from Diminished Air Pressure.—ln ordinary air and 
in mixtures, death ensues when the tension of the oxygen is 
reduced below 4, or for normal air to a pressure of one-fifth 
of an atmosphere. With diminished pressure, the percentage 
of gas in the blood diminishes also, but in a little less propor- 
tion than the law of Dalton would show. The blood also loses 
relatively less oxygen than carbonic acid. 
An animal placed in a closed vessel, an animal respiring in a 
current of air the proportion of oxygen in which is steadily di- 
minishing, an animal respiring air the pressure on which is 
steadily diminishing: all three die in the same manner, viz., by 
true asphyxia. 
Increase of Pressure Above One Atmosphere. 
239. While the earth presents great elevations, by the ascent 
of which the effects of diminished pressure may be observed, it 
does not present depressions of sufficient extent to enable us to 
study those of increased barometric pressure. The only depres- 
sions of any consequence are the Dead Sea and the Caspian 
region; in these the depression is so insignificant that it may be 
disregarded. Mines and caves might give greater tension by 
increased pressure, but any increase in these instances is apt to 
be compensated by a poverty in oxygen (287). 
The actual conditions under which increased pressure arises 
are consequently artificial. They are Ist. Descent in the diving- 
bell; 2d. Descent in the diving-dress; 3d. Working in cais- 
sons used in construction of piers for bridges, in deep water; 
4th. Sojourn in the condensing cylinders of aeropathic estab- 
lishments. EFFECTS OF VARIATIONS IN DENSITY OF AIR, 
201 
240. Respiration of Pure Oxygen.—Though oxygen is the con- 
stituent of air which supports the function of respiration, it 
has been shown by direct experiment that hot-blooded animals 
can endure the respiration of pure oxygen but for a compara- 
tively brief time. 
In natural respiration the oxyhsemoglobin in the arterial blood 
is never completely saturated with oxygen. In respiration of 
pure oxygen it becomes in time completely saturated, and the 
venous blood also takes on the arterial hue. When this occurs 
the functions of the body are seriously disturbed. 
In the case of respiration of pure oxygen, the tension of the 
gas is 100. If the gas be breathed under a pressure of three 
atmospheres, the tension is equivalent to 300, and the gas acts 
as a virulent poison, quickly producing convulsions which ter- 
minate in death. 
By increasing the pressure on air to about five atmospheres, 
its tension becomes 100, and its physiological action when 
breathed is the same as that of pure oxygen. Increasing the 
pressure rapidly to 15 atmospheres, the tension becomes 300, 
and it has the same poisonous action as oxygen under a pressure 
of th ree atmospheres. 
Air below a pressure of five atmospheres may be breathed 
for a short time, and if the pressure is only two or three atmos- 
pheres, it may be respired for a considerable time, and often 
with excellent effect. We may, therefore, study the action of 
compressed air in two states: Ist. Under moderate pressures; 
2d. Under high tension, or over five atmospheres of pressure. 
Physiological Action of Moderately Condensed Air.—Under 
a tension of from 30 to 60, the following conditions appear. The 
bst is taken from the experiments of Vivenot. 
Ist. Uoises in the ear, arise also in decompression, from stop- 
pages in the Eustachian tube; are relieved by swallowing, and 
by blowing strongly into the tube, at the same time holding the 
nose and shutting the mouth. 
. 2d. Change of voice, higher note; nasal, difficult pronuncia- 
tuni; impossible to whistle or hiss; sometimes stuttering. 
3d. Smell, taste, and touch obscured. 
4th. Expansion during inspiration, and compression in ex- 
halation increased. 
. sth. Diminution in abdominal convexity by compression- of 
intestinal gas. 
6th. Diaphragm and base of lung lowered. 
tth. The lung1 during inspiration, as well as expiration, in 
front of the heart. 
Bth. Hence diminution of cardiac impulse on palpation, and 
diminution of its sounds on auscultation. 202 
GASEOUS MATTER. 
9th. Vital capacity of the lungs increased. 
10th. Return to normal pressure; the vital capacity falls below 
the normal. The lung does not for a time regain its primitive 
volume. 
11th. Repeated sojourns in the apparatus each day cause in- 
creased pulmonary capacity. After 3 months of air baths of 
one-half hour each day, pulmonary capacity was increased one- 
quarter without any diminution of contractile power in the lung. 
12th. The habits acquired by the diaphragm and thorax con- 
tinue after completion of the experiments. 
13th. These increments are common both to extreme and 
ordinary respiration. 
14th. Respiration less frequent by 1 to 4 movements per 
minute. 
15th, 16th, 17th, 18th. Repeat for frequency what has been 
said for depth from 10 to 13. 
19th. Inspiration is quicker, expiration slower; at first quick, 
then so slow as to have the appearance of a pause. 
20th. Increase in proportion of carbonic acid. With 3.7 
atmospheres there is 22 per cent, more of carbonic acid than at 
the normal pressure. 
21st. This augmentation is not in the same ratio of increase 
as that of pulmonary capacity. 
22d. It is common both to forced and tranquil respiration. 
23d. Comparing the increase of carbonic acid with the di- 
minished frequency of respiration, it is evident that the increase 
is due to the greater absorption of oxygen. 
24th. Consequently after a series of sojourns in condensed 
air, the venous blood becomes clearer, the temperature rises, 
muscular force is increased, hunger is greater. Though more 
nutriment is taken, the body becomes lean. If, on the contrary, 
the pressure is very moderate and a great deal is eaten, a person 
may fatten. 
25th. Frequency of pulse diminishes 4 to 7 in the minute, 
the diminution being greater when there has been an abnormal 
acceleration. 
26th. Return to air restores the normal rhythm of the pulse. 
27th. If the frequency of pulse has been caused by respiratory 
trouble, a permanent lowering follows treatment by compressed 
air. 
28th. Diminution in frequency of pulse seems to be merely 
a result of the mechanical action of compressed air. The in- 
creased pressure increasing the resistance to the arterial waves 
from the heart, the number of pulsations is consequently di- 
minished. 
29th. The curve of the radial pulse presents changes in form. 
Its height diminishes, the line of ascent is less rapid, more EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
203 
oblique, the summit straight or slightly convex. There is dimi- 
nution in the capacity of the vessels and of the quantity of 
blood they contain; increase in the systole of the heart, and 
greater obstruction in the capillary circulation. 
30th. With return to normal air, sphygmographic tracings 
assume their normal character. 
31st. The radial pulse is changed to the touch; it becomes 
small, thread-like, almost imperceptible. 
32d. Sphygmographic curve during increase of pressure is 
above that obtained in normal air. During this phase there is 
increase in the total pressure of the blood. 
33d. Diminution in calibre of the vessels of conjunctiva, 
retina, and in the ear of rabbits; decolorization of the pupil 
and iris in white rabbits. The pallor of the men who work in 
compressed air proves the repulsion of the blood from the surface 
to the interior organs. 
34th. Hence arise diminution in the intraocular pressure, 
contraction of the pupil, pulsation in the ear and jaw, pallor of 
tympanic membrane. 
35th. Introduction of a manometer into the jugular vein shows 
that the venous pressure diminishes in compressed air. 
36th. Temperature increases in the armpit. If exposure to 
compressed air be of sufficient duration, temperature in the 
rectum also increases. 
37th. Blood leaving the periphery of the body, many of the 
internal organs are congested, and, hence, the symptoms 
connected therewith. 
38th. Compression of air causes no direct evil results until it 
reaches four and a half atmospheres. 
39th. In relaxing the compression, if the release is too rapid, 
serious consequences arise. 
40th. Sojourn in compressed air is less dangerous than re- 
turn to ordinary air. This produces congestions, hemorrhages, 
pains, and derangements of the circulatory system. The evolu- 
tion of gas in this system can even bring on sudden arrest of 
circulation and death. 
41st. The only way to treat these accidents is by an instant re- 
turn to compressed air. 
In 28th, 29th, 33d, 34th, 37th, Yivenot confounds results with 
theory of effects of pressures; with the exception of the error 
thereby introduced, the summary gives an excellent review of 
the effects of moderate pressure. 
To this list of symptoms M. Bert adds the following state- 
ments : With air under pressures less than five atmospheres, 
the oxyhaemoglobin is never completely saturated with oxygen, 
though it becomes richer therein as the pressure surpasses the 
normal. These moderate pressures especially interest the phy- 204 
GASEOUS MATTER. 
sician and the hygienist, since they are employed in therapeutics 
and in various industries. 
What appears to be most interesting is the determination of 
the tension at which the maximum of intra-organic oxidation 
is attained. Direct determinations of the oxygen absorbed, of 
the carbonic acid and urea excreted in a given time, show that it 
is in the vicinity of three atmospheres or a tension of about 
sixty of oxygen. Indirect researches on the rapidity of putre- 
faction give the same result. 
In the higher animals organic oxidations augment in intensity 
as the point of saturation of oxyhsemoglobin is reached. Ob- 
servations on inferior creatures, as tadpoles and larvge, kept for 
some time under oxygen tensions between twenty-one and one 
hundred, show that though there may be improved rate in 
nutrition, there is a departure from the normal character or 
condition of the part. Germination of seeds is never better 
accomplished than under the normal pressure and tension of the 
air, or in a similar mixture of oxygen and hydrogen. 
Though the number of pulsations is diminished, and the 
maximum lung capacity is increased, yet the volume of air 
which traverses the lungs in a given time does not change 
sensibly in compressed air. 
The greatest lung capacity is produced by the mechanical 
compression to which the intestinal gases are submitted. Arterial 
pressure is augmented. 
The mechanical effects of pressure on intestinal gas diminish as 
the pressures increase, following the law of Mariotte. Passing 
from one to two atmospheres, the diminution is one-half; to 
four, to one-quarter; and so on. 
Though Vivenot’s theory of the action of compressed air in 
producing pallor is hardly tenable, yet it is not the less true 
that the blood is driven from the periphery to the central organs. 
From this arise important modifications in circulation and in 
the nutrition of different parts of the body; modifications from 
which therapeutics have been able to draw profit. 
In closing this article, we are constrained to mention 
Bouchard’s ingenious explanation of the pallor arising in com- 
pressed air. He attributes it to compression of the intestinal 
gases, the elasticity of the abdominal walls exerting a suction 
action in consequence thereof. 
242. Action of Oxygen Under High Tension,—The discovery of 
the poisonous action of oxygen under high tension is very in- 
teresting. Experiments on vegetables and animals, on air- 
breathing and water-breathing creatures of simple or of com- 
plicated structures, have shown in the most satisfactory manner 205 
EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
that if oxygen departs in its tension to any great extent from 
that which it has in air, death rapidly supervenes. 
Convulsions come on in hot-blooded animals quickly in air at 
twenty atmospheres of pressure; with great rapidity at twenty- 
five atmospheres; but evil effects are produced at as moderate 
pressures as six atmospheres. As is shown in Fig. 91, the 
Fig. 91. 
Dog poisoned by oxygen. 
rigidity arising from the convulsions is so great that the animal, 
when held by one foot, stands out.as stiff as though it was 
made of wood. 
243. Oxygen Poisoning.—lst. Oxj'gen acts as a poison when 
the quantity in the blood reaches thirty-five volumes in one 
hundred, the normal being fifteen to twenty. 
2d. The poisoning is characterized by convulsions which 
resemble those of tetanus and epilepsy, also those produced by 
strychnine and phenic acid. 
3d. These convulsions are quieted by chloroform, and are 
caused by an exaggeration of the excitor motor power of the 
spinal cord. 
4th. They are accompanied by more or less diminution in 
internal temperature. Regarding this, M. Bert says : “ When 
I for the first time saw a sparrow under the influence of con- 
densed oxygen and suffering violent convulsions, I thought that 
the intra-organic oxidations must produce exaggeration in the 
temperature. Imagine my surprise when the thermometer 
showed exactly the opposite result.” 
Microscopic germs which produce various fermentations die 
when they are submitted to the action of compressed oxygen; 
putrefaction is arrested. 206 
GASEOUS MATTER. 
At 6 atmospheres of pressure, normal air will introduce into 
the blood sufficient oxygen to saturate the haemoglobin, which 
is a dangerous condition. 
Above this pressure any addition of oxygen is as oxygen dis- 
solved in the plasma, in the corpuscles, and even in the tissues. 
Oxygen in this state quickly suspends all further action of the 
oxygen of the oxyhsemoglobin. The globules cannot surrender 
their oxygen, and are condemned to a perpetual saturation. 
Nothing is more extraordinary than this action by presence of 
dissolved oxygen, stopping, as it does, all further combinations 
instead of promoting them. 
This result occurs in all living creatures as well as in red- 
blooded animals. The action is permanent. It is a definite 
death. A grain that has been in a vacuum will germinate when 
it is planted in air. A dog which has been asphyxiated by 
diminution of pressure, will revive when restored to the air. 
But a grain which has been kept in compressed oxygen, or a 
dog which has breathed compressed oxygen to the production 
of continued convulsions, never revives. They cannot carry on 
the processes of life. It is as though the compressed oxygen had 
developed some deadly poison, which no remaining vitality can 
overcome. 
244. Relation of Animal Tissues to Oxygen.—Pasteur’s experi- 
ments have shown that microscopic beings may be divided into 
two groups: One consuming free oxygen, aerobics; the other 
deriving their oxygen from organic matters, which they decom- 
pose, anaerobies. The latter avoid free oxygen. 
The tissues of animals are of the anaerobic nature; they obtain 
their oxygen from oxyhsemoglobin, but when this is saturated 
with oxygen, and free oxygen is dissolved in the plasma and in 
the tissues, they become sick and die if the experiment has suffi- 
cient duration. 
It is the nervous system which succumbs first under oxygen 
poisoning. A dog placed in compressed air, first has convul- 
sions, and these disturbing the harmonies of the vital mechanism 
cause death before the other anatomical elements are acted 
upon. Action on the latter, however, is only a question of time. 
The blood of a dog which has died of oxygen convulsions will 
reanimate another dog which is exsanguiued; but if a portion of 
this same blood is still further submitted to the action of com- 
pressed oxygen, it will kill a healthy animal into whose circula- 
tion it is injected. 
245. Death from Increased Pressure.—Experiments made with 
various gaseous mixtures, more or less rich in oxygen, either EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
207 
with or without removal of carbonic acid by potash or other 
alkali, confirm the following general statements. 
The tension of a gas being represented by its percentage mul- 
tiplied by the pressure, death supervenes: 
Ist. When the tension of carbonic acid rises to 26 (whether 
the barometric pressure he above or below the normal). In this 
case the mixtures respired must be surcharged with oxygen. 
The same applies to other poisonous gases—e.g., carbon mon- 
oxide and sulphuretted hydrogen. 
2d. When the tension of oxygen reaches 800 (independent 
ot any special percentage and pressure). In the case of pure 
oxygen it is when the pressure becomes 3 atmospheres. 
An animal respiring air in which the percentage of oxygen is 
steadily increasing, and another respiring air in which the pres- 
sure is steadily increasing, both show the same symptoms. In 
pure oxygen a pressure of 8 or 4 atmospheres, in the air a pres- 
sure of 20 atmospheres, bring on oxygen poisoning. 
246. Therapeutical Effect of Respiring Oxygen.—From the time 
ot Priestley many have advocated the respiration of vital air or 
oxygen, and it was for a time employed; but having fallen into 
disuse, it has only recently been brought forward again as a 
therapeutical agent. 
As ordinarily prescribed for patients, it is given nearly pure, 
-the maximum quantity administered in France is 30 litres, 
which are consumed in from five to seven minutes. This method 
labors under two objections: Ist. We cannot expect that any 
permanent relief is to be obtained by a slight increase of the 
oxygen in the blood during ten minutes or so. 2d. As the 
oxygen is pure, it is quite possible that a sufficient quantity may 
be administered to over-pass that best calculated for the maxi- 
mum of intra-organic oxidations. So shock may be produced, 
which acts in the opposite manner to that intended. 
.If is to be hoped that hereafter pure oxygen will only be 
given in alarming cases of asphyxia, as in poisoning by carbonic 
oxide or by sewer gas, where there is but little time to act. The 
proper method is to employ an air containing about 60 per cent. 
°t oxygen, and to continue the inhalation for an hour. 
In the treatment of a chronic affection like anaemia, the better 
way is for the patient to respire an air containing about 25 or 
oO per cent, of oxygen, for a couple of hours every day. For 
fins time, there would be required about a cubic metre of the 
mixture. 
247. Therapeutical Uses of Compressed Air.—Our knowledge of 
he use of compressed air as a therapeutical agent is largely due 208 
GASEOUS MATTEE. 
to Junod, ot Paris; Tabarie, of Montpellier; and Pravaz, of 
Lyons. As the value is better appreciated every day, it will 
doubtless before long be more generally employed. More than 
twenty establishments are nowin operation in various European 
cities. Managers of these employ different degrees of compres- 
sion, varying from 10 to 30 centimetres of mercury. They re- 
port excellent results in the treatment of emphysematous asthma; 
chronic bronchitis; chloro-ancemia; passive hemorrhages. It is both 
tonic and sedative in its effects. 
Fig. 92. 
Aero-therapeutical establishment at Milan, 
In asthma moderately compressed air acts beneficially, chiefly 
for mechanical reasons. In anaemia, on the contrary, its favor- 
able action is owing to the better saturation of the oxyhsemo- 
globin with oxygen. This is evident from the fact that in the 
latter case equal advantages may be obtained by the respiration 
of air containing a greater percentage of oxygen. In asthma, 
though the increase in per cent, of oxygen improves the condi- 
tion of the patient, the amelioration is small compared with 
that obtained by breathing the compressed air of compression 
cylinders. 
There has been thus far too much timidity in the therapeutic 
use of compressed air. In the medical apparatus the extreme 
pressure has hardly ever reached two atmospheres. It might 
be pushed without inconvenience to three atmospheres—to the 
point, in fact, of maximum of intraorganic oxidations. 
Pravazhas employed compressed air in surgical operations. It 
is surprising that its application for the reduction of strangulated 
hernia has never been attempted where the intestine contains 
so much gas as to hinder reduction. A pressure of an addi- 
tional atmosphere would diminish the gas to one-half, which 209 
EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
would certainly be an advantage; and taxis might be commenced 
in the compression cylinders. 
In certain tympanitic affections where suffocation is imminent, 
relief quickly follows a brief sojourn in a compression cylinder. 
In this case the action is mechanical. 
The employment of pressures beyond three atmospheres for 
medical purposes is also worthy of trial; under these conditions 
there is diminution of oxidation. This offers an antiphlogistic 
remedy the value of which has not yet been determined. Phy- 
sicians having charge of workmen in the caissons used in bridge 
building have established the fact that oxygen at high tension 
exercises a favorable action on inflammatory phenomena. 
248. Hygienic Management of Compressed Air.—Men in the 
caissons used in construction of piers of bridges have not yet 
been submitted to pressures where compression of the air is 
dangerous. The greatest pressure thus far attained was in the 
bridge at Saint Louis, where it was nearly four and a half 
atmospheres. Amemia has appeared as a consequence of such 
severe pressure, but the complication of conditions is so great 
that it is difficult to affirm anything with certainty. 
The necessities of engineering may at some future time compel 
a resort to pressures greater than five atmospheres. The con- 
sequences to workmen will then become exceedingly grave, 
Pven a brief exposure to ten atmospheres would often be 
attended by sudden death. 
If the construction of a bridge requires that workmen must be 
exposed to pressures of more than live atmospheres, and its im- 
portance is so great that expense is a minor affair, the result may 
be accomplished by the employment of an air containing a smaller 
percentage of oxygen than normal atmospheric air; an air so adjusted 
that under the pressure to be employed the oxygen tension shall 
be between 21 and 60. 
Air of this character may readily be obtained by the apparatus 
pf Tessie du Motay, in which oxygen is prepared by separating 
!t from atmospheric air. Air voided from this machine consists 
chiefly of nitrogen, most of the oxygen having been removed. 
T»J adding to this nitrogen air proper proportions of atmos- 
pheric air, mixtures can readily be obtained which would at 
various pressures provide an atmosphere having an oxygen ten- 
sion similar to that of normal air. Hydrogen also might be em- 
ployed for the dilution of ordinary air. 
In preparing such mixtures, if it is desired to have the oxygen 
al the same tension as in air, all that is required is to divide the 
percentage of oxygen in air by the atmospheres of pressure. 
I or ten atmospheres of pressure the mixture would contain two 
Per cent, of oxygen. In practice it would doubtless be better 210 
GASEOUS MATTER. 
to use an air having double the oxygen tension of ordinary air; 
that is, 40 instead of 21. Under these conditions the mixture 
should contain four per cent, of oxygen. This under a pressure 
of ten atmospheres would give the tension of 40 required. 
249, Impurities in Compressed Air.—Air in caissons or tubes 
of compression is not pure. At pressures of three and a half 
atmospheres in the caissons of the bridge at Kehl, M. Bucquoy 
found 2.37 per cent, of carbonic acid gas. In this case work- 
men were breathing air which at normal pressures would contain 
carbonic acid gas of a tension equal to 8.80, which would be 
very dangerous. 
Hot only carbonic acid, but also carbon monoxide arises from 
the incomplete combustions attending the use of artificial lights, 
or following explosions necessary in mining. G-ases emitted 
from the strata traversed are also to be considered; in the com- 
pressed state many of these doubtless have their noxious power 
greatly increased. The proper remedy for all such possible 
contingencies is thorough ventilation. 
250. Effects of Decompression.—The difficulties' of compression 
having been conquered, it remains to deal with those of decom- 
pression or rarefaction, from the highly condensed air to that of 
the normal atmosphere. 
It is obvious that under high pressures a quantity of nitrogen 
will be dissolved in the blood, and as reduction of pressure takes place, 
this will assume the gaseous state. Even with ordinary air in the 
compressed state accidents have arisen from this cause. It is, 
therefore, evident that with condensed atmospheres so rich in 
nitrogen, the complication would be exceedingly grave, and 
danger imminent. 
This difficulty is to be met by a gradual relaxation of pressure. 
Even when the pressure does not exceed two atmospheres it 
is well to be careful, though there is rarely immediate danger. 
Workmen should be habituated to a gradual relaxation of pres- 
sure. 
Between two and three atmospheres it is best to allow half an 
hour for the relaxation of pressure. Between three and four 
atmospheres an hour should be allowmd, and the slowness of 
relaxation assured by a properly arranged stopcock. 
At this point a new difficulty arises and a very grave one. It 
is the intense cold which attends the expansion of air. This must 
be met by warm dry clothing, and the presence of steam heaters 
in the chamber. 
Another method for meeting this trouble is the use of two 
chambers of decompression both properly warmed, workmen EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
211 
passing from that of 8 to that of 2 atmospheres remaining about 
a quarter of an hour in each. 
The longer men have been in the tubes the slower should 
the decompression be, for the tissues having absorbed nitrogen, 
time must be given for it to pass first into the blood and then 
into the atmosphere. It is best not to oblige the workmen to 
work for long terms, and they should only labor one term in 
a day. 
In like manner, divers working about wrecks and in pearl 
and sponge fisheries, where the depth exceeds 100 feet, should 
be provided with means to enable them to return gradually to 
ordinary pressures. 
251. Nature and Treatment of Decompression Accidents.—In spite 
of all precautions accidents occur. Gas may be freed in the 
vicinity of the heart, in the heart, in the spinal cord. What 
then is to be done ? Oxygen should he inspired as quickly as possible. 
Tor this purpose a supply should always be at hand compressed 
111 steel gas holders. The patient should first be submitted without 
losing a moment to air more compressed than that from which he has 
come, so as to insure the return of the free gas to the state of 
absorption in the tissues. Then the pressure should be relaxed 
with- extreme slowness. 
When compression has exceeded four atmospheres it is always 
prudent to respire oxygen immediately on returning to the 
atmosphere. Especially should this precaution be taken by 
divers, even though there is no appearance of trouble. 
It paraplegia appears, recompression should at once be re- 
sorted to with respiration of oxygen; especially when the trouble 
appears some time after rhe return to air, should these be 
promptly used. It is no longer a probability of obstruction in 
the pulmonary circulation, hut a certainty of the formation of a gas 
oubble in the vessels of the spinal cord, and to remove this compres- 
sion must be resorted to, and thereby enable the blood to reab- 
sorb it. 
Workmen in compressed air suffer more or less from sudden 
expansion of intestinal gases on leaving the caissons. The froth 
termed in the liquids of the digestive apparatus when pressure 
18 too quickly relieved, occasionally causes indigestion. 
252. Relations of Barometric Variations to Natural History.—ln 
dosing his investigations on the physiological effects of varia- 
tions in pressure, M. Bert says: 
The effects of diminution of pressure on the geographical 
distribution of plants and animals, have been demonstrated. 
Ihe study of nature does not afford any equivalent illustrations 
°t the effects of increased pressure, at least as far as aerial 212 
GASEOUS MATTER. 
creatures are concerned. Regions lower than the level of the 
ocean, like the Caspian and Dead seas, have only slight depres- 
sion and few inhabitants. We should expect the case to be very 
different with creatures which live at depths of 4000 or 6000 
metres in the ocean. 
The Bathybius, which has played so important a part in 
modern theories of nature, and which some think belongs to the 
mineral kingdom, does not appear to suffer any mechanical in- 
convenience from the enormous pressure to which it is constantly 
submitted, and with which its parts are in equilibrium. It would 
be entirely different if a creature accustomed to live at 2000 
metres was suddenly translated to a depth of 4000 metres. The 
increase of pressure would produce a diminution in the volume 
of its body which could scarcely happen without injurious con- 
sequences. In like manner, a creature transferred from 4000 to 
2000 metres of depth, would undergo a dilatation that would 
have evil consequences. It is this dilatation that in all proba- 
bility causes the death of so many creatures brought from great 
depths in dredging operations. 
Compression and relaxation of pressure produce profound 
mechanical effects upon water creatures which have closed 
swimming bladders. In this case, as M. Moreau has shown, any 
sudden variation of pressure, by its action on their swimming 
bladder by diminishing its volume, can so modify their mean 
density as to carry them many metres above or below the zone 
in which they ordinarily find their habitat. Sudden exhaustion 
forces them to the surface, the swimming bladder dilating even 
to bursting. In the other case increase of density causes them 
to sink indefinitely in the ocean abysses, the bladder ever con- 
tracting, and the density of their bodies increasing in the same 
ratio as that of sea-water. Ordinary variations of barometric 
pressure are so limited that they do not appear to have any 
serious influence upon fishes. Indeed, if sufficient time be given, 
these creatures can increase or diminish the amount of gas in 
the air-bladder, either secreting oxygen from the blood or absorb- 
ing it from the bladder, as occasion requires. They thus adapt 
their size and density to such moderate variations of pressure as 
ordinarily arise. 
When compressed oxygen is forced into water under high 
pressure, aquatic creatures placed therein die. To produce this 
effect, the gas must be compressed independently of any pressure 
the column of water may bring to bear upon it. Whatever the 
depth of the column of sea-water may be, it cannot increase the 
proportion of dissolved oxygen. This fact has been established 
beyond a doubt by analyses of samples of water taken at great 
depths. Indeed, there is, according to the analyses of Lant EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
213 
Carpenter, a less percentage of oxygen in sea-water taken from 
great depths than in that at the surface. 
Sea-water contains an average of 2.8 volumes of gas to 100 
of water. This gas has the following composition : 
At surface. 
At great depth. 
Oxygen . 
. 25.00 
19 53 
Nitrogen ..... 
. 54.21 
62.60 
Carbonic acid gas 
. 20.84 
27.87 
Showing diminution both in oxygen and in nitrogen; from this 
two consequences ensue: Ist. A sojourn at great depths does not 
bring peril from increase of tension of the dissolved oxygen. 
2d. Rapid relaxation of pressure does not produce evil effects, 
smce there is no excess of nitrogen dissolved in the fluids or 
tissues. Free gas is never found in the tissues of a creature 
brought from great depths. 
It is a very different matter if there is a sudden influx of con- 
densed gas at the bottom of a sea, even at the moderate depth 
pt one hundred metres. Then the conditions for production of 
increased tension of the dissolved gas exist, and every moving 
creature that comes within its reach is destroyed. It was doubt- 
less owing to this cause that in the month of March, 1882, such 
extensive areas of the North Atlantic were covered with dead fish. 
If we consider the role which oxygen has played in past 
geological ages, we cannot fail to perceive that barometric pres- 
sure has acted a most important part in modifying the character 
°f life on the surface of the globe. 
In the first ages of our planet the tension of oxygen in the 
atmosphere must have been much greater than at present, and 
f°r two reasons: Ist. The thickness of the atmosphere was 
greater. 2d. The percentage of oxygen also was greater, since 
the rocks were not yet cool, nor had they, in many cases, reached 
their maximum of oxidation. At each successive epoch the 
atmosphere penetrated deeper and deeper into the soil, and the 
niass of oxygen diminished in proportion. We may, therefore, 
says M. Bert, imagine that there was a time when living creatures 
could not exist on the earth on account of the great tension of 
the oxygen of its atmosphere, and that finally the time arrived 
a hen, by reduction of its tension, their existence became a 
Possibility. 
There are, he adds, three conditions which practically control 
the existence of life. They are temperature, tension of oxygen, 
And of carbonic anhydride. Creatures which resist the greatest 
extremes of this triumvirate belong to the group of vibrios. It 
"as probably in them that life made its advent, and in them it 
WIH Toake its exit from our planet. 214 
GASEOUS MATTER. 
/ / 
253. Bert’s Resume of His Results.—To put the subject of physi- 
ological action of variations in tension of oxygen in as clear 
and concise a form as possible, Bert gives a resume of his work, 
of which the following is a condensation : 
а. Diminution of barometric pressure acts on living creatures 
by decreasing the tension of oxygen in the air they respire and 
in their blood (anoxyhemie of Jourdanet), and thus menacing 
them with asphyxia. 
б. Augmentation of barometric pressure acts by increasing 
the tension of the oxygen in air and in blood. 
Dp to about three atmospheres, increase of tension produces 
greater activity in intra-organic oxidations. 
Beyond five atmospheres the intensity of oxidation dimin- 
ishes, it changes in its character, and at last with sufficient in- 
crease of pressure ceases altogether. 
Consequently all living things, aerial or aquatic, animal or 
vegetable, complex or single celled; all anatomical elements, 
whether isolated (as blood corpuscles), or grouped in tissues, 
perish, with greater or less rapidity, when placed in air suffi- 
ciently compressed. The only exceptions to this law are the 
reproductive corpuscles of certain microscopic creatures. In 
higher animals death is preceded by tonic and clonic convul- 
sions of extreme violence. 
In vertebrates, sudden accidents produced by great tension in 
£he oxygen do not appear until the haemoglobin is saturated 
with oxygen, and this gas is brought in contact with the tissues 
in a state of simple solution. One can then say that the ana- 
tomical elements are anaerobies. 
c. The ferment diastase, venomous poisons, and vaccination 
virus resist the action of compressed oxygen. 
d. The evil effects of diminution in atmospheric pressure are 
effectually prevented by the respiration of an air sufficiently 
rich in oxygen to maintain this gas at its normal tension of 20.9. 
The effects of increase in pressure can, in like manner, be 
avoided by a sufficient diminution in the proportion of oxygen 
to a tension of 20.9. 
e. In a general way, respirable and noxious gases (oxygen and 
carbonic acid, for example) act on living beings according to the 
tension they possess in the atmosphere containing them. This 
tension is determined by multiplying their percentage by the 
barometric pressure. Increase in one of these factors may be 
compensated by diminution in the other. 
/. In animals with closed air-bladders (as ordinary fishes) or 
those with sacs which only communicate with air when empty- 
ing (intestinal canal of aerial vertebrates), and also those with 
sacs which communicate with air both during compression and EFFECTS OF VARIATIONS IN DENSITY OF AIR. 
215 
relaxation (lungs of aerial vertebrates), decrease or increase of 
pressure can only have physico-mechanical effects. 
g. Sudden release from pressure of many atmospheres, with 
few exceptions as in /, causes evolution of free nitrogen, which 
was previously dissolved in the blood and tissues. 
h. Wild animals all over the globe are accommodated to the 
tension of oxygen under which they live. Decrease or increase 
of pressure from the normal affects them injuriously when they 
are in health. 
. Therapeutics might draw a useful lesson from these modifica- 
tions in pathological conditions. 
l- Barometric pressure and percentage of oxygen in air have 
not always been the same. The tension of this gas has, and 
without doubt will continue to diminish. That is a factor of 
which no count has yet been taken in biological speculations. 
The difference in its powers under different tensions leads to 
the supposition that the microscopic creatures which were the 
first to appear will be the last to pass away when life is extin- 
guished from the insufficiency of oxygen for the continuation of 
its support. 
J• The common statement is not true that plant life must have 
appeared on the globe before animal life, in order to purify it 
from the great quantity of carbonic acid gas it contained. The 
fact is that germination, except in the case of a few moulds, 
cannot take place in air sufficiently charged with carbonic acid 
gas to be fatal to a hot-blooded animal. 
It is not right to explain the priority in appearance of reptiles 
before hot-blooded animals, on the hypothesis that they can 
qreathe an air richer in carbonic acid gas than animals can. 
i he truth is, reptiles succumb to this gas more readily than either 
birds or mammals. SECTION V. 
ULTRA-GASEOUS OR RADIANT 
MATTER. 
CHAPTER XVII. 
GENERAL AND SPECIAL PP.OPEETIES OP RADIANT MATTER. 
Idea of radiant matter descended from Faraday—Crooke’s argument for radiant 
matter—Crooke’s explanation of tRe kinetic tßeory of gases—Action of 
radiometer explained—Extent of mean free patß of the molecules in radiant 
matter—Radiant matter exerts pßosgenic action where it strikes—Proceeds 
in straigßt lines—lntercepted by solid matter casts a shadow—Radiant matter 
striking a solid produces change therein—lt exerts mechanical action where 
it strikes—ls deflected by the magnet—Radiant matter produces heat when 
its motion is arrested—The molecule the true matter—The absolute vacuum 
tube. 
The following account of ultra-gaseous or radiant matter is an 
abstract of a lecture given by Professor Crookes before the 
British Association, on August 22, 1879, and of articles pub- 
lished since that date. 
254. dea of Radiant Matter Descended from Faraday.—ln a 
lecture delivered by Faraday, in 1816, we find the first use of 
the term radiant matter. He says, “if we conceive a change as 
far beyond vaporization as that is above fluidity, and then take 
into account also the proportional increased extent of alteration 
as the changes rise, we shall, perhaps, if we can form any con- 
ception at all, not fall far short of that of radiant matter; and 
as in the last conversion many qualities were lost, so here also 
many more would disappear.” 
In 1819, Faraday says, “matter may be classed into four 
states, solid, liquid, gaseous, and radiant.” He adds: 
“As we ascend from the solid to the fluid and gaseous states, 
physical properties diminish in number and variety, each state 217 
losing some of those which belonged to the preceding state. 
When solids are converted into fluids all the varieties of hard- 
ness and softness are necessarily lost. Crystalline and other 
shapes are destroyed. Opacity and color frequently give way to 
a colorless transparency, and a great mobility of particles is 
conferred.” 
PROPERTIES OF RADIANT MATTER. 
“Passing onward to the gaseous state, still more of the evident 
characters of bodies are annihilated. The immense differences 
in their weight almost disappear. The remains of differences in 
color that were left are lost. Transparency becomes universal, 
and they are all elastic. They now form hut one set of sub- 
stances, and the varieties of density, hardness, opacity, color, 
elasticity, and form, which render the number of solids and 
fluids almost infinite, are now supplied by a few slight variations 
in weight, and some unimportant shades of color.” 
“To those, therefore, who admit the radiant form of matter 
no difficulty exists in the simplicity of the properties it possesses, 
but rather an argument in their favor. These persons show you 
a gradual resignation of properties in the matter we can appre- 
ciate, as the matter ascends in the scale of forms, and they 
would be surprised if that effect were to cease at the gaseous 
state. They point out the greater exertions which nature makes 
at each step of the change, and think that consistently it ought 
to he greatest in the passage from the gaseous to the radiant 
form.” 
255. Crooke’s Argument for Radiant Matter.—“ Gases are now 
considered to be composed of an almost infinite number of small 
particles or molecules, which are constantly moving in every 
direction with velocities of all conceivable magnitudes. As 
these molecules are exceedingly numerous, it follows that no 
molecule can move far in any direction without coming in con- 
tact with some other molecule. But if we exhaust the air or 
gas contained in a closed vessel, the number of molecules be- 
comes diminished, and the distance through which any one of 
these can move without coming in contact with another is in- 
creased, the length of the mean free path being inversely pro- 
portional to the number of molecules present. The further this 
process is carried, the longer becomes the average distance a 
molecule can travel before entering into collision; or, in other 
words, the longer its mean free path. The greater the mean 
free path, the more the physical properties of the gas or air are 
modified. Thus, at a certain point the phenomena of the radio- 
meter become possible. On pushing the rarefaction still further— 
*• e"> decreasing the number of molecules in a given space, and 
lengthening their mean free path, new and extraordinary experi- 
mental results are obtainable. So distinct are these phenomena 218 
ULTRA-GASEOUS OR RADIANT MATTER. 
from anything which occurs in air or gas at the ordinary tension 
that we are led to assume that we are here brought face to face 
with matter in a fourth state or condition, a condition as far re- 
moved from the state of gas as gas is from liquid,” 
“ There is one particular degree of exhaustion more favorable 
than any other for the development of the properties of radiant 
matter. Roughly speaking, it may be put at the millionth of 
an atmosphere. At this degree of exhaustion the phosphorescent 
effects are very strong, and after that they diminish until at last 
the spark refuses any longer to pass.” 
256. Crooke’s Explanation of the Kinetic Theory of Gases.—In 
dealing with this and with the properties of radiant matter we 
quote largely from Prof. Crookes’s own words. He says, it is 
not easy to make clear the kinetic theory, but we will try to 
simplify it in this way : Imagine that we have in a large box a 
swarm of bees, each bee independent of its fellow, flying about 
in all manner of directions and with very different velocities. 
The bees are so crowded that they can only fly a very short 
distance without coming into contact with one another or with 
the sides of the box. As they are constantly in collision, so 
they rebound from each other with altered velocities and in 
different directions, and when these collisions take place against 
the sides of the box pressure is produced. If we take some of 
the bees out of the box, the distance winch each individual bee 
will be able to fly before it comes into contact with its neighbor 
will be greater than wiien the box was full of bees; and if we 
remove a great many of the bees we increase to a considerable 
extent the average distance that each can fly without a collision 
This distance we will call the bees’ mean free path. When the 
bees are numerous the mean free path is very short; when the 
bees are few the mean free path will be longer, the length being 
inversely proportional to the number of bees present. Imagine 
a loose diaphragm introduced in the centre of the box so as to 
divide the number of bees equally. The same number of bees 
being on each side, the impacts on the diaphragm will be equal, 
and the mean speed of the bees being the same, the pressure 
will be identical on each side of the diaphragm and it will not 
move. 
Let us warm one side of this division so as to make it com- 
municate extra energy to a bee wLen it touches it. As before, 
a bee will strike the diaphragm with its normal mean velocity, 
but will be driven back with extra velocity, the reaction produc- 
ing a pressure on the diaphragm. It will be found, however, 
that although the diaphragm is free to move, the extra strength 
of the recoil on the warm side does not produce any motion. 
This at first sight seems contrary to the law of action and reac- PROPERTIES OF RADIANT MATTER, 
219 
tion being equal. The explanation is not difficult to understand. 
The bees which fly away from the diaphragm have drawn energy 
from it, and, therefore, move quicker than those which are 
coming towards it; they beat back the crowd to a greater dist- 
ance, and keep a greater number from striking the diaphragm, 
to the heated side of the diaphragm the density is less 
than the average, while beyond the free path the density is 
above the average, and this greater crowding extends to all 
other parts of the box. Thus it happens that the extra energy 
of the impacts against the warm side of the diaphragm is exactly 
compensated by the increased number of impacts on the cool 
side. In spite, therefore, of the increased activity communicated 
fo a portion of the bees, the pressure on the two sides of the 
diaphragm will remain the same. This represents what occurs 
when the extent of the box containing the bees is so great com- 
pared with the mean free path, that the abrupt change in the 
velocity of those bees which rebound from the walls of the box 
produces only an insensible influence on the motions of bees at 
so great a distance as the diaphragm. 
257. Action of Radiometer Explained.—lmagine that we gradually 
remove bees from the box, still keeping the diaphragm warm 
on one side. The bees getting fewer, the collisions will become 
less frequent, and the distance each bee can fly before striking 
its neighbor will get longer and longer, and the crowding in 
front of them will grow less and less. The compensation will 
also diminish, and the warm side of the diaphragm will have a 
tendency to be beaten back. A point will at last be reached on 
the warm side when the mean free path of the bees will be long 
enough to admit of their dashing right across from the diaphragm 
to the side of the box, without meeting more than a certain 
number of incoming bees in their flight. In this case the bees 
no longer fly quite in the same direction as before. They 
v dl now fly less sideways, and more forwards and backwards 
between the heated face of the diaphragm and the opposed wall 
ot the box. Because of this preponderating motion, and also 
because they will thereby less effectually keep back bees crowd- 
ing in 
from the sides, there will now be a greater proportionate 
Pressure both on the hot face of the diaphragm, and on that 
part of the box which is in front of it. Hence the pressure on 
ine hot side will now exceed that on the cool side of the 
niaphragrn, which will consequently have a backward move- 
Ba'communicated to it. 
We may diminish the size of the bees as much as we like, and 
ny correspondingly increasing their number the mean free path 
ivill remain the same. Instead of bees let us call them mole- 
cules, and instead of having a few hundreds or thousands let us 220 
ULTRA-GASEOUS OR RADIANT MATTER. 
have billions or trillions ; and if we also diminish the mean free 
path to a considerable extent we get a rough outline of the 
kinetic theory of gases. 
The explanation of the movement of the radiometer is this. The 
interior of the glass vessel being highly vacuous, the light or the total 
bundle of rays included in the term light, falling 
upon the blackened side of the vanes, becomes absorbed, 
and thereby raises the temperature of the black side ; 
this causes extra excitement of the air molecules which 
come in contact with it, and pressure is produced, 
causing the fly of the radiometer to turn round, the 
manner in which the motion originates being 
similar to that described in the latter part of the 
first paragraph of this article. 
Fig 93. 
258. Extent of Mean Free Path of Molecules in 
Radiant Matter.—Regarding this subject Prof. 
Crookes says: The mean free path of the mole- 
cules in air at the ordinary pressure is the 
ten-thousandth of a millimetre. I have long 
believed that a well-known appearance in 
vacuum tubes is closely related to the mean free 
patli of its molecules. If the negative pole is 
Action of 
radiometer. 
examined while the discharge from an induction coil is passing 
through an exhausted tube, a dark space is seen to surround it. 
This dark space increases and diminishes as the vacuum is 
varied. 
For the purpose of illustrating the mean free path, the instru- 
ment called the “dark space tube,” Fig. 94, has been contrived. 
Fig- 94. 
It has a pole in the centre formed 
of a metallic disk, and platinum 
wire poles at each end. The centre 
pole is made negative and the ter- 
minal poles positive. The induc- 
tion coil is then set in action. 
When the pressure is a few milli- 
metres of mercury, a halo of vel- 
vety light covers the surface of the 
pole; as the pressure diminishes,a 
dark space appears which separates this light from the surface of 
the metal. When the exhaustion is very good the dark space 
extends for a couple of inches on each side of the central pole, 
as is shown in the figure. 
Here we perceive the induction spark actually illuminating 
the lines of molecular pressure caused by the excitement of the 
negative pole. The thickness of this dark space—nearly two 
inches—is the measure of the mean free path between successive 
Dark space tube. PROPERTIES OF RADIANT MATTER. 
221 
collision of the molecules of the residual gas. The extra 
velocity with which the negatively electrified molecules rehound 
from the excited pole, keeps back the more slowly moving 
molecules which are advancing towards that pole. The conflict 
occurs at the boundary of the dark space, where the luminous 
margin bears witness to the energy of the discharge. 
The manner in which the dark space forms may he imitated 
by the following experiment: Let a stream of water fall from a 
fine jet on the centre of a horizontal sheet of glass. The water 
spreads over the plate and forms a thin film. The jet of water 
in the centre, from the velocity of its tall, drives the film of 
water before it on all sides, raising it into a ring-shaped heap. 
As the force of the jet is increased, the ring expands in 
diameter, the effect being analogous to a greater exhaustion in 
the tubes. The extra velocity of the falling particles of water 
drives the incoming water before them, and raises a ridge which 
exactly represents the luminous halo on the margin of the dark 
space in the tube. 
-259. Radiant Matter Exerts Phosgenic Action where it Strikes.— 
Certain precious stones, as the diamond, ruby, sapphire, possess 
the power of emitting light when sub- 
mitted to the action of the electric 
discharge. Other substances, as corun- 
dum, precipitated alumina, Becquerel’s 
luminous sulphides, uranium glass, 
mid English and German glass, also 
possess this property. In illustration 
°t the power of radiant matter to 
develop phosphorescence when it is 
under the influence of electricity, Pro- 
Fig. 95. 
Kuby tube. 
lessor Crookes has devised the apparatus called the “ ruby tube.” 
It is of the form represented in Fig, 95. In the lower part 
some chemically pure precipitated alumina, or other phospho- 
rescent substance, is placed. The terminals of the coil look down 
upon this material, and the tube is exhausted to about one- 
millionth of an atmosphere. 
The moment the coil is put in action, the alumina glows with 
a bright red light. Other specimens of alumina, on the con- 
trary, emit a green light. Diamonds are found to give brilliant 
colors of various hues—blue, apricot, red, yellowish, green, 
orange, and dark green. The glass of which the apparatus for 
illustrating the properties of radiant matter is made, emits a 
different color according to its composition. Uranium glass 
gives a dark green color; English glass, a blue; and the soft 
German glass, of which most of the instruments are made, 
a bright apple-green color. 222 
ULTRA-GASEOUS OR RADIANT MATTER. 
260. Radiant Matter Proceeds in Straight Lines.—ln the ordi- 
nary phenomena exhibited by vacuum it is customary, for 
the more striking illustration of their contrasts of color, to have 
the tubes bent into very elaborate designs. The positive 
luminosity caused by the phosphorescence of the residual gas 
follows all the convolutions and designs into which the glass is 
twisted. The negative pole being at one end, the positive at the 
other, the luminous phenomena seem to depend more on the 
positive than on the negative pole at exhaustions such as have 
hitherto given the best phenomena of vacuum tubes. The two 
bulbs, Fig. 96, are alike in shape and position of poles, the only 
Pig 90. 
Course of radiant matter. 
difference being that one is at an exhaustion equal to a few 
millimetres of mercury—such a moderate exhaustion as will 
give stratifications or the ordinary luminous phenomena—whilst 
the other is exhausted to about the millionth of an atmosphere. 
Connect the moderately exhausted bulb with the induction-coil, 
and, retaining the pole at one side, A, always negative, put the 
positive wire successively to the other three, poles, BCD, with 
which the bulb is furnished. As the position of the positive 
pole is changed, the line of violet light joining the two poles 
changes. In this moderately exhausted bulb, therefore, the 
electric current always chooses the shortest path between the two 
poles, and moves about the bulb as we alter the position of the 
polar wires. 
Repeat the same experiment with a tube that is highly exhausted, 
and as before make the side pole A the negative, the top pole B 
being positive. Notice how widely different is the appearance PROPERTIES OF RADIANT MATTER. 
223 
from that shown by the last bulb. The negative pole is in the 
lorm of a shallow cup. The bundle of rays from the cup crosses 
m the centre of the bulb, and thence diverging, falls on the 
opposite side as a circular patch of green light. Remove the 
positive wire from the top and connect it with the side pole C. 
The green patch from the divergent negative focus is still there. 
Make the lowest pole I) positive, the green patch still remains 
where it was at tirst, unchanged in position or intensity. If the 
negative pole points in the direction of the positive all very 
'yell, but if the negative pole is entirely in the opposite direc- 
tion it does not matter; the line of rays is still projected in a 
straight path from the negative pole. 
261. Radiant Matter Intercepted by Solid Matter Casts a Shadow. 
—The apparatus, Fig. 97, affords additional evidence of the fact 
that radiant matter moves in 
straight lines. In the middle of 
the pear-shaped vessel is a cross, 
hp of thin sheet aluminium. It 
18 niade the positive pole. The 
uegative pole is at A. In putting 
the coil in action the rays from 
the negative pole pass along the 
tube, and falling upon the broad 
end C produce phosphorescence, 
this phosphorescence a shadow, 
Shadow tube. 
of the cross appears, proving not only that the radiant matter 
has moved in straight lines from which it does not depart, but 
also that it is not a mere electrical action, for this would cease 
at the metallic surface which is the other pole. 
262, Radiant Matter Striking a Solid Produces Change Therein. 
In the preceding experiment the cross produces a dark shadow 
on a bright background. If the action is continued for some 
hnie the brightness of the phosphorescence gradually diminishes 
nnd almost disappears. If at this point the cross which is sup- 
ported on a hinge is thrown out of the path of the radiant 
niatter by a sudden movement, the parts of the glass which have 
hitherto been protected and dark, instantly flash out in brilliant 
phosphorescence, and a bright image of the cross appears on a 
'•ark background. In its turn this also Anally disappears. 
These facts demonstrate that the battering of the molecules 
°i the radiant material upon the surface of the glass produces 
a change therein. The exhaustion in this tube is much more 
perfect than in the dark space tube; the molecules not only 
passing throughout its whole length, but striking with such force 
°n the wide end that its temperature rises in consequence. 224 
ULTRA-GASEOUS OR RADIANT MATTER. 
263. Radiant Matter Exerts Mechanical Action where it Strikes. 
—To the apparatus represented in Fig. 98, Prof. Crookes has 
given the name of the railway tube. At either end on the upper 
part are the terminals of the coil. On a glass tramway a little 
below the axis of the tube, a delicatel}7 balanced wheel is placed. 
Its axis revolves on the tramway and the spokes of the wheel 
Fig. 98. 
Railway tube. 
terminate in rectangular vanes. When the coil is put in action 
the radiant matter projected from the negative pole passes along 
the upper part of the tube. In its passage it strikes upon the 
vanes of the upper part of the wheel with so much force that 
the wheel is set in rapid rotation, and despite the smallness of 
the circumference of the axis on which it is revolving passes 
quickly to the terminus of the track. Reversing the poles, the 
wheel passes in the opposite direction. 
264. Radiant Matter is Deflected by the Magnet.—Fig. 99 repre- 
sents a low vacuum tube, beneath which an electro-magnet has 
been placed. On passing the induction spark it assumes the 
form of a narrow line of violet light connecting the two poles 
Fig. 99. 
Action of magnet on low vacuum tube. 
of the tube. The polar wires of the electro-magnet being then 
connected with a voltaic battery, the line of light instantly dips 
down towards the magnet, but quickly rises again and pursues 
its original course. An essential point in connection with the 
phenomena produced is that the deflection of the line of light is 
only momentary. Reversing the current in the electro-magnet, 
the line of discharge is driven to the upper part of the tube. PROPERTIES OP RADIANT MATTER. 
225 
In Fig. 100, we have a highly exhausted tube with a negative 
pole, A, at one end, and a long phosphorescent screen, B C, down 
the centre of the tube. In front of the negative pole is a plate 
of mica, BD, with a hole, E, in it. When the current from an 
induction coil is turned on, a line of phosphorescent light is 
projected along the screen throughout the whole length of the 
Fig. 100. 
Action of magnet on high vacuum tube. 
tube in the line EF. On placing a strong magnet beneath the 
tube, the line of light becomes curved towards Gr under the 
Magnetic influence, and waves about like a flexible wand as the 
magnet is moved up and down. It is especially to be remarked 
that the deflection is permanent. In the preceding case it was 
temporary. In this case the matter in the tube has assumed a 
different condition. Its molecules are projected with great 
velocity and force from one end of the tube to the other; it is 
radiant matter. In the former case the molecules are vibrating 
m an exceedingly small space, they are much closer together. 
Ihe electro-current passes along them as along a broken con- 
ductor, forming a track of violet light. In the latter case the 
hght is the result of the impact or striking of the molecules 
upon a phosgenic surface, and is of a different color. 
265. Produces Heat When Its Motion is Arrested.—It has 
been stated that when radiant matter strikes upon glass, and 
produces green phosphorescence, after a 
short time the glass becomes warm. For 
of the intensity of the heat 
Produced, the adjoining tube was con- 
trived. The negative pole, IST, terminates 
lri a cup, A. At the focus of curvature 
ot the cup, B, there is a small square of 
thin sheet platinum. The positive ter- 
rumal is at P. On putting the coil in ac- 
tion, the radiant matter is thrown off from 
e. negative pole in converging lines, 
which meet at the focus upon the platinum, 
tn a few moments this becomes red-hot, 
aud if tpe cop fg 0f ffie right kind, and of 
sufficient strength, not only sheet platinum, 
out also the highly infusible iridium-pla- 
uium may be forced to melt. 
Fig. 101. 
Radiant matter produces heat 
where it strikes. 226 
ULTRA-GASEOUS OR RADIANT MATTER. 
266. The Molecule the True Matter.—ln summing up his won- 
derful results regarding radiant matter, Prof. Crookes says; 
“Matter in the fourth state is the ultimate result of gaseous ex- 
pansion. By great rarefaction the free path of the molecules 
is made so long that the hits in a given time may be disregarded 
in comparison to the misses, in which case the average mole- 
cule is allowed to obey its own motion or laws without inter- 
ference; and if the mean free path is compatible with the 
dimensions of the containing vessel, the properties which con- 
stitute gaseity are reduced to a minimum, and the matter then 
becomes exalted to an ultra-gaseous state. 
“But the same condition of things will be produced, if by any 
means we can take a portion of gas, and by some extraneous 
force infuse order into the apparently disorderly jostling of the 
molecules in every direction, by coercing them into a methodical 
rectilinear movement. This we. have shown to be the case in 
the phenomena which cause the movements of the radiometer, 
and I have rendered such motion visible in my later researches 
on the negative discharge in vacuum tubes. In the one case the 
heated lampblack, and in the other the electrically excited nega- 
tive pole supplies the force majeure, which entirely or partially 
changes into a rectilinear motion the irregular vibration in all 
directions; and according to the extent to which this onward 
movement has replaced the irregular motions which constitute 
the essence of the gaseous condition, to that extent do I con- 
sider that the molecules have assumed the condition of radiant 
matter.” 
Between the third and fourth states there is no sharp line of 
demarcation, any more than there is between solid and liquid 
states, or liquid and gaseous states; they each merge insensibly 
one into the other. 
These considerations lead to another and curious speculation. 
The molecule—intangible, invisible, and hard to be conceived— 
is the only true matter, and that which we call matter is nothing 
more than the effect upon our senses of the movements of mole- 
cules, or, as John Stuart Mill expresses it, “a permanent possi- 
bility of sensation.” Space covered by the motion of molecules 
has no more right to be called matter, than air traversed by a 
rifle-bullet can be called lead. From this point of view then, 
matter is but a mode of motion; at the absolute zero of tem- 
perature the inter-molecular movement would stop, and although 
something retaining the properties of inertia and weight would 
remain, matter as we know it would cease to exist. 
267. Absolute Vacuum Tube.—According to Prof. Crookes, the 
phosgenic action of radiant matter is best obtained by an ex- 
haustion to one millionth of an atmosphere. Both above and PROPERTIES OF RADIANT MATTER. 
227 
below this, the action is less intense. Indeed, if exhaustion be 
pushed as he has succeeded in doing to one twenty-millionth 
of an atmosphere, the ordinary phenomena of radiant matter 
disappear. 
In illustration of this fact, tubes are prepared in which ex- 
haustion is carried to the extreme of which chemical processes 
ai’e capable. Tubes so prepared, Prof. Crookes calls absolute 
vacuum tubes. These tubes are less than one inch in diam- 
otor, and about four inches in length. Piatinura poles pass 
from their extremities, and terminate about one-eighth of an 
Mich from each other in the interior. On making connection 
with an induction coil, and throwing it into action, the elec- 
tricity does not pass between these terminals; but if secondary 
terminals are placed in the air, the spark will pass between 
them though they are more than an inch apart. 
Though electric manifestations fail to traverse the limited 
distance between the terminals in these tubes, light traverses 
tbe tube in every direction with the same facility. It is, there- 
fore, evident that some form of matter still remains in the tube, 
though it is not one favorable to electric manifestations. Pos- 
sibly it may be, or approximate to, that universal form of matter 
which pervades all space, and to which the name of ether has 
been given (26). PART 11. 
ENERGY AND ITS FORMS. SECTION 1. 
POTENTIAL ENERGY-ATTRACTION. 
CHAPTER I. 
ENTERGY' ANTD EORCE. 
Ideas regarding energy—Potential and kinetic energy—Transformation of energy 
—Conservation of energy—Degradation of energy—Dissipation of energy— 
Subdivisions of energy—ldeas regarding force. 
268. Ideas Regarding- Energy.—Any agent capable of doing 
'York is said to possess energy. The quantity of energy is ex- 
pressed by the work it can do (296). The most concise descrip- 
£°?of modern ideas regarding energy is contained in Professor 
fait’s work on “Recent Advances in Physical Science.” I 
herefore give in this chapter an abstract thereof, in the form of 
a series of quotations. Concerning the introduction of the idea 
°± energy, Professor Tait says: “It is only within comparatively 
recent years that it has been generally recognized that there is 
something else in the physical universe which possesses as high 
a claim to objective reality as matter possesses, though it is by 
n° means so tangible, and, therefore, the conception of it was 
111 pH longer in forcing itself upon the human mind. The so- 
odlled ‘imponderables’—things of old supposed to be matter— 
smm as heat, light, etc., are now known by the purely experi- 
mental, and therefore the only safe method, to be but varieties 
m what we call energy—something which though not matter, 
ms as much claim to recognition on account of its objective ex- 
istence as any portion of matter. The grand principle of ‘ con- 
servation of energy,’ which asserts that no portion of energy 
fan lie put out of existence, and no amount of energy can be 
fought into existence by any process at our command, is simply 
a statement of the invariability of the quantity of energy in the 
universe—a companion statement to that of the invariability of 
6 9uantity of matter.” 232 
POTENTIAL ENERGY. 
269. Potential and Kinetic Energy.—Professor Tait remarks: 
“Wherein consists the difference between a mass of snow lying 
on the mountain side, and the same mass when it has fallen and 
rests in the valley below? Obviously the two substances are 
identical, except in so far as molecular changes, such as melting, 
may have altered the state of some portions of the mass during 
or after its descent. Yet the elevated mass possesses, in virtue 
of its elevation alone, a power of doing work or mischief which 
it has lost entirely when it has descended. By the mere fact 
then of its elevation, it possesses a power which it does not 
possess when it has fallen. This is called energy of position, or 
potential energy.” 
“But when the snow is detached from the mountain side, in 
descending it acquires another form of energy, depending 
entirely on its motion; and thus we distinguish between energy 
of position and energy of motion, or kinetic energy.” 
Energy, therefore, is of two kinds: kinetic and potential. 
A stone falling, a rifie-hullet in its course, a steamship in 
motion, all possess active actual kinetic energy. A stone on the 
verge of a precipice, the gunpowder in a rifle, on the other 
hand, have the power of producing kinetic energy; therefore 
they afford examples of potential or possible energjL The food 
we consume, and the air taken into the lungs, in like manner 
represent so much potential energy, which appears as kinetic 
energy in the muscular and other actions which result in the 
body. 
In his work on “ Solar Physics,” Lockyer illustrates the ideas 
of actual or kinetic and potential or possible energy by an 
example drawn from social life. “When,” he says, “a man 
pursues his course undaunted by opposition, unappalled by 
obstacles, he is said to be a very energetic man. By his energy 
we mean the power which he possesses of overcoming obstacles; 
and the amount of his energy is measured by the 'Amount of 
obstacles which he can overcome, by the amount of work which 
he can do. Such a man may, in truth, he regarded as a social 
cannon-ball. By means of his energy of character he will 
scatter the ranks of his opponents and demolish their ramparts. 
Nevertheless, such a man will sometimes be defeated by an 
opponent who does not possess a tithe of his personal energy. 
Yow, why is this? The reason is that, although his opponent 
may be deficient in personal energy, yet he may possess more 
than an equivalent in the high position which he occupies, and 
it is simply this position that enables him to combat successfully 
with a man of much greater personal energy than himself. If 
two men throw stones at one another, one of whom stands on 
the top of a house and the other at the bottom, the man at the 
top of the house has evidently the advantage. ENERGY AND FORCE. 
“So in like manner if two men of equal personal energy 
contend together, the one who has the highest social position 
has the best chance of succeeding. 
“But this high position means energy under another form. 
It means that at some remote period a vast amount of personal 
energy was expended in raising the family into this high 
position. The founder of the family had doubtless greater 
energy than his fellow-men, and spent it in raising himself and 
his family into a position of advantage. The personal element 
nray have long since vanished from the family, but it has been 
transmuted into something else, and it enables the present rep- 
resentative to accomplish a great deal, owing solely to the high 
position which he has acquired through the efforts of another. 
“We thus see that in the social world we have what may be 
justly called two kinds of energy, namely: 
“1. Actual or personal energy. 
“2. Energy derived from position. 
‘‘Let us now turn to the physical world. In this, as in the 
social world, it is difficult to ascend. The force of gravity may 
he compared to that force which keeps a man down in the world, 
“If a stone be shot upwards with great velocity, it may he 
said to have in it a great deal of actual energy, because it has the 
power of overcoming the obstacle interposed by gravity to its 
ascent, just as a man of great energy has the power of over- 
coming obstacles. 
“ This stone as it continues to mount upwards will do so with 
a gradually decreasing velocity until at the summit of its flight 
ah the actual energy with which it started has been spent in 
raising it against the force of gravity to this elevated position, 
-ft is now moving with no velocity, and may be supposed to be 
caught and lodged upon the top of a house. 
. “ Thus it is seen that during the upward flight of the stone 
As energy of actual motion has gradually become changed into 
energy of position, and the reverse will take place during its 
downward flight if we now suppose it dislodged from the top of 
the house. In this latter case the energy of position with which 
!t begins its downward flight is gradually converted into energy 
°f actual motion, until at last, when it once more reaches the 
ground, it has the same amount of velocity, and, therefore, of 
actual energy which it had at first. 
. “ Thus we have also in the physical world two kinds of energy: 
111 the first place we have that of actual motion, and in the next 
We have that of position.” 
. Transformations of Energy.—Of this we have an example 
ln the preceding article. A still better illustration of a multi- 234 
POTENTIAL ENERGY. 
plicity of transformations is afforded by the present method of 
producing the electric light. 
In this the initial act is the combustion or oxidation of coal. 
This is a chemical process by which heat is developed. Through 
the agency of the heat water is volatalized into steam, the elastic 
force of which is caused by suitable machinery to produce motion. 
In its turn the motion is converted into a compound develop- 
ment of magnetism and electricity, and the latter when passed 
between carbon points produces light and heat. Attendant on 
the motion, and likewise on the passage of the electric arc, 
sound also appears as an accidental result. 
Chemical affinity, heat, motion, magnetism, electricity, light, 
are, therefore, convertible one into another. Indeed, as a glance 
at the table of the divisions of energy shows, they are virtually 
mere modifications of the effects of energy. There is, therefore, 
nothing surprising in the fact of their mutual convertibility or 
transformation. ' 
An admirable example of the transformation or change of 
potential into kinetic energy is afforded by the 'pendulum in action. 
When at rest in its lowest position it may be said not to possess 
any energy, but when work is done upon it and it is raised to 
one end of the arc in which it swings, it possesses potential 
energy by virtue of its position, and can do work. Falling to its 
lowest position, it accomplishes work represented by its weight 
multiplied by the vertical height through which its centre 
of gravity has descended. In the lower part of its course 
gravity ceases to act, but it now possesses energy by virtue of 
the velocity it has acquired in its descent. This carries it against 
gravity to the other extremity of its arc, the kinetic being 
finally completely transformed into potential energy when it 
comes to rest and is prepared for a second descent. So the 
alternate conversion of potential into kinetic energy, and vice 
versd, continues until all the original energy is transformed in 
overcoming the friction and resistance of the air to which the 
pendulum has been submitted during its oscillations. 
271. Conservation of Energy.—Again quoting from Prof. Tait, 
“ the velocity of an avalanche of snow constantly increases as 
it descends, and exact calculation according to physical experi- 
ment shows us that the amount of potential energy lost in every 
stage of the operation is precisely equal to the amount of kinetic 
energy gained. The process may be inverted if we consider 
kinetic energy to be originally communicable to a body, suppose, 
for simplicity, in a vertically upward direction.” As in the 
illustration by Lockyer, “ a stone thrown into the air gradually 
loses velocity as it ascends higher and higher; for an instant, 
when it has lost all velocity, it pauses and then returns, gradually ENERGY AND FORCE. 
235 
gaining velocity as it in turn loses its advantage of position. 
Calculation applied to this case shows that at every stage 
whether of the ascent or of the descent, the sum of the poten- 
tial and the kinetic energies remains precisely the same except 
in so far as it is modified by resistance of the air. This, how- 
ever, gives us no exception to the general truth of the prin- 
ciple of conservation of energy, because any energy lost by the 
stone is communicated without loss of quantity to the sur- 
rounding air.” 
The conclusions arrived at from the experiments of Joule on 
the mechanical equivalent of heat (766) show that in the passage 
of energy from one form to another nothing is lost. Energy is 
as indestructible as matter itself. Its disappearance in one form 
is only its translation into an absolutely equivalent amount of 
some other form or forms. The total quantity of matter does 
not vary, neither does that of energy. To quote from Dr. 
Arnott ; 
“ There may be an ebb and flow between the relative amounts 
of the various energies, but the sum of them all is constant and 
invariable throughout our universe. There may, indeed, be a 
tendency of all the present energies of nature ultimately to pass 
nito one uniformly diffused heat-quiver; it may be indeed that 
m some incalculably remote age all the changes will have been 
I’ung upon the present distribution of the forms of energy, and 
that the vitality of all nature will exist merely as a universal 
Pulse. Yet the grand generalization of modern times constrains 
ns to believe that in that pulse will be found the exact represen- 
tative of every motion and form of energy at present operating 
or within us; that, in fact, energy is co-eternal with matter. 
We cannot say that we know fully the nature of the different 
energies such as magnetism, heat, electricity, and chemical 
nffipity; hut the principle of the Conservation of Energy, with 
which alone the facts discovered by modern experiment appear 
reconcilable, justifies us in regarding them all, either as some 
species of actual motion or as some sort of potential energy 
inherent in definite arrangements of those minute particles 
which form the foundation of the material universe.” 
272. Degradation of Energy.—Returning again to the work of 
Prof. Tait, he says : “We contemplate, therefore, with reference 
to energy, its conservation, which merely asserts its objective 
reality; its transformations, which render it indispensable to 
the existence of life and the physical changes in the universe; 
hut it has in addition another and even more curious property, 
've have seen that change is essential to the existence of phe- 
nomena such as we observe, and that this change may take place 
T is necessary that there should be constant transformations of 236 
POTENTIAL ENERGY. 
energy. But some forms of energy are more capable of being 
transformed than others, and every time that a transformation 
takes place there is always a tendency to pass, at least in part, 
from a higher or more easily transformable to a lower or less 
easily transformable form, 
“ Thus the energy of the universe is, on the whole, constantly 
passing from higher to lower forms, and, therefore, the possi- 
bility of transformation is becoming smaller and smaller, so 
that in the lapse of sufficient time all higher forms of energy 
must have passed from the physical universe, and we can imagine 
nothing as remaining except those lower forms which are in- 
capable so far as we yet know of airy further transformation. 
The low form to which all transformations with which we are 
at present acquainted seem inevitably to tend, is that of uni- 
formly diffused heat. We know, in fact, that in order to make 
any use of heat—to transform it into mechanical power or into 
any other form of energy—it is absolutely necessary that we 
should have bodies of different temperatures. We must, as it 
were, have a source and a condenser. Now, when all the energy 
of the universe has taken the final form of uniformly diffused 
heat, it will be obviously impossible to make any use of this 
heat for further transformation. Thus, so far as we can as yet 
determine, in the far distant future of the universe the quantities 
of matter and energy will remain absolutely as they now are; 
the matter unchanged alike in quantity and quality, but collected 
together under the influence of its mutual gravitation, so that 
there remains no potential energy of detached portions of 
matter; the energy also unchanged in quantity, but entirely 
transformed in quality to the low form of uniformly diffused 
heat.” 
273. Dissipation of Energy.—This is by no means well under- 
stood, and many of the results of its legitimate application have 
been received with doubt, sometimes even with attempted 
ridicule. Yet it appears to be at the present moment by far the 
most promising and fertile portion of natural philosophy, having 
obvious applications of which as yet only a small percentage 
appear to have been made. Some, indeed, were made before 
the enunciation of the principle, and have since been recognized 
as instances of it. Of such we have good examples in Fourier’s 
great work on heat-conduction, in the optical theorem that an 
image can never be brighter than the object; in Glaus’s mode of 
investigating electrical distribution, and in some of Thomson’s 
theorems as to the energy of an electro-magnetic field. 
There can be little question that the principle contains the 
whole theory of thermo-electricity, of chemical combination, of 
allotropy, of fluorescence, etc., and perhaps even of matters of 
a higher order than common physics and chemistry. ENERGY AND FORCE. 
Thus also it is possible that in physiology it may ere long 
lead to results of a different and much higher order of novelty 
aud interest than those yet obtained, valuable though these cer- 
tainly are. 
“It was a grand step in science which showed that just as the 
eonsumption of fuel is necessary to the working of a steam- 
engine or to the steady light of a candle, so the living engine 
requires food to supply its expenditure in the forms of muscular 
work and animal heat. Still grander was Eumford’s early 
anticipation that the animal is a more economic engine than 
any lifeless one we can construct. Even in the explanation of 
this there is involved a question of very great interest, still un- 
solved, though Joule and many other philosophers of the highest 
order have worked at it. Joule has given a suggestion of great 
value, viz., that the animal resembles an electro-magnetic rather 
than a heat-engine; but this throws us back again upon our 
difficulties as to the nature of electricity. Still, even supposing 
this question fully answered, there remains another—perhaps 
the highest which the human intellect is capable of directly 
attacking, for it is simply preposterous to suppose that we shall 
ever be able to understand scientifically the source of conscious- 
ness and volition, not to speak of loftier things—there remains 
the question of Life. It may be startling to some of you, espe- 
cially if 
you have not particularly considered the matter, to 
hear it surmised that possibly we may by the help of physical 
Principles, especially that of the dissipation of energy, some 
tlrne attain to a notion of what constitutes life—mere vitality, I 
u'peat, nothing higher. If you think for a moment of the 
Vitality of a plant or a zoophyte, the remark will not appear so 
strange after all. Do not fancy that the dissipation of energy 
to which I refer is at all that of a watch or such like piece of 
n).ere human mechanism, dissipating the low and common form 
?. energy of a single coiled spring. It must be such that every 
ittle part of the living organism has its own store of energy 
e°nstantly being dissipated, and as constantly replenished from 
external sources drawn upon by the whole arrangement in their 
harmonious working together. Sir W. Thomson’s splendid 
■ffiggestion of vortex-atoms, if it be correct, will enable us 
thoroughly to understand matter, and mathematically to in- 
vestigate all its properties. Yet its very basis implies the absolute 
necessity of an intervention of creative power to form or to 
destroy one atom even of dead matter. The question really 
stands thus : Is life physical or no ? For if it be in any sense, 
however slight or restricted, physical, it is to that extent a 
subject for the natural philosopher, and for him alone.” 
274. Subdivisions of Energy. The various phenomena ex- 
hibited by matter, and which result from the influence of energy POTENTIAL ENERGY. 
thereupon may therefore, be grouped under two grand divisions : 
Potential energy or attraction, and kinetic energy or motion. Each 
of these may be studied under three phases or conditions. Ist. 
Molar, or attraction and motion as related to masses of matter; 
2d. Molecular, or attractions and motions of molecules; and 3d. 
Atomic, or the attractions and motions of atoms. Molar attrac- 
tion and motion belong properly to mechanics; Molecular at- 
tractions and motions to physics ; Atomic attractions and motions 
to chemistry. Each of these in its turn presents minor subdi- 
visions, examples of which are given in the following tabular 
presentation of the subject. 
Potential or 
Energy of 
Position and 
Attraction. 
Molar, Mechanics . . . 
Molecular. Physics proper. . 
Atomic. Chemistry . . . 
Gravity. 
Cohesion. 
Adhesion, 
Affinity, or Chemism. 
Direct, or Rectilinear translation. 
Molar. Mechanics . . . 
Oscillatory, or Reciprocating. 
Rotatory 
Centrifugal and Centripetal. 
Axial. 
Eccentric 
„ Orbital. 
Kinetic or 
Energy of 
Motion. 
Molecular. Physics proper. - 
Direct or translation 
Vibratory . . 
Reciprocating. >- 
Rotatory . . j 
Capillarity. 
Diffusion. 
Sound. 
Light. 
Heat. 
Electricity and 
Magnetism, etc 
Atomic. Chemistry . . . 
Affinity or Chemism - 
Combination. 
Decomposition. 
motion belong to chemistry, they are eliminated from the present 
discussion. Molar attraction and motion we are obliged to 
examine to a certain extent to enable us to form proper concep- 
tions regarding molecular attractions and motions. Molecular 
Of the above divisions, since atomic attraction and atomic 
motion presents many phases attended by distinct and charac- 
teristic phenomena. 
275. Ideas Regarding Force.—According to Newton’s first law 
of motion, Force is any cause which alters or tends to alter a body's 
state of rest or of uniform motion in a straight line. 
Matter at rest cannot change its condition of itself; matter 
in motion cannot of itself change its course from uniform move- 
ment in a straight line. This property of matter has been 
described as inertia (42). Anything which produces motion in 
a material point or in a mass, or which changes the character 
or rate of a movement, is a force. Thus gravity, friction, ATTRACTION. 
239 
elasticity of springs and vapors, magnetism, are examples of 
force. 
Momentary forces are those which last but for a brief moment 
of time, and are called into play by explosions, electric dis- 
charges, and impulses of various kinds. Continuous forces are 
those which endure in their action, like gravitation or magnetism. 
A continuous force which does not vary is called constant. 
CHAPTER 11. 
ATTRACTION. 
Alolar attraction. Gravity—Molecular attraction—Adhesion ol solid and solid— 
Cements—Soldering—Adhesion of solid and liquid—Drops and minims 
—Solution—Adhesion of solid and gas. 
276. Molar Attraction. Gravity.—The fact that two masses of 
flatter exert an attractive influence on each other is shown by 
fhe following experiments: A small object, as a bullet, is 
suspended by a delicate thread, and made to oscillate across 
fee field of a microscope. The thread as it moves to the right 
and left passes to the same distance on each side of the cen- 
frc of the field of the instrument, as may be measured by a 
Mi the vicinity of the oscillating bullet, and the movements of 
file thread watched through a microscope, they will no longer 
be found to be equal in extent on each side of the centre of the 
ffsld, but will be greater in the direction towards the cannon- 
hall. The two masses of matter, therefore, exert an attractive 
Motion on each other, which is best seen in the case of the smaller 
bo(fy, but is also present in the larger, though it is not so evident 
011 accoiint of its greater size. 
fhat both masses are affected by the attractive force may Jie 
shown hy placing a globule of mercury on the stage of a pro- 
jection lantern. The stage of the instrument must be in a hori- 
zontal position. By means of a slender knife-blade the globule 
may be separated into smaller portions. As one of these is 
gently approached towards another, it will be seen on the screen 
o move quietly until a certain distance is reached, then the two 
Classes jump, as it were, towards each other and unite, forming a 240 
POTENTIAL ENERGY. 
single globule. In case one globule is greater than the other 
the motions occur in both, but the larger moves through a less 
distance than the smaller in proportion as its size is greater. 
Masses of matter, therefore, possess a mutual power of attrac- 
tion—this is inherent to all matter. It is the force by virtue of 
which the particles of all bodies tend towards each other. It 
exists between them when at rest and when in motion. It is 
effective no matter how great or how small the separating space 
may be, or whether it is occupied by other matter or not. 
For the conception of universal attraction we are indebted to 
Sir Isaac Newton, who determined the law of its action as is 
expressed in the following terms: “ The attraction between two 
material 'particles is directly proportional to the product of their masses, 
and inversely proportional to the square of their distances 
To indicate the attraction of the earth for objects on its sur- 
face, the word gravity is used. 
277, Molecular Attraction is of two kinds, cohesion and adhe- 
sion. Cohesion is the force which binds together molecules of 
the same kind. The experimental illustration of this force has 
been given in (18). Its variation in the different forms of solid, 
liquid, and gaseous matter, has also been discussed in the study 
of these varieties of matter. 
Adhesion is the force which binds together different kinds of 
molecules or different masses of matter. It may be considered 
under three divisions: Ist. Solid and solid. 2d. Solid and 
liquid. 3d. Solid and gas. By many, cohesion and adhesion 
are regarded as being essentially the same. 
278. Adhesion of Solid and Solid.—Two flat surfaces pressed 
firmly together will adhere more or less perfectly. Two pieces 
of glass, the surfaces of which are ground flat and which are 
called adhesion plates, will adhere when they are pressed 
together with a sliding motion. That the adhesion is in no way 
a result of pressure of the air, is shown by the fact that the 
plates remain adherent though suspended in a vacuum. The 
more the contact and pressure are prolonged, the firmer is the 
adhesion. It is by virtue of adhesion of this kind that germs 
of all varieties become attached to motes in the air, to clothing, 
and to walls of buildings. Friction is, to a certain, extent, the 
product of adhesion. 
279. Cements.—Adhesion may be rendered more perfect by 
the employment of liquid glue and other cements which leave 
no empty spaces on drying or hardening. In these cases adhe- 
sion of the cement is often so strong that fracture occurs more 
readily in other parts than in those which are cemented. The 241 
ATTRACTION. 
greater intensity of adhesive over cohesive force is shown by 
the fact that the thinner the layer of cement the stronger its 
action. 
Cements resemble in properties the bodies they unite. 
Stones are cemented by mortar made of lime and sand, which 
are rock-like in their origin. Organic bodies, as wood, paper, 
and leather, are joined with glue, isinglass, and gum, which are 
also organic. Metals, with solder made of other metals; the 
solder should have a rate of expansion under the influence of 
heat intermediate between the expansion rates of the two metals 
to be united (280). 
It is not easy to cement together bodies which are unlike in 
nature, as, for example, metal and glass. This is largely owing 
to differences in their rates of expansion. The only metal 
which can be directly united with glass is platinum. If the 
platinum is plated with aluminium the union is more satisfac- 
tory, since aluminium becomes coated with an oxide which 
approaches glass in its character, and so forms a more per- 
fect joint. 
The necessities of surgery often demand that various kinds 
°f surgical appliances consisting of heterogeneous substances 
should be united. To meet conditions already existing, and to 
suggest other appliances that might be devised, the following 
list of cements is given. 
Twister of Paris, with or without solution of borax. Roman or hydraulic 
cement hardens under water. Mastic cement made of Portland limestone finely 
ground, mixed with sand and litharge. This is made into a paste with raw or 
foiled linseed oil, when it is to be used. The surfaces to which it is applied should 
be oiled to secure adherence. 100 of the mixture require 7of oil. For Portland 
bh® fine dust from the sawing of slabs of marble may be substituted. 
The above are useful in the making of casts of tumors and malformations 
under various conditions. Mastic cement is especially useful for various hygienic 
aPplications, as cementing the .floors of cellars and so preventing ingress of 
moisture and emanations. It is used in London to cover brick-work. 
Resinous and glutinous cements are very numerous. In the preparation of 
Physical and chemical apparatus, the cement usually employed is a mixture of 
and beeswax, melted together and colored with very fine brick-dust, or 
ctter yet with vermilion, a very little of which goes a long way. The hardness 
ot this cement may be varied at pleasure during its preparation, by allowing a 
. 10p of it to dry on a piece of metal and testing it with the thumb-nail, and add- 
lrjg more beeswax or rosin as is necessary. It is very useful in cementing cork to 
S ass, and in closing the leakage through the pores of cork used in making ap- 
paratus for experimenting with gases. The layer of cement should be as thin as 
possible when it is used to unite surfaces. 
keven of rosin, one of beeswax melted, and a little plaster of Paris added, is 
Recommended as a cement for stones and earthenware. The substance must be 
°t enough to melt the cement, and the pieces should be very firmly pressed 
together. 
felted sulphur is used to unite metals and stone. 
A jeweller’s cement is made of isinglass soaked in water till it swells, this 
J dissolved in brandy or in rum. In two ounces of this mixture, a little gum 
gm ban urn or gUm ammoniacum is dissolved by trituration. A piece of mastic the 
lze °f a marble is then dissolved in as little alcohol as possible, and mixed with 242 
POTENTIAL ENERGY. 
the preceding at 150° F. The cement is kept in a closely stoppered vial. The 
vial is immersed in hot water when it is to be used. It resists moisture. 
Another cement which resists moisture is made by mixing a solution of isin- 
glass in proof-spirit with a solution of shellac in alcohol. 
Common glue melted without water, with half its weight of rosin and a little 
red ochre added to give it body, also forms a cement which resists water. 
Clay and oxide of iron make a cement which hardens under water, 
A cement for iron to close cracks and crevices, as in heating furnaces, may be 
made of 2 parts of sal-ammoniac, 1 of flowers of sulphur, 16 of cast-iron filings. 
These should be well pounded together in a mortar and kept dry. When used, 
1 part should be ground in a mortar with 20 of iron filings, and water added to 
form a paste of proper consistency to be applied to the joints. 
A cement lor boilers is made of 6 of clay, 1 of iron filings, and linseed oil suf- 
ficient to form a thick paste. 
A solution of caoutchouc or India-rubber in a mixture of 100 parts of bisul- 
phide of carbon, and 8 of alcohol, is an excellent cement for leather and similar 
substances. 
One of rubber, four of coal tar, with two of shellac added. When the solution 
is complete, and the whole heated in an iron vessel, it makes a very strong glue. 
Caoutchouc cements are waterproof. 
Regarding cements for microscopic preparations, Prof. Car- 
penter says: 
“Japanner’s gold size is the most trustworthy of all cements for closing-in 
mounted objects of almost any description. It takes a peculiarly firm hold of 
glass; and when dry it becomes extremely tough without brittleness. When 
new it is very liquid and runs rather too freely; it is often advantageous to 
leave open for a time the bottle containing it until the varnish is somewhat 
thickened.” 
“ Asphalt varnish. This is a black varnish made by dissolving half a drachm 
of caoutchouc in mineral naphtha, and then adding four ounces of asphaltum, 
using heat if necessary for its solution. It is very important that the aspjialtura 
should be genuine, and the other materials of the best quality.” 
“Black japan. The varnish sold at color-shops under this name may be used 
for the same purposes as the preceding. When employed for making ‘cement- 
cells,’ the slides to which it has been applied should be exposed to the heat of an 
oven not raised so high as to cause it to blister; this will increase its adhesion to 
the glass slide, and will flatten the surface of the rings.” 
“Dammar cement, made by dissolving gum dammar in benzole, and adding 
about one-third of gold size, has the advantage of drying very quickty ; and 
may be preferably used for a first coat when glycerine is used as the material for 
mounting.” 
“Canada, balsam is so brittle when hardened by time that it cannot be safely 
used as a cement, except for the special purpose of attaching hard specimens to 
glass, in order that they may be reduced by grinding.” 
“Shellac cement is made by keeping small pieces of picked shellac in a bottle of 
rectified spirits, and shaking it from time to time. It cannot be recommended as 
a substitute for any of the preceding; as when dry and hard it has little hold 
on glass. But it answers very well for making cells for dry-mounting.” 
“Marine glue, which is composed of shellac, caoutchouc, and naphtha, is dis- 
tinguished by. its extraordinary tenacity, and by its power of resisting solvents 
of almost every kind. Different qualities of this substance are made for the 
several purposes to which it is applied ; and the one most suitable to the wants of 
the microscopist is known in commerce as GK4. The special value of this 
•cement, which can only be applied hot, is in attaching to glass slides the glass or 
metal rings, which thus form ‘cells’ for the reception of objects to be mounted 
in fluid; no other cement being comparable to it either for tenacity or durability.” 
“For attaching labels and covering papers to slides either of glass or wood, 
and for fixing down small objects, nothing is preferable to a rather thick mucilage 
of gum arabic to which enough glycerine has been added to prevent it from ATTRACTION. 
drying hard, with a few drops of some essential oil to prevent the development 
of mould. The following formula has also been recommended : Dissolve 2 oz. 
of gum arabic in 2 oz. of water, and then add \ of an oz. of soaked gelatine (for 
the solution of which the action of heat will be required), 30 drops of glycerine, 
and a lump of camphor.” 
280. Soldering.—To unite metals, solders formed of tin and 
lead are commonly employed. Of these there are three, viz.: 
fine solder, 2 parts tin, 1 part lead; common solder, equal parts of 
each metal; and coarse solder, 2 parts lead, and 1 part tin. These 
m each case are fused together, and cast into bars. The surfaces 
to be united should be clean and bright. To prevent formation 
of oxide, which would injure a perfect union of the surfaces, 
pulverized rosin is dusted over the objects to be united; on 
the application of heat either by the hot bolt or blowpipe flame, 
the rosin melts and prevents action of the oxygen of the air 
upon the metals. 
Many metals, as copper, must be tinned before they can be 
united by soldering. To accomplish this, the surface is first 
scraped or filed clean, it is then heated, and a little chloride of 
zinc solution or a little powdered sal-ammoniac dusted on. It 
is then touched with the rod of tin. If sufficiently heated, it is 
instantly coated with tin. The excess of tin is wiped off, and 
the metallic surfaces united under a suitable temperature, more 
tin or solder being used if necessary. 
Silver solder contains 66 per cent, of silver with zinc and 
copper. The practical application of soldering arises continu- 
ally in electrical experimentation. 
281. Adhesion of Solid and Liquid.—Of this the following ex- 
periment is an example. A glass plate is suspended by threads 
so that its surfaces are horizontal, it is then lowered on a 
clean surface of mercury, which has been poured into a shallow 
dish or plate. The moment the glass and mercury come in 
pontact, they adhere with such firmness that considerable force 
18 required for their separation. 
This form of adhesion is stronger than that between solids, 
tf oil or water be placed between the adhesion plates (278), they 
adhere much more firmly than without it. In the case of lower- 
lng a suspended glass plate on the surface of water (18), adhesion 
°t the fluid for the solid is greater than cohesion of the molecules 
°f the fluid for each other. This is demonstrated by the fact 
that when the plates are separated, both surfaces are uniformly 
coated with liquid. The force which has torn the molecules of 
liquid asunder, has been inadequate to separate the molecules of 
liquid from those of the solid. 
The same solid may show different powers of adhesion, or 
wetting power for different fluids. A drop of alcohol falling 244 
POTENTIAL ENERGY. 
upon a surface of glass covered by a film of water, will drive the 
water before it, stripping it from the surface of the glass by 
virtue of its greater wetting or adhering power. On the other 
hand, mercury and melted metals show little or no wetting 
power for glass. 
It is the difference in wetting power or adhesion that causes 
water and mercury to stand with curved surfaces in glass 
vessels. The one with the concavity upwards, the other with it 
downwards. 
The condition of a surface also has an important influence on 
the wetting power of a liquid. To show its true adherent power, 
a surface must be chemically clean. Photographers are well 
aware of this fact, and resort to various devices to obtain the 
result. If they fail, they will in vain endeavor to secure the 
adherence of the film of collodion to the surface of the glass 
plates on which it is spread. 
282. Drops and Minims.—ln measurement of liquids for medi- 
cal purposes, both of these are employed. In the case of the 
minim it is a fixed measured quantity, the sixtieth part of a 
fluid-drachm. In the case of the drop the quantity is very 
variable. 
A drop is the resultant of three forces, viz,: gravity, cohesion, 
and adhesion. As these vary, so does the size of the drop vary. 
Liquids which are heavy, form small drops. Those which are 
very cohesive, form large drops. The material of which the 
vessel is made and the form of its lip, by influencing the adhe- 
sive force, regulates the size of the drop. In view of the 
importance of these facts in practical medicine, the following 
table of drops to the fluid-drachm of various medicines is 
given. It is taken from the U, S. Dispensatory. 
Drops. 
Drops. 
Acid, acetic (crystallizable) . 
Acid, hydrocyanic (medicinal) 
120 
Tincture of assafoetida, of fox- 
45 
glove, of guaiac, of opium 
120 
Acid, muriatic . 
54 
Tincture of chloride of iron . 
132 
Acid, nitric 
84 
Vinegar, distilled , . . . 
78 
Acid, nitric, diluted (1 to 7) . 
51 
Vinegar of colchicum . 
78 
Acid, sulphuric .... 
90 
Vinegar of opium (black drop) . 
78 
Acid, sulphuric, aromatic 
Acid, sulphuric, diluted (1 to 7) . 
120 
Vinegar of squill . . . . 
78 
51 
Water, distilled . . . . 
45 
Alcohol (rectified spirit) 
138 
Water of ammonia (strong) . 
54 
Alcohol, diluted (proof spirit) 
120 
Water of ammonia (weak) . 
45 
Arsenite of potassa, solution of 
57 
Wine (Teneriffe) . . . . 
78 
Ether, sulphuric .... 
150 
Wine, antimonial. . . . 
72 
Oil of aniseed, of cinnamon, of 
Wine of colchicum 
75 
cloves, of peppermint, of sweet 
almonds, of olives 
120 
Wine of opium . . . . 
78 
283. Solution.—When a solid dissolves in a liquid, cohesion 
of the molecules of the solid is broken by their adhesion for the ATTRACTION. 
245 
molecules of the liquid. The limit of solubility is reached or a 
saturated solution formed, when the attraction of adhesion and 
that of cohesion are balanced (339). The act of solution is 
usually attended by a fall in temperature, produced by conver- 
sion of sensible into latent heat. When solution of a solid is 
attended by chemical action, as the formation of a hydrate, 
there is a rise of temperature, as in the case of lime. 
Anything that reduces the force of cohesion favors that 
of adhesion. If we desire to dissolve salt or sugar more rapidly, 
me pulverize them. The solution is accelerated by suspending 
the solid just below the surface of the liquid. Heat also, by 
increasing the intermolecular spaces, generally favors solution. 
To this there are some curious exceptions. A solution of lime, 
tor example, made in cold water, will deposit a moiety of the 
solid material if raised to the boiling point. A solution of sul- 
phate of soda, made in ice-cold water, deposits hard gritty crys- 
tals on being warmed. 
The explanation of these phenomena seems to be, that both 
adhesive and cohesive attractions are diminished by an elevation 
°t temperature. Cohesive force being the most sensitive, gen- 
erally suffers more than adhesive; in exceptional cases the re- 
verse happens, the adhesion has then suffered the most, and 
solubility is consequently diminished. 
As a rule, solids dissolve in liquids which have similar prop- 
erties; crystalline bodies in water, metals in mercury, fats in 
eds, resins in alcohol. This constitutes a leading difference 
between the molecular adhesion of solution and chemical attrac- 
hou. In the latter, action is strongest between atoms or mole- 
cules which are unlike in their nature. The liquid which takes 
UP the solid is called the menstruum or solvent. 
When two or more salts are dissolved in water without 
chemical action on each other, three conditions result: Ist. The 
quantity of each salt held in solution is less than when it alone 
18 present, though the combined quantity is greater than when 
°uly one salt is used. 2d. The quantity of each is as great as 
v?hen only one is used, then the total quantity dissolved is the 
sum of that taken up in each single solution. 3d. The quantity 
dissolved is greater than when one alone is used; the addition 
uf the second salt in this case increasing the solubility of the 
urst, and often the first increasing also the solubility of the 
second. See (339). 
. 284. Adhesion of Solid and Gas.—When a sheet of glass is 
immersed in water, bubbles of gas appear on its surface. In 
ibis case the bubbles have arisen from the layer of air which 
covered the surface of the plate, and was carried down by it 
v ben it was immersed in the fluid. The bubbles of air which 246 
POTENTIAL ENERGY. 
soon appear on the inner surface of a goblet of freshly drawn 
cool water, also afford an example of the adherence of gas to 
solid surfaces. 
In certain cases the adherence of gas to a solid is very great, 
and requires resort to various devices to overcome it. An ex- 
ample of this is offered in the preparation of a mercurial 
barometer, in which it is necessary to raise the temperature of 
the mercury nearly to boiling point in order to expel the film 
and bubbles of air which adhere to the surface of the glass tube. 
When gases are evolved by electrolysis on the surfaces of 
plates of metal, the layer of gas which adheres to the plate has 
such increased density that it can cause chemical actions of 
which it is incapable in the free state. Gases in this condition 
are called nascent. See (335, 336). 
The employment of bodies in the nascent state or condition 
has proved of the utmost service in organic chemistry. It may 
be said that the great advances in this branch of science are 
largely due to the utilization of the property in question. SECTION 11. 
KINETIC ENERGY-MOTION. 
CHAPTER 111. 
GENERAL PHENOMENA OP MOTION. 
Motion and repose—Velocity—Trajectory and law of movement—Kinds of 
movement—Newton’s three laws of motion. 
285. Motion and Repose.—A body is in movement in relation 
to another, when the relative positions of these bodies or of their 
parts change in any manner whatsoever. 
A body is in repose in relation to another, when the relative 
Positions of these bodies or of their parts are tixed or invariable. 
I urther expression of these ideas will be found in (41), on 
Mobility. 
In the true or abstract idea of motion, independent of its 
causes, the form of the body is considered without regard to its 
other properties, whatever they may be. We, therefore, speak 
°f the motion of a point, a line, a surface, a volume, and not of 
a material body. The body or figure, the motion of which is 
studied, is called the mobile. 
In modern physics the study of motion in all its forms and 
peculiarities is of the utmost importance. It would almost 
seem that Aristotle was moved by the spirit of prophecy when 
he gave utterance to the aphorism “He who is ignorant of 
iuotion is necessarily ignorant of all natural things.” 
286. Velocity is the product of space and time: it represents 
the rate of movement. In English works when not otherwise stated, 
ie distance is understood to he measured in feet, and the time to be one 
second. So a velocity of 10 signifies 10 feet per second. The 
(’ate is also understood to be uniform unless otherwise stated. 
A hen the velocity is very great, as in the movement of electricity, 248 
KINETIC ENERGY MOTION. 
it is given in miles per second. The following are examples of 
velocities. Knowledge regarding them is frequently of use in 
medico-legal inquiries. 
Milos in 
one second. 
Electricity, short circuits . . . . . . not less than 200,000 
Light ........... 
. 192.500 
Electric currents in telegraph wires (voltaic) .... 
12,000 
Feet in 
one second. 
Belative motion of the sun in space ..... 
. 205,920 
Aerolites or shooting stars ....... 
. 114,000 
Mean rate of the earth’s centre in its orbit round the sun 
. 101,061 
Sound traversing solid bodies ....... 
11.280 
Mean velocity of air from explosion of gunpowder 
5,000 
Sound traversing water ........ 
4,480 
Volcanic stones projected from the volcano of Teneritfe, 1798 
3,000 
A 24-pound cannon ball (maximum) ..... 
2,450 
Bifle-ball (maximum) ........ 
1,600 
1.525 
A point at the surface of the earth under the equator 
A common musket-ball (maximum) ..... 
1,280 
Air rushing into a vacuum ...... 
1,280 
Volcanic stones projected from Etna ..... 
1,250 
Sound traversing air at a temperature of 60° 
about 1,120 
Sound traversing air at 32° ....... 
1,098 
A point at the earth’s surface, latitude of London 
950 
Bullet discharged from air-gun (pressure equal to 1500 pounds 
on 
the 
square inch) ......... 
697 
Maximum velocity of wave of Lisbon earthquake, 1755 
642 
Flight of a swift . . . 
252 
Minimum velocity of wave of Lisbon earthquake, 1755 
184 
The most violent hurricane ....... 
146 to 160 
Flight of a swallow ........ 
134 
Flight of an eider duck ........ 
132 
Waves in a heavy swell of the open South Atlantic Ocean 
130 
Flight of carrier pigeon ........ 
120 
A hurricane ......... 
117 
Current in nerve in man ........ 
108 
Locomotive (70 miles an hour) ...... 
102 
Flight of a Falcon ......... 
83 
Eace horse . . . 
80 
A storm (also a tidal wave in the British channel) . 
73 
Ordinary race horse ........ 
. 42 to 50 
Flight of a crow ......... 
37 
A brisk wind .......... 
36 
Steamship (18 miles per hour) 
25 
Man on a bicycle ........ 
24 
Current of most rapid rivers 
13 
A wind of mean intensity ....... 
10 
A carriage going six miles an hour . . . . . . 
. nearly 9 
The gulf-stream (maximum) ....... 
Man walking 
7 
6 
An ordinary wind ......... 
6 
Mean velocity of the current of rivers 
4 
Bate of arterial flow in dog '. ! 
1.6 to 0.75 
0.075 
Bate of venous flow in dog 
0.75 
0. very slight 
Snail ........... 
0.005 GENERAL PHENOMENA OF MOTION. 
249 
287. Trajectory and Law of Movement.—A point in movement 
describes a line which is either straight or curved. This line is 
called its path or trajectory. The trajectory is, therefore, the 
successive positions of a point in motion (293). 
The relation existing between any portions of the trajectory 
and the rate of movement, or time occupied by the point in 
making them, is the law of movement. 
The law of movement is expressed by an equation or, accord- 
ing to the graphic method, by a curve constructed in the fol- 
lowing manner: Two straight lines, 0 X and 0 Y, originate at 
O and pass therefrom at right-angle to each other. Of these 
Fiu. 102. 
dues let 0 Y represent distances in tenths of inches, or any 
other measure, as expressed by the values sd, lOd, on the scale, 
and 0 X times in seconds, as expressed by ss, 10s, 15s. To 
these lines the names axis of abscissas, 0 X, and axis of ordinates, 
0 T, are given. They are also called c/ordinate axes. 
Suppose a mobile point during a time equal to 5s has travelled 
a distance expressed by sd. The position of the point is found 
oy drawing a line from 5s parallel to 0 Y, and another from 5d 
parallel to 0 X, the intersection of these lines at 1 will then 
show the position of the point at the moment indicated. 
This position connected with O from which the two measures 
°ngmated, gives the line of movement, which in the case in 
question is straight, as is shown by 0 1. 
The line 0 X in the figure being the axis of abscissas, 0 5s is 
the^abscissa of the point 1. The line 0 Y being the axis of 
ordinates, the dotted line 5s 1 is the ordinate of the point 1. 
Suppose that in the additional time 2s, the point has travelled 
‘ln additional unit of distance, its position will then be at 2, and 
be direction of the line of movement will be changed as repre- 
sented. 
. ohowing the same method, the positions represented by the 
lntersections or crosses at 3, 4, 5, etc., are established, each 
expressing the time at which the point has travelled a given 
c ls^ance. These intersections being connected, give the curve of 
Movement, O I). 
Law of movement. 250 
KINETIC ENERGY MOTION. 
This method is not absolute unless it gives the character of the 
movement in the intervals between the recorded times. 
The law of movement being known or represented by its 
curve, we possess solutions of the following questions: 
Ist. In a given time from the moment of departure, what is 
the distance from the point of departure ? 
2d. A mobile point being a certain distance from the point of 
departure, how long from the time of departure has it taken to 
reach this position ? 
All kinds of phenomena may be represented by this method, 
which offers the great advantage of a direct appeal to the eye. 
Suppose, for example, we desire to show the solubility of a salt 
at various temperatures. In that case O Y being the tempera- 
tures, and O X the quantities dissolved, the curve 0 D is the 
curve of solubility of the salt under examination. Again, let 
0 Y represent the number of respirations, and 0 X the hours 
at which the count is taken, beginning at 1. The curve 
1, 2, 8, etc., D, is then the curve of respiration for the time. 
The record of the sphygmograph is another application of the 
same principle, in which the force in action records its own 
curve. On the abscissa and ordinate of this curve the relative 
force of the heart’s action at any moment is seen, both for a 
single beat and for a number of beats compared together. 
288. Kinds of Movement.—The simplest kind of movement is 
that called uniform movement, in which equal spaces are traversed 
in equal lapses of time. In this case the curve produced by the 
graphic method is a straight line. 
All movements which are not uniform are called variable. 
These may be uniformly varied or not. Of these, again, the 
simplest is the uniformly varied movement, which is either 
accelerated or retarded. Of accelerated movement, gravity is an 
example. Retarded movement is illustrated by the resistance of 
air. Of irregularly varied movement, the curve represented in 
Fig. 102 is an example, the motion being at one time accelerated 
and at another retarded, as is shown by flexure of the curve. 
289. Newton’s Three Laws of Motion.—Ist. A body free from the 
interference of external matter or force will either remain forever 
at rest, or will move uniformly in a straight line. 
2d. Any change in the amount or the direction of a body’s motion, 
must be due to the action of some force impressed on the body in the 
direction of that change, and is a measure of that impressed force. 
3d. There is no action or motion in the universe, but at the expense 
of an equal and opposite concomitant action, or “ action and reaction 
are equal and opposite.” 
Place a magnet in the pan of a balance and counterpoise it, MEASUREMENT AND REPRESENTATION OF ENERGY. 
251 
then approach a mass of iron under the pan and by weights 
measure the force required to overcome the attraction. Reverse 
the arrangement, place the mass of iron in the balance pan, 
counterpoise it and approach the magnet. If care has been 
taken that the relative distances apart of the magnet and iron 
are the same in both experiments, the force of attraction is the 
same in both cases. It matters not what the relative sizes of 
the magnet and mass of iron may be, for any given combi- 
nation the attraction of each for the other is the same, or, the 
action and reaction are equal. 
The approach of two boats freely floating, when a person in 
one is pulling at a rope attached to the other, the recoil of a 
rifle not firmly held, the action of a propeller, are familiar 
examples of the principle of equality of action and reaction. 
CHAPTER IY. 
MEASUREMENT AND REPRESENTATION OF ENERGY. 
Ue unit of time—The unit of space—Units of weight and mass—Representa- 
tion of forces by lines—The parallelogram of forces—Momentum and meas- 
ure of force—Work and unit of work—Measurement of energy. 
Three elenients enter into the measurement of force and 
energy. They are time, space, and weight or mass. For each 
°t these a definite unit has been devised. 
390. The Unit of Time is the second. Under ordinary circum- 
stances, the second employed is that of mean solar time. The 
time which elapses between two transits of the sun’s centre at a 
given meridian is called an apparent day. Since this interval 
Varies slightly from day to day, its average duration is taken 
and is called the mean solar day. It is divided into 24 hours, 
6ach of these into 60 minutes, and these into 60 seconds each. 
|he second, therefore, is the 86,400 th portion of a mean solar 
aT- It is determined in practice by the beat of the seconds 
Pendulum (306). 
. 391, The Unit of Space is triple, according as the measurement 
Ist. Of length or distance; 2d. Of area or surface; and 3d. 
volume. The English standard of length is the Imperial 252 
KINETIC ENERGY MOTION. 
yard, or the distance, at 60° F., between two marks on a 
metallic rod, which is preserved in the Tower of London. 
Custom has substituted the foot or one-third of the yard as the 
practical unit. The French standard of length is the metre; 
this is very nearly the ten-millionth of an arc of the earth’s sur- 
face extending from the pole to the equator. It also is practi- 
cally fixed by marks on a certain rod. 
, The length of the seconds pendulum in latitude 45° is 0.9935 
metre, which differs from a metre by only 6.5 millimetres. The 
English and French units bear the following relations to each 
other. 
The yard = 0.914388 metre. 
The metre = 1.093633 yard. 
The unit of area is a square each side of which is the unit of 
length. The unit of volume is a cube each edge of wdiich is the 
unit of length. 
292. Units of Weight and Mass.—Bodies are of equal weight 
if they counterpoise each other when weighed in vacuo. 
The English unit of weight is the pound (avoirdupois). It is 
a certain platinum weight kept in the Exchequer Office in 
London. All other weights are multiples or submultiples of 
this. The practical French standard is the gramme, which is 
the weight of one cubic centimetre of pure water. The kilo- 
gramme, or one thousand grammes, is also used as a unit; it is 
equal to 2.205 pounds avoirdupois. 
The weight of a body varies according to the action of gravity 
upon it. The mass of a body is, on the contrary, invariable, it 
is the quantity of matter it contains. 
Any given substance has the same mass wherever it is placed. 
On the moon its mass would he the same as on the earth, but 
since the attraction of the moon is less than that of the earth, 
its weight on the moon would be proportionally less. 
If the weight of a body at any given place is divided by the 
accelerative force of gravity at that place, the quotient obtained 
will be the same at all places, since weight varies with the 
force of gravity. This constant quotient is a valuation of the 
body for all locations, and, therefore, represents its mass. It is 
generally expressed by the formula: 
w 
m = —. 
9 
To find the mass of a body for the earth’s surface, the value 
of gat 45° latitude is taken. It is equal to 32.1724. 
293. Representation of Forces by Lines.—Both attraction and 
motion may be represented by means of lines. This method is 
commonly known as the graphic method. It is invaluable in MEASUREMENT AND REPRESENTATION OF ENERGY. 
253 
enabling us to detect the relations of various phenomena to each 
other, and to determine the laws under which they are produced. 
Such lines may be either straight or curved. The following 
is an example of this method taken from Ganot. 
Draw any straight line A B (Fig. 103), and fix on any point 
oin it. We may suppose a force to act on the point 0, along 
Fig. 103. 
Representation of forces by lines. 
the line AB, either towards Aor B; then Ois called the 'point 
of application of the force, A B its line of action; if it acts 
towards A, its direction is 0 A; if toward B, its direction is O B. 
It is rarely necessary to make the distinction between the line 
of action and direction of a force, it being very convenient to 
have the understanding that the statement, a force acts on a point 
O along the line OA, means that it acts from Oto A, Let us 
suppose the force which acts on 0 along* O A contains P units 
of force; from 0 towards A measure OA, containing P units 
of length; the line 0A is said to represent the force. The analogy 
between the line and the force is very complete; the line O IST 
is drawn from 0 in a given direction 0 A, and contains a given 
number of units P, just as the force acts on 0 in the direction 
OA, and contains a given number of units P. It is scarcely 
necessary to add that if an equal force were to act on O in the 
opposite direction, it would be said to act in the direction O B, 
and would be represented by O M equal in magnitude to 0 A. 
When we are considering several forces acting along the same 
line we may indicate their directions by positive and negative 
signs. Thus the forces mentioned above would be denoted by 
the symbols + P and P respectively. 
294. The Parallelogram of Forces is the name given to a device 
by which we may measure the result of the influences of two 
forces upon a point, when they both act at the same moment of 
Fig. 104. 
Parallelogram of forces. 
time. The method, as will be readily understood, also covers 
direction and velocity. It is an application of the principles 
described in the preceding article. 
When two forces act on a point A, Fig. 104, draw from that 254 
KINETIC ENERGY MOTION. 
point two lines A B and A D, representing the forces in direc- 
tion and magnitude. On these lines construct the parallelogram 
AB CD. The resultant of the forces will then be represented 
in direction and magnitude by the diagonal line A C drawn 
from the point A. See article (293). 
Examples of the application of this and the preceding para- 
graphs are found in the chronograph, for the measurement of small 
intervals of time; the myographion, for the study of the charac- 
ters of the movements of muscles. To these the tambour of 
Marey, for the transmission of action from one point to another, 
might be added. 
295. Momentum and Measure of Force.—Momentum is the pro- 
duct of the mass and the velocity of a body. A body having a 
mass equal to five, and moving with a velocity of ten feet per 
second, is said to have a momentum of fifty. 
If a force is constant, it is measured by the momentum it can 
communicate to a bod}7 in a unit of time. If it is variable, it is 
measured at any moment by the momentum it would give to a 
body if it continued constant from that instant. The English 
unit of force is, “ that force which acting upon a pound of matter 
would produce in one second a velocity of one foot per second.” 
lu the use of the terra, pound-weight, it must be remembered 
that since gravity differs at different parts of the earth’s surface, 
a pound weight at the equator is not the same as a pound weight 
at the pole. A weight of platinum which is counterpoised by 
the elasticity of a spring stretched to a certain point when it is 
at the equator, requires a different extent of stretching of the 
spring to balance it at the pole (299). 
The question of the momentum or force of winds occasionally 
becomes a matter of importance in connection with medico- 
legal inquiries. In this case the momentum is usually estimated 
as pressure on the square foot. 
Momentum of winds. 
Miles 
per hour 
Force in pounds 
on square foot. 
Character. 
5 
0.12 
. Gentle breeze. 
10 
15 
0.491 
1.11/ • 
. A brisk gale. 
20 
1.97 
. Very brisk. 
30 
35 
4.431 
6.03/ • 
. High wind. 
40 
45 
7.87 \ 
9.96 / • 
. Very high winds. 
50 
12.80 
A storm. 
60 
16.71 
. A great storm. 
80 
81.49 
. Hurricane. 
100 
49.20 
f A hurricane that tears up trees 
' \ and destroys all before it. MEASUREMENT AND REPRESENTATION OF ENERGY. 
255 
296. Work and the Unit of Work.—When a force produces 
acceleration of motion, or when it maintains motion unchanged 
in opposition to resistance, it is said to do work. Of all 
standards which might be employed for purposes of measure- 
ment, none is more invariable than gravity ; even resistance of 
air varies with its temperature, changes in which cause varia- 
tions in its weight. 
Work does not necessarily include time as one of its factors. 
The conveyance of 100 bricks to the top of a building requires 
double the work needed to raise 50 bricks to the same altitude. 
It is also independent of the origin of the force, whether pro- 
duced by man, horse, or steam. It is the result only which is 
dealt with, viz., the elevation of a certain weight to a certain 
height. 
The British unit of work is called the foot-pound. It may be 
defined as the energy required to raise one pound of any kind 
of matter through the vertical height of one foot at the latitude 
of London. , 
The French unit of work is called the kilogrammetre. It is the 
energy required to raise one kilogramme (292) to the vertical 
height of one metre (291). The kilogrammetre is equivalent to 
about 7.24 foot-pounds. 
To determine the amount of work resulting in any action : 
Multiply the whole weight in pounds by the vertical height in feet, and 
the product is the number of foot-pounds of work done. For the 
French system: Multiply the whole weight in kilogrammes by the 
vertical height in metres, and the work done is represented by the num- 
ber of kilogrammetres. 
297. Measurement of Energy.—A railway train going with 
double velocity possesses double quantity of motion, momentum, 
or shock-giving power; but its energy or power of overcoming 
resistance is four-fold that it had at half the speed. It will go 
four times as far before it stops after the steam is shut off. 
A ball which has the power of penetrating one plank when 
moving with a certain velocity, will penetrate four planks of 
oqual thickness if its velocity is doubled. Hence we have the 
following rule ; Penetrating power, or energy, increases as the square 
°f the rate at which the velocity increases. 
The penetrating power of projectiles from firearms is often a 
matter of medico-legal inquiry. Of course, it varies for dif- 
ferent parts of the body and for different persons according to 
fhe thickness of the organs traversed and their composition. 
In a general way, however, the average resistance of the body is 
given as being equivalent to about that of two inches of the 
soft wood called deal. At close range, therefore, a bullet KINETIC ENERGY MOTION. 
which has sufficient energy to penetrate a number of two inch 
deal planks, would pass through the bodies of an equal number 
of individuals. 
The relations of work and energy may be better understood 
by comparison of their units. That of work is the work done 
in lifting a one pound weight one foot high. That of energy is the 
energy expanded in lifting a one pound weight one foot high in one- 
second. 
Again, to find the work done, the weight in pounds is multi- 
plied by the height in feet. To find the energy in a moving 
body, the weight is multiplied by the square of the velocity and 
the product divided by or, for rough estimate, 64. 
CHAPTER Y. 
VARIETIES OF MOLAR MOTION. 
Rectilinear motion—Falling bodies—Sand-glass—Path of projectiles—Collision— 
Impact and transmission of impulse—Reflection of rectilinear motion—Oscil- 
lating or reciprocating motion—The pendulum—The metronome—The balance 
wheel—Rotation—Molar motions typical of intramolecular movements— 
Centrifugal and centripetal forces or motions—Applications of centrifugal 
force. 
Molar motion may be : Ist. Straight or rectilinear, 2d. Oscil- 
latory. 3d. Rotatory. 4th. Centrifugal and centripetal. 
298. Rectilinear Motion is also called direct, straight, and 
translatory; the latter term is also used in the case of motion 
in curved trajectories. 
In direct or rectilinear motion the molecules of a body are 
not disturbed in their relation to each other. The nearest 
approach to absolute rectilinear motion, as far as the earth is 
concerned, is offered by falling bodies in which the body 
is moving in the direct line of gravity or attraction. Movement 
of a body in any other direction is interfered with by gravity, 
which tends to draw it out of its straight course. We shall, measurement and representation of energy. 
257 
therefore, first take up the study of rectilinear motion as pre- 
sented by falling bodies. 
299. Falling Bodies.—The ancients maintained that the velocity 
of a falling body is proportional to its weight, and cited the 
example of a stone and a feather. When Galileo denied this, 
he was ridiculed by the disciples of Aristotle, and though he 
proved his opinion by dropping bodies of different weights 
from the leaning tower of Pisa, and showing that they all struck 
the pavement at the same time, they were still incredulous. 
The only force with which falling bodies have to contend, is 
resistance of the air. In the case of very light solids this is 
so great as to drive them from their rectilinear course, as 
is shown by the manner in which a feather or a piece of paper 
falls through the air. Removing this resistance and leaving the 
body to the simple action of gravity, as may be done in the ex- 
periment of the guinea and feather tube (193), we find, that in 
a vacuum all bodies have the same rate of movement at the 
same moment of time. The rate of movement or velocity of a 
falling body can, therefore, only be correctly measured in 
a vacuum. 
In the case of falling liquids it is partly resistance of the air 
which causes them finally to break into drops, or even into 
a fine mist, as is seen in the Falls of Montmorency and at the 
Staubach in Switzerland. In a vacuum liquids fall like solids, 
without disturbance of their molecules, as is shown by move- 
ment of the fluid in the instrument called the water hammer 
(196). 
The space traversed by a body falling in vacuo from a state 
°f Test, is roughly given at sixteen feet at the end of the first 
second, but it varies at different latitudes as is shown in the 
following table: 
St. Thomas . 
. hit. 0° 
25' N. 
it is 16.0478 feet. 
New York . 
. “ 40° 
43' “ 
“ 16.0797 “ 
Taris . . 
“ 48° 
50' “ 
“ 16.0909 “ 
Hammerfest . 
. “ 70° 
40/ << 
“ 16.1182 “ 
ITiese differences are owing to variations in the attractive 
force of gravity at these latitudes. A body near the equator 
tends to fly off from the surface by centrifugal force (311). By 
just so much is the force of gravity diminished. At the pole the 
centrifugal force is nothing. Again, the earth is not a true 
sphere, but is flattened at its poles. The polar regions, there- 
t°Te, being nearer to the centre of gravity of the earth than the 
equatorial, attraction of gravity is greater at the poles than at 
fbe equator. It is these causes taken together which increase 258 
KINETIC ENERGY MOTION. 
the gravity and weight of a body at the pole compared with that 
it has at the equator, and also increase the distance through 
which it falls in one second. At the equator the attraction is 
less by about jfj part of its value at the poles. 
The velocity of a falling body at any moment of time has 
been experimentally proved by various forms of apparatus, 
among which Atwood’s machine and that of Morin are worthy 
of special mention. In the latter a falling body traces its own 
curve of movement on a revolving cylinder. The investigations 
in question demonstrate that the velocity of a falling body is 
proportional to the time during which the motion has lasted. It 
increases in an arithmetical ratio or progression. At the end of 
the first second it is thirty-two feet per second; of the second, 
sixty-four; of the third, ninety-six; and so on. 
In all there are three laws under which the phenomena repre- 
sented by falling bodies may be grouped, as follows: 
Ist. In a vacuum all bodies fall with the same velocity from a state 
of rest. 
2d. Ihe distances traversed are proportionate to the squares of the 
times. 
3d. The velocities are proportionate to the times. 
300. The Sand-glass.—ln former times measurements of brief 
lapses of time were made by the movement of falling bodies 
such as water and sand. Where the first of these was used the 
clock produced was called a clepsydra. When sand 
or other finely divided solid was employed it was 
called a sand-glass. 
This instrument consists of two hollow glass 
cones set apex to apex, and communicating with 
each other by a fine opening at their apices A. 
The upper division contains such quantity of sand 
as requires a given lapse of time to fall through the 
opening into the lower division; according as this 
is 1, 3, 5, or more minutes, the apparatus is called 
a 1, 3, or 6 minute sand-glass. 
When time is to be measured, all the sand is run 
into the lower division; at the instant of beginning 
Fig. 105. 
Sand-glass. 
the measurement the glass is quickly inverted, bringing the filled 
division uppermost. As the last particle passes through the 
opening the operator calls time. The sand-glass is still em- 
ployed to measure time in casting the log by sailing vessels. 
301. The Trajectory of Projectiles.—lf we exclude resistance ot 
the air, the following presentation of this problem would be its 
solution when a spheroidal projectile is thrown in the horizontal 
direction. measurement and representation of energy. 
259 
Let a, Fig. 106, be a body thrown with a velocity of a b feet 
per second. If nothing interfered with its motion, it would in 
2, 3, 4, 5 seconds reach the points c, d, e,f. But during its 
transit gravity is acting upon it, the 
vertical positions 2, 3, 4, 5, represent 
the effect of this force during the time 
the original projectile force is in opera- 
tion, consequently the actual course or 
trajectory of the projectile is the re- 
sultant of these two forces. At the 
end of the first second the projectile is 
at b' instead of b; at the next, at cf, 
and so on. Connecting these points 
Me obtain the curved line af', which 
is a parabola. 
If the original line of projection is 
not horizontal, but forms an angle with 
the horizon, the theoretical trajectory 
of the object would still be a parabola, 
and the greatest range would be at- 
tained when the original course was 
Fig. 106. 
Trajectory of projectiles. 
at an angle of 45° with the horizon. In actual practice resist- 
ance of the air, elongated form of projectile, and the rotatory 
motion upon its long axis which is imparted by the rifling of 
the gun, produce a certain amount of variation from the theo- 
retical course. 
302. Collision.—Problems in connection with collision of in- 
terest to physicians are of three kinds. Ist. When a moving 
body strikes another body at rest. 2d. When both bodies are 
moving in the same direction, the rearmost one having the 
greater velocity. 3d. When the bodies are moving in opposite 
directions. In considering these propositions, we may take 
momentum as the means of comparison, and attribute it in the 
first case to the action of gravity. 
Momentum (295) is the product of the mass or weight of a 
body, and its velocity. Apply these data to the consideration 
M phenomena presented by the fall of a man from a scaffold- 
lng, estimating his weight at 128 pounds. 
fl'iine. 
Distance. 
Velocity. 
Momentum. 
1 second. 
16 feet 
32 feet per second. 
64 “ “ “ 
4.096 
2 u 
64 “ 
8.192 
3 u 
144 “ 
96 “ “ “ 
12.288 
4 u 
256 “ 
128 “ “ 
16.384 
The momentum acquired at the end of each second of fall is 
sufficient explanation of the terrible consequences of such acci- 
dents. 260 
KINETIC ENERGY MOTION. 
In the second case, where one body overtakes another, the 
momentum of impact will be the difference of their respective 
momenta. 
In the third case, where they collide with movements in oppo- 
site directions, the momentum of impact will be the sum of 
their respective momenta. Hence the severe consequences 
arising when two persons running in opposite directions collide, 
or when two railway trains meet in opposite courses. 
303. Impact and Transmission of Impulse.—ln the arrangement 
represented, Fig. 107, a rod of steel, A A', is firmly fixed in 
the jaws of the vice Y, Against the end of the rod at A, a 
ball of ivory, B, rests, suspended by a thread from C. On strik- 
Fig. 107. 
Impact and transmission of impulse. 
ing the extremity of the rod at A' with the hammer D, the im- 
pulse given by impact of the hammer is transmitted along the 
rod, and the ball B is thrown off from its opposite extremity, as 
is shown by the dotted line and the position E. 
Fig. 108. 
Collision balls. 
For investigation of the above, the apparatus, Fig. 108, may 
be employed. It consists of a series of balls, A, B, C, D, E, made measurement and representation of energy, 
261 
of ivory or other elastic material. These are suspended from a 
rod, their centres being in the same straight line, and surfaces 
touching each other. 
Raising the first ball into the position A, and-allowing it to 
fall, when it reaches the position indicated by the dotted line at 
Ait strikes against B; thence the impulse is delivered to C 
and D, without any appreciable motion of either; I) finally de- 
livers it to E, which being free to move, flies off to the position 
of the dotted line at E, the ball E exhibiting almost as much 
deviation from the perpendicular as was given to A, which de- 
livered the original impulse. 
Let us conceive that the balls in the above experiment repre- 
sent a line of molecules in the steel rod, Fig, 107. We then 
perceive that when such a rod is 
struck, the impulse produced by 
the impact is transmitted from 
molecule to molecule along the 
pod in straight lines, and is de- 
livered at its extremity with little 
pr no movement of the interven- 
ing molecules from their position. 
A motion such as that we have 
described is sometimes called a 
longitudinal impulse or vibration 
(365). In this, whatever movement 
or changes the particles undergo 
are in the same course as the 
track of the wave, and not at 
fight angles or transverse to it as 
m waves on the surface of water. 
Fluids as well as solids have 
the power of transmitting i mpulse. 
In Fig. 109, A is an India-rubber 
uug and tube, filled with water, 
and suspended from a bar. At B 
yIG- 109. 
a sphere of cork or other light 
material touches the surface of 
the sack of fluid. Tapping with 
impure through water. 
a small mallet C, or with the finger on the opposite side of the 
ag, the impulse is transmitted through the fluid, and the cork 
thrown oft' to the position D. 
■ The above is an experimental illustration of the principle 
upon which physicians depend in the employment of the fluc- 
tuation test for detection of accumulations of fluid in cavities 
°f the body, or in abscesses which have resulted from inflam- 
matory action. 262 
KINETIC ENERGY—MOTION. 
304. Reflection ot Rectilinear Motion: Its Law.—The apparatus, 
Fig. 110, consists of a spring enclosed in a box, A, so arranged 
that when the spring is released from tension a ball is projected 
from the box. At Ban elastic surface is adjusted. Setting the 
Fig. 110. 
Law of reflection of motion. 
spring free it propels the ball in the straight line A B; striking 
against B, the ball moves off in the new direction BC. If a 
line B P be drawn perpendicular to the point of impact on the 
surface B, the angle formed between this line and A B is equal 
to that between the same line and B C, or, in other words, the 
angle of reflection and incidence are equal. They lie in the 
same plane, and are on opposite sides of a perpendicular drawn 
to the point of impact on the reflecting surface. 
The above principle often affords a clew to the determination 
of the path a bullet has taken after striking a bone. In spite 
of the great velocity with which a bullet strikes a person, it may 
be deflected from its course if it chances to meet with any re- 
sisting medium at a very acute angle. In this way a pocket- 
book or bundle of letters has been known to deflect a bullet, 
and thereby prevent its reaching a vital organ. Even the fascia 
of the body produce the same effect. A bullet has presented an 
opening of entrance in front of the body, and of exit at the back, 
thus giving the impression that it had passed directly through; 
yet it had merely coursed around under the skin. 
305. Oscillating or Reciprocating Motion.—lf a hard elastic 
body, as an ivory ball, falls upon a hard surface, as a slab of 
marble or porcelain, it is thrown off* or rebounds therefrom. 
Rising to a certain height it comes under the influence of 
gravity, and falling on the slab again rebounds; so the move- 
ment continues until the original impulse is lost. The move- 
ment we have here produced is called an oscillatory or recipro- 
cating motion. It has arisen from a rectilinear or direct motion. 
Direct movement is, therefore, convertible into reciprocating 
motion. 
The examples of reciprocating motion are numerous. Ko 
better illustration can be offered than the motion of a piston in 
its cylinder. The sway or swing of a pendulum is also ato and 
fro or reciprocating motion. MEASUREMENT AND REPRESENTATION OF ENERGY. 
263 
306. The Pendulum.—The ideal, simple, or mathematical pen- 
dulum is a single heavy point suspended by a thread which is 
without weight. These conditions it is impossible to realize in 
practice, but they may he approached very closely. 
The compound or physical pendulum is that in 
actual use. In it a weight or bob is suspended by 
Fig. Hi- 
a solid rod, Fig. 111. 
If a ball of lead or platinum be suspended by 
a fine thread, we have an approach to a simple 
pendulum. If the distance from the point of sus- 
pension to the centre of the bob is three and a 
half feet, a pendulum will nearly beat seconds in 
its oscillations. If while it is beating, the string 
is suddenly caught between tbe thumb and finger, 
about half way between the point of suspension 
and the bob, and held steadily, the oscillations 
become more rapid, since the distance from the 
uew point of suspension to the bob has been re- 
duced one-half. As the free portion of string is 
made shorter, the oscillations are still more rapid. 
Releasing the string, and restoring the original 
length of the pendulum, the original rate of oscil- 
lation is regained. 
Again throwing the pendulum into motion 
wdh the full length of string, and watching the 
time required to make an oscillation, we find that 
so long as the amplitude of oscillation, or length of 
Pendulum. 
arc through which it beats, does not exceed five decrees, the 
j•O 1 o ' 
tlrne of oscillation or beat is always the same. 
We have here learned the two laws of the beat of the pendu- 
lum, viz.: Ist. Within an arc of Jive degrees the time of heat of the 
Pendulum is rigorously the same; 2d. The shorter the pendulum, the 
'more rapid its oscillation. It is these facts which enable us to em- 
ploy the pendulum for measurement of time by clocks. 
In (270) we have seen that the cause of the beat of the pen- 
dulum is gravity. In (299) we learned that the attraction of 
gravity varies on different parts of the earth’s surface. It is, 
therefore, evident that the length of the mathematical seconds 
Pendulum must differ at different latitudes. The extent of these 
differences at the level of the sea is shown in the following table. 
St. Thomas 
. lat. 0° 25'it is 
89.0207 inches. 
New York 
. “ 40° 43/ “ 
39.1012 “ 
Paris . 
. “ 48° 50' “ 
39.1285 “ 
Hammerfest t . 
. “ 70° 40' “ 
39.1948 “ 
307. The Metronome is an instrument employed by musicians 
0r the purpose of beating time correctly. It is represented in 264 
KINETIC ENERGY MOTION. 
Fig. 112, and consists of a clock movement, which is enclosed 
in the base, A, of the apparatus. The pendulum is short and 
Fig. 112. 
inverted, the weight or bob, B, being on the 
upper instead of the lower part of the rod. 
The boh is free to slide upon the rod, and 
thus different lengths may be given to the 
pendulum, and the rate of oscillation varied 
to meet requirements of the time to be beaten 
or measured. 
When in action the metronome emits a 
peculiar click, which serves to mark the time. 
It is employed in the measurement of time in 
physiological inquiries. In solution of such 
problems as the rate of nerve current, the 
more accurate device of the seconds pendulum, 
Metronome 
with or without the interruption of an electric current, is used. 
308. The Balance Wheel.—lf we conceive that the line of sus- 
pension of a pendulum is so shortened that the point of suspen- 
sion and centre of oscillation pass within the pendulum bob, 
and finally reach its centre, the character of the oscillation be- 
comes that which we see in a watch or chronometer balance 
wheel. 
In a true balance wheel, where the point of suspension is 
accurately at the centre of the oscillating mass, gravity has no 
influence of importance. The forces which produce the move- 
ments are a main spring which drives the system of wheels of the 
apparatus; and a very fine spring called the hair spring, which 
is attached to the balance wheel, and acts upon it in an opposite 
manner to that of the main spring. 
Both the pendulum and balance wheel are subject to vari- 
ations in rate of oscillation, produced by variations in tempera- 
ture. For the discussion of these, and means of correcting 
them, see (663). 
If the point of suspension in a balance wheel is exactly at its 
centre, there is no motion of the mass out of the area it occupies 
when at rest. If, on the contrary, the point of suspension or 
centre of oscillation is on one side of the centre, the area oc- 
cupied by the wheel in its oscillations is greater than its own 
area when at rest. . 
Applying these ideas to oscillations which the molecules in 
a mass of matter are executing, we can conceive that when a 
molecule is oscillating in a manner similar to that of a balance 
wheel, with the centre of mass and centre of movement coinci- 
dent, one kind or form of force is the result. If, on the con- 
trary, the centre of oscillation passes away from the centre of 
the molecule, conditions similar to those in a balance wheel MEASUREMENT AND REPRESENTATION OF ENERGY. 
265 
mounted eccentrically exist, and the character of the force is 
different, just as the movement is different. In the first case, 
for example, the product might be electricity; in the second, 
heat. 
309. Rotation.—If the bob of a physical pendulum be a cir- 
cular wheel, mounted on its centre or axis of rotation, C, on 
throwing it into action it moves like an ordinary 
pendulum. If while in full swing, and when the 
Fig. 113. 
movement is most rapid—that is, when the centre of 
the bob is vertically under the point of support— 
the bob be suddenly checked at the projection P 
by an object moving in the opposite direction, a 
portion of the oscillatory motion of the wheel will 
he converted into movement of rotation upon its 
centre or axis, C. The same result arises if quickly 
moving the finger in a straight line we strike the 
circumference of the wheel. Oscillatory and also 
direct movement may, therefore, be converted into 
a movement of rotation. 
Potation may be of three kinds: Ist. Centric, 
where the axis of rotation is in the geometric centre 
°f the mass, as in the wheels of a watch or any 
similar machine. 2d. Eccentric, where the axis of 
revolution is still within the mass, but not at the 
centre. 3d. Orbital, where the axis of rotation is 
exterior to the mass, as in the movements of planets 
around the sun. 
Orbital movements differ greatly. Sometimes 
they are circular, sometimes elliptical. They may 
a]so be parabolas or hyperbolas. 
Rotation. 
310. Molar Typical of Intramolecular Movements.—The move- 
ments of a planet with its moons around a central sun, the move- 
ments of double stars or suns around each other, and the com- 
plexity that involves the movements of their attendant planets, 
,° not interest the astronomer alone ; they also demand atten- 
ti°n from the physicist, and suggest to him the idea that in 
the structure of molecules of different kinds of matter the atoms 
c°niposin2; these molecules may also execute many different 
motions. 
feuch an hypothesis would explain how from a single kind of 
elementary atom all our so-called elements might originate, the 
differences between them being merely resultants of various 
movements which the constituent atoms of their molecules were 
executing. 
In modern theories of matter the molecules of elements are 266 
KINETIC ENERGY—MOTION. 
supposed to consist of two, three, or more atoms. It the hy- 
pothesis that hydrogen is the original element be true, a mole- 
cule of lithium would contain a number of atoms seven times 
as great as that in a molecule of hydrogen, a molecule of carbon 
twelve times as many, and so on. In this case the diversity of 
movements that might arise among the constituent atoms of a 
molecule of lithium or of carbon may be readily conceived to 
determine the differences between the molecules of those sub- 
stances. 
Passing from elementary to compound molecules which in 
the case of organic bodies may contain as many as fifty atoms, 
we find that bodies which have the same number of atoms may 
present very different properties, dependent on the relation of 
the motions of the constituent atoms to each other. 
The conversion of one kind of motion into another, which 
we have seen in the study of molar motions, would indicate the 
convertibility of one kind of atomic motion into another. The 
consequent possibility of the conversion of one kind of molecule 
into another, is, therefore, evident. See (28 and 29). 
Hot only motion, but the manner of grouping has its effect, 
as may be seen in the well-known kaleidoscopic appearances 
produced when several kinds of glass are grouped differently by 
merely revolving the instrument (11th, 480). If we conceive that 
the image of each piece of colored glass represents an atom en- 
dowed with a certain kind of motion, we quickly perceive how, 
as the grouping of these are changed, an almost innumerable 
variety of figures arise. In the case of molecules we can im- 
agine a similar change produced as their atoms vary in their 
relations to each other. Thus all the shades of colors in flowers, 
and the infinite diversity of materials produced in the inor- 
ganic and organic worlds, may possibly arise. 
Carrying out these suggestions, and those on conversion of 
motion in (805), to their ultimate conclusions, we find that the 
physics of the imponderables consists in the study of motions 
of molecules, while chemistry deals with the examination of 
movements of the atoms constituting molecules, and the manner 
in which they are grouped. 
-311. Centrifugal and. Centripetal Forces or Motions.—The terra 
centrifugal signifies flying from a centre of motion. Ho better 
example of this force or motion can be given than that of the 
ancient device of the sling, whereby a stone or other object is 
submitted to rapid orbital movement, and then suddenly released. 
At the moment of release the stone flies off in a straight line, 
driven, as wTe say, by centrifugal force. 
The term centripetal signifies moving upon or towards the 
centre of motion. We have already referred to the influence of measurement and representation of energy. 
267 
centrifugal force in lessening the weight of objects at the equa- 
torial region of the earth’s surface (299), In that case gravity 
acts as a centripetal force; by ft objects are attracted towards 
the earth’s centre, and were they free to do so would move to- 
wards it; as it is, gravity is the centripetal force which binds 
objects upon the earth’s surface and prevents the centrifugal 
torce generated by rotation from launching them into space. 
For illustration of centrifugal force and its action the ap- 
paratus known as the whirling table is employed. It consists 
°f a platform A, Fig. 114, to which rapid rotation may he given 
by suitable multiplying machinery B. Any loose body laid on 
the surface of the platform is quickly thrown off when it is put 
m motion. So great is this force, that not unfrequently grind- 
Fig. 114. 
Fig. 115. 
Whirling table. 
Gyroscope. 
stones and fly-wheels are torn to pieces when their revolution 
is very rapid. It is estimated that if the rate of rotation of the 
earth were seventeen times what it now is, gravity would be 
overcome, and objects would be tossed from its surface, prob- 
ably to form a distant ring like that which accompanies Saturn. 
The instrument known as the gyroscope, Fig. 115, offers an 
excellent illustration of the power of rotation to overcome 
gravity. It consists of a ring set in rapid revolution, while in 
Ibis state it may be made to assume positions contrary to those 
which gravity produces. 
312. Application of Centrifugal Force.—Among the practical 
Applications of centrifugal force we may mention the removal 
pf liquids from solids with which they may be intermingled, as 
ln the centrifugal clothes-wringer, in which clothing is placed in 
a drum-like cage made of wire which is subjected to rapid rota- 
fion. Under these conditions the water is thrown off from the 
Periphery of the drum, and the clothes come out almost dry. 
The centrifugal milk tester is another recent application of 
this force, the milk is placed in a stoppered tube upon the 
whirling table, the axis of the tube being in the line of a radius 
°t the platform of the table. Throwing the apparatus into rapid 268 
KINETIC ENERGY MOTION. 
rotation, the milk separates into the cream, curd, and aqueous 
solution of which it is composed. 
Dr. Arnott says, “Were a man to lie down on a quickly 
turning horizontal wheel, with his head near the edge, he would 
soon fall asleep, or might die of apoplexy from over-pressure of 
blood on the brain.5’ The suggestion is certainly worthy of 
examination. Applied in the manner he relates, it might prove 
of use in insomnia. Still more important results might be 
obtained by reversing the arrangement and placing a person 
suffering from congestion of the brain upon a whirling table 
with his feet towards the circumference, and his head over the 
centre of rotation. In that position the blood would be driven 
from the head to the opposite extremities, and relief attained. 
In other congestions and inflammations the same might be done, 
taking care to place the inflamed part over the centre of rotation. 
The action of centrifugal force upon plants in their growth 
was made a subject of experiment by a French botanist some 
years ago. A series of vessels in which seeds had been planted 
were attached to the circumference of a large wheel to which 
rapid rotation could be imparted. The results of experiment 
showed that no matter how rapid the rotation, the centrifugal 
force thereby developed did not appear to have any influence 
upon the manner of growth of the plant. The stem and roots 
were always in the same straight line. There was no tendency 
to grow parallel to each other and outwards from the centre of 
rotation, as he expected would be the case. SECTION 111. 
MACHINES AND INSTRUMENTS. 
CHAPTER YI. 
Relations of machines to force—The three orders of levers—Estimation of power 
in the action of levers—The wheel and axle—The inclined plane—The wedge 
—Scalpels and their management—The screw—The pulley—Friction. 
313. Relations of Machines to Force,—The forces provided by 
nature for the accomplishment of innumerable kinds of work 
are few in number, wind, a fall of water, animal power. These 
limit nature’s provisions of energy, which by agency of machines 
man has so adapted and controlled as to serve any purpose he 
may desire, from the act of lifting a rock or ship to the more 
delicate operations of setting type and printing a book. 
Wonderful and various as are the acts that machines can 
achieve, it must be clearly understood that in no case do they 
originate or increase the energy employed. They only modify 
if- As we watch a machine punching holes in plates of iron an 
mch in thickness, it looks as if it developed power, but it 
does not. It merely takes a rapid movement, representing a 
certain amount of energy, and converts it into a slower move- 
ment in which the same amount of energy is expended through 
Harrow limits, but within the bounds of "those limits it is almost 
HTesistible. 
The most intricate engines depend for their action upon a few 
machines of very simple form, to which the name of the me- 
chanical 'powers was formerly given. They are the lever, wheel and 
axle, inclined plane, wedge, screw, and pulley. These simple 
machines are all of more or less interest to the physician, either 
as occurring in different parts of the human mechanism, or in 
construction of the instruments he employs. 
314. The Three Orders of Levers.—The lever is so called from 
me Latin levo, to lift. It consists of an inflexible bar; when in 
Hse three additional elements are involved, viz.: A, the power; 
W the weight; C, the fulcrum. According as these three ele- 
ments vary in relative position to each other, a lever is said to 
cc of the first, second, or third order. 270 
MACHINES AND INSTRUMENTS. 
In levers of the first order, the fulcrum is between the weight 
and power, or the middle one of the three; in the second form, 
Fig. 116. 
The lever. 
the weight is in the middle; in the third, the power is in the 
middle. 
All the joints of the body which are endowed with motion 
belong to one or another of the three orders of levers. Of the 
first order, the movement of the skull on the atlas is an example, 
the face being the weight, and the muscle in the back of the 
neck the power. Of the second order, the ankle-joint is an illus- 
tration ; when we raise the body upon the toes, the weight is then 
in the middle, the ball of the great toe being the fulcrum, and 
the muscles on the back of the leg the power. Of the third 
order, flexing of the forearm on the arm is an example; the power 
being in the middle represented by the attachment of the biceps 
muscle, the hand the weight, and the elbow-joint the fulcrum. 
Fig. 117. 
Fig. 118. 
Fig. 119. 
Lever of first class. 
Lever of second class. 
Lever of third class. 
Among instruments in ordinary use, the first order of levers 
is represented by the elevator used to raise portions of bone in 
fracture of the skull, by scissors, and by bone or obstetrical 
forceps, which consist of two levers working against each other, 
the joint being the fulcrum. The second order is represented 
by the action of an oar in rowing, by nutcrackers, and wheel- 
barrows. The third order, by fire-tongs, and ordinary pincers 
of a surgical pocket case. 
A curious double lever, known as the Stanhope lever or toggle 
joint, is represented in the human body by the knee-joint; it is 
a very powerful form of machine, and admirably adapted to the WHEEL AND AXLE. 
271 
purpose it serves in the body, viz., that of raising it from a squat- 
ting position. 
315, Estimation of Power in the Action of Levers.—ln the ex- 
periment represented in Fig. 120, the conditions of equilibrium 
between the two sides of a lever of the first order are shown, A 
weight of one pound at one extremity of the lever, A, will ex- 
actly balance a weight of one pound, B, at the same distance on 
the opposite side of the fulcrum, D. The same weight, A, will 
Fig. 120. 
balance two pounds if suspended from C, which is half the dis- 
tance between I) and B; or it will balance four pounds if sus- 
pended from E, which is one-quarter the distance between I) 
ar*d B. Generalizing from these facts, and applying the rule to 
all forms of lever, we say, that in levers the power is to the weight 
1/1 the inverse ratio of their respective arms. 
If downward force be applied at A, the weight at B, which is 
at the same distance from the fulcrum, wall be raised with the 
sarne velocity through the same distance as that by which A is 
depressed. The weight at C, on the contrary, will under similar 
circumstances he raised only one-half the distance, and at one- 
balf the velocity with which A descends. At E the <liBtance 
will he only one-quarter, and the velocity one-quarter. From 
which we deduce that in the action of levers, what has been 
gained in weight raised is lost in distance and velocity. 
Law of levers. 
316. The Wheel and Axle acts upon the same principle as 
die lever. It has been called the perpetual lever. In Fig. 121, 
d is the axle, and D the wheel, both attached to the axis F. 
Ihe wheel has a radius four times that of the axle C. These 
two measurements representing the relative lengths of the two 
aims of a lever, a power of one pound, B, applied to the cord 
011 L, will raise a weight of four pounds, A, attached to the 
cord wound on the axle C. Viewing the respective radii of the 
wheel and axle, as the two arms of a lever, the rule for the esti* 
mation of the action of this machine is the same as for levers. 272 
MACHINES AND INSTRUMENTS. 
The wheel and axle is extensively used for hoisting heavy 
weights. In this form an endless rope passes around the wheel. 
The capstan used in weighing the anchor on ships is the same 
form of machine, in which the circumference of the wheel is 
dismissed, and only the spokes or radii employed. The winch 
used in raising water (185), and in many surgical appliances, 
is a wheel and axle in which only one spoke of the wheel is 
retained, as at E, Fig. 121. 
Pig. 121. 
Wheel and axle. 
The so-called fusee in a watch is an elegant example of the 
application of the wheel and axle to the production of a uniform 
force from the variable force exerted by a spring when unwind- 
ing. The systems of cog-wheels used in cranes for unloading 
ships, and of bauds and wheels in lathes, are instances of the 
principle of the wheel and axle, and their action is to be deter- 
mined by the same rule as that given for the wheel and axle. 
317. The Inclined Plane is the third method of balancing forces 
of different intensities. The principle of its action is as follows. 
Pig. 122. 
Inclined plane. 
Suppose a weight, A, rests on an inclined plane, the vertical 
height of which, DE, is just one-half its length, CD. It will be 
exactly balanced and retained in position by one-half its weight SCALPELS AND THEIR MANAGEMENT. 
273 
applied vertically at I>. The action of an inclined plane is, 
therefore, merely a modification of the lever. 
In ancient times the inclined plane was largely used in ele- 
vating great weights. It is supposed that by this device the 
Egyptians raised to their present height the immense blocks of 
stone used in constructing the Pyramids. 
It is curious to note how often the work required in the ascent 
of an inclined plane has been disregarded in the construction of 
country roads. The idea has been to build the road in a straight 
line from one point to another regardless of the hills that in- 
tervene, Hoads have been thus carried over hills when they 
might as readily have been carried around their bases with 
little increase in distance, and complete avoidance of the labor 
required to surmount the elevations. 
In the human body the principle of inclined planes is involved 
in the construction of the pelvis, for the purpose of producing 
changes in position of the head of the foetus during delivery. 
The study of the action of these planes in the mechanism of 
labor, demands close attention on the part of obstetricians. 
318. The Wedge may be described as an inclined plane forced 
in between substances or resistances, for separating or overcom- 
ing them. Estimation of their action is difficult, since the force 
employed is not one of pressure but of percussion. This power 
°f transforming force is marvellous; even a ship may be raised 
by proper application of wedges. 
Kumerous examples of the wedge are seen in domestic as 
well as surgical appliances. All cutting implements are wedges, 
fhe angle of the edge varying according to their application. 
I or working iron in a lathe a very obtuse angle is required in 
Hie cutting edge. In the blade of a pocket-knife, scalpel, or bis- 
toury, on the contrary, the angle of the cutting edge is very acute. 
319. Scalpels and their Management.—lf the edge of the keenest 
scalpel or razor be examined under a microscope, it will be 
Beeu to be jagged or saw-like. Such blades may be pressed with 
considerable firmness against the skin without producing a 
"Wound, but the moment they are drawn like a saw over the 
surface, though the pressure be very slight, they immediately 
enter the flesh. 
All surgical knives being made of steel, the greatest care 
should be taken to shield them from rust. So long as a steel 
surface is protected from moisture, oxygen has no action upon 
A but if it be coated with ever so thin a film, it is quickly oxi- 
dized or rusted. To avoid this, steel implements should first 
36 carefully cleansed, then thoroughly dried, and rubbed with 
'Gather before being placed in the case where they belong. 274 
SIMPLE MACHINES AND INSTRUMENTS. 
. Since a knife, scalpel, or other instrument has received in 
its. construction the proper angle for the work it is intended to 
do, care should be taken in sharpening to preserve that angle. 
If it is necessary to grind it down to restore the edge, it should 
be done on a true grindstone, the blade being applied and kept 
at the proper angle, and the action of the stone being from the 
back towards the edge. A thin or wire edge is thus obtained 
which is flexible, and maybe turned by pressure towards one or 
the other side of the blade. 
The next step is to remove the wire edge upon a hone or oil- 
stone; the surface of this should be as flat as possible. If it 
has been in use for some time and become hollow or concave, 
flatness should be restored by grinding it against the surface 
of a grindstone. The blade should be kept prone upon the hone 
throughout its application thereto. The movement should be 
from heel to point of blade with edge forward. 
To give all the microscopic teeth which form the edge of a 
cutting blade a set in the same direction, the sharpening should 
be finished upon a strap of leather, which must also be flat; 
sometimes tightly stretched coarse canvas imbued with soap is 
used. In this operation the movement is reversed, the blade 
being carried from heel to point with the back forward. The 
surfaces should be kept flat on each other as in the preceding 
case, and applied alternately with very moderate pressure. 
320. The Screw.—Form an inclined plane such as that de- 
scribed in (317), by cutting it out of paper, making the inclined 
Fig. 123. 
Screw. 
edge C D very long compared with the vertical edge C E. 
Applying the latter to a cylinder, A B, so that it is parallel 
to the axis of the same, and winding the narrow inclined plane 
on the cylinder, its edge will be found to have formed a screw 
upon the surface of the cylinder, _ We may, therefore, regard 
a screw as being virtually an inclined plane, and estimate its 
action in the same manner. 
To the portion of the apparatus described the name of male 
element is given. The socket in which it works is called the 
female element or nut. 275 
THE PULLEY. 
In the practical application of the screw, the handle by which 
it is driven acts as a lever; we, therefore, have usually a combi- 
nation both of the screw and lever principles. The endless 
screw is the name given to a combination of a screw and a cog- 
wheel, by which one tooth of the cog-wheel is advanced for each 
revolution of the screw. In lithotrites, it is adapted to crush- 
ing the stone or calculus grasped between the jaws of the instru- 
ment. In the splints employed in treatment of certain kinds or 
fracture it is also used to produce the extension required. 
In microscope work, very delicate screws are employed for 
measuring minute distances. Such are called micrometre screws. 
The head usually presents a graduation, by which small fractions 
of a revolution may be measured. Suppose the threads are 
°f an inch apart, and the head presents 100 divisions, a move- 
ment of one division on the head is equivalent to a movement 
°f xFFrolfi °I an inch i'l tlm direction of the axis of the screw. 
The difficulty with such micrometres is irregularity in the thread, 
m which it presents an irregular instead of a regular inclination. 
To this the term drunkenness is applied. In accurate work error 
m this respect must be carefully studied to 
find the proper correction. In some cases 
drunkenness is corrected in the divisions of 
tbe screw head, these being made shorter or 
longer as the case requires. 
Fig. 124. 
321. The Pulley is another device by which 
masses of different weights may be made to 
balance each other by giving them varying 
velocities. In this case the pulley is movable, 
carrying the weight, with one end of the cord 
firmly fixed. Where the pulley is stationary, 
fi merely serves to change the direction of a 
fimce, and does not interfere with its inten- 
sity. 
In the figure, it is evident that one-half of the 
Weight I) is supported by the portion of the 
Pulley. 
at AC, and the other half by the part at BE. If D weighs 
100 pounds, it may be raised by a force of fifty pounds applied 
lor every foot of height that D is raised. 
I>y increasing the number of wheels or sheaves in the pulley 
block, we add to the number of folds of rope by which the 
Weight is sustained, and thereby multiply intensity of the action, 
lb for example, we have four supporting cords, a force of one 
pound will balance or move a weight of four pounds attached 
to the movable block. In these combinations the fixed block has 276 
SIMPLE MACHINES AND INSTRUMENTS. 
no influence except to change direction of the motion as de- 
scribed above. 
Combinations of pulleys are used occasionally in the reduction 
of dislocations of the hip-joint. A knowledge of their action 
is, therefore, of use to surgeons. In the body no example of 
combination of pulleys exist. Examples of the use of the fixed 
pulley for changing the direction of a force are offered by the 
patella, which signifies a pulley; and also by the tendinous 
pulley or loop at the inner side of the orbit, by which the direc- 
tion of the contraction of the superior oblique muscle is changed 
and brought to bear upon the eyeball. 
322. Friction.—Wherever there is motion of one substance 
upon another there is friction. All fluids and gases in their 
movements develop friction; especially is this true of solids. 
As we have seen (277), the force of adhesion which exists 
between different masses of matter affords a certain degree of 
resistance to any movement of such masses upon each other. 
Here, therefore, we find one cause of friction. Another, per- 
haps more potent, is roughness of the surfaces which come in 
contact with each other. Even the most highly polished sur- 
faces are not mathematically true, but present projections and 
depressions of greater or less magnitude; these fitting into each 
other like the projections of cog-wheels, cause an equivalent 
development of friction. 
Friction may be of two kinds: Ist. Sliding friction; and 2d. 
rolling friction. In the latter case the resistance to movement is 
practically much less than in the former. Wherever, therefore, 
the sliding can be converted into the rolling variety, it is done. 
The apparatus known as friction rollers offers the best example 
of the application of this principle. 
The friction developed in the sliding of one surface on another 
depends to a certain extent on the intrinsic nature of the material 
forming the surface. For the examination of this problem an 
inclined plane, the angle of which may be varied, has been 
employed, and the angle of inclination at which movement com- 
menced measured for different materials. 
In Fig. 125 the results of these experiments are presented. 
The various unguents reduce friction to the lowest point; next 
follows friction of metal on metal; then of wood on wood; 
and lastly, of bricks and stones. Since the projections and de- 
pressions in two pieces of the same variety of material are more 
apt naturally to fit into each other, it is evident that substances 
of different kinds are less apt to develop friction than two bodies 
of the same nature, hence the use of iron as the axle or shaft, and 
of bronze in place of iron as the journal for the wheels or pro- 
pellers of steamships. Another application of the same principle FRICTION. 
277 
is offered by the steel pivots and jewelled bearings or journals 
in a watch. 
Three general principles govern the amount of friction de- 
veloped between two plane surfaces, one being fixed and the 
other sliding. 
Ist. Friction is exactly proportional to the pressure between surfaces. 
2d. Extent of surface does not influence amount of friction. 
3d. Friction is independent of the relative velocity of the sliding 
surface. 
Fig. 125. 
Friction. 
In the use of lubricating materials for reducing friction, differ- 
ent lubricators are to be employed for dissimilar substances: 
oils for metals; soap, grease, black-lead, for woods. An oil 
which reduces friction in metals, increases it when used for 
woods. 
In the structure and operation of the joints of animals, great 
Perfection is shown in the means adopted for reduction or avoid- 
ance of friction. The bones are covered by elastic cartilage, 
which is coated by a membrane presenting a wonderfully 
smooth surface; this, in its turn, is lubricated by a fluid called 
synovia, more lubricating than any oil, and renewed as fast as 
required. No human invention approaches in its perfection that 
attained in the construction of joints in animals; even rolling 
18 generally substituted for the sliding form of friction, and 
every device which can reduce expenditure of muscular force to 
the lowest point is adopted. SECTION IV. 
TRANSLATORY MOLECULAR MOTION. 
CHAPTER VII. 
MOLECULES OE TWO MEDIA, ONE SET MOVING. 
Varieties of molecular motion—Divisions of translatory molecular motion—Phe- 
nomena of capillarity—Circumstances influencing capillarity—Surface tension 
of liquids—Causes of capillarity—Laws of capillarity—lnclined surfaces and 
capillarity—Capillarity and floating bodies—lmbibition and absorption—Fil- 
tration—Draper’s steam exhaust for filtration—Special filtration—Absorption 
of gases by solids—Disinfection by charcoal explained—Occlusion—Trans- 
piration of liquids and gases. 
To the contents of this Section the attention of students is 
especially directed, since the principles described are involved: 
Ist. In the absorption of chyme, chyle, and other fluids; 2d. In 
the circulation of blood, lymph, etc.; and, 3d. In the function 
of respiration, including introduction and conveyance of oxygen 
to the tissues, and removal of carbonic acid. 
323. Varieties of Molecular Motion.—Molecular motion is of 
two kinds: Ist. That taking glace between molecules of two or 
more media; 2d. That existing in molecules of each individual 
medium. 
In the first case, the movement may be compared to that of 
direct molar motion, the molecules undergoing a change of their 
position in relation to surrounding molecules. This division 
includes the examination of capillarity, diffusion, osmosis, etc. 
In the second case, the molecules are subject to oscillatory, 
vibratory, or even rotatory motions, and do not materially 
change their location, or if slight change does occur, return 
instantly to their original position. This division deals with 
vibrations which produce sound, light, heat, and other so-called 
imponderable forces. 279 
MOLECULES OF TWO MEDIA, ONE SET MOVING. 
In accordance with the plan followed with molar motions, we 
shall first take up the examination of direct or translatory 
molecular motion, disregarding for the present the fact that the 
molecules of each medium entering into the action have, at the 
same time, the vibratory or other individual movements which 
belong to the condition of the medium they form. 
324. Divisions of Translatory Molecular Motion.—This form of 
molecular motion may be studied under three conditions. First, 
where it occurs between molecules of two media, the molecules 
°f one moving, while those of the other are stationary, as, 
for example, capillarity, imbibition, occlusion. Second, where it 
occurs between molecules of two media, the molecules of both 
being in movement, as in diffusion. Third, where molecules of 
many media are under consideration, all or a portion being in 
movement, as in osmosis. 
325. Phenomena of Capillarity.—We have studied the attrac- 
tion between molecules of different kinds as adhesion (281, 284). 
When such attraction leads to movement, the phenomena of 
capillarity or movement in capillary (capillus, a hair) tubes arise. 
As with adhesion, capillary phenomena are entirely indepen- 
dent of pressure of the air, and appear equally well in a vacuum. 
The phenomena in question may be illustrated by dipping a 
Fig. 126. 
Fig. 127. 
Fig. 128. 
glass tube, A, of an inch bore, and open at both ends, into 
Plater, W, colored by any soluble pigment; ink will answer. 
I he fluid will be seen to rise in the tube at once, as in Fig. 126. 
4 here is capillary elevation. The experiment succeeds also with 
certain other fluids; for example, alcohol. To secure the greatest 
amount of rise in a given tube, the interior should be chemi- 
cally clean, and moistened with the fluid upon which the ex- 
periment is to be made. 
Capillary elevation. 
Capillary depression. 
Capillary action. 280 
TRANSLATORY MOLECULAR MOTION-. 
Extending the experiment to other fluids, we find that while 
many conform to the observation related, others do not. Of 
these, mercury is a notable example; instead of being raised 
by the tube, it is depressed, Fig, 127. 
The opacity of mercury presenting a difficulty in the way of 
seeing the result, we may remedy this by using the apparatus 
represented in Fig. 128. A tube, A, about an inch in diameter, 
terminates below in a narrow tube which is bent parallel to A. 
Pouring mercury into the large tube, it flows freely into the 
small one, but the level in the latter does not rise as high as 
in the former; there is capillary depression. Pouring water into 
the apparatus B, the level in the small tube rises above that in 
the large one: there is capillary elevation, as when the straight 
tube was dipped into ink. The advantage of this form of ex- 
periment is that it enables one to project the result by a lantern, 
and exhibit it to a large class. 
Another phenomenon which appears in connection with capil- 
larity is, that under the conditions which produce an elevation 
of liquid in the tube, the upper surface of the liquid is concave, 
its exterior limits rising higher in the tube than the interior 
portions. On the exterior of the tube also, Fig. 126, a similar 
elevation of the fluid is seen. Where depression takes place, 
the opposite result is produced, the surface of fluid in the 
tube is convex instead of concave, and in place of its rising 
on the exterior of the tube, it is depressed. To the curved 
surfaces in the tube, the names concave and convex meniscus 
are given. 
Seeing that certain fluids are raised in capillary tubes, the 
question presents itself, What will happen in case the tube is 
broken off short of the point to which it can raise the liquid? 
Under such circumstances will it overflow? Experiment deter- 
mines that it merely rises to the plane of fracture,and there is 
no tendency to the establishment of an overflow, nor of a cur- 
rent in the tube (345). 
326. Circumstances Influencing Capillarity.—When a tube is 
moistened'with liquid, the amount of elevation depends entirely 
upon the character of the fluid; the nature of the tube does 
not in itself have any influence. The amount of difference ap- 
pearing for various liquids is shown by the following list, in 
which the diameter of the bore is one millimetre inch), and 
temperature 18° C. Of all substances water rises the highest. 
Water rises 
. 29.79 
millimetres. 
Nitric acid 
. 22.57 
11 
Alcohol 
. 12.18 
U 
Essence of lavender . 
. 4.28 
u MOLECULES OF TWO MEDIA, ONE SET MOVING. 
281 
In capillary depression, since the fluid does not wet the tube, 
the amount of movement is influenced both by the nature of the 
tube and of the liquid. 
Temperature affects both capillary depression and elevation. 
The movement diminishes with increase of temperature. Water, 
for example, which was raised 132 mm. in a tube at 0° C., was 
raised only 106 mm. in the same tube at a temperature of 100° C. 
The condition of the interior of a capillary tube is an essential 
factor in its action. If, for example, it has been smeared with 
oil, it will permit it to rise, but will depress water. If it has 
been moistened with water, that fluid will rise, and oil will be 
depressed. According as the character of the interior super- 
ficies of a capillary tube varies, so does it possess what might be 
called a selecting power, permitting one liquid to enter or 
traverse it, and denying passage to another. 
327. Surface Tension of Liquids.—All liquids act as though their 
superficial layer was subjected to tension which exerts a con- 
tractile force or pressure upon their interior mass. This is ex- 
plained by the fact that the superficial molecules are held 
together by a greater cohesive force than those in the interior. 
I hough this idea is regarded as a convenient fiction by some, 
others accept it as having an actual existence. Regarding it, 
Qanot says ; 
“Consider any particle at the surface of a liquid; it will be 
attracted in all directions except in that above the surface. The 
attractions acting laterally will compensate each other, and as 
there are no attractions above the surface to counteract those 
Acting from the interior, the latter will exercise a considerable 
Pull towards the interior. The effect of this is to lessen the 
Mobility of particles on the surface, while those in the interior 
are quite mobile; the surface, as it were, is stretched by an 
elastic skin. This surface tension, as it may he called, is greater, 
the greater the cohesion of the liquid; it is well illustrated by 
blowing a soap-bubble on a glass tube; so long as the other end 
°I the tube is closed the bubble remains, the elastic force of the 
eacl°sed air counterbalancing the tension of the surface; but 
Avhen the tube is opened, the latter being unchecked, the bubble 
gradually contracts and finally disappears.” 
“Insects can often move on water without sinking. This phe- 
nomenon is caused by the fact that, as their feet are not wet by 
the water, a depression is produced, and the elastic reaction of 
|he surface layer supports them in spite of their weight, Simi- 
arly a sewing needle gently placed on water does not sink, 
because its surface, being covered with an oily layer, does not 
become wet; but if washed in alcohol or potash it at once sinks 
t0 the bottom.” 282 
TRANSLATORY MOLECULAR MOTION. 
328. Causes of Capillarity.—Since capillary phenomena occur 
in an air-pump vacuum as well as in air, they cannot arise 
from action of the atmosphere. They originate in the rela- 
tions of molecules of the liquid for each other and for the 
molecules of the tube in which they are placed. These actions, 
moreover,, are confined to the superficial layer of the liquid 
and tube (326). The thickness of material forming the tube 
has no influence whatever on its action. It may, therefore, be 
said that capillarity is the resultant of the action of cohesion 
and adhesion; as one or the other is in the ascendant, so do 
phenomena vary. When adhesion of the fluid molecules for 
those of the tube is greater than their cohesion for each other, 
the liquid is raised and its surface is concave; when, on the 
contrary, cohesion of the fluid molecules for each other is greater 
than their adhesive attraction for the tube, the fluid is depressed 
and its surface is convex. 
According to modern theory as stated by Deschanel, the follow- 
ing are among the causes producing capillarity : 
Ist. Surface tension of liquids, as described in the preceding 
article. 
2d. For a given liquid in contact with a chemically clean 
solid, there is a definite angle of contact which is independent 
of the directions of the surfaces with regard to the vertical. 
Bd. This angle of contact determines the convexity or con- 
cavity of the free surface of the liquid. 
4th. In capillary depressions and elevations the superficial 
film at the free surface is to be regarded as pressing the liquid 
inwards or pulling it outwards, according as this surface is con- 
vex or concave. 
sth. Hence arise variations in the interior pressures of the 
liquid,a convex surface increasing, a concave surface diminishing 
them. 
6th. The extent of rise or fall of liquid in a tube, is the 
balance between the tensions of the surfaces of liquids within 
and without the tube. 
In his “ Chemistry of Plants,” Prof. J. W. Draper gives 
reasons for the opinion that the phenomena of capillarity, as 
well as of adhesion, are manifestations of electrical attractions 
and repulsions, since where they occur there is disturbance of 
the electrical conditions of the media entering into the action- 
329. Laws of Capillarity.—lf a number of tubes are employed, 
diameters of the channels of which are different, it is found that 
as the diameter of bore diminishes, its power to elevate fluid 
increases. Submitting these differences to as close a scrutiny as 
possible, Gay-Lussac evolved the following laws: MOLECULES OF TWO MEDIA, ONE SET MOVING. 
283 
_ Ist. Capillary elevations and depressions are inversely as the 
diameters of the tubes; all other conditions being the same. A 
tube half the diameter of a given tube, will raise the same liquid 
to twice the height. 
. If two flat glass plates are placed close together, and dipped 
into water, or other fluid, the fluid rises between the plates, but 
not to as great a height as in a tube. 
2d. Under similar conditions, capillary elevations and de- 
pressions, which occur between parallel plates, are to each other 
inversely as the distances between the plates. Under these cir- 
cumstances the extent of movement is one-half that in a tube of 
the same diameter as the distance between the plates. 
In the annular space produced when a solid cylinder is placed 
within a wide tube which nearly fills it, the height to which 
hquid rises is one-half that it ascends in a capillary tube of 
the same diameter as the width of the annular space. 
3d. In a tube the bore of which is irregular, the diameter of 
the portion in which the meniscus forms determines the amount 
°f elevation or depression. 
330. Inclined Surfaces and Capillarity.—By means of inclined 
plates we may obtain a very interesting and instructive illustra- 
tion of many points connected with the laws of capillarity. 
Eig. 129. 
In Fig. 129, let A B represent two glass plates, the surfaces 
°t which are perfectly flat and chemically clean, and B I) a vessel 
pentaining water the level of which is in the plane BD. Hold- 
ln£ the plates of glass so that they touch along their edges, A, 
anc| afe separated to the extent of a tenth of an inch along 0, 
dipping them into water, the fluid rises between them. As 
be distance between the surfaces of the plates is less and less, 
Je fluid rises higher and higher, finally arranging itself to 
Produce a curve, CE. This result is a self-made graphic repre- 
®?n^afi°n of the law—that as the distances between two plates diminish, 
e height to which liquid is raised increases. 
Capillarity between inclined plates. TRANSLATORY MOLECULAR MOTION. 
331. Capillarity and Floating Bodies.—The mutual attractions 
and repulsions shown by small bodies floating freely on water, 
are governed by the following laws: 
Ist. If both floating particles are moistened by the liquid, 
and sufficiently close to each other to destroy the natural level 
of the water, attraction results. The experiment may be made 
with balls of cork upon water. 
2d. If neither of the floating particles is moistened by the 
liquid, the same result happens when they are sufficiently near 
to each other. For example, pellets of wax. 
3d. If one particle dampens and the other does not, they 
repel one another when placed in close proximity. Example, 
cork and wax on water. 
It is curious to note that these three laws are the reversed 
counterpart of Du Faye’s laws of electrical attractions and re- 
pulsions (770). 
As in the case of other capillary phenomena, the above move- 
ments are now explained by the theory of surface tension. 
Another example of the same class of actions is seen when a 
piece of camphor is placed upon hot water; it immediately 
rushes about, often executing rotatory movements, first in one 
direction, then in anothA*. These are produced by diminution 
in the surface tension of the water as it dissolves the camphor. 
Surface currents radiate in all directions from the particle of 
camphor, and as the rate of solubility varies in different parts, 
the pressure varies, hence the movement and changes therein. 
A pellet of potassium or sodium on cold water exhibits similar 
movements. 
332. Imbibition and Absorption of Liquids.—In a physiological 
sense imbibition refers to the taking up of fluid by an inani- 
mate solid, while absorption is applied to the same action in a 
living animal, or plant surface, or in a medium. In physics they 
are equivalent terras for a modified form of capillary attraction, 
in which capillarity is the result sometimes of clustered tubes, 
or, again, of fissures. Examples of this action are offered 
by a mass of sponge which by its porosity takes up nearly its 
own bulk of water. In like manner a glass tube filled with 
sand will imbibe a considerable quantity of water, raising it 
above the original level, Wicks employed in lamps act after 
the same fashion; indeed, they may be regarded as bundles of 
capillary tubes. 
The upper rooms of a building the foundations of which are 
in damp soil may in this way become damp, moisture passing 
from brick to brick throughout its whole extent. A few threads, 
or the end of a towel hanging over the side of a basin of water, 
will act as a capillary siphon, and in time empty the basin. MOLECULES OF TWO MEDIA, ONE SET MOVING. 
285 
In the general use of these terms imbibition is confined to 
liquids, absorption when speaking of liquids and gases. 
In the practice of surgery the use of lint is an example of 
the application of imbibition. In their ordinary condition the 
absorptive power of lint is much greater than that of cotton. 
Recently, however, cotton has been prepared in such a manner 
as to increase its absorptive property, and it is extensively 
employed as a substitute for lint. Another instance of the ap- 
plication of absorptive property, is the use of powders of various 
kinds on the person for taking up excretions of the superficial 
glands. The more effective consist largely of starch, and of the 
spores of cryptogams, among which lycopodium may be men- 
tioned. 
333. Filtration.—Upon this process chemists depend mainly 
for the means of separating solid and liquid substances. It con- 
sists in the application of the absorptive power of unsized, 
bibulous, or filtering paper as it is called. 
The best is nearly pure cellulose, and is 
sold as Swedish filtering paper. The 
Paper is cut into circles of different diame- 
ters according to the quantity of material 
to be operated upon. Having selected a 
Piece of suitable size, it is folded twice 
along the dotted lines shown at A; thus 
the quadrant B, is obtained, consisting 
°1 four layers of paper. These are sepa- 
rated, to give three on one side and one 
on the other; a conical cup is thus formed, 
which is fitted to the interior of a funnel 
ns at C, and the funnel placed in a cylin- 
drical vessel. Fis. 130, 
Fig. 130. 
Filtration. 
To secure proper action of the filter, the paper cone should 
ht the interior of the funnel as accurately as possible; the first 
action involved is absorption of the fluid portion of the con- 
tents of the filter by the bibulous paper; this passing to the 
exterior of the paper enters the annular space between the 
Paper and funnel, where it is again submitted to the action of 
capillarity, and the outward flow of liquid assisted. The rapid 
conduction of this portion of the operation depends largely upon 
tne accuracy of tit between the filter and funnel. Hence care 
should be taken to select funnels of the proper angle. This 
18 readily done by trying with a paper cone prepared in the 
banner described. 
Phe rate of filtration may be greatly favored by adapting the 
innnel, A, Fig. 131, to a two-necked bottle, B, and establishing a 286 
TRANSLATORY MOLECULAR MOTION 
Fig. 131. 
partial vacuum therein by connecting the tube 0 
with a filter pump (177). To support the point 
of the filter and protect it from the effects of 
increased pressure, a small cone of platinum 
foil is dropped into, the apex of the funnel. 
334. Draper’s Steam Exhaust for Filtration.— 
When a column of water sufficient for work- 
ing a Bunsen pump is not available, a device, 
of which I published an account in the London 
“Philosophical Magazine,” for May, 1870, may 
be used. Its essential parts are represented in 
Eapid filtration. 
Fig. 132. ABis a wide tube, drawn to a small opening at A, 
and closed by a cork at B. Through the cork a tube, S, passes 
which terminates in a tine opening near the end of the large 
Fig. 132. 
Draper’s steam exhaust. 
tube at A. When steam under pressure is passed through S, 
and the small openings of the two tubes are properly adjusted 
to each other, exhaustion is produced in the interior of A B. 
By means of the tube E this rarefaction may be applied to the 
tube C of the filter bottle, Fig. 131. By a pressure of one 
atmosphere in the steam boiler, an exhaustion equal to 8 inches 
of mercury is easily attainable in the filter bottle. 
When the tube E is disconnected from the filter bottle, and 
air permitted to enter freely, the mixture of air and steam which 
issues from the nozzle of A is a very grateful and soothing ap- 
plication to the surface of the skin, and I have suggested its use 
in inflamed conditions of this organ, as, for example, erysipelas. 
334 A. Special Filtration.—By filtration, various objectionable 
substances may be separated from water. The action is, prop- 
erly speaking, chemical, and consists in the oxidation of noxious 
bodies. They are of sufficient physical interest to command 
our attention. 
Ist. Filtration by masses of compressed charcoal is recom- 
mended as deodorizing and clarifying. These filters, however, 
very quickly become clogged, and in their interior germs of 
various kinds develop. They are not employed to any extent. MOLECULES OF TWO MEDIA, ONE SET MOVING. 
287 
2d. By finely divided charcoal. In this process, a funnel- 
shaped porcelain vessel, through which many holes are punc- 
tured, is fitted mouth down and water-tight to an opening in 
the bottom of a cylinder, which holds the water to be purified, 
bhe funnel is covered by asbestos cloth, fastened with string of 
the same material. Finely divided charcoal is then mingled 
with enough water to cover the funnel, and poured over it. As 
the water drains through, it leaves a covering of charcoal on the 
asbestos cloth. The space between the funnel and cylinder 
IXI ay be filled with coarse charcoal. 
The filter being thus prepared, fluid is poured into it. It 
Passes through peifectly clear and well adapted for use in 
domestic economy. As it percolates, fresh portions may be 
added, and the action kept up for days or weeks, depending 
upon the character of water filtered. 
3d. Spongy iron filters consist of a tall cylinder with per- 
forated bottom. In this cylinder a layer of coarse gravel, 
°ue inch thick, is placed, upon this a layer of fine clear quartz 
sand, then a layer of coarsely powdered pyrolusite about three 
Ruches thick, and finally a layer of four or five inches of spongy 
lron. Water poured on the top layer, is delivered below 
Purified. 
. The action of spongy iron in the presence of water and air 
18 to remove all organic matter, at the same time forming a proto- 
salt of iron. In the layer of pyrolusite, this is peroxidized, and 
deposited as red peroxide of iron; the lower layers of fine and 
coarse sand arrest the peroxide, and the water flows out below 
iree from admixture therewith. 
4th. Paper-pulp filters. In preparing these 
paper is beaten to a pulp with water, and 
poured into a vessel like that used for fine char- 
coal filters. The asbestos thus becomes covered 
Vlth paper pulp, through which the filtration 
takes place. Modifications of this form are 
ri°w used in the manufacture of beer and wine, 
t0 separate certain impurities. 
Fig. 133. 
335. Absorption of Gases by Solids.—If a tube, 
be filled with dry ammoniacal gas at a 
Mercurial trough, B, and a piece of freshly pre- 
pared charcoal, C, passed through the mercury 
Jnto the gas, the charcoal will immediately begin 
0 absorb the gas, and the action will continue 
Uotil it has imbibed many times its own volume. 
Charcoal made from boxwood possesses this 
Absorption of gases 
by solids. 
property in a very high degree. For this substance the absorp- 
tlVe power is as follows, for different gases at ordinary pressures. 288 
TRANSLATORY MOLECULAR MOTION 
Those taken up in largest quantity are the more liquifiable. 
The amount increases with the pressure. 
One volume of boxwood charcoal takes up of 
Ammonia ...... 
. 90 volumes. 
Hydrochloric acid . - . 
. 85 “ 
Sulphurous acid ..... 
. 65 “ 
Sulphuretted hydrogen 
. 55 
Carbonic acid ..... 
. 35 
Carbonic oxide ..... 
Oxygen ...... 
. ' . 9.2 “ 
Nitrogen ...... 
. 7.5 “ 
Hydrogen ...... 
. 1 8 “ 
The power of chestnut charcoal is still greater, one volume 
taking up 171 of ammonia, 108 of cyanogen, and 73 of carbonic 
acid. Pine charcoal has about half the power of boxwood coal. 
Corkwood coal, though very porous, has little or no absorbent 
power, neither has graphite. 
These results are to be attributed to the property which cer- 
tain substances possess of condensing gases upon their surfaces 
(284). It is evident that in the case of charcoal the extent of 
surface is enormously increased by its sensible pores, hence 
there is nothing very surprising in the power with which it acts. 
336. Disinfectant Action by Charcoal Explained.—We have had 
occasion (284) to refer to the nascent condition, and energetic 
chemical action of gases condensed on the surface of metals in 
electric decompositions. This action offers an explanation of the 
power of charcoal, and certain other porous bodies, to destroy 
evil odors and emanations. 
Whenever gases are submitted to surface condensation by 
solids their chemical activity is increased. The oxygen of air 
when absorbed by the pores of charcoal is condensed upon their 
surfaces; in this condition its chemical activity is greater, at the 
same time the gaseous constituents of the odors or emanations 
are also compressed into smaller compass in the pores of the 
charcoal, and their proneness to oxidation is in like manner 
advanced. The action, therefore, works both ways, the ten- 
dency of the oxygen and the oxidizable matter to go into union 
is increased, with the result of producing new combinations 
which would not be possible at ordinary temperatures in the 
absence of charcoal. 
337. Occlusion.—Among metals platinum in the form of powder, 
called platinum black, possesses high absorbent power. So also 
does spongy platinum, which is said to condense 250 times its 
volume of oxygen at ordinary temperatures. The intensity of 
the affinity of oxygen and hydrogen condensed in the pores MOLECULES OF TWO MEDIA, ONE SET MOVING. 
289 
of spongy platinum becomes so great that the temperature runs 
up to the point of ignition, and the hydrogen takes fire as in the 
■Dbbcreiner lamp, Fig. 134, which consists of a small hydrogen 
generator, ABC, in which when a certain quantity of gas has 
collected the apparatus ceases to act. By means 
pf a stopcock, D, the gas issues through a fine 
jet and impinges upon a small mass of spongy 
platinum E, with the result described. 
If ordinary platinum be heated and then allowed 
f° cool in hydrogen, it absorbs four times its 
volume of gas. Palladium offers a still more re- 
piarkable example, absorbing hydrogen not only 
Hi cooling but also when cold. If this metal is 
used as the pole of a voltaic battery in the electric 
decomposition of water, it will absorb no less than 
times its volume of hydrogen gas. Under 
these circumstances the density of the gas is 
Fig. 134. 
Dobereinor 
lamp. 
enormously increased. In this state it probably acts like a 
metal, forming an alloy with the palladium. 
hhe gas which is taken up by metals in the manner described 
cannot be removed by ah air pump; for its expulsion elevation 
°r temperature is required. Graham has called these phenomena 
m absorption of gases by metals occlusion, and conceives that 
they occur under circumstances in which there are no pores, 
tii regard to this opinion the student is referred to (48), in which 
ue existence of sensible pores in gold and other metals is dis- 
cussed. If their existence is granted, the phenomena of occlusion 
lecome a mere exaggeration of surface condensation of a gas 
-Fores of a solid, as explained in (335). 
Ihe experimental illustration of the occlusion of hydrogen by 
palladium may be shown by making two long slender strips of 
118 metal the terminal electrodes of a voltaic battery, and im- 
mersing them in water in a decomposition cell. One side of 
micn strip should be varnished to prevent contact with the water. 
uu passing the current through the cell the palladium pole from 
the hydrogen is evolved occludes'the gas only on its 
Unvarnished surface; hence there is expansion on that side 
‘ one and the strip becomes curved in accordance therewith. 
Reversing the current the strip which curved becomes straight, 
udole the opposite strip curves. Thus acting like a finger, each 
np in its turn designates the track the current of electricity 
18 taking. 
-[he fact of the occlusion of hydrogen by iron has led to ex- 
amination of the meteors which from time to time come from 
ie regions of space to the earth. Whenever these contain iron 
18 found to present occluded hydrogen,, thus demonstrating 290 
TRANSLATORY MOLECULAR MOTION. 
the existence of both of these elements in regions exterior to 
the atmosphere. 
338. Transpiration of Liquids and Gases.—This term is applied 
to the passage of liquids or gases through capillary tubes under 
pressure. The experiments of Poiseuille have determined the 
following laws of effusion or efflux, both of which terms are em- 
ployed, 
Ist. The flow increases directly as the pressure. 
2d. With tubes of equal diameters, the quantities discharged 
in equal times are inversely as the lengths. 
3d. The material of which the tube is made does not influence 
the result. 
4th. For liquids in tubes of equal length but different diam- 
eters, the rate of efflux is as the fourth powers of the diameters. 
sth. For gases, as the temperature rises the transpiration is 
slower. 
CHAPTER YIII. 
MOLECULES OF TWO MEDIA, BOTH SETS MOVING. 
Solution and mixture contrasted—Diffusion between liquids or solutions—Crys- 
talloids and colloids—Amoeboid movements imitated—Diffusion between 
gases—Absorption of gases by liquids. 
In this case we have the following conditions: Ist. The move- 
ment of the molecules of a solid among those of a fluid forming 
a solution. 2d. The movement of the particles of one fluid or 
solution into another. 3d. Movement of molecules of one gas 
among those of another. 4th. Movement of gaseous molecules 
among those of a liquid. 
339. Solution and Mixture Contrasted.—ln (283) the subject of 
solution has in part been discussed. It is a phenomenon very 
difficult to place, involving both simple adhesion and molecular 
motion. 
Solution may be of two kinds: Ist. Chemical, in which there 
is more or less change of composition and properties, so that we 
do not regain the same solid on evaporating the solution to dry- 
ness. 2d. Physical, in which the properties of the body are MOLECULES OF TWO MEDIA, BOTH SETS MOVING. 
291 
not altered, and it can be regained in its original form by simple 
evaporation of the dissolving menstruum. 
Movements attending either of these acts are largely due 
to increased gravity of the solution formed over that of the 
menstruum in which it is produced. They may be shown 
by the arrangement in Fig. 135. It consists 
°t a glass cell, A, the sides and surfaces of 
V’hich are fiat and parallel. The space en- 
closed is about three inches square, and half 
an inch thick. A morsel of sugar, B, is sus- 
pended by a platinum wire in the interior of 
the cell in the position indicated, and the 
arrangement placed upon the stage of a pro- 
Fig. 135. 
Solution illustrated. 
jcetion lantern and focussed upon the screen. Water is then 
poured into it until it reaches or covers the sugar, when, at once, 
the action begins, and the currents established form a most 
interesting spectacle. 
. This action continues until the equilibrium between the cohe- 
Sl-ce and adhesive forces described in (283) is attained; it then 
ceases, and the solution is said to be saturated. The point of 
saturation for any solid in a given menstruum is, however, 
variable for different temperatures, though the same at any 
given degree. 
In the case of the intermingling of fluids like alcohol and 
'vater, there is no limit of solubility or saturation, either one 
V’ay or the other. These are called .mixtures. In certain in- 
stances, the first stage of the preparation of such mixtures is 
attended by change in temperature, as with sulphuric acid and 
mater. It is, therefore, thought by some that solution may, in 
these instances, be a low form of chemical action or chemism. 
On the other hand, there are cases in which two liquids do 
nnt form mere mixtures, but true solutions which show a point 
saturation; examples of this are offered in the relations of 
Mater to volatile oils, many of which are soluble only to a 
definite point, when the solution may be said to he saturated. 
Certain mixtures separate easily, as those of fats in water and 
‘dimmen. These are known as emulsions; of this group fresh milk 
18 an example. In time it separates spontaneously. Objection 
rillght be made to this instance, on the score of the chemical 
changes that at the same time take place. Such objections are, 
however, not valid in the separation of the constituents of milk 
I mere centrifugal action (812). 
|n true solutions of saline bodies, separation of the constituents 
onv takes place by the act of crystallization, when the point of 
saturation of any one of its components is reached. 
340. Diffusion Between Liquids or Solutions.—Though all liquids 
appear to resemble each other closely, there are nevertheless 292 
TRANSLATORY MOLECULAR MOTION. 
essential differences between them. Water, for example, will 
intermingle freely and in all kinds of proportions with alcohol 
if agitated therewith, but not at all with certain oils. Water and 
alcohol not only form a mixture when shaken together, but 
also when merely placed in contact, the alcohol being carefully 
floated on the surface. Under these circumstances, in spite of 
the greater specific gravity of the water, it passes upwards to 
mix with the alcohol, and the light alcohol penetrates to the 
very lowermost layers of the water, until finally they form a 
uniform mixture throughout. To this phenomenon of the 
spontaneous intermingling of miscible liquids, the name of 
simple diffusion is given. 
The laws which govern simple diffusion, or that form in 
which there is no barrier between the liquids, have been 
thoroughly investigated by Graham. The 
method he finally adopted was to take a wide- 
necked bottle, A, with a capacity of about four 
ounces. The edge of the lip of this was 
ground, and a disk of thin glass, C, fitted 
thereto. The bottle was filled with the liquid 
or solution to be examined, and the cover put 
in position. It was then placed in a jar, B, as 
is shown in Fig, 136, and the jar filled with 
distilled water to a height of one inch over the 
cover. Uniformity in this respect was an im- 
portant element in all his experiments—the 
amount of water employed was about 20 ounces. 
The disk was then removed with as little dis- 
turbance as possible, and after the lapse of 
sufficient time replaced, and successive layers 
■Fig. 136. 
Diffusion illustrated, 
of the water removed, and their composition determined. 
Under this method of examination various solutions exhibited 
different powers of diffusion. The following table gives the 
times of equal diffusion. 
Substance. 
Hydrochloric acid 
Minutes, 
. 1.0 
Chloride of sodium 
. 2.3 
Sugar .... 
. 7.0 
Magnesium sulphate . 
. 7.0 
Albumen 
. 49.0 
Caramel 
. 98.0 
Elevation of temperature increased the quantity of solution 
diffused. The rate for hydrochloric being one at 15° C., was 
more than doubled at 49° C. 
When substances which do not combine are mingled, that 
which is more diffusive passes out of the bottle more rapidly; MOLECULES OF TWO MEDIA, BOTH SETS MOVING. 
293 
the two bodies are thus partially separated. Sometimes chemical 
decomposition results from this action. 
34:1. Crystalloids and Colloids.—ln the list of substances given 
hi the preceding diffusion table, some are crystalline and some 
are amorphous. Of crystalline or saline bodies, magnesium 
sulphate is one of the least diffusible, yet it diffuses seven times 
as fast as albumen, and fourteen times as fast as caramel. Other 
bodies, as starch, dextrine, gum, hydrated silicic acid, resemble 
albumen and caramel in their low rate of diffusibility, and form 
a distinct group. To this group Graham has given the name of 
colloid or glue-like, in contradistinction to the saline or crystal- 
loid substances which have so much greater diffusive power 
(347). 
342. Amoeboid Movements Imitated.—ln connection with the 
phenomena of diffusion of liquids, I have for a few years past 
exhibited to my classes a very curious and instructive original 
experiment in which the actions seen in amoeba under a micro- 
scope, are imitated with singular fidelity. 
The apparatus consists of the cell described in (339). The 
inner wall must be perfectly clean. It is half filled with pure 
water, and placed upon a lantern stage. A layer of alcohol is 
gently poured on the water to the depth of about a tenth of 
au inch; the cell is then cautiously tilted to moisten one of its 
Sldes, and returned to the normal condition. 
After a short time drops form on the surface of the glass, 
hhese are focussed upon the screen, in order that their move- 
ment may be seen to advantage. They are perfectly outlined, 
a,id move about extruding and withdrawing curious processes, 
exactly after the fashion of amoeba. If they approach closely 
hi each other they cohere, and become one. Thus far it is easy 
hi conceive that one is watching the movements of amoeba. 
h>ut even more extraordinary motions are executed. From time 
time, one of these singular protean forms approaches the 
surface of the liquid, and assuming the outline of a very short- 
uecked flask, begins a rapid movement which is an exact 
counterpart of the act of drinking. 
These marvellous movements on the wall of the glass cell 
continue for some time. I have often watched them for two 
hours continuously. As one gazes upon them as though fas- 
pmated, it is almost impossible to divert the mind from the 
idea that the motions are executed by some one of the lower 
lornis of animal organisms. We look upon phenomena like 
those we have described, as one of the most characteristic 
tcatures of animal life, yet we here find them executed by mere 
unorganized drops of fluid. 294 
TRANSLATORY MOLECULAR MOTION. 
Though we have introduced the above experiment in this 
division of our subject, it is to be understood that in addition to 
the acts of diffusion on which they are based, other influences, 
such as evaporation and adhesion to the glass surface, are in- 
volved. The latter is a most essential element of success, for 
without proper attention to cleansing the cell, the experiment 
is not satisfactory. 
343. Diffusion Between Gases.—Gases also diffuse when brought 
in contact with each other, and form a perfect mixture, no matter 
how great the difference in their specific gravities may be. 
In Fig. 137, the interior of the jar H is first moistened with 
strong hydrochloric acid; it is thus filled with hydrochloric acid 
gas. It must be kept mouth upwards, as the gas 
is heavier than air. In like manner, the bell Ais 
filled with ammoniacal gas, the operation being 
conducted at a distance from 11, and the bell being 
kept mouth downwards to retain the light gas. 
They are then brought mouth to mouth. At 
once the gases intermingle in spite of their differ- 
ent gravities, white fumes of ammonium chloride 
appearing, which almost immediately fill the jars. 
In the above arrangement one is impressed with 
the great rapidity with which gases diffuse when 
compared with liquids. The result grows out of 
the fact of the greater mobility of the gaseous 
molecules, and is a proof of the hypothesis that 
the particles of these elastic fluids are in constant 
active motion. 
If the diffusion of gases into the atmosphere is 
hindered, by placing them in closed vials which 
communicate with the air by tubes about ten 
Fig. 137. 
Diffusion between 
gases. 
inches in length, and a small fraction of an inch in diameter, 
the relative rate may be easily determined. From experiments, 
conducted in this manner, Graham arrived at the following 
results: 
Relative diffusibility of gases into air. 
Gas. 
Sp. gr. 
Kate. 
Hydrogen 
1 
94.5 
Carb. hydrogen 
. 8 
62.7 
Ammonia 
. 8.5 
59.6 
Olefiant gas 
. 14 
48.3 
Carbonic anhydride 
. 22 
47.0 
Sulphurous anhydride 
. 32 
46.0 
Chlorine .... 
. 35.4 
39.5 
Showing that the lighter the gravity, the more rapid the rate 
of diffusion. molecules of many media, a portion moving. 
295 
Vapors also move into each other, and into gases. Under 
ail circumstances of diffusion of gases and vapors, they never 
again separate by virtue of their differences, but constitute a 
uniform mixture until decomposed by suitable chemical means. 
344. Absorption of Gases by Liquids may be either chemical 
or physical. In the first case, the amount taken up is definite 
and fixed, as of carbonic acid and chlorine in a solution of 
caustic soda. In the second, the proportion varies with tem- 
perature and pressure. 
As regards the effect of pressure on physical solution of gases, 
the law is very simple, the amount dissolved varying almost 
directly as the pressure. For this result, we find an explanation 
m Boyle’s or Mariotte’s law (223). The effect of temperature 
cannot be so readily brought under the influence of any stated 
law. In a general way, gases are less soluble at high than at low 
temperature; there are, however, many exceptions: hydrogen, 
for example, is equally soluble in water between 0° and 25° C. 
CHAPTER IX. 
MOLECULES OF MANY MEDIA,' A PORTION MOVING. 
Establishment of continuous flow in capillary tubes—The endosmometer— 
Osmosis—Dialysis—Applications of dialysis Osmosis of gases through 
porous media—Hygienic importance of osmosis of gases—Osmosis of gases 
through metals—Vitiation of air by stoves—Capillarity and chemism. 
Where the molecules of all the media present are in move- 
ment the conditions are similar to those given in Chapter VIII. 
Where the molecules of one of the media are at rest, the con- 
ditions are a combination of those presented in Chapters VII. 
and VIII., and new and very important phenomena arise. To 
ffiese we shall devote special attention. 
-345. Establishment of Continuous Flow in Capillary Tubes.—ln 
(325) it is stated that a capillary tube does not allow a liquid to 
overflow when it is broken short of the height to which it can 
laise the liquid. 
This is true so long as nothing is done to remove the liquid 
tls it reaches the fractured extremity. If, on the contrary, the 296 
TRANSLATORY MOLECULAR MOTION. 
liquid being water, we from time to time touch the end of the 
tube with a slip of blotting or other bibulous paper, the fluid is 
taken up by it, and more rises to fill its place. In like manner, 
the fluid being alcohol, it may be evaporated at the end of the 
capillary tube, and an upward current thereby established. 
We have seen in (340) that liquids diffuse into each other. 
If, therefore, we make a capillary tube, C, the means of com- 
Fig. 138. 
raunication between a vessel. A, contain- 
ing alcohol, and another, W, tilled with 
water, as fast as the contents of W reach 
A they will be removed by diffusion into 
the larger mass of alcohol, and a continuous 
flow from Wto A established. On the 
other hand, as fast as the alcohol passes 
through the capillary to W, it will in its 
turn be removed and a flow established 
from A to W. 
Flow in capillary tube. 
Thus through a fine tube two liquids may be moving in 
opposite directions at the same time under the combined in- 
fluence of capillarity and simple diffusion. In such a movement 
the liquid which has the greater capillarity and diffusive power 
will have the advantage, and move in larger quantity or more 
rapidly. 
346. The Endosmometer was so called by its inventor, Du- 
trochet. It consists of a glass tube, E, a couple of feet in length, 
to the lower extremity of which a 
small bladder, A, is attached without 
leakage. The bladder being filled with 
alcohol the arrangement is immersed 
in water contained in the vase W. 
Fig. 139. 
The temperatures of the alcohol 
and the water being the same, when 
the bladder is first placed in the water 
the liquid occupies the lower part of 
the tube E. Soon, however, it begins 
to rise, and forming drops at E, these 
fall one after another and a consider- 
able overflow of a mixture of alcohol 
and water may be collected in a suit- 
ably placed vessel Y. 
Yarious other liquids can be sub- 
stituted for alcohol in the bladder A, 
with a similar result, viz., accumula- 
Enclosmomoter. 
tion of fluid therein. Among such articles are syrup, milk, 
gum water, albumen, or any solution denser than water, and 
miscible therewith. As a rule, accumulation of fluid takes place molecules of many media, a portion moving. 
297 
on the side of the denser liquid ; to this there are, however, 
exceptions, alcohol being one of the most notable. 
Since in the experiments we have described there is a move- 
ment towards the interior of the bladder, and an accumulation 
therein, Dutrochet gave to this phenomenon the name of endos- 
Wosis, from two Greek words signifying inward movement. 
The explanation of the action of the endosmorneter is furnished 
m (345). The membrane which separates the two liquids is to 
be regarded as a porous partition. These pores, whatever their 
shape or character, may be conceived to be equivalent to short 
capillary tubes or crevices, extending from one surface of the 
membrane to the other and terminating at each end in open 
mouths; one in contact with alcohol, the other with water. 
Under these conditions since water moves along capillary 
crevices with greater facility, accumulation is in the interior of 
the bladder, and endosmosis results. The exceedingly minute 
calibre of the pores in such membranes gives them enormous 
power, according to the laws of capillarity (329). 
347. Osmosis.—ln the preceding article we have dealt only 
Math the result as far as the interior of the bladder is concerned, 
ai)d have seen that there is an accumulation of a mixture 
°t alcohol and water therein. Let us now examine the con- 
dition of the fluid on the exterior of the bladder. By analysis 
We find that it is no longer pure water, but that a certain pro- 
portion of alcohol is present. While water has been passing in- 
wards into the bladder, alcohol has been passing outwards to the 
water. To this movement the name of exosmosis was given 
by Dutrochet; the double action is included under the term 
osmosis, which was introduced by Graham. 
From the above, it is evident that often where endosmosis 
exists, exosmosis is present. The movements are in opposite 
directions, and at different rates. In some cases movement is 
011 I.V in one direction. 
The exhibition of exosmotic action may be readily shown by 
reversing the charging of an endosmorneter, putting water in 
tbe bladder, and filling the vase with alcohol. Under these 
c°nditions instead of the wall of the bladder becoming more 
tense and forcing liquid up the tube, it becomes flaccid, showing 
a loss of its contents. 
So strong are these osmotic actions that they can often over- 
come feeble chemical affinity, in the case of dilute alcohol for 
example. Since water moves much more rapidly through a 
niembrane than alcohol, if a bladder containing dilute alcohol 
?8 suspended in a current of air to promote evaporation from 
its exterior, the alcohol in the interior will become stronger and 298 
TRANSLATORY MOLECULAR MOTION. 
stronger, until at last it is almost completely dehydrated by the 
exosmotic action on the water and its removal by vaporization. 
348. Dialysis.—Liquids not only traverse porous membranes, 
but they also pass or diffuse through jelly-like media or septa, 
which are supposed not to possess pores in the ordinary sense 
of the term, though about this there may he some question, as 
they certainly have physical pores if they may not present sen- 
sible ones. This diffusion through jelly-like septa Graham has 
called dialysis. Deschanel says such septa act as solvents taking 
up crystalloids on one side and surrendering them on the other. 
The best substance for a dialytic medium is parchment paper. 
It is unsized paper which has been immersed for a few seconds 
in sulphuric acid diluted with one-third its bulk of wTater, and 
then washed with weak ammonia and dried. Thus treated the 
paper becomes very tenacious or parchment-like. If dipped 
in water, it swells and becomes translucent. Parchment paper 
may also be prepared by a solution of chloride of zinc. 
In (341) Graham’s division of bodies into crystalloids and 
colloids has been discussed. The colloid group may still further 
be divided into those somewhat soluble in water, and those 
almost absolutely insoluble. To the latter belongs parchment 
paper. 
By simple diffusion (340), a mixture of less diffusible or 
colloid bodies, and highly diffusible or crystalloid bodies, under- 
goes partial separation. The difference in the relative rate of 
passage of colloids and crystalloids is enormously increased 
when an insoluble colloid septum like parchment paper is intro- 
duced between the mixture and the water. Through such a 
septum the passage of soluble colloids is resisted. It is this fact 
which is applied by Graham in his dialyzer. 
Fig. 140. 
Dialysis. 
A convenient form of this instrument is represented in Fig. 
140. It consists of a hoop of glass or other material, A, the 
lower opening of which has been closed by parchment paper 
put on wet and fastened in position by a string or rubber band. 
It should pass up on the outside of the hoop higher than the Molecules of many media, a portion moving. 
299 
level the fluid is to occupy on the interior. We may be satisfied 
°f its soundness by sponging it with pure water on the inside, 
and seeing that no wet spots form on the outside. In case they 
d<h the openings may be stopped by a varnish of albumen, 
which is then coagulated by heat. Parchment bags may be 
ftiade in the same way. 
The mixture to be dialyzed is introduced into the hoop to a 
depth of about half an inch, and the arrangement placed in a 
vessel of water, B, its lower surface immersed to a slight depth. 
After the lapse of 24 to 48 hours, the operation will be com- 
plete, the colloids remaining in the dialyzer, and the crystal- 
loids being almost entirely in the water on the outside. From 
this dilute solution, the crystalloids may be obtained by evapo- 
ration, precipitation, or any other suitable method. 
349. Applications of Dialysis.—Among these, three are of 
interest to the physician, not only on account of their 
Intrinsic value, but because they may suggest other instances 
ln which this method may be applied. 
Ist. Soluble peroxide of iron, also called dialyzed iron, is pre- 
pared by this process; the operation is described by Graham, as 
follows: Perchloride of iron solution is first saturated with per- 
oxide of iron by adding carbonate of ammonium as long as the 
precipitated oxide continues to redissolve on stirring. Pro- 
longed exposure increases the quantity of iron dissolved. The 
r^(l liquid formed is already somewhat colloidal. It is then 
dialyzed in the usual way for many days. 
. Id an experiment recorded by Graham, he began with a liquid 
the dialyzer, containing 5 per cent, of solid perchloride of 
Won, which held in solution about five equivalents of iron. In 
Ihe course of eight days, it consisted of about 97 per cent, of 
peroxide to 3of acid. In nineteen days, the hydrochloric acid 
Was reduced to 1.5 per cent. The solution was then transferred 
1° a vial, in which it remained fluid for twenty days, and then 
Jellied spontaneously. 
Water containing one per cent, of this substance has the 
dark red color of venous blood. When sufficiently concentrated 
dy boiling, a coagulum forms spontaneously, which closely re- 
sembles a clot of blood, though more transparent. In its fluid 
slate, soluble peroxide of iron is the most useful and agreeable 
form in which this metal can be administered. 
2d. In the detection of poisons the process of dialysis is a 
m°st valuable adjunct, by which crystalline poisons may be 
separated from the organic material with which they are mixed. 
Being thrown on the dialyzer, and submitted to its action for a 
c°Dple of days, the separation is almost complete. On evapo- 
rating a portion of the exterior liquid, and allowing it to crys- 300 
TRANSLATORY MOLECULAR MOTION. 
tallize over sulphuric acid, if necessary, we may often detect 
at once the presence of noxious agents, which present charac- 
teristic forms of crystals. To the concentrated diffusate the 
ordinary processes of qualitative and quantitative analysis can 
be applied, and its character determined. 
3d, In the examination of urine, dialysis has been applied for 
the separation of the crystalloid constituents, and urea has in 
this way been obtained in so pure a condition as to yield its 
characteristic crystalline form. 
350. Osmosis or Diffusion of Gases Through Porous Media.—The 
outward and inward movements of gases through porous barriers 
may be demonstrated by the arrangement in Fig. 141. It con- 
«/ O O 
sists of the porous earthenware cell of a Grove 
battery, A, to the mouth of which a glass tube, B, 
has been attached air tight. The lower end of 
the tube dips under the surface of water in the 
vase C. 
Fig. 141. 
At first the level of liquid in the tube B and 
vessel C is the same, and both are filled with air. 
Enclose the porous jar A in a bottle, D, filled 
with hydrogen ; that gas instantly flashes through 
the pores of the battery cup, and mingles with 
the air therein, accumulating to so great an extent 
in the interior that it rushes out in bubbles through 
the water. When the escape of bubbles has nearly 
ceased, remove the bottle I), and expose A to the 
air. Instantly a movement in the opposite direc- 
tion takes place, the water rises rapidly in the tube, 
and almost reaches the porous jar in spite of the 
downward action of gravity. 
Here, we have endos- and exosmosis exhibited in 
a remarkable manner, and far more energetically 
and promptly than in the case of liquids. This, a 
little reflection would have led us to expect, con- 
sidering the greater mobility of gaseous molecules, 
Diffusion of gases 
through barriers. 
which, we have already seen, exerts so great an influence on the 
phenomena of simple diffusion. 
The details of the action are as follows. At the beginning, 
the interior and pores of the vessel A are filled with air, into 
this the hydrogen diffuses, and since its diffusion power is much 
greater than that of air there is rapid accumulation in the in- 
terior of A. This movement continues until the relative pro- 
portions of hydrogen and air in the inside of A, and in the 
bottle Don the outside are the same. It then ceases. On un- 
covering A, and exposing it to the air, the conditions are 
reversed. Inside of A there is a mixture of gases, the chief molecules of many media, a poktion moving. 
301 
constituent of which is hydrogen. On the outside there is air. 
To this the hydrogen instantly diffuses. In its outward passage 
a partial vacuum is formed, and to till this the water rises in the 
tube, forced up by atmospheric pressure. 
In the example of osmosis we have here examined, a special 
point of interest is the use of an inorganic septum, showing 
that the phenomena of osmosis are not confined to organic 
niedia. In place of the porous jar we might have used a septum 
of India rubber or bladder, but the results would not have been 
us striking. 
Another matter of interest is the fact that the movement is 
more rapid than when gases are freely exposed to each other, 
us in simple diffusion (343). This is to be attributed to the con- 
densing action which all surfaces and pores exert upon elastic 
fluids. 
351. Hygienic Importance of Osmosis of Gases.—The osmotic 
movement of gases through inorganic bodies is a matter of con- 
siderable importance from a hygienic point of view. As we have 
seen hydrogen flash instantly through the porous vessel A, so 
AVIII it pass through one or many thicknesses of brick, or through 
the plaster of which walls are formed. A person may even blow 
through a brick. Gaseous or vaporous emanations in one apart- 
ment of a building thus find their way into other rooms. The 
effluvia arising from leakage in a water-closet in one location, 
freely penetrates to all parts of a house. 
To a certain extent, free passage of gases through plaster, 
muck, and similar barriers, may be prevented by coating them 
Muth several thicknesses of paint. As regards floors, the use of 
thes and slabs of marble is for this reason to be preferred to 
mat of wood, unless the latter is of the pitch pine variety. 
Movable rugs are superior to carpets, since they secure better 
°Pportunities for cleanliness. 
dn like manner, hydraulic cement spread on the cellar floor 
°f a house built on made ground is a very imperfect protection 
the passage of noxious gases evolved from the earth, 
ft does not keep moisture out; it would be greatly improved 
h saturated with bitumen, which should be applied hot and 
Pressed with heavy hot rollers, as in laying bitumen pavements. 
The hygienic benefits arising from sleeping in a tent during 
a camping-out excursion are largely to be attributed to purity 
°t the air which results from free gaseous osmosis through the 
canvas of the tent. On well-drained ground, with a close 
boarded floor covered with rugs, and double canvas overhead, 
tent offers in fair weather better hygienic conditions than can 
be attained in most houses. TRANSLATORY MOLECULAR MOTION. 
352. Osmosis of Gases Through Metals.—ln iron or steel cylin- 
ders, hydrogen may be compressed under a pressure of 50 or 
more atmospheres, and preserved therein without sensible loss 
for an indefinite lapse of time. This statement is perfectly true 
while the temperature is that which we ordinarily find existing 
in air; but if this condition be changed, and the temperature 
raised to a red heat, iron can no longer retain gas, not even at 
ordinary pressures. With elevation of temperature its prop- 
erties in this respect are so altered that it permits the diffusion 
of hydrogen with a facility rivalling that of the porous battery 
jar employed in the experiment (350). 
Hot only iron, but platinum and other metals, permit the 
osmosis of gases at high temperatures even more readily than 
India-rubber does at the ordinary temperature of air. Graham 
found, for example, that a square metre of caoutchouc 0.014 
millimetre thick would permit the passage of 129 cubic centi- 
metres of hydrogen at 20° C. A platinum tube 1.1 millimetre 
in thickness and the same extent of surface, during the same 
time permitted the exosmosis of 489 cubic centimetres of that 
gas. 
353. Vitiation of Air by Stoves.—At first glance the principle 
discussed in the preceding article would appear to be of little 
practical value to physicians. Hot so, however, when we 
examine it in all its bearings. 
The economic solution of the problem of warming, in the 
United States, consists in the almost universal use of stoves or 
hot-air furnaces, in w7hich the burning mass is in direct contact 
with a vessel of iron; under these conditions the iron becomes 
red hot, and in that state is permeable to gases. 
Among the products of combustion in a stove or furnace there 
are two gases which exert a highly noxious action upon the 
human economy; these are carbon monoxide or carbonic oxide, 
and carbon dioxide or carbonic acid gas. Both pass freely 
through red-hot iron, and may be readily found by collecting 
the layer of air immediately in contact with the exterior sur- 
face of the red-hot iron, and submitting it to chemical analysis. 
Osmosis of these gases may be prevented by lining the in- 
terior of the combustion chamber with soapstone or fire-brick. 
These are very permeable to gases, but by their use iron does 
not have its temperature raised high enough to allow them to 
pass; their escape is, therefore, prevented. 
The use of such a lining involves considerable loss of heat. 
This, however, can be counteracted by increasing the surface of 
pipes or tubes through which the products of combustion pass. 
Various devices in the form of drums have been applied to the 
accomplishment of this purpose. PHYSIOLOGICAL APPLICATION. 
303 
354. Capillarity and Chemism.—ln (345) we have seen that by 
pieans of physical agencies a continuous flow may be established 
lrJ capillary channels. Suppose that in addition to physical 
phenomena we also have to deal with changes in chemical 
affinity or chemism under conditions like those which follow: 
what will the result be ? 
Let AY, Fig. 142, represent a capillary vessel, and grant 
lhat a liquid having an affinity for its walls enters at A, drawn 
ln by capillarity. Under ordinary conditions, the liquid would 
Fig. 142. 
simply pass into the tube, but a continuous flow would not 
be established. If as the liquid passed towards V its affinity 
for the capillary walls was gradually lost, it is evident that con- 
ditions favorable to an unbroken flow would then exist. The 
Diert liquid would be pressed out by the onward movement of 
the active fluid entering behind it. Loss of affinity would be 
equivalent to a removal of the liquid as fast as it reached a 
certain position and movement would result. Suppose Ato 
represent arterial blood and V venous, moving in a capillary, 
uud the bearing of tbe proposition is evident. 
In the preparation of the articles thus far forming this Section, 
we have been compelled to resort to considerable condensation. 
-Those who desire a more extended acquaintance with the subject 
will And it fully discussed in Graham’s “ Chemical and Physical 
Researches,” and also in Watt’s “Dictionary of Chemistry.” 
Motion in a capillary tube. 
CHAPTER X. 
physiological application of tPvANslatory molecular 
motion. 
Wscent of sap in trees—Absorption in animals—Harvey’s mechanical theory of 
circulation—lnsufficiency of simple mechanical theory of circulation— 
Draper’s physico-chemical theory of circulation—The physics of respiration. 
355. Ascent of Sap in Trees.—Compared with circulation in 
animals that in plants is the more remarkable, since it is accom- 
plished by osmotic action alone, without the agency of a heart 304 
TRANSLATORY MOLECULAR MOTION. 
or other mechanical pumping organ. In the Sequoia Welling- 
tonia of the Sierra Nevada, the sap rises to a height of four 
hundred and fifty feet above the ground. A giant Eucalyptus, 
measured by G. Klein, on the Black Spur ten miles from Healcs- 
ville, in Australia, reaches the height'of four hundred and eighty 
feet, yet its topmost leaves are freely supplied with the fluids 
necessary for their nourishment. 
To comprehend the manner in which this surprising result is 
attained, it is necessary to examine briefly the structure of the 
parts by which it is accomplished. In exogenous plants, or 
those having a true bark, the circulatory process is almost en- 
tirely confined to the new wood or outermost layer of wood, 
called sapwood or alburnum, and to the inner layer of bark, 
called the liber. At their junction these constitute the so-called 
cambium layer, which consists of young and forming cells, of 
which the innermost are being continually added to the wood, 
and the outermost to the bark. It is in the 
Fig. 143. 
wood cells that ascent of sap usually takes 
place. 
In his “Lessons in Botany,” Prof. Gray gives 
the following description of the wood cells or 
fibres. “These are small tubes, commonly be- 
tween one and two thousandths, but in pine- 
wood sometimes twro or three hundredths of an 
inch in diameter. Those from the tough bark 
of the basswood are only the fifteenth hun- 
dredth of an inch wide. Those of buttonwood 
are larger. Fig. 143 also shows the way wood 
cells are commonly put together, namely, with 
their tapering ends overlapping each other— 
spliced together, as it were—thus giving more 
strength and toughness to the stem. 
“Wood cells, like other cells (at least when 
young and living), have no opening; each has 
its own cavity, closed and independent. They 
do not form anything like a set of pipes open- 
ing one into another, thus conveying an un- 
broken stream of sap through the plant, in the 
way people generally suppose. The contents 
can pass from one cell to another only by getting 
through the partition in some way. So short 
are individual wood cells generally, that to rise 
Wood cells. 
a foot in a tree like the basswood, the sap must pass through 
about two thousand partitions. 
“ But although there are no holes (except by breaking away 
when old), there are plenty of thin places which look like per- 
forations, and through these the sap is readily transferred from PHYSIOLOGICAL APPLICATION. 
305 
one cell to another. Some of these are exhibited in Fig, 143, 
where A and B, looked directly down upon, appear as dots or 
holes, while in profile the cells seem as though they were cut 
through. The latter view shows what they really are, namely, 
very thin places in the thickness of the wall. A thin place in 
°ne cell exactly corresponds to one in the contiguous wall of 
the next cell.” 
Passing from the stem to the root the structure may be re- 
garded as being the same until the root tips are reached. These, 
according to Prof. Gray, “ are entirely composed of soft, new, 
and very thin-walled cellular tissue; it is only further back that 
some wood cells and ducts are found. The moisture (and prob- 
ahly also air) presented to them is absorbed through the delicate 
walls, which, like those of the cells in the interior, are destitute 
°1 openings or sensible pores.” 
. Exteriorly, in the air, plants terminate in leaves; “ these con- 
sist of both a woody and a cellular part. The woody part is 
Pie framework of ribs and veins; they serve not only to 
strengthen the leaf, but also to carry in the ascending sap, and 
distribute it by veinlets throughout every part. The cellular 
Part is the green pulp and is nearly the same as the green layer 
°t the bark, so that a leaf may be properly enough regarded 
as an expansion of the fibrous and green layers of the bark, 
in most leaves the green pulp forms two principal layers: an 
PPper one facing the sky, and an under one facing the ground. 
J-he upper side is constructed to bear the sunshine, and if the 
Taf i.s turned it twists itself to enable the proper side to receive 
the light.” 
u The moisture exhaled from the leaf escapes chiefly from the 
under surface, by the stomata or breathing pores. Of these fewT 
0r none are on the upper side. They are said to vary from 1000 
170,000 to the square inch.” 
. Erom this it is evident that “ plants have no general circula- 
tion (like that of animals, except the lowest) through a system 
°i vessels opening into each other; but in them each living 
ce]] carries on a circulation of its own, at least when young 
and active. This may be beautifully seen in the transparent 
stems of chara and many other water plants, and in the leaves 
°i the fresh water tape-grass (Yallisneria), under a good micro- 
Scope. Here the sap circulates, often quite briskly in ap- 
pearance (but the motion is magnified as well as the objects), 
111 a steady stream, just beneath the wall, around each cell, 
Passing up one side, across the end, down the other, and so 
|'°und to complete the circuit, carrying with it small particles or 
e larger green grains which make the current more visible. 
Gm movement belongs to the protoplasm or jelly-like matter 
lmder the cell wall; as this substance has the same composition 306 
TRANSLATORY MOLECULAR MOTION, 
as the flesh of animals, it is not so strange that it should exhibit 
animal-like characters. 
“ Although contained in cells with closed walls, nevertheless 
the fluids taken in by the roots are carried up through the stem 
to the leaves of the topmost bough of the tallest tree. What 
makes it ascend to the leaves ? 
“To anwer this question, we must look to the leaves and con- 
sider what is going on there. For (however it may be in the 
spring before the leaves are out), in a leafy plant or tree the sap 
is not forced up from below, but is drawn up from above. Water 
largely evaporates from the leaves; it flies off' into the air as 
vapor, leaving behind all earthy and organic matters—these 
not being volatile—the sap in the cells of the leaf becomes 
denser, and draws upon the more watery contents of the cells of 
the stalk, these upon those of the stem below, and so on from 
cell to cell down to the root, causing a flow from the roots to 
the leaves which begins in the latter, just as a wind begins in 
the direction towards which it blows” (662). 
The process of absorption and circulation we have here de- 
scribed, though simple in its nature and free from any complica- 
tion of muscular action, like that existing in the systems of 
animals, is nevertheless wonderfully energetic. No animal others 
the resistance to the elevation of fluid that plants present, yet 
the movement of their fluids is not more regular than that found 
in the loftiest plants. In such plants the principles of osmosis 
as presented by the root-tips, and actions of chemism in the 
leaves, suflice to carry on the diflicult circulation. Surely the 
action of such potent forces should not be overlooked in investi- 
gating these phenomena in animals. 
356. Absorption in Animals is three-fold in its nature. Ist, by 
veins or bloodvessels; 2d, by lymphatics; 3d, by the villi on the 
intestinal walls which deliver the fluid material or chyle Into 
the lacteals. For the differences in character of the material 
absorbed in these three cases, we must refer to works on physi- 
ology. The point we desire to emphasize in connection there- 
with is this: 
Whether the absorption by root-tip, bloodvessel, lymphatic, 
or villus, be osmotic or dialytic, it matters but little; so long as 
there are no chemical changes in medium or fluid both actions 
are molecular movements, the only difference being that in 
the one, movement occurs through sensible pores, and in the 
other, through physical pores or intermolecular spaces. The 
actions we witness in a capillary tube of sufficient diameter may 
be regarded as merely visible molar representations of what is 
taking place on the invisible molecular scale, both in osmosis 
through membranes and in dialysis. To so great an extent is 307 
PHYSIOLOGICAL APPLICATION. 
this true that many group all these phenomena together, and 
speak of them as phenomena of capillarity, including both 
visible or sensible and physical or molecular interstices under 
the term capillary. 
357. Harvey’s Mechanical Theory of the Circulation.—This 
explanation of the circulation of the blood was introduced by 
Br. Harvey, more than two hundred and fifty years ago. It is 
based upon the existence, actions, and relations of the valves of 
the heart and veins. It conceives that the phenomena are 
purely mechanical, the heart driving the blood through the 
arteries to the capillaries into the veins, and so back through 
the veins to the heart. 
By this theory the heart is supposed to act after the fashion of 
a simple force-pump, the only other force brought into play 
being the muscular and elastic coats of the vessels. 
To account for the peculiarities in the capillary circulation, 
the action of nerves upon the muscular walls of the minute 
arteries is admitted by modern physiologists, but further than 
this the majority have been unwilling to go, and yet with this 
addition Harvey’s explanation is by no means satisfactory when 
submitted to a careful and critical examination. It is good as 
far as it goes, but it does not meet all the circumstances even of 
the simplest condition of the case. 
358. Insufficiency of the Simple Mechanical Theory of Circula- 
tion.—Ist. The phenomena of transpiration (338, 4th) show 
that considerable force is required to drive the blood through 
such narrow channels as the capillaries, unless these vessels 
themselves assist the movement. In attempting to make minute 
ejections after death, and when all traces of rigor mortis have 
Passed away, the anatomist finds it very difficult to avoid rupture 
°f the capillaries. The increase in resistance of minute vessels 
to the establishment of flow under pressure, is as the fourth 
power of their diameters. The significance of this is not recog- 
nized until a calculation is made for a given case. 
2d. In plants the circulation is more extraordinary than in 
animals, yet they have no heart nor any substitute therefor. 
-Neither do they have a nervous system to regulate contractions 
°f the walls of their vessels. Osmosis in their cells and rootlets, 
and chemism in their leaves, suffice to overcome resistances 
Counting sometimes to more than fifteen atmospheres of 
Pressure. 
3d. In the lower types of animal creation there is often an 
energetic circulation without a heart. Even in insects, the 
highest of invertebrates, a dorsal vessel, as it is called, which 308 
TRANSLATORY MOLECULAR MOTION. 
has but the feeblest muscular power, is frequently all the apology 
that can be found for a heart. 
4th. The lowest of vertebrates, the lancelet or amphioxus, 
does not possess a heart. The only substitute for it is a large 
bloodvessel resembling the dorsal vessel of invertebrates. 
sth. In fishes there is no systemic heart. Sluggish as their 
circulation is, it is hardly possible to imagine that their pulmo- 
nary heart drives the blood through both pulmonic and systemic 
capillaries against all the obstacles that two sets of transpira- 
tion resistances offer. 
6th, Even after the heart is exsected, circulation is said to 
continue in the capillaries for a brief period of time. 
7th. In instances where twin monsters have gone well on 
to full period, and one happens to be acardiac, yet otherwise 
well developed, there has been circulation without a heart. 
Bth. In the human adult the portal circulation is without a 
heart, yet during absorption of digested food into the general 
circulation it returns more fluid than it receives. 
9th. In the kidney there is also a minute portal circulation 
between the vessels of the convoluted tubes and the Malpighian 
tufts. This has no propelling vessel like a heart attached to it. 
10th. The flow in capillary vessels is often continuous and 
free from pulsation, sometimes it undergoes retrogression, pass- 
ing backwards from arteries to veins. This is against the action 
of the heart. 
11th. After death the arteries are practically empty. It is 
very difficult to conceive that the heart alone could produce any 
such results as this. If we admit that the capillaries have 
any action in carrying on the circulation, the explanation is then 
a very simple matter. 
359, Draper’s Physico-chemical Theory of Circulation.—To over- 
come the incompetency of the simple mechanical hypothesis to 
meet these objections, a theory based on molecular forces and 
chemism was advanced by my father, Prof. J. W. Draper, in his 
“ Human Physiology/’ published in 1858. In this, the function 
of the heart in filling the great and small arteries is fully ad- 
mitted, but it is confined to that duty. The chief seat of the 
circulatory force is located in the systemic, pulmonic, and other 
capillaries. Just as in plants, it originates in the changes taking 
place in the leaves. 
In the systemic vessels there is a fluid containing cells charged 
with oxygen, and losing it to the surrounding parts, the condi- 
tions explained in (354) exist. Circulation of the contained 
fluid, he maintains, must, therefore, of necessity take place. 
In the pulmonic circulation, the conditions are merely changed PHYSIOLOGICAL APPLICATION. 
309 
or reversed; the prime cause in that ease is affinity of the 
oxygen of the air cells for the haemoglobin of the discs. 
So also in the portal and renal double capillary circulations, 
the explanation is found in the chemical relations existing be- 
tween the blood and the cells of the organ through which it is 
flowing. 
It is interesting to note how those who will not admit this 
simple and,all sufficient theory, so consonant with modern ideas, 
become involved in self-contradictions and obscurity. Take, 
for example, “Flint’s Physiology,” on page 294 of the volume 
on circulation, he says: “It is unphilosophical to invoke the aid 
of currents produced in capillary tubes in which liquids of dif- 
ferent characters are brought in contact, or a ‘ capillary power ’ 
dependent upon a vital nutritive attraction between the tissues 
and the blood.” 
On page 219, he is compelled by the facts to uphold the very 
doctrine to which he objects on page 294, for he says: “The 
distention of the heart in asphyxia is, therefore, due to the fact 
that the unaerated blood cannot circulate in the systemic capillaries.” 
"Why ? Evidently because it has lost its normal affinity for the 
vessels and tissues, and, therefore, cannot move, since it now 
falls under the influence of the laws of transpiration. 
So also in “Foster’s Physiology,” page 172, when speaking 
of the stasis preceding inflammation, he says: “It must, there- 
fore, be due to some new and unusual resistance occurring in 
tbe capillary area itself. The increase of resistance is not caused 
Dy any change confined to the corpuscles themselves, for if after 
temporary delay one set has managed' to pass away from the 
mflamed area, the next set is subjected to the same delay. The 
eause of the resistance must, therefore, lie in the capillary walls, 
0r in the tissues surrounding them, or, to speak more correctly, 
d depends on a disturbance of the relations which in a healthy area 
subsist between the blood in the capillaries, on the one hand, and the 
capillary walls with the tissues of which they are apart, on the other.'’ 
While treating of the causes of circulation, no active part is 
assigned by Foster to the capillaries, beside that of being mere 
channels. When endeavoring to explain phenomena of inflam- 
mation, disturbance in the relations of the blood to the walls 
°f the vessels is allowed, being unavoidable. Clearly the dis- 
turbance here admitted, acknowledges preexisting local con- 
ditions, which carried on the circulation, but have been inter- 
tered with and placed in abeyance. 
v erification of Prof. Draper’s explanation of the circulation 
of the blood is to be found in the unavoidable admissions of 
those who oppose it. What better proof of its truth could be 
demanded? 310 
TRANSLATORY MOLECULAR MOTION. 
360. The Physics of Respiration.—ln (188) the mechanical por- 
tion of the respiratory act has been described. By it air is 
introduced as far as the smaller bronchi, just as in the circula- 
tion of the blood the mechanical force suffices to deliver blood 
to the capillary bloodvessels. At this point in both systems, the 
actions become physical, and belong to the province of molecular 
forces and motions. 
Even in bronchi of moderate size, the principle of simple 
diffusion of gases (348) is resorted to, and an exchange accom- 
plished between the oxygen of the atmosphere and the impure 
gas of the air cells. For the interchange of the gas of the cells 
with the carbonic acid gas in the blood, the principles of diffu- 
sion through barriers and of solution in fluid are brought into 
play. The union of oxygen with the haemoglobin of the discs, 
we may regard as an action of chemism. 
Returning to the lungs, the changes which take place consist 
in the elimination of carbonic acid gas, vapor of water, and 
other bodies. The stages here are the same as for the introduc- 
tion of oxygen, hut occur in reverse order. For a detailed de- 
scription of these the student is referred to any modern text- 
book on physiology. Our purpose has been simply to show the 
direction in which the principles we have been studying are 
applied, and the necessity for some knowledge on the part of 
physicians regarding them. SECTION V. 
ACOUSTICS. 
CHAPTER XL 
nition and province of acoustics—Vibrations described—Relations of vibra- 
tions and undulations—Transverse vibrations—Longitudinal vibrations— 
Circular or elliptical vibration—Undulations and their graphic representation 
—Undulations in space—Undulations in tubes—Reflection of waves—lnter- 
ference of waves. 
VIBRATIONS AND UNDULATIONS. 
361. Definition and Province of Acoustics.—-The term is derived 
from a Greek word signifying to hear; it includes the study of 
B°unds in all forms in which they are appreciable by the ear, 
and of vibrations in elastic bodies by which sound is produced. 
Music treats of sound in relation to the pleasure it affords. 
Acoustics deals with the manner of production, propagation, 
Perception, and comparison of sounds. 
. All sounds originate in impulse, or in vibrations of the par- 
frcles of elastic bodies, which generally reach the ear through 
fhe medium of undulations in the air. We shall, therefore, in 
the first place inquire into the characters and varieties of vibra- 
tions and undulations. 
362. Vibrations Described.—Vibrations may be defined as rapid 
Movements of oscillation, similar in many respects to the move- 
ment of a pendulum (305). 
■ft may be illustrated by the arrangement Fig. 144, in which 
°ne end, C, of a long steel spring is gripped in the jaws of a 
vjce, A. The free end of the spring 1) is then drawn to one 
frde to jy ; on being released, its elasticity carries the free end 
yack to D, but the "kinetic energy it has gained in movement 
18 so great that it passes on to D" before it comes to rest. ACOUSTICS. 
Here potential energy being at the maximum, the free ex- 
tremity is carried back to D, and by kinetic energy to D', and 
so on. Each movement becomes less and less, as in the case of 
the pendulum, and finally ceases, its 
energy having been consumed in friction 
with the air. 
Fig. 144. 
The movement of the extremity of 
the spring from D' to D" or from H" 
to D', is called a single vibration by the 
French. The English and Germans 
call a vibration the movement from 
to ~D" and back again to D'. The 
vibration of the French system is, 
therefore, a semi - vibration of the 
English system. The English, as com- 
pared with the French, is a double or 
complete vibration. 
The time occupied in executing a 
complete vibration is called the period 
of vibration. 
The amplitude of a vibration in any 
part of the spring, is the distance from 
the middle position to either of its 
extreme positions. 
A moment’s observation shows that 
while the amplitude of vibration for 
different parts of the spring is very 
variable, the period for each part is 
Vibration of straight springs. 
the same. In respect to isochronism the spring resembles the 
pendulum. 
363. Relations of Vibrations and Undulations.—lf one taps with 
the finger upon a surface of still water in a large vessel a 
wave-like or undulatory movement of the surface of the liquid 
is produced, which originating at the point where the finger 
touches passes outwards to the borders of the vessel. The 
tapping or vibrating movement appears to be distinct from the 
wave-like or undulatory motion; while the vibration is in a 
vertical, the undulation is in a horizontal plane. The molecules 
of the liquid seem to pass in the direction of the wave move- 
ment, yet this is not the case, as may be readily proved. 
Place a cork or chip upon the surface of water in a pond; 
drop a pebble into the water at a distance of about five feet 
from the chip. The. water at the point of impact is thrown 
into a vibratory motion as in the tapping experiment. Undu- 
lations originate at this point and pass in a succession of circles 
to the shore, where they break and are lost. As each wave VIBRATIONS AND UNDULATIONS. 
313 
reaches the chip the latter is not driven forward, but simply rises 
and falls in a vertical plane. The chip can only move as the 
Molecules of water move. Since it moves in a vertical plane, 
it follows that the actual movement of the water molecules is 
also in a vertical plane, exactly as it was in the vibration which 
originated the wave motion. 
From the above facts, it is evident that the relations of vibra- 
tions and undulations are as follows : Ist. Undulations originate 
in a vibratory movement in a medium. The vibration is the 
cause, the undulation an effect. 2d. The passage of vibra- 
tions along the medium gives to the latter the wave-like or 
undulatory condition. 3d. While the vibratory movement is 
of very slight extent, the undulation may pass over considerable 
distances. 4th, In undulations it is the form only that advances, 
not the molecules or particles (130). The undulation is translated 
motion, not translated matter. 
364. Transverse Vibrations.—Vibrations may take place in 
different ways. The first of these is where they are at right 
angles or vertical to the course of the waves. Such are called 
transverse. In waves on water they approach this character, 
though, as we shall see later on, they are much more complex 
than they at first appear to be (366). 
A good illustration of transverse vibration is afforded by 
attaching one end of a long chain to a suitable support, and then 
holding it tolerably tense at the other. On moving the hand up 
Fig. 145. 
Transverse vibration. 
and down, each link of the chain takes on the up and down 
Movement imparted by the hand to the first link, and a wave- 
hke motion passes along the chain to the attached end. A long 
cord or rubber tube filled with sand may be used; in each case 
the particles move transversely, only the wave form advances. 
365. Longitudinal Vibrations.—In (303), transmission of a com- 
pression impulse along a rod was illustrated, and the manner ACOUSTICS. 
of transmission described by a series of suspended balls. As the 
action is along the length of the rod, or series of balls, it is 
called longitudinal. As we have longitudinal impulse, so we 
have longitudinal vibration, in which impulse after impulse is 
imparted to molecule after molecule of the rod, each molecule 
swaying backwards and forwards, but moving through an in- 
finitely minute distance compared with that traversed by the 
wave. 
The transmission of longitudinal vibration may be admirably 
imitated by means of the brass spiral. This consists of a brass 
wire, about one-fortieth of an inch in diameter, coiled in a 
close spiral one-half inch in diameter and thirty feet long. 
Fasten one end of the coil to a firm support, then holding it 
taut in the left hand, with the thumb and index finger of the 
right, nip the spiral about ten inches from the left hand, and 
draw that turn of the spiral towards the left hand. In this way 
the first sixty or one hundred turns of the spiral are drawn 
closer together or compressed. Suddenly releasing the spiral 
from the finger and thumb of the right hand, a wave-like move- 
ment of compression followed by relaxation passes along the 
spiral to the fixed extremity. In the passage of the wave each 
turn or coil of the spiral oscillates or vibrates forward and back- 
wards through a very slight extent, but the wave form of 
compression and relaxation passes throughout the extent of the 
coil. 
As in the spiral coil, we see a wave of compression and relax- 
ation passing along the spiral, so in all longitudinal vibration a 
similar wave of compression and rarefaction is produced. 
366. Circular or Elliptical Vibration.—Reference has been made 
to the fact, that in waves upon water, though movement of the 
particles appears to be simply up and down, it is quite complex. 
Regarding this, Prof. Weinhold says: 
Careful experiments have shown that, when a uniform series 
of waves follow each other along the surface of water, the 
particles of liquid which are disturbed by them move in ellip- 
tical or circular paths, and that hence each particle returns 
again to the point from which it started, while the onward 
motion of the whole wave is due to the fact that each liquid 
particle commences its motion somewhat later than the pre- 
ceding one. 
Fig. 146 is intended to illustrate the formation of waves by 
the circular motion of individual particles of water. For sake 
of clearness, only a few particles are represented in the figure, 
those shown being so far apart that each one begins to move 
Avhen the preceding one has completed the twelfth part of 
its circular motion; the portion of its path which each particle VIBRATIONS AND UNDULATIONS. 
lias already described at the instant to which each figure cor- 
responds is shown by the dotted curves. A represents the 
surface after the particle 0 has moved through one-twelfth of 
a circle; B after 0 has moved through two-twelfths and the 
particle 1 through one-twelfth of a circle. 'ln C the particle 0 
has passed through three-twelfths, or one-fourth of the circle; 
m 1) it has described a semi-circle; and in Eit has returned to 
Fig. 146. 
Molecular formation of waves. 
its original place. If only a single wave passes, each particle 
comes to rest after describing a circle. E represents the surface 
at the moment when the wave has moved onward through half 
its whole length further than it was in E; and if there are suc- 
cessive waves, each particle repeats its motion, as shown in G. 
By means of the spiral coil all forms of vibration we have 
considered may be illustrated and undulations produced. In 
circular vibration, the hand is moved in a small circle; in ellip- 
tical, in an ellipse. 
367. Undulations and their Graphic Representation.—Deschanel 
says; “An undulation may be defined as a system of move- 
ments in which several particles move to and fro, or round and 
r°und, about definite points, in such a manner as to produce 
continued onward transmission of a condition, or series of con- 
ditions.” 
The terms employed in connection with vibrations, as ampli- 
tude, etc., are also used in tbe case of waves. See 131, for wave 
measurements. ACOUSTICS. 
Undulations may be divided into three groups: Ist. Those 
produced by transverse vibrations; 2d. Those by longitudinal 
vibrations; and, 3d. Those by circular or elliptical vibrations. 
Each of these necessarily imparts special characters to the undu- 
lations it produces. 
The graphic representation of undulations is thus briefly 
described by Ganot: Draw a line of indefinite length and mark 
off A H, Fig. 147, to represent the time of one half-vibration r 
Fig. 147. 
Graphic representation of velocity of oscillating body. 
H H' to represent the time of the second half-vibration, and so 
on. During the first, velocity increases from zero to a maxi- 
mum at the half vibration, and then decreases during the second 
from the maximum to zero. Consequently, a curved line or arc, 
AOH, may be drawn, whose ordinate 0 M at any point 0 will 
represent the velocity of the body at the time represented by 
AM. If a similar curved line or arc HPH' be drawn, the 
ordinate P U of any point P will represent the velocity at a 
time denoted by AU, Put since the direction of the velocity in 
the second oscillation is contrary to that in the first, the ordinate 
U P must be drawn in the contrary direction to that of M 0. 
If, then, the curve be continued by a succession of equal arcs 
alternately on opposite sides of A D, the variations of velocity of 
the vibrating body will be completely represented by the varying 
magnitudes of the ordinates of successive points of the curve. 
368. Undulations in Space.—lf we examine the circles of waves 
produced on water when a pebble is dropped therein, we find 
that the altitude of each circular wave, or the amplitude of 
vibration of its particles becomes less as we pass outwards from 
the centre or point of origin. This was to be expected as a 
necessary consequence of diffusion over a greater space of the 
energy which originated them. 
What we see taking place on the surface of water is an indi- 
cation of what occurs in the case of undulations in air. In 
the latter instance, since movement is equally free in all direc- 
tions, the waves pass out from the centre of disturbance as 
spheres of compression, produced in the manner described under 
longitudinal vibration (365). Hence the energy initiating them 
is of necessity rapidly diffused over the ever-increasing space, and 
the amplitude of vibration of the particles steadily diminished. 
The power of air to transmit impulse, and also diminution 
of the violence of the same, with increased distance from the VIBRATIONS AND UNDULATIONS. 
point of origin, were well shown by the explosion of live tons of 
gunpowder in Regent’s Park, London, in 1874. The walls of 
houses were seriously damaged at a distance of four hundred 
yards. Windows, doors, and ceilings were broken at six hun- 
dred yards. Concussion was distinctly felt at two miles, and the 
sound reached Waltham, fifteen miles away. 
369. Undulations in Tubes.—ln the propagation of undulations 
ITI tubes, the loss is not so rapid as in open space. This may be 
easily demonstrated by producing waves in a long open trough of 
water the sides of which are vertical, smooth, and not very far 
apart; under these conditions the waves preserve their altitude 
with very little diminution throughout the length of the trough. 
To make the manner of propagation as clear as possible, sup- 
pose that M hi, Fig. 148, represents a tube tilled with air, and 
Fig. 148. 
Sound undulations in tubes. 
T a piston oscillating therein. When the piston moves from 
Wto a, the air in the tube is condensed. By virtue of its elas- 
ticity it is not compressed throughout its whole length at once, 
tnit only within the distance AH. This is called the condensed 
wave. 
Imagine the tube to be divided into lengths equal to A H, 
and each of these into layers parallel to the face of the piston. 
When the first layer of AH ceases to move the first layer of 
the second wave H H7 moves, and so on through the layers of 
the remaining divisions or waves. The compressed wave thus 
advances, its parts moving in succession with equal velocity and 
condensation. 
By return of the piston in the direction a A, a vacuum is 
Produced, and the layer in contact with its face is rarefied. As 
Avas the case with the condensed wave, a rarefied wave passes 
along the tube of the same length as the condensed wave, and 
following it. 
The condensed and expanded wave, taken together, form a 
complete undulation. As the vibrations are more rapid the 
undulations are shorter. 
During transmission of undulations through a medium, any 
tw° particles are in the same phase when they move with 
hke velocities in similar directions. When they move with 
equal velocities in opposite directions thej are said to be in ACOUSTICS. 
opposite phases. Separation by a whole wave length produces 
motions in the same phase; separation by half a wave length 
produces phases in opposite directions. 
In transmission of waves along a tube, there is not the same 
loss as in the case of spherical waves, since the force or energy 
is confined within equal limits and not allowed to diffuse itself 
over a great extent of space. 
370. Reflection of Waves.—When circular waves on the surface 
of water meet a resisting medium which presents a plane sur- 
face, the undulations undergo reflection according to the law of 
reflection (304), and pass backwards from the reflecting surface. 
Let a system of water waves originate at O, Fig. 149, their 
Fig. 149. 
Reflection of sound waves. 
crests and depressions being represented by the full and dotted 
circles. On meeting the plane surface they are reflected in the 
manner indicated, the second system of circles having their 
centre at O', the same distance from the plane surface as 0, but 
on the opposite side. An observer placed at M will refer the 
wave reflected from I, to O' as its point of origin. 
371. Interference of Waves.—Suppose two equal systems of 
water waves, Fig. 150, A, one represented by the continuous 
and the other by dotted lines. When they meet at M with crests 
corresponding to crests, and troughs to troughs, the wave height 
of the combined system will be increased, as at M M. 
If, on the contrary, the waves meet, or interfere as delineated 
at B, the crests of the dotted system fitting into the troughs 
of the other system, they will mutually destroy each other and 
smooth water will result. GENERAL PROPERTIES OF SOUND. 
In the experiment described in the preceding article, where a 
system of circular waves is reflected from a plane surface, the 
effects of interference are well illustrated. As the incident and 
reflected systems meet, every variety of conditions arise. In 
Fig. 150. 
Interference of waves. 
some positions the waves are seen surmounting each other and 
producing increased wave height; in others neutralizing and 
restoring the original level of the water. In the approach of a 
steamboat to her dock, these interferences of wave systems may 
be seen to perfection, as the waves from the paddle-wheel 
undergo reflection from the sides of the pier. 
CHAPTER XII. 
-Noise and sound—Origin of sound—Sounds from inanimate nature—Propagation 
of sound—Manner of propagation of sound—Dissipation of sound—Con- 
duction of sound—The stethoscope and auscultation—Velocity of sound in 
gases—Velocity of sound in liquids—Velocity of sound in solids—Reflection 
of sound from plane surfaces—Reflection of sound from curved surfaces— 
Refraction of sound—Polarization of sound. 
GENERAL PROPERTIES OF SOUND. 
372. Noise and Sound.—It is not easy to draw a sharp line o± 
distinction between noise and sound. We may, however, say 
that by noise we understand either brief vibration, or impulse, 
like the discharge of a cannon; or a mixture of discordant 
sounds, like the passage of a carriage, the rolling of thunder. 
A true sound, or a "musical sound, on the contrary, is more or 
loss sustained and continued, and euphonious or well-sounding. 
Its valuation or rate of vibration is fixed and uniform, and easily 
determined. ACOUSTICS. 
373. Origin of Sound.—ln (361) it is stated that all sounds 
originate in impulse, or in vibrations of the particles of elastic 
bodies. Of this we offer proof. 
Vibrations may be caused either by shock, or by friction, as 
with the bow of a violin or the tremulous movements of reeds 
(393). Any substance which may be made to produce sound 
is called a sonorous body. 
The existence of vibration during the emission of sound may 
be shown by the experiment, Fig. 151, in which a bell jar is 
Fiq. 151. 
Vibration and sound. 
held horizontally in the manner indicated, and struck with a 
small wooden mallet. If while still sounding a little piece of 
metal is tossed into the interior, it is thrown into rapid motion 
by oscillations of the jar. Placing the hand upon the jar these 
may be felt, though contact causes them to cease. 
In illustration of vibration by the spring and vice, Fig. 144, 
while the spring projects for a considerable distance vibra- 
tions are perceptible to the eye, and a low humming sound is 
produced. On lowering the spring in the vice, as it becomes 
shorter the rate of oscillation grows more rapid, and the sound 
more shrill. At last, when a very short portion of the spring 
projects, the movements are so small in extent, and brief in 
duration, that the eye fails to perceive them, though they can 
still be detected by the ear and sense of touch. 
In the course of the above experiment, since sounds of many 
degrees have been obtained, and in every case attended by vibra- 
tion, we conclude that all sounds take their origin in oscillations 
of the molecules of bodies. 
374. Sounds from Inanimate Nature.—Setting aside the crash 
and rolling of thunder, the rumble of an earthquake, the ex- 
plosive discharge of volcanoes, the splashing and roar of water, 
it may be said that the sounds produced by inanimate nature 
take their origin in the movements of winds. These often throw 
various objects into vibratory movement. All who live in the 
vicinity of telegraph wires in exposed positions, and have heard 
the sound produced therein, have had frequent opportunities of 
verifying this statement. The infinite variety of sounds evoked GENERAL PROPERTIES OF SOUND. 
m a forest during a storm arise from the vibrations which wind 
has produced in the leaves, twigs, stems, and shafts of trees. 
A pleasant application of wind to evoke sonorous vibrations is 
made in the Aeolian harp. This consists of a long box of thin 
wood, on the upper surface of which violin strings are stretched. 
Excepting one, which is heavier than the rest, they are tuned in 
unison; when placed in a window where currents of wfind may 
pass over its strings they are thrown into vibration. “After a 
pause a low solemn note is heard, like the bass of distant music 
m the sky; the sound then swells as if coming near, and other 
tones break forth, mingling with the first and with each other. 
In the combined and varying strain, sometimes one clear note 
predominates and again another, as if single musicians alter- 
nately led the band; and the concert seems to approach and 
recede, until with the unequal breeze it dies away, and all is 
hushed,” 
A strong current of air passing through chinks in walls, 
cracks in doors, or through keyholes, originates sounds which 
rise and fall as the force of the moving air varies. Thus the 
deep bowlings which issue from capacious chimneys of ancient 
houses take their origin. 
Kot only do sounds originate by the action of winds, but 
such impalpable agents as light can also be made to initiate 
sound vibrations. In following up the experiments which led 
io the discovery of the photophone (487 A) Prof. Bell says: 
“ In my Boston paper the discovery was announced that thin 
disks of very many different substances emitted sounds when ex- 
posed to the action of a rapidly interrupted beam of sunlight. 
I he great variety of material used in these experiments led me 
t° believe that sonorousness under such circumstances would be 
found to be a general property of all matter.” 
“At that time we had failed to obtain audible effects from 
Masses of the various substances which became sonorous in the 
conditions of thin diaphragms, but this failure was explained 
upon the supposition that the molecular disturbance produced 
oy light was chiefly a surface action, and that under the circum- 
stances of the experiments the vibration had to be transmitted 
through the mass of the substance in order to affect the ear. It 
was, therefore, supposed that, if we could lead to the ear air that 
Was directly in contact with the illuminated surface, louder 
s°unds might be obtained, and solid masses be found to be as 
sonorous as thin diaphragms. The first experiments made to 
verify this hypothesis pointed towards success. A beam of sun- 
ught was focussed into one end of an open tube, the ear being 
Placed at the other end. Upon interrupting the beam, a clear, 
Musical tone was heard, the pitch of which depended upon the ACOUSTICS. 
frequency of the interruption of the light, and the loudness upon 
the material composing the tube.” 
“In order to study these effects under better circumstances 
the materials were enclosed in a conical cavity, B, in a piece of 
brass closed by a hat plate of glass. A brass 
tube leading into the cavity served for con- 
nection with the hearing-tube A. When this 
conical cavity was stuffed with worsted or 
other tibrous materials the sounds produced 
were much louder than when a tube was em- 
ployed,” 
Fig. 152. 
“ Upon smoking the interior of the conical 
cavity, and then exposing it to the intermit- 
tent beam, with the glass lid in position, the 
effect was perfectly startling. The sound was 
so loud as to be actually painful to an ear 
placed closely against the end of the hearing- 
tube.” 
Intermittent beam of light 
develops sound. 
“In regard to the sensitive materials that 
can he employed, our experiments indicate 
that in the case of solids the physical condition and the color 
markedly influence the intensity of the sonorous effects. The 
loudest sounds are produced from substances in a loose, porous, spongy 
condition, and from those that have the darkest or most absorbent 
colors.” 
“ The materials from which the best effects have been obtained 
are cotton-wool, worsted, fibrous materials generally, cork, 
sponge, platinum and other metals in a spongy condition, and 
lampblack.” 
“The loud sounds produced from such substances may, per- 
haps, be explained in the following manner: Let us consider, for 
example, lampblack—a substance which becomes heated by 
exposure to rays of all refrangibility. I look upon a mass of 
this substance as a sort of sponge, with its pores filled with air 
instead of water. When a beam of sunlight falls upon this mass, 
the particles are heated, and consequently expand, causing a 
contraction of the air-spaces and pores among them. Under 
these circumstances a pulse of air should be expelled, just as we 
would squeeze out water from a sponge.” 
“ The force with which the air is expelled is greatly increased 
by the expansion of the air itself, due to contact with the heated 
particles of lampblack. When light is cut off, the reverse takes 
place. The lampblack particles cool and contract, thus enlarg- 
ing the spaces between them, and the enclosed air also becomes 
cool. Under these circumstances a partial vacuum is formed 
among the particles, and the outside air reabsorbed, as water is 
by a sponge when the pressure of the hand is removed.” GENERAL PROPERTIES OF SOUND. 
u I imagine that in some such manner as this a wave of con- 
densation is started in the atmosphere each time a beam of sun- 
light falls upon lampblack, and a wave of rarefaction is origin- 
ated when the light is cut off. We can thus understand how it is 
that a substance like lampblack produces intense sonorous vibrations in 
the surrounding air, while at the same time it communicates a very 
feeble vibration to the diaphragm or solid bed upon which it rests.” 
375. Propagation of Sound.—The apparatus Eig. 158 consists 
°f a glass globe; in the interior a small bell is suspended. A 
stopcock closes the aperture, and by means of 
the screw it may be attached to an air-pump 
and exhausted. 
Commencing the experiment with the globe 
ln an exhausted condition, if the vacuum is 
nearly perfect, scarcely any sound can be per- 
ceived no matter how violently we ring the 
bell. What little sound we do hear passes 
along the suspending rod to the metallic cap. 
If this has been made of poor conducting 
naaterial, no noise whatever is heard. There- 
f°re, sound cannot pass through a vacuum. 
Admitting air to the sphere and keeping the 
Fig. 158. 
Propagation of sound, 
bell in vacuo. 
cell in motion, we soon begin to hear its ring, which, as air 
enters, becomes louder and louder, reaching its maximum when 
the interior and exterior pressures are equal. We consequently 
conclude that sound is propagated through air. We would add 
that, as a rule, it always reaches the ear through this medium. 
Again exhausting the sphere, and tilling it in succession with 
various gases, we find that while they all permit conduction 
Pt sound from the bell, they differ greatly in ability to do so. 
Hydrogen, for example, transmits a feeble sound, while denser 
§ases, according to their increase in specific gravity, transmit 
louder sounds. Increase in pressure also favors passage of 
B°und through any gas. 
In like manner, sound is propagated through water and other 
hpuids, and also through all elastic solids. Evidence of this 
W]ll be given when we treat of the velocity of sound through 
various media. 
“Peschel states that the greatest known distance to which 
B°nnd has been carried through the atmosphere is 845 miles, as 
is asserted that the very violent explosions of the volcano of 
Vincent have been heard at Deraerara. There is no doubt 
lljat sound travels to a greater distance and more loudly through 
Jhe earth’s surface than the air. Thus, in the wilds of Africa, 
the roar of a lion is heard for many miles around. This is 
cnving to the animal placing its nostrils within a short distance ACOUSTICS. 
of the ground, and the transmission of the sound by the surface. 
It is stated on good authority that the cannonading at the battle 
of Jena, in 1806, was heard, though but feebly, in the open 
fields near Dresden, a distance of ninety-two miles; while in 
the casemates of the fortifications (underground) it was heard 
with great distinctness. So it is said that the cannonading of the 
citadel of Antwerp, in 1832, was heard in the mines of Saxony 
at a distance of 370 miles.” 
376. Manner of Propagation of Sound.—ln the discussion of the 
relations of vibrations and undulations (363), it was stated that 
vibrations produce undulations. Vibrations of a sonorous body 
originate sound waves, or undulations in the air, in which the 
molecules of air are thrown into longitudinal vibrations, just as 
an oscillating piston produces undulations in a tube (369). 
Vibrations in a sonorous body may be either transverse, as in a 
string, or longitudinal, as in a rod; but in their passage through 
air as a conducting medium, they of necessity become longitu- 
dinal; as Dr. Arnott puts it: “There is no cohesion to link the 
air-particles together, so loieral motions of any one particle would 
not be passed on to the next, only forward impulses, impacts, 
or pushes, can be communicated.” Herein we find an illustra- 
tion of the necessity of drawing a distinction between vibrations 
in a sonorous body, and those in the medium the sound traverses. 
Of the passage of sound in air, Weinhold says: The motion 
of the particles of air during propagation of sound resembles 
to some extent that of the particles of water during the trans- 
lation of a wave; hence, sound is said to be conveyed by an 
undulatory or wave-like motion in air. 
The resemblance is, however, confined to the fact that each 
particle performs the same definite movement, but commences 
its motion somewhat later than the preceding one. The path 
described by each is essentially different in the two cases. When 
a wave is propagated through water, each particle describes a 
circle (366); when sound is propagated through air, the mole- 
cules move in a straight line, backwards and forwards, in the 
direction the sound is propagated. 
A wave on water is formed by a series of crests and hollows 
(or elevations and depressions); a wave of sound, by a series of 
alternating compressions and rarefactions of air. Such com- 
pressions and rarefactions of air take place whenever a body, 
surrounded by air, is set in rapid vibration—that is, when 
its parts are made to move rapidly to and fro through a short 
space. Suppose a tuning-fork is struck, and, for sake of sim- 
plicity, that one of it's prongs vibrates exactly in a direction 
towards and away from us. As soon as the prong begins to 
move towards us, the nearest particles of air are compressed, GENERAL PROPERTIES OF SOUND. 
while those further away are unaffected by the impulse in conse- 
quence of their inertia. Before the prong begins its backward 
motion, the compressed particles of air expand again, and the 
expansion takes place in whatever direction they meet least 
resistance. 
“ The tuning-fork does not perform merely a single vibration, 
but the movements are uniformly repeated, and a series 
of condensations and rarefactions follow each other in 
rapid succession, and are propagated to the ear; the 
last portion of air close to the ear vibrates to and fro, 
exactly like that close to the proim of the fork, only 
a little later.” 
Fig. 154. 
The motion of the particles of air during the pro- 
pagation of sound may be further demonstrated with 
the help of Figs. 154 and 155. A narrow slit, SS, is 
cpt out of a piece of stiff paper (Fig. 155), which is 
either black, or at any rate of a dark color; this slip 
pf paper is then placed upon Fig. 154, so that the slit 
18 exactly along the dotted line. A is now slowly 
drawn along in the direction of the arrow, the piece 
°f paper being held in the same position. At first 
fhe lower extremity of the curved line Fig. 154 is 
Fig. 155. 
Seen through the slit; but as A is drawn along, portions to 
right, and to the left, come successively in view; the small 
wMte dot, which is the only visible portion of the curved line, 
Fig. 15G. 
Movement of molecules in propagation of sound. 326 
ACOUSTICS. 
appears as a point which moves first to the right and then 
to the left, and imitates closely the motion of a vibrating 
particle of air, the rate being, however, much slower. If now 
the slit be placed over the dotted line Fig. 156, and the slip C 
drawn along underneath it in the direction of the arrow, a rep- 
resentation is obtained of the motion of a series of particles of 
air which are acted on by a number of successive equal undu- 
lations or waves. Each particle merely moves a little right and 
left, and always comes back to its starting point; but the con- 
densations and rarefactions, represented by the lines being 
respectively closer together or further apart, are gradually 
transmitted through the whole series from one end to the other. 
377. Dissipation of Sound,—When sound passes out into space 
in what may be called the radiant form, as where the sonorous 
body is vibrating freely in air, it is evident from (368), that by 
diffusion of the energy producing the undulations, the sound 
must ultimately diminish and finally be lost. 
The theoretical rate at which the loudness of a sound should 
change under these conditions, is inversely as the squares of the 
distances. According to Deschanel, this assumption is not 
strictly true, inasmuch as vibration implies friction, and friction 
implies generation of heat at the expense of the energy which 
produces vibrations. Sonorous energy must, therefore, diminish 
with distance somewhat more rapidly than according to the law 
of inverse squares. All sound, in becoming extinct, is converted 
into heat. 
378. Conduction of Sound.—lf in place of creating sound in 
open space it is produced in a cylindrical tube filled with air, as 
described in (369), the rate of loss is greatly reduced. The 
sonorous waves are no longer propagated as concentric spheres, 
but are reflected from the walls of the tube, and their intensity 
being thereby conserved, they may be conveyed to great dis- 
tances. 
In the experiments of Biot with the Paris water pipes, it was 
found that conversation in a very low tone could be carried on 
through a pipe 1040 yards long. Roughness in the sides of a 
tube diminishes its ability to convey sound. A very useful ap- 
plication of this property of air tubes to prevent dissipation of 
sound and carry it to a distance is seen in the speaking tubes 
generally introduced into dwellings. In these it is not only con- 
veyed, but made to traverse curves and angles. 
Sounds may also be conducted along such narrow channels as 
cords. An example of this is offered by the toy telephone or 
lover’s telegraph, in which a string a hundred or more yards in 
length is attached to the bottom of a couple of small boxes of GENERAL PROPERTIES OF SOUND. 
wood or tin ; these act as sounding boards, and are held at the 
lull distance of the string from each other, with the cord taut. 
If a person speaks or whispers into one box, the vibrations 
pass along the string to the other box, and can be easily heard 
by applying the ear thereto. Fine metallic wires are substituted 
for string, with excellent results. 
Along rods of wood sound waves pass with facility. Of this 
we have an example in the passage of sound along a billiard cue 
when one end is applied to the ear and the other scratched by a 
pm or touched to a musical box in action. 
The wonderful facility with which sound passes along wooden 
rods received an admirable illustration some years ago in an 
exhibition called the Magical Orchestra. On the stage ap- 
peared a set of stringed instruments each supported by a 
slender wooden rod. The other extremity of the rod communi- 
cated with a similar instrument in a room beneath. When the 
performance began the musicians operated upon the instruments 
m the room below, the vibrations from these passed along the 
rods to the visible instruments, and the music was produced 
before the audience, the performers being invisible. 
The vibrations in any rod along which sound is passing may 
be distinctly felt on touching it with the tip of the finger, but 
they are stopped at the moment of contact. It is on this prin- 
ciple that the dampers of pianos and other musical instruments 
act. Other bodies as wool, hair, feathers, leather, paper, or 
anything which does not, or is not in condition to conduct 
sound, will destroy it if they touch a vibrating body. 
Among other solids, earth and stone also allow the propaga- 
tion of sound through their mass even better than it can pass 
through air. So the savage detects the vicinity of his prey or 
enemy by applying his ear to the earth. In the transmission 
°t sounds along the stone and brick of walls and beams of floors 
°f houses we often find the explanation of singular and otherwise 
unaccountable noises which superstition has attributed to super- 
natural causes. 
379. The Stethoscope and Auscultation.—Practical application 
°I the difference in the conduction of sounds by solid, liquid, 
and gas, is made in medicine for the detection of changes which 
have taken place in the lungs and other organs. To this method 
°f physical examination the name “ auscultation ” is given. 
Auscultation consists in the direct application of the ear to 
tbe yhest, or other part in which sound is to be detected; or 
the intervention between the ear and chest of an instrument 
called the stethoscope. 
The earlier or Laennec stethoscope was a wooden cylinder 
Perforated through its axis and enlarged at its extremities. It ACOUSTICS. 
possessed a certain advantage over direct application of the ear 
to the chest, in that vibrations were collected from a smaller 
area, and sounds heard could be located to greater advantage. 
To this, various forms of flexible stethoscope have succeeded. 
Some are double, the ear piece being arranged to have both ears 
brought into use at the same time. 
In "Fig. 157 an improved form of this instrument, contrived 
by Konig, is represented. It consists of a hollow metallic 
Fig. 157. 
Stethoscope. 
hemisphere, the mouth of which is closed by two disks of rubber 
or membrane AC. By means of a stopcock the space between 
the membranes may be inflated with air or other gas, and a 
double convex lens formed. To the metallic hemisphere a 
number of tubulures with elastic tubes are fitted, enabling 
several persons to make observations at the same time. The 
outer membrane of the mouth is applied to the chest in the 
usual manner, when the sounds of the heart and lungs pass into 
the cavity between C and A, and thence by the tube to the ear. 
By auscultation, physicians detect new sounds that have ap- 
peared in the various organs in the thoracic or other cavities of 
the body of which a brief account is given in (397), and also 
sounds produced in the abdomen by the beating of the foetal 
heart. 
In addition to the rales, rhonchi, etc., referred to above, auscul- 
tation enables us to detect changes in structure which attend con- 
solidation of the lung by fibrinous and cellular material. We 
have seen in the study of the propagation and conduction of 
sound (375, 378), that, as a rule, solids are better conductors 
of sound than gases. In health the cells of the lung are filled 
with air, and by causing a person to speak while one’s ear is 
placed on the chest-wall, the sound of the voice is transmitted 
in a muffled manner through the bronchial tubes and air-cells. 
When the lung is consolidated by pneumonic or phthisical 
deposits, sound is conveyed better from the larynx and tubes. 
The voice, therefore, is louder, as though the person was speak- 
ing immediately under our ear, in his chest; at the same time GENERAL PROPERTIES OF SOUND. 
329 
its character is greatly changed, it becomes unpleasant and 
endowed with a nasal twang. 
When fluid is poured into the cavity of the pleura from that 
membrane, the action is different to that described above. In 
this case the effusion presses the lung away from the chest-wall, 
the air-cells and smaller bronchi are closed, and all natural 
respiratory sounds are lost; even the intensity of the voice is 
reduced, since sonorous vibrations are not readily communicated 
from gas to fluid. Sometimes, just along the edge which marks 
the surface of the fluid, and where the lung is consolidated by its 
pressure, the effects of compression described above are pro- 
duced, but they are limited in extent. 
380. Velocity of Sound in Gases.—A sound produced near at 
band appears to reach the ear instantly, but this is not the case 
ln reality. We know that the lightning flash has caused the 
thunder, but we may not hear the latter for some seconds after 
the flash has vanished. Sound, therefore, requires time for its 
passage through air. This we might have foretold from the 
manner of propagation from molecule to molecule, one taking 
up the vibration a little later than the other. 
Among the best experimental determinations of the velocity 
°t sound are those of Moll and Van Beck, made by firing 
cannon on two hill-tops about eleven miles distant from each 
other, and noting the time between the flash and report. 
J-he average result of these was 1093 feet or 333 metres per 
second, at a temperature of 0° C., and a pressure of 760 m. 
-Estimates varying slightly from this are given. They are due 
the different conditions of the layers of air through which 
the sound passed. 
The effect of temperature on the velocity of sound is shown 
by the experiments of Kendall in his North Pole Expedition, in 
which the rate was reduced to 314 metres per second, at a tem- 
perature of —4o°. The increase in rate above 0° C. is about two 
met per second for each degree centigrade. In England the 
estimate at 60° F. is 1120 feet per second. 
The average velocity at ordinary temperatures may be taken 
at 340 metres per second. Since an English mile is about 1609 
metres, sound requires about 4|- seconds to traverse that space. 
r°m these data we may easily compute the distance of a 
cannon, by taking the time between flash and report. A 
hghtning flash with its attendant thunder also gives means for 
estimating the remoteness of a cloud or storm. An interval of 
half a minute, in this case, indicates that it is a little more than 
Slx miles away. The computation of time and space may be 
made by the pulse, each beat being equal very nearly to { of a 
mile. ACOUSTICS. 
The fact, that when an air is played by a band at a distance, 
we hear all the notes in their proper relation of time to each 
other, indicates that all sounds travel the air with equal velocities. 
While this may be true for sounds of equal strength, it is not 
the case when they differ greatly, for a violent sound is then 
found to have a greater velocity than a feebler one. Illustration 
of this was offered by artillery practice during the Arctic Expe- 
dition of Captain Parry, in which persons stationed at a con- 
siderable distance heard the report of the gun before they heard 
the order of the officer in command. In blasting operations, 
Mallett found that the larger the charge of powder, the louder 
the report, and the greater the velocity of transmission. With 
2000 pounds of powder the velocity, according to his estimate, was 
967 feet per second; with 12,000 pounds, 1210 feet per second. 
As regards transit in altitude, Bravais and Martins found 
that sound moved at the same rate from the summit to the base 
of the Faulkorn, as from base to summit. 
The following table gives the results of Regnault’s experi- 
ments on the velocity of sound in different gases, through a 
tube 2000 metres in length : 
Air .... 
Metres 
per second. 
333.00 
Feet 
per second. 
1093 
Oxygen 
317.17 
1040 
Hydrogen 
. 1269.50 
4166 
Carbon dioxide 
261.60 
856 
Carbon monoxide . 
. 387.40 
1107 
Protoxide of nitrogen . 
. 261.90 
859 
Olefiant gas . 
. 314.00 
1030 
The velocity of sound is less in damp air; the loudness is also 
less. Dry frosty air is favorable to the transmission of sound. 
In country regions farmers often predict a change in weather 
by the manner in which the ringing of distant church bells is 
conveyed through the atmosphere. 
According to Peschel sounds may be heard at the following 
distances in yards: 
Musket report ..... 
Yards. 
. 8000 
Marching company of soldiers 
. 600 to 800 
Squadron of cavalry at foot pace 
. 750 
Squadron of cavalry at gallop 
. 1080 
Heavy artillery at foot pace 
. 660 
Heavy artillery at gallop 
. 1000 
Strong human voice 
. 280 
381. Velocity of Sound in Liquids.—The velocity of sound in 
liquids was determined by Colladon and Sturm, in the Lake of 
Geneva. A bell was struck under water by means of a string, 
which at the same moment ignited powder. The observer was 
stationed at a distance with an ear trumpet, the mouth of which GENERAL PROPERTIES OF SOUND. 
was covered by membrane and placed under water. The time 
being measured between appearance of the flash and hearing 
the stroke on the bell, the velocity of transmission of the sound 
was obtained. At a rough estimate, it was four times the rate 
through air. The velocity of sound in different liquids, as 
determined by Wertheim, is as follows: 
Ether .... 
Metres 
per second. 
. 1159 
Essence of turpentine 
. 1265 
Water .... 
. 1437 
Sea water 
. 1455 
Mercury .... 
. 1471 
Nitric acid 
1 
. 1521 
Aqua ammonia 
. 1820 
Ganot: 
The effect of temperature is shown by the following, from 
Temp 
Feet 
per second. 
River-water (Seine) . 
River-water (Seine) . 
. 13° C. 
4714 
. 30° C. 
5018 
382, Velocity of Sound in Solids.—Many solids transmit sound 
better than either water or air. The rate in some is, however, 
less than the rate in air. The following table in feet per second 
is from Ganot: 
Caoutchouc 
197 
Oak 
. 12,622 
Wax 
. 2,394 
Ash 
. 13,314 
Lead 
. 4,030 
Elm 
, 13,516 
Gold 
. 5,717 
Fir . 
. 15,218 
Silver 
. 8,553 
Steel wire 
. 15,470 
Pine 
. 10,900 
Aspen 
. 16,677 
Copper . 
. 11,666 
Iron 
. 16,822 
In wood, velocity is greatest with the grain. 
Mallett gives the following results of his experiments: 
Wet sand ...... 
Feet 
per second 
. 825 
Stratified quartz and slate . . . 
. 1088 
Discontinuous granite .... 
. 1806 
Solid granite ...... 
. 1664 
The experiments of Genl. H. L. Abbot, in connection with 
mining operations at Hallet’s Point, in which 50,000 pounds 
°f dynamite were fired at a single explosion, and other experi- 
ments made since that time, give1 far higher velocities for the 
passage of waves through the earth, and show that the problem 
is a very complex one, the results being influenced by a number 
°f conditions. Among these are the character of the explosive, 
and the power used in examining the tremor waves on the sur- 
face of the mercury of the seismometer. In an article on this sub- ACOUSTICS. 
jectinthe “Am. Journal of Sciences and Arts,” vol.xv. page 181, 
he says: “The velocities observed, all tend to confirm the idea 
that a slow-burning explosive, like gunpowder, generates a series 
of gradually increasing tremors, which, at a distance of a mile, 
are at first quite invisible with a less sensitive seismometer; and 
are only detected by it when near their maximum intensity. If 
Lieut. Leach’s estimate of time for the arrival of the maximum 
wave be accepted, we have, therefore, for the first mile”— 
Magnification. 
Feet per second. 
Power of 12 gives .... 
8415 
Power of 6 gives .... 
5559 
Minimum power gives 
1240 
383. Reflection of Sound from Plane Surfaces.—Where a system 
of sound undulations meets a barrier which presents a plane 
surface, the waves undergo reflection according to the principles 
laid down in (370). Thus, echo is produced in large rooms, and 
if the positions of the walls are in proper relation to the speaker, 
repetitions of the words uttered may be so frequent as seriously 
to impair their acoustic properties. At the villa Simonetta, near 
Milan, a pistol report is sometimes repeated fifty times, and at 
Pavia a building has been constructed in which the last syllable 
of a question is answered or echoed thirty times. Anything 
which presents broken surfaces diminishes the echo. It is, for 
example, less in a room filled with an audience than when empty. 
Curtains and hangings of all descriptions cause a diminution in 
the number of repetitions. 
Reflection of sound waves or echo also takes place in the open 
air; especially is this noted along rivers with precipitous banks. 
The discharge of a gun, or explosion of a blast in quarrying 
rock, will often be repeated many times, taking on the character 
of rolling thunder. 
In treating of the conduction of sound along speaking-tubes, 
we have referred to the reflection of the vibrations from the walls 
of a tube. After their direction has been changed they tend to 
advance in the new direct course, and not to spread out as when 
radiating from the point of origin. Upon this principle the 
speaking-trumpet depends for its action; the sound is thus 
directed by the speaker to whatever point he may desire with 
far less loss from lateral diffusion than if it were not employed. 
Sounds are also reflected from such impalpable surfaces as 
clouds; of this we have an example in the reverberations of 
thunder. When the lightning flash is unbroken, and free from 
the zig-zag form, it is frequently attended by rolling thunder, 
the echoing reports being partly the results of reflections from 
the clouds. GENERAL PROPERTIES OF SOUND. 
384. Reflection of Sound from Curved Surfaces.—ln the study of 
motion (304), and undulations (370), we have seen that reflection 
takes place on the opposite side of the normal or perpendicular, 
drawn to the point of impact of the incident molecule or wave; 
that the angle of reflection is equal to the angle of incidence; 
and both lie in the same plane. 
Since any curved surface may be conceived to consist of an 
infinite number of plane surfaces, the law also applies in this 
case, and if the curvature is of proper shape, the inclinations of 
the plane surfaces forming it may cause the convergence of the 
sound waves. For a full explanation the student is referred to 
(481). 
Illustration of the reflection of sound waves from curved 
surfaces is offered by means of the parabolic or conjugate mir- 
rors used in experimenting with light and heat. If a watch is 
placed at the focus of one of the mirrors, the ticking sound it 
emits will be reflected in parallel lines, Fig. 158. Falling on 
Fig. 158. 
Sound in conjugate mirror. 
the opposite mirror, the undulations are again reflected, and 
converged to the focus. A tube placed at this point will convey 
them to the ear, as indicated in the figure. 
If sound is produced at the centre of a sphere, it is reflected 
hack with wonderful intensity to the same point, constituting a 
powerful echo. If produced at one side of a circular space 334 
ACOUSTICS. 
under a hemisphere, a similar though less marked result is 
obtained. The circular gallery under the dome of St. Paul’s 
Cathedral, in London, affords so good an illustration of this fact, 
that it is known as the whispering gallery. By whispering close 
to the wall on opposite sides of this space, two persons may 
readily carry on a conversation with each other. In like manner 
in rooms of an oval form, two individuals may converse in a 
whisper by standing at the foci, while those at a short distance 
from them are unable to hear their conversation. 
Dr. Arnold relates: “It happened on board a ship sailing 
south in the Atlantic, towards Bio de Janeiro, while out of sight 
of land, that one day, persons on the deck, when near a par- 
ticular part of it, thought they heard distinctly the sound of 
bells. All were attracted to listen, and the phenomenon was 
mysterious. Weeks afterwards it was ascertained that, at the 
time of observation, the bells of the city of St. Salvador, on the 
Brazilian coast, had been ringing on the occasion of a festival; 
their sound, therefore, favored by the wind at the time, had 
travelled over at least 100 miles of smooth water, and had been 
condensed by the concave sail to a focus on the deck of the 
vessel where it was listened to. In remote country places there 
is reason to believe that the reflection of distant sounds from the 
walls of lonely and uninhabited houses has sometimes led to the 
report that they were haunted.” 
Practical applications of the phenomena with which we have 
been dealing are found in the external ears or conchs of men 
and animals. These are constructed of cartilage covered intern- 
ally by smooth skin, with the curvatures arranged to reflect 
sound undulations into the auditory canal. The ear-trumpet 
also acts on the same principle, collecting a great extent of waves 
by the expanded lip of its mouth, and reflecting them down the 
tube to the narrow exit, which is applied to the auditory canal 
of the ear of the person using it. The flexible stethoscope acts 
in part in the same manner. 
The speaking-trumpet is another example, Peschel states, 
that the voice of a strong man sent through a trumpet eighteen 
to twenty-four feet in length, has been heard at a distance of 
three miles. 
385. Refraction of Sound.—The experimental illustration of 
refraction and of its laws is best attained in the case of light 
(492). Sound undulations follow the same laws of refraction as 
do those of light. This was demonstrated by Sondhauss, wdio 
took a large spherical, collodion balloon, and cutting segments 
a foot in diameter therefrom, fitted them to a circular ring. A 
double convex lens (528), a foot in diameter and four inches 
thick in the axis, was thus formed. On filling this wfith carbonic SONOROUS BODIES. 
335 
acid gas, and placing a watch at a distance of a couple of feet in 
the axial line, its ticking could be found in the same line on 
the opposite side of the lens, at a proper position. This could 
°nlj occur by a refraction of the sound in the same manner 
that light and heat are refracted. 
The India-rubber balloons used as children’s toys, if inflated 
with carbonic acid gas produce a similar result; if with hydrogen, 
they cause a dissipation of the sound, acting as a concave instead 
of a convex lens. 
385 A. Polarization of Sound.—ln the “Journal of the Franklin 
Institute,” for 1881, Professor S. W. Robinson describes a series 
°t experiments which tend to show that by means of suitable 
arrangements sound waves present phenomena of polarization 
resembling those offered by light. The apparatus employed con- 
sisted of polarizer and analyzer formed of tubes of a peculiar 
shape tilled with coal-gas. 
CHAPTER XIII. 
SONOROUS BODIES. 
Titrating strings—Laws of transverse vibrations—Nodes and loops—Vibrating 
rods—Vibrating plates and bells—Vibrating membranes—Vibrating columns 
of air—Reed instruments—Singing flames—Sympathetic vibrations—Sensi- 
tive flames—Production of abnormal sounds in the chest. 
386, Vibrating Strings.—The term is applied both to the tense 
catgut cords and the wires used in the construction of pianos 
and violins. Stretched cords or strings may show either trans- 
verse or longitudinal vibrations. In practice only the former 
are used. The string is sometimes thrown into motion by pluck- 
lng_, or pulling it to one side, and then letting it free suddenly, 
as. in the harp; again by a bow the threads of which are coated 
With resin, as in the case of the violin; or by a quick sharp blow, 
as in a piano. 
Transverse vibrations may be illustrated to advantage by 
stretching a white cord in front of a dead-black surface. If it 
18 long and heavy, the swaying motion of the cord when plucked 
can be followed by the eye, but as its length is diminished, or 
tension increased, the vibrations become so rapid that the eye can 336 
ACOUSTICS. 
no longer detect them. The cord then assumes the appearance 
of a fusiform figure in front of the black surface, and a musical 
note is produced. 
387. Laws of Transverse Vibrations may be studied by means 
of the monocord, or sonometer, Fig. 159. It consists of a rectan- 
gular wooden box, about live feet in length, and five inches 
Fig. 159. 
The sonometer. 
square on the euds. It must not have any bottom. The long 
sides ma}i be half, and the end pieces at least three-quarters of 
an inch thick, and made of hard wood. The top should be con- 
structed of soft pine as thin as possible, a mere veneer one- 
twelfth of an inch in thickness, in a continuous piece, with its 
grain true and running lengthways, is the best. A wire or 
string is attached to a peg at the end D, and passes immediately 
over a triangular-shaped piece of wood, B, called a bridge. At 
the other end of the box it passes over another bridge, A, thence 
over the pulley H, and terminates in a rod on which weights may 
be placed, M. 
In this apparatus we may, Ist,- vary the tension by changing 
the weight on the rod M; 2d, the thickness of the wire; 3d, the 
weight or density of the wire; 4th, its length, by means of the 
movable bridge C. The laws resulting from these experiments 
are as follows: 
Ist. Other things being equal, the number of vibrations per second 
is inversely as the lengths of the strings. 
2d. Other things being equal, the number of vibrations per second is 
inversely as the diameters of the strings. 
3d. Other things being equal, the number of vibrations per second is 
as the square roots of the tension weights. 
4th. Other things being equal, the number of vibrations per second 
is inversely as the square roots of the densities. 
These laws receive their practical applications in the construc- 
tion of all kinds of stringed instruments. SONOROUS BODIES. 
337 
388, Nodes and Loops.—Suppose the string on the monocord 
to be vibrating throughout its whole length,"and then suddenly 
caught on the movable bridge B at one-third the distance from 
Dto A. The section I) B vibrates about these two new fixed 
points. At the same time all parts of the string tend to move 
Fig. 160. 
Nodes and loops. 
111 unison with the section D B, consequently the section B A 
does not vibrate as a whole, but it subdivides at C, giving two 
sections, B C and C A, each equal in length to D B. 
Suppose the movable bridge be made to touch the cord at 
°oe-quarter its length. The results are then shown in the 
lower diagram, in which the remaining portion of the string 
from B to A vibrates in three sections, as indicated by the con- 
tinuous and dotted lines. The points BGC' A in the strings 
arc called nodes. The central part of the fusiform portion of the 
string between these points is called a loop, or ventral segment. 
The position of the nodes and loops in a vibrating cord may 
be made more evident by placing paper riders upon the string. 
Those at the nodes are quiet, while those on the loops are so 
violently agitated that they are thrown off. 
The bridge must be made to arrest the cord at some aliquot 
part of its length, to form sections which bear the relation of 
whole numbers to each other, otherwise the nodes will not be 
Properly formed, and the vibrations will quickly destroy each 
other. 
389. Vibrating Rods.— All elastic rods, especially those made 
°f steel, can be made to vibrate both transversely and longitudi- 
nally. They are excited by fixing the rod firmly at one end, and 
noting upon the free portion with a violin bow. To produce 
longitudinal vibrations, the rod is held in a narrow-jawed vice, 
nnd then rubbed in the direction of its length with a piece of 
oloth coated with resin. 
. The laws of longitudinal are similar to those of transverse 
vibrations. The longitudinal note given by a wire or rod is, 338 
ACOUSTICS. 
however, of much higher pitch than the transverse note of the 
same length of wire. This results from the fact that the elastic 
force longitudinally is greater than that in the transverse direc- 
tion, consequently the number of vibrations is greater. A short 
piece of wire smartly rubbed will give a note so shrill that it is 
positively painful. 
To demonstrate the complicated character of the motions of a 
vibrating rod, a glass bead silvered on the inside should be at- 
tached by a piece of wax to the end of the rod. This, by 
reflecting the rays from a candle flame will produce curves of 
great beauty. 
The deepest note of a bar of steel, or rod of glass, is sounded 
by holding it about one-fourth or one-fifth of its length from one 
end, and then striking it upon the middle or end. It then 
vibrates in three segments. 
Among musical instruments which depend upon the trans- 
verse vibration of rods for their action, we may mention the 
Fig. 161. 
musical snuff box and tuning-fork. In the latter a 
rod is bent with the two nodes very near to- 
gether. It vibrates as illustrated by the dotted 
lines, Fig. 161. The handle of the fork is not 
coincident with either of the nodes, but between 
them, so when the prongs vibrate the handle 
is thrown into a vigorous up and down motion, 
and powerful vibration may thus be imparted 
to any resonant surface upon which it is placed. 
The vibrations of the prongs may be shown by 
bringing one of them in the vicinity of a sus- 
pended ball of cork or pith. 
Longitudinal vibrations are employed in Mar- 
loyl’s harp, which consists of a solid block of wood, 
into which some twenty thin wooden rods of differ- 
ent lengths are fixed. The vibrations are pro- 
duced by rubbing them lengthwise by the thumb 
Tuning-fork. 
and index finger which have been dipped in resin powder; their 
notes resemble those of Paris pipes. 
In the triangle while vibrations are transverse on the hori- 
zontal part, they are nearly longitudinal on the attached por- 
tions. 
390. Vibrating Plates and Bells.—A vibrating plate may be 
either square or circular. It can be fixed either by its centre, 
or edge; in the first case it is thrown into vibration by drawing 
a bow across the edge, in the second by drawing a string covered 
with resin through an opening in the centre. 
If a plate is fastened in the horizontal position, and fine sand 
dusted on its surface, on throwing it into vibration the sand SONOROUS BODIES. 
339 
enters into rapid movement, and finally accumulates in sym- 
metrical lines on the surface. These are called nodal "lines or 
Ohladni’s figures, Fig. 162. Their position may be determined 
by touching the plate at the desired point. The nodal lines 
separate portions of the plate in which the vibration is in oppo- 
site directions. As they are determined by the parts which are 
touched, or fixed, they represent portions of the plate at rest. 
Fig. 162. 
Chladni’s figures. 
If lycopodium powder be mixed with the sand, the lycopodium 
does not move to the nodal lines, but gathers in little masses on 
the vibrating parts, keeping up a violent movement. After 
Puzzling physicists for a long time, Faraday at last proved that 
this result was owing to inward and ascending currents of air 
could act upon the light powder in the manner described, 
and cymbals are examples of vibrating plates, and show 
uodal lines. 
A vibration rod when bent becomes a tuning-fork, so a bent 
plate forms a bell, goblet, or bowl, and is subject to the same 
jaws of vibration as a plate. Of this we may satisfy ourselves 
by turning a flat bell, like those used in a clock, mouth upwards, 
and sprinkling sand in the interior. On sounding the bell with 
a violin bow, the sand shows at once the presence of nodal lines. 
A finger glass or tumbler in which some water has been poured, 
ay be caused to sound by passing a wet finger along its edge. 
strong are the vibrations that the water is thrown into rip- 
ples. The deepest notes are produced when the surface is 
divided into sections. 
Vibrating Membranes,—Membranes can only produce 
sounds when stretched on a rigid framework. The smaller and 
me more tightly stretched, the higher the note emitted. 
Membranes are also thrown into vibrations by sounds pro- 
duced in their vicinity, when these are in unison with their 
ftotes. When thus vibrating, if tine sand is dusted on their 
surfaces, nodal lines are formed. The figures produced are not 
as fixed and invariable as in vibrating plates. 
The sound emitted by a membrane is rather a noise than a 
true musical note. Their use in music is chiefly to mark the ACOUSTICS. 
rhythm. The sound being compound, they are, therefore, sus- 
ceptible of vibration under a considerable range or variety of 
notes, a property of special interest in connection with the 
organ of hearing. 
392. Vibrating Columns of Air.—Air enclosed in tubes may be 
thrown into vibration and originate sounds. The note depends 
on the length of the column of air, or of the tube. The oscilla- 
tions of the air particles are similar in character to those by 
which sound is propagated in air. The movement is longitu- 
dinal, but the wave is not progressive, it is stationary. In a pro- 
gressive wave the particles take up the movement one a little 
after the other; in a stationary wave, on the contrary, they take 
it up at the same moment, though the distances through which 
they move are different. 
When a tube speaks, or emits sound, the particle at the centre 
does not oscillate; the rest do to a greater or less extent, 
those at the ends the most, and less and less towards the centre. 
The centre represents a node, while the end of the tube is the 
middle of a ventral segment. When the particles are most dis- 
tant from the position of rest, the return movement begins; they 
overpass the position of rest, and thus a swaying motion is 
established. 
A tube closed at one end acts like half of a tube open at both 
ends, the node being at the bottom, and the middle of a ventral 
segment at its mouth. It, therefore, gives out the same note 
as one of twice its length open at both ends. 
Air columns may be made to vibrate in various ways. Ist. 
By blowing air across the mouth of the tube. In Fig. 163 the 
vertical cylinder represents the mouth of a tube or bottle. By 
means of an India-rubber tube, pinched between the fingers to 
form a slit, a blast of air is directed across the mouth of the 
cylinder, when its proper note is sounded. The flute, whistle, 
and certain organ pipes are examples of this method of pro- 
ducing vibrating columns of air. 
Another method is represented in Pig. 164. In this a tuning- 
fork is made to vibrate over the mouth of a tall narrow jar. 
Water is then poured into the jar until the column of included 
air is of the proper length to vibrate in unison with the fork. 
A third method is thus described by Weinhold: “If a current 
of air is blown between two flexible bodies which are in mode- 
rately firm contact with one another; as, for instance, between 
the closed lips, or between the fingers of the hand placed flat 
upon the mouth, or between the lips and a leaf held close before 
them, a sound may be produced which is caused in a similar 
manner to that of the siren (407). The compressed air forces 
its way out by slightly pushing aside the two bodies; which, in SONOROUS BODIES. 
consequence of their elasticity, instantly return to their original 
position, and are immediately afterwards again pushed back by 
the current of air; the same movement is repeated many times 
m rapid succession; a series of impulses is thus given to the 
air, and a note is produced. The pitch of this tone naturally 
depends, as in other tubes, upon the length of the vibrating 
column of air.” 
Fig. 163. 
Fig. 163. 
Fig. 164. 
Sounding tube. 
Vibrating column of air. 
“It is thus that notes are produced in all wind instruments, 
except the flute. In brass instruments the lips form the soft 
vibrating parts; in wood instruments, for example in the cla- 
rionet, the air is forced through 4 reeds,’ formed of two thin 
elastic plates of wood or cane.” 
393. Reed Instruments.—The soft elastic plates of wood, cane, 
°r reed, used in the clarionet and similar instruments, differ 
essentially in action from the strong springy tongues in the con- 
certina, accordeon, harmonium, and reed pipes of the organ. 
In the former, the length of the column of air controls the rate 
°f vibration of the reed; they are called mouth instruments. In 
the latter, the rate of vibration is independent of the column of 
air> it is governed, as in the tuning-fork, by the length, thick- 
ness, and shape of the tongue or reed. Therefore, they are 
called reed instruments. 
“In reed instruments the metal tongues are thin, long, nar- 
row rectangular plates of hardened brass or German silver, fixed 
by their thicker ends upon a plate of metal, usually of zinc, 
nearly closing a rectangular slit in the plate. In Fig. 165, 
A represents the exterior, B a section of such a tongue. The 342 
ACOUSTICS. 
plate with the tongue fixed upon it is called a ‘ reed; ’ it is fas- 
tened forming one side of a small box into which air can 
be forced through an opening. That side of the plate upon 
which the tongue is fixed is turned towards the inside of the 
box; as the current of air escapes from'it, it presses the tongue 
in the direction of the small arrow into the slit of the plate, 
as indicated by the dotted line; the slit is for an instant 
more completely closed than before, and the current of air 
Fig. 165. 
Vibrating reed. 
almost entirely interrupted. The elasticity of the tongue im- 
mediately causes it to return to its first position; a passage is 
thus reopened for the air; the current is reestablished and 
carries the tongue with it, as before, so as again to obstruct 
its own path; the tongue then springs back, and the action 
Fig. 166. 
is repeated so long as air is forced into the box. If 
the tongue is simply bent down with the finger 
and released, it will vibrate to and fro, but no 
sound, or only a faint trace will be heard; hence, 
the sound is solely due to regular periodic inter- 
ruption of the current of air, as in the siren.” 
394, Singing Flames.—Musical sounds may also 
be produced by causing a gas flame to burn in the 
interior of a tube. An apparatus of this descrip- 
tion has long been known as the chemical harmonicon. 
It consists of an arrangement for the generation of 
hydrogen (164), in which the escape tube B passes 
directly upwards from the decomposition bottle, 
and is drawn to a fine jet, Fig. 166. After a suffi- 
cient amount of gas has been allowed to escape, 
and there is no longer any danger of an explosion, 
Singing flame. 
the gas is lighted. Glass tubes of different length and diameters, 
and open at both ends, are then lowered over the flame, as at A. 
At certain positions in some of these tubes the flame vibrates 
and sounds or musical notes are emitted. 
The cause of vibration under these circumstances is an irreg- 
ular union of the gas with the oxygen of air. By some it is 343 
SONOROUS BODIES. 
called explosive. The manner of union of the two gases, and 
the rate of production of “ explosions” are determined by the 
relations of the size of the flame to the diameter and length of 
the tube. Sometimes the sound is a rattling noise, at others a 
low, and then a high musical note. 
If, while the Tame is singing, we observe its reflection in a 
piirror rotating on a vertical axis, it is seen to be alternately 
increasing and diminishing. A series of images of the flame, 
consisting of elongated equidistant tongues with depressions 
between them, is thus produced, and the cause of the pulsations 
exposed. A coal-gas flame escaping from a circular jet, like 
that at B, may be used instead of the hydrogen flame. 
395. Sympathetic Vibration is also called vibration by influence. 
It may arise in two w7ays ; Ist. By direct contact with the vibrat- 
ing object, and transmission of the sonorous undulations there- 
from. 2d. By transmission of the waves through air without 
nny direct contact of the two sounding bodies, and when they 
are at a distance. 
Of the first form we have an example when the end of the 
handle of a vibrating tuning-fork is placed on a table or other 
resonant surface. The vibration is then communicated to an 
extended area, and the sound greatly increased, though it does 
not endure so long a time. Examples of the application of this 
principle are found in the sounding boards of pianos, violins, and 
many other musical instruments. 
Instances of the second form of sympathetic vibration are 
offered whenever the right note is sounded in the vicinity of a 
sonorous body capable of emitting that note. If, for example, 
a given note is struck on some instrument in the proximity of a 
piano, tuned in harmony therewith and with the dampers raised, 
the proper string on the piano is instantly thrown into vibration, 
and it answers back the note received. If two glass cylinders 
°f similar dimensions are adjusted by pouring water into them 
until they give forth the same note, and one is sounded, the 
other at once takes up the note, and continues to give it forth 
long after the first has become silent. A harp, or guitar, may 
often be heard taking part in the conversation in its neighbor- 
flood. The jingling sounds given forth by wine and other glasses 
when a piano is in action, arise in the same way. The violence 
of the tremor produced is frequently so great that a goblet may, 
oy sounding a note on a violin near by, be made to fall on the 
floor if the table be slightly inclined and bare of covering. 
396. Sensitive Flames.—Gas flames may in like manner be 
mfjusted to be affected by certain tones, and respond to them 
whenever produced in their vicinity. The best way of form- 344 
ACOUSTICS. 
ing such a sensitive flame is to burn coal-gas under sufficient 
pressure from a conical orifice to make a tapering flame about 
fifteen inches in length. If the hands be clapped in the vicinity 
of such a flame, after it has been properly adjusted, its tall quiver- 
ing form instantly drops to half its height. It may spread out 
laterally and'assume the fish-tail shape. The moment the sound 
ceases it instantly reassumes its proper form. 
Sensitive flames take cognizance of a great variety of sounds; 
a tap on a table, clinking of money, creaking of shoes, crump- 
ling of paper, shaking a bunch of keys, all throw it into a state 
of excitement. 
If a person whistle in the presence of a sensitive flame, when 
the proper note is produced it instantly shrinks and echoes 
back the same note. To a hiss such flames are especially re- 
sponsive, they will quiver every time a word containing the letter 
s is pronounced in their vicinity, though the person speaking 
passes away to a considerable distance. 
While affected by a great number and variety of sounds, 
sensitive flames do not respond to the bass notes of a piano. 
High notes on a violin affect them, and they will dance in 
perfect time to a tune played on most musical instruments. 
397. Production of Abnormal Sounds in the Chest.—According 
as the lungs, heart, and arteries of the chest are affected by dis- 
ease, certain abnormal sounds appear which are indicative of 
changes which have taken place therein (379). 
In diseased conditions of the lungs the normal respiratory 
murmur produced by the transit of air along the passages be- 
comes greatly altered. These changes are effected in various 
ways: Ist. The secretion of the mucous membrane may be 
deficient in quantity, thus a dryness is created by which the 
ordinary respiratory murmur becomes exaggerated by friction 
arising simply from the passage of air over a dry instead of 
a properly lubricated surface. 2d. There may be accumulation 
of fluid in the air cells and minute or capillary bronchi commu- 
nicating therewith. The bubbling of air through this gives 
rise to a fine crackling or crepitant sound. 3d. Plugs of tough 
mucus accumulating in the medium sized and large bronchi are 
thrown into vibration by the passage of air. The gaseous 
contents of the tubes are thus caused to oscillate, and hissing, 
squeaking, crowing, whistling sounds arise, these are the rales 
and rhonchi of which physicians speak, and which may often 
be heard at a distance of some feet from a person suffering with 
bronchitis. Finally the lung structure may become consolidated 
and the admission of air prevented; this, of course, is attended 
by complete suppression in the affected part of all natural 
sounds produced during healthy respiration. SONOROUS BODIES. 
345 
Passing from consideration of changes in the interior of 
the lung to those which take place in its covering membrane, 
°i’ pleura, and the cavity in which the lung is suspended, we 
find : That when fibrinous matter appears on the surface of the 
lung, or on the inner wall of the chest, the membrane or pleura 
losing its smoothness becomes roughened; the two surfaces no 
longer glide over in a noiseless manner, but various rubbing, 
and other harsh sounds arise which indicate the change that 
has occurred. 
In health the sounds of the heart are expressed by the syllables 
lubb-dup. Of these the second is simple, it is evidently caused 
hy closure of the semilunar valves. The first is compound, 
being possibly partly muscular, but chiefly valvular, and corre- 
sponding to closure of the auriculo-ventricular openings. With 
diseased conditions of the valves great changes in the heart 
sounds are produced. If, for example, their lips are roughened 
by fibrinous or osseous deposits, vibrations are created which 
originate new or abnormal sounds that attend the sound or 
passage of blood through them. If they fail to close the open- 
ings properly, the blood passing backwards after imperfect 
closure originates new regurgitant murmurs, or other noises, 
whicli attend proper heart sounds. 
In its passage along the great arteries of the chest, no sounds 
other than those of the heart are heard, but with changed con- 
ditions of the arteries, as in atheromatous or osseous deposits 
on their inner coat, or the formation of aneurismal sacs, noises 
produced by passage of the blood over rough surfaces or its 
entrance into the aneurismal cavity arise; these are known as 
aneurismal murmurs. 346 
ACOUSTICS. 
CHAPTER XIY. 
SPECIAL PKOPERTIES OF SOUND. 
Special properties of sounds—lntensity of sounds—Diminution in intensity of 
sounds—lncrease in intensity of sounds—Eeinforceinent of sounds—Kesonance 
and percussion—lnterference of sound undulations—Pitch or tone—Savart’s 
wheel—The siren—The graphic method—Limits of perception of vibrations 
—The octave—The gamut and chromatic scale—Musical notation—Number 
of vibrations to each tone—Harmonics, overtones—Quality or timbre—Wave- 
lengths of sounds in air. 
398. Sounds do not act alike upon our sense of hearing. The 
differences presented may be grouped under three divisions, 
viz.: Ist. Intensity or loudness. 2d. Pitch or height, by this 
we mean that it is high or low, acute or grave, in the musical 
scale. 3d. Quality, timbre, stamp, or color, by which terms we 
indicate that the same note varies when produced on different 
instruments; on the cornet and piano, for example. 
399. Intensity of Sounds.—Regarding the cause of the loudness 
of sounds, a very simple experiment will satisfy us. Let a given 
low or bass string on the piano be struck softly, the string in 
emitting the note will be seen to vibrate with a small amount of 
amplitude. Then’let the same note be struck with vigor, a 
much louder sound is produced, and the string is seen to have a 
far greater extent of vibration. As the note gradually dies 
away the amplitude of vibration becomes less and less until it 
is lost. 
The intrinsic or original intensity of any sound, therefore, 
depends upon the amplitude of vibrations in the sonorous body, 
or the force with which they are executed. In comparison with 
waves on water it would be represented by the height of the 
wave (131). Doubling or tripling the extent of vibration, in- 
creases intensity four and nine times. 
Lord Rayleigh determined the amplitude of oscillation in the 
case of waves produced by a pipe which sounded the note/iv, 
that could be heard at a distance of 820 metres, and found 
it was less than one ten-millionth of a millimetre. 
400. Diminution in Intensity of Sounds.—ln this, as in the dis- 
cussion of many other matters in connection with sound, the 
subject may be viewed in two ways : Ist, as regards vibrations SPECIAL PROPERTIES OF SOUND. 
347 
in the body wherein it originates; and, 2d, the waves by which 
it reaches the ear through the air or other conducting elastic 
medium. 
In the present case, diminution in intensity may arise from the 
fact that the original vibrations in the sonorous body are small 
in their amplitude. Setting this cause aside, and dealing with 
that of the propagation through the air or other medium to the 
ear, we have the following causes of diminution in intensity : 
Ist. The effect of distance in the open air; with this all are 
familiar. The law under which diminution takes place is that, 
the intensity of the sound is inversely as the square of the distance of the 
sonorous body from the ear. 
2d. Another cause is the diminution in density, or elasticity, 
of the air or other medium by which sound is transmitted. Of 
this we have an illustration in the experiment of the bell in 
vacuo; as the air is exhausted loudness of the sound diminishes. 
In rarefied air on a mountain-top a pistol report is insignifi- 
cant, and the voice becomes remarkably thin and weak. In 
like manner, if a bell be rung in an atmosphere of hydrogen, 
the intensity is less than in air. 
3d. Variation in the intensity of a sound at a distance is also 
produced by the action of winds. During a calm, sound is pro- 
pagated with great facility. While a wind is prevailing, sound 
is better heard at the same distance in the direction of the 
moving air than against it. 
4th. Stratification of the air exerts a singular effect in lessen- 
ing the intensity of a sound. Of this, Ganot says : “ Different 
parts of the earth’s surface are unequally heated by the sun, 
owing to the shadows of trees, evaporation of water, and other 
causes, so that in the atmosphere there are numerous ascending 
and descending currents of air of different density. Whenever 
a sonorous wave passes from a medium of one density into 
another it undergoes partial reflection, which, though not strong 
enough to form an echo, distinctly weakens the direct sound. 
This is doubtless the reason, as Humboldt remarks, why sound 
travels further at night than at daytime.” 
“It has generally been considered that fog in the atmosphere 
is a great deadener of sound; it being a mixture of air and glo- 
bules of water, at each of the innumerable surfaces of contact a 
portion of the vibration is lost. The evidence as to the influence 
of this property is conflicting; recent researches of Tyndall show 
that a white fog, or snow, or hail, are not important obstacles to 
the transmission of sound, but that aqueous vapor is. Experi- 
ments made on a large scale, in order to ascertain the best form 
of fog signals, give some remarkable results. 
“ On some days which optically were quite clear, certain sounds 
could not be heard at a distance far inferior to (even less than 348 
ACOUSTICS. 
one-third) that at which they could be heard during a thick haze. 
Tyndall ascribes this result to the presence in the atmosphere 
of aqueous vapor, which forms innumerable striae that do not 
interfere with its optical clearness, but render it acoustically 
turbid, the sound being reflected by this invisible vapor just as 
light is by a visible cloud. 
“In 1822 experiments were made on sound by a commission 
near Paris. In these cannon were fired at two stations twelve 
miles apart. On one occasion, while all the shots fired at the 
first station were heard at the second, only one out of the twelve 
fired at the second were heard at the first. As there was no 
wind at the time to account for this difference, Professors Stokes 
and Reynolds explained it upon the theory of refraction (385). 
The rays of sound, they said, like those of light and heat, are sub- 
ject to refraction when they pass from one medium into another 
of a different density. The sound under these circumstances is 
lifted from the ground, and may be heard at a high but not at a 
low level. 
“ These conclusions, first drawn from observations, have been 
verified by laboratory experiments. Tyndall has shown that a 
medium consisting of alternate layers of light and heavy gas 
deadens sound, and also that a medium consisting of alternate 
strata of heated and ordinary air exerts a similar influence. 
The same is the case with an atmosphere containing the vapors 
of volatile liquids. So long as the continuity of air is pre- 
served, sound has great power of passing through the inter- 
stices of solids; thus it will pass through twelve folds of a dry 
silk handkerchief, but is stopped by a single layer if it is 
wetted.” 
401. Increase in Intensity of Sounds may be produced : Ist. By 
increase in amplitude of the vibration in the sonorous body. 
This we need not discuss. 
2d. By increase in the density and conducting power of the 
medium through which the sound is passing. In operations in 
caissons, for example, when the foundations of the piers of 
bridges are to be laid in deep water, the compression of air 
may be carried to a number of atmospheres. Under these cir- 
cumstances its conducting power is greatly increased and sounds 
become intolerably intense. The substitution of a medium of 
higher density and conducting power, as of carbonic acid gas 
for ordinary air, also increases the intensity of transmitted sound. 
3d. By reinforcement. 
402. Reinforcement of Sounds may be accomplished in three 
ways: Ist. By resonance or synchronous vibrations in other 
bodies; 2d. By reflection; 3d. By refraction. SPECIAL PROPERTIES OF SOUND. 
Resonance may be defined as a sympathetic vibration (895), 
resulting from the accumulation of small periodic impulses im- 
parted by one sonorous body to another whose period or time 
of vibration is synchronous with it. Thus increased amplitude 
of movement is produced, just as when one person in swinging 
another gives a great extent of oscillation by repeated pushes 
°1 moderate force. 
The apparatus represented, Fig. 167, was contrived by Savart 
to illustrate this method. It consists of a brass bowl A, which 
Fig. 167. 
Reinforcement of son ml. 
|s made to vibrate by means of a violin bow. On bringing 
111 to its vicinity a hollow cylinder of card-board B, closed below 
apd open above, the intensity of sound is greatly increased, the 
air in the card-board box being thrown into vibrations which 
are synchronous with those of the brass vessel. By moving the 
bottom of the card-board cylinder higher up or lower down, 
and varying its capacity, its point of maximum action is easily 
found. 
The sounding-boards or boxes of stringed instruments act in 
a. similar manner, their vibrations and that of the included 
air resulting partly by transmission through the bridge, and 
partly by sympathetic vibration through the air. The smooth 
curved spiral surfaces of the interior of many shells enable them 
1° collect and reproduce sounds which reach them. Thus 
arises the “ curious murmuring resonance” that is heard when 
they are held to the ear, and which in the fancy of our fore- 
lathers was ascribed to some occult influence of their ocean 
home. 
According to some, the sound heard in a shell is the result of 
the contact of its mouth with the warm skin of the face, which 
establishes currents of air that are reverberated in its spiral 
depths. 
. The cause of reinforcement by reflection (384) arises in the 
*act, that a great extent of sound undulations is brought down 
1? the same focus. It is the reverse of what happens in the dis- 
sipation of sound (377). If under these conditions of reflection, 350 
ACOUSTICS. 
the undulations are of considerable wave-length, they will agree 
so nearly in phase that there will be but little interference, and 
the increase in intensity will follow very closely upon increase 
in the condensing surface, 
Reinforcement by refraction (385) is somewhat more complex 
in character than reinforcement by reflection. It requires the 
use in the convex membranous chamber of a gas denser than 
air, carbon dioxide, for example. The general principles are 
the same as for light (490). 
403. Resonance and Percussion.—As we have stated in the pre- 
ceding article, the accumulation of sonorous impulses by an 
•enclosed mass of air produces resonance, or an increase in the 
intensity of a sound. This property of resonance has valuable 
applications in the art of diagnosis, as it enables physicians to 
determine whether a given space or cavity contains air, or not. 
The simplest illustration of the resonant property of enclosed 
air may be obtained by tapping on the outside of a closed keg 
partly tilled with water. While the blows are delivered on the 
portion occupied by water, only a dull or flat sound can be 
elicited; but the moment they are transferred to the portion 
occupied by air, a loud resonant note is produced. 
In like manner, if we place the index finger of the left hand 
on the chest wall, and with the index and middle finger of the 
right hand strike quick sharp blows upon the index of the 
left, the chest emits a resonant sound as it is filled with air 
contained in the expanded lung. To this manipulation the 
name of 'percussion is given. 
If percussion is applied in the same way to the chest of a person 
in whom the lung is consolidated by pneumonic or tuberculous 
deposits, or whose pleural cavity is filled with fluid or other 
exudation, only a dull flat sound can be evoked; the resonance 
previously obtained is entirely lost, and the result may be com- 
pared to that produced by applying percussion to the muscles of 
the thigh. 
Any cause which increases the amount of air in the lung will 
add to its resonant property. Therefore, in emphysema or 
enlargement of the air-cells; in the formation of cavities which 
follows tubercle and gangrene; in perforation of the lung and 
escape of air into the pleural cavity, a notable increase in this 
respect is found on examination by percussion. 
Any change in the normal area occupied by the heart is also 
at once detected by an increase of the area of dulness it affords 
on application of percussion to the chest. Tumors of all kinds, 
especially those which are aneurismal, indicate their presence in 
the chest by creating abnormal regions of dulness. 
Percussion is also, at times, a valuable aid in determining the SPECIAL PROPERTIES OF SOUND. 
351 
condition of the abclominal viscera. Tympanites or increase ot 
air in the intestines, or its appearance in the abdominal cavity, 
18 at once detected by increased resonance. Enlargement of 
organs, as the uterus in pregnancy, the ovaries in the growths 
which affect them, and the liver in certain diseases, is at once 
demonstrated by increase or change in the areas of dulness 
which they give in the normal state. 
404. Interference of Sound Undulations.—ln (371) it was stated 
that two systems of waves on water may interfere in such a 
manner as either to reinforce, or neutralize one another. The 
same phenomena arise in the case of sonorous waves. 
If two systems of sound undulations pass along the same 
Wedium, the motion of any particle of the medium is determined 
by the motions of the two systems. If both the systems are in 
the same phase, the resultant is their sum. If in opposite phases 
}t is their difference, since they partially neutralize each other; 
jf the waves are equal as well as opposite, it is zero, and silence 
18 produced. 
For the complete extinction of two sets of soundwaves the 
rarefied parts of one system must be the exact equivalent of the 
condensed portions of the other. This is 
n°t easy of attainment in actual practice. 
n approximate, may, however, be reached 
h}7 the experiment illustrated in Fig. 168. 
I*l this A and B represent two tuning-forks 
°f the same note, and C a glass jar into 
which water has been poured to bring it in 
resonant relation with the forks. The fork 
F is then armed on one of its prongs with 
a small pellet of wax. If either of the 
lorks is,sounded over the jar, it gives forth 
a clear continuous sound. But, if both 
a sounded at the same time, the slight 
difference in the rate of vibration of B pro- 
duced by the pellet of wax causes the two 
Fig. 168. 
Interference of sound waves. 
systems of modulations to interfere, and the sound varies from 
Wonient to moment, being louder than either fork can produce 
a|one at one moment, and fading away to silence in the next. 
I bus a series of beats or pulsations is produced, the sound being 
{ouder when the undulations agree in phase, and silence result- 
lng when they are in opposite phases. 
&o long as the two notes are nearly alike, the beats are few, 
Bay from four to six in a second. When they are very dif- 
ferent the beats become partly fused on account of their greater 
frequency and a harsh grating sound is produced; with a still 
greater difference a cutting character is assumed. This is called 352 
ACOUSTICS. 
dissonance, and Helmholtz states that when Vhe beats reach 33 
per second the dissonance is intolerable; beyond this the rough- 
ness lessens and when the beats reach 132 per second it disap- 
pears. 
In the “ Am. Journal of Sciences and Arts,” vol. xii. page 329, 
Professor A. M. Mayer gives a very interesting account of the 
physiological effects of the interference of different sounds. The 
paper deals with the following subjects. Ist. The obliteration 
of the sensation of one sound by the simultaneous action on the 
ear of another more intense and lower sound. 2d. A sound 
even when intense cannot obliterate the sensation of another 
sound lower in pitch. 3d. Proposed change in management of 
orchestras in connection with these facts. 
405. Pitch or Tone.—The position of a tone in the musical 
scale, or its pitch, is determined by the number of vibrations in 
a second. If in this time 500 oscillations are made, then 500 is 
called the number of vibrations, and of a second the 
time of vibration or period. The greater the number of pulsa- 
tions the higher the pitch. This may be roughly shown by 
drawing the finger-nail across the teeth of a comb. If the 
movement is slow, and the number of strokes small, the sound 
is low or grave; if quick, and the number of strokes great, it 
is high or acute. 
Various methods have been devised for the determination of 
the number of vibrations required to produce a given tone. The}5, 
are Savart’s wheel, the siren, and DuhameTs graphic method. 
406. Savart’s Wheel consists of a wheel, B, its circumference 
armed with projections or teeth like those on a cog-wheel. Its 
Pig. 169. 
Savart’s wheel. 
axis carries a small pulley around which a band or cord, H, 
passes, which receives motion from a large wheel A, driven 
by the winch-handle M. At E a piece of card-board is brought SPECIAL PROPERTIES OF SOUND. 
353 
in contact with the teeth of B while in rapid revolution. The 
striking of the teeth on the card as they pass by its edge throws 
it into vigorous oscillation. According as the movement is in- 
creased in rate the vibration of the card is intensified, and a 
higher or more acute sound is produced. 
Counting the number of teeth in the wheel B, and the number 
of revolutions produced by each turn of the winch M, and 
multiplying them together, we have the total vibrations pro- 
duced in the card E for each turn of the winch-handle. It 
only remains to determine the rate of revolution of the winch- 
handle to find the number of vibrations of the card per second 
that yields any given tone. 
407. The Siren was so called by its inventor because it will 
give forth sound under water. In it, various tones are emitted, 
not by setting a solid body to vibrate, but by producing a series 
of puffs of air in rapid regular succession. It consists essentially 
of a circular series of holes in a disk of cardboard or metal, A, 
mounted on an axis of revolution. A tube, B, delivers a stream 
Fig. 170. 
of air against one side of the disk. When the opening of the 
air tube is opposite one of the holes a puff of air passes through, 
when opposite an interval the passage of air is obstructed. By 
means of suitable machinery rapid revolution is given to the 
disk, the number of puffs of air in a given time is thus increased 
?! the will of the operator, and any desired tone produced. 
The number of puffs passing through the disk is registered by 
The siren. 354 
ACOUSTICS. 
the instrument itself C, and the number of vibrations required 
for the sounding of any tone, is determined by merely reading 
the indications of the index. 
Comparing the tone obtained by a given number of vibrations 
as recorded by the siren, with that produced by the same num- 
ber by Savart’s wheel, we find that their pitch is the same. In 
music such tones are, therefore, said to be “in unison,” re- 
gardless of the instruments by which they may be formed. 
In the perfect kinds of siren the rate of revolution of the disk 
or lid is determined by the pressure of the air employed in work- 
ing the apparatus. The wind or air enters by the pipe B, from 
a bellows or other source, into the close box, in the lid of which 
is a series of holes corresponding with those in the rotating disk. 
The holes are not bored directly through, but obliquely, slanting 
in one direction through the lid of the box, and in the opposite 
direction through the disk A. 
The disk is impelled round its axis by the wind as it issues 
through the lower set of holes into the upper. To apply it to 
the determination of the number of vibrations producing any 
given tone, the pressure in the siren is increased until it gives a 
tone in unison with that to be measured. The siren is then 
sounded for a given number of seconds, the number of puffs or 
pulsations for that time determined, and from this the number 
ot vibrations per second obtained, by dividing it by the number 
of seconds during which the observation lasted. The siren thus 
demonstrates the cause of, and defines the exact relation between, 
those differences of pitch which are the basis of the musical 
sense, and discernible, with more or less 
nicety, by most individuals. 
Fig. 171. 
408. The Graphic Method.—ln both the 
preceding methods for the determination 
of the number of vibrations required to 
produce any given tone, a practised ear 
is required, and even then there is a 
certain amount of difference in the 
results obtained. In the graphic method 
of Buhamel this error is avoided. 
The arrangement is represented in 
Fig. 171. Ais a cylinder rotating about 
a vertical axis B. This is covered with 
a sheet of paper, on which a film of 
lampblack has been deposited, by holding 
raphic method. 
it in the smoke from burning camphor. This serves as the means of 
registration, as follows: 
Suppose the vibrations to be examined are produced b}T a steel 
rod. The rod is fixed in a vice C; to its extremity a fine wire SPECIAL PROPERTIES OF SOUND. 
355 
is attached which may he made to touch the surface of the 
cylinder. This being caused to rotate, and the point attached to 
the steel rod made to touch it, a straight line is formed by the 
removal of the lampblack. The rod is then struck, when at 
once the line produced is wave-like in character, corresponding 
to the oscillations of the rod. 
For the determination of the number of vibrations, a tuning- 
fork, which emits a tone of about the same pitch as the sounding 
rod, and the rate of vibration of which is known, is mounted in 
a block D. One arm of this also bears a pointer which may be 
made to touch the blackened paper. The fork and the rod are 
sounded at the same time, and their pointers brought in contact 
with the revolving paper. Two systems of wave-like registra- 
tions are thus produced one above the other. The number of 
waves in a given extent of each system is counted, when a 
simple calculation gives the rate of vibration of the rod. 
Suppose, for example, the rate for the fork is 500 per second, 
and that while the tuning-fork made 150 the rod made 165. 
Then, as the vibrations of the fork are to those of the rod, so 
18 the number per second of the fork to x, the number per 
second of the rod; or as 150 : 165 : : 500 : x = 550, the number 
°f oscillations per second of the rod. 
If the lower part of the axis of the revolving cylinder is a 
screw traversing in a nut, as the cylinder turns it will be either 
lowered or raised, according to the direction in which it rotates. 
Fy this device the pointers make a spiral, instead of a horizontal 
tracing, and records covering a number of revolutions may be 
obtained. 
409. Limits of Perception of Vibrations.—This varies with the 
auditory peculiarities of the observer, and to a certain extent 
with the method of experimentation. The different estimates 
are as follows: 
Before Savart’s time 
16 
9,000 
Savart’s experiments 
. 7 to 8 
24,000 
Hespretz .... 
16 
24,000 
Helmholtz .... 
. 30 to 40 
38,000 
Preyer 
. 16 to 24 
41,000 
Number of vibrations per second. . 
Lowest or grave tone. Highest or acute tone. 
Many persons were, however, found who could not appreciate 
Botes of 16,000 and even less than 12,000 vibrations per second. 
Great variations in the pitch of notes have arisen in the prog- 
i*ess of time. In an article by Mr. Ellis, in “ Nature,” vol. xxi. 
Page 550, it is shown that for A the variations have extended 
irom 370 to 567 vibrations per second, the present standard 
being 435.4, that of the “Diapason NTormal,” at the Conserva- 
toire at Paris. 356 
ACOUSTICS. 
410. The Octave. Two tones sounded separately may be 
musical, but it by no means follows that when they are sounded 
together they will produce a pleasing effect upon the ear. If 
they are not concordant the effect is harsh and grating. Inquir- 
ing into the numerical relation which two tones must possess to 
approach the nearest in their characters, we find that this is 
attained with the proportion of vibrations represented by 2=l, 
4 = 1, etc. 
So closely do two tones having the ratio of 2 to 1 in their 
number of oscillations approach each other, that in music they 
receive the same name. If, for example, the first receives the 
designation C, the other is called c, and the interval between 
them is termed an octave. 
Hot only does the octave, or eighth note to the first, present 
this peculiarity, but as we pass to the octave of this second note, 
and then to the octave of this, the whole series of octaves or 
eighth notes blend together to produce an agreeable effect. In 
music, therefore, the complete series of notes employed is divided 
into groups of octaves. 
411. The Gamut and Chromatic Scale.—The series of tones into 
which the interval between C and its octave c is divided, is 
called the gamut or diatonic scale.' It embraces seven tones, which 
are designated by the letters C D E F G O. 
The tones of the gamut are also known by names, do or ut 
standing for C, and followed by re, mi, fa, sol, la, si, in order. 
The octave is subdivisible into a much greater number of 
recognizable intervals than the gamut. In the musical system 
generally adopted five notes are added to the gamut. These are 
represented on the piano by short raised black keys, each of 
which is called the flat of the white note above, or the sharp of 
the white note below. To the complete series of twelve thus 
produced the name of chromatic scale is given. 
412. Musical Notation.—To designate any given tone in the 
ordinary range of music, the following system or notation has 
been recommended. The octave of which the cis produced by 
an eight foot organ pipe, receives the capitals C, D, E. E, G, A, 
B. The next octave above, the letters c, d, e, etc.; the next 
c', d', e', etc. The octaves below C are designated by the capi- 
tals with the subsign, e.g., Cv, Dv, etc. We thus obtain the series 
of octaves, viz.: 
Cu Cv C cc' c" c"'. 
In written music, notes are indicated by signs placed upon a 
series of five lines, called a stave. According to this method, the SPECIAL PROPERTIES OF SOUND, 
357 
octave of the treble cleft, of which the top note is the standard 
c/, and the bottom the middle c, is written as follows : 
Treble stave. 
When the notes pass beyond the five lines, they are written 
on additional short lines, called ledger lines, as is the case with c. 
For the lower notes a base cleft is employed. The base and 
treble may be said to meet in the middle c, written in the treble 
cleft as 
in the base as 
413. Number of Vibrations to each Tone.—On a piano of seven 
octaves the middle note c, of which we have been speaking, 
is produced by the white key to the left of the two black keys 
nearest to the middle of the key-board. Musicians have gener- 
ally assumed that this note corresponds to 256 double vibrations 
in a second. The number is arbitrary, and was selected partly 
on grounds of convenience, since it is a power of two. 
The adjustment of “ unison,” or tuning of instruments to each 
other, is obtained by means of the tuning-fork, described in 
(389). To increase the intensity of its tone, it 
inay be fixed in a resonance box open at one 
end, Pig. 172. For some time past the pitch 
°i the standard forks in the opera houses of 
the great European cities has gradually in- 
creased at different rates, which caused con- 
siderable annoyance to musicians in passing 
from one to another. To avoid the confu- 
sion thus arising, a normal tuning-fork was 
adopted in France. It vibrates 437,5 times 
lr> a second, and gives the standard note a of 
the treble stave (412). In reference to this 
standard the middle c on the piano is pro- 
duced by 261 vibrations in a second. 
Fig. 172. 
Resonance box and fork. 
In addition to the standard tuning-forks referred to, the 
English committee appointed by the Society of Arts recom- 
mended one with 528 double vibrations per second, which repre- 
sented c' in the treble stave (412), or 264 for the middle c. It 358 
ACOUSTICS. 
is virtually the same as the Stuttgardt tuning-fork adopted in 
1834, which makes 440 vibrations per second, and corresponds 
to ain the same stave. According to either of these values, 
256, 261, or 264, for the middle c, the number of vibrations for 
any note of the gamut may he estimated from the following for- 
mula, m denoting the number for the middle c. 
ut or do 
re 
mi 
fa 
sol 
la 
si 
c 
d 
e 
/ 
9 
a 
h 
c' 
m 
f m 
|- to 
f m 
•| to 
TO 
m 
2 TO 
264 
297 
330 
352 
396 
440 
495 
528 
With the key note making 440 vibrations per second, the 
lowest note of orchestral instruments is the Ev of the double 
bass, produced by per second. Organs go down to Cu, or 
32, and in grand pianos Au with 27J per second is reached. 
The notes below E; are not perfect. 
On the treble side pianos reach cT, with 4224 vibrations. The 
piccalo flute reaches d\ with 4752. Though the sounds per- 
ceptible to the ear range, as we have seen (409), from 16 to 41,000 
per second, or over eleven octaves, those which are capable of 
exciting pleasure are confined to about seven octaves, or from 
near 40 to about 4000. 
The question of the number of vibrations producing given 
tones is of especial importance, since the tuning-forks originating 
these are employed in the physiological measurement of brief 
periods of time, and of rates of vibration, as in (408). 
414. Harmonies, Overtones. —The formation of nodes and loops 
has been described in (388). When the string of the mono- 
cord is made to vibrate throughout its whole length, the sound 
produced is called the fundamental tone. Touching the string 
at the centre with the soft point of the finger, and plucking it 
near one end, the string will vibrate in two sections, a node 
being formed at the point touched. The rate of oscillation of 
the two ventral segments will be double that made by the whole 
length of the string, and the tone emitted will be an octave 
higher than the fundamental tone. 
Touching the string again at its length from either end, it 
vibrates in three sections with two nodes; the number of move- 
ments is now three times that of the fundamental tone, or fof 
the octave, which is the twelfth above the fundamental tone, and 
the fifth above the octave. 
Again touching it at one-fourth its length from either end, and 
plucking it, three nodes and four ventral segments are formed, 
each making four times the number of vibrations of the funda- 
mental tone, and producing the tone two octaves above the fun- 
damental tone. This may be continued to the formation of 5, 6, SPECIAL PROPERTIES OF SOUND. 
359 
7, 8, or 12 ventral segments, each having a number of vibrations 
inversely as the number of segments, and producing in addition 
to the tones already mentioned, the third, fifth, and a tone 
between the sixth and seventh of the second octave, and so on. 
These higher tones of a fundamental tone are called its over- 
tones or harmonics. Whenever a string vibrates throughout its 
whole length, it also vibrates in halves, thirds, fourths, etc., the 
motion not being simple but exceedingly complex. That this is 
the case is proven by the fact that a trained ear can detect, in 
addition to the fundamental tone, its octave, twelfth, and other 
overtones. 
If the overtones are not easily heard, they may be made evident 
by touching a nodal point of the string with the finger. The 
fundamental tone is thus stopped, while the overtones corre- 
sponding to the node touched will be heard. In this manner the 
presence of one overtone after another may be demonstrated. 
Kearly all sonorous bodies besides strings produce overtones 
in addition to their fundamental tone when thrown into vibra- 
tion. These tones taken together constitute a note, as distin- 
guished from a simple tone. 
415. Quality or Timbre.—This third character of sound, by 
which we recognize a note of the same pitch as it is produced 
°n different instruments, is the result of a variety of causes. 
It is in part the effect of feeble sounds which attend the 
manner of production of the note, for example, the rushing of 
the air which forms the notes of a flute; the rapid or gradual 
decrease in intensity as in the piano, or the uniformity of in- 
tensity which attends the notes of an organ. 
Another and far more potent cause of quality in a note is 
the nature of the overtones which accompany the fundamental 
Fig. 173. 
Characters of waves. 
tone. These are different, not only in various sonorous bodies, 
but also for the same body according as the sound is produced. 
As these elements vary, the character of the wave produced 
differs, and with it the quality. The figure will enable us to 
perceive how this may arise. 360 
ACOUSTICS. 
Suppose ABC are three waves having the same amplitude 
and the same period. It is evident that, as shown in Fig. 173, 
their mode of vibration may be entirely different. It is also 
clear that there may be an infinite number of such variations. 
It is to this change in manner or form of vibration, that differ- 
ence in quality is to be ascribed. 
416. Wave Length of Sounds in Air.—As in the examination of 
the intensity of a propagated sound, the amplitude of vibration 
of the air-waves was compared to the height of waves on water, 
so in the case of pitch we may institute a like comparison, and 
speak of sounds as having different wave lengths. The wave 
length of any tone is obtained by dividing the velocity of sound 
(380) by the number of oscillations. From this it follows that 
the length of the aerial waves diminishes as the pitch of the 
notes rises. For shrill notes they are short and rapid, and for 
low notes long and slow. When the middle cof the piano is 
struck, it vibrates about 264 times in a second, and hence sets 
up air-pulses of 1120 feet divided by 264, or feet in length. 
The first A of the bass (in a seven-octavo piano) produces air- 
waves about 41 feet in length, while the last a of the treble 
sends on pulses not quite 4 inches long. The latter are 128 
times more rapid than the former, which are correspondingly 
longer. If the sensibility of the ear nerves is to be judged by 
the range of audibility of musical tones, it far surpasses that of 
the optic nerves. The former ranges over eleven octaves, while 
the latter barely exceeds a single octave. 
CHAPTEE XY. 
ANALYSIS AND SYNTHESIS OF SOUNDS. 
Helmholtz’s resonators—Konig’s manometric flames—Konig’s sound analyzer— 
Synthesis of sounds—Results of Helmholtz’s researches—Lissajou’s method—- 
Illustration of Lissajou’s curves—Leon Scott’s phonautograph—Edison's 
phonograph—Acoustic attraction and repulsion. 
417. Helmholtz’s Resonators.—The properties of sympathetic 
vibration, and resonance possessed by enclosed masses of air 
have been discussed in (395) and (402). In accordance therewith 
Helmholtz devised the apparatus called the resonator. 
In its earlier form this instrument was a spherical copper or ANALYSIS AND SYNTHESIS OF SOUNDS. 
361 
brass vessel. On one portion of the surface there was an opening 
which received the sound; opposite to this a smaller opening or 
tuhulure conveyed it to the auditory canal. 
With variation in the capacity of resonators, so do they respond 
to different tones; it is, therefore, only necessary to be supplied 
with a battery of these instruments of different sizes, corre- 
sponding to the tones to be detected, and we have the means of 
analyzing any sound or note. 
Konig has introduced an important modification of the original 
resonator; in this the body of the instrument is composed of 
two hollow cylinders one of which slides 
telescopically into the other, as shown in 
Fig. 174. Thus the volume of the interior 
can be increased or diminished, and is easily 
tuned or adjusted to a number of different 
tones. To the tuhulure a rubber tube is fitted 
by which vibrations are conducted to any 
desired point. 
When the resonator is used one ear is 
carefully closed, and the rubber tube at- 
tached to the tuhulure introduced into the 
auditory canal of the other. All sounds 
then appear to be stifled, and are heard as 
though at a distance, except when the proper 
tone of the resonator is produced, this at once 
sounds with extreme intensity, booming out 
dear and defined from amongst the confused 
hum of the others. 
Fig. 174. 
Konig’s resonator. 
In reality the resonator not only reinforces 
jts own proper tone, but also the harmonics of that tone; but 
ln this case the intensity is so much less than that of the true 
tone of the instrument, that there is no difficulty in forming a 
correct opinion. 
Applying one resonator after another to the ear, the presence 
or absence of the tones they represent in any given sound may 
be determined, and thus an exact analysis of the sound accom- 
plished. By this method Helmholtz demonstrated that the 
quality of any note depends upon the number, pitch, and loud- 
ness of the harmonics or overtones it possesses. 
418, Konig’s Manometric Flames.—The method of analysis by 
resonators applied to the ear, can only be used by one person 
at a time. To meet this objection Konig has devised an inge- 
nious apparatus, whereby a number of persons may at the same 
time witness the results of experiments for the detection and 
analysis of sounds or notes. The principle upon which this is 
accomplished is as follows. 362 
ACOUSTICS. 
In (391) we have seen that tense membranes undergo vibra- 
tion when sounds are produced in their vicinity. Acting upon 
this fact, Konig received sonorous undulations upon one side of 
a membrane, the other being part of the wall of a small cavity 
Fig. 175. 
or box through which gas passed on its way 
to a burner. When ignited at the burner, 
the flame by its movements at once indicated 
any changes in the pressure on the gas re- 
sulting from the oscillation of the membrane. 
In Fig. 175, the essential parts of this arrange- 
ment are represented. KK, is the box or 
cavity, divided into two portions by a thin 
membrane, h. The tube a communicates 
with a trumpet-like mouth-piece, along which 
vibrations are imparted to the diaphragm 
h. By the tube b illuminating gas is de- 
livered to the portion of the cavity on the 
opposite side of the septum, thence it passes 
by the tube C to the jet A, where it is ignited. 
Gas-flame manometer. 
So long as there is no sound, in the vicinity of the mouth- 
piece, the gas burns in a tranquil manner, and the flame is quiet; 
but the instant sound is received by the mouth-piece, it is thrown 
Fig. 176. 
Kouig’s manometric flames. 
into violent agitation, as in the singing flame of the chemical 
harmonicon. So closely do the movements follow each other 
that it is impossible for the unaided eye to determine their char- ANALYSIS AND SYNTHESIS OF SOUNDS. 
363 
acter; to overcome this difficulty they are viewed by means of 
the analyzing mirror, 
This consists of a cubical box, the vertical sides formed of 
mirrors, M. By a vertical axis and cog-wheels, Fig. 176, it is 
rotated, when the reflected image of the flame F is viewed 
therein. When the flame burns steadily, and is not affected by 
sound, the image in the revolving mirrors is a simple band of 
light. But the moment the flame is thrown into oscillation by 
the action of the sound vibrations upon the membrane A, Fig. 
175, the band-like appearance is lost, and a series of tongue- 
like figures appears. 
Providing the note entering the mouth-piece of the apparatus 
18 a simple or fundamental tone, the appearance produced is that 
In Fig. 177. 
Fig. 177. 
Fundamental note. 
With the same rate of rotation of the mirror, if the octave of 
the preceding note is sounded, the result is seen in Fig. 178. 
Fig. 178. 
Octave of preceding. 
Adapting a T-shaped tube to a (Fig. 175), in order that the 
sound of the fundamental tone and its octave be conveyed 
1° the flame at the same time, the effect in Fig. 179 is obtained. 
Fig 179. 
Fundamental note and octave. 
If the fundamental note and its third be sounded, a different 
appearance is produced. 364 
ACOUSTICS 
If the vowel o be sung on the notes c and c' it gives the result 
in Fig. 180. 
Fig. 180. 
Vowel 0 on c and c'. 
419. Konig’s Sound Analyzer is represented in Fig. 181. It 
consists of a battery of Helmholtz’s resonators, to each of which 
a raanometric flame, with capsule 
and vibrating membrane, is attached. 
The images of the flames are then 
viewed in the analyzing mirror. 
For analysis of any given note the 
resonators are arranged to correspond 
to it and its harmonics. 
Fig. 181. 
Applying this apparatus to the 
analysis of the same note as given 
forth by different instruments, it is 
found that the sound of a diapason, 
or tuning-fork, is almost absolutely 
simple; the same is the case with the 
flute. In the piano, on the contrary, 
the fundamental tone is accompanied 
by six harmonics; the violin shows 
a greater number. The clarionet 
Analysis of sound. 
gives uneven harmonics, and in brass wind instruments, like the 
trumpet, the higher harmonics are very intense or loud. 
A crude analysis of complex sounds may be made by pro- 
ducing them in the vicinity of a piano, with dampers raised. 
The strings of the piano corresponding to the note will vibrate, 
and indicate the tones entering into the formation of the com- 
plex sound. 
420. Synthesis of Sounds.—Hot content with the decomposition 
or analysis of sounds into their constituents, Helmholtz has de- 
monstrated his theory of the quality of sounds beyond cavil, by 
synthesis, or the putting together of their constituents. 
In the apparatus by which this is accomplished the source of 
each sound is a diapason or tuning-fork, to which the proper 
resonator is attached, its mouth partly or entirely closed, and 
the sound intensity varied. The vibration of the fork is main- 
tained by means'of an electro-magnet. A series of such arrange- 
ments, representing a fundamental tone and its harmonics, is ANALYSIS AND SYNTHESIS OF SOUNDS. 
provided. The fundamental tone with its harmonics in greater 
or less number and intensity, may in this way be sounded, and 
the results obtained by analysis proved. 
421. Results of Helmholtz’s Researches.—These are summed up 
as follows by Ganot: 
1. Simple tones, as those produced by a tuning-fork with a 
resonance-box, and by wide covered pipes, are soft and agreeable 
without any roughness, but weak, and in the deeper notes dull. 
2. Musical sounds accompanied by a series of harmonics, say 
up to the sixth, in moderate strength, are full and musical. In 
comparison with simple tones they are grander, richer, and 
more sonorous. Such are the sounds of open organ-pipes, of 
a piano-forte, etc. 
3. If only the uneven harmonics are present, as in the case of 
narrow covered pipes, of piano-forte strings struck in the mid- 
dle, clarionets, etc,, the sound becomes indistinct; and when a 
greater number of harmonics are audible, the sound acquires a 
nasal character. 
4. If the harmonics beyond the sixth and seventh are very 
distinct, the sound becomes sharp and rough. If less strong, 
the harmonics are not prejudicial to the musical usefulness of 
the notes. On the contrary, they are useful as imparting char- 
acter and expression to the music. Of this kind are most 
stringed instruments, and most pipes furnished with tongues. 
Sounds in which harmonics are particularly strong acquire 
thereby a peculiarly penetrating character; such are those 
yielded by brass instruments. 
5. To form a given vowel sound one or more characteristic 
notes which are always the same must be added. These change 
with the syllable pronounced, but depend neither on the height 
°f the note, nor on the person who emits them. 
422. Lissajou’s Method consists in the production of certain 
dgures by the action of sound vibrations upon a line of light, 
big. 182, The apparatus required for the experiment is an 
Argand lamp, the chimney surrounded by a cylindrical metallic 
screen, in which a pin-hole, A, has been made. Through this 
rays of light pass in the direction of the dotted line. These fall 
upon a tuning-fork, B, placed vertically, one prong armed with 
a small mirror, and the other provided with a balance weight, 
that the vibrations may not be changed. From this mirror the 
rays pass along the dotted line to a second fork C, of the same 
tone as the first. Its vibrations are produced horizontally. 
One of its prongs bears a mirror, and the other a counterpoise. 
At a suitable distance an observing telescope, D, is placed. The 
forks are in unison. 366 
ACOUSTICS. 
Both forks being at rest, and the angles of the mirrors prop- 
erly adjusted, on looking through the telescope the image of the 
Lissajoil’s method. 
pin-hole in the screen around the lamp chimney is seen as a 
minute dot of light. If one of the forks is thrown into vibra- 
Fiq. 183. 
Lissajou’s figures. 367 
ANALYSIS AND SYNTHESIS OF SOUNDS. 
Bon, the dot of light becomes a line. If the other fork alone 
is thrown into vibration, again the dot appears as a line, hut 
at right angles to that previously produced. Throwing both 
forks into vibration at the same time, the image formed is a 
curve which is some form of ellipse, though oblique lines and a 
circle may arise as exceptional results. These are found in the 
upper row, Fig. 183, 
If one of the forks differs from the other by an octave, the 
series of figures in the second row appears; if by a fifth, the 
curves in the lower row are obtained. 
By using an electric or oxycalcium light as the source of 
illumination, and passing the beam therefrom through a convex 
lens before it falls on the first mirror, a dot-like image of the 
pin-hole may be projected on a screen placed in the position of 
ffe telescope. On throwing the mirrors into vibration Lissajou’s 
linages appear in perfection. 
423. Illustrations of Lissajou’s Curves.—By means of Black- 
burne’s pendulum, Lissajou’s curves are reproduced by a slow 
motion. It consists of a cord, ABC, attached at two fixed 
Points A and C, in a horizontal line and with a certain amount 
°f slack. To the centre of this another cord, BD, is fastened, 
Fig. 184. 
Blackburne’s pDndulum 
)vhich carries a spherical metallic ball at D, a pointed wire pro- 
jecting from the lower part. If the bob is set in motion in the 
plane A B C, it will vibrate in that plane, the point of suspen- 
-Bl.°n, B, not moving. If in a plane perpendicular to this, it will 
vibrate in that plane, the whole system moving with Eas the 
point of suspension. In the one caseß I) represents the length 
°f the pendulum, and gives a certain rate of vibration. In the 
other, E B, as it is longer, it gives a slower movement. 
. If the bob is drawn aside in any other plane than those men- 
tioned, it no longer oscillates in a straight line, but executes 
movements resulting from a combination of those already given, 368 
ACOUSTICS. 
and produces curves exactly the counterpart of those of Lissajou. 
Preparing a little plateau of sand half an inch deep, and six or 
eight inches square on a board, and allowing the pointer of the 
bob to play therein, very beautiful figures are formed. 
424. Leon Scott’s Phonautograph is an instrument for the regis- 
tration of all kinds of sounds and noises. It consists of an 
ellipsoidal barrel one end open, and turned in the direction of 
the sound. The opposite end gives passage to a narrow brass 
tube closed exteriorly by a delicate membrane. Hear the centre 
of this a hog’s bristle is attached, the free end touching a revolv- 
ing cylinder carrying a paper covered with lampblack (408). 
Setting the apparatus in movement, while sound is not 
received the bristle traces a straight line on the lampblack 
surface, but the moment sound waves enter the ellipsoid the 
membrane is thrown into vibration and the bristle records an 
undulating line corresponding thereto. 
425. Edison’s Phonograph is an admirable and ingenious im- 
provement upon the preceding apparatus, as it not only records 
but reproduces sounds received. 
Its receptive parts consist of a mouth-piece, E, into which the 
Fig. 185. 
Edison’s phonograph. 
operator speaks. The voice is directed upon a thin metallic 
disk, which is thrown into corresponding vibration. This 
metallic membrane E, carries a fine steel point S, which plays 
upon the'cylinder C. Instead of blackened paper, the cylinder 
is covered with tinfoil. By means of the winch M, it is thrown 
into rotation, and as the axis A bears a screw cut, a movement 
of translation is imparted as it rotates. 
The cylinder being freshly covered with foil, if the winch is 
rotated the steel point describes a spiral line of uniform depth 
thereon. Continuing the movement at a regular rate, and 
speaking into the mouth-piece, the unbroken spiral line disap- 
pears, and in its place a dotted line is produced, made up of 
depressions or perforations. These represent the record of ANALYSIS AND SYNTHESIS OF SOUNDS. 
369 
vibrations, similar to that in the apparatus of Leon Scott. Here, 
however, comparison ends, for if the cylinder of Edison’s in- 
strument is readjusted with the apex of the recording needle 
on the spot where the record began, by moving the winch, as 
tpe point attached to the metallic disk passes over the depres- 
sions in the foil, it throws the membrane into vibration, and 
causes it to give forth the sounds received from the voice. 
All kinds of sounds, as singing, speaking, squeaking, hissing, 
uiay be reproduced. Even the quality of different voices is 
readily recognized, the only change being a slightly nasal twang 
°r modification. Edison claims that by this machine 40,000 
words can be recorded on a space of ten square inches. 
Professor Blake, of Brown University, has recorded vocal 
sonorous vibrations by the agency of the photograph. The 
result was attained by attaching a steel mirror to a vibrating 
disk of ferrotype iron, two and three-fourths inches in diameter, 
A beam of sunlight was directed by a heliostat upon the mirror, 
and after undergoing reflection was brought to a focus by a 
lens upon a sensitive plate which moved at right angles to the 
track of the ray. So long as the ferrotype disk was at rest a 
nnear stain was produced upon the plate, but the moment it 
Was thrown into vibrations by the voice, a record similar in 
appearance to that formed by a sphygmograph was obtained. 
Pppies of such records and a fuller description of the apparatus 
Will be found in the “ Am. Journal of Sciences and Arts,” vol. 
Xvi. page 54. 
426. Acoustic Attraction and Repulsion.—A body in a state of 
sonorous vibration has been found to exert an influence some- 
times of attraction, and again of repulsion upon other bodies 
freely suspended in its vicinity. Attraction is exerted when it 
|s heavier, and repulsion when lighter. A balloon of gold- 
beater’s skin filled with carbonic acid gas, brought near the 
of the resonance box of a tuning-fork, is attracted. A 
balloon filled with hydrogen is under the same circumstances 
repelled, though loaded with wax. 
Li like manner, a tuning-fork in vibration will attract a piece 
. card-board suspended by a string. If, on the contrary, the 
vibrating fork is suspended, and the card-board fixed, the latter 
vpll attract the former. Two suspended tuning-forks while 
vibrating attract each other. A vibrating fork repels a candle 
flame placed near its extremity, or flattens it it held over it. 
If very light resonators are brought near to the sounding 
pox or resonator of a tuning-fork with which they are vibrating 
ln unison, they undergo repulsion. If they are mounted at the 
extremities of a small four-armed wind-mill, the repulsion is 
sufficient to produce a continued rotation of the mill. These 370 
ACOUSTICS. 
phenomena are hardly explicable on an hypothesis of the action 
of currents in the air, neither can they be attributed to heat. 
They are of especial interest and worthy of careful investigation, 
as in all probability they hold the clew to the explanation of 
electric, and other attractions and repulsions. 
CHAPTER XYI. 
PHYSIOLOGICAL PRODUCTION AND PERCEPTION OF SOUND. 
Voice in the lower creatures—The human voice—The larynx and song—The 
mouth and speech—Ventriloquism—Simple ear of lower creatures—The ear 
in man—The external ear—The middle ear—The internal ear—The audi- 
phone—The photophone. 
427. Voice in the Lower Creatures.—Many forms of sound- 
producing apparatus are found in the lower or invertebrate 
creatures. Sometimes, as in certain insects, it is a mere vibratory 
action of the wings upon the air. Again, special resonance 
cavities are provided, which are sounded by the friction of rough 
horny surfaces on each other. It is also the result of a sudden 
spasmodic movement of portions of the body or extremities. 
Even mollusks are not entirely voiceless, for certain kinds give 
forth booming or bell-like sounds. 
428. The Human Voice.—In common with all air-breathing 
vertebrates, man employs air expired from the lungs for the 
production of voice, and establishing communication with his 
fellow-creatures. 
For practical purposes we may consider the vocal apparatus 
under three divisions: Ist. The respiratory portion, consisting 
of the lungs, bronchi, and trachea, wherein air is compressed 
by the action of the diaphragm and expiratory muscles of the 
chest; 2d. The larynx, in which tones or notes are produced, 
as in simple song, by vibrations imparted to the outgoing air; 
and, 3d. The mouth and parts above the trachea, where sounds 
produced in the larynx undergo modification to form articulate 
speech. 
429. The Larynx and Song.—The larynx may be briefly de- 
scribed as a box formed of articulated plates of cartilage moved PRODUCTION AND PERCEPTION OF SOUND. 
371 
by means of muscles. It is placed at the summit of the trachea 
or wind-pipe, and through it outgoing air passes. 
The cavity of the larynx is not entirely free, but bears upon 
its walls certain membranous structures, called the vocal chords. 
By the action of muscles the tension of these chords may be so 
changed that at one time the passage is almost without obstruc- 
tion, as during ordinary respiration; while at another, it is re- 
duced to a mere slit. When air is forced through this chink- 
like opening or glottis, the vocal chords or valves are thrown 
into vibration, and notes are sounded. 
According as the tension on these chords or ligaments is 
varied, a higher or lower note is formed; a high note arising 
when the tension is greater. In their action the vocal chords 
may be likened to the vibrating tongues of reed instruments 
(393), the sound being caused by a series of impulses wdiich 
arise in the reaction of the issuing current of air upon the elas- 
ticity of the reeds or vocal chords. There is, however, this im- 
portant difference, that whereas the metal tongue of the reed 
can only yield a single note of a fixed pitch, the vocal chords 
emit many notes of different pitch, according to the wish of the 
singer. 
The notes given forth by men are lower than those formed 
by women. Since the larynx is larger, and the vocal ligaments 
longer and thicker, they, therefore, vibrate more slowly and 
produce a lower tone. When the vocal chords vibrate through- 
out their whole length the so-called chest notes are formed; when 
confined to the free edges, falsetto notes arise. 
The average extent of scale of the human voice is about two 
octaves. To this, important exceptions are occasionally seen. 
Catalini, for example, is said to have had a compass of three 
and a half octaves. 
“Although a few exceptional singers can, so to speak, acro- 
batize in music to the wonder of the public, yet the really good 
and usable part of their compass for every-day work is com- 
paratively limited, and if they are called upon frequently to sing 
cither at their highest or lowest, the voice rapidly deteriorates, 
and wonder is changed to compassion. Violins cannot be 
‘ screwed up or down’ too much. It is better to alter the thick- 
ness of their strings. The thin strings are particularly objec- 
tionable in instruments only too prone to be played cuttingly. 
Clarionets, oboes, and trumpets, when made short and narrow 
for high pitch, are simply fit to be heard out of doors, as in 
military bands.” 
The wave length of the sounds of the ordinary voice in women 
during conversation is from two to four feet. With man’s voice 
it is eight to twelve feet. 372 
ACOUSTICS. 
430. The Mouth and Speech.—To the larynx the mouth or 
buccal cavity acts the part of a resonator, causing the whole 
apparatus to bear a close resemblance to a reed-organ pipe. 
While the intensity of the human voice depends upon the 
force with which air is driven through the glottis, and its 
pitch upon the tension of the vocal chords, the quality is the 
result of a variety of causes. Among these are the form of each 
larynx; length and elasticity of its vocal chords; resonance 
value and action of the buccal and nasal cavities, and other 
parts in the vicinity. 
The chief point of interest in connection with the mouth is 
its agency in the formation of articulate speech. Words con- 
sist of vowels intermingled with consonants. 
Since a note can only be said or sung on a vowel, these may 
be regarded as the essential elements of speech. Foster says, 
whenever a note is sounded by the larynx we recognize in it 
features by which we detect one or another of these sounds. 
Vowels are in reality exaggerated examples of quality in which 
certain overtones are intensified, as found by their analysis 
(419). The particular tones which are reinforced in the different 
vowel sounds may also be determined by holding vibrating 
tuning-forks of various tones, one after another in front of the 
mouth when it is arranged for pronunciation of different vowels, 
and observing those that have their note intensified. 
The adjustments of the buccal and pharyngeal cavities by 
which this prominence of special overtones is produced, is 
illustrated as follows. When for example, ee in feet, or ain 
fat, is sounded the larynx is raised, the lips retracted, and the 
buccal cavity or resonator made very short. In producing ain 
father, the mouth is opened wide, the buccal cavity assuming a 
funnel shape with the point at the pharynx. For o, the same 
shape is again assumed, but the lips are protruded and the length 
of the resonator increased. The greatest elongation of the reso- 
nator tube is reached in producing u, with the sound 00. 
By means of Konig’s manometric flames vowels are found to 
have the following composition, 
A, contains in addition to the fundamental tone, the 2d har- 
monic feeble, the 3d strong, and the 4th feeble. 
E, the fundamental tone feeble, 2d harmonic strong, 3d feeble, 
4th strong, sth feeble. 
I, very high harmonics, the sth especially strong. 
O, the fundamental, 2d harmonic strong, 3d and 4th feeble. 
U, fundamental with 3d harmonic moderate. 
In euphonious or pure speech the posterior nares are closed by 
the soft palate, for if a candle flame be held in front of the 
nostrils, it proves that air is not escaping through that channel. 
If the closure is imperfect, the sound at once becomes nasal in PRODUCTION AND PERCEPTION OF SOUND. 
character, and air passes from the nostrils. The nasal character 
is also caused when the anterior nares are closed by holding 
the nose between the thumb and forefinger, the nasal cavity then 
acting as a resonator. 
Consonants arise from various interruptions and modifications 
of the expiratory blast of air, and are not produced by vibra- 
tions of the vocal chords. They are classified according to the 
manner and position of interruption, as follows ; 
Explosives. 
Labials, 
without voice . 
. P. 
\ “ 
with voice 
. B. 
Dentals, 
without voice . 
. T. 
u 
with voice 
. D. 
Gutturals, 
without voice . 
. K. 
(( 
with voice 
. G (hard). 
Labials, 
U 
without voice . 
. F. 
with voice 
. Y. 
Dentals, 
without voice . 
. S, L, Sh, Th (hard). 
U 
with voice 
. Z, Zh (in azure, the 
French j), Th (soft). 
Gutturals, 
without voice . 
. C H (as in loch). 
U 
with voice 
. G H (as in lough). 
Aspirates. 
Resonants. 
Labials .... 
M. 
Dentals .... 
N. 
Guttural .... 
N G. 
Labial .... 
. Not known in Euro- 
pean speech. 
Dental .... 
. R (common) 
Guttural .... 
. R (guttural). 
Vibratory. 
A whisper is speech without sounding the vocal chords; it is 
produced by action of the lips and tongue upon the expired 
air. 
431. Ventriloquism is simply an accurate imitation of sounds 
as they would be heard by the ear of the listener if given forth 
in various positions, as in a box, behind a door, or in an adjacent 
apartment. It implies deception both as regards distance and 
direction of a sound. 
432. Simple Ear of Lower Creatures.—The most rudimentary 
form of ear consists of a sac filled with an albuminous fluid. 
On its walls the auditory nerve terminates in minute filaments. 
In the fluid there are certain hard stony particles, the presence 374 
ACOUSTICS. 
of which has caused the entire apparatus to be called an oto- 
lithic sac. 
Regarding the function of the stony particles there is dispute. 
Some think that when sound vibrations fall on the sac, the 
particles are thrown into action, and produce sensation by a 
kind of tapping upon its sensitive wall. Others, on the con- 
trary, imagine that their function is to act as dampers and stop 
vibrations as soon as they have produced their effect. 
433. The Ear in Man.—ln man, and in higher mammals, the 
auditory apparatus is very complex in its structure. We know 
how compound a wave of sound may be; how it involves loud- 
ness, pitch, and quality, the latter implying the superimposing 
of many harmonics upon the fundamental tone. It is, therefore, 
not at all surprising that an organ adapted to the determination 
of so many data, should require many parts for the accomplish- 
ment of its purpose. 
For sake of convenience, the ear is studied under three divi- 
sions: Ist, external; 2d, middle; and, 3d, internal. Of these, 
the latter appears to be the most essential, the others occu- 
pying a subordinate position. This conclusion is based upon 
the fact, that in many vertebrates, and in all invertebrates, there 
is no true external ear. In creatures which live in water, the 
middle ear is also wanting, though some imagine that the 
swimming bladder in fishes operates in this manner, as it is 
connected with their auditory apparatus. Under this hypo- 
thesis it is supposed that sonorous vibrations are received from 
water, and passing through the body, are communicated to the 
air in the swimming bladder. Admit- 
ting that this is the case, the auditory 
apparatus in these creatures acts in the 
same manner as in air-breathing animals. 
In Fig. 186 the relative positions of 
the leading divisions of the ear are repre- 
sented. The external extends to the 
line g; the middle from this line to the 
zig-zag line beyond b; the rest comprises 
the internal portion or division. Each 
Fig. 186. 
The ear. 
of these parts consists of subdivisions, the most important of 
which we shall describe. 
434. The External Ear.—This division consists of the pinna a, 
or major portion of the external organ which leads to the audi- 
tory canal or tube, by which sonorous vibrations reach the 
tympanic cavity or middle ear. The smooth portion of the 
pinna at the entrance of the tube is sometimes designated as PRODUCTION AND PERCEPTION OF SOUND. 
375 
the concha. This term is also applied to the whole expanded 
part of the external ear. 
In the majority of mammals, the pinna or concha is very 
provable, and is directed to the point whence sound is proceed- 
ing. In man this is not the case, the appreciation of direction 
being accomplished by moving the head, though in some persons 
there is a slight power of movement of the ears. 
It need hardly be added that, the function of the pinna is to collect 
sounds from a greater area, and so increase the intensity of the vibra- 
tions transmitted by the auditory canal. 
In the formation of the external ear of mammals, the followers 
of Darwin find one of their arguments in support of the hypo- 
thesis of the origin of man from the lower orders. On the outer 
cartilaginous curve of the human ear, and above the opening 
of the auditory canal or meatus, there is a little tubercle of 
cartilage, which in the ears of many people is exceedingly well 
marked. This, philosophers tell us, is the remnant of the tip of 
the ear of the lower animals, and is regarded as evidence of the 
source from which the human organ has been developed. It is 
certainly very curious and interesting to note, in different indi- 
viduals, that the passage of the ear through what may be called 
Satyr type to its perfect form may be easily traced. 
435. The Middle Ear.—Entering the petrous part of the tem- 
poral bone, the auditory canal expands to form the cavity of 
the middle ear b. This is separated from the canal by a 
membrane which occupies the position g, Fig. 186. It is called 
the drum membrane, or membrana tympani. The drum or 
middle ear is filled with air, and to insure equality of pressure 
on each side of the membrane a tube f, called the Eustachian 
tube, communicates with the back part of the mouth. Stop- 
page of this tube by mucus, or otherwise, is at once attended 
by a muffling of the sense of hearing. 
Across the drum cavity b a chain of three little bones is ex- 
tended. They are called the malleus, incus, and stapes. The 
handle of the malleus is fixed by its top near the centre of the 
membrana tympani, and the stapes or stirrup to another mem- 
brane which closes an aperture leading to the internal ear, and 
called the fenestra ovale. To these little bones certain muscles 
are attached, which by their movements increase or diminish 
tension in the membrana tympani. 
The function of the drum membrane is evidently to receive 
the vibrations which have been collected by the pinna. The 
Peculiar facility with which such tense septa are affected by all 
kinds of vibrations fits it eminently for this purpose (391). 
Regarding the function of the chain of bones there is dispute. 
Some conceive that their chief duty is to convey sonorous 376 
ACOUSTICS. 
vibrations to the internal ear; to this the jointed structure is an 
objection. Others, on the contrary, think that since they serve 
as attachments for delicate muscles, they merely aid the latter 
to determine the amplitude of vibration of the membrana tym- 
pani, by the force they exert to hold it tense, and so measure 
the intensity of sounds falling thereon. 
436. The Internal Ear is also called the labyrinth. This differs 
essentially from the other parts in that it is filled with liquid 
instead of air. It consists of three portions: Ist, the vestibule 
or entrance, Fig. 186, e; 2d, the cochlea, d\ and 3d, the semi- 
circular canals, c. On, and in these, the ultimate filaments of 
the auditory nerve are distributed. 
The vestibule is the entrance to the cochlea and canals; it is 
represented at e, Fig. 186. Floating in the fluid with which 
the cavity is filled is an ovoid membranous sac, constricted at 
its centre; and dumb-bell like in shape. To the two divisions 
the names of saccule and utricle are given. It is also filled with 
fluid, called the endolymph; that on the outside is called peri- 
lymph. The membranous walls of this sac receive a copious 
supply of nerve fibres, and in its interior minute stony par- 
ticles are found; in its entirety it resembles the otolithic sac of 
inferior animals. 
In addition to its use as the way of approach to the innermost 
portions of the ear, the vestibule, from its structure, evidently 
has some other function. What this is, it is difficult to say. 
Its resemblance to the otolithic sac of lower animals favors the 
supposition that it serves for the mere detection of noise. 
The cochlea, represented at d, Fig. 186, is so-called from its 
resemblance to the spirally coiled shell of a snail or other 
gasteropod mollusk. It may be described as a conical tube, the 
axis very long compared with its diameter. This tube is wound 
spirally around a central axis. The spiral canal thus formed is 
divided throughout by a septum, called the lamina spiralis. 
This bears the so-called organ of Corti; in its structure it may 
be likened to a piano, which involves no less than some 3000 
nerve fibres or strings. 
In (419) we have learned that the resonators of Helmholtz in 
Konig’s apparatus for analysis of sound, respond by their sensitive 
flames to the fundamental and overtones of any note in their 
vicinity. So the fibres of the organ of Corti, acting like reso- 
nators, determine the fundamental tone, or pitch, and the over- 
tones, or quality, of each note that gains access to the cochlea. 
We have disposed of the measurement of intensity, pitch, 
and the quality of sounds, yet there still remains a very im- 
portant part of the labyrinth the function of which is involved 
in obscurity, viz., the semicircular canals. These are three small PRODUCTION AND PERCEPTION OF SOUND. 
377 
tubes, represented at c, Fig. 186. They are each bent in the 
form of a semicircle and arranged to occupy three planes at 
right angles to each other. As they embrace the dimensions of 
length, breadth, and thickness, it has been supposed that they 
determine the direction whence sounds reach the ear. This 
may, however, be accomplished in other ways as, for example, 
by biaural audition. In connection with this question, Prof. 
Graham Bell has published an interesting memoir in the “Ameri- 
can Journal of Otology.” From this, the following deductions 
may be drawn; Ist, The perception of the direction of a source 
of sound is possible by a single ear. 2d. It is more perfect by 
biaural than by monaural observation. 3d. It is more accurate 
in the axial line of the ears. 4th. The error increases with the 
departure from this line, until at 90° from the axial line it may 
amount to 180°. The experiments were made in a room, and 
represent the results obtained under conditions influenced by 
reflection from the walls. 
437. The Audiphone is an instrument contrived by Mr. R. G. 
Rhodes, of Chicago. As its name indicates, it is intended to 
improve the hearing in persons partially deaf. In its original 
form it consists of a thin sheet of ebonite fashioned into the form 
of a fan. One side of this is curved by strings which pass from 
its upper margin to the handle. When in use the convex 
surface is turned away from the person, and the edge pressed 
against the front teeth of the upper jaw. 
In a modified form suggested by Colladon, a strip of elastic 
card-board, known as satin-board or shalloon-board, is used. 
The edge where pressed against the teeth is varnished. 
Another modification consists in the use of birch-wood veneer; 
this is steamed and bent into the same shape as the instrument 
of Rhodes, and does not require the use of strings. 
For description of the telephone, the student is referred to 
(897). 
437 A. The Photophone This instrument, the discovery of 
Rrof. Graham Bell, is thus described by S. P. Thompson in 
“Uature.” “It bears the same relation to the telephone as the 
heliograph bears to the telegraph. You speak to a transmitting 
instrument, which flashes the vibration along a beam of light 
to a distant station where a receiving apparatus reconverts the 
light into audible speech. As in the case of that exquisite in- 
strument, the telephone, so in that of the photophone, the means 
to accomplish this are of extreme simplicity.” 
“ The transmitting device consists of a plane silvered mirror of 
thin glass or mica. Against the back of this flexible mirror the 
speaker’s voice is directed; a powerful beam of light is caught 378 
ACOUSTICS. 
by a lens from the sun and directed upon the mirror, so as to be 
reflected straight to the distant station. This beam of_ light is 
thrown by the speaker’s voice into corresponding vibrations. 
“At the distant station the beam is received by another mirror, 
and concentrated upon a simple disk of hard rubber fixed as a 
diaphragm across the end of a hearing tube, flhe intermittent 
rays throw the disk into vibration in a way not yet explained, 
yet with sufficient power to produce an audible result, thus re- 
producing the very tones of the speaker. Other receivers may 
be used, in which the variation in electrical resistance of selenium 
under varying illumination is the essential principle. The ex- 
perimental details have been worked out by Prof. Pell in con- 
junction with Mr. Sumner Tainter. They have discovered that 
other substances beside hard rubber, gold, selenium, silver, iron, 
paper, and notably antimony, are similarly sensitive to light.” 
“ The singular production of mechanical vibrations by rays of 
light is even more mysterious than the production of vibrations 
in iron and steel by changes of magnetization. It was, indeed, 
this latter fact which led the discoverers to suspect the analogous 
phenomenon of photophonic sensibility in selenium and in 
other substances. Hitherto, in consequence of the mere optical 
difficulties of managing the beam of light, the distance to which 
sounds have been actually transmitted by the photophone is less 
than a quarter of a mile, but there is no reason to doubt that 
the method can be applied to much greater distances.” SECTION VI. 
OPTICS. 
CHAPTER XVII. 
THEORIES AND SOURCES OF LIGHT. 
Optics and light defined—Theories of light—The ether—Vibrations in the ether, 
their rate—Sources of light—The sun—Energy of solar action, its cause— 
Stars, planets, and satellite?—Comets—Atmospheric sources of light—Phos- 
phorescence—Fluorescence—Calorescence—lncandescence and oxyhydrogen 
lights—Electric arc and light—Motion and light—Combustion or chemical 
action—lllumination by gas flames—Forms of gas burners—lllumination by 
flames from fluids—lllumination by flames from solids—Constitution of flame 
—Light and life. 
438. Optics and Light Defined.—The study of phenomena con- 
nected with light, and their application, is called optics. Light 
18 that form of energy tohich by its action upon the retina or nervous 
coat of the eye produces the sensation of vision. 
Of the five special senses with which man has been endowed, 
that of sight is the most perfect. Seeing is believing, is one of 
fhe most ancient of all aphorisms. The sense of touch acts by 
direct contact. That of taste, by touching bodies soluble in saliva, 
omell, by drawing in vaporous or gaseous substances through 
file nostrils. The ear perceives bodies when in certain condi- 
tions of vibration, and at moderate distances. Vision, on the 
contrary, not only assures us of the presence of bodies when 
vibrating in such a manner as to emit light, but also when in 
the presence of others from which light is in process of emis- 
Sl°n. It is, moreover, vastly superior to hearing, as it can under 
proper circumstances make us acquainted with objects at almost 
infinite distances, and stive us accurate perceptions regarding 
their direction. 380 
OPTICS. 
439. Theories of Light. There are two theories of light. 
First, the emission or corpuscular theory. Second, the unclu- 
latory theory. 
The emission theory is generally accredited to Newton. It 
assumes that luminous bodies throw off particles or molecules 
with inconceivable velocity in straight lines, and that these 
falling upon the retina or sensitive nervous coat of the eye pro- 
duce the impression of light In view of recent ideas regarding 
“ radiant,” or “ ultra-gaseous matter,” it has been suggested 
that the corpuscular theory may be true, at least for the propa- 
gation of light through space, while the undulatory theory is 
correct as regards the relation of this form of energy to at- 
mospheric and other transparent terrestrial media. 
The undulatory theory was first promulgated by Huyghens and 
afterwards by Euler, who were unable to overcome the support 
given by Newton to the emission theory. It was, however, 
shown by Young and Fresnel that by means of the undulatory 
theory many phenomena of diffraction and polarization might 
be explained; this led finally to its general adoption. 
According to this theory, all space, both intermolecular and 
interstellar, is filled by an exceedingly attenuated medium, to 
which the name of the luminiferous ether is given. As sound 
comes to us by vibration or waves in the atmosphere, so light 
results from an inconceivably rapid vibration of the molecules of the 
luminous body; these vibrations, moreover, are transmitted through the 
luminiferous ether as wave-like movements, and fcdling upon the retina 
cause the sensation of light. 
In addition to these, an electro-magnetic theory of light has 
been brought forward by James Clark Maxwell. The main 
proof of this theory lies in the fact, that the rate at which an 
electro-magnetic wave disturbance would travel may be calcu- 
lated from electrical measurements. The rate at which light 
travels has been determined within very narrow limits of error. 
The two velocities are almost identical. Maxwell’s generaliza- 
tions on this subject were founded on Faraday’s experiments, 
showing that powerful magnets could rotate a beam of polarized 
light. 
In discussing this theory before the London Institution on 
December 6, 1880, Dr. Lodge says: “On the one hand, elec- 
trical energy may exist in either of two forms—the static form, 
when insulators are electrically strained by having had elec- 
tricity driven partially through them (as in the Leyden jar), 
which strain is a form of energy because of the tendency to dis- 
charge and do work; and the kinetic form, where electricity is 
moving through conductors, or whirling round and round them, 
which motion of electricity is a form of energy, because the THEORIES AND SOURCES OF LIG-HT. 
381 
conductors and whirls can attract or repel each other and thereby 
do work. 
“And, on the other hand, that light is the rapid alternation of 
energy from one of these forms to the other—the static form 
where the medium is strained, to the kinetic form, where it 
ftioves; it is just conceivable then that the static form of the 
energy of light is electro-static, that is, that the medium is elec- 
Ifically strained, and that the kinetic form of the energy of light 
is electro-kinetic, that is, that the motion is not ordinary mo- 
don, but electrical motion—in fact, that light is an electrical 
vibration, not a material one.” 
440. The Ether.—The idea of the ether, upon the existence of 
which the undulatory theory is based, was first introduced by 
Aristotle, who taught there were four mundane elements, earth, 
air, fire, water, and a fifth, or extra mundane, to which he gave 
the name of ether, “not because of its fire, hut because of Us ethereal 
circular movement.” Regarding the presence of some such ex- 
tremely attenuated medium in celestial space, Ganot says; 
“Although it presents no appreciable resistance to the motion 
°f the denser bodies, it is possible that it hinders the motion of 
the smaller comets. It has been found, for example, that 
Fncke’s comet, whose period of revolution is about years, has 
its period diminished by about 0.11 of a day at each successive 
rotation, and this diminution is ascribed by some to resistance 
°f the ether.” 
Concerning the nature of the ether, and the character of 
luminous vibrations, Deschanel observes: “ From the extreme 
facility with which bodies move about in it, we might be dis- 
posed to call it a subtle fluid; but the undulations which it serves 
f° propagate, are not such as can be propagated by fluids. Its 
Gastic properties are rather those of a solid, and its waves are 
analogous to the pulses which travel along the wires of a piano 
rather than to the waves of extension and compression by which 
sound is propagated through air. Luminous vibrations are trans- 
verse, while those of sound are longitudinal.” 
441. Vibrations in the Ether, their Rate.—“Vibrations are capa- 
ble of producing other effects than illumination. They consti- 
tute radiant heat, and create chemical effects, as in photography. 
Those of high frequency, or short period, are the most active 
ebemically. " Those of low frequency, or long period, have 
usually the most powerful heating effects; while those which 
affect the eye with the sense of light are intermediate.” 
. The rate of vibration also varies with the color of the light, 
111 the case of red light being 482,000,000,000,000 or 482 (unit) 
12 per second; and for violet 707,000,000,000,000, or 707 (unit) 382 
OPTICS. 
12. In like maimer, the wave length varies, being about g-4 *0- 
inch for red, and for violet light. 
As with sound, amplitude of vibration increases intensity, so 
with light, brilliancy is dependent upon an augmentation of the 
amplitude of vibration. 
An advantage arises in the study of light at this point, as the 
visibility of its course through smoky air enables us to illustrate 
many properties which it possesses in common with heat. The 
latter may, therefore, be better understood after the former has 
been examined. 
442. Sources of Light.—The most convenient plan to adopt in 
the consideration of this subject, is to divide all sources into 
natural and artificial. The sun, the chief source of the energy 
which comes to this earth from the exterior, heads the list as 
being the most important. With it we may associate the stars 
and nebulae, which are self-luminous. Then among celestial 
bodies comets would follow, shining partly by intrinsic light 
and partly by reflection; then the planets and their satellites, 
which give out only reflected light. 
Following upon celestial are the atmospheric natural sources, 
as meteors, lightning, and auroras, which originate their own 
light, the first by combustion, the others by electric action ; and 
cloudlight, twilight, and rainbows, which are modifications of 
sunlight, resulting from reflection and refraction. To these, 
certain terrestrial sources, as phosphorescent and fluorescent 
actions, are to be added. 
Among artificial sources, the Ist, from its simplicity and uni- 
versal application, is combustion, whether of gas, oil, solid fat, 
wax, wood, or coal. 2d, on account of its intrinsic brilliancy, 
the electric arc. 3d, ignition either by the electic current, or 
by heat from an oxyhydrogen flame, or other source. 4th, 
mechanical action, as the impact of a bullet, or indirectly 
through intervention of magnetism and electricity, as in lights 
developed by dynamo-electric machines. 
443. The Sun.—The distance of the sun from the earth was 
formerly given at 95,000,000 miles, recent experiments and cal- 
culations put it about 91,500,000 miles. Its diameter is 865,000 
miles. Its mean density, one-quarter that of the earth. 
As regards its structure, various opinions are held. Some 
conceive that it consists of a dark internal core, outside of this 
are envelopes, the first being the photosphere, or light-emitting 
layer; exterior to this the chromosphere, and outside of all, the 
corona, extending a million miles or more. 
Regarding the physical condition of the material which emits 
solar light, Professor Tait, after discussing the formation of THEORIES AND SOURCES OF LIGHT. 
383 
dark absorption lines in a spectrum, and the existence of these 
lines in the solar spectrum, says, page 219: “We arrive, there- 
fore, at the conclusion that the sunlight must have come origin- 
ally from some black body, or opaque substance, which is in- 
tensely self-luminous, and which may be either in a solid or 
m a liquid state—possibly even in the state of extremely com- 
pressed gas. However this may he, the source of light in the 
sun, whatever it is, must, in so far as we can see, give off all 
kinds of radiations, so it is practically a black body.” Again, 
page 248, he adds: “The source of sunlight may not be a solid 
or even liquid globe—it may be merely a great thickness of very 
hot and highly compressed gas; in fact, it seems quite possible 
that no portion of the sun may be as yet even liquid.” 
Of the chemical nature of the materials composing the sun 
our knowledge is still imperfect, owing to changes in the 
spectra yielded by various elements under different tempera- 
tures, and other causes. For information regarding these the 
student is referred to the admirable paper of Lockyer, in “Na- 
ture,” vols. xxii. and xxiv.; and of Prof. Young, “Am. Journal 
of Sciences and Arts,” vol. xii. page 321. It may, however, be 
said that a sufficient number of coincidences between the dark 
lines of the solar spectrum and the lines yielded by different 
metals have been obtained to show that the majority of 
metals exist in the sun. Regarding the non-metallic elements, 
opinion varies. In the case of oxygen, certain well-known lines 
which I submitted to photographic examination, are represented 
by exceedingly faint dark lines in the solar spectrum. These 
only appear when dispersion is very great, and the slit used in 
forming the spectrum exceedingly narrow. See “Am. Journal 
of Sciences and Arts,” vol. xvi. page 256, and vol. xvii. page 448. 
444. Energy of Solar Action, its Cause.—Since sunlight is asso- 
ciated with heat, the latter affords us means of making an 
estimate of the energy of the actions taking place in our central 
luminary. The experiments and computations of Pouillet and 
Herschel show that the heat received by the earth from the sun 
is sufficient in one year to melt a layer of ice about one hundred 
feet in thickness, covering the surface of the earth. On this 
basis, since “ the earth occupies only a very small extent in space 
as viewed from the sun; if we take into account the radiation 
in all directions, the whole amount of heat emitted by the sun 
will be found to be about 2,100,000,000,000 times that received 
by the earth, or sufficient to melt a thickness of two-fifths of a 
mile of ice per hour over the surface of the sun,” 
Concerning the production of this immense quantity of heat, 
and also of light, three hypotheses have been advanced. The 
first was that of chemical combination or combustion, this can 384 
OPTICS. 
now scarcely be said to have any upholders. Regarding the 
others, Beschanel says, “ The only causes that appear at all 
adequate to produce such an enormous effect, are the energy of 
the celestial motions, and the potential energy of solar gravita- 
tion, The motion of the earth in its orbit is at the rate of about 
96,500 feet per second. The kinetic energy of a pound of 
matter moving with this velocity is equivalent to about 104,000 
pound-degrees Centigrade, whereas a pound of carbon produces 
by its combustion only 8080. The inferior planets travel with 
greater velocity, the square of the velocity being inversely as 
the distance from the sun’s centre, and the energy of motion is 
proportional to the square of velocity. It follows that a pound 
of matter revolving in an orbit just outside the sun would have 
kinetic energy about 220 times greater than if it travelled with 
the earth. If this motion were arrested by the body plunging 
into the sun, the heat generated would be about 2800 times 
greater than that given out by the combustion of a pound of 
charcoal. We know that small bodies are travelling about in 
the celestial spaces, for they often become visible to us as 
meteors, their incandescence being due to the heat generated by 
their friction against the earth’s atmosphere, and there is reason 
to believe that bodies of this kind compose the immense circum- 
solar nebula called the zodiacal light, and also, possibly, the 
solar corona which becomes visible in total eclipses. It is prob- 
able that these small bodies, being retarded by the resistance of 
an ethereal medium, which is too rare to interfere sensibly with 
the motions of such large bodies as the planets, are gradually 
sucked into the sun, and thus furnish some contribution towards 
the maintenance of solar heat. But the perturbations of the 
inferior planets and comets furnish an approximate indication 
of the quantity of matter circulating within the orbit of Mercury, 
and this quantity is found to be such that the heat which it 
could produce would only be equivalent to a fewT centuries of 
solar radiation.” 
“ Helmholtz has suggested that the smallness of the sun’s 
density—only one-fourth of that of the earth—may be due to 
the expanded condition consequent on the possession of a very 
high temperature, and that this high temperature may be kept 
up by a gradual contraction. Contraction involves approach 
towards the sun’s centre, and, therefore, the performance of 
work by solar gravitation. By assuming that the work thus 
done yields an equivalent of heat, he arrives at the conclusion 
that, if the sun were of uniform density throughout, the heat 
developed by a contraction amounting to only one ten-thousandth 
of the solar diameter, would be as much as is emitted by the 
sun in 2100 years.” THEORIES AND SOURCES OF LIGHT. 
385 
445. Stars, Planets, and Satellites.—Like our sun, the stars are 
m themselves luminous. Our present knowledge regarding 
them has been obtained chiefly by the study of their spectra. 
See spectrum analysis (647). Professor Tait gives the follow- 
ing as a summary thereof. 
“ When we compare the spectra of different stars with that 
of the sun, we come to some very curious conclusions. We find 
four classes of spectra, as a rule, among the different fixed stars 
which have seemed of importance enough to be separately ex- 
amined. The first class of spectra are those of white stars. 
Lou see an admirable example in Vega, and another in Sirius-, 
or the dog-star. All these white stars have this characteristic, 
that they have an almost continuous spectrum with few dark 
lines crossing it, and these few for the most part lines of hydro- 
gen. These stars are in all probability at a considerably higher 
temperature than the sun. Then you come to the class of yellow 
stars, of which our sun is an example. In their spectra you 
have many more dark lines than in those of the white stars, but 
you have nothing of the nature of nebulous bands crossing the 
spectrum such as you find in the third class; still less have you 
curious zones of shaded lines which you have in the fourth class 
ot stars. This classification seems to point out the period of 
life, or phase of life of each particular star or sun. When it is 
tormed by the impact of enormous quantities of matter coming 
together by gravitation, you have the very nearly continuous 
spectrum of a glowing white hot liquid or solid body (or, it may 
he, dense gas), the sole, or nearly sole, absorbent being gaseous 
hydrogen in comparatively small quantity, and the spectrum 
having, therefore, few absorption lines. As it gradually cools, 
more and more of those gases surrounding its glowing surface 
become absorbent, and so you have a greater number and variety 
°f lines. Then, as it still further cools, you have those nebulous 
bands which seem to indicate the presence of compound sub- 
stances which could not exist in the first two classes, because 
there the temperature is so high as to produce dissociation. 
Still further complexity of compounds will be found in the at- 
mospheres of the fourth class. But sometimes, as in the case 
°f temporary stars, a spectrum of the fourth class is suddenly 
crossed by the bright lines of hydrogen—showing either a last 
effort in the discharging of red flames, or a flicker due to some 
last chance impact of meteoric matter. So that we can study, 
as it were, not the succession of phases of life in any one par- 
ticular star, but different simultaneous phases in many; we can 
study some stars, as it were, starting into life, others getting 
older, others older and older; and we occasionally find a most 
remarkable circumstance happening with a star that has prac- 
tically died out—a star which is scarcely noticeable by the OPTICS. 
astronomer. Such a star occasionally has an outburst rendering 
it for a little time—sometimes for several years—as bright as 
Jupiter itself. One such case very luckily occurred within the 
spectroscope period. It was carefully examined by Huggins, and 
the result of the examination was to show that it was a star 
which had gone on cooling, or at all events had reached the 
lowest of its cooling stages, but suddenly became bright because 
of an outburst of hydrogen. Bright lines broke out across its 
spectrum, showing that the incandescent gas which was in its 
atmosphere was at a higher temperature than the star itself.” 
The planets which belong to our system and their moons or 
satellites, all shine by reflected light, which originates in the 
sun. They do not, therefore, present any additional points of 
interest. The same may be said of other celestial sources of 
light, with the exception of comets. 
446. Comets.—Of all celestial phenomena, that ot the comet 
with its wonderful expanse of tail has always commanded the 
attention of men. In ancient days they were thought to be the 
evidence of the anger of an avenging deity, and men sought 
to avert impending doom by supplications and sacrifices. The 
belief is now almost universal, that by collision with one of 
these wanderers in space, the earth will meet its destruction. 
While we have neither space nor inclination to enter upon the 
discussion of so improbable an event, there is one point regard- 
ing the structure of comets of especial interest to physicians. 
It is derived from the study of their spectra. Regarding them, 
Professor Tait says: 
“ Such small comets as have been observed have given spectra 
which are extremely well worth noticing. These observa- 
tions seem to show, first of all, that the tail of a comet gives a 
spectrum like that of the moon, or other body illuminated by 
sunlight; in other words, that the tail of the comet is not self- 
luminous—that it shines by scattered sunlight. But the head 
of the comet shows in general a spectrum which indicates the 
presence of glowing gas; that is to sa}7, its spectrum is not con- 
tinuous, nor is it visibly intersected by dark lines. It consists 
of three bright bands of light, each sharply terminated towards 
the red end of the spectrum, and shading away upwards to the 
violet end. How Mr. Huggins, who first observed this, was 
struck by the resemblance of this spectrum (as he saw it in the 
telescope) to a terrestrial spectrum which he had noted before; 
and going over his note-book, he found it resembled the de- 
lineation of the spectrum of a hydrocarbon, such as olefiant 
gas, rendered incandescent lyy passing an electric discharge 
through it.” 
Setting aside the question of luminosity, that of the presence THEORIES AND SOURCES OF LIGHT. 
387 
of a hydrocarbon (which might possibly be an organic body) in 
the nucleus of comets, has given rise to the wildest speculations. 
It has been suggested, and not altogether in sport, that in some 
occult way a comet may first have brought the germs of life to 
the earth. 
447. Atmospheric Sources of Light.—Among the atmospheric 
sources of light (442), are auroras and lightning. These pos- 
sess a certain interest by virtue of their relations to the 
electric conditions of air, and the formation of ozone, or active 
oxygen; and also from their effects upon the compass, and dip- 
ping needles. Since their relation to man and his interests are 
rather through electric than luminous properties, we shall defer 
consideration of them to the domain of electricity. 
448. Phosphorescence may be defined as the power which many 
bodies possess of emitting light under the influence of certain 
stimuli. This is attended by little or no heat. The conditions 
favorable to the development of phosphorescence are: 
Ist. Spontaneous phosphorescences resulting: Ist, from ner- 
vous action; 2d, slow oxidation; 3d, decay of organic substances. 
Examples of the first are seen in certain articulates, as the glow- 
worm and firefly; in numerous acalephce, or jelly-fish, some of 
which are very large; in minute rhizopods; certain tropical 
animalcules emit a luminous matter so diffusive, that when 
placed in a tumbler of water they illuminate the entire mass of 
fluid. 
Examples of production of light by slow oxidation are seen in 
fbe case of active phosphorus and of many of its solutions. 
Organic matter, both vegetable and animal, at a particular 
stage of decay emits light. Certain kinds of wood, among 
which is the willow, possess this property in a marked degree, 
and it is not improbable that to this cause the ignis fatui may be 
aftributed. Among animal structures many fish, as herring, 
Mackerel, smelt, when dead, often become phosphorescent in 
the dark. The same phenomenon has also appeared in the 
dying, and recently dead, human body. It disappears the 
moment putrefaction has fairly set in. 
2d. Mechanical action; like friction, cleavage, percussion, as 
when two quartz pebbles are rubbed or struck against each 
other, or when pieces of white sugar are rubbed together or 
broken in the dark. 
3d. Heat. In the case of many minerals, temperatures of 
300° F., or less, suffice for the development of phosphorescent 
light. Among such bodies are certain diamonds, and particu- 
Jarly chlorophane, a species of fluor-spar. 388 
OPTICS. 
4th. Electricity; especially in the case of sparks from the 
frictional machine and induction coil. The substances which 
become luminous by the action of this agent are generally those 
which attain this property when submitted to sunlight. 
sth. Insolation. Many substances exposed to sunlight become 
phosphorescent in the dark; diffuse daylight causes the same 
result in a less degree. This was first observed in the case of 
the sulphide of barium or Bolognese phosphorus in 1604. 
Since then many other substances have been added to the list, 
their power being in the order their names are given. 
Sulphide of calcium. 
Sulphide of strontium. 
Yellow and other diamonds. 
Fluor-spar. 
Cyanide of calcium. 
Many strontium compounds. 
Many barium compounds. 
Many magnesium compounds 
Paper, dry. 
Silk. 
Calcareous concretions. 
Chalk. 
Apatite. 
Heavy-spar. 
Nitrate of calcium, dry. 
Chloride of calcium, dry. 
Cane and milk sugar. 
Amber. 
Teeth, etc. 
Variously colored lights act differently with substances. The 
tint of the light of a phosphorescent body varies with the manner 
of preparation. The duration is also very changeable, from a 
few seconds in some, to thirty hours in the cases of the sul- 
phides of calcium and strontium. 
449. Fluorescence is by many confounded with phosphorescence. 
The term is applied by Stokes to the fact that certain bodies 
possess the property of changing the refrangibility (490) of the 
rays falling upon them. Among such substances especial men- 
tion is made of solution of the sulphate of quinine, which renders 
the invisible ultra-violet rays of the spectrum visible. A similar 
result occurs when these rays fall upon paper impregnated with 
sesculine (from the horse chestnut), or with alcoholic solution of 
stramonium. The crystalline lens of the eye is also slightly 
fluorescent. Among dense solids which possess this property is 
canary colored uranium glass. 
In the majority of instances, fluorescence arises by the action 
of the more refrangible or ultra-violet rays, which undergo a 
diminution in refrangibility, but is not confined to these. While 
glass absorbs the more refrangible rays, quartz allows their 
passage. If a prism and trough formed of quartz are used, 
and the spectrum received on paper imbued with solution of 
sulphate of quinine, two spectra are obtained, that on the qui- 
nine portion extending beyond the line 11, to a distance equal 
to the whole visible spectrum. 
Fluorescence may be shown without the use of a prism. Let 
light be admitted through blue glass into an otherwise dark THEORIES AND SOURCES OF LIGHT. 
389 
room, hold in the track of the blue light a test tube partly filled 
with solution of the sulphate of quinine, on which ethereal solu- 
tion of chlorophyle has been poured. By transmitted light the 
quinine will appear colorless, and the chlorophyle green, while 
by reflected light the quinine will be blue, and the chlorophyle 
red. 
By the electric light and quartz apparatus fluorescent spectra 
of great length may be obtained. Some flames of moderate 
illuminating power produce marked effects. Writing made 
with stramonium solution is invisible by daylight, but if illu- 
minated with the flame of burning sulphur, or sulphide of car- 
bon, it instantly appears. 
450. Calorescence is a term applied by Tyndall to the fact 
that invisible heat rays may be transformed into bright light if 
received upon certain opaque surfaces. His demonstration of 
this fact is as follows: The light from an electric arc is passed 
through a rock-salt cell containing iodine dissolved in sulphide 
of carbon. This stops all the rays of light, but allows the heat 
rays to pass freely. These being received upon a concave mirror 
are brought to a focus which is invisible, but the moment a 
piece of thin platinum foil is placed therein it becomes lumi- 
nous, emitting a white light which shows all colors of the spec- 
trum when viewed through a prism. In this case light is in no 
way the product of chemical action, as with numerous other sub- 
stances that might be used. The platinum comes out of the 
ordeal unchanged as far as oxidation is concerned. The light 
bas, therefore, arisen solely from the conversion of dark radiant 
heat into bright rays. 
451. Incandescence and Oxyhydrogen Lights.—The term incan- 
descence is generally used to indicate the emission of light by 
a solid or liquid by virtue of elevated temperature, and inde- 
pendently of any chemical action in the luminous body. In the 
preceding article on calorescence, the platinum is incandescent. 
The same effect is produced when it is plunged in the almost in- 
visible flame of pure hydrogen. 
Among the best examples of incandescence are the lights pro- 
duced when a burning oxyhydrogen jet impinges upon certain 
oxides, as lime, magnesia, and zirconia. These solid bodies 
under the intense heat become highly luminous. There is no 
proper chemical action, though a portion of the oxide under- 
goes volatilization, the zirconia less than the others. 
For the purpose of class room demonstration by the projection 
of photographs, or microscopic objects upon a screen, these 
lights are well adapted. They do not possess the intrinsic 
brilliancy of the electric arc, but they are steady, and not so 390 
OPTICS. 
trying to the eyes. By virtue of its low power of volatiliza- 
tion, the zirconia light offers the most satisfactory results. 
For the preparation of this oxide, and the formation of pencils 
or cylinders suitable for the oxyzirconia light, the student is 
referred to an article I published in the “ American Journal of 
Sciences and Arts,” for Sept. 1877, page 208. 
Another, and very interesting example of incandescence re- 
sults when an electric current is forced to pass along a narrow 
conductor, as, for example, a thin platinum wire, or a thin 
channel of charcoal enclosed in a vacuum, or an atmosphere 
which is a non-supporter of combustion. The recent applica- 
tion of this method for artificial illumination is well known. 
In all the cases cited, analysis of the light by a prism shows 
a continuous spectrum, containing all seven colors, though there 
is more or less variation in intensity in different regions. A 
magnesium light, being very rich in the more refrangible and 
chemical, and the zirconian in the less refrangible and heat 
rays. 
Incandescence in liquids does not show any great difference 
from that in solids. The phenomena are best seen in molten 
metals the volatilizing point of which is sufficiently high. 
Gases and vapors may also be rendered incandescent by means 
of electricity; especially is this the case when the spark from 
an induction coil is employed, and a condenser intervened in 
the course of the current. The spectrum, under these circum- 
stances, ordinarily consists of certain colored bands or lines. If, 
however, the gas is compressed, and the temperature sufficiently 
intense, there is reason to suppose that the spectrum may be- 
come continuous, as with the photosphere of the sun, which is 
generally thought to consist of highly condensed gaseous matter 
at an exceedingly high temperature. 
452. Electric Arc and Light.—When the poles of an electric 
battery are brought together and then separated, the current of 
electricity flows across the break (providing it is not too great 
for its strength), and produces the most' brilliant of all artificial 
lights. Any conductor will answer for the formation of the 
electric arc, but for its continuation for a length of time only 
the most infusible substances can be employed. It is, there- 
fore, found, in the practical application of this light, that rods 
made of gas-carbon are to be preferred to all others, on account 
of the comparative incombustibility, and resistance to volatili- 
zation. 
Even in the electric arc conveyance of matter from one pole 
to the other takes place. It is, therefore, not at all improbable 
that the light is that of incandescence either of a solid, liquid, THEORIES AND SOURCES OF LIGHT. 
391 
or gaseous body. This view is borne out by the fact, that 
the spectrum is continuous. 
453. Motion and Light.—When a ball from a heavy piece of 
ordnance strikes an iron target, at the moment of impact a 
bright flash of light is seen. Herein we tind the conversion of 
motion into light. At the same time heat is also developed, as 
is proven by the fact, that the temperature of minute portions of 
the missile, or target, are raised sufficiently high to cause their 
fusion. 
The practical conversion of motion into light is admirably 
illustrated in modern dynamo-electric machines. By their 
agency, energy derived from combustion, gravity, or any other 
source, is, through the intervention of magnetism, made to pro- 
duce electric currents. So great is the power of these currents, 
that they far surpass that of any electric battery thus far con- 
structed. The importance of this source of light cannot yet be 
estimated. Obtaining motion from falling water, or from tidal 
action, its cost after the construction of the necessary machinery 
is insignificant. Experiments have thus far shown its adapta- 
bility for out-door illumination, and any day may witness the 
perfection of means for its utilization for household purposes. 
454. Combustion or Chemical Action.—Though the burning of 
phosphorus and magnesium yield brilliant light, yet, from a 
practical point of view, only combustions in the air of bodies 
rich in hydrogen and carbon deserve our attention. Among 
these we may consider: Ist, illuminating and other kinds of 
gas; 2d, fluids, as different kinds of oils, alcoholic and other 
solutions; 3d, solids, as fats, wax, resins. 
The question of artificial illumination in dwellings, is one 
physicians cannot afford to neglect. Especially in diseased con- 
ditions of the eye is its consideration paramount. We shall, 
therefore, devote sufficient space to its examination, to give a 
clear account of the principles involved, and the best means for 
their application. 
455. Illumination by Gas Flames.—The simplest case of com- 
bustion is that offered by ordinary illuminating gas; for the 
sake of convenience, we may regard it as being practically pure, 
consisting of compounds of hydrogen and carbon. Such gas 
may be burned with three different results: 
Ist. If the supply of air is insufficient, an elongated smoky 
flame is produced, which possesses slight illuminating power. 
On lowering into this any cool surface, as, for example, a porce- 392 
OPTICS. 
lain capsule, it is instantly covered with a copious deposit of 
lampblack, or carbon, in a state of exceedingly tine subdivision. 
2d. If the gas is mingled with a sufficient proportion of air 
before ignition, as in the Bunsen burner, a non-luminous pale 
light is obtained; lowering a porcelain surface into this, it may 
remain therein for some time without the formation of any 
deposit. 
3d. By arranging the form of the issuing jet of gas to give 
proper exposure to the air, a highly illuminating flame is pro- 
duced, as with duplex burners. Lowering a porcelain surface 
into this, we again obtain the deposit of carbon or soot, though 
moderate in amount. 
From the consideration of these results we arrive at an ex- 
planation of the source of light in ordinary illuminating flames, 
and we find that, as in many other instances, it is produced by 
incandescence of matter at an exceedingly high temperature. 
Recalling the case of the non-luminous flame of hydrogen, 
and the immediate incandescence of the platinum foil when 
placed therein, let us apply the same experiment to the non- 
luminous Bunsen flame. At once the platinum glows, and 
light of considerable intensity is emitted. There is, therefore, 
in that flame sufficient heat to develop light. Wherein lies the 
reason of its non-appearance? 
The method employed for the production of the Bunsen 
flame consists in mingling the combustible gas with a consider- 
able proportion of air before ignition. By this operation both 
constituents of the gas are completely burned or oxidized by 
oxygen of the air. The hydrogen produces vapor of water, and 
the carbon, carbonic acid gas. At the temperatures and pres- 
sures reached in ordinary flames, neither of these bodies pos- 
sesses the power of emitting light to any extent when compared 
with that of a solid. Therefore, since the Bunsen flame does 
not contain solid matter, it is non-luminous; but the moment 
we place a solid, as platinum, therein, light is at once produced. 
When illuminating gas is burned with an insufficient supply 
of air, we may say that only the hydrogen has been consumed. 
The carbon of the gas not being oxidized, separates as smoke 
or soot easily collected on a cool surface on which the flame is 
caused to impinge. In this case, we have a certain degree 
of luminosity attending the presence of solid matter, but the 
temperature attained by the burning hydrogen is not sufficient 
to heat the carbon to the requisite degree for the copious 
production of luminous effect. 
In the third case, the supply of oxygen of the air is adjusted 
to produce the most intense degree of heat. The whole of the 
hydrogen and a portion of the carbon are burned in a small 
compass. The unconsumed carbon is, therefore, raised to a very THEORIES AND SOURCES OF LIGHT. 
393 
high temperature, and the luminous effect proportionately in- 
creased. 
In addition to facts given showing that luminosity of hydro- 
carbon flames is produced by the presence of particles of solid 
carbon therein, we quote the following summary by Prof. Barker, 
°t Heumasen’s argument on this point. 
“ Ist. The increased luminosity which chlorine gives to weakly 
luminous or non-luminous flames, is due to its well-known 
property of separating the carbon as such. 2d. A rod held in a 
flame is smoked only on the lower side, the side opposed to the 
gas stream; were the carbon there as vapor, as Frankland 
assumes, it would be condensed by a cooling action and so all 
around the rod. 3d. A body held in the flame is smoked even 
when it is in a state of ignition; this, therefore, cannot he con- 
densation of a vapor. 4th. These particles can be actually seen 
111 the flame when it is made to strike against a second flame or 
an ignited surface, the particles aggregating together to form 
visible masses. sth. The luminous portion of a flame is not 
very transparent, no more so than the layer of smoke of the 
same thickness which rises above a flame fed with turpentine. 
And, 6th, flames which unquestionably owe their luminosity to 
the presence of solid particles give a shadow with sunlight, 
precisely as do hydrocarbon flames; while luminous flames 
poniposed of ignited gases and vapors only, give no such shadow 
in sunlight. ‘Liebig’s Annalen,’ clxxxiv. 206, Dec. 1876.” 
To this theory of the dependence of luminosity upon the 
presence of solid matter at a very high temperature in flames, 
there are certain exceptions. Among these, we may mention 
the flame of arseniuretted hydrogen burning in air. Here we 
have a highly luminous result quite ind-ependent of the presence 
of any solid matter. It is true, that arsenious oxide is formed, 
hut this substance volatilizes below a red heat. All the products 
combustion are, therefore, in the gaseous state, and offer 
ovidenee that in certain conditions gases or vapors may be 
luminous, and not under very great pressures or temperature. 
456. Forms of Gas Burners. Ordinary illuminating gas is 
usually burned from jets called fish-tail or fan-lights. In the 
former, the apertures from which it escapes are circular, with 
two streams impinging upon each other producing a thin sheet 
of gas, which on ignition gives a flame resembling the tail of a 
hsh. Under these conditions of combustion, when the supply 
and force are properly regulated by a stop-cock a very high 
temperature, yielding a satisfactory degree of illumination, is 
the result. 
In fan-light burners the aperture of escape is in the form of 
a slit, sometimes double. The manner of action is similar to 394 
OPTICS. 
the fish-tail; the flame, however, is much broader, being in the 
form of a fan. In duplex burners two flames burn side by side. 
They may be either gas or kerosene. 
In these varieties the character of the material forming the 
jet sooner or later has a marked influence upon the form ot the 
flame. If the tip is of brass or other metal, it becomes corroded, 
the jet is changed and the gas not burned to the best advan- 
tage. It is true the openings may be cleansed, but after this has 
been done a few times, they become enlarged and no longer 
work well. To avoid this difficulty jets are made of lava, which 
does not undergo change, and may be freed from dust without 
alteration of form. 
While the fish and fan tips answer perfectly well for ordinary 
purposes of illumination, the flickering or irregular manner in 
which they consume gas is a serious objection against their use 
by the student. To avoid this, and at the same time procure a 
more intense and whiter light, the Argand burner was con- 
trived. It consists of a series of small openings arranged in the 
form of a ring, air having access to the interior and exterior of 
a hollow cylinder of flame. By means of a glass chimney the 
draught or supply of air is increased, and a more intense heat 
and greater illuminating powder attained. At the same time 
the flame is perfectly steady, and the injurious effects ot flick- 
ering avoided. When used with a porcelain or ground glass 
shade or globe this form gives the best light for the student 
and reader. 
457, Illumination by Flames from Fluids is one of the earlier 
methods for obtaining artificial light. The most ancient form 
of lamp, which is still in use in the south of Europe as a night- 
light, consists of a hutton-like disk of wood through which a 
short piece of cloth or coarse thread is passed. This is floated 
upon the surface of oil placed in a cup, and answers as_ a wick 
when ignited. With the common oil lamp, all who live in rural 
regions are familiar. It is a mere modification of the preceding. 
Before petroleum and kerosene were introduced as sources 
of artificial light, it had been found that the best, purest, and 
brightest flame was obtained by burning oil freely supplied to a 
hollow cylindrical wick, in the interior of a glass chimney. No 
light has ever surpassed that of the Carcel or mechanical lamp, 
the action of which was based upon this principle, the oil being 
pumped up to the wick by machinery driven by clock-work. 
Rape seed or other vegetable oils are best suited to these lamps. 
In the so-called student’s lamp, a similar free supply of com- 
bustible is obtained by placing the reservoir of oil in such posi- 
tion that the supply of fluid is assisted by gravity, Fig. 187. _ 
The light given by the modern kerosene lamp is admirable m THEORIES AND SOURCES OF LIGHT. 
395 
its character. The method of combustion is that employed in 
the Carcel and student’s lamps, an increased rate of burning 
being obtained by means of a glass chimney. The supply of 
air, however, requires greater care in its regulation. The best 
results are attained by increase or diminution in the quantity of 
air, by increasing or diminishing the size of 
the openings through which it passes. The 
proper adjustment of the shield through 
which it is thrown upon the wick, is also 
necessary. 
The Argand, kerosene, Carcel, and 
student’s lamp flames, should be softened 
by porcelain or ground-glass shades. The 
light should also be prevented from falling 
upon the eyes, by means of opaque shades 
of paper or other suitable material. Especial 
attention must be paid to this precaution 
when eyes are weak or sensitive. 
In the combustion of oil the fluid is prac- 
tically a compound of hydrogen and carbon, 
and is converted into a gaseous body as the 
action goes on. The source of the luminous 
Fig. 187. 
Student’s lamp. 
effect is, therefore, virtually the same as with ordinary illuminat- 
ing gas. The method to be followed is to regulate the supply 
of air to burn the hydrogen completely, and the carbon in part. 
The combustion action should be kept within the narrowest 
limits, in order to gain the highest temperature, and thereby 
force the remaining portions of carbon to emit light of the 
greatest intensity. In addition to natural oils and naphthas, 
solutions of various combustible bodies in alcohol and other 
fluids have been used. Among these, camphene may be men- 
tioned. They have, however, now been generally supplanted by 
the different petroleum derivatives. 
458. Illumination?- by Flame from Solids.—The first attempt 
of man to utilize combustion for artificial light was doubtless the 
torch, made either of wood naturally rich in resin and similar 
compounds of hydrogen and carbon, or reeds and rushes dipped 
in melted tallow. Even now, savage people resort to this method 
of obtaining artificial light. 
Prom the rush light to the candle, the step was natural, and 
though there are many flames far more brilliant than that from 
a wax candle, no one is so well adapted to the illumination of 
file human countenance. Therefore, it still holds its own at 
entertainments in the houses of the wealthy, ladies of fashion 
well knowing that under its light they appear to the best ad- 
vantage. 396 
OPTICS. 
In recent times various solid fats, resulting from tlie distilla- 
tion and refining of crude petroleum, have been substituted for 
tallow and wax in making candles. 
The manufacture of a perfect candle requires especial atten- 
tion, as regards the manner in which the wick is woven. That 
it may burn to the best advantage, the tip of the wick must 
be consumed at the proper rate, otherwise a smoky flame is 
produced. In the days of our forefathers, a pair of snuffers 
for removal of the charred tips were provided, but candles of 
modern times snuff themselves. This result is attained by the 
ingenious device of weaving the wick 
in such a manner that, as the candle 
burns, it turns to one side and the tip is 
consumed on the margin of the flame, 
where the heat is very intense and sup- 
ply of air copious. 
The philosophy of combustion in a 
candle is the same as in a lamp. The 
first action of the flame is to melt a 
portion of the solid fat or wax. A minia- 
ture lamp is thus formed, from the small 
reservoir of which the wick, by its capil- 
larity, raises the melted oil. 
As in the lamp, oil is converted into 
gaseous matter before it is burned, so 
is it in the candle. Of this we may 
satisfy ourselves by taking a tube of 
moderate diameter, B, and, holding it 
inclined, Fig, 188, place one end in 
the interior of a candle flame A. If it 
has been previously warmed, an up- 
ward current of gaseous matter traverses 
Fig. 188. 
Gas from candle flame. 
the interior, which can be lighted as it escapes from the upper 
extremity. The cause of luminosity is the incandescence of 
solid carbon at an exceedingly high temperature. 
459. Constitution of Flames.—lf we lower a sheet of coarse 
copper wire gauze into the flame of an alcohol lamp, it is 
stopped by the gauze, and we can look vertically down into the 
section. Under these conditions it appears to be ring-like, the 
interior being dark. There are no signs whatever of burning 
therein. Since the same result is obtained on the examination 
of all ordinary flames, we conclude that they are hollow, and 
that combustion is confined to the exterior. In this fact we find 
an explanation of the greater brilliancy when flames are forced 
to assume the form of thin sheets as in different kind of gas- 
jets, and in hollow burners of Carcel and similar lamps. THEORIES AND SOURCES OF LIGHT. 
Not only are flames hollow, but their interior is positively 
cold, compared with the temperature we should expect to find 
therein. For illustration of this, take a porcelain cup two 
or three inches in diameter, and fill with water nearly to the 
brim. On the surface pour a layer of ether a sixteenth of an 
inch thick. Setting fire to the ether a copious blaze is produced. 
If a piece of phosphorus is placed in a spoon and ignited, it 
burns fiercely in the air, but the moment it is immersed in the 
interior of the flame, not only does combustion cease, but the 
phosphorus does not volatilize with any freedom, thus verifying 
the statement, that a flame is hollow, and its interior cool. 
An exception to this condition is found in oxy hydrogen flames, 
in which the gases are mingled before ignition, combustion 
taking place through and through. Such flames are, so to 
speak, solid, and therefore we understand why they possess 
such intense heat, and can produce the highly luminous effect 
witnessed when caused to impinge upon zirconia, and similar 
oxides. 
In the Bude light, formed by saturating ordinary illuminating 
gas with volatile hydrocarbons, and burning the product in a 
state of mixture with oxygen, an exceedingly brilliant light is 
produced. The cause of the intensity is evidently the high 
temperature reached by making the flame burn through and 
through, and confining it to the smallest possible limits. 
460. Light and Life.—ln closing this Chapter on the sources 
of light, we direct attention to the intimate relations between 
light and life. It is to the sun’s rays that plants are indebted 
for the energy by which they are enabled to decompose water 
und carbonic acid, and build tissues therefrom. It is true, as 
I stated in an article on “ Evolution of Structure in Seed- 
Hugs,” published in the “American Journal of Science and 
Arts,” for November, 1872, that plants can evolve all their 
structures in the dark. Yet in this act they depend entirely 
upon nutriment stored in the seed. No substantial gain in 
solid matter is made in any flowering plant until light falls upon 
its leaves and carbonic acid is decomposed. Plants being the 
source from which animals ultimately derive their sustenance, 
we may truly say that all life upon our globe results from 
energy given forth by the sun in the form of light and warmth. 
Independently of the question of nutrition, light appears to 
uxert a notable influence upon the life of young growing crea- 
tures, and even of adults. Evidence of this is found in the 
puny forms and blanched appearance of children living in dark, 
unwholesome places, compared with those where light has 
flee access. This fact was taken advantage of a few years 
ugo by a society in France, which collected miserable waifs born 398 
OPTICS. 
of scrofulous and syphilitic parents, and feeding them upon 
milk, kept them in the sunshine all day at the sea-coast. Under 
this treatment, most of these infants developed into healthy, 
hardy youngsters, and the results were attributed by those in 
charge as much to free exposure to light as any other cause. 
Reversing the relations, we discover (448) that many ciea- 
tures possess the power of emitting light. The significance of 
this production of light by nervous or vital action can hardly be over- 
estimated. It proves to us how intimate the connections are between 
all forms of energy, not excepting life itself. So strongly has this 
been impressed upon many minds, that there are those who 
think that life after all is only a specific form of energy, and 
that the “ vital spark” is a literal as well as metaphoric expres- 
sion of the facts of the case. 
The recognition of the relation between light and life receives 
innumerable illustrations in the world of literatuie. In dealing 
with the question of condition and place of abode of the spirit 
after death, an ancient writer asks, “ Whither goeth the flame 
when it is puffed out? ” 
CHAPTER X Y 111. 
TRANSMISSION, ABSORPTION, AND INTENSITY OF LIGHT. 
Transparent and absorbent media—Propagation of light in homogeneous medium 
—Ray, pencil, and beam—Shadow and penumbra—lmages from small 
openings—Velocity of light—Qualities of light—Laws of intensities of light 
—Photometers The candle and other light units Relative intensities of 
different sources of light. 
461. Transparent and Absorbent Media.—I he term medium is 
understood to include space as well as gaseous, fluid, and solid 
bodies. Through the most perfect vacuum that can be formed, 
light passes as freely as through air, or any colorless gas; the 
mere fact that it allows the passage of luminous vibrations causes 
it to be regarded as a medium. 
In their relations to light, media are classified into transparent, 
translucent, and opaque. Transparent media are those which 
not only permit the passage of luminous rays, but also allow the 
outline and color of objects to be clearly seen through them. 
In this group, air, colorless gases, water, humors of the eye, TRANSMISSION, ABSORPTION, INTENSITY OF LIGHT. 
399 
glass, rock-crystal, and many other bodies are included. They 
are sometimes called diaphanous. Translucent bodies allow the 
passage of light, but do not permit definition of outline when at 
a short distance therefrom. Examples of this form are found in 
glass ground on both sides, porcelain, oiled paper, etc. They 
are called opalescent. Opaque bodies are those which cut off all 
passage of light, as wood and metals. By such substances it is 
said to be absorbed. It does not, however, disappear, but is 
converted into another form of energy, as, for example, heat. 
Transparency and opacity are, at the best, relative terms. 
Even the purest air reduces the brilliancy of the light which 
traverses it. Dense metals, as gold and silver, may be obtained 
in layers thin enough to be transparent, as in the process for the 
deposition of silver on glass in making silver mirrors. 
Regarding the absorbent action of air on the light traversing 
it, Bouguer gives the following results according as the angle of 
elevation of the sun varies. 10,000 is supposed to represent the 
intensity of light, if the air was absolutely transparent: 
Sun’s altitude. 
Intensity. 
Sun’s altitude. 
Intensity. 
0° 
6 
20° 
5474 
1° 
7 
25° 
6136 
2° 
292 
30° 
6613 
3° 
454 
40° 
7237 
4° 
802 
50° 
7624 
6° 
1201 
70° 
8016 
10° 
3149 
90° 
8123 
15° 
4535 
The table is of value as showing the great difference in the 
light transmitted during summer and winter, according as the 
sun varies in altitude. 
462. Propagation of Light in Homogeneous Medium.—A homo- 
geneous medium is understood to be one which has the same 
chemical composition, and the same density in all its parts. 
Through such, if it be transparent, light is propagated in straight 
lines. Of this, in the case of air, we may obtain proof by inter- 
vening any opaque object between the luminous source and the 
eye, when the light is at once obscured. Another and better 
demonstration is to place in line a series of screens, each having 
a small opening in the centre. While in a straight line, light 
is visible to the eye, but if one be moved ever so slightly out 
of position, it is at once obscured. 
As sound and heat radiate from their sources, so light passes 
out, or is propagated in radiant lines from a luminous point, 
therefore, these forms of energy are by some denominated 
radiant energy. 400 
OPTICS. 
463. Ray, Pencil, and Beam Defined.—A luminous ray is the 
direction along which light is propagated. In its true mathe- 
matical sense it has neither breadth nor thickness. It is the 
trajectory merely. 
A 'pencil of light is considered by many to be a portion of the 
rays issuing from a luminous point; in this form a pencil of 
light is composed of divergent rays. Others, on the contrary, 
call any path of light having a measurable section, a pencil; 
according to this view, it may be made up of either parallel, 
divergent, or convergent rays. 
By a beam of light, a pencil of considerable dimensions is indi- 
cated ; it may be parallel, divergent, or convergent. 
464. Shadow and Penumbra.—When an opaque screen is inter- 
vened between the ear and a source of sound, there is but slight 
diminution in intensity; whereas, in the case of a luminous 
point, the light is completely cut off, and a sharp shadow pro- 
duced. The cause of this phenomenon is the exceeding short- 
ness of light waves compared with the sound waves. The latter, 
by virtue of their length, are able to double around a corner, 
whereas the former pass in straight lines. 
In the discussion of the formation of shadows, two conditions 
are to be considered : Ist. Where light is emitted from a point. 
2d. Where it is given off by a body of greater or less dimensions. 
Fig. 189. 
Umbra. 
In Fig. 189, S represents a luminous point, and M an opaque 
body placed in the divergent cone of rays from the point S. The 
outline of the shadow cast under these circumstances upon the 
screen P will be sharply defined, as shown by the lines drawn 
from the luminous point to the screen; it is called an umbra. 
In Fig. 190 the source of light is a sphere represented at S L; 
the opaque body is at M FT. Under these conditions, the shadow 
differs from the preceding in that it is not separated by a sharply 
defined limit from the illuminated part of the screen, but 
between the two there is a dusky ring.* To this lighter ring- 
like shadow, the name of penumbra is given. The cause of its 
production is seen, if we draw lines from the limits of the 
luminous sphere, past the opaque sphere, to the screen P, Fig- TRANSMISSION, ABSORPTION, INTENSITY OF LIGHT. 
401 
190. We find that the strong shadow which would he cast by 
the pencil of light from S, has to contend with that which falls 
upon the screen from the pencil issuing from L; the shadow is, 
therefore, diminished in intensity at the margin, and the penum- 
bra formed. 
For sake of simplicity, we have in the discussion of shadows, 
conceived that the rays of light pursue an absolutely straight 
Fig. 190. 
Penumbra 
line past the opaque body. In actual fact, this is not so, they 
do undergo a slight deviation from the straight line. Of this, 
we shall speak at greater length in the discussion of diffraction 
(607). 
465. Images from Small Openings.—If one side of a thin box 
18 removed, and a pinhole made in a remaining side, on placing 
a candle flame opposite the small aperture, as in Fig. 191, an 
inverted image of the flame, A B, will be cast on the interior 
Fig. 191. 
Image through pinhole. 
°f the side of the box at ab, opposite the aperture. The course 
°f the rays and the cause of inversion are also evident. 
In the same manner, if a room is made perfectly dark, and 
a small opening pierced in the shutter, an inverted image of 
tbe landscape facing it will be cast upon the side of the room 
opposite the aperture. 
It is not necessary that this should be circular, a triangular 
opening, or any other shape, will produce the result equally 402 
OPTICS. 
well, providing it is small enough. Distance lends to the en- 
chantment, for the further away the object the more clearly or 
sharply is it defined. Of this, as well as the failure of the shape 
of the opening to affect the image, we have an example in the 
circular presentations of the sun produced wherever its light 
has passed through irregular openings between the slats of a 
shutter and fallen upon the opposite wall. If the wall receives 
the beam at any other angle than 90°, the form of the image is 
more or less elliptical. This can readily be corrected, by receiv- 
ing it upon a hook or screen held vertically to its track. 
466. Velocity of Light.—The first determination of the velocity 
of light was made by Iloemer, a Danish astronomer, in 1675. 
The method employed was by the observation of Jupiter’s 
satellites. The first satellite, E, is occulted or passes behind 
the planet J at equal periods of about forty-two and a half 
Fia. 192. 
Velocity of light. 
hours. When the earth passes from ato b, on the side of 
its orbit nearest to Jupiter, there is hut little difference in its 
distance from day to day, and, therefore, but little variation 
between two occultations. When, on the contrary, the earth in 
its revolution around the sun passes from T to T7 on the opposite 
side of its orbit, it is found that there has been a total retarda- 
tion of the actual from the calculated time of occulation of about 
sixteen and a half minutes. This represents the time required 
for the light to pass from one to the other side of the earth’s 
orbit. Taking the earth’s distance from the sun at 95,000,000 
miles, Roemer computed the velocity of light at 190,000 miles 
per second. At the modern estimate of 91,500,000 miles for 
the sun’s distance from the earth, the rate is 185,500 miles per 
second. 
About fifty years after Roemer’s determination, Bradley, an 
English astronomer, calculated the velocity of light from the 
aberration or apparent displacement of the stars. He found 
the rate to be ten thousand times greater than that of the earth 
in its orbit. Since the latter is about eighteen and a half miles TRANSMISSION, ABSORPTION, INTENSITY OF LIGHT. 
per second, the velocity of light would be 185,500 miles per 
second. 
In 1849, Fizeau determined the velocity of light by measuring 
the time required for its transit from Suresnes to Montmartre 
and back, a distance of 28,334 feet. The apparatus consisted of 
a toothed wheel capable of varied and rapid rotation. The 
teeth were of the same width as the spaces between them. 
The wheel being still, a beam of light was sent from one station 
to the other, and reflected therefrom by a mirror back to the 
tirst position. The wheel then being thrown into revolution, 
when its rate was sufficiently rapid, the light which passed 
through an interval between two teeth did not return soon 
enough to pass through the same interval, but was obstructed 
hy falling upon the projecting tooth. The rate of revolution 
then being doubled, the light again became visible by passing 
through the next interval beyond the tooth. The velocity of the 
wheel, the number of teeth, and the distance between the stations 
being known, the rate was computed at 196,000 miles per second. 
Hecent experiments by Cornu, made by Fizeau’s method and 
with more perfect instrumental means, gave a velocity of 185,420 
miles per second. This agrees closely with the figures obtained 
from the transit of Venus in 1874. 
In 1850, Foucault applied Wheatstone’s method by a revolving 
mirror to the determination of the velocity of light, and obtained 
the rate of 185,157 miles per second, which is less than that 
ordinarily assumed, but agrees closely with the recent determi- 
nations of the solar parallax. In these experiments the whole 
apparatus was contained in a small room, and the light traversed 
a > distance of about fourteen feet twice. In one series of 
trials a tube ten feet in length, filled with pure water, wras 
intervened in the track of the ray, when the velocity was found 
to be less than in air. This is a most important result of Fou- 
cault’s experiments, since it is regarded as a crucial test of the 
nndulatory theory that the velocity of light should be less in a 
more highly refracting medium. The details of Foucault’s 
method may be found in the works of Deschanel and Ganot. 
mecent determinations by Mr. A. A. Michelson, U. S. Havy, 
give 186,360 miles per second. 
. At the rate of 185,500 miles per second, it requires about 
eight minutes for light to pass from the sun to the earth, 
about four hours from Neptune, and ten years from one of the 
nearest fixed stars, 61 Cygni. Stars only visible through the tele- 
scope may be so distant as to require thousands of years for their 
light to pass to our globe. It is possible that in some cases they 
may have become extinct before it has reached it. 
467. Qualities of Light. —Luminous sensations present two 
characteristics which are generally referred to the rays them- 404 
OPTICS. 
selves. They are coloration and intensity. The rays do not 
possess these properties, but have characters which in their 
action upon the eye give the appearances in question. The 
subject of coloration will be dealt with after we have studied 
the spectrum. 
By the intensity of a light we mean its strength or weakness, 
cither on directly viewing it with the eye or in relation to 
its power to illuminate objects upon which it falls. Various 
methods have been devised for determining the relative and ab- 
solute intensity of different sources of light; their examination 
constitutes the art of photometry. 
468. Laws of Intensity of Light.—The greater the distance 
between a light and a surface, the less the intensity of illumina- 
tion. This is a well-known fact within the observation of all, 
and the law of diminution of intensity may be readily deduced 
from consideration of Fig. 193. Let 12 3 represent three sur- 
Fig. 198. 
Intensity of light. 
faces placed at the relative distances, 1, 2, 3, from a candle flame 
L, or other source of illumination. The dotted lines represent 
the course of the radiant lines from a luminous point in the 
flame, and the relative sizes of the surfaces. The actual amount 
of light cast upon the three is evidently the same, but’in the 
case of 2 it is spread over a space four times as great as in 1. 
Its intensity, therefore, in any part must be one-fourth of that on 
any part of 1. In 3it is diffused over a surface nine times as 
great as in 1, therefore, its intensity must be one-ninth. From 
this we find that the intensity of light is inversely proportional to 
the square of the distance from the luminous point. 
Two luminous bodies at different distances from a surface 
cannot illuminate the latter with equal intensity unless the 
further gives out more light, or has greater illuminating power. 
The intensity of a light at twice the distance being one-fourth, 
and at thrice one-ninth, it follows that if two flames produce 
equal illumination of a surface when one is twice as far off* as 
the other, the further must have four times the illuminating 
power of the nearer; or, if the illumination is equal when the TRANSMISSION, ABSORPTION, INTENSITY OF LIGHT. 
405 
distances are as one to three, then their illuminating power 
must be as nine to one. Therefore, when two sources of light produce 
equal illumination of two surfaces at different distances therefrom, the 
illumination poicers of the sources of light are in the ratio of the square 
of their distances from the illuminated surfaces. The application of 
this law will be seen in photometry. 
We have thus far examined only cases in which light falls 
perpendicularly. When it falls at an angle, experiment has 
shown that the law is as follows : The intensity of illumination 
when light falls obliquely upon a surface is proportional to the cosine of 
the angle which the luminous rays make with the normal, or perpen- 
dicular to the illuminated surface. 
469. Photometers.—Of these there are a number: Ist. Those 
acting on the principle of comparing illumination ; 2d. Those by 
comparing the intensity of shadows; and 3d. Those by the 
relative chemical effects of the flames or sources of light under 
examination. 
Bouguer’s 'photometer is based upon the first principle. It con- 
sists of an opalescent or translucent screen of white paper, 
Fig. 194. 
Bouguer’s photometer. 
ground glass, or thin porcelain, A, divided into two parts by a 
partition, Fig. 194. The two sources of light are placed on oppo- 
site sides of the partition B, and their distances adjusted until 
the two sides of the screen are equally illuminated. The dis- 
tances are then measured, when the illuminating power of the 
lights is as their squares. 
A modification of this method is represented in Fig. 195. 
AA' is a rectangular box about a foot long, one or two inches 
square in section, and open at both ends. At T, a tube opens 
mto it. The interior of box and tube are blackened. At the 
Position W, a wedge is placed, the section of which is equi- 
lateral ; it is covered with white paper. The flames to be ex- 
amined are then placed opposite the openings L and F, and their 
distances therefrom adjusted until the eye applied at the upper 
opening of the tube T, sees the two sides of the wedge equally 406 
OPTICS. 
illuminated. The distances of the lights from the upper edge 
are then measured, when the illuminating power is as the square 
of their distances therefrom. 
Fig. 195. 
Photometer, 
In Bouguer’s instrument the partition casts a strong shadow 
between the illuminated portions of the screen. In a modifica- 
tion made by Foucault, the partition is movable, and by with- 
drawing it to a greater or less distance, the dark strip may be 
made to vanish, when the bright portions being exactly con- 
tiguous are compared with greater precision. 
Humford’s photometer depends upon the second method for its 
principle of action. An opaque rod is placed at a short distance 
Fig. 196. 
Illumination photometer. 
from a screen, the two sources of light are then arranged, as in 
Fig. 196, so that each forms a shadow of the rod upon it. The 
lights are then moved until the shadows are of equal intensity. 
Since that from the lamp is illuminated by the candle, and that 
from the candle by the lamp, the illumination of the screen by 
the two sources of light is equal. The intensities of the lights 
are, therefore, as the squares of their distances from the screen. 
Bunsen1 s photometer acts by the illumination of a spot of grease 
upon a piece of bibulous paper. It is made with a solution of transmission, absorption, intensity of light. 
407 
spermaceti in naphtha. If a piece of paper, A, Fig. 197, with 
a grease spot upon it is illuminated by the candle B, placed in 
front, it appears dark upon a light ground. If by another 
light, C, from behind, it appears light upon a dark ground. 
When the flames are adjusted to illuminate it equally, the spot 
and the rest of the surface show no difference in appearance. 
This result having been attained, the intensities of the two lights 
Fig. 197. 
Bunsen’s photometer 
are as the squares of their distances from the paper. In a recent 
improvement the thickness of the paper is reduced and the 
effect of the spot better obtained. 
In another photometer devised by Wheatstone, a bead which 
executes a double system of revolutions is used, a rose-like re- 
flection of the lights compared is thus produced: The details 
of this are given in Ganot. 
Various chemical methods for the measurement of light have 
been suggested. Among these is the chlor-hydrogen photometer, 
first described by Prof. J. W. Draper, in the “ Philosophical 
Magazine,” and afterwards claimed by Bunsen and Roscoe. 
Another form, in which intensity of light was determined by 
its power to precipitate gold, is described by me in the “ London 
°n Philosophical Magazine ” for August, 1859. It is adapted 
for comparison of sunlight from day to day. In chemical pho- 
tometers results differ with the reagents employed, according 
as they are more sensitive to rays of different refrangibility. 
In the case of colored lights, Professor Rood has proved, by 
oxperiment, the correctness of Grassmann’s assumption, “ that 
the total intensity of the mixture of masses of differently colored 
fights is equal to the sum of the intensities of the separate com- 
ponents.” “ Am. Journal of Sciences and Arts, vol. xv. page 81. 
470. The Candle and other Light Units.—Since a photometer 
does not measure the quantity of light, but only the relative 
intensities of two lights under examination, the attempt is 
made to obtain what may be called quantitative results, by using 
a standard light for one of the flames under comparison. For 
ordinary purposes a standard candle is employed. “It is a sperm 
candle of six to the pound, and burning 120 grains per hour.” 
When a gas flame is tested against such a standard, the 408 
OPTICS. 
form or character of the burner, the pressure, temperature, and 
volume of gas consumed in a given time must all be determined. 
The value of the gas or other light is then given in terms of 
candlelight. If, as is the case with an ordinary gas flame, it 
has an intensity sixteen times that of a single standard candle, it 
is called a sixteen candle light. In like manner, electric lights 
are estimated at hundreds or thousands of candle power. 
For measurement of lights of feeble intensity, a unit, ob- 
tained by heating a platinum wire of definite size in a hydrogen 
flame produced under uniform conditions, was devised by me, 
and described in the “ Scientific American,” Oct. 21, 1871. 
471. Relative Intensities of Different Sources of Light.—The 
electric light from 50 large Bunsen cells, is one-fourth as strong 
as sunlight. Sunlight is about equal to the light of 5500 candles 
at a distance of one foot. It is 600,000 times as strong as moon- 
light, and 16,000,000,000 the strength of that from a Centauri, 
the third in brilliancy of all the stars. 
CHAPTER XIX. 
REFLECTION AND MIRRORS. 
Law of reflection from polished surfaces—Reflection from unpolished surfaces— 
Intensity of reflected light—Mirrors and process for silvering them—lmages 
from plane mirrors—Virtual and real images—Multiple images from plane 
mirrors—Deviation by rotation of mirror—Applications of plane mirrors— 
Spherical concave mirrors—Principal and conjugate foci—Real and virtual 
foci—Spherical convex mirrors—Formation of images by spherical mirrors 
—Spherical aberration and caustics—Parabolic mirrors—Cylindrical mirrors, 
anamorphosis—Application of curved mirrors. 
472. Law of Reflection from Polished Surfaces.—lf in the course 
of a ray of light through a given medium, a second is inter- 
vened, certain new phenomena arise. If the second is a trans- 
parent, or a translucent body, a portion of the light passes into, 
or traverses it, but in all cases a greater or less portion, after 
changing its direction, continues its course in the first medium. 
To this result the name of reflection is given. 
Reflection presents itself under various aspects, according as 
the surface producing it is more or less perfectly polished. We 
shall examine the two extreme conditions of perfect polish and REFLECTION AND MIRRORS. 
409 
exceeding irregularity. Between these limits all degrees are 
included. 
In the case of a perfectly burnished regular or specular sur- 
face, the laws for reflection of light are the same as for reflec- 
tion of motion, viz.: 
plane determined by the incident ray CB, 
and a normal or perpendicular N drawn 
to the reflecting surface M M' at the point 
of incidence. 
Ist. The reflected ray A B is in the 
Fig. 198. 
2d. The angle r made by the reflected 
fly with the normal (angle of reflection) 
is equal to the angle i which the incident 
fly makes with the same normal (angle of 
incidence). 
These laws may be easily demon- 
Reflection. 
strated by directing a horizontal beam from a projection lantern 
npon a polished surface, producing conditions as in Fig. 198. 
In reflection from regular or specular surfaces, the object seen 
is not the surface, but an image of the body which is the primary 
or secondary source of the light. When, for example, a pencil 
of sunlight falls on a mirror in a dark room, the more perfectly 
the light is reflected the less visible is the mirror. A perfectly 
polished surface, if it could be made, would be invisible. 
473. Reflection from Unpolished Surfaces.—When a beam of 
light falls upon an unpolished surface, its rays are reflected in 
all directions. It is diffused or scattered. It was formerly said 
to be irregularly reflected, but this is not the case; it obeys the 
laws of reflection, but since the surface is composed of project- 
ing particles which receive incident rays at all angles, when 
deflected they pass off in every direction and the body becomes 
a secondary source of luminosity. 
It is by scattered or diffused light that we are enabled to see 
and determine the position of bodies. When sunlight falls on 
a mirror, the eye .perceives not its image, but that of the sun. 
If flour, or any powder, be dusted on" the reflecting surface, 
injuring its polish, or power of regular reflection, as the image 
°f the sun diminishes in intensity that of the mirror becomes 
better marked. By diffusion of sunlight by the air, places which 
do not receive direct light are brightened. In this manner, in 
the upper strata of air before sunrise, and after sunset, the 
Phenomenon of twilight is produced. 
474. Intensity of Reflected Light.—The power of reflection of 
a surface and consequent intensity of reflected light varies: 
Ist, with the brilliancy of the original source of light; 2d, with 410 
OPTICS. 
the perfection of polish; 3d, with the angle formed by the 
incident ray; 4th, with the nature of the substance—silver, for 
example, reflects more light than other metals; sth, the nature 
of the medium travelled by the ray before and after reflection— 
polished glass, for example, when immersed in water has its re- 
flecting power seriously impaired. 
475. Mirrors and Process for Silvering Them.—Mirrors are de- 
fined as bodies with polished surfaces which reflect objects pre- 
sented to them. The place at which the body appears to be 
situated is called its image. According to their shape, they are 
called plane, concave, convex, spherical, parabolic, conical, etc. 
The mirrors used by the ancients were made of speculum 
metal, an alloy of tin, copper, and other metals. Modern look- 
ing-glasses were introduced in the 12th century. They are 
polished plates of glass, coated on the back with an amalgam 
of tin and mercury. Since pure silver possesses a higher 
reflecting power than other metals, various processes have 
been contrived for depositing it on glass. The coating as 
formed presents a great advantage over the ordinary amalgam 
in that it may be polished and used as a true specular surface. 
When so burnished either side may be employed. 
The method I have generally employed, and with excellent 
results, is known as the Rochelle salt or Cimeg’s process. 
476. Images from Plane Mirrors.—The effect of a plane mirror, 
as is well known, is to produce behind it images which accu- 
rately represent in size and form the objects in front. This 
result may be explained according to the laws of reflection. 
In the figure a divergent pencil of light proceeds from a 
luminous point at the top of a candle flame A, and is reflected 
from the mirror at B. After reflec- 
tion the rays on entering the eye 
have the same divergence as when 
they impinged upon the mirror, and 
if produced backwards meet at a 
point C, which is the position of the 
image of the top of the flame. In 
like manner, every point appears in 
its proper position, and a complete 
image is observed. 
The images produced by plane 
mirrors are erect images, but they 
are not exact duplicates of the ob- 
jects, since they differ from them 
exactly as the right hand differs 
Fig. 199. 
image in plane mirror. 
from the left. This may be readily seen, if we examine the 
reflected image of a page of print in a mirror, when it appears REFLECTION AND MIRRORS. 
411 
as when viewed through the back of the page, or like the sur- 
face of the type from which it was printed. 
477. Virtual and Real Images.—According as rays are divergent 
or convergent after reflection, so do the images differ. In the 
experiment represented in the preceding article, the rays after 
leaving the reflected surface, enter the eye as a divergent pencil; 
if, however, they are supposed to he projected through the mirror 
they meet at a point. The eye is then affected as though the 
rays proceeded from this point; and though seen, there is no 
real image formed. Rays do not come from the other side of 
tile mirror. These are called virtual images. 
When, On the contrary, the rays converge after reflection, as 
in concave mirrors, they do meet in front of the mirror, on the 
same side as the object, and when received upon a screen 
properly placed, a real image is formed. These facts may be 
concisely stated as follows ; Real images are 'produced by the re- 
flected rays themselves; virtual images by their prolongation backwards. 
478. Multiple Images from Plane Mirrors,—While metallic or 
specular mirrors give a single image, ordinary glass mirrors give 
a series, as may be seen by examining the reflection of a candle 
flame in an oblique line in a looking-glass. Images of different 
intensities viewed under these circumstances result from reflec- 
tions from the anterior and posterior surfaces of the glass, and 
from secondary reflections from one to the other. 
. ft an object, O, be placed between two parallel mirrors, and 
viewed as delineated in Fig. 200, a great number of images are 
Fig. 200. 
Fig. 201. 
Parallel mirrors. 
Lateral inversion of image. 
perceived, of which a few only are shown. Theoretically the 
pnmber should be infinite, but since in. practice a portion of light 
18 tost at each reflection, they become dimmer and dimmer, and 
Anally disappear. If the surfaces are true and exactly parallel, 
they will be arranged in a straight line, as in the figure. But, 412 
OPTICS. 
if inclined at an angle, they appear to be on the circumference 
of a circle. Practical application of this fact has been made in 
the parallel adjustment of mirrors. If two plane reflectors are 
placed at right angles to each other as S S2, Fig, 201, three 
images of the object are produced; if the angle be made more 
and more acute, the number becomes greater and greater, and 
when parallel they are theoretically infinite, as stated above. 
Upon this principle of multiplication of images the kaleidoscope 
depends for its action. 
479. Deviation by Rotation of Mirror.—ln Fig. 202, A B repre- 
sents the edge of a plane mirror receiving the incident ray I C 
Fig. 202. 
perpendicularly. The ray will then 
he reflected back along the line I C. 
Let the mirror be turned or rotated 
about an axis passing through its 
face at the point C, until its edge 
assumes the position A' B', and 
forms the angle .A' C A, with its 
first position. The reflected ray will 
then pass off in the line C R, making 
with the normal, C FT, an angle, 
ICR, which is equal to I C I, the 
angle of incidence. The total devia- 
tion of the reflected ray is, therefore, 
double the angle I C FT or A C A', 
Effect of rotating mirror. 
through which the mirror has been turned. The same will be 
found for any other amount of rotation. It, therefore, follows 
that: When a 'plane mirror is rotated in the plane of incidence, the 
direction of the reflected ray is changed by double the angle through 
which the mirror is turned. 
480. Applications of Plane Mirrors.—Among the applications 
of plane mirrors are: 
Ist. For toilet purposes, this has come down from the most 
ancient times. Two or more mirrors are sometimes used, 
enabling a person to examine the back and sides of the head 
and figure. 
2d. In drawing rooms, to increase the apparent size of the 
apartment, and multiply the objects therein by repeated reflec- 
tions. 
3d. By physicians, in the laryngoscope, for examination of the 
larynx or other cavities not easily reached by direct vision; and 
by dentists, for examination of the posterior surface of teeth. 
In the endoscope a plane mirror is applied to examination of the 
urethral canal. REFLECTION AND MIRRORS. 
413 
4th. In the microscope, to direct the light along the axis of the 
instrument. 
sth. In the heliostat, the use of which is to keep a beam of 
sunlight permanently in a straight line; the result is obtained 
by driving a plane mirror by clockwork, in a manner to pro- 
duce the desired result. Among heliostats, an excellent one is 
that of Pragmoski. Such an apparatus is absolutely necessary 
for microscope photography by sunlight. 
6th. Mance's heliograph is an instrument for giving signals at 
great distances by flashes of sunlight produced by a mirror. 
The system consists in giving flashes to the right and left. 
From these an alphabet is made up, as in the Morse telegraphic 
system of dots and dashes. In this way messages at the rate of 
twelve words per minute have been sent to a distance of forty 
miles in fine weather. 
7th. The measurement of small angles, as in the deflection of 
magnetic needles, is often made to the best advantage by the use 
of a mirror, as represented in the figure. The observing tele- 
scope A 0 is attached to a scale s s, the axis of the instrument 
Fig. 203. 
Measurement of small angles. 
corresponding to zero of the scale. At NS a magnet is sus- 
pended, bearing a'mirror m m, arranged with its plane perpen- 
dicular to the axis of the magnet H S. 
The apparatus is adjusted to have the zero of the scale ap- 
pear on the cross wires of the telescope. When by any cause 
the magnet and its mirror are deflected, the image of some 
other figure on the scale appears. Suppose, for example, the 
figure at a represents the angle a c O, and it appears, then the 
actual deflection of the magnetic needle is one-half of this angle, 
according to the principle laid down in the article on deviation. 
In the goniometer, an instrument employed for the measurement 
°f the angles of crystals, the principle of reflection is also em- 
ployed. 414 
OPTICS. 
Bth. The sextant or quadrant, invented by Newton and re- 
invented by Hadley, is another example of the application of 
Fig. 204. 
this method, together with that 
of transparent or semi-transpar- 
ent mirrors. 
The essential parts of the in- 
strument are a plane glass mirror 
partially silvered and fixed to 
the frame at A, Fig. 204. This 
not only reflects light received 
in the direction A B, but also 
enables the observer to see ob- 
jects in the line A H through 
the telescope T, which is also 
stationary. A second mirror, B, 
is mounted on the axis of the 
pointer I, which traverses the 
graduated arc QP. When they 
are parallel to each other, the 
index is at P, the zero of the 
The sextant. 
scale, the incident ray H' B, parallel to H A, will, when it falls 
on B, be reflected along the line B A to A, and thence along 
A T to the observer at the telescope, who thus sees by two 
reflections, at B and A, the same objects at H that he views 
directly through the partially silvered mirror. 
Suppose it be desired to determine the altitude of the sun 
above the horizon. The. observer holds the sextant in such a 
manner that the rays of sunlight falling upon B are reflected 
to A, and produce an image in the eye at T. He then 
moves the arm I, until this sun image is made to appear on the 
horizon, as at H, through the partially silvered mirror A. The 
number of degrees through which the arm I has been moved 
over the scale to cause the coincidence of the images S and H 
is then read off. According to the preceding section on devia- 
tion by mirrors, this is double the angle that S and H actually 
form with each other; one-half the angle obtained, therefore, 
represents the angular height of the sun above the horizon. 
In practice the sextant is graduated to half degrees, which are 
valued in the enumeration as whole degrees. The correction 
mentioned is thus avoided, and the true result obtained by the 
actual reading. In addition to this device others, as dark glasses 
to reduce the brightness of the sun’s image, and a vernier, and 
reading microscope, in place of the pointer I, are employed. 
9th. In the determination of the altitude of a star, it is often 
difficult to fix the position of the true horizon. This is sur- 
mounted by a device known as the artificial horizon. A telescope 
provided with cross lines is mounted on a horizontal axis, to REFLECTION AND MIRRORS. 
415 
traverse a vertical circle which is carefully graduated. The 
instrument is turned to the star, and the position of the tele- 
scope read off on the circle. A cup containing mercury is then 
placed in front of the apparatus, and the reflected image of the 
star viewed therein, and brought upon the cross lines. The new 
position is then read off, when half the angle included between 
the two positions represents angle of altitude of the star above 
the horizon. 
10th. The device of a transparent mirror is sometimes resorted 
to in theatrical representations. A large mirror of unsilvered 
glass is placed at a suitable angle upon the stage, which is dimly 
lighted. Through this sheet of glass the audience sees every- 
thing upon the stage. Beneath, in such a position that it may 
be reflected to the audience, is the ghost or other object, bril- 
liantly illuminated. As this moves about, it appears, from the 
auditorium, to pass among the things and actors upon the stage. 
Thus the deception of the ghost in the play of Hamlet is pro- 
duced. By other and suitable arrangements, the illusions of 
the magic cabinet and disembodied head are accomplished, 
llth. The kaleidoscope invented by Sir David Brewster, and 
now used in the arts of design, is another application of reflect- 
ing property of mirrors. It consists of a tube in which two 
glass mirrors are inclined at an angle of sixty degrees to each 
other, and extending along its whole length. One end is closed, 
excepting a small hole in the centre, to which the eye is applied. 
The other is provided with two plates the outermost of ground 
glass. Between these a number of pieces of colored glass are 
placed. Directing the tube to the sky or other source of light, 
and revolving it while looking through the eye-hole, the pieces 
°t colored glass as they fall into new positions form symmetri- 
cal patterns which are very beautiful. 
By the introduction of a third glass mirror, thus forming a 
combination the section of which represents an equilateral 
triangle, effects equal to three simple kaleidoscopes are pro- 
duced. 
481. Spherical Concave Mirrors.—In a spherical mirror, as the 
term indicates, the reflecting surface is a portion of a sphere; if 
formed by the interior, it is called a concave ; if by the exterior, 
a convex mirror. 
The distances, C A, C M, C H, etc., represent the radii upon 
which it has been constructed, they are, therefore, called the 
radii of curvature. To the point C, the terms centre of curvature 
and geometrical centre are applied. The radius of curvature C A 
is called the principal axis. All other radii or lines passing 
through C, and touching the surface of the mirror are called 416 
OPTICS. 
secondary axes. The point A, at which the principal axis touches 
the mirror is called the pole. The angle M C IST, included between 
the extreme radii of curvature is the aperture. A section made 
by cutting it by a plane containing its principal axis is called a 
principal or meridional section. The section, Fig. 205, is of this 
description. 
The laws governing the action of spherical, are the same as 
for plane mirrors; the former is made up of an infinite number 
Fig. 205. 
Focus of spherical concave mirror. 
of plane surfaces, called elements. A normal to the curvature 
at any point is a perpendicular to the element at that point. 
Since all normals to the surface of a sphere pass through its 
centre of curvature, one may be readily constructed. 
482. Principal and Conjugate Foci.—Applying the principles 
laid down in the last paragraph to Fig. 205, let C B be a normal 
to a point on the surface of the mirror, and II B an incident 
ray to the same point; it will be reflected on the opposite side 
of the normal, and the angles HB C and C B F will be equal. 
In the case under consideration the incident ray H B is parallel 
to the principal axis. Take another ray, GD, also parallel to the 
principal axis; it obeys the law of reflection, and following the 
line D F cuts it at the same point as BF. In like manner, 
every incident ray parallel to the principal axis after reflection 
from a concave mirror of less aperture than ten degrees crosses 
it at F. The point of meeting of the rays in F, is, therefore, 
called the principal focus. 
Rays falling upon a mirror may be made to meet at other 
positions than that represented; therefore, foci receive special 
designations according to the manner produced. 
Where rays are parallel to the principal axis, it is formed 
upon that axis, and is called the principal focus. The distance, 
A F, of the principal focus from the surface of curvature is one-half 
of the radius of curvature. This distance is also called the principal 
focal distance of the mirror. 
Where rays are divergent, as from a luminous point, a 
brief application of the laws of reflection shows that their di- 
vergence will be diminished, but the character of the reflected REFLECTION AND MIRRORS. 
417 
pencil and position of the focus will vary greatly, according to the 
position of the luminous point. Three cases may be examined. 
Ist. When the point whence divergent rays issue is at the 
focus of the mirror, Fig. 205, the reflected rays will be parallel, 
tor this is simply a reversal of the process by which parallel 
rays were converged. If it is desired to produce a beam of 
parallel rays, it may be obtained by placing the source of light 
at the focus of a concave mirror. 
2d. If the luminous point L be moved along the principal 
axis to a point between the principal focus F and the centre of 
curvature C, the reflected raj's L K and L I will meet beyond the 
centre of curvature at L. Conversely, rays from a luminous 
point at L will converge at I within the centre of curvature. 
Since these two positions bear this mutual relation to each 
Fig. 206. 
Conjugate foci. 
other, they are called conjugate foci. If the luminous point is at 
the centre of curvature, since the rays are then normal to the 
surface of curvature C, they will be reflected back upon it, and 
the conjugate foci are in this case identical. In all cases where 
a concave mirror converges rays, the rays are divergent after 
they pass the focal point. From a beam of parallel rays, therefore, 
a convergent or a divergent pencil of light may he obtained by a 
concave mirror. 
If the luminous point be passed nearer to the mirror than 
its focal distance, though the divergence of the rays is diminished, 
they retain this character and do not 
come to a true focus. This state of 
affairs is shown irr Fig. 207, L being 
the luminous point between the focus 
-f and the surface of the mirror A, 
the incident rays L M and L H are 
reflected in the paths M E and IST H, 
'which are divergent. 
Fig. 207. 
483. Real and Virtual Foci.—In the 
. r§t and second conditions studied 
Virtual focus. 
ln the preceding article, if a small screen, as a piece of white 
Paper, be placed at the focus, an image of the object is formed. 
In the first case, the sun or the moon being the source of light 418 
OPTICS. 
the rays are practically parallel, and an image of either of these 
objects will be formed on the screen at the principal focus. In 
this manner the principal focus for any mirror may be deter- 
mined; its distance multiplied by two gives the radius of curva- 
ture. In the case of conjugate foci, an image of a candle flame 
or other luminous object will be formed at one focus, the object 
being at the other. The actual image formed upon the screen 
under these conditions, is called a real focus. 
In the third case in the preceding article, the reflected rays 
are divergent, and there is no real focus, but if we imagine these 
divergent reflected rays, M E, and hi H, Eig. 207, to be prolonged 
backwards through the mirror in the directions M I, and hi I, they 
meet at the point I. To this point the name of virtual focus is 
given. As in the case of virtual images formed by plane mirrors, 
we may, therefore, say, that a real focus is formed by the reflected 
rays themselves; a virtual focus, by their prolongation through the 
mirror. 
484. Spherical Convex Mirrors.—These have but few practical 
applications besides that of obtaining a point of light, or increas- 
ing the divergence of rays in a reflected beam. Application of 
the laws of reflection shows that they can only have virtual foci. 
485. Formation of Images by Spherical Mirrors.—From con- 
sideration of the image of a luminous point we pass to that of 
any object possessing appreciable size. Where a mirror is con- 
cave, two cases present themselves: Ist, the image is real; 2d, 
it is virtual 
Let A B, Fig. 208, represent the object placed beyond the 
centre C. To determine the focus of the point A, draw thence 
Fig. 208. 
Heal image. 
to the mirror the secondary axis A E, and also an incident ray 
AD. Construct a normal to D, and draw the reflected ray Da, 
taking care that the angle of reflection C D a is equal to the 
angle of incidence ADC. At the point a, where the reflected 
ray cuts the secondary axis A E, the image of the point A, will 
be formed, the same being its conjugate focus. In like manner, 
draw an incident ray and secondary axis from B, when it will be REFLECTION AND MIRRORS, 
419 
found that after reflection the former cuts the latter at b, where 
the image of B appears at its conjugate focus. All points of the 
objects A B may thus be examined, when it will be found that 
their conjugate foci lie between a and b. It, therefore, follows, 
that the image of the object A B placed beyond the centre of curvature 
is formed at a b, between the centre of curvature and the principal focus ; 
it is also real, inverted, and smaller than the object. 
If the object is at a b, between the principal focus and the 
centre, the reverse conditions are presented, and the image is 
formed at AB. It is real, inverted, larger than the object, its size 
increasing as the object is placed nearer to the principal focus. 
When it is at the principal focus, the reflected rays from 
each point being parallel to the secondary axis drawn there- 
from, an image is not formed. 
When it is between the mirror and its principal focus, the 
rays do not come to a focus, but are divergent; a real image, 
therefore, is not formed, but the eye, when properly placed, 
perceives one which is virtual, erect, and larger than the object. 
By placing one’s self in front of a concave mirror, all these facts 
piay be verifled. At a certain distance, a real inverted smaller 
image is seen, on approaching this becomes confused, and when 
at the focus it disappears; passing within the focus an enlarged 
virtual erect image appears. 
In the case of convex mirrors only virtual images are pro- 
duced. At any position before these the image is always 
erect, and smaller than the object, as can be shown by direct 
experiment, or by the construction of a diagram, as with con- 
cave mirrors. 
-486. Spherical Aberration and Caustics.—The statements thus 
far made regarding mirrors, are only correct while the angle 
°f aperture is not more than ten degrees. When it passes be- 
yond this, the rays reflected from the exterior portions reach a 
tocus nearer to the mirror than 
those reflected from the regions 
übout the pole, as at B, the 
image is, therefore, blurred, 
-to this effect and its cause the 
term spherical aberration is ap- 
plied. It is represented, Fig. 
209, where the ray from L, re- 
flected from A, cuts the prin- 
Fig. 209. 
Spherical aberration. 
cipal axis within the point at which the raj reflected from B 
peaches it. By connecting the points of intersection, the curve 
F is obtained. This is called the caustic. It is perceivable 
Avhen lamp or candle light is reflected from the interior of a 
tumbler upon milk or other fluid contained therein. 420 
OPTICS. 
487. Parabolic Mirrors. —To avoid the aberration in spherical 
mirrors of aperture greater than ten degrees, a parabolic curva- 
ture is employed. 
In Fig. 210, conceive that the arc A M of a parabola is caused 
to revolve about its axis A X, a 
mirror of the form in question 
would result. The figure also indi- 
cates that in a parabola any straight 
line, F M, drawn from the focus 
to any point, M, and there meeting 
a line, M L, parallel to the axis 
will form equal angles with a tan- 
gent, T T', to the curve at their 
point of intersection, M. From 
this it follows, that all rays parallel 
to the axis will be reflected to the 
focus; and, conversely, a luminous 
Fig. 210. 
Parabolic mirror. 
point at the focus will give parallel rays. Hence the use of 
these in railway and carriage reflectors. 
488. Cylindrical Mirrors. Anamorphosis.—The distortion by 
convex mirrors of this form is very great. When the axis is 
Fig. 211. 
Anamorphosis. 
vertical, it acts like a plane mirror, as regards the angular mag- 
nitude under which height of the image is seen, and like a REFLECTION AND MIRRORS. 
421 
spherical in relation to its breadth. The reflected image is, there- 
fore, greatly contracted in its horizontal dimensions. 
By drawing pictures with the proper distortions, and viewing 
them by reflection in a cylindrical mirror, as in Fig. 211, the 
confused appearance existing is corrected, and the image repre- 
sents a recognizable form. This method of restoration of true 
proportion is called anamorphosis. 
Concave cylindrical and tubular mirrors are used in exami- 
nation of different cavities of the body. They serve to direct 
light into such cavities. They vary in form and size according 
to the use for which they are applied. Among these are the 
aural speculum ; nasal, or rhinoscope; also rectal, vaginal, and urethral 
specula. 
489. Applications of Curved Mirrors are chiefly for condensing 
light, and for use in reflecting telescopes. 
In many forms of microscope, a concave mirror is attached to 
the posterior face of the plane mirror, which reflects the light 
through the stage of the instrument. By either of these direct 
or oblique illumination is obtained as desired. 
The ophthalmoscope consists of a concave silvered mirror with 
an aperture through the pole. It is used to direct a convergent 
beam of light into the eye under examination. The interior 
thus illuminated is viewed by the operator placing his eye at 
the aperture. The inspection can be conducted with or without 
the aid of magnifying glasses. 
In the laryngoscope, already mentioned (480, 3d), a mirror such 
as that described, is used in conjunction with a plane reflector. 
The latter is held by a handle at a suitable angle at the back 
part of the mouth, the condensed light from the ophthalmo- 
scope mirror is thus reflected into the larynx, the plane re- 
flector serving to direct the light into the organ, and enable the 
operator to view its interior. 
In the Lieherkilhn objective for microscopes, the glass objective 
is placed in the pole of a reflecting mirror, opaque objects are 
thus subjected to a more brilliant illumination (584). 
In reflecting telescopes concave mirrors are employed to 
produce images of celestial and terrestrial objects. These are 
also called catoptric telescopes. Various forms have been con- 
structed. In the Herschelian telescope the reflector is set at a 
slight angle to the tube, and the image is produced at one side 
near the mouth, and there viewed directly by the eye of the 
observer. In the Newtonian reflector it is set at right angles to 
the tube. In the axis of this near its mouth, a plane mirror 
reflects the converging beam to one side whence it passes through 
an aperture and is viewed by the eye. In the Gregorian form it 
is perforated through its pole; the rays, as in the Newtonian, 422 
OPTICS. 
are received upon a plane mirror, which is set parallel to the 
concave mirror; the converging beam is, therefore, sent back 
to the aperture in the centre of the concave mirror, and there 
viewed by the eye. 
By the process for silvering glass, telescope and other mirrors 
are now made of this substance and covered with pure silver. 
Accurate curvature, high reflecting power, and lightness are 
thereby obtained. 
CHAPTER XX. 
REFRACTION AND PRISMS. 
Refraction illustrated—Refraction power of different media—Laws of single 
refraction—lndex of refraction—Critical angle. Total reflection—Atmos- 
pheric refraction and mirage—Media with parallel surfaces—The prism— 
Track of ray in prism. Angle of deviation—Minimum deviation—Reflect- 
ing prisms. 
490. Refraction Illustrated.—Much of the light falling upon 
a surface is reflected; the quantity so disposed of is greater 
as the color of the body is lighter and its polish more perfect. 
Even the whitest and most accurately polished surfaces do 
not reflect the whole of the incident light, but a portion 
always penetrates the substance. In opaque bodies the whole 
is absorbed very near the surface. In those which are trans- 
lucent it is taken up slowly, and a portion may pass out from 
the opposite side if the medium is not too thick. In those 
highly transparent, a small portion is reflected, the greater 
part passing through with but slight loss. 
In the passage of a ray of light from one transparent medium, 
air, to another, water, the track does not undergo any change of 
direction, providing it enters the second perpendicularly. If, 
on the contrary, it penetrates it in any other course than the 
normal or perpendicular, it no longer follows the same track, 
but suddenly breaks therefrom at the surface, and pursues a 
straight line in a different direction. To this phenomenon the 
term refraction is applied. 
The direction in which the course of a ray is broken differs 
with the relative densities of the two media concerned. Of this 
the following experiments are illustrations. Let A B represent 
a rectangular aquarium with the vertical end A covered by a 
board, or blackened to render it opaque. At C a candle flame REFRACTION AND PRISMS. 
423 
is placed, the rays therefrom being obstructed by the opaque 
side only illuminate the upper part of the aquarium, and the 
whole of the bottom is in deep shade when observed from the 
side as in Fig. 212. Now let the tank be slowly filled with 
Fig. 212. 
Refraction. 
water; then viewing it as before, as the fluid rises higher and 
higher, more and more of the bottom is illuminated, until when 
full to the brim the rays reach as far forward as B. 
In the latter case the light has passed from a light medium, 
mr, into a denser medium, water. It has also impinged upon the 
surface of the latter at a considerable angle to the normal. It 
has consequently been refracted from the course C A, into A B, 
the new track being bent towards the side of the tank at which 
the ray entered. Viewing that side as a perpendicular in the 
medium to its surface, we say that the refraction is towards the 
perpendicular or normal. The plane separating the two media 
is called the refracting surface, and each of the media a refracting 
uifdium. 
Empty the tank and place a silver coin, A, upon its bottom, 
so the eye at C can see it in a straight line, then move to E; 
Fig. 213. 
Refraction in tank. 
here the coin is invisible on account of the intervention of the 
opaque side B, Filling the vessel with water, the position of 
the eye not changing, it again comes into view, and together 
with the bottom appears to rise, so that the vessel seems to be 
shallower than before. 
These appearances are all due to refraction. The ray A B 424 
OPTICS. 
proceeding from the coin takes the direction A C when the 
tank is tilled with air; but when with water, the ray A B, on 
leaving the surface at B, undergoes refraction, and takes the 
new course BE, the eye perceiving Aas though at E. If we 
compare the new or refracted path B E, and its preceding path 
B C, with the normal H G-, we find that in passing from the 
dense into the light medium, the ray has been refracted from, 
instead of towards the normal. 
491. Refraction Power of Different Media.—ln the experiment 
with the coin, the course of the emergent or refracted ray was 
bent away from the normal at the point of emergence. In the 
trial with a candle it was bent towards the normal. In this, as 
in all cases of refraction, the medium in which the ray makes 
the smaller angle with the normal is said to have the greater re- 
fractive power. 
Though generally this is true, it is not always so. In place, 
therefore, of speaking of the denser and rarer medium, it is more 
accurate to use the terms more refractive and less refractive. 
In gases, liquids, glass, and uncrystallized media., the refrac- 
tion is single. In many crystalline bodies, as Iceland spar and 
selenite, on the contrary, the refracted ray is divided. This is 
called double refraction. 
492. Laws of Single Refraction.—These were first stated by 
Snell, and afterwards enunciated by Descartes. They are gen- 
erally known as the laws of Descartes, or as the law of sines. 
Let I, Fig. 214, represent the point of impact of the ray 
R upon the surface separating two media, and I S its refracted 
Fig. 214. 
course in the second. The angle 
made by RI or R' I, and the nor- 
mal to the surface, is the angle of 
incidence, and the angle made by 
I S and the normal, is the angle of 
refraction. Continuing the course 
of the ray R I to R' we have the 
angle R' I S formed, which is the 
deflection of the ray R I from its 
original course. This is called the 
angle of deviation. 
Describe a circle around I as a 
centre, and from S let a perpen- 
dicular fall on the normal, it will 
cut it at P. The line S P then 
Law of refraction. 
becomes the sine of the angle of refraction SIP. From R', 
the point of intersection of the prolonged incident ray and the 
circumference of the circle, draw a second perpendicular to the REFRACTION AND PRISMS. 
425 
normal, it will intersect it at P', and the line R' P; will represent 
the sine of the angle of incidence. As one of these sines varies, 
the other changes in a constant ratio. From these facts we have 
the following laws. 
Ist, The refracted and incident rays are in the same plane, and 
at right angles to the surface between the two media. 
2d. For all angles of the incident ray, the ratio of the sine of the 
angle of incidence and of the sine of the angle of refraction is con- 
stant for two given media, but varies for different media. 
493. Index of Refraction.—The ratio between the sines of the 
angles of incidence and refraction is called the index of refraction. 
It varies with different media. From air to water it is from 
air to glass it is -|. If the course of the ray is considered in the 
opposite direction, the index is reversed, being from water to 
air A, and from glass to air f. 
When a ray passes from a vacuum into a medium, the ratio 
18 greater than unity, and is called the absolute index of refraction 
or simply the index for the medium in question. In air, the 
absolute index is so small that it may be neglected when com- 
pared with liquids and solids. 
Indices op Refraction 
Diamond . 
2.47 to 
2.75 
Oil of turpentine, sp. 
Phosphorus 
2.224 
gr. 0.885 
1.478 
Sulphur . 
2.115 
Alcohol . 
1.372 
Sapphire . 
1.794 
Albumen . 
1.360 
Ruby 
1.779 
Ether 
1.358 
Carbon bisulphide . 
1.678 
Crystalline lens, outer 
Iceland spar, 
ordi- 
layers . 
1.337 
nary ray 
1.654 
Crystalline lens, inner 
Iceland spar, 
extra- 
layers . 
1.379 
ordinary 
1.483 
Crystalline leus, cen- 
Flint glass 
1.575 to 1.642 
tral 
1.400 
Rock salt 
1.545 to 1.550 
Sea water, 
1.343 
Rock crystal 
1.548 
Vitreous humor 
1.339 
Plate glass, St. 
Gobin 
1.543 
Aqueous humor 
1.337 
Crown glass 
1.631 to 1.563 
Pure water 
1.336 
Linseed oil, s 
p. gr. 
Ice .... 
1.310 
0.932 . 
1.482 
For solids and liquids. 
Gases at 0° C. and 760 mm. 'pressure. Refractive indices of gases. 
Vacuum 
. 1.000000 
Carbonic acid 
1.000449 
Hydrogen . 
. 1.000138 
Hydrochloric acid 
1.000449 
Oxygen 
. 1.00027-2 
Nitrous oxide 
1.000503 
Air 
. 1.000294 
Sulphurous acid . 
1.000665 
Nitrogen 
. 1.000300 
Olefiant gas 
1.000678 
Ammonia . 
. 1.000385 
Chlorine 
1.000772 
The relative index of refraction from any medium, A, into a 
second, B, is always equal to the absolute index of B divided by 
fhe absolute index of A. 426 
OPTICS. 
494. Critical Angle. Total Reflection,—Consideration of the law 
of sines shows, that if the incident ray is in the less refractive 
medium, there is always a corresponding angle of refraction. 
This is not the case when the incident ray is in the more refract- 
ing medium. When it passes from water into air, for example, 
there is an angle at which the angle of refraction becomes 90°; 
beyond this the ray is totally reflected at the surface. 
In Fig. 215, let S 0 be a ray of light traversing water from S 
to O, and suppose that at 0 it is refracted in the direction 0 R. 
Fig. 215. 
Any ray, P 0, making a greater angle with 
the normal than the angle SOB, cannot 
emerge, but will of necessity undergo re- 
flection at 0, and follow the direction O Q. 
The angle SOB being the limit at which 
the refracted ray can emerge from the fluid, 
is the critical angle. From water to air this 
is 48° 85'; from glass to air, 41° 48'. 
Examples of total reflection are seen in 
the brilliancy of the surface of bubbles of air 
Critical angle. 
in water, when viewed at a certain angle. 
If a plain glass tumbler, or a beaker, is 
filled with water, and held above the head, until the line of 
vision is through the side of the vessel to the surface, as it is 
raised, an angle is soon reached at which objects on the ground 
appear, their images being produced by total reflection from the 
under surface of the liquid. 
495. Atmospheric Refraction and Mirage.—As light is refracted 
on its exit from air to water, it likewise changes its course on 
passing from vacuous space into the atmosphere. Consequently 
only those celestial bodies actually overhead appear in their true 
Fig. 216. 
Twilight. 
position, since their rays enter the air at the normal. The light 
from a star at A, Fig. 216, is refracted on entering the air at c, 
and the observer at d sees it as though at a. At B, the sun is 
represented after it has passed below the horizon; its light is 
refracted as it enters the air at e, and the observer at d sees it as REFRACTION AND PRISMS. 
427 
though at h. Light from the sun is, therefore, brought to us by 
refraction as twilight after that luminary has disappeared below 
the real horizon. The same happens in early morning, and he 
appears before the horizon has actually been reached. Thus 
the day is lengthened a little morning and evening. 
In the figure the lines d c d e are drawn as though straight. 
This is not actually the case. The layers of air nearest the earth 
are the densest, consequently the refraction there is greatest, 
and the light follows a curved course. 
Since some objects on the earth’s surface absorb the sun’s rays 
more readily than others, they are, consequently, warmer. From 
their surfaces upward currents of heated gas are rising. These 
being lighter than other portions of air, have a different refrac- 
tive power; in addition, they are continually in motion; and so 
media of variable powers of refraction are continually passing 
between the eye and distant objects. The result is continual 
change in positions, which gives to them the appearance of 
dancing. The same effect is caused when we view anything 
through air rising from the surface of a hot stove. 
In the phenomenon known as mirage, inverted images of 
distant objects appear to travellers on deserts, as though re- 
flected from a surface of tranquil water. The explanation of 
this, as given by Dr. Arnott, is as follows: “The strata of air 
immediately above the heated sandy soil, are greatly expanded 
and rarer than the strata above them, which, in spite of the law 
°f diffusion, remain denser. Rays of light proceeding from 
objects in a direction a little above the level of the earth, and 
nearly parallel to it, meet the heated and rarer strata at a very 
obtuse angle. They take the course of a curve as the result of 
gradual refraction, until at length the angle of incidence, which 
goes on increasing, reaches the point at which refraction is 
changed into reflection, and the 
rays meet the eye of the spectator 
as if proceeding from an object 
below the level of the earth. This 
gives to it the appearance as if it 
was reflected from the surface of 
water.” 
Fig. 217. 
Mirage effects are not confined to 
hot climates, they have been noticed 
oy Arctic navigators at high lati- 
tudes. 
496. Media with Parallel Surfaces. 
When a ray impinges at a right 
angle, hi I, upon a medium, the 
Eefraction through parallel plate. 
surfaces of which are parallel, it passes through without change 
of direction. If at an angle, as 8 I, it is bent towards hi lon 428 
OPTICS. 
entering; and on emerging into the less refractive substance, it 
is bent from the normal F7, and the emergent ray RS' is parallel 
to the continued incident ray S I. 
497. The Prism can be made of any solid or liquid substance 
which is transparent. The material usually employed is glass, 
but liquids possessing great refractive power, as bisulphide of 
carbon, are frequently used. The form generally adopted is 
that of a wedge, or column, a section of which is an equilateral 
triangle, as at AB C, Fig. 218. In such sections Ais spoken 
Fig. 218. 
of as the summit or apex, and B C the base. The line of meet- 
ing, A, of the two faces represented edgewise at A B and A C, 
is called the edge. Any section perpendicular to this is called 
a principal section. If perpendiculars be drawn from each side to 
the opposite angle of the triangle, forming a principal section of 
an equilateral prism, they all meet at a point called its centre. 
A line drawn through this perpendicularly to a principal section, 
is its axis. When a fluid is used, a cell of the form in question, 
made of clear glass, is filled therewith. 
From a purely optical point of view, only the two plane faces 
forming the edge are considered. The angle embraced between 
these is called the refracting angle. An equilateral prism is, 
therefore, called a prism of sixty degrees, since that is its re- 
fracting angle. 
498. Track of Ray in Prism. Angle of Deviation.—With varia- 
tion in the angle of incidence, made by the ray and the surface 
of the prism upon which it impinges, the track through the prism 
will also vary. It may be made to undergo reflection at the 
second face, and emerge at the third. To avoid ambiguity we 
shall, therefore, confine our explanation to what takes place 
when it is in the best position. 
In Fig. 218, ABC represents a principal section of a prism 
of sixty degrees, S I is an incident ray falling upon the face REFRACTION AND PRISMS. 
429 
A B, and making the angle of incidence SIN with the normal 
A. Passing from air into glass, it is bent towards the normal 
I M, drawn therein, and the angle of refraction r is less than 
the angle of incidence i. Impinging upon the opposite face 
A C, it is again refracted on emerging, and follows the direction 
R, and the angle of refraction %' is greater than the angle of in- 
cidence r', according to the law for passing from a highly re- 
fracting medium to one of less power. 
If the incident light S I is a beam of sunlight, while the prism 
does not interfere, the image is produced at S', the prolongation 
of SI. When the prism is intervened and properly adjusted, 
the light on emerging takes the direction R. It has been 
changed or deviated from its course. To measure the extent of 
this, the line of refraction R is prolonged until it intersects the 
line of incidence S S' at 0, when the angle 1) represents the 
angle of deviation. 
Prom this it is obvious that a ray of light in its passage 
through a prism is deviated or deflected towards its base. 
499. Minimum Deviation. Suppose a beam of sunlight be 
directed across a room by the mirror of a heliostat, it forms a 
spot of light or image of the sun on the opposite wall. If it is 
caught upon an equilateral prism, held with its axis vertical, 
rotated thereon, the spot of white light will disappear, and 
m its place a colored elongated image is produced. The direc- 
tion in which this is formed shows that the light on emerging 
trom the prism is deviated towards its base. 
Rotating the prism upon its axis, the angle of incidence di- 
minishes, the colored image moving along the wall nearer to the 
priginal location of the spot. Continuing the rotation, a point 
is finally reached at which the image begins to recede from this 
position. There is, therefore, a particular angle of deviation 
&t which the colored image is nearest to the original line of 
light from the heliostat mirror. This deviation being less than 
m any other case, it is called the angle of minimum deviation. It 
!s to this angle that a prism must be set when used for spectrum 
work. 
In Pig. 218, the prism is shown in its position of minimum 
deviation. The slightest rotation upon its axis, to right or 
left, causes the image to undergo greater deviation, and ap- 
proach C. It will be noticed that the angles of incidence i and 
emergence under the adjustment of minimum deviation, are 
equal. 
. Since rays of different colors vary as regards their refrangi- 
mlity, it is necessary to set the prism for the minimum deviation 
°1 the ray in which work is done, when great accuracy is 
desired. OPTICS. 
500. Reflecting Prisms.—The principle of total reflection (494) 
is applied in many optical instruments. The simplest example 
Fig. 219. 
is ottered by prisms which present a 
right angle in their principal section. 
Let ABC represent a principal 
section of a glass prism, and 0 a ray 
incident to the surface CB, Since 
it is normal or perpendicular to this, 
it enters without being refracted and 
impinges upon the hypothenuse A B 
at H. The angle formed by 0 H 
with a normal to A B is 45°. The 
critical angle for glass (494) is 41° 48'; the ray OH, therefore, 
undergoes total reflection, and passes out of the third face of the 
prism in the line AT, as indicated. The eye consequently per- 
ceives the object 0 in the position O'. 
Eight angle prism. 
CHAPTER XXI. 
COMPOSITION OP LIGHT. 
The prismatic spectrum—Normal dispersion—Abnormal dispersion—•Spectrum 
colors are simple, and of different refrangibility—The rainbow—Newton's 
theory of composition of white light—Recomposition of white light—The 
achromatic prism—Heat in prismatic spectrum—Chemical action in prismatic 
spectrum—Maxima of energies in prismatic spectrum—Light, heat, and 
chemical action are modes of vibration. 
501. The Prismatic Spectrum,—ln discussing the action of a 
prism in the preceding chapter, it is stated that after light has 
passed through, it is no longer white, but forms a colored elon- 
gated image upon the screen. This image is called the prismatic 
spectrum. 
For study of the spectrum, the following method and arrange- 
ment, Fig. 220, may be adopted. Admit a beam of sunlight 
through a horizontal narrow slit in the shutter of a dark room 
at A (a parallel beam from an oxycalcium lantern may be substi- 
tuted). The line A X then represents its track until it falls 
upon the screen X, Intervene the prism P with its edge down- 
wards, Revolve it upon its axis until the centre of the colored 
image formed on the screen is brought as near as possible to X, 
the original line of light. It is then adjusted to the angle of COMPOSITION OF LIGHT. 
431 
minimum deviation for the central part of the spectrum. Sub- 
mitting this to close inspection, we find: 
Ist. That it presents an infinite number of tints which grad- 
ually merge into each other. For convenience, seven of these 
Fig. 220. 
were selected by Newton and spoken of as the seven 'primitive 
colors, viz., violet, indigo, blue, green, yellow, orange, red. 
2d. The order in which the colors are arranged is that given ; 
the violet being deviated the most from the original course of 
light, and the red the least. The deviation of the others is in- 
termediate between these. 
The spectrum. 
502. Normal Dispersion.—The spectrum presents a certain 
length from the violet to the red; this spreading out of light, 
and its separation into different colors, is called dispersion. Its 
extent is measured by the angle of separation of any two rays, 
9--> red and violet. In Fig. 220 this is represented by EP Y, 
tts ratio to the mean deviation of the two rays is called the 
dispersive power. It is constant for any given medium, while the 
refracting angle is small. The dispersive power of different 
substances varies greatly, flint glass having nearly double that of 
crown glass. 
In colored artificial lights, the spectrum differs from that of 
sun, the intensity of some colors being diminished. The 
color which predominates in the flame is the chief in the spec- 
trum. Sometimes a portion of the solar spectrum colors are 
"Wanting in flames. 
All media which give spectra in which the colors are in the 
order stated, are said to produce normal dispersion. 
If the light which has passed through one prism be received 
Uffon a second, placed to increase the deviation in the same 
direction as that produced by the first, the dispersion or increase 
ln the length of the spectrum will be augmented in a similar 432 
OPTICS. 
ratio. Thus by using a number of prisms, all acting in the same 
direction, dispersion may be increased to any required degree. 
503. Abnormal Dispersion.—Certain solutions, as indigo and 
permanganate of potassa, give spectra in which the order of 
colors is not the same as in normal dispersion. If, for example, 
a hollow glass prism be tilled with an alcoholic solution of 
fuchsine, the following spectrum results: violet is least deviated ; 
then red, and yellow the most. Kundt has found that all sub- 
stances with surface color exhibit abnormal dispersion when con- 
verted into optical prisms. 
504. Spectrum Colors are Simple and of Different Refrangibility. 
—White light having been decomposed by a prism, the question 
arises : What will occur if each of the seven colors be passed 
through a second prism ? In Fig. 220 the experimental exami- 
nation of this proposition is delineated In the screen on which 
the spectrum is formed an opening is made. This is adjusted 
to allow the red ray to pass through the perforation, it then im- 
pinges upon a second prism, P', placed as the first, edge down- 
wards. The ray is again deviated or refracted, but no further 
decomposition of light takes place. Changing the position of 
the prism until the ray is refracted downwards, sideways, or in 
any other direction, the color remains unaltered. We, there- 
fore, conclude that in decomposition of light by a prism, since 
each color undergoes no change but that of deviation, the colors 
'produced in the prism,atic spectrum are simple. 
The formation of the prismatic spectrum is, in itself, an evi- 
dence that the rays of different colors possess varying degrees 
of refrangibility, otherwise they would not undergo different 
Fig. 221. 
degrees of deviation. Many additional facts might be cited in 
demonstration of this; the following will answer our purpose. 
If a series of small squares, VI B GY OR, representing 
the seven colors of the spectrum, are arranged in order, as at mn, 
and viewed through a prism held with edge parallel to the row, 
the violet will be displaced the most, the red the least, while the 
Dispersion and deviation. COMPOSITION OF LIGHT. 
433 
intermediate colors form a series of steps between the two as 
at M N. 
In another experiment contrived by Newton, the light as it 
emerges from a prism adjusted to give a vertical spectrum, is 
forced to pass through another, the edge of which is vertical, or 
at right angles to that of the first. Thus treated, the spectrum 
changes, it moves to one side, being deviated towards the base 
of the second prism. The spectrum is no longer vertical, nor 
horizontal, but takes an inclined or oblique position, the violet 
being refracted the most, the other colors in their order, and the 
red the least. 
In the figure the manner of change is exhibited, mn being the 
spectrum as formed by the first prism, M N the position when 
it has passed through both, the violet ray Y being refracted the 
most, the yellow ray Y intermediately, and the red ray R the least. 
505. The Rainbow.—This, one of the most interesting of natu- 
ral phenomena, is the result of decomposition of light by refrac- 
tion in drops of water. It is only visible when the sun is shin- 
ing. It, therefore, appears when it emerges from the clouds 
while it is still raining in the vicinity, or when sunlight falls 
upon spray produced by waterfalls, fountains, or mists. 
Sometimes more than one bow is seen; in all cases a line 
joining the observer and the sun is the axis of the bow or bows. 
The track of the rays of light in 
drops of water in the formation of 
a primary bow is shown in Fig. 
222, The solar ray S I falling on 
a drop of water at I is refracted to 
Y, there it undergoes total reflec- 
tion, passes to I', where it is again 
Refracted, and emerges in the direc- 
tion I' M. In this case it is sub- 
mitted to two refractions, and one 
Reflection; in the secondary bow, 
*t is refracted twice, and reflected 
twice. 
Fig. 222. 
506. Newton’s Theory of Composi- 
tion of White Light.—Having broken 
Primary bow. 
up white light into a number of different colored rays by aid of 
the prism, Newton promulgated his theory of the composition 
°f white light, briefly stated as follows. White light is made 
up of seven colors of unequal refrangibility, these are called sim- 
ple or primitive lights. The variation in their refrangibility is the 
cause of their separation in traversing a prism. 
In chemistry the composition of a body is demonstrated in 434 
OPTICS. 
two wTays: Ist, by analysis; 2d, by synthesis. In analysis the 
constituents of the body are found by separating them from 
each other, or decomposing the body. By an electric current 
water is separated into oxygen and hydrogen, and we say we 
have demonstrated its composition by analysis, derived from two 
Greek wTords signifying to loosen or separate from one another. 
Having proved the existence of these two constituents in water, 
and the proportions in which they are present by analysis, we 
take the two substances, oxygen and hydrogen, in the propor- 
tions found, and by applying a spark determine whether they 
will unite without any remainder of either body. Actually per- 
forming the experiment, we find they do, water being the result. 
Hence the composition of water having been determined by 
uniting its constituents in proper portions, we state that we have 
proved its composition by synthesis, also derived from the Greek 
and signifying a putting together of constituents. 
In decomposition of white light by a prism, Newton showed 
its character by analysis. If, by a process of synthesis, it should 
again be proved to be compound, its true nature is demonstrated 
beyond doubt. 
507. Recomposition of White Light.—lst. Let a ray of light S 
be received upon a prism placed edge downwards, as in Fig. 
223, and adjusted to produce a spectrum. The usual phenomena 
Fig. 223. 
Kecomposition of light. 
of deviation and dispersion will appear upon a screen properly 
placed. Then receive the rays from the first upon a second 
prism, arranged close thereto, with edge turned in the opposite 
direction or upwards, as in Fig. 223. The spectrum formed by 
the first at once disappears, and in its place a spot of white light 
is formed upon the screen in the direction E, parallel to the 
course of the ray incident on the first prism. The second, 
acting in an opposite sense to the first, has recompounded white 
light out of the seven prismatic colors. Its compound nature is 
thus demonstrated by synthesis, as well as by analysis. 
2d. If a convex lens is placed to receive the whole of the 
spectrum formed by a prism, the different colored rays are 
superimposed at its focus, and white light produced. 
3d. If a concave mirror is arranged to receive all parts of a 
spectrum, white light is formed at its focus. COMPOSITION OF LIGHT. 
435 
4th, If seven plane mirrors are adjusted to receive the seven 
colors of the spectrum, and their angles arranged to reflect all 
the colored rays to the same spot, white light is the product. 
6th, If powders representing the seven spectrum colors are 
ground together in a mortar, a grayish-white mixture is ob- 
tained. The resultant color is not as perfect as in the preceding, 
since the colors of powders are not as pure as those of the 
spectrum. 
6th. By the device of Newton’s disk, another demonstration 
of the recomposition of white light is obtained. It consists of a 
circular card, to which rapid rotation may be imparted by suit- 
able mechanism (519). Upon its face the seven spectrum colors 
are painted, each color occupying a space extending from the 
centre to the circumference. When rapid rotation is given, the 
colors disappear, and it seems to be of a uniform light-gray tint. 
The rotation causes the impressions of the colors to overlap 
each other on the retina, and their actions are combined, as with 
the powders, and the effect of white light produced. 
7th. By imparting a rapid oscillatory movement to the prism, 
the colors of its spectrum overlap, and reproduce white light in 
the central parts of the spectral image. 
-508. The Achromatic Prism.—ln the first experiment showing 
composition of white light by synthesis, the second prism was 
similar in all respects to the first, both as regards material and 
angles. Under these conditions the course of the ray as it 
emerges from the second is parallel to that of the incident ray 
on the first. The two taken together have acted like a single 
block of glass in which the surfaces are parallel, and there is no 
refraction other than that caused by a medium with parallel faces. 
If in place of prisms of the same, those of different materials 
ure employed, in which the indices of refraction and dispersive 
powers are unlike, we may by a suitable adjustment of angles 
produce one which will refract a beam of light to a considerable 
extent, and at the same time give a colorless 
or achromatic image. Crown and flint glass 
furnish media having these properties (502). 
In Fig. 224, let B C F represent the sec- 
Pig. 224. 
tion of a crown-glass prism, and CDF 
another of the same material. The two 
acting together would have the effect of 
one, ABF, and the emergent beam would 
show refraction and dispersion, and form 
Achromatic prism. 
a spectrum. 
Then, suppose the second prism, C D F, is made of flint instead 
of crown glass. The dispersion of the first is now neutralized, 
while its refraction is but slightly altered. The emergent ray 436 
OPTICS. 
E 0 passes out of the second still refracted, but without disper- 
sion, and gives upon the screen a white spot or image of the 
sun. To such apparatus the name of achromatic prism is given. 
509. Heat in Prismatic Spectrum.—Let the central portion, 
VIB Gr Y OR, Fig. 225, represent the colors of a solar spec- 
trum formed by a prism. Herschel discovered 
that if it fell upon blackened paper moistened 
with water, the surface it covered dried more 
rapidly than the surrounding parts, and thus an 
image of the spectrum was produced. Close in- 
spection showed, in addition, that drying began in 
the lower part of the red, and spread gradually 
upwards to the violet. At the same time it did 
not stop in the red, but extended to a consider- 
able distance below. 
From this it is evident: Ist, that the prismatic 
spectrum contains heat as well as light; 2d, that 
the heat spectrum extends far below the visible 
or light spectrum; and, 3d, that the heat or caloric 
rays in sunlight are less refrangible than luminous 
rays. 
Pig. 225. 
510. Chemical Action in Prismatic Spectrum.—For 
blackened paper, substitute a surface coated with 
chloride, or other compound of silver sensitive to 
light. Shield it from light, except that part upon 
which the spectrum falls. The portion occupied 
by the violet will soon darken, and the sombre 
hue will gradually extend through the indigo and 
blue; at the same time it will pass beyond the vio- 
let into the region indicated as chemical, Fig. 225. 
It is, therefore, evident: Ist. That the prismatic 
Maxima and mi- 
nima of energies in 
prismatic spectrum. 
—7 7 - X 
spectrum contains rays capable of producing chemical action, as 
well as heat and light; 2d. As with heat rays, the chemical or 
actinic extend beyond the luminous, in the region of the violet. 
The distance beyond the violet to which they may be detected 
is greater than that of the heat rays which extend beyond the 
red; 3d. Chemical are more refrangible than light rays. 
The statements made regarding the position of the stain or 
darkening by chemical action, must be understood as being the 
effect of the spectrum upon sensitive silver compounds. Other 
bodies which undergo change under the action of light are more 
readily affected in other regions of the spectrum. 
511. Maxima of Energies in Prismatic Spectrum.—lf fine writing 
is placed in the spectrum, it can be read with greater facility CHROMATICS. 
437 
and distinctness in the yellow than in any other region. We, 
therefore, conclude, that for the eye yellow has a greater in- 
tensity of action than other colors, and the maximum strength 
of the light energy of a spectrum is in the yellow. 
For the heat energy of the prismatic spectrum there is like- 
wise a position of maximum action. This is in the lower part 
of the red, or just below it, as is shown by Herschel’s experi- 
ment, or by direct measurement with a thermo-electric apparatus. 
Chemical energy, in like manner, gives a position of maximum 
intensity, which for silver salts is in the violet. The place of 
the chemical maximum varies in different compounds. As 
silver salts are usually employed in photographic operations 
there is a practical reason why it is given for these substances. 
512. Light, Heat, and Chemical Action are Modes of Vibration.— 
In discussing theories of light, it is obvious that modern physi- 
cists believe it is a form of energy, which, originating in vibra- 
tions of molecules of a luminous body, is transmitted to us as 
undulations in the ether. Since the1 spectrum also presents 
caloric, and heat energy, which accompany light in its trans- 
mission, reflection, refraction, and differ from it chiefly as re- 
gards the degree in which they act towards media in these 
respects, we conclude, that as light originates in vibrations of 
molecules, so also do heat and chemical energy. 
CHAPTER XXII. 
CHROMATICS. 
Monochromatic light—Color of opaque bodies. Pigments—lridescence—Color 
of transparent bodies—Colors of mixed powders—Mixtures of colored lights 
—Methods of mixing colored lights—Complementary colors—The primary 
color sensations—Accidental color images Color blindness—Color and 
musical pitch. 
513. Monochromatic Light.—Flames like sunlight present a 
combination of colors, as shown on examination with a prism. 
It occasionally happens that a physical or physiological research 
requires a simple light of special tint. Where convenient, it 
niay be obtained by a prism, the required color being passed 
through an opening in a screen, as in (501). 438 
OPTICS. 
It may also be prepared by the use of monochromatic flames; 
or by passing white light through colored glass, or through trans- 
parent cells tilled with certain solutions. 
For many purposes a yellow light is necessary. This may be 
formed by placing a platinum loop armed with carbonate or 
other compound of sodium in a Bunsen flame, which gives a 
pure bright yellow light. 
A blue light, such as that required in microscope photography 
to secure coincidence of visual and chemical focus, is obtained 
by the use of a glass cell with parallel sides filled with a solution 
of ammonio-sulphate of copper made by adding aqua ammonia 
to a sulphate of copper solution until the blue precipitate is 
dissolved. 
A nearly pure red may be formed by filling the cell with 
solution of sulpho-cyanide of iron. A good red is also prepared 
by staining glass with suboxide of copper. For some purposes 
a red flame is produced by introducing a platinum wire armed 
with chloride of strontium into a Bunsen flame. 
514. Color of Opaque Bodies. Pigments.—When a spectrum is 
caused to fall upon variously colored bodies, they only appear 
of their true tint when placed in the same color. In the other 
parts they are dark or black. The reason of this is, that they 
only reflect the color which is of their natural tint, all others 
being absorbed. The proper material for a screen is, therefore, 
white, which reflects all colors. 
Monochromatic flames or other similar lights produce like 
results. By the light of the sodium flame, the human coun- 
tenance takes on a ghastty appearance, only the yellow being 
reflected, while the red tints are lost or suppressed and appear 
dark. 
The experiment detailed, in which a substance of a given 
color reflects spectrum light of its own tint succeeds only in 
white light. Take blue, for example: when white light falls 
upon a surface which appears blue, though the seven primitive 
colors are present in the incident light, the blue alone is re- 
flected, and the body appears of the tint of the light it reflects. 
All the rest are absorbed, and converted into some other form 
of energy, or they may be transmitted. 
The color of pigments and other opaque substances, therefore, 
arises from the surface decomposition of white light by reflec- 
tion, sometimes one, but more frequently a greater number of 
colors are thrown back, and thus the various grades are pro- 
duced. The character and composition of the reflected light 
may be determined by examination with a prism. 
515. Iridescence.—In this there is a play of various colors of 
brilliant hues. Green, blue, and red tints rivalling those of the CHROMATICS. 
439 
solar spectrum in splendor, are associated with many natural 
objects; as, for example, the feathers of numerous species of 
tropical birds. Often, as in the humming bird, these undergo 
change with slight alteration in the angle of incidence of the 
light. The same is also seen in the nacreous or pearly matter 
lining certain shells, as the earshell or haliotis. These colors 
are produced by decomposition of light by ruled surfaces. 
In other instances, iridescence is developed by thin films, the 
surfaces of which are in close approximation to each other. An 
example of this is found in very thin mica, also in soap bubbles, 
or where oil is diffused over water. Here again light undergoes 
what might be called a spectrum decomposition or dispersion, 
like that in ruled surfaces; different colors appearing according 
as the angle of incidence upon the film is changed. 
Iridescence is seen even in the absence of tenuous films of 
solid or liquid matter, like glass blown exceedingly thin, or 
a soap bubble expanded to the point of bursting. In cracks 
or crevices in the interior of glass and other transparent bodies, 
the most brilliant colors often appear. In many such cases 
there is no air present. The decomposition of light, there- 
fore, takes place in vacuo, between the walls of the fissure. 
Hew ton made a special examination of these phenomena, in 
connection with the formation of rings between convex and 
parallel surfaces, which we shall study later on in connection 
with interference, when it will be seen how strongly all the 
facts connected with iridescence, and the production of color by 
polarization, support the undulatory or wave theory of light. 
516. Color of Transparent Bodies.—The color of a transparent 
body is owing to the decomposition of light by absorption 
during its transmission. Nothing new is added to the light, 
only certain of the colored components of white light are stopped 
°nt. According to their thickness the tints of transparent 
bodies vary. Solution of chromium chloride appears green in 
thin layers, and reddish-brown when thick. In this, and similar 
cases, different 'colors are removed by selective absorption, the 
light passed being the sum of the remaining rays of white 
bght. 
When glasses of different tints are placed behind each other, 
the color finally transmitted consists of the combination of 
those which pass both glasses freely. The final color is not the 
sum of those of the glasses, but what remains when these are 
subtracted from white light. The transmitted tint is generally 
that occupying a space in the spectrum between the others. So, 
if a yellow and blue are used, green is passed. A combination 
of red glass made with oxide of copper, and blue or violet glass 440 
OPTICS. 
of equalj[depth of tint forms a medium which is almost black 
or opaque. 
When substances are colored by transmitted light, the re- 
maining rays of the spectrum are not always absorbed, some- 
times they are reflected from the first surface, or scattered in 
the interior. An alcoholic solution of chlorophyle appears red 
by reflected light or when viewed sideways, and green when ex- 
amined by transmission. These are called dichroic. Very thin 
gold-leaf exhibits similar properties, being yellow by reflected, 
and greenish-blue by transmitted light. 
517. Colors of Mixed Powders.—ln his “Physiological Optics,” 
Helmholtz says: In colored powders each particle is to be re- 
garded as a minute transparent substance, which colors light 
by selective absorption ; since, when we examine thin slices of 
the substance of which they are formed, they are seen to be 
transparent. For example, verdigris and cobalt glass. The 
light reflected from the absolute surface is often nearly white, 
but the deeper the layer from which reflection takes place the 
darker is the tint; hence coarse powders of a given material are 
of a deeper tint than those which are very fine. 
Reflection from the surfaces of particles is weakened if they 
are covered with a fluid having an index of refraction near their 
own instead of air. A layer of water, and still more one of 
highly refracting oil, deepens the color, 
Since light reflected by powders consists of that from their 
surfaces, and from different depths, it follows, that in mixtures 
of powders the final tint, as in superposed glass plates, repre- 
sents the colors of white light which have not been removed by 
absorption. A mixture of two pigments is, therefore, darker 
than would be expected. Vermilion and ultramarine lights, if 
mixed, produce a purple; but a combination of colored powders 
of these substances produces a dark gray, with scarcely any 
purple, since each of these pigments is almost opaque to the light 
reflected by the other. 
518. Mixtures of Colored Lights.—By this we mean the im- 
pressions caused where two kinds of light having different rates 
of vibration fall upon the same part of the retina at the same 
time. 
In the case of sound vibrations the quality of tone as it 
affects the ear differs with each change in its formation. A 
given quality can only be produced by one set of fixed condi- 
tions. In the case of colors, on the contrary, each as it appears 
to our eyes can be formed by a great variety of combinations. 
Ordinary white light, for example, is composed of all seven 
colors of the spectrum, but white light, not distinguishable 
from this by the eye, may be made by taking any elementary CHROMATICS. 
441 
color, from the extreme red to the yellowish-green, and com- 
bining it in proper proportion with another color on the opposite 
side of the green. Though the eye cannot detect the difference, 
it is discovered at once on analysis with a prism. 
519. Methods of Mixing Colored Lights.—Of these a number 
are given in Deschanel’s and other works on physics. Our space 
only permits a brief description of the more convenient, which 
are applied to other purposes. 
Pig. 226. 
rotating disk. 
The first is known as the method by hfewton’s rotating disk, 
Fig. 226. It is provided with a series of paper disks, the sur- 
faces divided into sectors. On one of these the sectors are 
painted with the seven colors of the spectrum, as described 
111 (507, 6th). On the other disks they are made of such size 
and colors as the purposes of the experimenter require. The 
banner of use- and mode of action have been described in 
(507, 6th). 
A second method is represented Fig. 227. One colored 
°bject, say a blue wafer, is placed at b, and another, a green 
Wafer, at g. A sheet of clear glass with 
parallel faces is then held in the posi- 
fion P, so the eye at 0 sees h by trans- 
mission of its light through the glass, 
g by reflection therefrom. The 
mipressions produced by the two colors 
are thus mingled upon the retina, and 
the desired result obtained. 
Another method is by forcing two or 
Pig. 227. 
Complementary colors. 442 
OPTICS. 
more spectra to overlap, the results obtained under these cir- 
cumstances are the sums of the overlapping spectra. When 
these are projected upon a screen, beautiful combinations of 
color may be obtained. 
520. Complementary Colors are those pairs of tints which give 
white light when mingled together. According to Deschanel, 
they are: 
Bed 
complementary to Bluish-green 
Orange 
“ “ “ Skyblue. 
Yellow 
“ “ “ Yiolet-blue. 
Greenish-yellow 
“ “ “.Violet. 
Green 
“ “ “ Pink. 
In the case of spectrum colors, the list as given by Ganot is: 
Red 
complementary to Gi'eenish-yellow. 
Orange 
“ “ “ Prussian-blue. 
Yellow 
“ “ “ Indigo-blue. 
Greenish-yellow 
“ “ “ Violet. 
521. The Primary Color Sensations.—Though seven or more 
colors may be regarded as primary for purposes of physical 
investigation, they cannot all be considered as 'primary sensations 
of color. According to Brewster there are three primary color 
sensations—red, yellow, and blue. According to Young, Helm- 
holtz, and most modern physicists, they are red, green, and 
violet. These are called fundamental colors. 
Recent investigations by Hering, made upon a physiological 
basis, tend to a different result. He concludes that there are 
four primary color sensations essentially distinct from each 
other, viz., red, yellow, green, and blue. These are moreover 
reducible to two complementary pairs : Ist, red and green; 2d, 
yellow and blue. Hering also believes that “ complementary 
colors are the result of opposite actions upon the retina, so that 
there are only two essentially distinct color-affections of that 
organ, which, with their opposites, produce the two pairs of 
complementary colors; the one with its opposite produces red 
and green ; the other with its opposite, yellow and blue. 
522. Accidental Color Images,—After looking steadily for some 
time at a bright color, if we turn the line of vision to a white 
wall, an image of the colored object appears in its comple- 
mentary color. This is explained upon the hypothesis that the 
nerves which have been strongly impressed by the bright color 
have so lost their sensibility, that the balance of action required 
to cause the sensation of white is lost, and those factors which 
have not been exhausted are more strongly impressed. Such 
subjective results are known as negative accidental images. CHROMATICS. 
443 
Certain curious effects of contrast may be explained in a 
similar manner. If white paper is viewed upon a background 
of strong color, instead of white it often appears of a color com- 
plementary to the background. So also beams of sunshine 
passing into a room through yellowish blinds, produce blue 
bands when they fall upon a white surface as a tablecloth. 
Sometimes when a painfully bright object is regarded in- 
tensely, a positive accidental image is produced, which after a 
little is followed by a negative or complementary image. These 
may be regarded as extreme instances of persistence of im- 
pression. 
523. Color-blindness consists in the want of the elementary 
sensation representing red. Persons thus affected see the solar 
spectrum as two strong colors connected by a white or gray 
band near the Fraunhofer line F. One of these colors is prob- 
ably blue. Its maximum is midway between the lines F and G, 
and it reaches beyond G to the limit of the visible spectrum. 
The other color extends into the red part of the spectrum, the 
Maximum being midway between the lines D and E, and van- 
ishes where crimson appears to the normal eye. The scarlet 
probably appears to the color-blind as a deep dark green; orange 
and yellow as a brighter shade of the same tint; and bluish- 
green is nearly white. 
From a consideration of these facts Deschanel concludes that 
“what is called color-blindness should rather be called dichroic 
vision, normal vision being distinctly designated as trichroic. 
To the dichroic eye any color can be matched by a mixture of 
yellow and blue, and a match can be made between any three 
(instead of four) given colors. Objects which have the same 
color to the trichroic eye have the same to the dichroic eje.” 
In an article in the “Am. Journal of Sciences and Arts,” vol. 
xiii. page 32, Professor Pood says: “Tait has described an 
interesting observation, which has perhaps some bearing on 
Thomas Young’s theory of color. While suffering from indis- 
position, he noticed each time on awakening from a feverish 
sleep, that the flame of a lamp seen through a ground-glass 
shade, assumed a deep-red color, the effect lasting about a 
second. He suggests that the nerve fibrils in the retina also 
partook of sleep, and on awakening the green and violet nerves 
resumed their function somewhat later than the red. I have in 
my own case noticed some instances which seem to point out 
that after a nervous shock, sudden or prolonged, the green nerves 
(adopting the theory of Young) recover their activity later than 
the red, and probably later than the violet nerves. The first 
°bservation was made twenty years ago, while recovering from 444 
OPTICS. 
the effects of chloroform, which had been administered by a 
dentist well known at that time in Munich. Upon regaining 
consciousness, and raising my eyes to the face of the operator, I 
was a little surprised at not having previously remarked his 
unusually ruddy complexion, but the next instant saw that this 
was due to an optical illusion, for his hair appeared of a bright 
purplish-red hue. The singular appearance lasted perhaps a 
couple of seconds, when his hair resumed its natural color, 
which was white. This observation corresponds with that made 
by Tait. 
“ I give now an instance where chronic effects of a similar 
character were noticed by me for a couple of weeks continuously, 
during convalescence from typhoid fever. In this case white 
objects appeared of a not very intense orange-yellow hue, the 
general effect on a landscape being such as is produced by the 
orange-yellow rays of the setting sun. Here the activity of the 
green and violet nerves was diminished relatively to that of the 
red. The auditory nerve was also evidently affected during the 
same period, but precisely in what way I did not ascertain. 
“It is a matter of yearly observation with me, that effects, 
similar in kind with those first noticed, are produced by pro- 
longed exposure to bright white light out of doors. Under such 
circumstances white objects no longer appear pure white, but 
are tinted plainly purplish-red, and rather dull greens assume a 
gray hue, as though all the green in them had been neutralized, 
while strong greens are considerably reduced in intensity (satu- 
ration). Upon leaving the blinding glare and entering a dark- 
ened room, it often for several seconds appears filled with a 
greenish haze. 
“Two of these cases, and probably that of Tait, point out that 
our apparatus for the reception of waves of light of medium 
length, is more liable to be over-strained by nervous shocks or 
by prolonged excitation, than is the case with those designed 
for the reception of waves of greater or less length. Hervous 
derangement and prolonged excitation are then causes which 
may produce temporary green color-blindness.” 
Since the use of red lights for signalling, either by lanterns or 
rockets, is almost universal, the substitution of some other 
device, as variable forms in place of different colors, is very 
desirable. Accidents which now occur from color-blindness of 
railway engineers and pilots would be less frequent, and com- 
munities could still enjoy the services of men thus affected 
without taking serious risks. 
524. Color and Musical Pitch.—The existence of variation in 
rate of vibrations as the cause of difference in color, has led to LENSES. 
445 
the attempt to establish an analogy between colors and musical 
sounds, the seven primary colors of Newton and the seven 
notes of the gamut (411) being regarded as octaves respectively 
of light and sound. The resemblance is, however, a forced one, 
the gradual transitions which mark the spectrum being in strong 
contrast to the step-like advance from note to note in the musical 
scale. 
Helmholtz, moreover, directs attention to the fact, that if the 
lavender rays beyond the violet were included, the spectrum has 
an extent of an octave and a fourth instead of an octave. 
CHAPTER XXIII. 
LENSES. 
Varieties of lenses—Parts of spherical lenses—Forms of spherical lenses—Action 
of convex lenses explained—Action of concave lenses explained—Principal 
and conjugate foci of convex lens—Action of convex lens on convergent rays 
—Determination of foci of lenses—Optical centre. Secondary axes—lmages 
formed by convex lenses—lmages formed by concave lenses—Spherical aber- 
ration—The coma—Chromatic aberration—Achromatic lenses—Aberration by 
curvature of field—Depth of focus—Stops and diaphragms. 
525. Varieties of Lenses,—A lens may be defined as a trans- 
parent substance, which according to the curvatures of its sur- 
htces causes either convergence or divergence in the rays of light 
which traverse it. Though any transparent medium may be 
used in their construction, they are, in practice, made almost 
entirely from crown or flint glass, or a combination of both. 
They are, therefore, spoken of as crown, flint, or compound 
Senses. The other substances which are occasionally used in 
uiaking them for special purposes are quartz or rock-crystal, 
Iceland spar, and rock-salt. A few have been made of diamonds 
and other gems. 
As regards their form, those employed in optics usually have 
spherical curvatures, but elliptical, parabolic, and cylindrical 
are also employed. 
526. Parts of Spherical Lenses. —ln spherical lenses one or 
both surfaces are parts of the surface of a sphere. Fig. 228 446 
OPTICS 
illustrates the section of such a 
lens made through its centre. The 
term spherical has no reference to 
the circumference of the lens by 
which it is fitted into the brass or 
other tube, but solely to the curva- 
tures represented in section by 
DXD' andDX'D'. 
The line EX', by which the 
curve D X; D' is described, is its 
radius of curvature, and the point 
on which the radius revolves is 
the centre of curvature; on the op- 
Pig. 228. 
convex lens. 
posite side the centre of curvature for DID' is found. 
A line connecting the two centres, and piercing the lens at 
X X', is the principal axis of the lens. Where one surface is 
plane, the principal axis is the line let fall from the centre of 
curvature of the spherical face perpendicularly upon the plane 
face. 
The line D D', drawn from one point of the circumference to 
that exactly opposite is called the diameter. The axis and 
diameter are perpendicular to each other. 
The aperture of a lens is the angle between lines connecting 
the extremities of a diameter with the principal focus. 
527. Forms of Spherical Lenses.—There are six forms of spheri- 
cal lens produced by plane and curved surfaces, as represented 
in Fig. 229. Of these, Xos. 1, 2, and 3 are thicker in the axis. 
Fig. 229. 
Forms of convex lens. 
All such lenses exercise a convergent action upon rays of light 
which pass through them. 4, 5, and 6, on the contrary, are 
thinner at the axis, and produce divergence. 
In the convergent series, 1 has both surfaces curved outwards; 
it is, therefore, called a double convex. 2 has one surface plane, LENSES. 
447 
and the other convex; is known as plano-convex. 8 has one sur- 
face concave, the other convex; and is termed a converging con- 
cavo-convex. In the divergent series, 4is a double concave; 5, a 
plano-concave; and 6, a divergent convexo-concave. 
Where one surface of a lens is convex or bulging, and the 
other concave or hollow, as in Uos. 3 and 6, it is called a 
meniscus. So 3is a converging meniscus, and 6 a diverging meniscus. 
Where the two curvatures are parallel, and little or no true lens 
action is exerted, the term simple meniscus is applied. 
528. Action of Convex Lenses Explained.—lt was stated in (498) 
that a ray of light in its passage through a prism is deviated, 
or deflected towards its base. Upon this and other properties 
possessed by prisms, all the actions of lenses may be explained. 
In the discussion of this subject we quote from Weinhold. 
“ In Fig. 230 let B represent a small prism of glass which re- 
Fig. 230. 
Convex lens dissected. 
fracts a ray of light proceeding from A in such a manner that 
it reaches the point C. The prism I), having a smaller refracting 
angle than B, produces less deviation, and if the refracting 
angle he suitably adjusted the ray A I) may also be refracted 
towards C ; similarly, if the prism E has a still smaller refracting 
angle, and the latter is properly chosen, the ray A E will meet 
the other rays also at C. These three prisms have their re- 
fracting edges directed upwards; three corresponding prisms, 
with their refracting edges downwards, viz., the prisms f OH 
will, if their refracting angles have the required magnitude, 
refract the rays from A also towards C. Finally, the central 
ray between the prisms passes from A to C without refraction. 
It follows that, with a suitable arrangement of prisms, a number 
°f rays which diverge from A may be brought to converge 
again at a point C. 
“It will be easily seen that the series of prisms need not be 
arranged one vertically above the other. The figure may be 
supposed to represent a section through a series of prisms ar- 
ranged in a horizontal line; and, in fact, whatever the arrange- 
ment of the series, whether horizontal or vertical, or inclined 
to either of these directions, the effect will be the same: the 448 
OPTICS. 
rays from A which impinge upon the prisms will be refracted 
towards a point C. 
“ It follows further, since the deviation of a ray does not 
depend on the distance of the refracting surfaces from one 
Fig. 231. 
another, but solely upon the angle between 
them, that a mass of glass of the shape rep- 
resented in B, Fig. 231, must have pre- 
cisely the same effect as the combination of 
separate prisms represented at A in the same 
figure. The upper and lower portions of B, 
viz., a and g, are exactly equal to the prisms 
a and gin A; b and fin B have their refracting 
surfaces further apart than h and/in A, but 
they are in both cases equally inclined to one 
another, hence they produce the same devia- 
tion ; c and e in B are much thicker than c and 
e in A, but here also the refracting angles, and 
consequent!} 7 the deviation, is the same. The 
Structure of convex 
lens. 
central portion d in B has parallel faces, and a ray of light 
passes through it without suffering deviation ; it is the same as 
if the rays were passing through the empty space d in the 
centre of A.” 
“ A lens of glass, such as C, may thus be considered as a 
combination of an infinite number of prisms called its elements, 
the refracting angles of any consecutive pair of which differ 
infinitely little from each other, and such a lens will serve better 
for collecting rays which emanate from a luminous point, and 
bringing them to convergence at some other point, than a series 
of separate prisms whose refracting angles differ considerably.” 
The plano-convex lens 2, Fig. 229, and the converging meniscus 
3, act in the same manner. For all three forms of converging 
spherical lens the point of crossing of the rays is called the 
focus. As with a concave mirror, it is a real focus, and will pro- 
duce an image upon a screen. 
529. Action of Concave Lenses Explained.—ln this, as in the 
preceding case, the principle involved is that of the power of 
prisms to deflect rays towards their base. Conceive that in Fig. 
230, instead of having the bases of the prisms towards the 
central space, their edges look inwards, it is then evident that 
the rays from A instead of being converged towards C, would 
be forced to undergo still greater divergence, and a combination 
having a divergent action would result. We may, therefore, 
conclude that a concave lens is made up of an infinite number of 
prisms, the sections of which have their apices looking towards 
the centre, or axis of the lens, and their bases towards the cir- 
cumference. As in the case of convex lenses, the action of the LENSES. 
449 
other forms of concave lenses is explained upon the same prin- 
ciples as for the double concave. 
It will be remarked that concave lenses act in a similar 
manner to convex mirrors, causing the rays which have fallen 
upon them to diverge. Like their companion mirrors they, 
therefore, do not have a real focus; but a virtual one may be 
found by prolonging the course of the emergent rays backwards 
through the lens. 
530. Principal and Conjugate Foci of Convex Lens.—The prin- 
cipal focus of a convex lens is its focus for incident rays L B, 
which are parallel to its principal axis M IST. All such rays will 
Fig. 232. 
Focus of convex lens. 
be converged very nearly to the same focus F upon the principal 
axis MF, providing the arc DAE does not exceed 10°. The 
distance F A is the principal focal distance. 
In all ordinary crown glass lenses where the radii of curvature 
of the two faces are equal, the principal focus, and the centre of 
curvature are nearly coincident. When, in place of being 
parallel the rays falling on a convex lens are divergent, or pro- 
ceed from a luminous point, the position of the focus and 
character of the emergent pencil will vary greatly. As with 
concave mirrors, numerous conditions present themselves, 
Ist. When the luminous point is at the focus of the lens the 
emergent rays will be parallel, for the conditions are a simple 
reversal of those in Fig. 232, in which parallel rays are brought 
f° a focus. 
2d. Take the same lens and represent its focus for parallel 
rays by the dotted lines SBB F, Fig. 233. Then, if a luminous 
Point L is placed on its principal axis at a greater distance than 
fhe principal focal distance F', the divergent pencil from L will 
oe brought to a focus at I, beyond the principal focus F on the 
opposite side. In like manner, a luminous point at I will be 
brought to a focus at L. Hence, these are called conjugate foci, 
as with concave mirrors. 
3d. When a luminous point I is at double the focal distance 
°f the lens, the rays are brought to a focus at an equal distance 
on the opposite side, and the object and its image are of equal 
dimensions. 450 
OPTICS. 
4th. As the luminous point I moves nearer to the principal 
focus F, the focus for the emergent pencil L moves further 
away; finally, when I reaches F, the rays are parallel, and there 
is no focus, or it is at an infinite distance. 
Fig. 233. 
Conjugate foci. 
sth. When a luminous point is nearer to a lens than its prin- 
cipal focal distance F, as at L, Fig. 234, though the rajs hi K 
and G M, which emerge on the opposite side, have undergone 
convergent action, and are less divergent than before, they still 
Fig. 234. 
Virtual focus of convex lens. 
diverge, and cannot form a true focus. In this, as in a similar 
condition of affairs in a concave mirror, hy prolonging the rays 
K H and M G along the dotted lines a virtual focus is found at I. 
531. Action of Convex Lens on Convergent Rays.—ln Fig. 234, 
IetKHM G represent a convergent pencil of light coming from 
a long focus lens which would reach a focus at I; and IF G a 
double convex lens with F as the principal focus for parallel 
rays 8. When the convergent pencil HIM I is caught upon 
the lens, the convergence is increased, and the (rays are brought 
to a focus at L. 
By combining together a number of lenses, and increasing the 
convergence of the pencil of light step by step, the exceedingly 
short focus and high magnifying power used in microscopes are 
obtained. 
532. Determination of Foci of Lenses.—To determine the prin- 
cipal focus of any convex lens, it must receive the sun’s rays 451 
LENSES. 
parallel to its axis. The emergent pencil is then projected upon 
a piece of paper, when the point at which the sun’s image is 
smallest and sharpest is the principal focal distance. 
When direct sunlight is not available, the following plan may 
he followed: Place the lens in front of an object, and project 
the image upon a screen. Then adjust the relative positions of 
the screen and lens, until the image and the object are of the 
same size. Measure the distance from the object to the screen, 
divide it by four, and the quotient is the focal distance of the 
lens (530, 3d). 
For a double concave lens, cover the face with lampblack, 
remove this at two small spots, which should be in the same 
principal section, and at equal distances from the axis. A beam 
of sunlight is then received on the opposite face, and the screen 
adjusted, until its position is such that the two spots of light on 
the screen are twice the distance from each other. This is equal 
to the focal distance. 
533. Optical Centre. Secondary Axes.—The optical centre of 
every lens is upon its principal axis, and any ray passing through 
this point does not undergo angular de- 
viation, since the track of the emergent 
ray is parallel to that of the incident ray. 
The position of this point may be found 
as follows: Let C A and C' A' be two 
pa-rallel radii, drawn respectively from the 
centres of curvature C and C' The two 
plane elements (528) at A A' on the sur- 
face of the lens are then parallel, since 
they are perpendicular to these lines. The 
Fig. 235. 
Optical centre. 
ra.Y A A', therefore, passes through a medium with parallel faces, 
and the emergent ray is consequently parallel to the incident 
raJ. The point Oat which the ray AA' cuts the principal axis 
°t the lens is its optical centre. 
The optical centre of double concave and meniscus lenses 
can be found by the same method. In plano-concave or convex 
lenses it is the point where the axis pierces the curved surface. 
All straight lines which pass through the optical centre of a 
lens without cutting the centre of curvature are secondary axes. 
If the secondary axes make small angles with the principal 
axes, they may be considered as equivalent thereto, as regards 
all that has been said concerning foci. This is of importance in 
the explanation of the formation of images by lenses. 
, 534. Images formed by Convex Lenses may be real or virtual, 
since the image of an object, as in mirrors, is the collection of 
tbe foci of the points forming it. 452 
OPTICS. 
The manner of formation of a real image may be seen from 
an examination of Fig. 236. A B is the object, placed at a 
greater distance than the principal focus. A a is a secondary 
axis passing through 0 the optical centre. ACis a ray which 
on reaching the lens is refracted first at C and then at D, and 
cuts the secondary axis at a. All other rays from the point A 
will also meet in aas their conjugate focus. A secondary axis 
Fig. 236. 
Formation of image by convex lens. 
drawn from B, and a ray therefrom, will in like manner meet 
at b. All points of A B will thus have their conjugate foci 
between a and b, and a real inverted image of A B will be pro- 
duced at a b, which may be projected upon a screen or seen 
directly by the eye. 
If, on the contrary, a b is the object, its image appears at A B. 
From these facts important consequences follow: 
Ist. A large object at a great distance from a convex lens produces 
a small real inverted image a little beyond the principal focus of the 
lens, as in an ordinary photographic camera. 
2d. A small object a very little beyond the principal focus of a 
convex lens, forms a large real inverted image at a considerable dis- 
tance beyond the principal focus. Illustrated in the case of the pro- 
jection lantern. 
3d. In the first case, the greater the distance the smaller the image. 
In the second, the nearer the object to the focus the larger the image. 
Fig. 237. 
Virtual image by convex lens. 
It remains to examine the case where the object is placed 
between a convex lens and its principal focus, as in the simple LENSES. 
453 
microscope or magnifying glass. Under these circumstances 
only virtual images are formed. In the figure let A B represent 
the object. Draw a secondary axis 0 a through the point A. 
The ray A C emerges at D, and if the emergent ray O be pro- 
longed backwards to «, it cuts the secondary axis at a, which is, 
therefore, the virtual focus of A. In like manner B finds its 
virtual focus at 6, and all points between A and B have foci be- 
tween a and b. The eye placed in the position indicated sees 
the image of A B at a b. The image, moreover, is virtual, 
erect, and larger than the object. 
535. Images Formed by Concave Lenses.—Like their foci, the 
images by a concave lens are always virtual. In the figure A B 
is an object placed in front of a 
concave lens. A 0 is then a secon- 
dary axis to A. Bays, as A C and 
A I from A, are twice refracted, 
and emerging from the lens in the 
directions I) E and Gr H, diverge 
from the secondary axis A 0. 
Prolonging the track of the emer- 
gent rays D E and G H back- 
wards they cut the secondary axis 
at a,, where a virtual image of the 
point A is seen by the eye placed 
Fig. 238. 
Virtual imago by concave lens. 
on the opposite side of the lens. In like manner, images of all the 
points of A B appear between a and b. Therefore, a b becomes 
the image of AB. It is virtual, erect, and smaller than the object. 
-536. Spherical Aberration.—ln discussing the question of the 
foci of lenses, it has been assumed thus far, that all rays 
falling upon the lens meet at the 
same focal point on the opposite side. 
This is practically correct while the 
aperture (526) is not greater than 10°. 
When it exceeds this, as in Fig. 239, 
the rays r' r', which emerge from 
the central parts, L, have a longer 
focal distance, c, than those, r r, which 
emerge from the parts near the edge, 
as at fin the figure. To this phe- 
nomenon the name of spherical aherra- 
Fig. 239. 
Spherical aberration. 
tion by refraction is given, and the intersections of the refracted 
rays are called caustics by refraction. 
By Fig. 239, it is also evident that spherical aberration may 
be examined in two ways: Ist. As regards the distance from c, 
tbe focus of the central rays to /, that of the marginal. This 454 
OPTICS, 
is called longitudinal spherical aberration. 2d. The rays r' r' come 
to their focus at c, while r r reach theirs at/', and then diverging 
form an aureola around the image produced by the central por- 
tions of the lens. The diameter of this is represented by ah. 
To it the name of lateral spherical aberration is given. The 
position of least aberration is between/' and/. 
Longitudinal aberration increases or diminishes as the square 
of the diameter of the aperture, and inversely as its focal 
length. Lateral is proportional to the cube of the aperture, and 
inversely proportional to the square of the focal length. Or, 
double the diameter, and the longitudinal is increased four times, 
and the lateral eight times. The diameter remaining the same, 
and the focal length being doubled, the longitudinal is reduced to 
one-half, and the lateral to one-fourth. 
It being impossible to obtain clear or sharp definition while 
spherical aberration exists, various methods are resorted to 
for its correction. 
Ist. The aperture is reduced by means of stops (542). Their 
action is to cut off the rays from the circumference, and allow 
only the passage of a central pencil. Thus greater sharpness of 
definition is gained, but at serious cost in the brightness of 
illumination. At the best this plan is only partial, never com- 
plete in its action. 
2d. By constructing the lens with faces of different radii of 
curvature—A CB, AD B. The extent and character of this 
variation depends upon the distance of the object. If 
the radiating point is at infinity, the most convex sur- 
face should be turned towards it, and for crown glass 
the radii of curvature should be as 1: 6. 
As the radiating point approaches the lens, the sur- 
face towards it should become less and less convex 
as regards the other face; e.g., the radii should be 
2:5 3:4 4:3 —until when it reaches the prin- 
cipal focus it should be 6:1, or the reverse of what 
it was when at infinity. 
Lenses made on this principle are called lenses of 
best form, and also crossed lenses. 
3d. In place of using a single one of short focus, 
two or three convex lenses of longer focus are placed 
close together. Thus a combination of the same 
Fig. 240. 
Crossed lens. 
q ( , 
short focus, but with considerably less spherical aberration, is 
obtained. 
4th. By combining a concave lens with the convex. The 
material of the second may be similar to that of the first or 
unlike. Usually it is different. 
The manner in which this acts is easily understood when we 
reflect, that in the concave or diverging lens the thickness is LENSES. 
455 
greatest at the circumference, hence the aberration is in an 
opposite direction to that of the convex, and corrects it. It is, 
therefore, only necessary to secure a proper relation of radii 
of curvatures in both, when a converging combination almost 
entirely free from spherical aberration is obtained. Lenses of 
this description are called aplanatic. 
537. The Coma.—Spherical aberration has thus far been con- 
sidered only as applied to rays parallel to the principal axis. 
It remains to speak of the consequences arising when rays 
fall upon a lens obliquely to its axis. In Fig. 241, suppose 
Fig. 241. 
The coma. 
the aberration for parallel rays is represented by A, the space 
between the interior and exterior circles being the aureola of 
aberration. B and C then represent the changes that take 
place as the rays become more and more oblique to the axis, 
until finally the appearance at Dis produced. To this the 
term coma is applied, 
A lens which is aplanatic for rays parallel to its axis, is not 
so for those oblique thereto. The correction for this condition is 
attained in part by the use of properly placed diaphragms. 
538, Chromatic Aberration.—All simple lenses give images the 
uiargins of which show coloration which does not belong to the 
original. This sequent of lens action is called chromatic aberra- 
tion. 
In describing the action of lenses (528) it was shown that the 
principle involved was that of refraction, as with prisms. Since, 
a lens is in fact a combination of an infinite number of prisms, 
follows that as a prism not only refracts light, but also decom- 
poses and disperses it into different colored rays, a lens must 
have the same effect, and hence the coloration of the margins 
°f the images it produces. 
In Fig. 242 this action is represented, A being the luminous 
Point, L the lens. As the violet rays are the more refran- 
gible, they come to a focus at Y, while the red are prolonged 
f° R. The maximum for light is in the yellow (511), while that 
for chemical rays is in the violet region. Setting aside the 
annoyance arising to the eye from marginal coloration, it 456 
OPTICS. 
therefore follows, in photographic operations, that when an 
image is sharply focussed on the ground glass, the photographic 
picture is badly out of focus. Hence we perceive there are 
two foci for a simple lens, viz., the visual focus and the chemical 
focus. 
Fig. 242. 
Chromatic aberration. 
Correction for chromatic aberration in photographic opera- 
tions may be obtained by using a blue or violet monochromatic 
light. The method by passing the light through ammonio- 
sulphate of copper (513) is the best, especially for microscopic 
photography. This does not answer for removal of marginal 
coloration in optical contrivances used by the eye, as micro- 
scopes, telescopes, etc., as the natural colors of the object would 
also be changed or interfered with. For such instruments the 
lenses themselves are corrected as follows. 
539. Achromatic Lenses are so called because they furnish 
an image free from the marginal coloration we have been 
considering. 
In (508) the achromatic prism is described. It is composed 
of crown and flint glasses, the dispersive power of which is so 
different, that by a combination of the two dis- 
persion is corrected, while considerable refractive 
power remains. It is upon this principle that the 
achromatic lens first made by Dolland depends for 
its mode of action. 
In Fig. 243, A represents a concave or diverging 
meniscus of flint glass, and B a convex or con- 
verging lens of crown glass. These have one face 
in common, by which they are usually cemented 
together. Their curvatures are, moreover, so ad- 
Fig. 243. 
Achromatic lenses. 
justed that they are aplanatic, and not only chromatic but also 
spherical aberration (536) is corrected. 
While achromatic lenses give an admirable optical image, 
they often fail to give good photographs from a want of coin- 
cidence in the visual and chemical foci. This can be corrected 
either by making a suitable change in the position of the plate, 
which is determined by trial, or by passing the light through an 
ammonio-sulphate of copper solution (538). LENSES. 
457 
540. Aberration by Curvature of the Field.—Let ABC repre- 
sent a plane at a distance from the convex lens D. The rays 
from the point B will come to a focus 
at E, while those from A and C will 
reach their foci at F and G respec- 
tively. The points E F G, being 
nearly equidistant from the optical 
centre of the lens, the field will con- 
sequently be curved, and an image 
cannot be formed on the plane H L, 
in which both the central and marginal 
portions are sharply defined. To this 
aberration the name of curvature of 
the field is given. In the eye the 
Fig. 244. 
Convex image. 
image is received upon the interior of a sphere which offers 
a field of the curvature in question. 
The correction of this in photographic lenses is accomplished 
by a proper relation of the position of the diaphragm to the radii 
of curvature of the lenses forming the combination. 
541. Depth of Focus is the property of giving well-defined 
images in planes of unequal distances from the optical centre 
of the lens. This may be experimentally illustrated as follows. 
Take an opera glass and focus it for objects at a distance. Then 
direct the glass to those nearer, they will appear equally well 
defined, yet the foci for the near and distant are not the same. 
Again direct the glass to a distant object, it will then be found 
that the eye-piece may be moved forwards and backwards 
through a small distance without injury to sharpness of defini- 
tion. This distance represents the depth of focus of the lenses. 
This property varies with the aperture, as in Fig. 245. Let D 
represent a lens in use with its full aperture exposed, the parallel 
Fig. 245. 
Depth of focus 
rays rr’ come to a sharp focus at ain the plane A. Movement 
of the ground glass receiving the image towards the planes 
b- or B, instantly injures the definition. 
Suppose that a stop is placed in front of the lens and its 
diameter reduced as at J)f. The parallel rays rr’ passing 458 
OPTICS 
through this portion, since they converge at a much smaller 
angle than in the preceding instance, appear to give equally 
sharp images, whether the screen is at the distance A, or at B 
or C. 
A convergent lens can, therefore (in apparent contradiction 
to the law of conjugate foci), give sharp images in planes some- 
what distant from each other. This, however, only takes place 
when the object is distant from it; as it approaches, the depth 
of focus diminishes. 
542. Stops and Diaphragms.—Formerly these terms possessed 
the same significance in physics, but great advances in con- 
struction of photographic lenses have led to a special applica- 
tion of each terra. The apparatus is the same, consisting of a 
disk of metal equal in diameter to the lens, and having a cen- 
tral aperture which varies in each, so a series 
with different openings is formed which can be 
used either as stops or diaphragms, according to 
their position. 
When used as a stop, it is placed close to the 
lens Masin 0 D, Fig. 246. It then cuts down 
the aperture to the diameter of the opening of 
the stop, and only the central portions, ABCD, 
are in use, and represent the full size of the 
pencil of rays that can pass it. 
When, on the contrary, it is placed at a 
proper distance it becomes a diaphragm. The 
full aperture is employed, and only those rays 
from different parts of the lens which it is 
Fig. 246. 
Stops and diaphragms. 
necessary to cut off are interfered with. In all ordinary optical 
instruments their position has been fixed by the maker, and care 
should be taken not to change or disturb them. 
In explanation of the action of a diaphragm, let us consider 
the conditions Fig. 247. ABC represent three distant points, 
and L L a convex lens. The rays from B indicated by the 
dotted lines, come to a focus at F. Hot so with those from A, 
which are marked I, 11, HI, IY, Y. Of these, AI is refracted 
to a, AII to b, 111 to c, IY to d, Yto K A similar result 
occurs with C 1, 2, 3, 4, 5. 
How suppose a diaphragm be placed in the position indicated 
by OP. The conditions in Fig. 248 then arise. Only the rays 
4 and IY, 5 and Y, from A and C, which have their focus near 
the same plane as F, can reach the ground glass screen. Others 
which injure definition have been thrown out, and the image 
gains in sharpness thereby. 
It is, in addition, evident that the smaller the opening of the 
diaphragm the cleaner cut the image. To this there is a limit, LENSES. 
459 
as after a certain size is reached any further diminution causes 
phenomena of diffraction to appear, which injure the definition 
Fig. 247. 
of bright objects. A star, for example, in place of appearing 
as a point, seems surrounded by rings. 
Spherical aberration. 
Fig. 248. 
Action of diaphragm. 
In place of diaphragms formed in the manner described, a 
very ingenious arrangement called the iris diaphragm is attached 460 
OPTICS. 
to microscopes and other instruments. It consists of a series of 
radiating plates which surround a central opening. By revolving 
a ring on the exterior, their position and the size of the central 
opening are altered. The change of aperture imitates that seen 
in the iris of the eye. 
CHAPTER XXIY. 
FORMATION OF IMAGES BY REFRACTION. 
The camera lucida—The camera obscura—The magic lantern—The solar micro- 
scope—The oxyhydrogen lantern—Photo-electric lantern—The megascope. 
543. The Camera Lucida is an instrument frequently used in 
sketching objects viewed through the microscope. In that in- 
vented by Wollaston, in 1804, the principal section is as repre- 
sented, Fig. 249. It is a four-sided glass 
prism, acting by total reflection. The angles 
are, two of 67° 30', one of 90°, and one of 135°. 
A ray entering normally in the direction 
x r', is totally reflected from the face d c, in 
the direction r' r, impinging upon the face 
da, since the angle formed is again greater 
than the critical angle, it undergoes a second 
total reflection, and emerges in the line 
ra. The eye placed at p p perceives the 
object in the direction indicated by the dotted 
Fig. 249. 
camera incida. 
lines, and if the adjustment is such that the edge of the prism 
only occupies half of the field of vision, it is projected upon a 
surface of white paper placed at a distance of about ten inches 
from the eye. If the point of a pencil is placed thereon it is 
seen with equal distinctness, and the image may be easily traced 
with it. In some cases a lens is added, as at pp. 
544. The Camera Obscura was the invention of Porto, a Nea- 
politan physician. In its first form it was a long double rec- 
tangular box. One section, B, was smaller than the other, 0, 
enabling it to slide therein, as in an ordinary telescope, making 
the box of different lengths. At one end, L, a minute opening 
was made. The opposite end was formed of a flat sheet of ground 
glass, E. Directing this towards an illuminated landscape, the FORMATION OF IMAGES BY REFRACTION. 
461 
rays therefrom formed an inverted image on the ground glass 
the size and brightness of which were varied by sliding this 
section of the box nearer to or further from the aperture. 
In place of using a minute aperture for the entrance of the 
rays, Porta soon found that by substituting a convex lens L a 
Fig. 250. 
Camera obscura. 
much brighter image was produced, the definition of which was 
easily perfected by a slight forward or backward movement of 
the ground glass. 
In this form, with various improvements in the character of 
the lenses L L', and means of focussing D A, the camera obscura 
has now become the well-known photographic camera. 
The term camera obscura, as its name indicates, is also ap- 
plied to rooms of considerable dimensions, and generally in the 
form of a tent. At the apex of this there is a lens and prism so 
combined, that the latter reflects the image produced by the 
former in a downward direction upon a table placed in the 
centre of the room, as the screen of the Visitors look- 
ing at the table, obtain a panoramic view of all that passes across 
the field of view outside the building. 
.545. The Magic Lantern is an instrument the operation of which 
is exactly the reverse of the camera, for while the latter produces 
a diminished image of the object, the lantern forms an enlarged 
one. 
The essential parts of the apparatus are a tin box, in which a 
lamp of some form is the source of light. By means of a para- 
bohc mirror, A, as much as possible of 
the light is passed through the convex 
lens B, and concentrated upon Y, the 
pbject to be reproduced. At C there 
18 a double convex lens, the position of 
which from Y is a little more than its 
°wn focal distance. The action of the 
Fig. 251. 
Magic lantern. 462 
OPTICS. 
apparatus is to form a real and magnified image of the object 
upon a screen. 
The so-called dissolving views are produced by using two 
similar lanterns, in which different pictures, or slides, have been 
placed, and directing the images upon the same parts of the 
screen. As the light is gradually shut off from one and turned 
on the other, the former merges gradually or dissolves with the 
latter. 
546. The Solar Microscope is a magic lantern in which the sun is 
used as the source of light. The objects are very minute, and 
subjected to great magnifying power—like the magic lantern, it 
is used in a darkened room. 
The parts are: Ist. A plane mirror by which the solar rays 
are directed along the optical axis of the instrument. 2d. A 
condensing arrangement consisting of two convex lenses. 3d. 
A suitable stage for support of the object at the focus of the 
condensing system. 4th. The projecting apparatus generally 
formed of one or more achromatic lenses, the whole having a 
very short focus, and consequent high magnifying power. 
The intense heat at the focus is apt to injure objects submitted 
to its action; to avoid this, the solar rays are passed through a 
saturated solution of alum, enclosed in a glass cell, with flat 
parallel walls. 
547. The Oxyhydrogen Lantern.—The oxycalcium light resulting 
from projecting the flame of mixed oxygen and hydrogen gases 
upon a cylinder or pencil of calcium oxide is generally employed. 
It is fixed in its position in the optical axis of the apparatus, and 
thrown into operation with comparative facility when cylinders 
containing the compressed gases are available. It has sufficient 
intrinsic brilliancy for the majority of experiments. The diffi- 
culties in the way of its use are, however, serious, and it is very 
desirable they should be lessened. They arise chiefly from the 
volatility of the calcium oxide at the intensely high temperature 
employed. The volatilized material depositing on the condens- 
ing lenses prevents the passage of luminous rays, and the cavity 
formed in the cylinder of lime at the spot where the flame im- 
pinges soon diminishes the brilliancy of the light; this necessi- 
tates a change in position of the lime cylinder to present a new 
surface to the flame, and this in its turn implies a distraction of 
the attention of the experimenter, which interferes seriously 
with the thorough management of his subject. Though attempts 
have been made to avoid this difficulty by clockwork, or other 
mechanical contrivances, they are still unsatisfactory in their 
action. Another serious objection is the necessity of placing FORMATION OF IMAGES BY REFRACTION. 
463 
the cylinders in a closed vessel when not in use to protect them 
from action of the air. 
The oxymagnesium light is similar to the preceding, differing 
only in the substitution of a cylinder or pencil of magnesium 
oxide for calcium oxide, and the light emitted is of equal bril- 
liancy. Following the instructions given for preparation of 
these cylinders, I have taken the greatest pains to procure sam- 
ples of magnesium oxide of the utmost purity. I have also 
tried various other methods, among which the combustion of 
the metal in oxygen may be mentioned, but failure has thus far 
attended all efforts to make pencils or cylinders able to with- 
stand the intense heat of the flame of mixed oxygen and hydro- 
gen gases without undergoing volatilization. The pencils ob- 
tained were fully equal in this respect to those of calcium oxide; 
hut 1 did not find any superiority that repaid me for my trouble. 
The oxyzirconium light produced by action of the flame of 
mixed oxygen and hydrogen gases on a cylinder of zirconium 
oxide meets every requirement. It has intrinsic and invariable 
brilliancy, a fixity of position in the optical axis of the appa- 
ratus, and does not volatilize under the heat employed. The 
condensing lenses remain free from deposit, and after the light 
is once adjusted the experimenter can carry on his demonstra- 
tions without any distraction of attention that attends the use of 
other lights. All that is necessary is, according to the size of 
the reservoirs of compressed gas, to open the cocks a little as 
pressure diminishes. There is also no need to remove the zir- 
conium oxide pencil from its position, as with calcium oxide; it 
may, on the contrary, remain in situ for any length of time, and 
18 always ready for use. 
In lanterns as ordinarily constructed for projection of photo- 
graphic or other images on a screen, the support or stage on 
which the photographic slide is placed is close to, and at an 
invariable distance from, the condensing lens. While the objects 
projected are nearly equal in size to the diameter of the con- 
denser, this is the only adjustment that can be made to illuminate 
their whole surface; but, when the diameter of the field occupied 
hy them is only one-half or one-quarter that of the condensing 
lens, the brilliancy of result obtained may be greatly increased 
by removing the supporting stage or object-carrier to a greater 
distance from the condenser, allowing a convergent beam of 
light to fall on the object. To accomplish this I have constructed 
fbe following form of lantern: 
In Fig. 252, a is a zirconia light, mounted on an adjustable 
base (see “American Journal of Science and Arts/’ Sept. 1877, 
page 208), which may be used with a condensing lens of very 
short focus, since the zirconia is not burrowed into cavities 
where the oxyhydrogen flame impinges, which happens with lime 464 
OPTICS. 
cylinders, and causes the flame to be reflected upon the con- 
densing lens, thereby destroying it. In the jet employed, the 
gases are mixed just before ignition, hbis a short focus con- 
densing combination, c the stage or support carrying the pho- 
Fig. 252. 
Projection lantern. 
tographic or other design to be projected, d the projection 
lens formed of three sets of lenses, and giving a perfectly flat 
rectilinear field, ac d are mounted on a base board, e/, to the 
end of which the lantern box a b is attached, freely open above 
and below to permit perfect ventilation. The base carries lateral 
grooves in which a c d slide, allowing them to be placed at vary- 
ing distances from b, and fixed by suitable binding screws, c 
and d are also connected by a rod r carrying an adjustment 
screw at r, by which change of distance between d and c, re- 
quired in giving the correct focus, is obtained. The base ef is 
attached to a second or under base g h by a hinge at h, which 
allows the end e of the movable base e f to be raised to any 
required angle, at which it may be maintained by a block at t. 
So convenient and compact is this lantern that it can readily be 
stowed away in a small trunk. 
When a series of objects of different sizes is projected, as with 
microscopic photographs taken under the same adjustments, it is 
a great gain in the projection of smaller objects if the circle of 
light used for illumination is reduced; and at the same time 
increased in brilliancy. This is accomplished as rapidly as can 
be desired by removing d c together, along the slide of the base 
ef to a sufficient distance from the face of the condenser b to 
allow the convergent rays from the latter just to cover a circle 
which will include the object. The greater intensity of illumi- 
nation thus obtained renders the definition of fine markings or 
other peculiarities on small objects as clearly visible at consider- 
able distances as are coarser ones on those of a larger size under 
a weaker light. FORMATION OF IMAGES BY REFRACTION. 
465 
For projection of the spectrum a slit is placed in front of the 
condensing lens. This is brought to a focus.on the screen by 
the projecting lens. One or more prisms, according to the 
character of the experiment, are then placed on a platform in 
front of, or close to the outermost lens of the projecting com- 
bination, when a fine spectrum will appear in the proper posi- 
tion. To obtain the best results, the prisms should be adjusted 
for minimum deviation. 
The form of this lantern also permits its use as a projecting 
microscope. An alum cell (546) is placed between the con- 
denser b b and the stage c. A microscope objective combination 
is substituted at d. Thus arranged, I have shown the circula- 
tion in the web of a frog’s foot, so that blood-corpuscles could 
be seen moving in single file through the smallest capillaries, 
each perfectly distinct, and about an inch in length. 
For projection experiments in polarization, the outer element 
h of the condenser is removed, and a nearly parallel beam ob- 
tained. This is received upon a reflecting polarizer of fifteen 
or twenty plates. The polarized beam is thus cast downwards, 
when it is received on a surface of polished silver, and sent 
through the axis of the projecting lens, which must be placed 
lower for the purpose, and armed with a Mcol or a double 
image prism, as an analyzer. By this arrangement I have ex- 
hibited on the screen all the usual experiments in polarization, 
including the colored rings and black cross of calc-spar, and 
demonstrated the method of determining the strength of sugar 
solutions. In the latter case the amount of rotation was shown 
by taking a portion of the transmitted beam and by suitable 
mirrors causing it to act as an index. Movements of the spot 
of light through an arc of forty-five degrees were readily obtained 
by solutions of sufficient strength. 
548, Photo-electric Lantern.—Of all artificial lights the electric 
arc is the most brilliant and its use in lanterns has often been 
attempted. The difficulty, however, is, that no regulator has 
yet been contrived which can furnish a perfectly steady light. 
Where the dynamo-electric current is employed, the variation 
therein, produced by slipping of bands, and other irregular 
actions of the mechanism, cause a distressing effect upon the 
eyes of those who are watching the projected images. By the 
use of the new condensing batteries it is possible that this trouble 
may be overcome. Until this is done, the electric light, in spite 
°f its intrinsic brilliancy, cannot equal the zirconia light in the 
Projecting lantern. 
549. The Megascope is employed for the projection of images 
of coins and other opaque objects. It requires the use of lenses 466 
OPTICS. 
of considerable diameter, and a most brilliant illumination of the 
object. The magnifying power obtained is not very great, but 
is sufficient to enable the experimenter to exhibit such phe- 
nomena as the pulsation of the heart to a large audience. 
CHAPTER XX Y. 
THE EYE AND VISION. 
Parts of the eye—The mechanical mechanism—The optical mechanism—The 
sclerotic and cornea—Crystalline lens—The humors of the eye—The iris—■ 
The second tunic or choroid—The third tunic or retina—Terms applied to 
optical mechanism—Accommodation—Normal action of optical mechanhm— 
Abnormal action of optical mechanism—Spectacles—Binocular vision—The 
stereoscope—Size and distance of objects. 
550, Parts of the Eye.—As the ear is the organ of time, so the eye 
is the organ of space. Its function is to form images of external 
objects upon the retina, and bring them under the cognizance 
of the brain or organ of the mind. The eye is generally de- 
scribed as consisting of: Ist, the mechanical mechanism by which 
the principal axis of the organ is directed towards the object 
to be viewed; 2d, the optical, by which the image is formed 
upon a screen, and brought to a sharp focus; 3d, the nervous, 
by which the image is perceived by the mind; 4th, certain ap- 
pendages as the eyelids, eyelashes, lachrymal glands, ducts, and 
mucous membrane or conjunctiva. Of these the Ist and 2d 
especially command our attention. The 3d and 4th are more 
purely physiological in their character. 
551. The Mechanical Mechanism consists of muscles and tendons 
so attached to the eyeball and the cavity or orbit in which it is 
placed, as to move the principal axis of the organ in different 
directions. Four of these pass straight forwards from the apex 
of the orbit to the ball; they direct the axis upwards, down- 
wards, to the right or left. By means of two others, called the 
oblique, the ball is rotated upon its axis. In all of these except 
one the action is direct. In the superior oblique the tendon is 
long, and passes through a tendinous ring in the inner side ot 
the orbital cavity, giving an example of the application of the 
pulley to the change in direction of a line of force. An exces- THE EYE AND VISION. 
467 
sive contraction of any one of these muscles constitutes the con- 
dition called squinting or strabismus. 
552. The Optical Mechanism may be likened to a camera 
obscura, as regards its parts and manner of action. The box is 
represented by the sclerotic and cornea; the lenses by the crys- 
talline lens, aqueous and vitreous humors; the diaphragm is the 
iris, and the screen is formed by the retina, or nervous mech- 
anism, and the black pigment. 
553. The Sclerotic and Cornea taken together form a nearly 
spherical box about an inch in diameter. They constitute the 
exterior coat or first tunic of the eye, as at a and d in the outline 
of the eyeball, Fig. 253. All the wall, excepting a small an- 
Fig. 253. 
Diagram of a horizontal section of the eyeball. 
a. Sclerotic coat. 
b. Choroid and black pigment. 
c. Retina, 
d. Cornea. 
e. Ciliary muscle. 
/. Iris. ' 
!]. Crystalline lens. 
h. Vitreous humor. 
i. Posterior chamber. 
I. Optic nei’ve. 
m. Ciliary ligament. 
n. Hyaloid membrane. 
o. Canal of Petit. 
r. Sinus circularis. 
s. Ciliary process. 
I. Suspensory ligament. 
terior portion, is composed of the sclerotic, which is a dense, 
tough, opaque, fibrous tissue, and appears in what is known as 
the white of the eye. The anterior portion is the cornea, d; it 
may he regarded as the continuation of the sclerotic, since it is 468 
OPTICS. 
made up of the same tissue. It differs, however, in that it is 
transparent, and its curvature also is greater. As its surfaces 
are parallel to each other, it is a simple meniscus, having of itself 
but little lens action. Its real function is to form the anterior 
surface of the aqueous humor, and give to that fluid a true len- 
ticular form and function. 
554. Crystalline Lens is a double convex lens, g, Fig. 253, of 
unequal curvatures, the anterior surface being less convex than 
the posterior. It is one-third of an inch in diameter, one-sixth 
thick, and enclosed in a membrane, called its capsule. It has 
sufficient consistency to retain its figure when removed from its 
position, though it yields readily to pressure. It is built of 
layers the density of which gradually increases towards the cen- 
tre, as shown in the following determinations of their refractive 
indices, by Brewster: 
Exterior layers of crystalline 
. 1.3767 
Central layers of crystalline . 
. 1.3990 
By this increase in refractive power towards the centre spherical 
aberration is diminished. 
The position of the lens is governed by the suspensory liga- 
ment t, ciliary muscle e, and ciliary processes s. The action of 
these is largely involved in the accommodation of the focus of the 
eye to objects at differ,ent distances. 
555. The Humors of the Eye.—These are two in number, the 
aqueous and the vitreous. The first lies between the posterior 
surface of the cornea and the anterior surface of the lens. It 
is, therefore, a fluid concavo-convex lens. The second h, occu- 
pies the space between the posterior face of the lens and the 
retina at the back of the ball; it also forms a concavo-convex. 
Both of these have a density less than that of the lens. As 
regards its physical appearance, the aqueous is, as its name indi- 
cates, quite fluid in character. The vitreous, on the contrary, 
has a consistency similar to that of the white of an egg. It is 
enclosed in a membrane called the hyaloid. In connection with 
the crystalline lens which lies between them, these keep the 
hollow sphere or cavity of the sclerotic and cornea distended, 
and maintain its spherical form. 
The refractive power of the media composing the eye as 
compared with water, is as follows, according to the determina- 
tions of Brewster: 
Water ...... 
. 1.3358 
Aqueous humor .... 
. 1.3366 
Vitreous humor .... 
. 1.3394 
Crystalline average 
. 1.3839 THE EYE AND VISION. 
469 
556. The Iris is in the aqueous humor, and close to the crys- 
talline lens, g. It is represented at /, Fig. 253. It forms 
the colored (blue, gray, or brown) portion of the eye, which we 
observe when we look into that organ. In the centre there is 
an opening, called the pupil. In the normal state this always 
appears black, because through it we see the dark coating, or 
black pigment, which with the retina forms the screen. 
The iris divides the aqueous humor into the anterior and 
posterior chambers, i. It is not perfectly flat, its central region 
bulging slightly forwards, as in the figure. It is highly vascular, 
and composed of radiating fibres which pass from its circumfer- 
ence to the circular elastic band forming the margin of the 
pupil, and acts as its sphincter. By contraction of this the 
diameter of pupil is diminished, by relaxation it is increased. 
It thus regulates the size of the pencil of light entering the 
eye. Being close to the lens, it acts as a stop thereto, and by 
excluding rays from its margin aids in correcting spherical aber- 
ration. 
557. The Second Tunic or Choroid.—lf we make a section of 
the eyeball from before backwards, through its centre, Fig, 253, 
we find that nearly all that portion of the wall which lies behind 
the iris and includes the vitreous humor, is composed of three 
layers or coats. The exterior is the sclerotic a, which we have 
examined. Immediately within this, and in close contact, is a 
second coat, b, made up of bloodvessels, and cells filled with 
black pigment which give to it a dark, velvety look. This is 
the choroid. 
In its anterior portion it separates from the sclerotic near 
where the latter becomes cornea, and turning inwards and being 
supplied with muscle cells forms the iris,/, described in the last 
article. As it leaves the sclerotic, it separates into two laminpe, 
the anterior forming the iris, and the posterior a series of loops 
which surround the lens. These are known as the ciliary 
processes, s; they are about seventy in number. Beneath the 
ring of these, and in contact with the sclerotic, there is a band 
of radiating muscular fibres called the ciliary muscle, e, which 
has a most important relation to the accommodation of the eye 
for objects at different distances. 
558. The Third Tunic or Retina, is the expansion of the optic 
nerve, Fig. 253, c. By some it is regarded as the screen of the 
optical mechanism, as well as the organ by which the image is 
perceived. By others the black pigment of the choroid coat is 
considered to be the screen, while the retina perceives the image 
produced thereon. Those who believe the retina is both screen 
and organ of perception, allow that the duty of the black pig- 470 
OPTICS. 
merit is merely to extinguish the light after it has served its 
purpose. A very interesting view of the function of the black 
pigment will be found in Prof. J. W. Draper’s “Human Physi- 
ology,” page 390. He directs attention to several points, which 
show that its true function is to act as the screen, while the 
retina perceives the image formed thereon. One of the most 
significant of the facts brought forward, is, that the sensitive 
columns of the retina are directed backwards toward the pig- 
ment, and not forwards toward the lens, as would be the case 
if they formed the true screen. 
There are four layers of the retina, according to Muller. 
These are arranged radially, from within outwards, in the fol- 
lowing order: Ist, fibres of optic nerve; 2d, vesicular layer; 3d, 
granular layer; 4th, Jacob’s layer of cones and rods. 
559. Terms Applied to Optical Mechanism.—lst. Optic centre of 
lens, which may be determined according to method given in 
(533). 
2d. Optic axis, also called the principal axis of the eye, is the 
axis of its figure. It is the straight line h, Fig. 253, passing 
through the centre of the pupil and the optic centre of the 
crystalline lens. 
3d. Optic angle, is that formed between the two optic axes 
when the eyes are directed towards the same point. It is less 
and less as the object is more and more distant. 
4th. Visual angle, is the angle A 0 B formed between second- 
ary axes drawn from the optic centre 0 of crystalline lens to the 
outer limits of the object. It increases with its magnitude, and 
diminishes with its distance, as in Fig. 254, in which the angle 
subtended is much greater at A B than at A' B'. If the visual 
Fig. 254. 
angle is less than half a minute, the true form of an object 
cannot be discerned. A white square of one yard on each edge, 
at a distance of five miles, appears as a bright spot, not distin- 
guishable from a circle of that diameter placed at the same 
distance. 
Visual angle. 
560. Accommodation.—By this is meant the adjustment of the 
optical mechanism until images of objects at different distances 
are brought to an accurate focus on the screen of the eye. 
There are three ways by which this can be accomplished; 
Ist. The elongation of the apparatus in its principal axis, and THE EYE AND VISION. 
471 
thereby moving the screen further from the cornea. The 
method would be similar to that adopted in an ordinary camera 
obscura. The manner in which the result was imagined to be 
attained was, that when the recti muscles all acted together, they 
compressed the zone of the ball to which they were attached, 
causing it to be elongated from before backwards, and assume 
an egg-shape. This is now abandoned. 
2d. Change in distance between the crystalline lens and the screen. 
It having been satisfactorily shown that the eyeball does not 
change its figure, it was then stated that the result was attained 
by moving the lens towards or from the screen. This, it was 
supposed, was accomplished by action of the ciliary muscle. 
3d. Change in curvature of the lens. That this certainly takes 
place is proven by the following experiment; Take a young per- 
son with normal vision, hold a lighted candle in front and a 
little to one side of one of his eyes. Look into his eye from the 
opposite side, three images of the candle flame will be seen : the 
first very bright and erect, this is produced by reflection from 
the cornea; the second not so bright, also erect, comes from the 
anterior surface of the lens; the third fainter, is inverted, and 
is from the posterior surface of the lens. Direct the person 
to look into remote distance. Observe accurately the relative 
size and position of the images. Then let him change the point 
of observation to an imaginary object close at hand, but in the 
same line of light as before, it will at once be noticed that the first 
and third images do not change, while the second alters its 
position and grows smaller. It is, therefore, evident, that the 
anterior surface of the lens has changed its figure, and be- 
come more convex, as it is this which forms the image. These 
differences are represented in Fig. 255, in which the lens is 
Fig. 255. 
Accommodation. 
divided by a line which shows on one side, F, the condition when 
the point of vision is far off, and on the other, N, when it is near. 
a is the aqueous humor, d ciliary muscle, e ciliary process. 
Helmholtz thinks that the manner in which the change in 
%ure is accomplished is as follows: “The lens is invested by a 
thin, transparent membrane, which extends outwards from its 
edge as a circular curtain, and is attached all around to the 472 
OPTICS. 
sclerotic. This membrane is naturally drawn tight by the elastic 
rigidity of the sclerotic, and presses gently on the elastic lens, 
flattening it slightly. This is the normal passive condition, as 
when gazing at a distance. Now there are certain muscular 
fibres (ciliary muscle) which, arising from the exterior fixed 
border of the iris just where it is attached to the sclerotic, run 
backward, radiating, and take hold upon the outer edge of the 
lens curtain. When these contract, they pull forward the tense 
curtain to a smaller portion of the globe, and thus relax its ten- 
sion. This relaxing, relieves also the pressure of the capsule on 
the lens, which, therefore, immediately swells or thickens in pro- 
portion to the degree of relaxation.” According to Helmholtz, 
then, we adjust the eye to near objects by contraction of the ciliary muscle. 
The normal eye in a passive state is adjusted to infinitely 
distant objects. By change of form of the lens, it can adjust 
itself to all .distances up to about five inches. The range of 
adjustment or of distinct vision is, therefore, within these limits. 
It is only at comparatively near distances, however, that the 
change is great. Between twenty feet and infinity the adjust- 
ment is almost imperceptible. 
561. Normal Action of Optical Mechanism.—The following phe- 
nomena present themselves in connection with this subject; some 
purely optical, others partly or wholly connected with the ner- 
vous mechanism. 
Ist. The image of the object is formed at its conjugate foci. 
2d. The images are inverted. 
3d. The eye is not an achromatic apparatus in the usual ac- 
ceptation of the term, since the refractions are all in the same 
direction. The experiments of Mliller, Young, and others, 
have shown that neither is it so in an absolute sense. In spite 
of this, we nevertheless see objects free from chromatism. 
Ganot says: “The cause of this achromatism cannot be accu- 
rately stated. ” 
4th, The best visual distance for small objects, as fine print, is 
ten or twelve inches. This is called 
normal vision. 
sth. The accommodation for differ- 
ences in distance by means of the sus- 
pensory ligament and ciliary muscle is 
perfect, while the eye is in the normal 
state. 
6th. Irradiation. White or bright ob- 
jects appear larger than they really are, 
Fig. 256. 
Irradiation. 
when viewed on a dark ground. A white square on a black 
ground seems to be larger than a black square of exactly the 
same size viewed on a white ground. THE EYE AND VISION. 
473 
562. Abnormal Action of Optical Mechanism.—The term emme- 
tropy is employed to indicate the perfect acting or normal eye. 
In it the focus ranges from five inches to infinity. If removed 
from the orbit, it is found to be adjusted for objects at an infinite 
distance. To adjust it for those nearer requires muscular effort. 
Srom this perfect condition we find the following departures, 
some depending upon imperfect construction, and others upon 
functional derangement. 
Ist. Myopy, or near-sightedness, is a structural defect. Owing 
to excessive refractive power, the focus for objects at a great 
distance falls in front of the retina instead of on it. The rays 
when they reach it are divergent, and to form a sharp image 
the object must be brought nearer. In the emmetropic eye the 
range of vision is from five inches to infinity; in the myopic, 
from one inch to five, from three inches to a yard, or between 
any other two fixed points. Within these limits the property 
of adjustment is as perfect as in the normal eye. 
The myopic eye has been compared to a camera used for 
taking objects close at hand, and when shortened as much as 
possible is still too long to bring those at a distance to a focus 
on the ground glass. 
2d. Presbyopy, or old-sightedness, sometimes incorrectly called 
long-sightedness, is a functional disease. In it the power of ad- 
justment for near objects is lost, or impaired. In other respects 
it is normal. The focus for distant objects, or for parallel rays, 
18 on the retina. As far as known, the trouble is a want of 
elasticity in the crystalline lens, whereby it fails to become more 
convex, or shortens its focus when the ciliary muscle relaxes the 
tension of its curtain. 
The presbyopic eye resembles a camera made to bring distant 
objects to a focus on the ground glass, but by misuse or rust the 
adjustment apparatus fails to focus those which are near. 
3d. Hypermetropy is a structural defect; it is the true reverse 
of myopy. In it the refractive power of the lens is below 
normal, and parallel rays are brought to a focus beyond the 
black pigment instead of on it. While the power of adjust- 
ment is perfect, objects at a distance are brought to a sharp 
focus on the retina, but this is not possible with those near at 
hand. 
Le Conte likens the hypermetropic eye to a camera, which 
when entirely pushed up "is too short for imaging any objects; 
when drawn out will bring distant ones to a focus, but not 
those near at hand. 
4th. .Astigmatism is a structural defect. In it the curvatures 
°f the lenses are not symmetrical. An upper or a lateral half 
pf the lens, or cornea, is not exactly like the opposite half, 
fhe rays are consequently not brought to a focal point but to 474 
OPTICS. 
a line. They may be brought to two separate foci, thus con- 
stituting diplopy, or double vision. Diplopy also arises from 
the concerted action of two dissimilar eyes. 
563. Spectacles are convergent or divergent lenses of glass or 
quartz made for correcting forms of abnormal vision. Each 
requires its proper kind of lens, 
Ist. Myopy requires concave or divergent glasses, which just 
correct the excessive refraction action of the eye. The trouble 
being structural, they should be worn habitually. 
2d. Fresbyopy needs convex glasses to bring objects near at 
hand to a focus. When those at a distance are examined they 
are removed. They should not be worn habitually, but only 
when examining objects close at hand. In very old people, 
when the curvature of the lenses diminishes, it frequently be- 
comes necessary to use convex lenses for distant objects. 
3d. Hypermetropy necessitates the habitual use of convex spec- 
tacles to make the action normal. As age advances, two pairs 
are requisite, one for distant objects, and one for those close at 
hand. 
4th. Astigmatism. In this the curvatures of the different parts 
of the eye not being alike, compound sectional lenses must be 
arranged which correct those departures from the normal, and 
produce on the retina a single well-defined image. When the 
diplopy depends upon a simple difference between the eyes, it 
can be corrected by selecting a lens for each independently of 
the other. 
Spectacles were formerly made either from double convex or 
double concave lenses. These have now been replaced by the 
concave or convex meniscus (527), placed with their curvature 
in the same direction as that of the eye. By these so-called 
periscopic glasses a wider range of vision is attained. 
In closing this article on spectacles, we give the following 
excellent advice from an eminent writer: 
“Men engaged in literary pursuits should read most by day 
and write most bjT night. It is worthy of note that reading 
causes more strain to the eye than writing, and that copying 
work in writing makes a greater demand upon the organ of 
vision than off-hand composition. Twilight and a mixture of 
twilight and artificial illumination should be avoided for any 
kind of work. The pale cobalt-blue tint is the best that can be 
employed when protection for the eye from intense glare is 
sought, as in the case of travelling upon snow-fields in bright 
sunshine. The green glass that is often adopted for this pur- 
pose is not by any means so worthy of confidence. Reading iw 
railway travelling is objectionable in the highest degree for a 
very obvious reason. The oscillation of the carriage continually THE EYE AND VISION. 
475 
alters the distance of the page from the eye, and so calls for 
unceasing strain in the effort to keep the organ in due accom- 
modation for the ever-varying distance of the dancing image.” 
“The exact fitting of the framework of spectacles to the face and 
eyes is of more importance than is generally conceived. If the 
centres of the lenses of the spectacles do not accurately coincide 
with the centres of the pupils of the eyes, the consequence is 
that the images in the separate eyes are a little displaced from 
the positions which they ought to hold, and that a somewhat 
painful and injurious effort has to be made by the eye to bring 
those images back into due correspondence for accurate vision. 
An incipient squint is apt to be in this way produced. People 
should look to the centring of their spectacles for themselves. 
Phis may be easily done by standing before a looking-glass with 
the spectacles in their place. If the fit is a good one, the centre 
°t the pupil should then appear in the centre of the rim. Fully 
formed spectacles are always to be preferred to folding frames, 
because they permit of more satisfactory adjustment in this par- 
ticular, and because they are more easily kept in the right posi- 
tion with regard to the eyes. The only advantage which the 
Pebble or quartz enjoys over glass for the construction of spec- 
tacles is the immunity which it possesses against scratching on 
account of its greater hardness.” 
664. Binocular Vision.—Hold a six-sided pencil vertically at a 
distance of ten inches from the eye, and view it first with the 
right, and then with the left. A difference is perceived in 
each case, the right seeing more or further on the right side, 
while the left sees further on the left side. The image produced 
|8 really flat, and presents only two dimensions, length and 
breadth, as in a picture. When we view the object with both 
eyes, the two images are blended into one, and the impression 
°f relief, depth, or the third element of space is produced. 
Regarding the impression of relief, Weinhold says, “It is 
true that we scarcely fail to perceive this when we look at 
°hjects with one eye shut, but this is the result of a rapid mental 
Process of which we have become unconscious in consequence 
of our constant experience of the succession of things in depth. 
fetill our estimation of depth in space is not trustworthy if we 
rely 
on the information conveyed by one eye only. An ac- 
curately drawn picture of an object makes the same impression 
upon a single eye, at least as regards the external form, as the 
object itself, for one eye is as little able to estimate directly the 
relative distances of the various parts of the object as the picture 
18 °f giving a direct representation of these distances. As a 
consequence of this, a picture produces the greatest resemblance 
ro reality when viewed with one eye only; as soon as the other 476 
OPTICS. 
eye is opened, the picture presents of course the same aspect to 
either eye, and the difference between it and the appearance of 
the real object is at once detected. Thus after viewing with one 
eye the picture of a church interior, or of a row of pillars, the 
depth of the space represented will make the impression of 
reality. This illusion, however, will at once be destroyed on 
opening the other eye; the parts of the picture which form the 
foreground appear to recede, the background seems to move 
forward, and the whole merges into the flat surface of the 
picture,” 
565. The Stereoscope is an instrument by which the impression 
of relief is produced by a combination of two pictures of any 
object taken at a proper angle to each other. Each eye sees 
only the picture opposite it, but by suitable catoptric or dioptric 
contrivances, the images are made to coincide, and appear in 
the same place. Weinhold makes the principle involved very 
clear in the following diagram and explanation based on the 
dioptric method. 
“ Let the left eye be at A, Fig. 257, and the right at B; let 
a and b be the corresponding pictures for each eye, and Px and,P2 
Fig. 267. 
two prisms of glass through which they 
are seen. A prism refracts rays of light 
so that objects viewed through it appear 
to be nearer to the refracting edge; the 
prism P1? therefore, refracts the ray 
a Pj in the direction P2 A, as if it pro- 
ceeded from c. The prism P2 refracts 
the ray h P2, so that to the eye at Bit 
also appears to proceed from c. The 
effect of this is—provided that the two 
pictures, a and b, are drawn just as a 
body at c would appear to the eyes at 
A and B, if the prisms were not there— 
that the object really appears to be at c. 
And as the points a and b combine to 
The stereoscope. 
form the point c, so d and e unite to form the point/, g and h to 
form the point i.” 
Similar effects of relief may be produced by the projection 
on the same spot of two photographic images of any object 
taken at a suitable angle to each other. 
566. Size and Distance of Objects.—Our estimation of these 
depends: Ist, upon comparison with those of known size m 
the same locality; 2d, upon the visual angle; 3d, upon the optic 
angle. Regarding the latter, Ganot says : “ This angle increasing 
or diminishing according as objects approach or recede, we THE MICROSCOPE AND THE TELESCOPE. 
477 
move our eyes so as to make their optic axes converge towards 
the object which we are looking at, and thus obtain an idea of 
its distance. Nevertheless, it is only by long custom that we 
can establish a relation between our distance from the objects 
and the corresponding motion of the eyes. It is a curious fact 
that persons born blind, whose sight has been restored by an 
operation for cataract, imagine at first that all objects are at 
same distance.” 
The phenomena presented by the action of the retina apper- 
tain rather to physiology than to physics. An admirable dis- 
cussion of these and of all matters connected with vision will 
be found in Le Conte’s book on “ Sight.” 
CHAPTER XXYI. 
THE MICROSCOPE AND THE TELESCOPE. 
The simple microscope—The compound microscope—Parts of modern micro- 
scope—Dry objectives—lmmersion objectives—Choosing and testing objec- 
tives—Eye-pieces—Tube and accessories—The body—The stage—Focussing 
apparatus—The stand or foot—lllumination—Simple axial illumination— 
Diaphragms—Condensed axial illumination—Oblique illumination—Re- 
flected illumination—Polarized illumination—Sources of illumination— 
Augmentation of magnifying power—Measurement of magnifying power— 
Care of microscope—Care of the eyes—Errors in interpretation—Non-vital 
motion—Binocular and chemical microscopes—Fixation of images—Prepa- 
ration of slides and covers—Preparation of objects—Hardening and section- 
cutting— Simple microtome—lnjection—Staining—Chemical testing—Pre- 
servative medium—The microscope and disease germs—Telescope. 
The microscope and the telescope are instruments which 
depend upon refraction for their action. Their function is 
fo assist normal vision. The former, as its name indicates, 
enables us to find and magnify minute objects, and determine 
their structure and the relation of their parts to each other. 
The latter, to discover and satisfactorily examine objects at a 
distance. 
To physicians, the microscope is by far the more important 
°f these instruments, and since the requirements of modern 
medicine demand not only a knowledge of its parts and their 
pse,but also the methods of preparing various objects for exam- 
ination, a brief description of these has been given in the latter 
part of this Chapter, 478 
OPTICS, 
56T. The Simple Microscope consists of a convex lens (528) of 
short focus, suitably mounted; it is often called a magnifying 
glass, and is commonly used as a dissecting microscope. The 
object is placed between the lens and its principal focus (530), 
when an erect and magnified image (534, 535) is produced. 
A very good impromptu instrument may be formed by making 
a circular hole in a piece of thin metal, card-board, or wood, 
and suspending a small drop of clear water in the aperture. 
In the earliest and simplest forms, the lens is a double-convex 
of equal curvatures; there is consequently serious spherical (536) 
and chromatic aberration (538) in the image. To reduce the 
spherical aberration diaphragms and stops (542) are employed. It 
is also greatly diminished by the use of two plano-convex lenses, 
with the plane faces turned towards the object. Improved defi- 
nition under equal power is thus gained with moderate loss of 
illumination. This combination is known as the Wollaston 
doublet. Other methods are described in (536). 
Chromatic aberration may be avoided, when desired, by the use 
of an achromatic lens (539). 
The distinctness of the image depends largely on the position 
of the eye. The object and eye should be in the line of the 
principal axis of the lens (526) and maintained at the proper 
focal distance. 
The magnifying power is usually measured in diameters or 
linear increase. It is the ratio of the apparent to the real diameter 
of the object, both being viewed at the same distance. Work- 
ing powers as high as 120 diameters are reached in simple 
microscopes. Magnifying power is also measured in terms of 
the focal distance of the lens, e.g., two inch, half inch, etc., the 
greater power belonging to that of shorter focus. 
When used for dissection the lens is generally mounted in 
some form of stand. “Lenses most serviceable for hand magni- 
fiers range in focal length from two inches to half an inch; 
and a combination of two or three in the same handle with an 
intervening perforated plate of tortoise-shell (which serves as a 
diaphragm when used together) will be found very useful. 
When such a magnifying power is desired as would require a 
lens of a quarter of an inch focus, it is best obtained by the sub- 
stitution of a ‘ Coddington. ’ ” 
The Coddington lens. “ The first idea of this was given by Dr. 
Wollaston, w-ho proposed to apply two plano-convex or hemi- 
spherical lenses by their plane sides with a ‘ stop ’ interposed, 
the central aperture of which should be equal to one-fifth of the 
focal length. The great advantage of such a lens is, that the 
oblique pencils pass, like the central ones, at right-angles to the 
surface, so that they are but little subject to aberration. The 
idea was further improved upon by Sir D. Brewster, who pointed THE MICROSCOPE AND THE TELESCOPE. 
479 
out that the same end would be much better answered by taking 
a sphere of glass and grinding a deep groove in its equatorial 
part, which should be then tilled with opaque matter, so as to 
limit the central aperture. Such a lens gives a large field of 
view, admits a considerable amount of light, and is equally 
good in all directions, but its power of definition is by no means 
equal to that of an achromatic lens, or even of a doublet. This 
form is chiefly useful, therefore, as a hand magnifier, in which 
neither high power nor perfect definition is required; its pecu- 
liar qualities rendering it superior to an ordinary lens for the 
class of objects for which a hand magnifier of medium power 
18 required. Many of the magnifiers sold as ‘ Coddington ’ 
lenses, however, are not really portions of spheres, but manu- 
factured out of ordinary double-convex lenses, and, therefore, 
destitute of the special advantages of the real ‘ Coddington.’ ” 
The tStanhope lens somewhat resembles the preceding in ap- 
pearance, but differs from it essentially in properties. It is 
nothing more than a double-convex, having two surfaces of un- 
equal curvatures, separated from each other by a considerable 
thickness of glass; their distances so adjusted, that when the 
naost convex is turned towards the eye, minute objects placed 
°n the other shall be in the focus of the lens. 
568. The Compound Microscope in its simplest form consists of 
two convex lenses, Fig. 258, one 0 L, of short, and the other, 
Fig. 258. 
Compound microscope. 
-E L, of long focus, mounted on the same optical axis O E. 
The shorter focus is placed near the object O; it is, therefore, 
called the objective. The image formed by this is viewed through 
the other, EL, by the eye placed at E; it is called the eye-piece. 
The principle involved in the action of the compound micro- 
scope is illustrated in Fig. 259. The object AB is placed a 
little further from the objective O than its focal distance F; a 
r_cal image magnified and inverted is produced on the opposite 
side of the lens at A' W. This is viewed at E through the second 
lens E in such a way that it is between the lens D and its focus 
T'. Thus examined, a virtual and still further magnified image 
is seen at a' h'. 
The final image a' h' is erect as regards A' B', but inverted as 480 
OPTICS. 
regards the object AB. A compound microscope, therefore, is 
a “ simple microscope applied not to the object, but to its image 
already magnified by the first lens.” 
Fig. 259. 
Relation of eye-piece and objective. 
569. Parts of a Modern Microscope.—From the simplest form, 
great departures have been made, which render it necessary to 
take up the consideration of the several parts of the instrument. 
It is to be remembered, however, that in all cases the principles 
involved remain the same as in that already described. The 
parts may be discussed in the following order: Ist. Objectives, 
both dry and immersion. 2d. The eye-piece. 3d. The shaft 
or tube, with the attached parts. 4th. The stage. sth. The 
methods of illumination. 6th. The source of illumination. 7th. 
Arrangement of magnifying power. To these, miscellaneous 
subjects relating to the care of the instrument, preparation of 
objects, etc., may be added. 
570. Dry Objectives.—The simple double-convex lens, described 
in (568), has long since given way to objectives of greater and 
Fig. 260. 
greater complexity of structure. This has 
been found necessary in order to obtain the 
high magnifying powers required in biologi- 
cal and other researches. Not only are all 
microscopes now fitted with achromatic objec- 
tives, but these are sometimes made up of a 
number of such lenses. In Fig. 260 an ob- 
jective of this character, consisting of three 
achromatic lenses, 1, 2, 3, each composed of a 
double-convex crown, and a plano-convex flint 
is represented. In addition to an increase in 
the number of lenses, contrivances for chang- 
ing their distance from each other are added, 
whereby corrections for thickness of cover on the object are 
made, ab c represents the angular aperture. 
While greater perfection is theoretically attained by increase 
Achromatic objective. THE MICROSCOPE AND THE TELESCOPE. 
481 
in the number of lenses, there is an additional loss of light by 
virtue of the numerous surfaces and media through which it is 
obliged to pass. In the objective we have described there are 
twelve surfaces to be accurately ground, and fitted to each other. 
This implies considerable liability to imperfection in workman- 
ship; the fewer the surfaces, the less the liability to error as well 
as the less the loss of light. To gain the advantages arising 
from a smaller number of lenses, Amice substituted a single 
plano-convex of crown glass in the 'front combination, thus 
reducing the surfaces to ten. This has again been modified by 
adding a lens to the back-combination. Such objectives consist 
of two flint-concaves and four crown-convexes. In more recent 
combinations, the chromatic correction is made “entirely in the 
middle lens by a double-concave of dense hint between two 
convexes of crown, both back and front lenses being simple 
piano-con vexes of crown; the surfaces have thus been again 
reduced to ten.” 
Ko objective of a given power can do all the work required 
°f it to perfection. Especially is this so with high powers. The 
following qualities are involved in the action of a microscope 
objective. 
Ist. Magnifying power. This has been discussed in the simple 
microscope (567). 
2d. Angle of aperture and numerical aperture. The first of 
these has been described in article (526). It is also shown at 
a b c in the achromatic combination, Fig. 260. Regarding Pro- 
fessor Abbe’s system of numerical aperture, Professor Carpenter 
Writes : 
“ It can be easily demonstrated mathematically, that the 4 aper- 
ture ’ of a single lens used as a magnifying glass—that is, its 
capacity for receiving and bringing to a remote conjugate focus, 
the rays emanating from the axial point of an object brought 
very near to it—is determined by the ratio between its absolute 
diameter (or clear 4 opening’) and its focal length; while that 
°f an ordinary achromatic objective, composed of several 
lenses, is determined by the ratio of the diameter of its back 
lens (so far as this is really utilized) to its focal length. 
“ When, however, the medium in which the objective works 
18 not air, but a liquid of higher refractive index—such as water 
or oil—an additional circumstance has to be taken into consid- 
eration ; for we may now have three angles of aperture expressed 
by the same number of degrees, which yet denote quite different 
‘ apertures.’ For instance, an 4 angle ’of 90° in oil will give a 
greater 4 aperture’ than one of 90° in water; and the latter a 
greater aperture than 90° in air. 
“ Taking as a standard of comparison a 4 dry ’ objective of the 
maximum theoretical angle of 180°, whose numerical aperture 482 
OPTICS. 
is the sine of 90°,= radius or 1.00, we find this standard to be 
equalled by a ‘water’ immersion objective of only 96°, and by 
an 4 oil ’ or ‘ homogeneous ’ immersion lens of only 82° ; the 
4 numerical apertures ’ of these, obtained by multiplying the sines of 
their respective semi-angles by the refractive index of water in one case 
and of oil in the other, being 1.00 in both. Each, therefore, will have 
as great a power of receiving and utilizing divergent rays, as 
any 4 dry ’ lens can even theoretically possess,—an angle of 
nearly 70° being the limit of what is practically attainable. 
But as the actual angle of an 4 immersion ’ objective can be 
opened out to the same extent as that of an 4 air’ objective, it 
follows that the 4 aperture’ of the former can be augmented 
beyond even the theoretical maximum of the latter; the maxima 
of numerical aperture being 1.52 for oil-immersion, and 1.33 for 
water-immersion objectives, as against 1.00 for 4 dry; ’ and these 
being nearly attainable in practice. 
44 This important doctrine may be best made practically in- 
telligible by a comparison, Fig. 261, of the relative diameters 
of the back lenses of 4 dry ’ with those of 4 water ’ and 4 oil ’ 
immersion objectives of the same power, from an 4 air-angle ’ of 
60° to an 4 oil-angle’ of 180°; these diameters expressing in 
each case the opening between the extreme pencil-forming rays 
at their issue from the posterior surface of the combination, to 
meet in their conjugate foci for the formation of the image; the 
extent of which opening in relation to focal length (not that of the 
rays entering the objective) is the real measure of the aperture of the 
combination. The dotted circles in the interior of 1 and 2 are of 
the same diameter as 3; and, therefore, show the excess in the 
diameters of the back lenses of the 4 oil ’ and 4 water ’ immer- 
sion-objectives, over that of the 4 dry ’ at their respective theo- 
retical limits. 
“A wide-angled 4 immersion’objective can utilize rays from 
an object mounted in a dense medium, such as balsam, which 
are entirely lost when the same object is in air, or is observed 
through a tilm of air. And this loss cannot be compensated for 
by an increase of illumination ; because the rays which are lost 
are different rays, physically, from those obtained by any illumi- 
nation, however intense, in a medium like air. 
44 It is by increasing the number of 4 diffraction spectra,’ that 
the rays admitted from the object contribute to the ‘resolving 
power’ of the objective for lined and dotted objects; the truth 
of the image formed by the recombination of these spectra being, 
as formerly shown, essentially dependent upon the augmentation 
of the number which the objective can be made to receive. 
“Upon the 4 aperture ’ of an objective are dependent (1) its 
illuminating power, (2) its resolving power, and (3) its pene- 
trating powTer;—the first varying as the square of the numerical THE MICROSCOPE AND THE TELESCOPE. 
483 
aperture, the second being in direct, and the third in inverse 
proportion to the numerical aperture.” 
3d. Working distance is the actual space between the front 
element of the objective and the object. It does not bear a fixed 
relation to the focal length, for while 
this is equal to the magnifying power 
of a single lens of given curvature, 
the working distance depends upon 
the manner in which the parts or ele- 
ments of the combination are con- 
structed, and upon its angular aper- 
ture. Increase is not only of advan- 
tage in securing side illumination, 
but of vital importance in the highest 
powers to gain sufficient space for the 
covering glass, as well as for attaining 
the required penetration and resolving 
properties. 
4th. jDefining power depends upon the 
perfection of the correction for spheri- 
cal and chromatic aberration, especially 
upon the first. In immersion lenses 
Fig. 261. 
180° oil-angle. 
(1.52 num. ap.)» 
180° water-angle. 
(1.33 num. ap.) 
180° air-angle. 
96° water-angle. 
82° oil-angle. 
(1,00 num. ap.) 
finer results may be attained with wide 
angle lenses than in the dry system. 
The character of the eye-piece exercises 
an important influence on this quality, 
and should always be taken into con- 
sideration in forming a correct judg- 
ment of defining power. The estima- 
tion of this is obtained by comparing 
7° air-angle. 
(0.75 num. ap.) 
60° air-angle. 
(0.50 num. ap.) 
■ Numerical aperture. 
the action of different lenses upon some object with which the 
examiner is familiar. 
sth. Penetrating power, or focal depth, is the vertical depth 
above and below the true focal plane through which objects 
niay be defined with sufficient clearness to make out their cor- 
rect relations to others in that plane. In opaque objects this 
quality is of the utmost importance. In watching the actions in 
a living organism, as amoeba, it is also essential. In an exceed- 
ingly thin membrane, on the contrary, all portions being nearly 
in the same plane, it is objectionable, since it demands a certain 
sacrifice in sharpness of definition. As a rule, it may be said, 
that objectives of the longest working distance have the greatest 
penetration, while those of wider aperture have lower. 
6th. Resolving power is the property of separating and clearly 
defining very closely placed dots or lines. It strengthens with 
increase in angular aperture, not on account of the greater ob- 
liquity of the rays entering the lens, but of its power to recom- 484 
OPTICS. 
bine the diffraction spectra produced. For the best working of 
the lens in the resolution of surface markings, the proper degree 
of obliquity must be given to the illumination. When, on the 
contrary, it is desired to determine special points in relation to 
internal structure, as the process of division in cell-nuclei, axial 
illumination is preferable. Prof. Abbe has shown that the 
maximum resolving power attainable with an angular aperture 
of 180 degrees is equal to 118,000 lines to the inch. A* reduc- 
tion of the aperture to 106 degrees, lowers the number to about 
94,000. 
7th. Flatness of field determines the practical extent of the 
field of the instrument. With some objectives the marginal 
portions of an object are indistinguishable, while the central 
parts are in sharp focus. Regarding this property, Prof. Car- 
penter writes: “With a really good objective, not only should 
the image be distinct even to the margin of the field, but the 
marginal portion should be as free from color as the central. 
In many microscopes of inferior construction, the imperfection 
of the objectives in this respect is masked by the contraction of 
the aperture of the diaphragm in the eye-piece which limits the 
dimensions of the field; and the performance of one objective 
within this limit may scarcely be distinguishable from that ot 
another, although, if the two were compared under an eye-piece 
of larger aperture, their difference of excellence would be at 
once made apparent by the perfect correctness of one to the 
margin of the field, and by the entire failure of the other in 
every part save its centre. In estimating the relative merits of 
two lenses, therefore, as regards this condition, the comparison 
should be made under an eye-piece giving a larger field.’’ 
Bth. Cover adjustment. Again we quote from the same 
authority: “ When objectives of short focus and of wide angular 
aperture are in use, something more is necessary (save in the 
case of 4 homogeneous-immersion ’ lenses) than exact focal 
adjustment; this being the adjustment of the objective itself, which 
is required to neutralize the disturbing effect of the glass cover 
upon the course of the rays proceeding from the object,—unless 
(as in the objectives now commonly made for students’ micro- 
scopes) they are constructed for working only with cover-glasses 
of a certain standard thickness. For such adjustment, it will 
be recollected, a power of altering the distance between the 
front pair and the remainder of the combination is required; 
and this power is obtained in the following manner: The front 
pair of lenses is fixed into a tube, Fig. 262, A, which slides over 
an interior tube, B, by which the other two pairs are Held; and 
it is drawn up or down by means of a collar, C, which works in 
a furrow cut in the inner tube, and upon a screw-thread cut in 
the outer, so that its revolution in the plane to which it is fixed THE MICROSCOPE AND THE TELESCOPE. 
485 
by the one tube gives a vertical movement to the other. In 
one part of the outer tube an oblong slit is made, as seen at D, 
into which projects a small tongue screwed on the inner tube- 
at the side of the former two hori- 
zontal lines are engraved, one 
pointing to the word ‘ uncovered/ 
the other to the word ‘covered;’ 
whilst the latter is crossed by a 
horizontal mark, which is brought 
to coincide with either of the two 
lines by the rotation of the screw- 
collar, whereby the outer tube is 
moved up or down. When the 
mark has been made to point to 
the line ‘ uncovered,’ it indicates 
that the distance of the lenses of 
the object-glass is such as to make 
it suitable for viewing an object 
without any interference from thin 
glass; when, on the other hand, 
the mark has been brought by the 
Fig. 262. 
Adjustment for cover. 
revolution of the screw-collar into coincidence with the line 
‘ covered,’ it indicates that the front lens has been brought into 
such proximity with the other two, as to produce a ‘ positive 
aberration ’ in the objective, fitted to neutralize the ‘ negative 
aberration ’ produced by the interposition of a glass cover of 
extremist thickness. But unless this correction be made with 
the greatest precision to the thickness of the particular cover in 
use, the enlargement of the angle of aperture, to which opticians 
have of late applied themselves with such remarkable success, 
becomes worse than useless; being a source of diminished in- 
stead of increased distinctness in the details of the object, which 
are far better seen with an objective of greatly inferior aperture, 
possessing no special adjustment for the thickness of the glass. 
1 be following general rule is given by Mr. Wenham for securing 
the most efficient performance of an object glass with any ordi- 
nary object: ‘ Select any dark speck or opaque portion of the 
°bject, and bring the outline into perfect focus; then lay the finger 
°n the milled-head of the fine motion, and move it briskly back- 
wards and forwards in both directions from the first position. 
Observe the expansion of the dark outline of the object, both 
when within and when without the focus. If the greater ex- 
pansion, or coma (537), is when the object is without the focus, 
0r furthest from the objective, the lenses must be placed further 
asunder, or towards the mark ‘ uncovered.’ If the greater 
coma is when the object is within the focus, or nearest to the 
objective, the lenses must be brought closer together, or towards 486 
OPTICS. 
the mark ‘ covered.’ When the object-glass is in proper ad- 
justment, the expansion of the outline is exactly the same both 
within and without the focus.’ ” 
571. Immersion Objectives.—Amici first showed that the inter- 
vention of a drop of water between the object, or its covering 
glass, and the front lens of the objective, greatly diminished 
the loss of light. This was afterwards utilized by Hartnack 
and Cachet, in the construction of the so-called immersion-lenses 
of high power and wide aperture. In discussing this system 
Prof. Carpenter says : 
“The loss of light increases with the obliquity of the incident 
rays; so that when objectives of very wide angle of aperture are 
used ‘dry,’ the advantages of its increase are in great degree 
nullified by the reflection of a large proportion of the rays fall- 
ing very obliquely upon the peripheral portion of the front lens. 
When, on the other hand, rays of the same obliquity enter the 
peripheral portion of the lens from water, the loss by reflection 
is greatly reduced, and the benefit derivable from the large 
aperture is proportionally augmented. Again, the ‘ immersion 
system’ allows of a greater working distance between the ob- 
jective and the object than is otherwise attainable with the same 
extent of angular aperture; and this is a great advantage, not 
merely in regard to convenience in manipulation, but also in 
giving a greater range of penetration or ‘focal depth.’ Further, 
the observer is rendered less dependent upon the exactness in 
the correction for the thickness of the covering-glass, which is 
needed where objectives of large angle are used ‘dry,’ for as the 
amount of ‘negative aberration’ is far smaller when the rays 
which emerge from the covering-glass pass into water, than 
when they pass into air, variations in its thickness produce a 
much less disturbing effect. And thus it is found practically 
that ‘immersion’ objectives can be constructed with magnifying 
powers sufficiently high, and angular apertures sufficiently large, 
for all the ordinary purposes of scientific investigation, without 
any necessity for cover adjustment; being originally adapted to 
give the best results with a covering-glass of suitable thinness, 
and small departures from this in either direction occasioning 
very little deterioration in their performance. For ‘ water-im- 
mersion’ objectives of the very largest aperture, however, to be 
used upon the most difficult objects, exact cover-correction is 
still necessary. Whilst ‘immersion’ objectives constructed on 
the original plan can only be employed ‘wet’ (that is, with the 
interposition of water), Messrs. Powell and Lealand, followed 
by other makers, have so arranged their combinations, that by 
a change in the front lens they may be used ‘ dry,’ as in the 
ordinary manner. And in Mr. Wenham’s system not even this THE MICROSCOPE AND THE TELESCOPE. 
487 
change is required, the change from ‘ wet’ to ‘ dry,’ and vice versa, 
being accomplished by an alteration in the distance of the front 
lens from the middle triplet, made by the screw collar, as in 
ordinary cover-correction.” 
“ Homogeneous immersion consists in the replacement of the 
water previously interposed between the covering-glass and the 
front surface of the objective, by a liquid having the same re- 
fractive and dispersive power as crown-glass; so that the rays 
issuing at any angle from the upper plane surface of the cover- 
ing-glass, shall enter the plane front of the objective without 
any change either by refraction or dispersion, and without any 
sensible loss by reflection—even the most oblique rays proceeding 
m their undeflected course, until they meet the convex back 
surface of the front lens. It is obvious that all the advantages 
derivable from the system of wafer immersion are obtainable 
with still greater completeness by this system of homogeneous 
immersion, provided that a fluid can be found which meets its 
requirements. After a long course of experiments, Prof. Abbe 
discovered that oil of cedar-wood so nearly corresponds with glass, 
alike in refractive and in dispersive power, that it serves the 
purpose extremely well, except when it is desired to take special 
advantage of the most divergent or marginal rays, oil of fennel 
being then preferable. Objectives of ith, and -jL-th inch 
focal length have been constructed on this plan by Zeiss; and it 
appears certain that by its means a larger angle of aperture can 
be effectively obtained than on any other construction. Whether 
any tests can be resolved by its use, on which other objectives 
fail, is a point not yet satisfactorily determined. But there can 
be no doubt that the system of ‘ homogeneous immersion ’ will 
greatly facilitate the use of objectives possessing the largest 
angular aperture, and capable of affording the highest magnify- 
lng power for the ordinary purpose of scientific research. It is 
precisely in the case of such objectives that the ‘ cover-correc- 
tion ’ needs to be most exact. And although the practised micro- 
scopist has no difficulty in making this, when the object at 
which he is looking (such as a Diatom, a Podura-scale, or a 
band of Robert’s ruled lines) is known to him, yet the case is 
entirely different when the object is altogether unknown. For 
ia examining such an object he may be only able to satisfy 
himself after repeated trials, involving much expenditure of 
Pme and patience as to the cover-correction which gives the 
truest representation of the object; whilst, in using a‘homo- 
geneous ’ or ‘ oil-immersion ’ objective, he is able to feel an abso- 
lute certainty that, without any adjustment at all, the view 
which he gains of an unknown object is in every respect at least 
equal to that which he can obtain from the best ‘ dry ’ or ‘ water- 
immersion ’ objective, most exactly adjusted for thickness of 
cover.” 488 
OPTICS. 
572, Choosing and Testing Objectives.—44 The most perfect ob- 
jective for general purposes is obviously that which combines 
all the preceding attributes in the degree in which they are 
mutually compatible. But it seems to be now clear that the 
highest perfection of the two primary qualities, 4 defining 
power’ and 4 resolving power,’ cannot be obtained in the same 
combination; so that the choice between two objectives, one 
distinguished by the former of these, and the other by the latter, 
will depend upon the work on which it is employed. 
44 In estimating the value of an object-glass, it should always 
be considered for what purpose it is intended ; and its merits judged 
of according to the degree in which it fulfils that purpose. We 
shall, therefore, consider what are the objects proper to the 
several‘powers ’ of object-glasses—low, medium, and high; and 
what are the objects by its mode of exhibiting which each may 
be fairly judged. 
“By objectives of low power we may understand any whose 
focal length is greater than half an inch; they give a range of 
amplification of from 10 to 70 diameters with the A eye-piece, 
and of from 16 to 120 diameters with the B eye-piece. An 
4 adjustable’ low power is made by Zeiss, of Jena, in which, by 
varying the position of the front lens by means of a screw-collar, 
a range of power is obtainable from about 8 to 16 diameters with 
the A eye-piece, and from 12 to 24 with theß eye-piece. Objectives 
of low power are most used in the examination of opaque objects, 
and of transparent objects of large size and of comparatively 
coarse texture; and the qualities most desirable in them are a 
sufficiently large aperture to give a bright image, combined with 
such accurate definition as to give a clear image, with 4 focal 
depth ’ sufficient to prevent any moderate inequalities of surface 
from seriously interfering with the distinctness of the entire 
picture, and with perfect 4 flatness ’ of the image when the ob- 
ject itself is flat. The proboscis of the blow-fly is one of the 
best transparent objects for enabling a practised eye to estimate 
the general performance of object-glasses of low power; since 
it is only under a really good lens that all the details of its struc- 
ture can be well shown. In particular, all the outlines and 
edges should be seen clearly and sharply, without any haze or 
fringe; the tracheal spires and rings well-defined, without any 
color between them. 
44 We may consider as objectives of m.edium power the half- 
inch, qVths inch, ifh inch, and jfth inch; the magnifying power 
of which ranges from about 90 to 250 diameters under the A 
eye-piece, and from about 150 to 400 diameters with the B eye- 
piece. When used by reflected light they can be advantageously 
employed in the examination of such small opaque objects as 
Diatoms, Polcystines, portions of small feathers, capsules of the THE MICROSCOPE AMD THE TELESCOPE. 
489 
lesser mosses, hairs, etc.; they should he so mounted on cones 
as to allow of side illumination. The great value of these 
powers lies in the information they enable us to obtain regarding 
the details of organized structures, and of living actions, by the 
examination of properly prepared transparent objects by trans- 
mitted light. Eo single object is so useful as the Podura-scale 
for the purpose of testing these qualities in a vth inch or ith 
inch objective; and it may be safely said that a lens which 
brings out its markings satisfactorily will suit the requirements 
of the ordinary working microscopist, although it may not re- 
solve difficult Diatoms. 
“All object-glasses of less than ith inch focus may be classed 
as high powers. The magnifying powers which objectives from 
15-th to inch focus are fitted to, afford range from about 320 
to 1250 diameters with the shallower eye-piece, and from 480 to 
1850 diameters with the deeper: but by the use of still deeper 
eye-pieces, or by the objective of inch, or the recently 
constructed by Messrs. Powell and Lealand, a power of 4000 or 
more may be obtained. It is seldom, however, that anything 
is really gained thereby. The introduction of immersion lenses 
bas considerably increased the utility of what may be called 
moderately high powers, such as -|th, and Tmth. 
“For resolving power the best tests are afforded by the lines 
artificially ruled by M. Robert, and by the more ‘difficult7 
Diatoms, What is known as Noberfs test is a plate of glass, on 
a small space of which, not exceeding of an inch in breadth, 
are ruled from ten to nineteen series of lines, forming as many 
separate bands of equal breadth. On the nineteen-band test- 
plate the lines are ruled at the following distances, expressed in 
parts of a Paris line, which, to an English inch is usually reck- 
oned as 0.088 to 1.000, or as 11 to 125 : 
Band 1. 
1-1000th. 
Band 8. 
l-4500th. 
Band 14. 
l-7500th. 
u 
2. 
1-1500th. 
“ 9. 
l-5000th. 
“ 15. 
1-8000th. 
“ 
3. 
l-2000th. 
“ io’. 
l-5500th. 
“ 16. 
l-8500th. 
u 
4. 
l-2600th. 
“ 11. 
l-6000th. 
“ 17. 
l-9000th. 
U 
5. 
l-3000th. 
“ 12. 
l-6500th. 
“ 18. 
l-9500th. 
u 
6. 
l-3500th. 
“ 13. 
l-7000th. 
“ 19. 
1-10000th, 
u 
7. 
l-4000th. 
“ The following estimates of the numbers of lines to the 
English inch, in some of the bands, are given by Dr. Poyston 
Digott: 
Band. No. of spaces Band. No. of spaces Band. No. of spaces 
per inch. per inch. per inch. 
I. 
11,259 
IX. 
56,297 
XV. 
90,076 
III. 
22,519 
XI. 
67,557 
XVII. 
101,335 
iy. 
33,778 
XIII. 
78,816 
XIX. 
112,595 
VII. 
45,038 
“Prof. Rogers, of Cambridge, has also ruled test-plates which 
are very accurate in the placement of their lines, and are now 
111 general use. 490 
OPTICS. 
“The greater part of the Diatoms employed as test objects are 
comprehended in the genus Pleurosigma of Professor Smith; 
which includes those Naviculce whose ‘frustules’ are distin- 
guished by their sigmoid (S-like) curvature. 
Direction in 1-lOOth of an inch—. 
of striae. Smith. Sollitt. 
1. 
Pleurosigma formosum 
diagonal 
34 
32—20 
2. 
Pleurosigma strigile . 
transverse 
36 
30 
8. 
Pleurosigma Balticum 
transverse 
38 
40—20 
4. 
Pleurosigma attenuatum . 
transverse 
40 
46—35 
5. 
Pleurosigma hippocampus 
transverse 
40 
45—40 
6. 
Pleurosigma strigosum 
diagonal 
44 
80—40 
7. 
Pleurosigma quadratum 
diagonal 
45 
60—35 
8. 
Pleurosigma elongatum 
diagonal 
48 
9. 
Pleurosigma lacustre 
transverse 
48 
10. 
Pleurosigma angulatum 
diagonal 
52 
51—46 
11. 
Pleurosigma sestuarii . 
diagonal 
54 
12. 
Pleurosigma fasciola . 
transverse 
64 
90—50 
13. 
Navicula rhomboides 
transverse 
85 
111—60 
14. 
15. 
Nitzschia sigmoidea . 
Amphipleurapellucida (navicula 
acus) ..... 
transverse 
transverse 
85 
130—120 
“ Good specimens of the first ten of the foregoing list may be 
resolved, with judicious management, by good small-angled 
or Ith inch objectives, and even, with very oblique illumination, 
by objectives of \ and T4g-th inch, having an angular aperture of 
ninety degrees; the remainder require the larger aperture proper 
to the |th inch or higher power, for the satisfactory exhibition 
of their markings. The first column of measurements in the 
above table gives the numbers stated by Professor Smith as 
averages; the second column gives the numbers subsequently 
assigned as the extremes by Mr. Sollitt, who pointed out that 
great differences exist in the fineness of the markings of speci- 
mens of the same species of the Diatom obtained from different 
localities, a statement now so abundantly confirmed, as to be 
entitled to rank as an established fact. 
“ As a test for those qualities of objectives which best fit them 
for the general purposes of biological investigation, Prof. Car- 
penter is of the opinion “ that nothing is better than the scale of 
the Lepidocystus cervicollis, commonly known as the Podura. An 
objective may serve by virtue of its wide angular aperture, to 
resolve Diatom-tests of considerable difficulty, and may yet fail 
utterly on the Podura-scale, in consequence of its inferior de- 
fining power; and such an objective can be of very little ser- 
vice to the biological investigator. On the other hand, although 
the exact structure of the Podura-scale is still (like that of the 
Diatom-valve) a matter of discussion, yet all are agreed as to 
the appearances it presents, under objectives that combine in the 
fullest degree the attributes already specified as best qualifying 
them for scientific work; so that any glass which shows these THE MICROSCOPE AND THE TELESCOPE. 
491 
appearances satisfactorily, may be safely accounted suitable for 
that purpose. The surface of this scale when viewed under a 
sufficiently high amplification, is seen to be covered with the 
peculiar markings shown at A and B, Fig. 263, which are some- 
Fig. 263 
Test for objectives, 
times designated ‘ spines,’ but are more commonly known as 
‘notes of admiration’ or ‘exclamation-markings.’ These should 
be clearly separated from each other, and their margins well- 
defined. An objective of small angle (such as a Jth inch of 60°) 
will show the ‘spines’ dark throughout, as at A; a |th inch of 
100° will show a light streak extending from the large end, 
down the centre of each marking; and a further enlargement 
°f the aperture will show an extension of this streak through 
the entire length of each ‘spine,’ B. The degree in which these 
Markings retain their brightness and distinctness under deep 
eje-piecing, may be considered a most valuable test of the ex- 
cellence of the defining power of the objective. As it is impos- 
sible that large-angled objectives used ‘dry,’ should be perfectly 
corrected for spherical aberration (so as to possess the greatest 
Possible defining power) without some residuum of chromatic 
aberration, all the best defining glasses will show the thick part 
°f the spines tinged with either blue or red. Perfect achro- 
matism, on the other hand, is only attainable with ‘ dry’ lenses 
at some sacrifice of resolving and defining power; and many 
microscopists prefer to keep the latter to their highest point, 
even at the expense of complete color-correction. Most physi- 
ologists, however, will prefer the highest attainable achromatism 
at some sacrifice of aperture. But it is one of the advantages of the 
immersion system ’ that the residual aberrations of even large-angled 
objectives can he much more perfectly compensated than they can be in 
firy’ objectives ;so that on this as on several other accounts, their use 
18 io be recommended whenever permitted by the nature of the research.” 
When the Podura-scale is employed as a test, allowance 
mould be made for the differences existing between different 
scales. These are as great as with any of the Diatoms. The 
msect from which this test is derived is commonly known as the 
spring-tail ” and may be found near decaying wood and in 
saw-dust. 492 
OPTICS. 
Two or three objectives are sometimes mounted on a swinging 
arm called the nose-piece. These revolve upon a common axis 
and one power after another can be quickly brought into the 
optical axis of the instrument. 
573. Eye-pieces.—That in general use consists of two plano- 
convex lenses, the convexity of each being toward the objective. 
The lens, A, nearest the objective is called the field 
lens; the other, B, the eye-lens. Taken together 
these form an achromatic combination. This eye- 
piece was invented by Huyghens for the telescope; 
he employed it to correct spherical aberration, 
and did not know that it wras achromatic. It was 
applied to the microscope by Campani. The rays 
from the objective pass through the field lens 
before they reach their focus. The image pro- 
duced under these circumstances is real and 
chromatic, but when examined by the eye-lens of 
the combination, the chromatism is corrected, and 
Fig. 264. 
Eye-piece, 
a still more magnified achromatic virtual image produced. “ A 
diaphragm, C, must be placed between the two lenses in the visual 
focus of the eye-glass, which is, of course, the position wherein 
the image of the object will be formed by the rays brought into 
convergence by their passage through the field-glass.” 
“Another advantage of a well-constructed Huyghenian eye- 
piece is, that the image produced by the meeting of the raj7S 
after passing through the field-glass, is by it rendered concave 
towards the eye-glass instead of convex, so that every part of if 
may be in focus at the same time, and the field of view thereby 
rendered flat. Two or more Huyghenian eye-pieces of different 
magnifying powers, known as A, B, C, etc., are usually supplied 
with a compound microscope. By some makers the eye-pieces 
are designated by the focal distance of the combination. The 
utility of the higher powers will mainly depend upon the ex- 
cellence of the objectives; for when an achromatic combination 
of small aperture, which is sufficiently well corrected to perform 
very tolerably with a ‘ low ’ or ‘ shallow ’ eye-piece, is used with 
an eye-piece of higher magnifying power (commonly spoken of 
as a ‘ deeper’ one), the image may lose more in brightness and 
in definition than is gained by its amplification; wTiilst the 
image given by an objective of large angular aperture and very 
perfect correction, shall sustain so little loss of light or of defini- 
tion by 4 deep eye-piecing,’ that the increase of magnifying 
power shall be almost clear gain. Hence the modes in which 
different objectives of the same power, whose performance with 
shallow eye-pieces is nearly the same, are respectively affected 
by deep eye-pieces, afford a good test of their respective merits; THE MICROSCOPE AND THE TELESCOPE. 
493 
since any defect in the corrections is sure to be brought out by 
the higher amplification of the image, whilst a deficiency of 
aperture is manifested by the want of light. The working 
microscopist will generally find the A eye-piece most suitable, 
B being occasionally employed when a greater power is required 
to separate details, whilst C and others still deeper are useful 
for the purpose of testing the goodness of objectives, or for 
special investigations requiring the highest amplification with 
objectives of the finest quality. When great penetration or 
‘ focal depth ’ is required, low objectives and deep eye-pieces 
will often be found convenient. 
“For viewing large flat objects such as transverse sections of 
wood, under low magnifying powers, the eye-piece known as 
Kellner’s may be employed with advantage. In this construction, 
the field-glass, which is a double-convex lens, is placed in the 
focus of the eye-glass, without the interposition of a diaphragm ; 
and the eye-glass is an achromatic combination of a plano- 
concave of flint with a double-convex of crown, which is slightly 
under-corrected, so as to neutralize the over-correction given to 
the objectives for use with Huyghenian eye-pieces. Aflat, well- 
illumined field of as much as fourteen inches in diameter may 
thus be obtained with very little loss of light; but, on the other 
hand, there is a certain impairment of defining power, which 
renders the Kellner eye-piece unsuitable for objects presenting 
ruinute structural details; and it is an additional objection, that 
the smallest speck or smear upon the surface of the field-glass is 
ruade so unpleasantly obvious, that the most careful cleansing 
°t that surface is required every time this eye-piece is used. 
“ A solid eye-piece made on the principle of the ‘ Stanhope ’ 
lens is sometimes used in place of the ordinary Huyghenian, 
when high magnifying power is required for testing the per- 
formance of objectives. The lower surface, which has the lesser 
convexity, serves as a ‘ field-glass ;5 whilst the image formed by 
this is magnified by the highly convex upper surface to which 
the eye is applied; the advantage supposed to be derived from 
this construction lying in the abolition of the plane surfaces of 
the two lenses of the ordinary eye-piece.” 
574. Tube and Accessories,—The tube of the instrument serves 
to maintain the objective and the eye-piece in proper relation to 
each other in the same optical axis. 
The objectives are fitted into the lower end by a screw; a 
collar with a uniform thread, known as the society screw, has 
been adopted by the majority of makers. By the use of this 
any objective may be adapted to the instrument. Other special 
contrivances are sometimes furnished for attachment of very 
bigh-angled low powers. 494 
OPTICS. 
The eye-piece is slipped into the upper part, the exterior of 
its cylinder and the interior of the tube being ground to give a 
smooth movement. 
Diaphragms found in the eye-piece or the tube of a micro- 
scope should not be displaced; or if desired to do so, their 
location should be carefully marked beforehand, in order that 
they can be replaced in their proper position. 
The draw-tube is a second tube sliding into the tube proper. 
While the objective is attached to the latter, the eye-piece is 
carried by the former. When the former is partly withdrawn 
the distance between the eye-piece and objective is increased, 
and greater magnifying power attained. 
An amplifier is a concave lens interposed between the objective 
and eye-piece. In the Tolle’s form “it is an achromatic 
concavo-convex lens of small diameter, screwed into the lower 
end of the draw-tube, so as to be at no great distance behind 
the objective, the power of which it doubles without producing 
sensible deterioration of the image. Dr. Devron states that the 
nineteenth band of a Hebert plate could be resolved by its aid, 
by objectives under which without it no resolution could be 
obtained.” 
The erector. “ This instrument, first applied to the compound 
microscope by Mr. Lister, consists of a tube about three inches 
long, A B, having a meniscus at one end, and 
a plano-convex lens at the other (the convex 
sides being upwards in each case), with a dia- 
phragm nearly half-way between them; this is 
screwed into the lower end of the draw-tube, as 
shown in Fig. 265 (C D being the 
Its effect is (like the corresponding erector of 
fhe telescope) to antagonize the inversion of 
the image formed by the object-glass, by pro- 
ducing a second inversion, so as to make the 
image presented to the eye correspond in posi- 
tion with the object-arrangement. This is of 
great service in cases in which the object has to 
be subjected to any kind of manipulation. The 
passage of the rays through two additional 
lenses, of course occasions a certain loss of light, 
and impairment of the distinctness of the image; 
but this need not be an obstacle to its use for 
the class of purposes for which it is especially 
adapted in other respects, since these seldom 
require a very high degree of defining power. 
By the position given to the erector, it is made 
Fig. 265. 
Erector. 
subservient to another purpose of great utility; namely, pro- 
curing a very extensive range of magnifying power, without THE MICROSCOPE AND THE TELESCOPE. 
495 
any change in the objective. For when the draw-tube, with the 
erector fitted to it, is completely pushed in, the acting length 
(so to speak) is so greatly reduced by the formation of the first 
image much nearer the objective, that, if a lens of two-thirds of 
an inch focus be employed, an object of the diameter of inches 
can be taken in and enlarged to no more than 4 diameters; 
whilst, on the other hand, when the tube is drawn out 4J inches 
the object is enlarged 100 diameters. Of course, every inter- 
mediate range can be obtained by drawing out the tube more or 
less ; and the facility with which this can be accomplished, espe- 
cially when the draw-tube is furnished with a rack-and-pinion 
movement (as in Messrs. Beck’s Compound Dissecting Micro- 
scope), renders such an instrument very useful in research.” 
575. The Body.—B carries the tube A, just described, with 
objective and eye-piece; the stage C on which the object is 
placed; the focussing adjustment D D', and the illuminating 
Fig. 266. 
shaft with mirrors E, diaphragms, condenser, and polarizer F, 
*ig. 266. 
The microscope. 
576. The Stage is for the support of the object. It is attached 
t° the body in such a manner that the plane of its upper surface 
is at right angles to the optical axis of the tube. 496 
OPTICS. 
In its simplest form, the stage is a single circular plate of 
brass with an aperture in the centre. Its upper surface is ground 
smooth and flat; on this the object slide is placed. By inter- 
vening a drop of water between the glass slide and the metal 
plate, the former is held in position, and yet may be easily and 
steadily moved on the metal, to bring any desired part of the 
object into the field of the instrument. As a rule, even the 
simplest stages are provided with clips, springs, or other con- 
trivances for keeping the slide in contact while the former is 
moved about by the fingers. 
In its more advanced condition it consists of two parallel 
plates, with more or less complex attachments for moving the 
upper upon the lower. The upper plate carries the object and 
slides upon the lower, which is firmly attached to the body of the 
instrument. 
In the various forms of microscope a majority of the fol- 
lowing movements of the object are attainable. 
Ist. Right or left across the field by turning one or the other 
of the mill-headed screws on the side of the stage, which drives 
the rack movement between the two plates of the stage. 
2d. Oblique by turning both screw heads at the same time. 
3d. Rotary, by loosening a binding-screw which holds the two 
parts of the stage together, when the upper may be rotated upon 
the lower by the finger or by a tangent screw. 
4th. Inclination of the plane of the stage to the optical axis of 
the instrument. In this the lower plate is so attached to the 
body that by loosening a binding-screw, the movement in question 
may be executed. 
sth. One or all of these may be provided with graduated 
scales, arcs, and verniers, that they can be measured, recorded, 
and restored if desired. 
To secure the greatest obliquity in transmitted light, the stage 
should be made as thin as possible. 
577. Focussing Apparatus,—This consists of appliances, D O', 
which cause the tube to approach to or recede from the stage. 
In the simplest form the tube is supported in a metallic ring 
lined with cloth, and the movement in question is accomplished 
by sliding it up and down. 
In the better forms of microscope, the arrangement de- 
scribed is sometimes retained as a coarse adjustment. As a 
rule, however, this is attained by a rack and pinion movement, 
the mill-heads of the latter being on each side the tube, while 
that which drives the lever of the fine adjustment is at the 
top of the body, where the lateral arm arises to support the 
main tube. In some cases the mill-head of the tine adjustment 
is on the tube. THE MICROSCOPE AND THE TELESCOPE. 
497 
In the low powers the coarse adjustment alone generally 
suffices to obtain a sharp focus. To give this the greatest 
smoothness the teeth of the rack and pinion should be set ob- 
liquely. “What is meant by ‘ spring,’ is the alteration which 
may often be observed to take place on the withdrawal of the 
hand; the object which has been brought precisely into focus, 
and which so remains while the milled head is between the 
fingers, becoming indistinct when the milled-head is let go. 
The source of this fault may lie either in the rack-movement 
or in the general framing of the instrument, which is so weak 
ns to allow of displacement by the mere weight or pressure of 
the hand; should the latter be the case, the ‘ spring ’ may be 
in a great degree prevented by carefully abstaining from bearing 
on the milled-head, which should be simply rotated between the 
fingers.” 
To obtain a well-defined image with objectives of less than 
half an inch focus the fine adjustment or slow motion must 
be used. “It should work smoothly and equably, producing 
that graduated alteration of the distance of the objective from 
the object which it is its special duty to effect without any jerk- 
ing or irregularity. It should be so sensitive that any movement 
of the milled-head should at once make its action apparent by 
an alteration in the distinctness of the image when high powers 
are employed, without any loss of time. And its action should 
not give rise to any twisting or displacing movement of the 
image, which ought not to be in the least degree disturbed by 
any number of rotations of the milled-head, still less by a rota- 
tion through a few degrees. One great use of this adjustment 
consists in bringing into view different strata of the object, and 
this in such a gradual manner that their connection with one 
another shall be made apparent. A clearer idea of the nature 
°f a doubtful structure is, in fact, often derived from what is 
caught sight of in the act of changing the focus, than by the 
most attentive study and comparison of the different views 
obtained by any number of separate ‘ focussings.’ The ex- 
perienced microscopist, therefore, whilst examining an object of 
almost any description, constantly keeps his finger upon the 
milled-head of the ‘ slow motion,’ and watches the effect pro- 
duced by its revolution upon every feature which he distin- 
guishes; never leaving off* until he is satisfied that he has 
scrutinized not only the entire surface, but the entire thickness of 
tiie object.” 
578. The Stand is generally some modification of a tripod, or 
tiiree-footed arrangement. This, if properly constructed, gives 
tim desired steadiness to the apparatus. In the earlier kinds 498 
OPTICS. 
of microscope the body was immovably attached to the stand, 
and only a vertical view down the tube could be obtained. In 
modern instruments, the attachment between the body, and 
stand is movable, and any desired obliquity can be given to 
the former. The microscopist is thus enabled to change his 
posture at pleasure, and the use of the instrument becomes less 
wearisome. Some think that an optical advantage is gained by 
using an inclined position of the tube, as there is less annoy- 
ance from the action of moisture upon the cornea. 
579. Illumination may be by ordinary or by polarized light. 
In the former, the light is either transmitted or reflected, 
according as the object is transparent or opaque. In the first 
of these it may again be direct or oblique, and either simple or 
condensed. Five conditions, therefore, present themselves: Ist, 
simple axial; 2d, condensed axial; 3d, oblique; 4th, reflected; 
and, sth, polarized illumination. 
580. Simple Axial Illumination.—All microscopes are provided 
with a plane silvered glass mirror, or reflector, by which light 
can be directed through the aperture in the stage along the 
tube to the eye. In simple forms, this is supported upon an 
immovable rigid arm, which is attached to the body and pro- 
jects beneath the stage. The mirror is mounted upon two axes 
at right angles to each other, that rays of light from any source 
may be directed along the tube. 
581. Diaphragms,—For various reasons it is often necessary to 
modify or lessen the illumination. This is accomplished by 
means of a ring pierced by circular or other openings of different 
sizes. The ring diaphragm is generally attached to the under 
side of the main stage in such a manner, that on revolving it 
openings of various diameters are passed beneath the aperture 
in the centre of the main stage, and its size varied as desired. 
Thus a greater or less amount of light is thrown upon the ob- 
ject. Sometimes the diaphragm is placed at a distance below 
the object, as in the box form of this arrangement. 
The iris diaphragm is a most ingenious piece of apparatus for 
varying the diameter of the pencil of light cast on the object. 
It is composed of a number of plates, which by means of a lever 
are made to encroach upon a central opening. It operates, as 
its name indicates, after the fashion of the iris, and gives most 
satisfactory results. 
582. Condensed Axial Illumination.—To throw a brighter illll' 
mination upon the object, the light is condensed by any of the THE MICROSCOPE AND THE TELESCOPE. 
499 
three following methods: Ist. concave mirror; 2d, simple con- 
densing lens; 3d, achromatic condenser. 
Concave mirror. The ring which carries the plane mirror, 
holds a concave one upon the opposite side, by which rays of 
light can be converged upon the object. To adjust the focus 
of this to near or remote sources of light, the ring slides upon 
the arm supporting it. It is thus made to approach, or recede 
from, the stage, and thereby bring the reflected rays to a focus 
upon the object. 
Simple condenser is a convex lens of moderately long focus, 
intervened between the source of light and the plane mirror. 
The relative positions of these are so arranged that the light 
is brought to a focus upon the object. The lens is supported 
m a sliding ring upon an independent stand. It may, therefore, 
receive any desired adjustment. 
Achromatic condensers. For condensing the illumination the 
lower objectives of the microscope may be used. Especial 
provision is made for mounting them by means of a second or 
sub-stage beneath the main stage of the instrument. The sub- 
stage is attached to the arm which carries the plane mirror. It 
is placed between that and the stage. By means of a rack and 
pinion movement, it traverses along the supporting arm, receiv- 
ing the proper adjustment to cast the focus of the achromatic 
combination upon the object. 
583. Oblique Illumination,—Where transparent objects present 
fine grooves or ridges, they are often invisible when submitted 
to axial illumination, but appear at once when the light is cast 
at the proper degree of obliquity upon them. According also 
as one side of a furrow is more or less inclined than the other, 
so will the direction in which the light falls make it more or less 
evident. 
The simplest method of obtaining oblique illumination is to 
niount the arm supporting the mirror and sub-stage upon a 
Pivot, the axis of which should pass through the plane of the 
object. The light may then be reflected upon it at any de- 
Slfed angle. If at the same time the movement of rotation is 
given to the stage, it will be presented to the light under every 
azimuth. 
The amici prism is a prism one face of which is lens-shaped, 
ft serves the purpose of a reflector and condenser in securing 
oblique illumination. It can be mounted on a separate stand, 
or attached to some part of the instrument. 
The parabolic illuminator is a column of glass, the upper por- 
tion being paraboloid in shape with a cup or depression in 
fbe centre. By it the object may be illuminated obliquely, and, if desired, made to appear on a black 
ground. 
Regarding oblique illumination, Prof, Carpenter 
says: “A good example of the variety of appear- 
ances which the same object may exhibit, when illu- 
minated from different azimuths, and with slight 
changes of focussing, is shown in Fig. 267, which 
represents portions of a valve of pleurosigma formo- 
sum, as seen under a power of 1300 diameters; the 
markings shown at A, B, and C, being brought out 
by oblique light in different directions, which, how- 
ever, when carefully used, does not produce these 
erroneous aspects; whilst at D is shown the effect 
of axial illumination with the achromatic con- 
OPTICS. 
Pig. 267. 
Varying effects of 
illumination. 
denser. It cannot be too strongly impressed on 
the young microscopist, however, that the special 
value of very oblique illumination is limited to the resolution ot 
‘test objects;’ and that for ordinary purposes of scientific study, 
and research, axial illumination is generally preferable.” 
584. Reflected Illumination is employed with opaque objects 
In this the light is thrown upon their upper surface and re 
Pig. 268. 
Illumination of opaque objects. 
fleeted thence along the shaft of the instrument. The simplest 
arrangement is found in Fig. 268. In this the rays from the 
source of light indicated by the dotted lines are condensed by 
a convex lens and brought to a focus upon the upper surface ox THE MICROSCOPE AND THE TELESCOPE. 
501 
the object. A plano-convex lens of great curvature, called the 
bull’s-eye condenser, is used for this purpose. It is mounted 
on a separate stand, and any desired movement can be given 
to it. 
“ The optical effect of such a bull’s-eye differs according to the 
side of it turned towards the light, and the condition of the 
rays which fall upon it. The position of least spherical aberra- 
tion is when its convex side is turned towards parallel or towards 
the least diverging rays; consequently, when used by daylight, its 
plane side should be turned towards the object; and the same 
position should be given to it when it is used for procuring con- 
verging rays from a lamp, this being placed four or five times 
further oft' on one side than the object is on the other. But it 
may also be employed for the purpose of reducing the diverging 
rays of the lamp to parallelism, for use either with a paraboloid 
or with the parabolic speculum; and the plane side is then to be 
turned towards the lamp, which must be placed at such a dis- 
tance from the ‘bull’s-eye,’ that the rays which have passed 
through the latter shall form a luminous circle equal to it in 
size, at whatever distance from the lens the screen may be held. 
For viewing minute objects under high powers, the smaller con- 
densing lens may be used to obtain a further concentration of 
the rays already brought into convergence by the ‘bull’s-eye.’ ” 
In some microscopes the arm which carries the plane mirror 
and achromatic condenser is not only turned to one side to give 
oblique illumination, as described in (583), but also above the 
stage to give reflected illumination, as with the bull’s-eye con- 
denser. 
The Lieherkuhn is a concave speculum, and received its name 
from the celebrated microscopist who invented it. “It is made 
to fit upon the end of the objective, having a perforation in its 
centre for the passage of the rays from the object to the lens ; 
and in order that it may receive its light from a mirror beneath, 
the object must be so mounted as only to stop out the central 
portion of the rays reflected upwards. The curvature of the 
speculum is so adapted to the focus of the objective, that, when 
the latter is duly adjusted, the rays reflected up to it from the 
fidrror shall be made to converge strongly upon the part of the 
°bject that is in focus; a separate speculum is consequently 
required for every objective.” 
The parabolic speculum of Mr. R. Beck is one of the most 
convenient methods for obtaining reflected illumination. “It 
18 attached to a spring-clip that fits upon the objectives (2 inch, 
inch, 1 inch, -|d inch), to which it is especially suited, and 
is slid up or down, or turned around its axis, when the object 
nas been brought into focus, until the most suitable illumination 502 
OPTICS. 
has been obtained. The ordinary rays of diffused daylight, 
which may he considered as falling in a parallel direction on 
the speculum turned towards the window to receive them, are 
reflected upon a small object in its focus, so as to illuminate it 
sufficiently bright for most purposes; but a much stronger 
light may be concentrated on it when the speculum receives its 
rays from a lamp placed near the opposite side of the stage, a 
‘ bull’s eye ’ being interposed to give parallelism to the rays.” 
Vertical illumination through objective. Mr. Wen ham, Prof. 
H. L. Smith, and others, have devised various methods for 
illuminating opaque objects by sending the light through the 
objective as a condenser. ‘ln the arrangement of Mr. Beck, a 
disk of thin glass is attached to a milled-head, by the rotation 
of which it may receive any desired angle ; this is introduced 
through a slot into the interior of an adapter interposed be- 
tween the objective and the nose of the microscope. The 
light which enters at the lateral aperture, falling upon the 
oblique surface of the disk, is reflected downwards, and con- 
centrated by the lenses of the objective upon the object beneath. 
585. Polarized Illumination.—In the application of polarized 
light to the microscope a bundle of thin plates may be used as 
the polarizer. The method usually employed is, by a “fsTicol” 
prism, fitted to the sub-stage. A second “ Mcol ”or tourma- 
line is used as an analyzer. It is placed near the objective. By 
means of polarized light important peculiarities of structure are 
made evident, which would otherwise be invisible. 
586. Sources of Illumination.—lst. Sunlight. “ The direct light 
of the sun is far too powerful to be ordinarily used with advan- 
tage, unless its intensity is moderated, either by reflection from 
a plaster-of-Paris mirror, or by passage through some ‘ modifier; 
it is, however, occasionally used by some observers to work out 
intricate markings or fine color, and may sometimes be of ad- 
vantage for these purposes, but without great care would be a 
fertile source of error,” 
2d. Daylight. “ The young microscopist is earnestly recom- 
mended to make as much use of daylight as possible; not only 
because, in a large number of cases, the view of the object 
which it affords is more satisfactory than that which can be ob- 
tained by any kind of lamplight, but also because it is much 
less trying to the eyes. So great, indeed, is the difference be- 
tween the two in this respect, that there are many who find 
themselves unable to carry on observations for any length of 
time by lamplight, although they experience neither fatigue 
nor strain from many hours continuous work by daylight.” THE MICROSCOPE AND THE TELESCOPE. 
503 
3d. Cloud light. “ When daylight is employed, the micro- 
scope should be placed near a window, whose aspect should be 
(as nearly as may be convenient) opposite to the side on which 
the sun is shining; for the light of the sun reflected from a 
bright cloud is that which the experienced microscopist will 
always prefer, the rays proceeding from a cloudless blue sky 
being by no means so well fitted for his purpose,, and the dull 
lurid reflection of a dark cloud being the worst of all.” 
4th. Lamplight. “ For the examination of the greater pro- 
portion of objects, good daylight is to be preferred to any other 
kind of light: but good lamplight is preferable to bad daylight, 
especially for the illumination of opaque objects. When re- 
course is had to artificial light, it is essential, not only that it 
should be of good quality, but that the arrangement for fur- 
nishing it should be suitable to the special wants of the micro- 
scopist.” The most useful light for ordinary use is that furnished 
by the steady and constant flame of a flat-wicked lamp, fed with 
one of the best varieties of paraffin oil. For all ordinary pur- 
poses a flat kerosene flame used edgewise answers admirably. 
sth. Position of the light. “ When the microscope is used by 
daylight, it will usually be found most convenient to place it in 
such a manner that the light shall be at the left hand of the 
observer. It is most important that no light should enter his 
eye save that which comes to it through the microscope; and 
the access of direct light can scarcely be avoided when he sits 
with his face to the light. Of the two sides, it is more con- 
yenient to have the light on the left; first, because it is not 
interfered with by the right hand, when this is employed in 
giving the requisite directiomto the mirror, or in adjusting the 
illuminating apparatus; and second, because, as most persons 
m using a monocular microscope employ the right eye rather 
than the left, the projection of the nose serves to cut off those 
lateral rays which, when the light comes from the right side, 
glance between the eye and the eye-piece. The lamp should 
always be placed on the left side, unless some special reason 
exists for placing it otherwise; and if the object under ex- 
amination be transparent, the lamp should be placed at a 
distance from the eye about midway between that of the 
plage and that of the mirror; but when the instrument can be 
inclined, the lamp may be most advantageously placed in the 
axis of the achromatic* condenser or other illuminator, so that 
its light may be transmitted to the object without intermediate 
reflection. If, on the other hand, the object be opaque, the lamp 
should be at a distance about midway behind the eye and the 
stage, that its light may fall on the object at an angle of about 
ds° with the axis of the microscope.” 504 
OPTICS. 
587. Augmentation of Magnifying Power.—“ When the micro 
scopist wishes to augment his magnifying power, he has a choice 
between the emplo3Traent of an objective of shorter focus, and 
the use of a deeper eye-piece. If he possess a complete series of 
objectives, he will frequently find it best to substitute one of these 
for another without changing the eye-piece fora deeper one; 
but if his ‘powers’ be separated by wide intervals, he will be 
able to break the abruptness of the increase in amplification 
which they produce, by using each objective first with the shal- 
lower, and then with the deeper eye-piece. In the examination 
of large opaque objects having uneven surfaces, it is generally 
preferable to increase the power by the eye-piece rather than by 
the objective; thus a more satisfactory view of such objects may 
usually be obtained with a 3 inch or 2 inch objective, and the B 
eye-piece, than with a inch or 1 inch objective, and the A 
eye-piece. The use of the draw-tube enables the microscopist 
still further to vary the magnifying power of his instrument, 
and thus to obtain almost any exact number of diameters he 
may desire, within the limits to which he is restricted by the 
focal length of his objectives.” 
588. Measurement of Magnifying Power.— For this purpose 
various forms of micrometer have been adapted to the eye-piece. 
The method generally employed “depends upon a comparison 
of the real size of the object with the apparent size of the image; 
but our estimate of the latter will depend upon the distance at 
which we assume it to be seen; since, if it be projected at dif- 
ferent distances from the eye, it will present very different 
dimensions. Opticians generally, however, have agreed to con- 
sider ten inches as the standard of comparison; and when, there- 
fore, an object is said to be magnified 100 diameters, it is meant 
that its visual image projected at ten inches from the eye (as 
when thrown down by the camera lucida (543) upon a surface 
at that distance beneath), has 100 times the actual dimensions 
of the object. The measurement of the magnifying power of 
simple or compound microscopes by this standard is attended 
with no difficulty. All that is required is a stage micrometer 
accurately divided to a small fraction of an inch (the yi-g-th 
answer very well for low powers, the for high), and a 
common foot rule divided to tenths of an inch. The micrometer 
being adjusted to the focus of the objective, the rule is held 
parallel with it at the distance of ten inches from the eye. If 
the second eye be then opened whilst the other is looking 
through the microscope, the circle of light included within the 
field of view crossed by the lines of the micrometer will be seen 
faintly projected upon the rule; and it will be very easy to mark 
upon the latter the apparent distances of the divisions on the THE MICROSCOPE AND THE TELESCOPE 
505 
micrometer, and thence to ascertain the magnifying power. 
Thus, supposing each of the divisions of T(fyth of an inch to 
correspond with fi inch upon the rule, the linear magnifying 
power is 150 diameters; if it corresponds with half an incfy the 
magnifying power is 50 diameters.” 
589. Care of Microscope.—The best method for protecting a 
microscope when not in use is to keep it under a glass shade, 
the mouth closed by a piece of cloth laid on the table or stand 
on which it is kept. If there is any dust on the mirror or brass 
work it should be wiped off with a handkerchief before it is put 
away. 
If specks are seen on looking through the ej'e-piece, when the 
mirror is adjusted to illuminate the field, the eye-piece should 
be rotated, when, if the dust is upon its glasses, they must be 
carefully wiped. In case it is necessary to remove the lenses 
from the barrel to wipe their inner surface, they should be 
screwed up taut when returned to their places. The lenses of 
only one eye-piece should be taken out at a time, to prevent 
any chance of their becoming mixed. 
If the dust upon any lens is very fine, it can often be blown 
off. The vapor which condenses thereafter must be removed 
by quickly traversing the glass through the air. Lenses should 
not be wiped unless necessary, as the softest material is apt 
to injure or scratch the polish. If a puff of breath does not 
answer, the next best thing is a camel’s-hair pencil, and, finally, 
a piece of soft wash-leather out of which the dust has been 
beaten. 
If the objectives are kept in their cases, they will not often 
require the removal of dust. The chief danger to which they 
are liable is contact with fluids of various kinds when used by 
careless hands. When this happens they should be cleaned as 
quickly as possible. 
Whenever objectives are handled, the glasses should be kept 
as far as possible from the vicinity of the skin, to prevent 
condensation of its moisture upon them. Any cloudiness that 
fyay appear in their interior is best treated by the maker, espe- 
cially when it is between the parts of any of the achromatic 
lenses. 
590. Care of the Eyes.—ln regard to this matter we quote the 
experience of Prof. Carpenter: “Although most microscopists 
who habitually work with the monocular microscope acquire a 
habit of employing only one eye (generally the right), yet it will 
he decidedly advantageous to the beginner that he should learn 
fo use either eye indifferently; since by employing and resting 
each alternately, he may work much longer without incurring 506 
OPTICS. 
unpleasant or injurious fatigue, than when he always employs 
the same. Whether or not he do this, he will find it of great 
importance to acquire the habit of keeping open the unemployed eye. 
This, to such as are unaccustomed to it, seems at first very em- 
barrassing, on account of the interference with the microscopic 
image which is occasioned by the picture of surrounding objects 
formed upon the retina of the second eye; but the habit of 
restricting the attention to that impression only which is received 
through the microscopic eye, may generally be soon acquired; 
and when it has once been formed, all difficulty ceases. Those 
who find it unusually difficult to acquire this habit, may do well 
to learn it in the first instance with the assistance of a shade; 
the employment of which will permit the second eye to be kept 
open without any confusion. So much advantage, however, is 
derived from the use of the binocular arrangement, either 
stereoscopic or non-stereoscopic, that its use is strongly recom- 
mended to every observer, save in cases of exceptional difficulty. 
There can be no doubt that the habitual use of the microscope, 
for many hours together, especially by lamp-light, and with high 
magnifying powers, has a great tendency to injure the sight. 
Every microscopist who thus occupies himself, therefore, will do 
well, as he values his eyes, not merely to adopt the various pre- 
cautionary measures already specified, but rigorously to keep to 
the simple rule of not continuing to observe any longer than he can 
do so without fatigue.” 
591. Errors of Interpretation.—“ These, arising from the imper- 
fection of the focal adjustment, are not at all uncommon amongst 
young microscopists. Indistinctness of outline will sometimes 
present the appearance of a pellucid border, which, like the 
ditfraction-band, may be mistaken for actual substance. But 
the most common error is that produced by the reversal of 
the lights and shadows resulting from the refractive powers 
of the object itself; thus, the hiconcavity of the blood-discs of 
human (and other mammalian) blood occasions their centres to 
appear dark when in the focus of a microscope, through the 
divergence of the rays which it occasions; but when brought 
a little within the focus by a slight approximation of the 
object-glass, the centres appear brighter than the peripheral 
parts of the discs.” 
“ The student should be warned against supposing that, in all 
cases, the most positive and striking appearance is the truest; for 
this is often not the case. Mr. Slack’s optical illusion or silica- 
crack slide illustrates an error of this description. A drop of 
water holding colloid silica in solution is allowed to evaporate 
on a glass slide, and, when quite dry, covered with thin glass 
to keep it clean. The silica deposited in this way is curiously THE MICEOSCOPE AND THE TELESCOPE. 
507 
cracked; and the finest of these cracks can he made to present 
a very positive and deceptive appearance of being raised bodies 
like glass threads.” 
“A very important and very frequent source of error, which 
sometimes operates even on experienced microscopists, lies in 
the refractive influence exerted by certain peculiarities in the 
internal structure of objects upon the rays of light transmitted 
through them; this influence being of a nature to give rise to 
appearances in the image which suggest to the observer an idea 
of their cause that may be altogether different from the reality. 
Of this fallacy we have a ‘pregnant instance’ in the misinter- 
pretation of the nature of the lacunae and canaliculi of bone, 
which were long supposed to he solid corpuscles with radiating 
filaments of peculiar opacity, instead of being, as is now uni- 
versally admitted, minute chambers with diverging passages 
excavated in the solid osseous substance. For, just as the con- 
vexity of its surface will cause a transparent cylinder to show a 
bright axial band, so will the concavity of the internal surfaces 
of the cavities or tubes hollowed out in the midst of highly 
refracting substances occasion a divergence of the rays passing 
through them, and consequently render them so dark that they 
are easily mistaken for opaque solids. That such is the case 
with the so-called ‘ bone corpuscles,’ is shown by the effect of the 
infiltration of Canada balsam through the osseous substance; 
for when this fills up the excavations, being nearly of the same 
refractive power with the bone itself, it obliterates them alto- 
gether. The best method of learning to appreciate the class of 
appearances in question, is the comparison of the aspect of 
globules of oil in water with that of globules of water in oil, 
or of bubbles of air in water or Canada balsam. This com- 
parison may be very readily made by shaking up some oil with 
water to which a little gum has been added, so as to form an 
emulsion; or by simply placing a drop of oil of turpentine 
(colored by magenta or carmine) and a drop of water together 
on a slip of glass, laying a thin glass cover upon them, and then 
moving the cover several times backwards and forwards upon 
the slide. Now when such a mixture is examined with a suf- 
ficiently high magnifying power, all the globules present nearly 
the same appearance, namely, dark margins with bright cen- 
tres ; but when the test of alteration of the focus is applied to 
them, the difference is at once revealed; for whilst the globules 
°f oil surrounded by water become darker as the object-glass is 
depressed, and lighter as it is raised, those of water surrounded by 
oil become more luminous as the object-glass is depressed, and 
darker as it is raised. The reason of this lies in the fact that the 
high refracting power of the oil causes each of its globules to 
act like a lens of very short focus; and as this 508 
OPTICS. 
will bring the rajs which pass through it into convergence above 
the globule (i. e., between the globule and the objective), its 
brightest image is given when the object-glass is removed some- 
what further from it than the exact focal distance of the object. 
On the other hand, the globule of water in oil, or the minute 
bubble of air in water or balsam, acts, in virtue of its inferior 
refractive power, like a double-concave lens; and as the rays of 
this diverge from a virtual focus below the globule (i. e., between 
the globule and the mirror), the spot of greatest luminosity will 
be found by causing the object-glass to approach within the 
proper focus. A thorough mastery of these appearances is very 
important in the study of the £ protoplasm ’ of plants—the ‘ sar- 
code ’ of ahimals,—which includes oil-particles, together with 
spaces occupied by a watery fluid, which (having been at one 
time supposed to be void) are known as ‘ vacuoles” 
592. Non-vital Motions.—The power of self-movement is gen- 
erally given as the leading attribute of living creatures, but it is 
now known that all substances, organic and inorganic, will ex- 
hibit a kind of motion known as pedesis, if reduced to the 
proper degree of subdivision and suspended in a fluid. When 
the specific gravity of the liquid approximates closely to that 
of the particles of the solid a less degree of subdivision is 
required. 
This “ Brownian movement,” as it is also called, is oscillatory, 
the particles rotating backwards and forwards upon their axes, 
and changing their position slightly in the field of view. Among 
the substances that show it to good advantage are the fine kaolin 
prepared for photographers, when suspended in water, or very 
finely divided pumice. In examination of urine, minute crystals 
of certain phosphates exhibit this motion, which must not be 
confounded with that of bacteria and like organisms. 
593. Binocular and Chemical Microscopes.—ln the former the 
pencil of light from the objective is divided by a prism and 
passed along two shafts, each terminating in an eye-piece. By 
this device great advantages are gained over monocular instru- 
ments, in certain special investigations, especially in those 
binoculars arranged to produce stereoscopic effects. 
The chemical microscope differs from an ordinary instrument 
in that the shaft is placed below instead of above the stage. 
The object may, therefore, be examined by acids and other re- 
agents without injury to the objective, as it is protected by 
the glass slide on which the substance has been placed. 
For further information regarding these and all other matters 
concerning microscopes, the student is referred to Prof. Car- THE MICROSCOPE AND THE TELESCOPE. 
509 
penter’s work on the “ Microscope,” from which this Chapter 
has been so largely quoted, and of which we cannot speak too 
highly. 
593 A. Fixation of Images may be accomplished either by the 
hand and pencil with the aid of the camera lucida, or by means 
of photography. In the former the method is identical with 
that described for the measurement of magnifying power in 
(588). An improved camera lucida by Zeiss will be found to 
offer increased facilities for this operation. 
Where the photographic method is employed, an ordinary 
camera box, from which the lenses have been removed, is sub- 
stituted for the eye-piece of the microscope. The two instru- 
ments may be connected light-tight by means of black velvet or 
cloth, and the image focussed on the ground glass of the camera. 
A beam of sunlight rendered stationary by a heliostat, and con- 
densed if necessary, is the best method of illumination for high 
powers. To make the chemical and visual foci the same, and 
thereby avoid all difficulty in obtaining sharply defined pictures, 
the beam should be passed through a glass cell filled with am- 
nionio-sulphate of copper, which allows only violet and blue 
light to pass freely. Prof. J. W. Draper employed this method 
to obtain photographs for his work on “ Physiology,” and was 
the first to make photographs by the high powers of the micro- 
scope. 
594. Preparation of Slides and Covers.—For the support of the object 
under the objective, glass slides are required. These are made of a patent plate 
Manufactured for the purpose. It should be free from air-bubbles, veins, or other 
imperfections, and cut to a size of three inches by one, with the edges ground. 
They may be purchased for about the same cost as the glass itself, and sorted 
according to thickness into groups for different purposes. The thinnest should 
be used for investigations requiring high power, the medium for ordinary objects, 
and the thick for those which are to be ground down. 
To cleanse the slides, immerse them for twenty-four hours in strong sulphuric 
acid; then rinse in potash or soda solution, followed by distilled water; then 
wipe dry with a towel, and polish with an old handkerchief. Another method is 
to immerse them for a day in a fluid composed of— 
Potassium dichromate . 
. 2 oz. 
Sulphuric acid .... 
. 3 fl. oz. 
Water 
25 fl. oz. 
Before a slide is used, the dust should be carefully wiped oft. 
Old slides should have the varnish removed by scraping, then by a suitable 
solvent adapted to the nature of the varnish, then rubbed with a fluid composed 
°f equal parts of benzole, alcohol, and liquor sodce, and finally washed in clean 
Water. 
The thin glass required for covering and protecting the object may be purchased 
already cut in squares and circles. Pieces as thin as of an inch can be 
obtained. It is very brittle ; and if required of special size, must be laid on a 
Piece of wet plate glass, to prevent cracking, and cut with a writing-diamond. 510 
OPTICS. 
It should be sorted into three grades, the thickest for low, the medium and thin- 
nest for high powers. 
For injected specimens, and thick objects requiring space between the slide and 
cover, cells are constructed either with rings of cement, glass, or rubber, prepared 
for the purpose. These cements are also used for sealing the cells when the 
mounting is completed. 
Large, deep cells are built up of carefully ground pieces of plate glass. 
695. Preparation of Object.—The specimen examined may be either 
transparent or opaque, fluid or solid. The simplest case is a fluid containing 
free cells or corpuscles—as, for example, blood. In this instance, a drop is trans- 
ferred to the centre of the slide by a glass rod, the cover is then gently laid on 
in such a manner that it touches along one side first; the entrapping of air-bubbles 
is thus avoided. The margin of the cover is then touched with a piece of blotting- 
paper, which absorbs the excess of fluid by capillary attraction, and the specimen 
is ready for examination. 
If a sediment is to be examined, it may be transferred without additional mix- 
ture with fluid, by the use of a pipette (186); it is then covered, and excess of 
fluid removed, as in the preceding case. 
Soft solids, especially if fibrous, are prepared by taking a thin slice and teasing 
the fibres apart by needles. For this purpose, ordinary sewing needles can be 
fitted into wooden handles by the eye extremity. The free end is straight, or 
curved as required. To obtain the latter, raise the temperature of the free end 
for a moment to red heat: when cool, bend as desired. It is then again made 
red-hot, and while in that state immersed in cold water, to restore hardness. 
596. Hardening and Section-cutting.—ln a great number of cases it 
is necessary to harden animal substances before they can be cut into thin sections 
for examination. In many of the lower creatures the proportion of water is so 
great that its removal involves a shrinkage which completely obscures their 
structure. The following are the chief agents employed ; 
Alcohol: The material should be first soaked for a day or so in a mixture of 
equal parts of rectified spirit and water, then for a couple of days in rectified 
spirit, and then in absolute alcohol. The opacity arising from coagulation of the 
albuminous constituents is avoided by the addition of a little caustic soda. 
Chromic acid is very generally employed. It should be kept in one per cent, 
solution, and diluted when used. Carpenter recommends the following mode of 
procedure: 
“ The menstruum having been prepared by mixing two parts of a one-sixth per 
cent, solution of chromic acid and one part of methylated spirit, the material 
must be cut into pieces about half an inch square, and put into a wide-mouthed 
stoppered bottle holding from six to ten ounces of the fluid; this fluid should be 
changed at the end of twenty-four hours, and then every third day. The material 
will be sufficiently hard in from eight to twelve days. If not, the process must 
be continued, care being taken that it be not so prolonged as to render the sub- 
stance brittle. The hardening may afterwards be completed by transferring the 
substance first to dilute and then to stronger spirit. The spirit must be changed 
as often as it becomes foul; when it remains bright and clean, the specimen is 
ready for cutting.” 
Osmic acid: “ This agent is one of peculiar value to the microscopist whose 
studies lie among the lower forms of animal and vegetable life, as its application 
immediately kills them, without producing any retraction or shrinking of their 
parts, and not only preserves their tissues, but brings out differences in those 
which might otherwise escape observation. It is sold in the solid state in sealed 
tubes, and is most conveniently kept as a one per cent, solution in distilled water. 
The solution should be preserved in well-stoppered bottles secluded from the 
light, and should be used with great caution, as it gives forth a pungent vapor 
which is very irritating to the eyes and nostrils. To the histologist, its special 
value lies in its blackening of fatty matters and the medullary substance of nerve- 
fibres. The embryologist finds it of peculiar value in giving firmness and 
distinctness to the delicate textures with which he has to deal. Various degrees THE MICROSCOPE AND THE TELESCOPE. 
511 
of dilution of the one per cent, solution will be needed for these different purposes. 
Mr. Parker states that he has found this agent very serviceable in the preparation 
of delicate vegetable structures. The acid seems to he taken up bv each granule 
of the protoplasm, and these to be decomposed, giving to the granule the charac- 
teristic gray color, thus at the same time both hardening and staining. A mixture 
of nine parts of a one-fourth per cent, solution of chromic acid, with one part of a 
one per cent, solution of osmic acid, answers for many purposes better than osmic 
acid alone, the brittleness produced by its use being completely avoided. After 
being subjected to this agent, the specimens should be treated with thirty per 
cent, alcohol, gradually increased in strength to absolute.” 
Por cutting thin sections, various devices are employed. The simplest is that by 
small, keen-bladed scissors, which are either straight or curved. The best are 
provided with a spring, by the action of which the blades are self-opening. For 
finer work, and to secure parallel surfaces, Valentine’s two-bladed knife was for- 
merly used, but it has been superseded by better methods, among which is the— 
597. Simple Microtome, which is described as follows by Prof. Carpenter: 
“Various costly machines have been devised for this purpose, some of them char- 
acterized by great ingenuity of contrivance and beauty of workmanship ; but most 
of the purposes to which these are adapted will be found to be answered by a very 
simple and inexpensive little instrument, which may either be held in the hand, 
or (as is preferable) may be firmly attached by means of a T-shaped piece of wood, 
Ihg. 269, to the end of a table or work-bench. This instrument consists essen- 
Fig. 269. 
tially Of an upright hollow cylinder of brass, A, with a kind of piston which is 
pushed from below upwards by a fine-threaded or 1 micrometer ’ screw turned by 
a large milled-head, B ; at the upper end the cylinder terminates in a brass table, 
C, which is planed to a flat surface, or (which is preferable) has a piece of plate 
glass cemented to it, to form its cutting-bed. At one side is seen a small rnilled- 
uead, D, which acts upon a ‘binding-screw,’ whose extremity projects into the 
cavity of the cylinder, and serves to compress and steady anything that it holds. 
A cylindrical stem of wood, a piece of horn, whalebone, cartilage, etc., is to be 
fitted to the interior of the cylinder so as to project a little above its top, and is 
t° he steadied by the ‘ binding-screw;’ it is then to be cut to a level by means 
°f a sharp knife or razor laid flat upon the table. The large milled-head is next 
to he moved through such a portion of a turn as may very slightly elevate the 
substance to be cut, so as to make it project in an almost insensible degree above 
tee table, and this projecting part is to be sliced off with a knife previously dipped 
’n water. For many purposes, an ordinary razor will answer sufficiently well, 
but thinner and more uniform sections can be cut by a special knife, having its 
Microtome. 512 
OPTICS. 
edge parallel to its back, its sides slightly concave, and its back with a uniform 
thickness of rather less than one fourth inch. Such a knife should be four or five 
inches long, and seven-eighths inch broad ; and should be set in a handle about 
four inches long. The motion given to its edge should be a combination of drawing 
and pressing. It will be generally found that better sections are made by working 
the knife from the operator than towards him. When one slice has been thus 
taken otf, it should be removed from the blade by dipping it into water, or by the 
use of a camel’s-hair brush ; the milled-head should be again advanced, and another 
section taken ; and so on. Different substances will be found both to bear and to 
require different degrees of thickness ; and the amount that suits each can only be 
found by trial. It is advantageous to have the large milled-head graduated, and 
furnished with a fixed index, so that this amount having been once determined, 
the screw shall be so turned as to produce always the exact elevation required. 
Where the substance of which it is desired to obtain sections by this instrument is 
of too small a size or of too soft a texture to be held firmly in the manner just 
described, it may be placed between the two vertical halves of a cork of suitable 
size to be pressed into the cylinder ; and the cork, with the object it grasps, is then 
to be sliced in the manner already described, the small section of the latter being 
carefully taken off the knife, or floated away from it, on each occasion, to prevent 
it from being lost among the lamellae of cork which are removed at the same time. 
Vertical sections of many leaves may be successfully made in this way.” 
In Hailes's microtome the irregular action of the raising screw is corrected by 
the use of two cylinders, one working inside the other. 
When the substance is very soft, it is embedded in a cylinder of elder-pith, cut 
to fit the cylinder of the microtome. Plugs of paraffine, made by pouring the 
melted material into the cylinder of the microtome, are also employed. The sub- 
stance is set in the plug, which is then inserted into the microtome cylinder. To 
give greater consistency to the embedding material, especially where fats are used, 
various forms of freezing microtome have been devised. These are essential in 
the preparation of sections of such tissues asking, where the fat must be sufficiently 
soft to penetrate the interstices of the body to be embedded, and afterwards gain 
sufficient consistency to support the tissue before the edge of the knife. 
Thin sections of hard tissues, like bone, are prepared by grinding them down 
after attaching them to glass. 
598. Injection.—lnjections should be opaque where inequalities of form are 
to be shown, and transparent where the vessels of thin transparent membranes are 
to be displayed. The material generally used is fine size or gelatine of the 
consistence of a firm jelly when cold. The solution should be strained through 
new flannel while hot, and preserved from dust under a layer of alcohol in a 
covered jar. 
The best red coloring matter is levigated vermilion, about two ounces to the 
pint of size, thoroughly mixed therewith while melted, and the mixture strained 
through muslin. 
For a yellow, freshly precipitated chromate of lead may be employed. It should 
be prepared as follows : Dissolve 200 grains of plumbic acetate, in another portion 
of water 105 grains of potassium chromate, mix, stir, allow precipitate to settle; 
decant the fluid from the sediment, and mingle the latter with four ounces of size. 
An elegant method of injecting consists in throwing first one and then the other 
of these solutions into the vessels. For this purpose, the solutions should be 
saturated. In this case the nitrate of lead answers better than the acetate. 
For white injections, carbonate of lead is recommended. 
Blue injections do not answer well; they appear black. 
The syringe should be fitted with jet pipes of various sizes, or glass jets may be 
drawn down to fit the vessels accurately. Since delicate vessels are often easily 
cut by thread, the jets should be used without ligatures, as large a jet as possible 
being employed. The pressure upon the piston of the syringe should be moderate 
and steady. In place of a syringe, a vessel filled with the injection, and attached 
to a jet by along rubber tube, may be used; by raising the vessel to different 
heights any desired amount of uniform pressure may be obtained, or it may be 
gradually increased. THE MICROSCOPE AND THE TELESCOPE. 
513 
When the injection is not made into the vessels of the living creature, it should 
T p " V LlCdlUlCj It bllOUlCl 
De performed either at once after death, or when the rigor mortis has passed off. 
All by which the injection might escape should be tied, and if too 
minute for this, the tissues themselves must be ligatured. 
699. Staining- acts either by simply dyeing, or by chemically uniting with 
some of the organic constituents of the preparation, and thus differentiates them 
from others. The agents which dye the structures are chiefly animal or vegetable 
coloring matters ; it is generally necessary to fix these by means of some “ mordant.” 
Those which act chemically are mineral bodies. 
Staining is sometimes done before the section-cutting, sometimes afterwards. 
o , owiiiutlUiUO «.!LCI VV til CIS. 
J-he latter method is to be followed when the tissue has been hardened by the use 
of chromic acid. If the staining is to be en masse, the fluid should be weak and 
its action slow. In the case of thin sections, it should be conducted as rapidly as 
possible, and stopped at the right stage. Generally, watch-glasses or small capsules 
can be used for section-work, but when the lamime are very thin, the operation 
may be conducted on the microscope-slide on which the preparation is to be 
mounted. In this case the fluid is added and removed by means of a small 
syringe. Sometimes it is carried on even after the thin glass cover has been put on. 
Many different agents have already been successfully applied for this purpose, 
put the field is yet an extensive one and open to great improvement, although 
important results have been attained. Among the substances which have thus far 
been utilized, the following deserve especial mention: 
Carmine was one of the first used. It was introduced by Dr. Beale for dis- 
tinguishing protoplasm from other formed material. It has an especial affinity 
for cell nuclei. It is prepared as follows : 
Carmine 10 grs. 
Liquor ammoniae . . . . . . . fgss. 
Warm in a test-tube, and boil for a few seconds, cool, add— 
Aq. dest. 
Glycerine aa^ij. 
Alcohol -5 s3- 
After a while, filter. If, in time, the carmine deposits, add a drop or so of 
ammonia. 
To fix the carmine stain, immerse the section in dilute acetic acid, five drops 
to one ounce of water. 
Piero-carmine, diluted and used alone, gives a double-staining action, nuclei 
attracting the carmine, and the other tissues the picric acid. In water the picric 
acid is removed, and the carmine stain remains. In methylated spirit both colors 
are retained. 
Hcematoxylin, or extract of logwood, is commonly employed in place of carmine, 
-tt is used as follows : 
Extract of logwood 6 grammes. 
Alum . . . . . . . .18 “ 
Water ........ 28 cub. cent. 
filter, and add gj of alcohol; preserve in stoppered bottle for a week before use. 
J uuu ctvavt VII tAIVIUHUi J pi CSUI VO 111 oouwo ivi c* vyuciv UCIUIC USC. 
ben drops diluted with water in a watch-glass may be used for each section. The 
®°lor should be fixed with methylated spirit. The acetic acid mixture used to 
fix the carmine stain, will remove excess of haematoxylin stain. 
Magenta acts like carmine, but is apt to fade. 
Magenta crystals . grs. IJ. 
Aq. dest. . . f§vij. 
Alcohol . . . . . ■ 3SS. 
-Eosin gives a beautiful garnet-red color. 
Aniline dyes for blue and green colors. 514 
OPTICS. 
Argentic nitrate and Auric chloride are sometimes employed ; the former for 
epithelium cells, the latter for nerve, tendon, and cartilage cells. 
Valuable information may often he obtained by the use of two or three staining- 
fluids, each of which will be fixed by different tissues. If, for example, a section 
is made through the base of a cat’s tongue, and submitted to the action of a mix- 
ture of picro-carmine, rosein, and iodine-green, the muscle-fibres will take the 
first; the connective tissue and protoplasm cells, the second; the non-striated 
muscle, epithelial cells, the third. The effects are more striking if one fluid is used 
after another. 
600. Chemical Testing is best accomplished by means of a small glass 
syringe, upon the slide on which the object is to be mounted. For examination 
of inorganic bodies all kinds of reagents may be used, but in biological inves- 
tigations the following are of especial importance: 
Lugol’s solution turns starch blue, cellulose brown, and albuminous bodies an 
intense brown. 
Nitric acid, concentrated, gives intense yellow to albuminoids. 
Milton's reagent, acid nitrate of mercury, gives a red with albuminoids. 
Acetic acid acts upon certain tissues, so that nuclei are made more apparent. 
Fixed alkalies, in solution, act as solvents on many tissues; the cells of horny 
structures may thus be made evident. 
Ether dissolves resin, fats, and oils, when not protected by membranes soaked 
with water. 
Alcohol dissolves resins and some volatile oils, but not the ordinary oils and fats. 
It coagulates albuminoids, thus rendering such tissues more opaque. 
601. Preservative Media.—Regarding these, Prof. Carpenter says : 
“A broad distinction may be in the first place laid down between resinous and 
aqueous preservative media; to the former belong only Canada balsam and 
dammar, whilst the latter include all the mixtures of which water is a component. 
The choice between the two kinds of media will partly depend upon the nature of 
the processes to which the object may have been previously subjected, and partly 
upon the degree of transparence which may be advantageously imparted to it. 
Sections of substances which have been not only embedded in, but penetrated by, 
paraffine, wax, or cacao-butter, and have been stained (if desired) previously to 
cutting, are, as a rule, most conveniently mounted in Canada balsam or dammar, 
since they can be at once transferred to either of these from the menstruum by 
which the embedding material has been dissolved out. The durability of this 
method of mounting makes it preferable in all cases to which it is suitable ; the 
exception being where it renders a very thin section too transparent, which is 
specially liable to happen with dammar. When it is desired to mount in either 
of these media sections of structures that have been embedded in gum or gelatine, 
these substances must first be completely dissolved-out by steeping in water ; the 
sections must then be ‘dehydrated’ by subjecting them to mixtures of spirit and 
water progressively increased in strength to absolute alcohol; and, after this has 
been effected, they are to be transferred to turpentine, and thence to benzole. In 
this process much of the staining is apt to be lost, so that stained sections are often 
more advantageously mounted in some of those aqueous preparations of glycerine 
which approach the resinous media in transparence and permanence.” 
Among the aqueous media, the following have especial consideration : 
Distilled water, saturated with camphor, for minute protophytes. The addition 
of one-tenth part of alcohol is of advantage when the preservation of color is not 
desired. 
Carbolic acid solution, made with cold distilled water. 
Salicylic acid solution, in water, for delicate structures. 
Glycerine, either alone, diluted, or mixed with gelatinous substances. “ Two 
cautions should be given in regard to the employment of glycerine: first, that, 
as it has a solvent power for carbonate of lime, it should not be used for mounting 
any object having a calcareous skeleton; and, second, that in proportion as it 
increases the transparence of organic substances, it diminishes the reflecting power 
of their surfaces, and should never be employed, therefore, in the mounting °i THE MICROSCOPE AND THE TELESCOPE. 
515 
objects to be viewed by reflected light, although many objects mounted in the 
media to be presently specified are beautifully shown by 1 black-ground ’ illumi- 
nation.” 
Glycerine jelly, subject to the same cautions. It may be prepared as follows: 
“ Take any quantity of Nelson’s gelatine, and let it soak for two or three hours in 
cold water; pour off the superfluous water, and heat the soaked gelatine until 
melted. To each fluidounce of the gelatine add one drachm of alcohol, and mix 
well; then add a fluid-drachm of the white of an egg. Mix well while the gelatine 
is fluid, but cool. Now boil until the albumen coagulates, and the gelatine is 
quite clear. Filter through fine flannel, and to each fluidounce of the clarified 
gelatine add six fluid-drachms of Price’s pure glycerine, and mix well. For the 
six fluid-drachms of glycerine, a mixture of two parts of glycerine to four of 
camphor-water may be substituted. The objects intended to be mounted in this 
medium are best prepared by being immersed for some time in a mixture of one 
part of glycerine with one part of diluted alcohol (one of alcohol to six of water). 
A small quantity of carbolic acid may be added to it with advantage. When 
used, the jelly must be liquefied by gentle warmth, and it is useful to warm both 
the slide and the cover-glass previously to mounting. This takes the place of 
what wits formerly known as Deane’s medium, in which honey was used to prevent 
the hardening of the gelatine.” 
601 A. The Microscope and Disease Germs.—We have given the 
details of the processes of staining, section-cutting, etc,, to enable 
the student to understand the methods resorted to of late in the 
study of the relations of certain plant-germs to various diseases. 
That the importance of this subject maybe appreciated, we give 
a list of the specimens exhibited at the Biological Laboratory 
of the Health Exhibition at London, during the summer of 1884, 
preceding it with a brief account of the organisms themselves. 
They are known as Schizomycetes. They resemble algce, in 
that they live in water; and plants, in that they can feed upon 
ammonia for their nitrogenized material, but they cannot de- 
compose carbonic acid. Their carbon food is derived from 
carbohydrates. The following live well-delined groups are rec- 
ognized : 
1. Micrococci. Dark-colored spherical or oval minute cells. 
Sometimes spores of bacteria, or bacilli, but as they often do 
Fig. 270. 
Micrococci. 
not develop into anything higher than micrococci, must be re- 
garded as a special form. 
2. Bacteria. Minute oblong cells, usually attached in pairs 
cud to end, are sometimes single, reproduce by fission, usually 
ln vacillating movement by their flagella. Flagella frequently 
■sWoToth inch thick, in special ferments, as that of sour milk. 516 
OPTICS. 
Fig. 271. 
A. Bacterium termo, 4000 diameters. B, C, D. Bacterium lineola, 3000 diameters. 
Fig. 272. 
A. Bacillus subtilis, 4000 diameters. 
Fig. 273. 
Vibrio regula, 2000 diameters. 
Fig. 274 
A. Spirillum undula, 3000 diameters; B. Spirillum volutans, 2000 diameters. THE MICROSCOPE AND THE TELESCOPE. 
517 
3. Bacilli. Special character, extension of its cells into straight 
rods, sometimes very long, which divide transversely into sepa- 
rate cells with flagellum at each end. Move in a pausing manner, 
like a fish forcing its way through reeds. B. anthracis, to 
YoiiToth inch long. Multiply idefinitely in tissues, 
4. Vibriones resemble bacilli, but are flexible instead of straight. 
Formed chiefly in infusions of decomposing organic matter; have 
a wavy, serpentine movement. 
5. Spirilla are the largest of the group. Have the cell spirally 
coiled, and possess a corkscrew-like movement; found in stale 
liquids which have passed through the active stage of putres- 
cence. 
All these multiply either by transverse cell subdivision, or by 
the breaking up of their endoplasm into spores, the reproduc- 
tion of which is entirely non-sexual. 
Most of the specimens in the Biological Laboratory were cul- 
tivated in an infusion made as follows : 
Lean meat 
1 pound. 
Gelatine . 
Peptone 
. 10 “ 
Sodium chloride 
. . 1 “ 
Water, distilled 
. . 1 litre. 
The solution is boiled and kept in separate flasks plugged 
with cotton. The mouth of the tube is also protected from con- 
tact with air. 
The infusion, when cold, sets as a jelly, and in it the growths 
take place. Sometimes they liquefy it. In all cases the greatest 
care should be taken to sterilize the infusion by heating it one 
hour in the tube in which the experiment is to be performed, 
at 100° C., keeping the tube plugged with cotton. 
A single drop of London water drawn from the tap into a 
test-tube containing two inches of this infusion, quickly liquefied, 
and produced a copious deposit. 
Violet and fluorescent bacilli were exhibited; also bacilli from 
green and blue pus, and from blue milk. 
. Bacilli of tubercle, found in all tubercular and scrofulous 
diseases of joints, bones, glands, and in phthisis, were best cul- 
tivated in sterilized blood serum, maintained at the temperature 
°f the body. According to Dr. Koch, inhalation of, or inocula- 
tion by, these germs, produces tuberculosis in the lower animals. 
Bacilli of enteric fever, obtained from sections of intestinal 
ulcers, found also in the spleen, liver, and in the kidney, in 
colonies in the bloodvessels. Cultivated in meat solution. 
Bacilli of anthrax, occurring as wool-sorters’ disease, and ma- 
lignant carbuncle. Found in blood and in heart tissue. They 
arc the largest of bacilli. Cultivated in meat solution produce 
spores, but not in the body. Inoculation in lower animals, 518 
OPTICS. 
according to Dr. Koch, causes rapid development of the disease 
and death in a few hours, the blood being tilled with the charac- 
teristic bacilli. 
Bacilli of mouse septicaemia, found in decomposing fluids, are 
very small, produce haziness along track of needle in meat 
solution. Mice inoculated die in 40 to 72 hours, bacilli in the 
blood and in white corpuscles. Inoculated in ear of rabbit, 
causing swelling and redness extending to other ear. Disappears 
in 6 or 6 days, leaving the animal protected for a time against 
the disease, a point worthy of special attention. 
Bacilli of chicken cholera produce hemorrhagic enteritis of 
duodenum. Are very minute and stained at ends. Fowls and 
pigeons inoculated die in 17 to 20 hours with great number of 
bacilli in the blood. 
Micrococci of acute osteomyelitis in man occur in the pus, may 
be cultivated in meat solution or in blood serum. Introduced 
into rabbit’s veins, if the bones have been injured, cause death 
on the 12th day, the condition of the hones being the same as in 
man in this disease. Is found in the pus and blood in colonies. 
Micrococci of acute lobar pneumonia. Found in blood, sections 
of affected parts and their exudations, especially in death in the 
acute stage. Grow rapidly in meat solution, particularly at 
points of entrance of needle, hence called nail-like. No capsule 
in cultivated kinds, but developed in creatures inoculated with 
the cultivated material. Inhaled by mice cause pneumonia. 
Injected into pleural cavity give pleurisy and pneumonia. Dogs, 
guinea-pigs, mice affected; rabbits not. 
Micrococci of erysipelas in man. Found in lymphatic vessels 
at spreading margin of the redness, many tubes being com- 
pletely blocked with these organisms. Grow in chains; culti- 
vated in meat solution. This inoculated in ear of rabbit pro- 
duces disease like erysipelas in man, with same condition of 
lymphatics. In man lupus, rodent ulcers, and cancerous tumors 
have been supposed to be influenced favorably by cultivated 
erysipelas inoculation. (Dr. Febreisen, Berlin, 1883.) 
Micrococcus Tetragenus. Found in phthisical sputa where de- 
struction of lung is rapid. Unstained, resembles sarcina; stained, 
the groups are made up in fours. Inoculated in mice and guinea- 
pigs, they die in 2to 10 days. The 4 groups found in capil- 
laries of all the organs, large masses of these accumulating in 
the spleen burst through its peritoneal coat and cause peritonitis. 
In addition to these cultivated specimens, photographs of the 
following were exhibited. The power best adapted was 700 
diameters. 
Nos. 1, 2, 3. Pyaemia in rabbits, micrococci. 
Nos. 4, 5, 7, 8, 9. Erysipelas in man, micrococci. 
Nos. 10, 13. Osteomyelitis, micrococci. THE MICROSCOPE AND THE TELESCOPE. 
519 
No. 11. Diphtheritic inflammation of bladder in man, plugs 
of micrococci in kidney vessels. 
Nos. 14, 15. Progressive formation of abscess in rabbits, 
micrococci. 
No. 16. Recurrent fever in monkey. Spirilla among blood 
corpuscles. 
No. 18. Ditto in man, similar spirilla, 
_Nos. 19, 22, 23. Smallpox in man. Liver section plugged 
with micrococci. 
Nos. 20, 21. Pyelonephritis. Microorganisms in tubules. 
_ No. 25. Erysipelatous process in rabbits. Long delicate ba- 
cilli penetrating the tissues. 
Nos, 26, 27. Ulcerative endocarditis. Heart section. Plugs 
of micrococci in capillaries. 
Nos. 28, 32. Septicsemia in rabbits. Small intestine section. 
Capillary plugged with oval micrococci. Same in glomerulus 
of kidney. 
Nos. 30, 31. Septicaemia in mice, blood, and section of ear 
showing minute bacilli. 
Nos. 33, 34. Splenic fever in rabbits. Section of kidney, 
bacilli. 
Nos. 35, 36. Glomerulus with anthrax bacilli. Same in sec- 
tions of villus and of liver. 
602. Telescopes.—According as these depend upon concave 
mirrors, or convex lenses, for their action, they are called catop- 
tric and dioptric instruments. In the first the .pencil of light 
reflected from the concave mirror is passed through an eye-piece 
to the eye. In the second, the objective or lens is a convex- 
chromatic of long focus, and considerable diameter, from this 
the rays are also passed through an eye-piece. The latter is 
generally of the form described in (573). When a telescope is 
intended for use on land, or for objects at a moderate distance, 
!t is called terrestrial; when for contemplation of objects in the 
heavens, celestial. In the former the eye-piece is so modified as 
to present an erect image. In instruments for observation, or 
reading scales, and for other purposes, as the spectroscope, this 
form is commonly employed. 
The opera-glass is constructed upon the principle of Galileo’s 
telescope, which is the simplest. It consists of two lenses only, 
viz-, a double-convex as the objective, and a double-concave as 
the eye-piece. Thus a very bright erect image is produced. 520 
OPTICS. 
CHAPTER XXYII. 
DOUBLE REFRACTION, INTERFERENCE, DIFFRACTION, AND 
POLARIZATION. 
Double refraction—Ordinary and extraordinary ray—Interference of light—Dif- 
fraction—Diffraction spectra—Plane polarization by reflection—Angle of 
polarization—Polarization by single refraction—Polarization by double re- 
fraction—Polarizing instruments—Theory of polarized light—lnterference of 
polarized light—Depolarization—Action of thin films—Production of colored 
rings by polarized light—Detection of molecular change by polarized light— 
Elliptical and circular polarization—Theory of elliptical and circular polari- 
zation—Production of circularly polarized light—Production of elliptically 
polarized light—Production and theory of rotatory polarization—Coloration 
by rotatory polarization—Rotatory power of liquids—Saccharimeter. 
These are additional phenomena presented by light under 
special conditions, and produced by action of surfaces and 
media. They are all explicable upon the wave or undulatory 
hypothesis, and afford most satisfactory evidence of its correct- 
ness. To the physiologist and student of medicine they are of 
interest, either from their direct application in explaining the 
phenomena he witnesses, or in furnishing the principles upon 
which certain instruments are constructed which are used in 
determining the changes resulting from morbid actions in the 
system. 
603. Double Refraction.—lf a crystal of Iceland spar be placed 
upon a sheet of paper which bears a dark spot or dot, the latter 
Fig. 275. 
appears double when viewed through the crystal. To this phe- 
nomenon of splitting or bifurcation of the pencil of light in its 
Double refraction. REFRACTION, INTERFERENCE, DIFFRACTION. 
521 
passage, the name of double refraction has been given. All 
crystals which do not belong to the cubical system, show this 
property to a greater or less extent; Iceland spar being at the 
head of the list. Hon-crystalline substances, like glass, in their 
ordinary state are not double refracting, though they may be 
made to assume that property by unequal compression, or when 
unannealed. 
If any double refracting crystal is carefully examined, it will 
be found that there is one direction or axis in which the spot is 
not doubled. This is called the optic axis. In some two such 
axes are found. The first is called uniaxial, the second biaxial. 
604. Ordinary and Extraordinary Ray.—lf in the experiment 
related in the preceding article, the line of vision is perpen- 
dicular, and the crystal turned around with its face in continu- 
ous contact with the paper, that image of the dot nearest to the 
line of vision will remain unchanged, while the other will re- 
volve around it. The first of these is called the ordinary, the 
second the extraordinary ray, or image. The former follows the 
laws of single refraction, viz., the sines of the angles of inci- 
dence and refraction bear a constant relation to each other, and 
the planes of incidence and refraction are coincident (492). The 
latter, on the contrary, follows neither of these laws except in 
certain positions. 
According as the refractive indices of the ordinary and extra- 
ordinary rays of uniaxial crystals bear certain relations to each 
other, they are called negative and positive. If the ordinary 
index is greater than the extraordinary, it is called negative, 
nnd vice versa. 
Negative uniaxial crystals. 
Iceland spar. 
Euhy. Pyromorphite. 
Tourmaline. 
Emerald. Eerrocyanide of potassium 
Sapphire. 
Apatite. Nitrate of sodium. 
Positive uniaxial crystals. 
Zircon. 
Apophyllite. Titanite. 
Quartz. 
Ice. Boracite. 
Biaxial crystals. 
Nitre. 
Sugar. Sulphate of iron. 
Strontianite. 
Selenite. Mica. 
Arragonite. 
Anhydrite. Epidote. 
Heavy spar. 
605. Interference of Light.—Make two small apertures of the 
same diameter, and close to each other, in the shutter of a dark 
room; cover them with a sheet of red glass, two conical pencils OPTICS. 
of red light will be formed, which meet and overlap each other 
at a certain distance from the shutter. If a screen is introduced 
into their path beyond this position, it will be seen that the 
overlapping segment produces an image composed of alternate 
red and black bands. On shutting out the light from either 
aperture, the dark bands at once disappear. It is, therefore, 
evident, that the dark fringes have been caused by the interfer- 
ence of the two pencils when they have crossed, and that, as with 
sound, two systems of waves may interfere and destroy each other, 
producing silence; so with light, two systems interfere and pro- 
duce darkness. 
The same results are obtained with any other homogeneous 
light, the only difference being in the distances of the bands 
from each other. This experiment is regarded as giving the 
most satisfactory evidence of the correctness of the undulatory 
or wave hypothesis of light. In white light the component 
colors produce dark bands at different intervals, these being 
superimposed but not coincident; the dark lines of one color 
are illuminated by the others, and a series of colored bands arise. 
606. Diffraction.—lf a beam of sunlight is admitted through 
one of the apertures, and the pencil of red light passed through 
a short-focus convex lens, L, Fig. 276 ; on intercepting it beyond 
Fig. 276. 
Diffraction. 
the focus of the lens, by means of an opaque screen, e, with a 
sharp edge, a (a knife-blade, for example), the following appear- 
ances arise. 
Ist. The edge a does not cast a sharply defined or geometrical 
shadow upon the second screen, b, of which B is a front view, 
where it is cut by the plane, the edge of which is represented 
by the line a b, hut a faint light appears below this, and gradu- 
ally fades away. The rays' in passing over the knife-edge, have, 
therefore, been bent downwards. 
2d. The part of the screen above the line where it is cut by 
the plane a h, we should expect to be uniformly lighted, but 
this is not so; it presents a series of alternate red and dark 
bands or fringes, which are fainter as we pass above the plane a b, 
until they finally disappear. The limits between these are not 
sharp lines, but the bands are regions of maximum and minimum 
intensity, which gradually fade into each other REFRACTION, INTERFERENCE, DIFFRACTION. 
523 
3d. In the first of these there is a bending downwards of the 
rays, whereby a part of the geometrical shadow has been illu- 
minated. The same has also occurred in the second, and it is 
to this action which an edge impresses upon rays of light that 
the term diffraction is applied. 
4th. Light of every color shows the same phenomena, but 
the fringes are broader in the red, and become narrower as we 
pass through the spectrum towards the violet. In white light, 
therefore, the dark spaces of one spectrum color are illuminated 
by the light of the next, and thus an image composed of a series 
of colors is formed. 
607. Diffraction Spectra.—lf the experiment in the last article 
is modified, causing the pencil of light from the luminous point 
to pass through a narrow slit in a screen, and the image viewed 
through a telescope, or allowed to fall on white paper, the fol- 
lowing phenomena appear. The light being red, the image 
consists of a red band, on the right and left are alternate red 
and dark bands, the former gradually fading away. The series 
on both sides are alike in intensity and extent. As in (605), 
their breadth differs with the tint of the light. If white light is 
substituted for monochromatic, a series of similarly placed 
spectra appear on each side of the central bright line. 
If in place of a simple slit a number of parallel linear open- 
ings are made by stretching fine wire backwards and forwards 
across an opening, or by making exact parallel rulings on smoked 
glass, the spectra become greatly increased in intensity. The 
violet end of each spectrum is towards the central bright image 
and the red end outwards. The length or dispersion of the 
spectra increases with their distance from the central image, 
consequently the}" overlap each other, and unless special con- 
trivances are employed only the first, second, and part of the 
third can be used. 
Rulings are also made by a diamond upon metal or glass, and 
are called gratings. In the former they are used by reflection, in 
the latter by transmission, or, if the glass is silvered, the grating 
thereon may be used in the same manner as if it were metallic. 
According as the number of lines to the inch increase, it gives 
spectra of greater dispersion and further apart, or at a greater 
angle to the central bright bar. 
These are called diffraction or interference spectra, and, as in 
sunlight, the colors and dark lines are placed according to their 
wave lengths, they are also called normal spectra. 
_ Since in the diffraction spectrum the red undergoes more 
dispersion than in the prismatic, it is better adapted for investi- 
gations regarding the absorption spectra of various animal 524 
OPTICS- 
fluids, the dark bands they produce lying chiefly below the yel- 
low and in the red region. 
The brilliant iridescence or play of tints on certain shells 
and other surfaces, is caused by interference decomposition of 
light, they frequently being ruled like a metallic grating. In 
like manner the colors in a soap bubble, in thin films of mica, 
glass, and other substances; in fissures in glass, and in oil on 
water, are all examples of color produced by interference be- 
tween reflected from their two surfaces. 
Polarization of Light 
Of the phenomena considered in this Chapter, polarization is 
of peculiar interest on account of the various conditions under 
wdiich it arises, the diverse effects it produces, and the different 
characters it presents. Light may undergo plane, circular, 
elliptical, and rotatory polarization; these we shall examine in 
the order given, discussing their manner of production, pecu- 
liarities, and applications. 
608. Plane Polarization by Reflection.—lf a ray of light falls 
on a polished unsilvered glass surface, at an angle of 35° 25', 
it is not only reflected, but undergoes another extraordinary 
Fig. 277. 
change; for if the reflected ray is 
received at the same angle upon an- 
other sheet of similar glass, it is most 
completely reflected when the face of 
the second mirror is parallel to that 
of the first, as in Fig, 277, in which 
a is an incident ray of ordinary light 
reflected from the mirror M', in the 
direction be; on meeting the second 
mirror M" at c, it undergoes reflec- 
tion, following the line c d; on rotat- 
ing the mirror M" on its vertical axis, 
the reflected ray loses its intensity, 
and when M" has moved through 90°, 
the light falling on its surface from 
M' is no longer reflected. 
Polarization. 
To this change in the ray b c, in consequence of which it can 
only be reflected under certain conditions, and fails entirely in 
others, the term 'polarization is applied. The first mirror is 
called the polarizer, and the second, on account of its action, 
the analyzer. 
609. Angle of Polarization is that which the incident ray must 
make with the normal or perpendicular to the polished surface POLARIZATION. 
525 
°f any given substance, to produce complete polarization in the 
ray reflected from it. In glass, it is 64° 350r the complement 
of the angle given. If in Fig. 277, any other angle than this is 
given to the first mirror, the light reflected from it is not com- 
pletely polarized, as is proven by the fact that a portion will 
always undergo reflection from the second, in whatever position 
it may be placed. Under these conditions the reflected ray is 
said to be partially polarized. 
Hearly all surfaces possess the power of partially polarizing 
light. That reflected from water, a polished wooden surface, 
or a slate roof, is partially polarized; diffuse daylight is also 
found to have assumed this condition, especially when the sun 
is near the horizon. 
With difference in the nature of the substance there is change 
in the angle of polarization. For glass, it is 54° 35'; water, 
52° 45'; obsidian, 56° 30'; quartz, 57° 32'; and for diamond, 
68°. Different kinds of glass also show variation in the angle 
of polarization; between crown and flint glass it is frequently as 
much as a degree and a quarter. 
According to Brewster; “ The polarizing angle of any substance 
is that angle of incidence at which the reflected polarized, ray is at right 
angles to the refracted ray. 
“ The plane of polarization is the plane of reflection in which 
the light becomes polarized; it coincides with the plane of inci- 
dence, and, therefore, contains the polarizing angle,” 
610. Polarization by Single Refraction.—lf the ray which passes 
through the glass, in the experiment (608), is submitted to ex- 
amination by a second mirror in the same manner as the ray 
bc,it is polarized, though the action is only partial. At the 
same time it has undergone a certain amount of refraction. 
We, therefore, learn that in simple refraction polarization also 
occurs. 
611. Polarization by Double Refraction.—We discovered (603, 
604) that when a ray of light traverses a crystal of Iceland spar 
m certain lines, it undergoes double refraction, an ordinary and 
extraordinary ray being formed. If these are submitted to 
examination by an analyzer, it is found that they are composed 
°f polarized light*. The polarization in the two instances is, 
however, different, in that their planes are at right angles to 
each other. The position in which the analyzer gives complete 
passage to the ordinary ray, is the one in which it gives most 
complete denial to the passage of the extraordinary. 
612. Polarizing Instruments.—Ist. Norremberg’s apparatus is 
constructed upon the principle of polarization by reflection; 526 
OPTICS. 
the polarizer and analyzer being single plates of polished glass. 
It is a most simple and a very complete polarization apparatus, 
and can be used for demonstrating nearly all the experiments. 
2d. Apparatus of parallel plates. Though the proportion of 
polarized light in the refracted pencil (610) is small when the 
ray passes through a single plate of glass, it is increased by 
using a number of films or plates arranged parallel to the first. 
The surfaces must he as flat as possible, and parallel to each 
other. In this manner, good polarizers and analyzers built up 
of fifteen or twenty plates of glass made for microscope object- 
covers can be constructed at small expense; the plates being 
fitted at the proper angle into a metallic or wooden tube. Either 
the reflected or refracted ray from such bundles is used. 
Bd. Tourmaline. If a plate be cut parallel to the axis of this 
negative uniaxial crystal, it produces an ordinary and an extra- 
ordinary ray polarized in planes at right angles to each other. 
The plate also possesses the property of rapidly absorbing the 
ordinary ray, if, therefore, it has sufficient thickness, the extra- 
ordinary alone will escape. A second similar plate may be used 
as an analyzer; through such an arrangement the light which 
has been polarized by the first plate passes with but little loss, 
while the second is set parallel to the first; but is completely 
stopped when they are at right angles. 
The thickness required to cause complete absorption of the 
ordinary ray is a serious objection to the use of tourmaline 
plates, on account of the great loss of light it necessitates. 
4th. Double refracting prisms. The ordinary and extraordinary 
rays which emerge from a natural rhomb of Iceland spar, are 
parallel to each other; the amount of their separation, there- 
fore, is dependent upon the thickness of the prism. The extent 
of this can be increased by cutting the crystal until its faces are 
inclined. In the prism thus formed, though the desired sepa- 
ration may be obtained, a new difficulty arises, the emergent 
light being colored by decomposition. To remedy this evil, it 
is necessary to achromatize the prism by uniting it with one 
of glass, with its refracting angle in the opposite direction. To 
obtain the greatest divergence between the rays, the refracting 
edges are cut parallel to the optic axis. 
A prism such as that described, generally permits the emer- 
gence of an ordinary and extraordinary ray, the relative inten- 
sities of which vary as it is revolved. There are, however, two 
positions in which only the ordinary ray emerges, and two others 
at right angles to these in which the extraordinary alone escapes. 
The apparatus, therefore, not only informs us whether the light 
is polarized, but also the plane wherein the polarization has 
taken place. POLARIZATION. 
527 
sth. NicoVs prism is, for many purposes, the best means of 
polarizing light, as it is exceedingly transparent, polarizes com- 
pletely, and transmits only the extraordinary ray. It is made 
of Iceland spar, and is a column the height of which is about 
three times its breadth. The crystal is cut in twain along 
a plane connecting its obtuse angles. The parts are then 
cemented together with Canada balsam. 
Fig. 278. 
Nicol’s prism. 
The principle of action of the Hicol is, that the refractive 
index of the balsamic cement being less than the ordinary index 
of the spar, and greater than the extraordinary, the ordinary ray 
undergoes total reflection at the surface of the balsam, B D, and 
is refracted out of the crystal at its side, A B, while the extra- 
ordinary passing onwards emerges at the end, BC. The Aicol 
can be used as polarizer or analyzer. 
In Foucault’s prism the Canada balsam is omitted. While 
this is shorter, it has the disadvantage of giving a smaller field 
of view, and the loss of light by reflection is greater. 
613. Theory of Polarized Light.—lt has been stated in (441), 
that luminous vibrations are transverse, while those of sound 
are longitudinal. This hypothesis regarding the manner of 
vibration of the ethereal particles in the production of light is 
supported by the phenomena of polarization. 
Considering the double refraction action of Iceland spar, 
Glanot says,.“ How it can be shown to be in strict accordance 
with mechanical principles that, if a medium.possesses unequal 
elasticity in different directions, a plane wave produced by trans- 
versal vibrations entering that medium will give rise to two 
plane waves moving with different velocities within the medium, 
and the vibrations of the particles in front of these waves will be 
in directions parallel respectively to two lines at right angles to 
each other. If, as is assumed in the undulatory theory of light, 
the ether exists in a double refracting crystal in such a state of 
unequal elasticity, then the two plane waves will he formed as 
described, and these, having different velocities, will give rise 528 
OPTICS. 
to two rays of unequal refrangibility. This is the physical 
account of the phenomenon of double refraction. It will be 
remarked that the vibrations corresponding to the two rays are 
transversal, rectilinear, and in directions perpendicular to each 
other in the rays respectively. Accordingly, the same theory 
accounts for the fact that the two rays are both polarized, and 
in planes at right angles to each other.” 
614. Interference of Polarized Light.—The laws which govern 
the phenomena of interference of rays similarly and differently 
polarized, are stated as follows by Ganot : 
“ 1. When two rays polarized in the same plane interfere 
with each other, they produce by their interference fringes of 
the very same kind as if they were common light. 
“ 2. When two rays of light are polarized at right angles to 
each other, they produce no colored fringes in the same circum- 
stances under which two rays of common light would produce 
them. When they are polarized in planes inclined to each 
other at any other angles, they produce fringes of intermediate 
brightness, and if the angle is made to change, these gradually 
decrease in brightness from 0° to 90°, and are totally obliterated 
at the latter angle. 
“3. Two rays originally polarized in planes at right angles 
to each other, may be subsequently brought into the same plane 
of polarization without acquiring the power of forming fringes 
by their interference. 
“4. Two rays polarized at right angles to each other, and 
afterwards brought into the same plane of polarization, produce 
fringes by their interference like rays of common light, provided 
they originated in a pencil the whole of which was originally 
polarized in any one plane. 
“5. In the phenomena of interference produced by rays that 
have suffered double refraction, a difference of half an undula- 
tion must be allowed, as one of the pencils is retarded by that 
quantity from some unknown cause.” 
615. Depolarization.—Suppose a polarizing apparatus, wdth its 
polarizer and analyzer so adjusted that the passage of light 
through the latter is completely stopped. Then intervene a 
plate of double refracting crystal, cut parallel to its axis, and 
of moderate thickness, between the polarizer and the analyzer. 
The intensity of the transmitted light varies as the plate is turned, 
reaching its maximum when the principal plane of the plate is 
at 45° to the plane of reflection, and disappearing if they coin- 
cide, or are at right angles to each other. From the effect pro- 
duced upon the light transmitted by the polarizer, a plate like 
that described is called a depolarizing plate. POLARIZATION. 
529 
616. Action of Thin Films is thus described by Ganot: “ Take a 
thin film of selenite or mica between the twentieth and sixtieth of 
an inch thick, and interpose it as in the last article. If the 
thickness of the film is uniform, the light now transmitted 
through the analyzer will be no longer white, but of a uniform 
tint; the color of the tint being different for different thick- 
nesses—for instance, red, or green, or blue, or yellow, according 
to the thickness; the intensity of the color depending on the 
inclination of the principal plane of the film to the plane of 
reflection, being greatest when the angle of inclination is 45°. 
Let us now suppose the crystalline film to be fixed in that posi- 
tion in which the light is brightest, and suppose its color to be 
red. Let the analyzer (the Nicol’s prism) be turned round, the 
color will grow fainter, and when it has been turned round 45°, 
the color disappears, and no light is transmitted; on turning it 
further, the complementary color, green, makes its appearance, 
and increases in intensity until the analyzer has been turned 
through 90°; after which the intensity diminishes until an 
angle of 135° is attained, when the light again vanishes, and, 
on increasing the angle, it changes again into red. Whatever 
the color proper to the plate, the same series of phenomena 
will be observed, the color passing into its complementary 
when the analyzer is turned. That the colors are really com- 
plementary is proved by using a double refracting prism as 
analyzer. In this case two rays are transmitted, each of which 
goes through the same changes of color and intensity as the 
single ray described above; but whatever the color and in- 
tensity of the one ray in a given position, the other will have 
the same when the analyzer has been turned through an angle 
of 90°, Consequently, these two rays give simultaneously the 
appearances which are successively presented in the above ease 
by the same ray at an interval of 90°. If now the two rays are 
allowed to overlap, they produce white light; thereby proving 
their colors to be complementary.” 
617. Production of Colored Rings by Polarized Light.—ln the 
preceding experiment, while the rays traverse the film perpen- 
dicularly to its faces, the tint is uniform; but if at different 
obliquities, colored rings are produced. Regarding these, Ganot 
says: 
“ The best method of observing these new phenomena is by 
rneans of the tourmaline 'pincette. This is a small instrument con- 
sisting of two tourmalines, cut parallel to the axis, each of them 
being fitted in a copper disk. These two disks, which are per- 
forated in the centre, and blackened, are mounted in two rings 
of silvered copper, which is coiled to form a spring, and press 
together the tourmalines. The tourmalines turn with the disk, 530 
OPTICS. 
and may be arranged with their axes either perpendicular or 
parallel/’ 
“The crystal to be experimented upon, being fixed in the 
centre of a cork disk, is placed between the two tourmalines, 
and the pincette held before the eye to view diffused light. 
The tourmaline furthest from the eye acts as polarizer, and the 
other as analyzer. If the crystal thus viewed is uniaxial, and 
cut perpendicularly to the axis, and a homogeneous light—red, 
for instance—is looked at, a series of alternately dark and red 
rings are seen. With another simple color similar rings are 
obtained, but their diameter decreases with the refrangibility 
of the color. On the other hand, the diameters of the rings 
diminish when the thickness of the plates increases, and beyond 
a certain thickness no more rings are produced. If, instead of 
illuminating the rings by homogeneous light, white light is used, 
as the rings of the different colors produced have not the same 
diameter, they are partially superposed, and exhibit very bril- 
liant variegated colors.” 
Biaxial crystals also give colored rings, but their form is more 
complicated. 
618. Detection of Molecular Change by Polarized Light.—Under 
ordinary circumstances glass does not possess the power of 
double refraction. This property may, how- 
ever, be imparted to it by changing the rela- 
tions of its molecules either by compression, 
curvature, or heat. If, under these condi- 
tions, a beam of polarized light traverses the 
glass, the changed conditions of its molecular 
structure are at once made evident, by the 
production of colored rings, or curved figures, 
like those described, the forms of which are 
according as the piece of glass is circular, trian- 
gular, or rectangular, and as the compression 
or other force is altered in intensity. Some 
idea may be gained of the changes in question 
from Fig, 279, which represents the effects pro- 
duced, as a circular piece of compressed glass 
is revolved in its own plane between the polar- 
izer and analyzer. 
Fig. 279. 
Compressed glass and 
polarized light. 
The results we have been discussing show the great impor- 
tance of polarized light in investigation of questions having rela- 
tion to molecular structure. Its use in the study of numerous 
inorganic crystalline forms, and, also of organic structures as 
starch, yields most efficient aid in determining their character 
when applied in connection with the microscope. POLARIZATION. 
531 
619. Elliptical and Circular Polarization.—“ In the cases hitherto 
considered the particles of ether composing a polarized ray 
vibrate in parallel straight lines; to distinguish this case from 
those we are now to consider, such light is frequently called 
'plane polarized light. It sometimes happens that the particles of 
ether describe ellipses round their position of rest, the planes of 
the ellipses being perpendicular to the direction of the ray. If 
the axes of these ellipses are equal and parallel, the ray is said 
to be elliptically polarized. In this case the particles which, when 
at rest, occupied a straight line, are, when in motion, arranged 
in a helix round the line of their original position as an axis, 
the helix exchanging from instant to instant. If the axes of the 
ellipses are equal they become circles, and. the light is said to 
be circularly polarized. If the minor axes become zero, the 
ellipses coincide with their major axes, and the light becomes 
plane polarized. Consequently, plane polarized light and circu- 
larly polarized light are particular cases of elliptically polarized 
light.” 
“ Circular or elliptical polarization may be either right-handed 
or left-handed, or what is sometimes called dextrogyrate and Icevo- 
gyrate. If the observer looks along the ray in the direction of 
propagation, from polarizer to analyzer, then, if the particles 
move in the same direction as the hands of a watch with its face 
to the observer, the polarization is right-handed.” 
620. Theory of Elliptical and Circular Polarization.—Regarding 
the relations of elliptical, circular, and plane polarization to each 
other, Ganot says : “ Let us in the first place consider a simple 
Pendulum vibrating in any plane, the arc of vibration being 
small. Suppose that, when in its lowest position, it received a 
blow in a direction at right angles to the direction of its motion, 
such as would make it vibrate in an arc at right angles to its 
arc of primitive vibration, it follows from the law of the com- 
position of velocities, that the joint effect will be to make it 
vibrate in an arc inclined at a certain angle to the arc of primi- 
tive vibration, the magnitude of the angle depending on the 
magnitude of the blow. If the blow communicated a velocity 
equal to that with which the body is already moving, the angle 
would be 45°. Next suppose the blow to communicate an 
equal velocity, but to be struck when the body is at its highest 
point, this will cause the particle to describe a circle, and to 
move as a conical pendulum. If the blow is struck under any 
other circumstances, the particle will describe an ellipse. Now 
as the two blows would produce separately two simple vibrations 
iu directions at right angles to each other, we may state the 
result arrived at as follows : If two rectilinear vibrations are 
superinduced on the same particle in directions at right angles OPTICS. 
to each other, then: A. If they are in the same and opposite 
phases, they make the point describe a rectilinear vibration in 
a direction inclined at a certain angle to either of the original 
vibrations. B. But if their phases differ by 90° or a quarter 
of a vibration, the particle will describe a circle, provided the 
vibrations are equal. G. Under other circumstances the particle 
will describe an ellipse.” 
“To apply this to the case of polarized light. Suppose two 
rays of light polarized in perpendicular planes to coincide, each 
would separately cause the same particles to vibrate in perpen- 
dicular directions. Consequently—A. If the vibrations are in 
the same or opposite phases, the light resulting from the two 
rays is plane polarized. B. If the rays are of equal intensity, 
and their phases differ by 90°, the resulting light is circularly 
polarized, C. Under other circumstances the light is elliptically 
polarized.” 
621. Production of Circularly Polarized Light is accomplished 
by means of Fresnel’s rhomb, which decomposes a ray of 
Fig. 280. 
plane polarized light forming two equal rays 
polarized in planes at right angles to each 
other, but differing by a quarter of an undu- 
lation. The instrument is made of glass, 
the acute angle being 54°, and the obtuse 
126°. “If a ray, <2, Fig. 280, of plane 
polarized light falls perpendicularly on the 
face A B, it will undergo two total internal 
reflections at an angle of about 54°, one at 
E, and the other at F, and will emerge per- 
pendicularly to C. 
“ If the plane A B C D be inclined at an 
angle of 45° to the plane of polarization, 
the polarized ray will be divided into two 
Circular polarization. 
coincident rays, with their planes of polarization at right angles 
to each other, and it appears that one of them loses exactly a 
quarter of an undulation, so that on emerging from the rhomb 
the ray is circularly polarized. If the ray emerging as above 
from Fresnel’s rhomb is examined, it will be found to differ 
from plane polarized light in this, that, when it passes through 
a double refracting prism, the ordinary and extraordinary rays 
are of equal intensity in all positions of the prism. Moreover, 
it differs from ordinary light in this, that if it passed through a 
second rhomb placed parallel to the first, a second quarter of an 
undulation will be lost, so that the parts of the original plane 
polarized ray will differ by half an undulation, and the emergent 
ray will be plane polarized; moreover, the plane of polarization 
will be inclined at an angle of 45° to A B C D, but on the other 
side from the plane of primitive polarization.” 533 
POLARIZATION. 
622. Production of Elliptically Polarized Light.—“ In addition 
to the method already mentioned, elliptically polarized light is 
generally obtained whenever plane polarized light sutlers reflec- 
tion. Polarized light reflected from metals becomes elliptically 
polarized, the degree of ellipticity depending on the direction 
of the incident ray, and of its plane of polarization, as well as 
on the nature of the reflecting substance. When reflected from 
silver the 'polarization is almost circular, and from galena almost plane. 
If elliptically polarized light he analyzed by a NicoVs prism, it never 
vanishes, though at alternate positions it becomes fainter; it is thus 
distinguished from plane and from circular polarized light. If analyzed 
by Iceland spar neither image disappears, but they undergo changes in 
intensity.” 
“ Light can also be polarized elliptically in Fresnel’s rhomb. 
If the angle between the planes of primitive polarization and of 
incidence be any other than 45°, the emergent ray is elliptically 
polarized.” 
623. Production and Theory of Rotatory Polarization.—“Rock- 
crystal or quartz possesses a remarkable property which was 
long regarded as peculiar to itself among all crystals, though it 
has been since found to be shared by tartaric acid and its salts, 
together with some other crystalline bodies. This property is 
called rotatory polarization, and may be described as follows : 
Let a ray of homogeneous light be polarized, and let the ana- 
lyzer, say a Hicol’s prism, be turned till the light does not pass 
through it. Take a thin section of a quartz crystal cut at right 
angles to its axis, and place it between the polarizer and the 
analyzer, with its plane at right angles to the rays. The light 
will now pass through the analyzer. The phenomenon is not 
the same as that previously described, for, if the rock-crystal is 
turned round its axis, no effect is produced, and if the analyzer 
turned, the ray is found to be plane polarized in a in- 
clined at a certain angle to the plane of primitive polarization. 
If the light is red, and the plate one millimetre thick, this angle 
18 about 17°. In some specimens of quartz the plane of polari- 
zation is turned to the right hand, in others to the left hand. 
Specimens of the former kind are said to be right-handed, those 
of the latter kind left-handed. This difference corresponds to a 
difference in crystallographic structure. The property possessed 
oy rock-crystal of turning the plane of polarization through a 
certain angle was thoroughly investigated by Biot, who, amongst 
other results, arrived at this : For a given color the angle through 
which the plane of polarization is turned is proportional to the 
thickness of the quartz. The explanation of the phenomenon 
described is as follows : When a ray of polarized light passes 
along the axis of the quartz crystal, it is divided into two rays 534 
OPTICS. 
of circularly polarized light of equal intensity, which pass through 
the crystal with different velocities. In one the circular polari- 
zation is right-handed, in the other left-handed, The existence 
of these rays was proved by Fresnel, who succeeded in sepa- 
rating them. On emerging from the crystal, they are com- 
pounded into a plane polarized ray, but since they move with 
unequal velocities within the crystal, they emerge in different 
phases, and consequently the plane of polarization will not coin- 
cide with the plane of primitive polarization. The plane of 
polarization will be turned to the right or left, according as the 
right-handed or left-handed ray moves with the greater velocity. 
Moreover, the amount of rotation will depend on the amount of 
retardation of the ray whose velocity is least—that is to say, it 
will depend on the thickness of the plate of quartz.” 
624. Coloration by Rotatory Polarization.—For different colors 
the amount of rotation varies according to the refrangibility 
Pig. 281. 
of the rays, being greatest for the violet. 
A quartz plate one millimetre thick will 
rotate the plane 17° for red, and 44° for 
violet light. If white light is used, it under- 
goes decomposition, the colors appearing in 
order from the less to the more refrangible 
with a right-handed crystal, as the FTicol is 
turned to the right, and with a left-handed 
Rotatory polarization. 
crystal in the opposite order. 
If, in place of a JSTicol, a double refracting prism is used, two 
brilliant colors are produced which are complementary to each 
other and yield white light where they overlap. Fig. 281. 
625. Rotatory Power of Liquids.—Many liquids possess this 
power in different degrees, and in several directions, so that 
variations in composition may thereby be found when little or 
none is shown by chemical analysis. If, for example, cane sugar 
is acted upon by dilute acids, we obtain two sugars of the same 
chemical composition, hut one rotates the plane of polarization 
to the right, while the other turns it to the left. 
In fluids the power of rotation is much less than in quartz. 
In concentrated solution, cane sugar, the most powerful of all 
liquids in this respect, has only about the power of quartz ; 
in order, therefore, to give it sufficient influence over the ray, 
columns eight inches in length are employed. 
626. Saccharimeters are instruments depending upon polar- 
ized light for their action. That of Biot determines the ampli- 
tude of rotation produced by sugar or other solutions 
this power. The polarizer in the original form is a mirror of POLARIZATION. 
535 
black glass, and the analyzer a double refracting achromatic 
prism mounted in the interior of a graduated circle, so that 
changes in position of the prism are read by means of an index 
traversing the scale Between these the tube containing the 
solution is placed, with its axis coincident with the conjoined 
JPig. 282. 
The polariscope. 
axes of the analyzer and polarizer. The tube is about 20 centi- 
metres in length. The apparatus is adjusted to have the extra- 
ordinary ray disappear when the index is at zero. The in- 
troduction of water, alcohol, or ether causes no change in the 
phenomena observed. 
If it is then filled with a solution of cane sugar the extra- 
ordinary ray reappears, and to cause it to fade the analyzer 
joust be turned to the right of zero through a certain num- 
ber of degrees, which measures the amount that the sugar has 
turned the plane of polarization to the left. If a longer tube be 
used with a solution of the same strength the analyzer must be 
turned through a greater number of degrees. According as the 
strength of the solution differs, so does the angle at which the 
uualyzer must be set vary. It is, therefore, a simple matter to 
ostiniate the amount of sugar in any given solution by deter- 
mining its power to rotate a beam of polarized light. 536 
OPTICS. 
Since white light is decomposed in the preceding experiment, 
the extraordinary image is not entirely extinguished in any posi- 
tion of the analyzer. ■ This difficulty is met by using colored glass, 
or other medium which shall make the light monochromatic. 
The colors usually employed are either red or yellow; the latter 
is best obtained by means of a soda flame produced by immersing 
a platinum wire bearing a globule of biborate of soda in a 
Bunsen flame. Since the angle differs for each color used, it is 
mentioned along with the angle of deviation of the ray, and 
the sign +, or —, added to show whether rotation is to the right 
or the left. 
In the manufacture and refining of sugar, the saccharimeter 
is of the utmost importance, as the sales of this commodity are 
based upon its indications. In the practice of medicine it is 
used for determining the percentage of sugar in diabetic urine, 
and in other fluids. 
Soldi’s saccharimeter differs from the preceding in that it does 
not measure the angle of rotation, but the amount of compen- 
sation required to overcome it. The medium employed is a 
plate of quartz, the thickness of which may be varied until the 
rotation is overcome; the amount necessary to produce this 
result is then measured. For a description of the parts of this 
instrument the student is referred to Gan of s “ Physics.” 
CHAPTER XXYIII. 
SPECTEOSCOPE AND SPECTKUM ANALYSIS. 
The spectroscope—Parts of single prism spectroscope—Slit and collimator—Prism 
and telescope—Scale of collimator—Sources of light—Multiple prism spectro- 
scope—Direct vision spectroscope—Grating spectroscope—Continuous spectra 
—Bright-lined spectra—Banded spectra—Nebular spectra—Gaseous absorbent 
spectra—Solar spectrum—Ultra-violet solar spectra—lnfra-red solar spectra 
—Wave-lengths of lines of spectra—Use of solar lines as a scale—Atmos- 
pheric spectrum lines—Planetary and stellar spectra—Absorbent spectra by 
colored liquids Absorbent spectra by colorless liquids—Blood spectra—- 
Spectra of bile and Pettenkofer’s lluid—Spectra of wine and ale. Abnormal 
spectra. 
627. The Spectroscope, as its name indicates, is an instrument 
for studying the composition of light by the formation of a 
spectrum. In (500 to 505) we learned how light can be de- SPECTROSCOPE AND SPECTRUM ANALYSIS. 
537 
composed by the action of an optical prism, and its character 
determined through the formation of a prismatic spectrum. In 
(607) the decomposition of light by a ruled surface or grating 
was explained, and also the difference between the diffraction 
or interference spectrum thereby produced and the prismatic 
spectrum. Either of these methods can be employed in the 
construction of the spectroscope, but thus far the one in general 
use has been that by the prism; we shall, therefore, direct our 
attention especially to this form. 
The action of the spectroscope being to separate or disperse 
a mixture of colors into its components, it follows that an amount 
of dispersion which will answer in one case may be insufficient 
in another. We consequently find that, according to the dis- 
persion required, the spectroscope contains one or more prisms 
arranged as described in the final paragraph of article (602). 
628, Parts of Single Prism Spectroscope.—This form of instru- 
ment will generally answer for the physiologist and physician. 
It consists of a prism upon which the axes of three telescopes 
are directed; a narrow slit, and a scale for measurement of the 
relative positions of lines or colors. Of the telescopes one is 
attached to the slit, its lens forms the collimator; another receives 
and transmits the spectrum image formed by the prism, it is 
called the observing telescope; the third forms an image of the 
scale. In considering these parts, we shall take them up in 
the order which the light passes through them to the eye. 
629, The Slit and its Collimator.—The bright and dark lines 
visible in the spectroscope are images of the slit. This is situated 
at 1, Fig. 283. It consists of two sharp metallic edges set at a 
short distance from each other, allowing a narrow beam of light 
to pass between them into the tube to which it is attached. 
These must be perfectly true and smooth, like those of a knife, 
and set exactly parallel to each other. They should be pro- 
tected from dust, and as they are commonly made from steel, 
care should be taken to prevent their rusting hy moisture or 
fumes. Dust or rust upon their edges produces longitudinal 
striae in the spectrum. To avoid rusting, they are sometimes 
uiade of obsidian. 
In its simplest form the jaws are at a fixed distance from each 
other, and the width of the beam of light admitted to the eye is 
invariable. In more improved kinds one of the jaws is moved 
by a screw, so that the slit may be entirely closed or opened to 
any required extent. Sometimes the screw head carries a scale 
and index, by which the aperture can be measured, and changed 
or restored at will. 
In ordinary use the slit is placed quite close to the flame to OPTICS. 
be examined, and so adjusted that the latter is in the vertical 
axial plane of the tube which carries the slit, as at 7, Fig, 283. 
When necessary to compare the spectra of two flames, one-half 
of the vertical aperture is covered by a small prism so adjusted, 
that if the second is placed at one side of the first, its rays will 
be directed down the tube, and while those from one source of 
Fig. 283. 
The spectroscope. 
light occupy the upper half of the vertical axial plane, those 
from the other occupy its lower half. Thus two spectra are 
presented to the observer one immediately above the other, and 
their minutest details may be accurately compared. The device 
is known as the comparison prism. 
In the spectrum apparatus of Fraunhofer the slit was placed 
at a distance of twenty-four feet from the prism, presenting 
a nearly parallel beam of light to its action. A great improve- 
ment was made upon this by Prof. Swan, who achieved the 
same result by means of a convex lens called the collimator, 
placed at its principal focal distance from the slit, and with its 
exposed face close to the prism. It is located at 2, Fig. 283. 
The slit and collimator are mounted in a tube provided with a 
second or draw tube, thus allowing any focal adjustment. 
630. The Prism and Telescope are for the formation and ex- 
amination of the spectrum. The former occupies the position 
at 3, Fig. 283. It is usually equiangular or a prism of 60°. It 
is set at its angle of minimum deviation (499). According as SPECTROSCOPE AND SPECTRUM ANALYSIS. 
539 
greater or less dispersion is desired it differs in its character. 
One of crown glass gives a moderate dispersion; ordinary flint 
a greater, and heavy glass a still greater. Hollow prisms filled 
with liquid, as the bisulphide of carbon, are also employed. 
The observing telescope is represented at 4. It is supported on 
a movable arm, in order that any portion of the spectrum image 
emerging from the prism can be passed down its axis, and sub- 
mitted to examination under the most favorable conditions. 
631. The Scale and its Collimator.—These are shown at 5 and 
6, and form the third telescope of the apparatus. The former is 
at the outer end, and is usually photographed upon glass. It is 
illuminated by a candle or other flame, as at 6; at the inner end 
at 5, there is a convex lens or collimator, from this the rays from 
the illuminated scale are directed upon the face of the prism 
adjacent to the object-glass of the telescope, in such a manner, 
that they are reflected down its axis, and a bright image of the 
scale is seen above or below the spectrum, according to the 
direction given to the axis of the scale tube. 
Another method consists in placing the scale immediately in 
front of the eye-piece and illuminating from one side by a pecu- 
liarly constructed prism, which accomplishes the object by two 
reflections. 
In some instruments a micrometer eye-piece is used, as in the 
microscope. In others, the arm supporting the observing tele- 
scope traverses over a graduated arc. The positions of the lines 
in the spectrum are determined thereon by bringing the cross- 
wires of the eye-piece of the telescope to intersect them, and 
reading the degree on the arc. 
632. The Source of Light.—When sunlight is employed, it must 
be directed by a mirror upon the slit along the axis of its colli- 
mator-tube. The beam should be made steady by a heliostat. 
For ordinary chemical examinations a Bunsen flame is used 
in the position indicated at 7. Into this the substance is intro- 
duced by means of a platinum wire, supported by a stand, as 
at 8. 
If a more intense heat than that furnished by a Bunsen 
flame is required, an oxyhydrogen jet may be substituted, and 
in the same position. For still greater intensity the electric 
spark, either derived directly from an induction apparatus, or 
concentrated by a condenser, is employed. 
633. Multiple Prism Spectroscope is composed of a number of 
prisms acting- in the same direction, and so arranged that they 
can all be adjusted for their angle of minimum deviation for 
any ray. In some forms light passes in one direction through 540 
OPTICS. 
the battery of prisms, and in the last of the series is made to 
undergo reflection, by which it is returned through the same 
system. Thus an amount of dispersion is attained equal to that 
produced by double the number of the effective prisms. Spec- 
troscopes of this nature are only used for special astronomical 
investigations. Sometimes a double prism instrument is de- 
sirable in certain chemical examinations. 
634. Direct Vision Spectroscope.—lt has been stated in (502) 
that the dispersion power of flint glass is nearly double that of 
crown. The difference in their deviation power is at the same 
time not so great. It is, therefore, possible to combine a number 
of these prisms in such a manner, that while the ray of light 
undergoes little or no deviation from its original course, there 
is sufficient dispersion between its colors to produce a spectrum 
available for spectroscopic uses. 
In Fig. 284, such an arrangement is represented. It consists 
of three crown prisms marked C C C, and two flint marked 
FF. The two kinds are so adapted to each other, that their 
bases being in opposite directions, they neutralize each others 
Fig. 284. 
Direct vision spectroscope. 
action. In respect to deviation, this neutralization is perfect. 
As regards dispersion, it is not, consequently the component 
colors of white light are separated in its passage through the 
system, as at r v ; and a spectrum is formed. 
635. Grating Spectroscope.—ln (607) the production of diffrac- 
tion or interference spectra by means of gratings was described. 
Though in this method of formation there is a decided loss of 
light, the original beam being divided into a great number of 
spectra, there is a gain in the greater dispersion obtained in the 
red region. 
For physiological purposes a grating of about 5000 lines to 
the inch, ruled on glass, the surfaces flat and parallel, is sub- 
stituted for the prism, and mounted in its place. 
The best form of spectroscope to accomplish this is that in 
which measurements are made by traversing the telescope upon 
a graduated circle. The grating may be mounted either for 
transmitted or reflected light. In the former the adjustments 
are as follows: 
Ist. The graduated circle being placed in the horizontal plane, 
the narrow opening of the slit should be set vertically. SPECTROSCOPE AND SPECTRUM ANALYSIS. 
541 
2d. The centre of the slit, the axis of its collimator-tube, the 
axis of the telescope, and the intersection of its cross-lines being 
in the same straight line, the index of the telescope should 
point to the zero of the graduated circle. 
3d. The unruled surface of the grating should be turned to- 
wards the collimator, and set so that the axis of the latter shall 
be perpendicular to the ruled surface and pierce its centre. 
4th. The position of the grating face should be so adjusted, 
that if its central line was prolonged vertically downwards, it 
would coincide with the centre of the axis upon which the ob- 
serving telescope moves. 
The above adjustments having been carefully attended to, if 
the telescope is moved to the right a spectrum will appear, the 
violet being the first to enter the field, color after color passes 
in review, then a blank space; then a second spectrum enters, 
the violet in the van. This is more dispersed than the first, so 
a third, fourth, and higher orders of spectra display themselves 
as the telescope is moved onwards. In these, owing to greater 
dispersion, they overlap each other, and the colors are very much 
confused; they are also very faint. For most purposes the first 
and second orders will be found the most useful. If required 
to separate the colors in the higher orders, it can be done by 
a prism. 
If the telescope is returned to the zero of the scale, and 
traversed to the left the same phenomena occur, and a similar 
series of spectra appear. Taking a given line in that produced 
by sunlight, or the sodium line in that from a flame; if the 
apparatus is sufficiently perfect in the construction of all its parts, 
it will be found that the telescope must be moved through the 
same angle on each side of the zero, to bring the selected line 
of a spectrum of an order of the same number upon its cross- 
lines. 
Where it is desired to use the grating for reflected light, its 
ruled surface must be silvered. Spectra of greater brilliancy 
are thus produced. It is, however, necessary to set the grating 
at an angle to the axis of the slit collimator, and swing the 
telescope to the collimator side of the circle. 
In making photographs of the solar spectrum by a silvered 
grating I resorted to the device of passing the beam of light 
from the slit beneath the grating, and then reflecting it from a 
plane silvered mirror upon the grating. For a description of 
the method and results, the student is referred to the “ American 
Journal of Sciences and Arts,” vol. xvi. page 256. 542 
OPTICS. 
Spectrum Analysis. 
Four kinds of spectra present themselves for investigation ; 
Ist, continuous or unbroken; 2d, bright-lined and banded; 3d, 
absorbent; 4th, abnormal. 
636. Continuous Spectra are produced by light emitted from 
ignited or incandescent solids and liquids. If a body is at low 
red heat the spectrum consists of red only, or at the best of 
red and orange: as the temperature rises colors of greater 
and greater refrangibility appear in their proper order, until 
finally the seven colors of Newton are present (501). Ordinary 
illuminating flames, in which carbon at a high temperature is 
the source of light, furnish excellent examples of this class. 
Where greater brilliancy is required, the light produced by 
causing the oxyhydrogen flame to impinge upon a cylinder of 
lime, magnesia, or zirconia may be used. That from a strip of 
platinum or carbon rendered incandescent by an electric current 
is also employed. Continuous spectra are chiefly of interest to 
the physician, because they furnish a basis for the production of 
absorbent spectra of various animal fluids. For this purpose 
any oil or illuminating gas flame answers. 
637. Bright-lined Spectra.—lf a Bunsen burner be placed in 
front of the slit of a spectroscope, and access of air be cut off 
by the valve, an illuminating flame will be produced which on 
being viewed through the instrument will give a continuous 
spectrum of incandescence. Admitting air to it, its luminosity 
will at once disappear, on account of the complete combustion 
of carbon; it becomes a pale blue and violet and is known as 
the Bunsen flame. Looking through the spectroscope a spec- 
trum will no longer be visible, or at best only a very faint light 
in the more refrangible region. 
If a platinum wire dipped in a solution of chloride of sodium 
or common salt, be immersed in the Bunsen flame, the latter be- 
comes yellow, and on looking through the spectroscope a bright 
yellow line appears in the space formerly occupied by the yellow 
of the incandescent spectrum. This is known as the sodium 
line. With a spectroscope of feeble dispersion it is single ; but 
when two or more prisms are used, with a slit sufficiently 
narrow, it appears as a double line. When a heat more intense 
than from an ordinary Bunsen burner is employed other lines 
appear in the sodium spectrum and it finally becomes con- 
tinuous. So delicate is this test for sodium, that it has been 
estimated that the two hundredth-millionth of a grain of that SPECTROSCOPE AND SPECTRUM ANALYSIS. 
543 
element can thus be detected. Indeed in this respect it stands 
first among all metals. 
In their turn many other substances give special colors to the 
Bunsen flame, and these when viewed through the spectroscope 
present characteristic spectra composed of bright lines. So that 
of potassium produced in the same manner as that of sodium, 
consists of a red and a violet line. Calcium, lithium, strontium., 
and rubidium, all present strongly marked lines in certain posi- 
tions in the red together with other lines, Ccesium gives a 
characteristic blue line; thallium & green; indium an indigo. The 
great value of the spectroscope in chemical research is empha- 
sized by the fact, that within a few years a number of new 
elements have been discovered by its aid; among these, the 
flrst were caesium and rubidium, and later thallium, indium, 
and gallium. 
Since chlorides of metals are as a rule more volatile than other 
compounds, these salts should be employed to show their spectra. 
It is also well to moisten the platinum wire with a drop of hydro- 
chloric acid before dipping it into the pulverized salt. In the 
form of chloride, copper gives a superb spectrum when immersed 
in Bunsen flame, and so do certain other ordinary metals. 
An immense advantage possessed by spectrum analysis over 
all othermethods of investigation into the composition of a body 
is the fact, that it yields almost at a glance all the information 
it is capable of affording. Suppose, for example, in place of a 
single element we have a mixture, as sodium, potassium, lithium, 
calcium. Since each of these presents its own characteristic 
lines, none of which are coincident with those of the others, we 
detect the presence of each and all at once, exactly as we recog- 
nize the faces of different persons with whom we are acquainted, 
though mingled with a crowd of others. 
Bor accurate placement of the lines of any element by a 
given spectroscope, they must be studied in connection with 
the scale, and a record kept, to which reference can be made. 
The instrument being then adjusted with the sodium line always 
on a given line of the scale, the position of the lines found is 
read off, and their nature determined by reference to the record. 
While many metals give strong spectra at the temperatures 
reached by the Bunsen flame, there are others, like iron, which 
are not sufficiently volatilized at that heat to give a result. 
These can all be made to assume the vaporous state by aid of 
the electric arc, or by the simple or condensed spark of an in- 
duction coil. By one or another of these agents, spectra of all 
the elements have been obtained, that of each being often dif- 
ferent according to the temperature at which it is volatilized. 
Bor the physician, however, who desires to examine the ash of 
tissue or excretions for certain elements, the use of lined spectra OPTICS. 
is confined to the detection of calcium, sodium, lithium, and 
other substances volatile in the Bunsen flame. The more potent 
appliances are, therefore, left almost entirely in the hands of the 
chemist and physicist. 
638. Banded Spectra,—ln place of lines, the spectra of some 
gases and vapors are composed of bright bands. This is the 
case with the spectrum of cyanogen. Ignited nitrogen affords 
another example of the same result. Under an increase of tem- 
perature bands are broken up into tine lines, sometimes of 
greater and sometimes less refrangibility than those from which 
they were formed. It is thought that at lower temperature 
bands may arise from some compound of a substance, while at 
higher these may be dissociated, and the true bright lines of the 
element appear. 
The spectra of gases are best obtained by the aid of Geissler’s 
and Plucker’s tubes, which contain the gas or vapor in a state of 
extreme exhaustion. Those generally employed consist of two 
elongated bulbs connected by a capillary tube. A platinum 
electrode passes through the distal end of each, and affords con- 
nection with the poles of an induction coil, or a Holtz appa- 
ratus. On passing the sparks the slender column of attenuated 
gas in the capillary tube becomes brilliantly illuminated, and 
placed in front of the slit, the spectrum under the prevailing 
conditions is seen. 
639. Nebular Spectra.—The importance of the application of 
spectrum analysis to investigating the chemical constitution of 
the heavenly bodies was quickly recognized by a number of 
astronomers. It was observed that there was a marked dif- 
ference between the spectra of the various nebulse, and those of 
the fixed stars and planets; in that the former generally gave 
bright-lined spectra like those of ignited gases, while the latter 
gave continuous spectra crossed by dark lines. 
640. Gaseous Absorbent Spectra.—A sodium flame produces a 
spectrum consisting of a bright yellow line. It might be ex- 
pected, that if this was interposed between an oxyhydrogen 
lime-light and the spectroscope through which it is viewed, the 
yellow of the former would intensify that of the continuous 
spectrum of the latter. Such, however, is not the case; on the 
contrary, the sodium flame absorbs the yellow of the calcium 
light, and a dark or black line appears in its place. In the 
same manner potassium, strontium, and other vapors were found 
to produce dark lines in a continuous spectrum, when intervened 
between the spectroscope and an oxycalcium light. To this 
class of phenomena the term absorbent spectra is applied, and SPECTROSCOPE AND SPECTRUM ANALYSIS. 
it was soon proven, that whenever an incandescent vapor forms 
a spectrum of bright lines, it will produce a reverse spectrum of 
dark lines when intervened between the spectroscope and an 
incandescent solid or liquid. 
641. Solar Spectrum.—lf a spectroscope be directed towards 
the sun, or if sunlight be reflected down the tube, while the 
slit is wide open a very brilliant continuous spectrum is seen. 
On reducing the aperture the intensity of color diminishes, and 
when sufficiently narrow well-marked dark lines appear as 
shown, Fig. 285. These are known as the Fraunhofer lines, and 
Fig. 285. 
Solar and stellar spectra. 
were named by their discoverer AB CD, etc. Continuing the 
reduction in aperture and increasing the dispersive power, these 
lines appear by thousands. 
For long, the origin of the dark lines of the solar spectrum 
was an inexplicable riddle; but at last the enigma was solved 
through agency of the facts with which we have been dealing. 
It was the fortune of Kirchoff to discover that the strong dark 
line in the yellow of the solar spectrum, which Fraunhofer called 
D, was coincident with the yellow line of sodium. He, there- 
fore, argued that since incandescent sodium vapor produced a 
dark line in the spectrum of incandescence from a lime-light, 
it was evident that in the sun the light emitted from the interior 
photosphere must meet with sodium vapor in the exterior 
envelopes, and so by absorption produce the dark line in ques- 
tion. In like manner, the lines C and F were found to be coin- 
cident with and a reversion of two hydrogen lines, and over 
one hundred bright lines of the spectrum of iron were found to 
have their counterparts in dark lines of the solar spectrum. 546 
OPTICS. 
Little by little observations were extended until the convic- 
tion forced itself upon all scientific minds, that by aid of spec- 
troscopic examination of their light, information could be ob- 
tained regarding the chemical constitution of the heavenly 
bodies, and as the new science underwent extension, it was 
proved that nearly all substances existing on our earth are 
discoverable in the exterior envelopes of the sun. 
642. Ultra-violet Solar Spectrum.—The original Fraunhofer 
lines are confined to the visible spectrum, and terminate in the 
violet at H. By application of photography to the study of 
the spectrum, it was found that there existed beyond the violet 
an ultra-violet region, as rich in absorption lines as the visible 
spectrum itself. To certain great groups in this region the letters 
L, M, H, 0, P, Q, were attached. By use of screens of various 
phosphorescent or fluorescent substances, the spectrum was still 
further extended until the enumeration of these great groups 
reached the letters Y and W. Besides these the lesser lines 
were numbered by thousands. 
643. Infra-red Solar Spectrum.—As there is an invisible spec- 
trum in the more refrangible region beyond the violet, crowded 
with absorption solar lines, so in the less refrangible below the 
red there is an infra-red space presenting well-marked lines. 
In this, also, photography has been the agent by which the spec- 
trum has been extended. To give some idea of the extent of 
this, we may say that between A and H lies the visible spec- 
trum, about 4000 of Augstrora’s units in length. If we take 
this as representing the visible spectrum, that below extends 
six times as far, or through 24,000 units, most of which has been 
mapped. 
* 
644. Wave-lengths of the Lines of the Spectrum.—To avoid con- 
fusion arising from use of prisms and scales of varying values, 
attached to different instruments, a scale based upon the wave- 
lengths of the solar lines has been introduced. The unit is the 
tenth metre. According to this the wave-lengths of the principal 
Fraunhofer lines are: 
A 
= 7604.00 
a 
= 7185.00 
B 
= 6867.00 
C 
= 6562.01 
D 
= 5892.12 
E 
= 5269.13 
b = 
5172.00 
F = 
4860.72 
Gr = 
4307.25 
hx= 
3968.00 
h2= 
3933.00 
645. Use of the Solar Lines as a Scale.—ln (631) mention has 
been made of the ordinary methods of measuring the position SPECTROSCOPE AND SPECTRUM ANALYSIS. 
547 
of lines in a spectrum. In the ultra-violet and infra-red these 
are sometimes difficult of application or fail us altogether. In 
this, and, indeed, in nearly all cases, the dark lines of the solar 
spectrum provide the most reliable method by which the posi- 
tion of a given band or line can be satisfactorily determined. 
One way of applying it is to pass into the observing telescope 
two spectra, one above and coincident with the other. The first 
derived from the sun by turning its rays into the collimator by 
a comparison prism The second from the light to be compared 
therewith. When the lines of the visible spectrum are to be 
examined, the eye serves as the means of investigation; but 
when the ultra- or infra-spectral regions are under considera- 
tion, suitable methods of photography must be employed. 
When the position of the bands in the absorbent spectra of 
liquids is to be determined, the light of the sun being taken as 
the basis for the formation of the absorbent spectrum, it only 
remains to use a slit of sufficient fineness to produce the solar 
lines, and thereby obtain the means of measurement. Accord- 
ing as they are investigated in different spectra, observations 
should be. taken directly by the eye, or through the agency of 
photography. 
646. Atmospheric Spectrum Lines.—ln addition to the fine lines 
of the solar spectrum to which attention has been directed, there 
are certain bands and regions of absorption especially evident in 
the earlier and later portions of the day, when the sun is near 
the horizon, and when his rays come to us through a greater 
thickness of the atmosphere. These have been called atmos- 
pheric and telluric bands or lines. They originate in the ab- 
sorptive action of the vapor of water in the earth’s atmosphere; 
but the field has not yet received the cultivation it deserves, 
and it is probable that, in the future, research will discover other 
and important explanations of value to the science of meteor- 
ology, and, consequently, to medicine. 
647. Planetary and Stellar Spectra.—In moons and planets, 
except Uranus, the spectra are the same as that of the sun, as 
their light is derived therefrom. In the fixed stars it is not so, 
their dark lines differing from those of the sun, and from each 
other. Secchi makes out no less than four types of stellar 
spectra. “ The first embraces the white stars and includes the 
well-known Sirius and a Lyrse. Their spectra usually contain 
a number of very fine lines, and always include four broad dark 
Hues which coincide with the bright lines of hydrogen. Out of 
346 stars, 164 were found to belong to this type. The second 
group embraces those having spectra intersected by numerous 
tine lines like those of our sun. About 140 stars, among them OPTICS. 
Pollux, Capella, Aquilse, belong to this collection. The third 
embraces the red and orange stars, such as a Orionis, p Pegasi; 
the spectra of these are divided into eight or ten parallel 
columnar clusters of dark and bright bands, increasing in in- 
tensity to the red. Group four is made up of small red stars 
with spectra, and is constructed of three bright zones, increasing 
in intensity towards the violet. It would thus appear that fixed 
stars, while differing from one another in the matter of which 
they are composed, are constructed on the same general plan as 
our sun, and have a photosphere surrounded by a gaseous 
atmosphere.” 
648. Absorbent Spectra by Colored Liquids.—lt has been shown 
that colored flames possess the property of absorbing their own 
tint of light from the spectrum of an incandescent solid, pro- 
ducing dark lines therein. As might be expected, colored 
liquids have a similar power, and those which appear colorless 
also exert a certain absorbent action. 
If a solution of permanganate of potash in a cell with flat 
parallel walls is placed immediately in front of the slit of a 
spectroscope, at the same time that rays from the sun or some 
incandescent solid are passing into the instrument, the spectrum 
seen through the telescope presents great bands or gaps, and 
its length is reduced both in the more and less refrangible 
regions. 
Passing from an inorganic to an organic body, if a solution of 
chlorophyll the green coloring matter of leaves, be put in the 
same position, dark bands appear in the red, the yellow, and the 
violet. In both of these instances the gaps or dark bands are 
produced by the absorbent action of the fluid, and the fact of 
their being in a spectrum becomes the evidence of the presence 
of these fluids in the cell, and an analytical test for the same. 
649. Absorbent Spectra by Colorless Liquids.—Russell and Lap- 
raik have made an extensive examination of these spectra. The 
spectroscope had a single prism of heavy glass. Before the 
light reached the slit it traversed a column of the liquid from 
2to 8 feet in length. Water gave a band at 600 to 610 of the 
scale, with a second at 705 to 723. Alcohol one at 630. Methyl, 
propyl, and amyl alcohols give them nearer to the red as alcohol 
is higher in the series. Ethyl iodide a second from 716 to 724. 
Amyl nitrate, acetate, and iodide give bands like that of amyl 
alcohol, but a little nearer the blue. Chloroform a faint one 
from 607 to 616, and a strong one from 711 to 717. Aldehyde 
and acetic acid, large absorption at the red and a faint band. 
Benzine two, one at 606 to 616, the other from 703 to 714. 
Phenol two, one near the water band, the other from 679 to SPECTROSCOPE AND SPECTRUM ANALYSIS. 
549 
710. Ammonia five, the darkest from 649 to 654, one coin- 
ciding with the water, the other with the alcohol band, a narrow 
sharp one from 566 to 570, and a fifth from 698 to 708. The only 
liquids which did not give bands were carbon disulphide and 
tetrachloride. See “Journal of Chem, Soc.,” 168, April, 1881. 
650. Blood Spectra.—The red coloring substance of the blood 
discs, called haemoglobin, presents an absorbent spectrum which 
varies according as an additional portion of oxygen is associated 
therewith or not. In the venous blood the discs are of a darker 
red, and contain haemoglobin. In their passage through the 
lungs, an additional portion of oxygen is taken up by their 
coloring matter; they become a brighter red, the haemoglobin 
passing into oxyhaemoglobin. Again, coursing through the sys- 
temic circulation the latter is deoxidized, and the former pro- 
duced. After undergoing these alternating changes a number 
of times, the haemoglobin is at last decomposed, and passes into 
haematin, which is also a red colored substance. 
All three of these states of the red coloring matter of blood 
are represented by changes in the absorption spectrum of that 
substance. The spectrum in each case is given in the following 
diagrams 
Fig. 286. 
Absorbent spectra of blood. 
The letters indicate the Fraunhofer lines. The first spectrum 
represents that obtained from arterial blood, or oxyhaemoglobin. 
In the second the oxyhaemoglobin is reduced by ammonium 
sulphide to haemoglobin. The third shows that given by haema- 
tin when the solution is acid. The fourth is that of haematin 
reoxidized. It is very nearly the same as that produced by the 
action of carbon monoxide upon blood. This gas also imparts 
a bright red tint, which cannot be removed by the same agen- 
cies as those which remove the red tint from blood reddened 
by oxygen. 
651. Spectra of Bile and Pettenkoffer’s Test.—Certain coloring 
matters are obtained from bile by the action of strong reagents 550 
OPTICS. 
give characteristic spectra. By passing nitrous vapors 
into bilirubin a body called choletelin is formed, which in acid 
solution gives a broad band extending from b to beyond F. 
Another product formed in Gmelin’s reaction gives in strong 
solution one from I) to b. The appearance of this indicates 
grave disturbance of the system. 
The spectrum of Pettenkofier’s test gives a band outside of D, 
and a broad one at E. Campbell gives the spectrum of sodium 
taurocholate as three, one between C and D, one between D and 
E, and a third near F. 
652. Other Spectra. Abnormal Spectra.—Certain coloring mat- 
ters in wine, beer, and ale also give characteristic absorbent 
spectra. 
When a hollow glass prism is filled with indigo solution, 
potassium permanganate, or alcoholic solution of fuchsine, the 
distribution of colors is changed. In fuchsine the violet is the 
least refracted, then the red, and then the yellow, which is re- 
fracted the most. Kundt says that all substances with surface 
color give abnormal spectra. SECTION VII. 
HEAT. 
CHAPTER XXIX. 
THEOEIES AND EFFECTS OF HEAT. 
Theories of heat—Sources of heat—Effect of heat on physical properties—Effect 
on composition—Expansion—Expansion of solids—Expansion of liquids— 
Maximum density—Expansion of gases—Winds—Effect on measures of time 
and quantity. 
Life is possible between the temperatures which determine 
the fluid state of water. No living creature can survive a heat 
above 212° F., for the liquid constituents of the body would be 
dissipated. Certain low germs, however, retain their vitality. 
None but germs can bear a temperature below 32° F. It is 
true that a creature may in itself possess the power of gener- 
ating heat and thus resist low temperatures, but remove this 
faculty, let the circulating juices of its body fall below 32° F,, 
and unless they are enclosed in capillaries, movement becomes 
impossible, and death supervenes. 
For plants and animals, heat is the all-important condition. 
Without it the globe would be a dreary, barren waste. The 
ancient fire worshippers made sacrificial offerings to the sun as 
the emblematic source of heat and of all earthly good. To the 
Egyptians a burning torch was the emblem of life. 
To the earlier inhabitants of the globe heat meant merely 
the means of cooking, and the promotion of the comfort of their 
dwellings. To the modern, it is emblematic of power and a 
mastery over the earth. Locomotives on land, steamers on the 
sea, innumerable applications in factories, and those wonderful 
electro-dynamic engines yielding force and light, are all results 
of modern applications of heat to generating various kinds of 
force. Take away the applications of heat which are now so 
universally employed in giving us the comforts of life, and life 552 
HEAT 
itself would hardly be worth its existence. We may, therefore, 
profitably employ ourselves with inquiring into the nature of 
this all-important form of energy. 
653. Theories of Heat.—The first is the theory of emission, 
which holds that the molecules of bodies are surrounded by a 
subtle imponderable fluid, which can pass from one to another. 
These heat molecules cause repulsion of those of the substance 
and oppose cohesion. 
The second is the undulatory theory. As with light,, this de- 
mands existence of the ether, the molecules of which are in a 
state of vibration. These motions may be communicated to 
the molecules of bodies. The hottest bodies are those in which 
the movements have the greatest velocity and the greatest am- 
plitude. According to this view, heat is a condition of matter 
and not a substance. It is the theory now generally accepted. 
654. Sources of Heat.—The first is the sun. It is estimated 
that enough heat is received by the earth from this body each 
year to melt a layer of ice over 100 feet in thickness. As it 
only receives the small quantity the passage of which its surface 
obstructs, we perceive how enormous the amount which escapes 
into space. 
Regarding the source of the sun’s heat, various opinions are 
held. Some maintain that it is the result of mechanical action, 
arising from attraction of the sun for meteoric matter floating 
in space, which, when it comes within the range of the sun’s 
action, is drawn into that body, and the temperature is sus- 
tained by the continuous pelting of this matter striking the sun 
with inconceivable velocity. • 
Another theory, held for some time, was that of combustion, 
but there is nothing to show that this is true. It is generally 
maintained that oxygen does not exist in the sun, but I have 
demonstrated that the spectrum of that body shows exceedingly 
fine lines, which correspond with those of the bright spectrum 
of oxygen, “American Journal of Science and Arts,” Oct. 1878, 
and June, 1879 (443). Granting that oxygen does exist in the 
solar envelope, it has nothing to do with its heat, since at the 
temperature which prevails compounds cannot form. The ele- 
ments all exist in their elementary state; and if compounds 
could be formed in one locality they would instantly be disso- 
ciated by the surrounding intense heat. 
Helmholtz maintains that the smallness of the sun’s density, 
only one-quarter that of the earth, suffices to explain the origin 
of the high temperature. Assuming that slow contraction is 
going on, he estimates that a shrinkage equivalent to i owoth of THEORIES AND EFFECTS OF HEAT. 
553 
the sun’s diameter would evolve as much heat as has been 
emitted from that luminary during 2100 years (444). 
The second is the internal heat of the earth. Shafts which 
have been sunk in the earth’s crust show a uniform elevation of 
temperature with increase of depth. The rate varies in different 
parts, but may be stated as 1° F. for every 50 to 100 feet. At 
a depth of 30 feet all evidence of seasonal change is lost, and a 
regular increase of temperature is established. At this rate, it 
is estimated that within a distance of 50 miles from the surface 
everything, even the most refractory, is in a molten state. Geolo- 
gical considerations also tend to show that a section of the earth 
would be represented by an external solid zone 30 to 50 miles 
thick, then one of liquid matter of unknown depth, then a core 
or nucleus of solid matter. As we descend, the melting point 
would under the enormous pressure become so high, that it 
could not be maintained in that state. 
The third is chemical action of all kinds. Every process of 
oxidation, whether a rapid combustion or a slow rusting, every 
act of fermentation, putrefaction, or decomposition, evolves more 
or less of this form of energy. 
The fourth is mechanical action, as friction of all kinds. By 
blows or percussion a blacksmith may make a small portion of 
iron red-hot. A bullet discharged against an iron target melts 
by the sudden arrest of its movement. Indeed, heat is the final 
form of energy to which all other forms tend, and in which they 
will all be finally dissipated. 
Fifth, electric action, as when a current of voltaic electricity 
is forced to pass along a narrow conductor; a principle which 
has recently been utilized in the incandescent carbon or plati- 
num light of Edison. 
655. Effect of Heat on Physical Properties.—The form of a sub- 
stance is absolutely dependent on its temperature. Water, for 
example, below 32° F., is a solid, between that and 212° F. a 
liquid, above 212° F. a vapor. In Fig. 287 we give some of its 
crystalline forms assumed as it passes into the solid state; the 
hexagonal predominates. All solids become liquids under a 
sufficient elevation of temperature. 
Color also is dependent on temperature. The iodide of starch, 
prepared by adding a little tincture of iodine to a solution of 
starch, is of a rich dark-blue hue, raise its temperature nearly 
to the boiling point, and it becomes colorless. Cool it, and the 
blue tint is restored. So also red iodide of mercury sublimes 
yellow; white oxide of zinc heated turns yellow, and a host of 
other bodies, if submitted to a change of temperature, show 
change in color. HEAT 
Size is controlled by temperature. If we take a copper 
sphere and fit it accurately to a ring so that it just passes 
through when cold, and then raise its temperature, it fails to 
Fig. 287. 
Ice flowers. 
pass. It has swollen or undergone expansion by the action of 
heat. Cool it, and it passes. Fig. 1. 
From this experiment we perceive that heat expands a body, 
and loss of heat, diminution of temperature, or cold, causes it to 
contract. Its size is absolutely dependent upon its temperature. 
656. Effect on Composition.—lf oxide of mercury be placed in 
a test-tube and submitted to a sufficiently high temperature it THEORIES AND EFFECTS OF HEAT. 
555 
undergoes decomposition, oxygen being set free, and mercury 
subliming in minute globules on the walls of the tube. This 
separation of a compound into its elements by action of heat is 
called dissociation. 
While a few inorganic bodies undergo dissociation below 
1000° F., there is no organic substance which can resist that 
temperature. 
A portion of wood, starch, muscle, or other organic body, 
placed in a tube and heated, soon begins to undergo change, 
gases are discharged, and water is given off, various volatile 
fluids with either a pleasant or an unpleasant odor escape, and 
a residue of black carbon remains. Heated on platinum in the 
air, such bodies catch fire and burn, a charred mass of carbon 
remaining for a time, which by continued application of heat 
is finally oxidized, and a white ash obtained. Heat, therefore, 
is the test for differentiation between an inorganic and an organic 
body, especially when used in connection with air. The black 
residue of carbon which arises, and which is completely oxi- 
dized by prolonged application of a high temperature, proving 
the substance to be organic. 
In addition, heat determines whether the organic body is 
nitrogenized or not. If during the combustion the fumes do 
not have an odor resembling that of burning hair, the absence 
of nitrogen may be inferred. If, on the contrary, this odor 
is perceived nitrogen is present, and we are dealing with a 
nitrogenized substance. 
657. Expansion.—ln the experiment of the ball and ring (655) 
it was found that temperature governs the size of a solid; it 
remains to examine its effect on other forms of matter. 
Take a flask, A, Fig. 288, with a long neck, and place in it 
some colored alcohol, or any other fluid, mark on the neck its 
position, and then apply heat to the bulb. As 
the temperature augments the liquid rises in the 
neck, showing that it has undergone expansion. 
We also find that this is far greater than with 
the solid, when we were obliged to resort to the 
use of delicate means of measurement to de- 
monstrate that there was an increase. Now 
remove the flame, contraction begins and, with 
return of the original temperature, the normal 
size is gained. 
Oases also follow this law, as illustrated by 
placing a flask, B, with the mouth of its neck 
under water, and adjusting, so that the level of 
Fig. 288. 
Expansion of liquid 
and gas. 
the fluid is half-way up the stem, and the rest filled with air. 
Apply a flame to the bulb, the merest touch suffices to cause an 556 
HEAT 
instant expansion of the included air, and if we are not careful 
some of it will escape from the vessel. With return to its former 
temperature the original size is gained. 
All forms of matter, therefore, solid, liquid, and gas, are ex- 
panded by increase of temperature, and contract when it de- 
creases. For the three forms we also learn that for solids the 
expansion is small, for liquids greater, and for gases the greatest 
of all. 
658. Expansion among Solids.—Take a thin strip of iron, A, 
and a similar one of brass, B, about three feet in length, and 
half an inch broad. Rivet them firmly together, so that at 
ordinary temperatures the compound bar is straight. Fix one 
Fig. 289. 
Expansion compound bar. 
end of this in a vice, and allow the other to play over a scale. 
If heat is then applied to its under side, the free end at once 
begins to traverse the scale. Remove the heat and it moves in 
the opposite direction. 
From this we perceive that there has been a difference in the 
rate of expansion in the metals by the application of heat, as 
shown by the curvature produced in the apparatus. The metal 
which expands the most is that on the outside of the curve. In 
this experiment it is the brass. When the original temperature 
is gained the bar is again straight, but as we pass beyond that 
to a lower, curvature in the opposite direction takes place, the 
metal contracting, the most being on the inside, and we again 
find it is the brass. 
Brass and iron, therefore, have very different rates of expan- 
sion for the same elevation of temperature, and it may be said 
that no two solids expand exactly the same for a given rise of 
temperature. 
Coefficients of linear expansion of solids between 0° and 100° C. 
Pine, 0.000003000 
Marble, 0.000008490 
Tin, 0.000021730 
Lead, 0.000028575 
Oast iron, 0.000011250 
Zinc, 0.000029417 
Sulphur, 0.000064130 
Copper and brass, 0 000017182 
Silver, 0.000019097 
Paraffine, 0.000278540 
The coefficient of linear expansion is the elongation of the 
unit of length when the temperature rises from 0° to 1° C. 
The coefficient of surface expansion multiplied by three gives 
that of cubical expansion. THEORIES AND EFFECTS OF HEAT. 
557 
Numerous instances of this are seen on all sides. Telegraph 
wires sway lower as the temperature rises. Steam pipes in 
houses must be arranged to allow play for their expansion, or 
they quickly get out of order and leak. In the Brooklyn bridge 
the vertical movement in the centre owing to variations in tem- 
perature amounts to several feet. 
Sometimes this expansion and contraction of rods of metal is 
employed to bring the walls of buildings out of plumb into a 
straight line. A series of rods are passed through the walls, 
each having a screw head at one end. Alternate ones are then 
heated by spirit flames, they expand, the screws are brought up 
tight, and they cool. Their contraction draws the walls up a 
little. The other set is then heated and the slack taken up; 
as they cool they bring the walls a little more together. This 
is continued until they are brought to the vertical and properly 
secured. 
Where a substance is a poor conductor, as glass, heat does 
not permeate quickly if it is thick. By the unequal expansion 
which follows, fracture takes place from the 
strain put upon the molecules. At the same 
time if it is very thin, as in flasks and retorts, 
and properly annealed, they will bear contact 
of the hottest Bunsen flames while filled with 
cold water. 
Fig. 290. 
659. Expansion among Liquids.—ln liquids 
great differences in expansion are found. 
To demonstrate this take two bulbs with 
long tubes as nearly alike as possible as re- 
gards diameter of bulb and calibre of tube. 
Fill one, A, with alcohol, and the other, W, 
with water to the same level, and immerse 
them in a vessel, Y, containing water at a 
temperature of 140° F. Expansion will im- 
mediately begin, but the former will rise 
more rapidly than the latter and attain a 
considerably higher level. As they cool the 
Difference in expansion of 
liquids. 
alcohol will contract more rapidly, until original temperature 
and size are gained, and they stand at the same level. 
Liquids, therefore, expand differently, their rates being as 
follows ; 
Coefficient of expansion of liquids between 1° and 100° C. 
Mercury . 
0.01543 
Nitric acid 
. 0.11 
Water 
0.0466 
Alcohol . 
. 0.116 
Sulphuric acid 
0.06 
Bisulphide of carbon 
. 0.125 
Ether 
0.06 
Chloroform 
. 0.157 558 
HEAT 
660. Maximum Density.—Water and certain other fluids do not 
expand uniformly, but as they approach their boiling and solidi- 
fying points begin to move in an irregular manner. Especially 
is this the case with water. If we begin to mark its manner of 
contraction at 60° F. or thereabouts, we find that as the tem- 
perature diminishes it contracts in a uniform and orderly manner 
for each degree of descent until it reaches 45°, then irregularities 
appear. When 4° Cent, or 39° F. is reached, contraction ceases, 
expansion sets in and continues to the freezing point. At 4° C. 
or 39° P. water is in its most compact or condensed condition, 
whether heated or cooled it expands. It is, therefore, said to 
be in the state of maximum density. 
Other fluids which have this property are cast-iron, and pre- 
eminently, type metal. It is this which enables the latter alloy 
to copy the fine lines of a mould so accurately. Sulphur also 
expands as its point of solidification is approached, and can, 
therefore, be used in the preparation of casts of medals. 
661. Expansion of Gases.—While the rates of expansion for 
solids and liquids show great variation among themselves, it 
is very different with gases. Here the great tenuity of the 
substances brings them nearer in relation to each other, and 
but slight variations are perceptible. Indeed, in an ordinary 
course of experimentation they are not visible, and require great 
care and exact means of measurement for their determination. 
We, therefore, say that for gases the rate of expansion is very 
nearly the same, being about -^T of their volume at 32° F. for 
every degree F. of temperature above that point. 
Coefficient of expansion of gases between 1° and 100° C., for a single degree. 
Air 
0.003667 
Nitrous oxide . 
. 0.003719 
Hydrogen . 
0.003661 
Cyanogen . 
. 0.003877 
Carbon dioxide 
0.003710 
Sulphurous acid 
.. 0.003903 
A practical application of the expansion of air is made in the 
Ericsson engine. In this arrangement a small quantity is forced 
into a fire, where it maintains the combustion. In its expanded 
condition, as product of oxidation, it is employed to work a 
piston in a cylinder and produce motion. 
662. Winds.—By the action of heat great waves of air, called 
winds, are initiated in the atmosphere. In their formation a 
portion of the earth is heated. The air expands and an upward 
movement is produced. Under these circumstances the sur- 
rounding air flows into the vacant space and a wind is estab- 
lished. It is clear that it takes its origin in, and blows toward 
the place where the upward current originated. It would, 
therefore, be proper in the case of a wind to speak of it in THEORIES AND EFFECTS OF HEAT 
559 
reference to the point to which it is tending, and not to that 
from which it is coming. 
Their character is best seen on ocean islands. During the 
day, from eight in the morning to three in the afternoon the 
land is warmer than the sea, and the wind sets from the latter, 
it then dies away, and at sunset springs up from the opposite 
direction, giving a sea breeze by day and a land breeze by night. 
In the Indian Ocean the monsoons, which are semi-annual 
alternations, are produced in a similar manner. The trade winds 
which blow continuously in the same direction on each side of 
the equator, result from the ascensional property and from the 
earth’s rotation. Detween them there is a zone 5° or 6° wide, 
where calms and variable winds prevail. 
While at the surface of the earth the wind is setting towards 
the equator, in the upper regions it is moving towards the poles. 
At the former, rotation of the earth causes the air to drag. In 
the latter, it is moving more rapidly than the earth as it tends 
towards polar regions. Thus easting and westing are given to 
what would be north and south currents if the earth was at rest. 
In the northern hemisphere the movement is towards the right 
of a person travelling with the wind; in the southern, towards 
the left. 
A west wind has an excess of centrifugal force which tends 
to carry it towards the equator. An east wind has a tendency 
towards the poles. In the northern hemisphere the deviation is 
to the right, in the southern to the left. If in the former, 
there is a sudden diminution of pressure over a considerable 
area, the surrounding air moves toward it. The converging 
streams before they meet are deviated to the right, and thus 
cause an eddy or cyclone. 
Instruments called anemometers are used for the measurement 
of the velocity of winds. They are four hollow half hemi- 
spheres set at the extremities of two diameters of a circle and 
mounted on an axis. The wind causes the apparatus to rotate, 
when its rate is measured by clockwork attached to the axis. 
In this instrument the centre of each cup moves with a rapidity 
one-third that of the wind. The velocity of the cup, therefore, 
being known, that of the wind is easily estimated. 
663. Effect on Measures of Time and Quantity.—The measure- 
ment of time is accomplished by the beat of a pendulum in a 
clock, or the oscillations of a balance wheel in a watch. For 
these to beat true time the length of the pendulum rod, or 
diameter of the balance wheel, must be invariable. With ordi- 
nary clocks and watches no care is taken, but in finer instru- 
ments it is accomplished by the following devices. 
Ist. The gridiron pendulum, Fig. 291, so called because it 560 
HEAT 
consists of nine parallel rods, which give it a fancied resem- 
blance to that domestic implement. Four of these are copper, C, 
Fig. 291. 
Fig. 292. 
Compensation strips. 
and five iron, F. They are ar- 
ranged to have the latter expand 
downwards from an upper fixed 
support, while the former expand 
upwards from a lower one. The 
centre of oscillation is thus kept 
at the same distance from that 
of suspension, and the pendulum 
beats uniformly. 
2d. Compensation strips, Fig. 
Fig. 293. 
Gridiron pendu- 
lum. 
292, consist of a compound bar of brass and 
iron, 1, fitted at right angles to the rod of the 
pendulum near the bob, and bearing small 
spheres at their extremities. The size of these 
and the length of rod are properly proportioned 
to that of the bob. The brass of the compen- 
sation bar being placed downwards, when the 
temperature rises the balls at its extremities are 
raised, as at 2, while the bob of the pendulum 
is lowered. On cooling, the reverse takes 
place, as at 3. The centre of oscillation is thus 
kept invariable and the pendulum beats true 
time. 
3d. Mercurial pendulum. In this the bob is 
a jar or jars of mercury, fitted in a stirrup at 
the end of the pendulum rod, Fig. 293. As 
the latter expands and tends to lower the centre 
of oscillation, the mercury by its expansion in 
the opposite direction raises it, and the balance 
is preserved. 
4th. Compound balance wheel. The circum- 
ference of the balance wheel of the watch is di- 
Mercurial pendulum. 
vided into two semi-circumferences, both compound bars. One 
end of each is fitted to a diameter of the wheel, the other is free. MEASUREMENT OF HEAT. 
561 
It bears a weight consisting of screws. As the temperature 
varies the position of the screw heads changes, making the centre 
of oscillation of the wheel invariable, and it beats true time. 
All measures of quantity are subject to variations in their 
dimensions as their temperature changes. To obviate this, that 
at which it is taken should always be given. English measures, 
particularly those of capacity, are generally graduated either at 
60° or 62° F., the average heat at which they are employed. 
The best method is to make the scale at this standard; it may 
be taken at any degree, and the proper correction for change 
in volume of the vessel and the fluid or gas made. 
CHAPTER XXX. 
MEASUREMENT OF HEAT. 
Sanctorio’s thermometer—Differential thermometer—Liquid thermometers—Cali- 
bering the tube—Preparing and filling—Graduation of the thermometer—The 
scale—Medical thermometers—Registering thermometer—Displacement of 
zero Absolute zero Remarkable temperatures Pyrometers Breguet’s 
thermometer—What thermometers measure. 
664. Sanetorio’s Thermometer.—Expand a bulb, A, on the end 
of a tube, place the latter with its mouth permanently under the 
7 JL «/ 
surface of colored liquid, B. Expand the air in the 
former by heat and expel a portion of it through 
the fluid. When the bulb cools the fluid will rise 
in the tube, and form an air or Sanctorio’s ther- 
mometer. The slightest breath of warm air causes 
the index liquid to move downward, the least appli- 
cation of cold produces action in the opposite direc- 
tion. It is a most delicate thermometer. The diffi- 
culty with it is, that it also indicates the slightest 
variation in pressure. 
Place the instrument under an air-pump bell and 
proceed to exhaust, the least action of the pump pro- 
duces movement in the liquid, and to a far greater 
extent than that caused by heat. 
The sudden elevation and depression of the ap- 
paratus will also cause considerable change in the 
■Fig, 294. 
Sanctorio’s 
thermometer. 
index fluid. In its original and simple form the air thermom- 
eter is not reliable as a heat measurer. 562 
HEAT , 
665. Differential Thermometer.—Take two bulbs, A B, and hav- 
ing introduced some liquid into one, cement them together and 
Tig. ‘295. 
bend the tube twice at right angles, 
to bring the bulbs opposite each 
other, Fig. 295. Now blacken B 
and we have a differential ther- 
mometer, or one which measures 
the differences in temperature be- 
tween its bulbs. The slightest breath 
of warm air on B causes the index 
fluid to pass away from it towards A. 
A little cold water applied to B pro- 
duces movement in the opposite di- 
rection. Place the instrument under 
an air-pump bell, and the liquid index 
is not affected by the most complete 
exhaustion. Though limited to de- 
termination of differences in the 
temperatures of its bulbs, it is most 
satisfactory and reliable when it can 
be employed. 
Differential thermometer. 
666. Liquid Thermometers.—Practically, these are confined to 
mercury and alcohol. The great advantage in the former is 
that it moves in a cleanly way in the tube, does not adhere to 
or soil it, and gives very accurate indications. Its high boiling 
point, and low temperature required for solidification (a range 
from about 660° F. to nearly —4o° F.), and its rapid movement, 
fit it admirably for this purpose. 
Where temperatures lower than —4o° F. are to be measured, 
colored alcohol is employed. This boils at about 176° F., and 
does not solidify until —22o° F. is reached; even at this point 
it can hardly be called solid. It soils or wets the wall of the 
tube; therefore, considerable time should be permitted for it to 
gain its true level when it has fallen, before an exact reading 
can be made. 
667. Calibering the Tube.—By this we understand that all parts 
of the tube are to be proved to have the same diameter. For 
an alcoholic thermometer the bore must be circular, for the 
mercurial it may be either circular or elliptical. The advan- 
tages of the latter are that a very small quantity of mercury may 
be made to give degrees of considerable size in a bore the diam- 
eter of which in one direction may be six to ten times that of 
the diameter at right angles to it. 
Having selected the tube, it is calibered by placing in it a 
column of mercury one inch in length, the measurement being 563 
MEASUREMENT OF HEAT. 
made by a pair of compasses. The column is then traversed to 
another position, and its length measured. In this way all parts 
are examined, and if the mercury is of the same dimensions 
throughout, the caliber is uniform, and it will answer. If, on 
the contrary, it varies ever so little, it is useless. 
668. Preparing and Filling.—The tube is drawn off in the blow- 
pipe flame, and the extremity closed. It is also elongated at 
the other end to a suitable length. The sealed portion is then 
heated in the blowpipe flame and air quickly forced in through 
the open end. After two or three trials a uniform bulb is ex- 
panded, and the apparatus being allowed to cool, is ready for 
the liquid. 
The bulb being gently warmed, to expand the air contained 
therein, the open end is quickly placed under the surface of 
fluid. As it cools the latter gradually rises, and a small quan- 
tity gains access to the bulb. This is heated until it boils, and 
the bulb and tube are filled with vapor. The mouth is then 
again immersed in the liquid, when as the vapor condenses the 
fluid rises, filling the tube and bulb. This process may be facili- 
tated by expanding a small funnel in the top of the former and 
filling it with clean dry mercury. It may then be kept in the 
vertical position throughout the operation. 
The extremity is now to be closed. To accomplish this the 
bulb is heated, the fluid expands and escapes from the open 
end; when the boiling point is nearly attained the lamp is 
removed, a blowpipe flame directed on the pointed end, and 
the, glass fused. Communication with the external air is thus 
destroyed. The instrument should then be put aside for some 
months before the scale is adapted, since a certain amount of 
shrinkage of the bulb is apt to occur. 
669. Graduation of the Thermometer.—There are two fixed 
points on all thermometric scales. The lower is the melting 
of ice, the upper the boiling of water. It will not answer to 
niake the former the freezing of water, for this is a variable 
point, and, therefore, unreliable. It is determined by tying a 
thread around the tube, and then placing the entire instrument 
in a tall jar filled with cracked ice and water; the thread is 
from time to time adjusted as the liquid falls, and when the final 
adjustment is attained, a delicate mark is made with a triangular 
file or diamond. The higher point is then fixed by placing 
another thread around the tube and immersing it in a flask half 
full of water, until it nearly touches the fluid. The mouth 
should be lightly closed with a plug of cotton. When the water 
is boiling strongly, and the flask filled with clear steam, the 
thread around the tube is adjusted, and a mark permanently 564 
HEAT 
made as the higher fixed point. The barometer should indicate 
760 millimeters. A difference of 27 millimeters in pressure 
would make a variation of one degree in graduation. 
670. The Scale.—Of these there are three, Fahrenheit, Centi- 
grade or Celsius, and Reaumur’s. Each possesses certain ad- 
vantages. In the first the degrees are small, there being 180 
between the two fixed points. The lower is 32°, and there is a 
considerable march beyond this before zero is reached, and the 
use of minus (—) quantities becomes necessary. The Celsius, 
on the contrary, has large degrees, nearly twice the size of the 
former, and fractions are often necessary in expressing ordinary 
temperatures. The use of the sign as soon as the freezing 
point is passed often leads to error by its omission. The division 
is more scientific, however, and of the centesimal character 
towards which all modern methods of measurement tend. Yet 
it does not appear to force its way with English-speaking people, 
and it will doubtless be some time before our thermometric 
readings are given in this scale. The third, or Reaumur’s, has 
80 degrees between the two fixed points. It presents all the 
disadvantages of the Centigrade, and none of its advantages. 
In adapting the scale to the thermometer, if the Fahrenheit is 
used, the space between the two fixed points is divided into 180°. 
To the lower the value 32° is given, to the upper 212°, and the 
graduation is extended above and below. In the Centigrade, 0° 
is given to the lower, and 100° to the upper; in the Reaumur, 0° 
to the lower, and 80° to the upper. 
The best plan is to mark the scale directly on the tube, either 
with a diamond or by etching with hydrofluoric acid. Other 
methods are, however, employed, ivory, bone, paper, metal, all 
bear the graduation in common instruments, and answer very 
well. 
For conversion of Fahrenheit into Centigrade the formula 
is: F. = 32° F. For the opposite, C. = ~ •32 xs^ 
A simple and rapid formula for conversion of C. into F. is : 
Double the degree Centigrade given, subtract of the 
product, and add 32°. 
In alcoholic thermometers the lower fixed point is deter- 
mined as stated. The upper, by comparison with a good mer- 
curial thermometer. 
671. Medical Thermometers.—The recent demands of medicine 
have caused the construction of thermometers in which fractions 
of a degree can be easily indicated in the vicinity of 94° F., and 
the column of mercury held at the 'point to which it has risen. 
In these the bulb is made cylindrical, A, and the lower part of MEASUREMENT OF HEAT. 
565 
the tube contracted, B. The movement of the fluid past this 
when expanding is not interfered with, but when contraction 
begins, the column breaks, and the thermometer in- 
dicates the highest temperature it has reached. When 
the instrument is used again the broken column is 
united by a slinging motion of the hand, bringing 
centrifugal force into play. The movement is re- 
peated two or three times, until the purpose is attained. 
For accuracy, such thermometers should be retained 
in their position for three to five minutes, to allow 
the mercury time to gain its true place. 
These, and others which accompany urinometers, 
are often graduated only to 120°, or thereabouts. 
Care must be taken not to immerse them in liquids 
of a higher temperature, or they will be destroyed. 
Fig. 296. 
672. Registering Thermometers.—These are used for 
meteorological purposes. They are known as maxi- 
mum and minimum thermometers. They consist of 
two, a mercurial for high, and an alcoholic for low 
temperatures. The column of mercury in the first 
may be broken by the preceding device of a capillary 
tube, as in the bTegretti, or it may push a delicate 
Medical 
thermometer. 
, 7 O 7 
index before it which it leaves at the highest it reaches, thus 
registering the upper temperature. The alcoholic instrument 
carries an index in the fluid. When expansion takes place the 
latter passes the former, but in the opposite movement the for- 
mer is drawn by the latter and remains where it is carried, the 
fluid passing it when it again expands, thus the low temperature 
is marked. The index usually contains a piece of iron wire, 
and can be adjusted by a small magnet accompanying the in- 
strument. 
673. Displacement of the Zero.—Thermometers used for a long 
time often show a change in position of the zero. In describing 
their construction, it was stated, that as perfect a vacuum as 
possible is made over the fluid to prevent introduction of dust, 
loss by evaporation, and to allow the column to be broken when 
desired. It, therefore, follows that they must bear the full 
pressure of air, viz., 15 pounds on every square inch. Under 
this the delicate film of glass forming the bulb yields, and after 
a time a change of two or more degrees will be found in the 
position of zero. Allowance must be made for this in all 
readings. , 
673 A. Absolute Zero.—Air expands of its volume for every 
degree F. we give it above 43° F., or for every degree C. 566 
HEAT 
above 0° C. It, therefore, follows that the lowest temperature 
we could express by an air thermometer would be —459° F. or 
—273° C. These values are called the absolute zeros, and tem- 
peratures estimated from them are called absolute. 
674. Remarkable Temperatures.—The following are taken from 
Ganot’s “Physics.” They are in Centigrade values. 
Centigrade. 
Greatest artificial cold produced by a bath of bisulphide 
of 
carbon and liquid nitrous acid .... 
—140° 
Greatest cold produced by ether and liquid carbonic acid 
—110° 
Greatest natural cold recorded in Arctic expeditions 
—58.7° 
Mercury freezes ........ 
—39.4° 
Mixture of snow and salt ...... 
—20° 
Ice melts ......... 
0° 
Greatest density of water ...... 
+4° 
Mean temperature of London ..... 
9.9° 
Blood heat ......... 
36.6° 
Water boils 
100° 
Mercury boils ........ 
350° 
Sulphur boils ........ 
440° 
Bed heat (just visible) (Daniell) .... 
526° 
Silver melts “ 
1000° 
Zinc boils “..... 
1040° 
Cast-iron melts. “ 
1530° 
Highest heat of wind furnace (Daniell) 
1800° 
675. Pyrometers,—The first of these was the invention of 
Wedge wood, the porcelain manufacturer. It consisted of two 
inclined bars fitted firmly into a base, nearer together below 
than above. One of these bore a scale. Portions of porcelain 
clay were moulded, dried, and fitted to the upper or widest 
division. It was then submitted to heat, and when cool, again 
placed in the apparatus, when the shrinkage showed the tem- 
perature to which it had been subjected ; thus the melting point 
of various metals was determined. It was, however, found 
that clay acts peculiarly under the influence of heat, a low 
degree applied for a long time producing as much shrinkage as 
a high temperature applied for a brief period; time is, there- 
fore, an important element, and not to be overlooked, otherwise 
grave errors will arise. 
Another form consists of a rod of brass or steel, its expansion 
being measured by means of multiplying machinery consisting 
of levers or cogs and wheels. All these are of little or no value 
on account of their irregular movements. 
676. Bregnet’s Thermometer is, in fact, a compound bar consist- 
ing of a slim strip of platinum soldered to one of silver, and 
rolled down to the hundredth of an inch in thickness. From 
this, slips about Ath of an inch wide are cut, their length being 
10 or 20 inches. One is wound into a spiral, AB, which is fixed SPECIFIC HEAT AND HEAT OF FORM. 
567 
at one end, A, and free to move at the other. The latter bears 
an index, B, which traverses a graduated circle bearino- decrees 
cn mi mn 4- /~v /-s, 1 
similar to and of equal value with the 
Centigrade scale. This form is exceed- 
ingly delicate. The gentlest breath on 
the spiral suffices at once to carry the in- 
dex to the temperature of the expired air. 
It loses its heat as quickly, and returns 
to the original degree. It is curious that 
the Breguet has not been adopted in 
medical practice, when it is so admirably 
fitted to yield the indications sought by 
the physician. 
Fig, 297. 
677. What Thermometers Measure.—If 
we take a series of vessels of increasing 
size and fill them with water from the 
same source, and then place a thermome- 
ter in each in succession, it marks the same degree. Yet we 
know that the largest vessel contains as much more heat than 
the smallest, as its size is greater. From this we perceive that 
the thermometer does not measure the quantity of heat in a given 
mass. It merely indicates the temperature intensity or the degree of 
heat. The quantity is to be determined in other ways. 
Breguet’s thermometer. 
CHAPTER XXXI. 
SPECIFIC HEAT AND HEAT OF FORM. 
Heat required to warm a substance—The calorimeter—Determination of specific 
heat—Calorie and thermal unit—Fusion and solidification—Variation in 
fusion and solidification—Change of volume in fusing—Annealing—Latent 
heat—Latent heat and climate—Freezing mixtures—Crystallization. 
678. Heat Required to Warm a Substance.—lf we take equal 
volumes of mercury and water and place them in front of a fire, 
the temperature of the former rises much more rapidly than that 
of the latter. If we use the same weights of the two substances 
the difference is far more striking. From this we learn that 
different bodies require different quantities of heat to warm them equally. 
In solids the same thing is evident. Take bullets of zinc and 
lead, and warm them equally by exposure to boiling water, 568 
HEAT 
giving them time to take up all the heat they will. Then drop 
them on a slab of wax, about half an inch thick. The zinc melts 
its way through very quickly. The lead follows at a considerable 
interval. The heat held by the former was greater than that of 
the latter. 
To this the name of specific heat, or capacity for heat, is given. 
By it we mean the amount of heat required to raise the temperature of 
a substance one degree compared with that required to raise the tem- 
perature of the same weight of water one degree. 
If, therefore, it is stated that the specific heat of lead is 0.0314° 
C., it means that the quantity which would raise the temperature 
of a given weight of lea.d one degree C., would only raise that 
of the same weight of water 0.0314° C. In all instances the 
comparison is with water. 
By the sudden compression of a gas the specific heat or caloric 
diffused throughout, say 100 cubic inches, may suddenly be 
forced into one cubic inch. The temperature will, therefore, be 
increased one hundred-fold, for a mere instant of time. An 
illustration is offered by the fire-syringe, in which the piston is 
armed with black tinder; the lower part of the cylinder is closed. 
The latter being filled with air, the former is introduced and 
suddenly driven to the bottom, the heat developed by compres- 
sion of the air is so great that the tinder catches fire, and a flash 
of light is seen. Here we have a beautiful illustration of the 
conversion of work into heat. The force applied to the piston 
is not lost, but converted into heat. If we instantly release the 
compression before this has had time to be conducted away, it 
disappears in the expansion of the gas to reach its original vol- 
ume. It is reconverted into work represented by the restoration 
of the piston to its original position. 
Three methods are used for the determination of specific 
heats : Ist, by the calorimeter or melting of ice; 2d, by mixtures; 
3d, by cooling. 
679. The Calorimeter, in its simplest form, consists of a block 
of ice with a cavity hollowed out in the interior, the mouth of 
Fig. 298. 
which is closed by a slab of the same ma- 
terial accurately fitted, The object of the 
experiment, a liquid, is placed in a thin 
flask, its weight accurately determined, 
and its temperature carefully noted. The 
cavity is then emptied of any water it may 
contain, the flask placed therein, and the 
mouth instantly closed. The temperature 
of the flask and contents at once begins to 
fall, and in so doing melts the ice. When 
Ice calorimeter. 
the process is completed the flask is removed from the cavity, 
the water produced by melting is carefully measured or weighed; SPECIFIC HEAT AND HEAT OF FORM. 
569 
this indicates the amount of heat contained in the substance 
under examination. By a simple calculation the quantity for 
each degree, F. or C., is estimated. 
If great accuracy is required, a correction must be made for 
the glass of the tlask by repeating the operation with it alone. 
It is also better to use a sponge to remove the fluid from the 
cavity, weighing it before and after the operation, the difference 
in weight represents the quantity of water. 
The difficulty in obtaining blocks of ice of sufficient size and 
compactness, led to the introduction of the calorimeter of La- 
voisier, in which ice is placed in a vessel surrounded by a jacket 
also filled with ice. The exterior layer in the jacket protected 
the interior from the action of air. The water resulting from 
the experiment is drawn off by faucets. 
680. Determination of Specific Heat.—A given weight of water 
is first placed in a flask in the calorimeter, its temperature 
taken, and the amount of fluid it produces by melting carefully 
determined. The quantity for each degree is calculated. An 
equal weight of the substance to be examined is then placed in 
the flask, its temperature taken, and the quantity of liquid it 
can form determined, and that for each degree estimated. This 
is compared with the result obtained in the first experiment, 
when a simple calculation gives the specific heat of the second 
body, water being 1. 
In the method by mixtures, the temperature of a given weight 
of the body is raised to a certain point, it is then immersed in 
a mass of water of known weight and degree. From the tem- 
perature of the water after mixture, the specific heat of the body 
is calculated. 
The method by cooling consists in the determination of the 
relative times required by given weights of different bodies to 
cool through a certain number of degrees. 
A knowledge of specific heat is of considerable importance 
in the determination of the atomic weights of elementary bodies. 
681. Calorie and Thermal Unit, etc.—A calorie is the quantity 
of heat required to raise one kilogramme of water through one degree 
Centigrade. A thermal unit is the quantity of heat required to raise 
one found of water through one degree Centigrade. 
One calorie = 2.2 thermal units. One thermal unit = 0.45 calorie. 
The other heat units employed are the gramme-degree, or the 
quantity of caloric required to raise one gramme of water one degree C. 
The pound-degree, the caloric required to raise one pound avoirdupois 
of water one degree F. or C. 
The foot-degree, the caloric required to raise one cubic foot of water 
one degree F. or C. 570 
HEAT 
682. Fusion and Solidification.—The first effect of heat on a 
solid is to cause expansion, this continues for a certain time, 
when the body liquefies; to this the name of fusion is given. 
The laws are as follows. 
Ist Law. A given solid begins to melt with few exceptions, 
easily explained, at a fixed temperature. This is called its 
point of fusion. It is a specific character of the substance. 
The range for solids is very great, as shown in the following 
table; 
Centigrade. 
Centigrade 
Carbonic acid . 
. —78° 
Tin 
. 228° 
Mercury . 
. —40° 
Lead 
. 332° 
Ice 
0° 
Silver . 
. 1000° 
Phosphorus 
. 44.2° 
Gold . 
. 1200° 
Wax . 
64° 
Iron 
. 1500° 
Sulphur 
. 115° 
Platinum 
. 2000° 
2d Law. During fusion the temperature of a body remains 
fixed, that of the fluid rises in spite of the most active stirring. 
Solidification, When a liquid is cooled it contracts and 
finally assumes the solid state, under the law that a liquid begins 
to solidify at the same degree at which the solid begins to melt. 
In other words, the solidification and the fusion point are, as a 
rule, the same. 
683. Variation in Fusion and Solidification Points.—lf water is 
kept perfectly still the temperature may be carried considerably 
below 32° F. without the assumption of the solid state, and it 
may be lowered to 0° F. If it is then touched, or the slightest 
agitation communicated to it, a portion instantly solidifies and 
the temperature rises to 32° F. Though it may be cooled below 
32° F. without freezing, by no device can ice be warmed above 
that degree without melting. Melting of ice is, therefore, taken 
as the lower fixed point on the thermometric scale. 
Under great pressures water retains its fluidity below 32° F. 
Broken ice may be compressed into lenticular, cylindrical, and 
other forms. This is what is known as regelation, a term intro- 
duced by Tyndall in explanation of the plastic nature of ice in 
glaciers. 
684. Change of Volume in Fusing.—When a substance enters 
into fusion there is generally a rapid expansion. In a few in- 
stances, however, the reverse happens. Of all bodies the most 
notable exception is water; in the act of fusion it shrinks greatly, 
losing no less than one-ninth of its volume. 
In solidification the reverse occurs, passing into the state of 
ice it expands. The increase in bulk is about one-ninth, hence 
it is that ice floats, and forms on the surface. SPECIFIC HEAT AND HEAT OF FORM. 
571 
This fact exerts a most important influence on climate. By 
virtue of it ice forms on the surface of ponds, rivers, lakes, and 
by its con-conducting power cuts off further loss of heat from 
the water beneath. In the spring it is most favorably exposed 
to the action of the sun’s rays, and in the best position for beiim 
melted. We can hardly realize the difficulties that would arige 
were it not for its maximum density, and its sudden expansion 
as water assumes the solid state, Rivers and all collections 
would congeal from below. They would solidify throughout, 
and a long period of time would be consumed in the spring in 
melting the gigantic accumulations of winter ice. 
685. Annealing.—ln passing to a solid from a liquid state the 
molecules of bodies must have time to adjust themselves to the 
new conditions presented. Especially is this the case with most 
metals, and with glass. The process of annealing consists in a 
gradual depression of temperature, and the allowance of a suffi- 
cient time for this adjustment to take place at least in a partial 
manner. Glass which has been suddenly chilled is exceedingly 
prone to fly in pieces if touched by a point or scratched; of this 
the Prince Rupert drops are an example. The larger the mass 
the greater the difficulty in annealing it. The iron cylinders 
of great marine engines require weeks for the accomplishment 
of this process. In glass works it is an essential part of the 
manufacture, and the value of an article and its power to with- 
stand rough usage depend entirely on the care with which it 
has been annealed. By recent devices, the so-called malleable 
glass, which will bear the roughest usage, is prepared. Pieces of 
it may be thrown violently on the floor without undergoing 
fracture. 
686. Latent Heat.—lf a pound of water at 80° C. be mingled 
with a pound at 0° C., the temperature of the mixture will be 
40°, or the average of the two. If in place of the latter a pound 
of ice is used, it will be 0° C. We, therefore, perceive that 
the sensible heat of the wafer has been lost in melting the 
ice; in other words, it has become latent or hidden. Lalent heat, 
therefore, is that heat which disappears when a substance changes its 
form. It is the heat of form. 
To determine exactly how much heat is lost, take a mass of 
ice at 32° F., and arrange to have it warmed at the rate of 
one degree P. per minute. At the end of ten minutes it has 
risen 10°, and it steadily rises until 32° F. is reached. Here 
it stops and begins to melt. This continues for 140 minutes, at 
the end of which the march of temperature recommences. 
During this 140 minutes the ice received one degree of heat per 572 
HEAT 
minute, which was rendered latent, and consumed in changing- 
water from solid to liquid. It is evident that this 140° F. repre- 
sents the caloric of fluidity or the latent heat of the liquid. 
Again continue the application of heat, and the rise of tem- 
perature continues steadily at the rate of one degree per minute 
until 212° F. is reached, it then stops, and the'water begins to 
boil. Place a thermometer in the boiling liquid, it registers 
212° F.; place it in the steam rising therefrom, again it marks 
212° F.; both have the same temperature. At the close of 1000 
minutes the water has disappeared as steam, and has carried off 
1000° F. of heat in the latent form; we say, therefore, that 
the latent heat of steam is 1000° F. 
687. Latent Heat and Climate.—The loss of latent heat before 
it can assume the solid state, has its influence in moderating 
the climate of regions in the vicinity of collections of water. 
The 140° F. of caloric which it must surrender suffice for a long 
time to resist reduction of temperature, and in the vicinity of 
great water surfaces sudden changes are the exception and not 
the rule. The variations by which the thermometer indicates a 
cold of —4o° F,, or a summer heat of over 100° F., belong to 
regions at a distance from the shore. 
Between Hew York and the immediate coast a difference of 
five and often ten degrees is experienced in very cold weather. 
This is owing to the fact that, while land easily reaches a tem- 
perature below freezing, water, when 82° F. is reached, surren- 
ders its caloric of fluidity, and resists the tendency to a further 
depression. 
Elevation of temperature is, in like manner, retarded, for ice 
must have its caloric of fluidity before it can assume the liquid 
form. By its demand for latent heat water tends to regulate 
temperature, resisting sudden movements in either direction 
above or below the freezing point. 
688. Freezing Mixtures are forced fusions in which one sub- 
stance is compelled to melt by the action of some other, as salt 
and ice. Salt attracts water and forces it to assume the liquid 
state. To accomplish this the ice must have its caloric of fluidity, 
and it takes it from any substance in its vicinity, reducing the 
temperature nearly to 0° F, Here, however, action ceases, and 
the water rejecting the salt with which it had combined reas- 
sumes the solid state if subjected to a further diminution of 
temperature. 
689. Crystallization.—Where bodies pass slowly from the liquid 
to the solid state they tend to assume special geometrical forms, VAPORIZATION. 
573 
€. g., cube, prism, etc. These are called crystals. The process 
may take place either from a fused condition of the substance 
or by evaporation of a solution in water. In the former it is 
said to be by the dry way, in the latter by the moist way. 
CHAPTER XXXII. 
VAPORIZATION. 
Temperature of formation—Properties of vapors—Causes influencing vaporiza- 
tion—Evaporation in vacuo—Vaporization a cooling process—lce machines— 
Effect of vapors on climate—Vapors and furnace heat—Elastic force of vapors 
—High-pressure engines. 
690. Temperature of Formation.—Though water vaporizes most 
rapidly at its boiling point, the process goes on at temperatures 
far below this. Films of ice, for example, which have formed 
on a window during a cold night slowly evaporate during the 
day, without assuming the liquid state, if rays of the sun fall 
upon them. Water, in the solid state, therefore, gives off 
vapor—indeed, vaporization may be said to take place at all 
temperatures. . 
Faraday attempted to determine, in the case of mercury, 
whether there was a lower limit to the process. To this end he 
enclosed a portion in a vessel, and suspended a piece of gold leaf 
over it. He concluded that vaporization ceased when a tem- 
perature of —lo° C. was reached. 
Many solids—for example, iodine and camphor—vaporize 
rapidly without assuming the liquid state. On the other hand, 
no substance fails to vaporize if its temperature is raised suffi- 
ciently. Gold, platinum, and the most refractory metals under 
the influence of a voltaic arc of sufficient intensity may be dissi- 
pated in vapor. 
In certain cases—as with camphor—light seems to influence 
the process, A bottle of camphor placed on a shelf, and left 
undisturbed for a few months, shows a copious deposit of crys- 
tals on the part turned away from the light, while not one is 
found on the side towards it. 574 
HEAT 
691. Properties of Vapors.—Fill a matrass, which is a long- 
necked flask, with water to within half an inch of its mouth. 
Fig. 299. 
On this pour ether, close the opening with 
the finger, and immerse it mouth down 
in water, B; remove the finger, and the 
water remains suspended in the flask. At 
the same time the ether rises, and takes its 
place in the globe of the flask, A. 
Let heat be applied to A; after a time 
the ether changes its form and assumes 
the vaporous state. The matrass may be 
filled with it, and yet but a small part of 
the fluid disappears. Pour cold water on 
the globe, and the ether reassumes its 
normal condition. 
Prom this experiment we learn; Ist. 
That vapors occupy a much greater space 
than the liquids which produce them. 2d, 
They are not foggy but perfectly transparent, 
though, as with iodine and bromine, they may he 
colored. 3d. They are easily condensed into fluid. 
Properties of vapors. 
A vapor, moreover, differs from a gas only in its relative con- 
densability. It may be defined as a gas condensing easily under 
increase of pressure, or reduction of temperature, while a gas requires 
great pressure and intense cold to produce its condensation. 
692. Causes Influencing Vaporization.—Bate of vaporization 
depends, Ist, on temperature, either as regards its degree or ex- 
tent of surface exposed. A free supply yielding heat to be 
rapidly made latent will increase the rate. Increased extent of 
surface, by bringing the fluid in better contact with heat, will 
produce the same result. Therefore, the use of tubular boilers 
for locomotives and other kinds of apparatus in which steam is 
to be generated rapidly. 
2d. Increased surface favors vaporization. Hence, the form 
given to the so-called evaporating dishes, A, Fig. 300. A 
given quantity of water placed in a flask and in an evaporating 
dish, and equal sources of heat applied, that in the latter will 
disappear as vapor, while the former will have lost only a small 
portion. When we wish long digestion with heat, the latter is 
the proper form of apparatus to employ. When to get rid of 
fluid, the evaporating dish. 
3d. Removal of the damp atmosphere from the surface of a 
liquid hastens evaporation. Of this we may satisfy ourselves 
by blowing on a fluid in an evaporating dish, when the process 
will be greatly accelerated, and the temperature lowered several 
degrees. VAPORIZATION. 
575 
4th. Dryness of the air also favors vaporization. It is in vain 
that we attempt to dry clothing when the air is saturated with 
moisture. In the laboratory, the hot-air oven, by raising the 
temperature while the dew point remains the same, offers a 
practical example of the application of this principle. 
sth, Pressure exerts a notable effect on evaporation. Take 
the apparatus (691), place it under a tall air-pump bell, and pro- 
ceed to exhaust. After a few moments, when about half the 
air is removed, the ether fairly flashes into vapor. Restore the 
pressure, and as quickly it reverts to the liquid state. 
693. Evaporation in Vacuo.—Advantage is taken of the last 
property of vapors in a variety of manufacturing and chemical 
operations. When, for example, a suffi- 
cient elevation of temperature to secure a 
rapid vaporization would be attended by 
an alteration in the properties of the sub- 
stances experimented upon, the process is 
conducted in vacuo—that is, in a space, C, 
connected with an air-pump by which a 
vacuum may be maintained through D. 
An application of this principle is seen in 
sugar boiling. 
At the same time, if desired, dishes, B, 
containing strong sulphuric acid can be 
Fig. 300. 
Evaporation in vacuo. 
placed in a vacuum vessel, C. This favors vaporization, remov- 
ing moisture from the space at a very rapid rate and at ordinary 
temperatures. 
694. Vaporization a Cooling Process.—lf ether is poured on the 
bulb of a Sanctorio thermometer, it vaporizes and causes a 
rapid contraction of the air in the instrument. Anything which 
tavors evaporation increases production of cold and elevation 
of the index liquid. The cause of this is found in the fact, 
that for ether to assume the vaporous state it must have its 
caloric of vapor from the substance whereon it rests, or with 
which it is in contact. In this ease, it takes it from the bulb of 
the thermometer. 
Any liquid, as ether, alcohol, water, which can vaporize, if 
poured on the hand produces a cooling sensation. The more 
volatile the fluid the greater the effect. In the articles men- 
tioned, it is in the order given. If at the same time the surface 
is fanned, the action is increased. If water is placed in a bulb, 
and surrounded with cotton soaked in ether, and the apparatus 
whirled in the air, the cold will be sufficiently intense to cause 
it to freeze. Water placed in a watch-glass which rests in 
another containing ether, will, if placed on an air-pump plate HEAT 
and submitted to a vacuum, be quickly frozen by evaporation of 
the ether in the outer crystal. 
Ordinary fanning cools the surface of a body. The removal 
of the vapor favors vaporization, and in forming it afresh the 
surface is cooled by the abstraction of warmth to give this its 
latent heat. 
The cooling effect of vaporization is applied in surgery for 
production of local anaesthesia. A fine spray of ether is directed 
upon the surface by means of an atomizer. By its rapid evapora- 
tion heat is abstracted from the part and intense cold produced, 
attended by loss of sensibility, and the knife can be used with- 
out causing pain. A similar arrangement is utilized for freezing 
soft tissues in making microscope sections. 
695. Ice Machines.—These depend upon the property in ques- 
tion, Some highly vaporizable liquid, as ether or ammonia, is 
caused to volatilize by diminution of pressure, accomplished 
by a pump. An intensely cold fluid is produced, which is used 
by some suitable device to abstract caloric from the water to be 
frozen. The portions vaporized, are by the same machine re- 
condensed, and forced to reassume the liquid state, a large quan- 
tity of water at ordinary temperature being employed to carry 
oft the latent heat, which becomes sensible heat when they pass 
from the gaseous to a liquid state. Being thus regained, they 
are employed to freeze more water, and thus the same quantity 
is made to produce an indefinite amount of ice. 
In regions where ice is rare these machines are worked with 
considerable pecuniary profit. The loss of weight by long lines 
of transport, the high temperature and consequent shrinkage 
by melting, meeting the increased expenditure of coal required 
to work the apparatus. 
In some hot countries water is cooled by means of alcarrazas, 
or vessels of porous earthenware. When liquid is placed in 
one of these a portion permeates the walls. If it is then set 
in a current of air the evaporation of this exterior film, by its 
avidity for the latent heat necessary to form a vapor, cools the 
contents of the alcarraza. Thus a very agreeable drink is ob- 
tained at an exceedingly moderate expense. 
696. Effect of Vapors on Climate.—lf the temperature is taken 
on the Atlantic coast of Europe, and compared with that of 
the same parallel on the American side, it will be found that 
the average annual temperature is about 10° F. higher in the 
former case. The cause of this is chiefly the condensation of 
vapor in the formation of rain. The Gulf stream made up of 
warm water from the West Indies, passes across the Atlantic, 
and bathes the whole of the northern coast of Europe with a sea VAPORIZATION. 
577 
from which vapor is continually arising. This, taken up by the 
prevailing winds, is carried far into the interior of Europe, and 
coming in contact with the cold of those regions is condensed. 
In condensing, it surrenders its 1000° E. of caloric which gives 
it the vaporous form, and to this heat the moderation of climate 
is due. As the wind passes on, the vapor it contains is dimin- 
ished. Less and less rain falls, and less latent heat is made 
sensible. The air is drier, and with lack of moisture its moder- 
ating effect is lost, until finally a region is reached where the 
greatest extremes of cold are found. 
The effects of the cold, intensely dry air, on the systems of 
the inhabitants of these sections, and of our own western 
country where similar conditions exist, are well worthy of con- 
sideration. The air is not only cold, but almost entirely robbed 
of moisture. This passing into the lungs has a profound desic- 
cating action, which must seriously interfere with their func- 
tions and produce inflammatory conditions. 
697. Vapor and Furnace Heat.—American houses are generally 
heated by a furnace, which takes air into a chamber, warms it, 
and delivers it into the several rooms. In winter this air often 
has a temperature below the freezing point of water; it, therefore, 
contains but little moisture. In the furnace chamber it is heated 
to 72° F. or thereabouts. Here, therefore, there is a difference 
of 40° F. between the temperature and the dew-point of air, 
or that at.which it is saturated with moisture. 
Such air possesses intense desiccating power over all organic 
substances. Furniture is torn to pieces unless made of carefully 
prepared wood. Our systems are also profoundly affected unless 
something is done to give to the air the moisture for which it is 
so greedy. Generally this is accomplished by placing a large 
pan of water in the chamber of the furnace, which by its area 
may supply a portion of that required. In addition to this, ves- 
sels of water should be placed opposite the registers of rooms 
through which heated air is delivered. It is wonderful to note 
how much liquid will be evaporated in twenty-four hours. A 
gallon or more easily disappears. 
In the treatment of inflammations of the mucous membranes 
of the air passages, sufficient attention is not paid to this desic- 
cating action of furnace air. It may be modified by placing a 
dish of water opposite the furnace flue, and allowing towels to 
dip into it, which, taking it up by capillary action, present it to 
the incoming rush of hot air, thus furnishing a portion of the 
moisture it needs. At the same time, care should be taken that 
the pan in the furnace chamber is large, occupying the whole 
floor, and kept properly tilled. 578 
HEAT 
Proper attention to these conditions will do more to alleviate 
and cure a patient than all the medicine administered. 
698. Elastic Force of Vapors.—Prepare a barometer by filling 
with mercury a tube over thirty inches in length, A, closed at 
one end. Carefully remove all air, and place it 
mouth down in a cistern of mercury, B. Let it 
stand in the vertical position, remove the finger and 
the liquid will fall from the top to about thirty 
inches above the cistern, and the barometer is pre- 
pared. Introduce beneath its mouth a pipette filled 
with ether, the tip curved for the purpose, and blow 
it into the interior. The mercury will instantly fall 
and stand at about fifteen instead of thirty inches. 
Incline the instrument and warm the ether it con- 
tains, the mercury will be driven lower. Cool it, 
and it will rise. 
Fig. 301. 
The experiment demonstrates that ether vapor is 
possessed of elastic force. If we warm it, this is in- 
creased and the mercury depressed. If we cool it, it 
is diminished, and air pressing upon the fluid in the 
cistern forces it up into the tube. 
By means of an ingenious device, known as the 
candle bomb, the elastic force of steam may be illus- 
trated. It consists of a small bulb blown on the end 
of a stout glass tube inch diameter, which is drawn 
oft’ as close as possible to the bulb, the end being 
Elastic force 
of vapors. 
- - ± - - 7 
left open. The latter is warmed, a portion of the air expelled, 
and the stem placed under water. By contraction of the air a 
little water is drawn into the bulb. The tip is then sealed. The 
stem is inserted in the wick of a spirit-lamp, the alcohol ignited, 
and the apparatus put in a safe place. After a short time a 
violent explosion results, the intensity furnishing a good idea 
of what happens when large quantities of water exert their 
elastic force explosively as in the bursting of boilers. 
699. High-pressure Steam Engines are examples of the applica- 
tion of the elastic force of vapor of water. Steam is generated 
in a boiler, where it is confined and, not allowed to escape except 
as used. Under these conditions its elastic force is increased, 
and pressures of sixty pounds, or four atmospheres upon the 
square inch, are easily obtained. This, admitted into a cylinder 
provided with a piston, gives the latter motion represented by 
this amount of pressure on every square inch of its surface. By 
suitable appliances the apparatus is made to work automatically. 
When the piston reaches one end of the cylinder, steam is ad- 
mitted on the other side and it is driven in the opposite direction. LIQUEFACTION. 
579 
A reciprocating motion is thus obtained, the regularity of which 
is maintained by means of a fly-wheel, and constitutes the ordi- 
nary high-pressure engine. 
In boilers of locomotives, marine, and other engines the solid 
matter contained in the water becomes concentrated as it is 
converted into steam, until finally, if care is not taken to blow 
this solution off, deposits accumulate to the thickness of an inch 
on the tubes of the boiler. When this has formed, as it is a 
poor conductor, heat does not traverse it freely. The metal 
which it covers becomes superheated, sometimes red hot, and 
oxidizes rapidly; finally, by weakening the boiler, it causes an 
explosion. 
Various devices have been applied to prevent formation of 
these deposits; among them is the introduction from time to 
time of chloride of ammonium into the water. Another, bolting 
bars of zinc in the boiler. These are combined with frequent 
blowing off. 
In low-pressure engines the difficulty is avoided by using 
water from the condenser, a little additional supply being pro- 
vided from time to time, as from various causes it is lost. In 
locomotives the surest remedy in a limestone district is to 
collect and use rain water. Every other scheme is open to ob- 
jection. Artesian wells will not answer, as they contain more 
dissolved mineral matter than waters which are superficial. 
CHAPTEE XXXIII 
LIQUEFACTION. 
Instantaneous condensability—Low-pressure engines—Pulse glass, cryophorus, 
and water-hammer—Fog. Cloud. Meteorology—Kain—Kain and miasm— 
Snow and hail—Distillation. 
700. Instantaneous Condensability of Vapors.—Adapt a tube, A, 
to a cork which closes the mouth of a flask, B. About three 
inches from the cork bend it, giving it a short and long leg. 
Place water in the flask, say one-sixth full, adapt the combina- 
tion thereto. Apply heat and boil the liquid until steam escapes 
freely from the open extremity of the tube. 
Having filled the apparatus full of steam, place the mouth of 
the long arm under water in a large vessel, C; condensation 580 
HEAT 
soon begins and little by little the water rises in the tube; at 
last a drop falls into the flask, when instantly all the vapor it 
contains is condensed, a vacuum is formed, and the fluid is 
Fig. 302. 
Instantaneous condensation of steam. 
forced up by pressure of the air on the surface of liquid in the 
reservoir, it rushes in with such violence that the flask is gener- 
ally crushed. 
701. Low-pressure Engines.—Advantage is taken of this prin- 
ciple in the construction of this form of engine. A large vessel, 
called the condenser, is kept cool and as vacuous as possible. 
When the piston has reached one end of the cylinder com- 
munication is established between it and the condenser. In- 
stant condensation of the steam follows, a vacuum is formed, 
and pressure of the air forces the piston back, at the same 
time steam is admitted on the opposite side, so its movement is 
the resultant of two forces, pressure of steam assisted by pressure 
of air or a vacuum on the reverse side. 
In recent marine engines the high and low pressure forms 
are united. A small cylinder receives the high-pressure steam 
at sixty or more pounds to the square inch. From this it passes 
into large cylinders over a hundred inches in diameter, in which 
it acts on the low-pressure principle. Thus the utmost effect 
of which steam is capable is obtained at a minimum expense. 
702. The Pulse-glass, Cryophorus, and Water-hammer.—The first 
consists of a tube about one-half an inch in diameter with a 
bulb at either extremity. This contains colored alcohol. All 
air is carefully removed, and as perfect a vacuum as possible LIQUEFACTION. 
obtained over the liquid. Grasping one of the bulbs in the 
hand and inclining the tube at a proper angle, the fluid takes 
up a pulsatile movement between the two, vapor being venerated 
in one and carrying a portion of the fluid along with*it to the 
581 
other, where it is condensed 
and returned to the flrst. 
The cryophorus or frost- 
bearer is similarly constructed. 
In place of alcohol, the upper 
bulb is partly filled with water. 
The lower is empty; all air 
being removed. A freezing 
mixture is applied to the lower, 
which condensing the moisture 
therein, promotes evaporation 
in the upper. This goes on at 
so rapid a rate that the cold 
produced is sufficient to freeze 
the fluid in the latter. Thus 
we have water frozen by the 
Fig. 303. 
The pulse-glass. 
application of cold at a distance. For description of the water 
hammer see (196). 
703. Fog. Cloud. Meteorology.—The interior of the flask in 
the experiment on instantaneous condensability, though filled 
with vapor, is perfectly clear and transparent. Not so, however, 
with the material which escapes from the mouth of the tube. 
It possesses the ordinary smoky appearance belonging to steam. 
Collect some of this upon a microscope slide, and examine it with 
that instrument. It will be found to consist of minute vesicles 
or hollow spheres of water. We, therefore, discover that steam 
while in the state of a true vapor is clear and transparent, and 
only assumes the form of fog when converted into these hollow 
spheres. What issues from the tube is not steam, it is con- 
densed steam or water. 
The formation of these vesicles, containing what is supposed 
to be in part ozone, is exceedingly instructive. They are quite 
permanent, and offer the first indication of what may be re- 
garded as the cell wall. Indeed, it is a question whether all 
forms in plant life may not depend upon the water they con- 
tain. After a night’s strong frost we find our windows covered 
with films of ice which present every variety of fern and other 
lowly plant forms. There is nothing present but water, and its 
assumption of these outlines, as it becomes converted into ice, 
is exceedingly suggestive of the source whence the fern forms 
are produced. 582 
HEAT 
Cloud is by some supposed to consist of hollow vesicles, by 
others of solid minute particles; both are correct, as it is some- 
times one, sometimes the other. The varieties are as follows: 
Ist. Cirrus is a feathery, wispy cloud, occupying the upper 
regions, A. Sailors call them mares' tails. They are at the 
highest elevations, and probably consist of particles of ice. 
Fig. 804. 
Forms of clouds. 
2d. Cumulus is formed of rounded masses, I>, convex above 
and flat below. They are known as cotton balls and wool packs. 
They prevail in summer. 
3d. Stratus consists of horizontal sheets, C. It is low in the 
atmosphere. It is formed at sunset, and disappears at sunrise. 
4th. Cirro-cumulus consists of small cumuli floating higher 
than cumulus. It is the variety which gives the mackerel sky. 
sth. Scud from its low elevation, appears to move with great 
rapidity. 
6th. Nimbus is any cloud which is discharging rain, I). 
All matters relating to phenomena of the atmosphere which 
appear aloft are dealt with by the science of meteorology, derived 
from the Greek periupog, signifying aloft. It was originally ap- 
plied to bright objects, as shooting stars, but now includes 
clouds, rain, lightning, and other phenomena. 
704. Rain is produced by condensation of fog vesicles in the 
clouds, or by coalescence of minute drops, until at last those of 
greater and greater size are attained and rain begins to fall. LIQUEFACTION. 
583 
The annual rainfall in different regions varies greatly. In 
equatorial parts of the globe it often reaches a depth of over 100 
inches annually. In our vicinity it is from 25 to 30. Meas- 
urement is made by means of the rain gauge. For this purpose 
a large funnel placed in a measuring-glass may be employed. 
The area of the former being known, the latter gives the cubic 
centimetres or cubic inches of water falling thereon. The 
instrument should be placed on top of a post away from trees or 
other obstacles to its free collection from all sides of the rain 
which falls. 
The best illustration of the variation in annual rainfall over 
a limited extent of country, is offered by the table of Mr. Sy- 
mons, for the rainfall of Great Britain. 
Lincoln and Stamford 
20 inche 
Buford and Witham 
. 21 
London and Edinburgh . 
. 24 “ 
Dublin and Pesth . 
. 30 “ 
Exeter and Clifton . 
. 33 “ 
Liverpool and Manchester 
. 35 “ 
Glasgow and Cork . 
. 40 “ 
Galway ..... 
. 50 “ 
Greenock and Inverary . 
. 64 “ 
Dartmoor .... 
. 86 “ 
Ben-Lomond .... 
. 91 “ 
705. Rain and Miasm.—Whenever the annual rainfall in any 
section is diminished, the ponds and marshes, losing their usual 
supply, expose the dark muck which forms their beds to the 
action of the sun’s rays. Under these conditions miasm of an 
exceedingly virulent nature is evolved. Every effort should, 
therefore, be made to retain the water in such places at its 
natural level. Under no conditions should it be drained, except 
in the winter season, when evolution of miasm is at its minimum. 
706. Snow and Hail.—Condensation of vapor of water by the 
intense cold of the upper regions of the air forms minute spicules 
of perfectly clear ice, which may be perceived in these regions 
as minute floating motes. Their coalescence and union pro- 
duces snow. Some idea of this intensity of cold at great alti- 
tudes is gained from the fact that Barral and Bixio, in an ascent 
made on July 27,1850, at 7000 metres above the earth suddenly 
encountered a temperature of—39° C. 
Formation of hail is' usually attended by great electric dis- 
turbance. The size of hailstones is sometimes very great. 
Parent says, that on May 15, 1703, he saw some as large as his 
fist. In 1844 many fell in France which weighed five kilo- 
grammes, or about ten pounds. 
707. Distillation consists in vaporizing a liquid, such as water, 
and condensing its vapor. In ordinary distillation the fluid is 584 
HEAT 
heated in a vessel called the still. It should not boil, but only 
simmer gently, the formation of spray, and carrying over of 
minute portions are thus avoided, and a purer distillate obtained. 
As vapor arises in the still it is received in the worm, which is 
a tube coiled spirally immersed in cold water. In this the steam 
is condensed and escapes below in a fluid state. 
Special forms have been devised to secure perfect freedom 
from impurity. One of these is the ancient device of the alembic, 
which was contrived to return a portion of the less condensable 
vapors to the still. 
Various modern kinds of apparatus accomplish the same 
result, and by exceedingly slow distillations we can obtain the 
most vaporizable liquids in a state of almost absolute purity. 
For liquefaction of distillates in the laboratory, Liebig’s con- 
denser is used. Cold water is delivered into it by the funnel ab, 
and flowing through a metallic jacket which surrounds the tube, 
e e, keeps it cool and condenses the vapor as it passes from the 
Fig. 305. 
Liebig’s condenser 
retort through d. The overflow of the former is caught at c, 
and the condensed vapor is delivered at d'. 
As a rule, the first fifth and the last two-fifths of a specimen 
are not collected. The first contains vapors which are objec- 
tionable. The last two, salts in increasing quantity, and the 
liability to formation of spray and destruction of the whole 
distillate is very great. 
It is an excellent practice, to follow a species of fractional 
distillation, collecting the distillate by tenths, and mingling those 
which are pure. HYGROMETRY. 
585 
CHAPTER XXXIY. 
HYGEOMETEY. 
Hygrometry—Mason’s hygrometer—Method of taking dew-point—Dew-point and 
sensation of temperature—Moisture exhaled from the lungs—Moisture exhaled 
from the skin—Etfect of exercise on insensible perspiration. 
708, Hygrometry.—We have referred to the presence of 
moisture in air. It is not to be supposed that this is in any 
way held by the air. The two things air and vapor simply 
coexist in a given space independently of each other. A vacuum 
will hold the same quantity of the latter at a given temperature 
as if filled with the former. The measurement of the amount of 
vapor in a given area constitutes the science of hygrometry. 
The effect of moisture and dryness on organic substances is 
well known. The splitting of articles of wood, as furniture, 
in drying is familiar to all. The simplest hygrometers are based 
on this property. 
The hair hygrometer consists of a human hair carefully deprived 
of its grease by ether, one end attached to a firm support, the 
other to an index, arranged as a lever of the third order—that 
is, with the power or hair between the fulcrum and the weight 
and near to the former. When it expands the lever falls, and 
marks its effect on the scale: when it contracts, it rises. It is 
graduated by exposing the instrument to the full effect of: Ist, 
a very dry, and 2d, a saturated or wet atmosphere. 
The compensation bar hygrometer is composed of a piece of 
whalebone firmly glued to a strip of wood cut across the grain. 
One end is attached to a fixed support, the other plays over a 
scale suitably divided. Tig. 289. 
A registering hygrometer is formed of a thin rectangular strip of 
wood cut across the grain, about one inch wide and ten long. 
Pins are then passed Through the four corners at equal angles 
of obliquity. Their points look in the same direction. When 
placed upon a table, if the air is damp the hinder pins take hold 
of the wood, and as the strip expands the fore pins are moved 
ahead. When it contracts the latter take hold, and the former 
are drawn forwards. Thus it gradually travels over the table 
registering the alternate expansions and contractions of the 
strip of wood under influence of the variations in moisture of 
the air. 586 
HEAT 
709. Mason’s Hygrometer consists of two thermometers, A and 
B, Fig. 306, alike in all respects. One is the dry bulb, the other 
the wet. The latter is covered exteriorly with a strip of linen 
which dips into a vessel of water, C. This by capillary attrac- 
tion rises therein, and bathes the surface of its thermometer. 
The moisture thus raised is evaporated by the heat. If the air 
is dry, evaporation is rapid, and the cooling effect sufficient to 
depress the mercury in the thermometer a considerable number 
of degrees, compared with the point at which it stands in the 
dry bulb. If amount of moisture is greater, cooling effect and 
depression of the thermometer are less. The indications of the 
instrument are given as dry bulb so many degrees, wet bulb so 
many. 
Fig. 306. 
Fig. 307. 
Mason’s hygrometer. 
Taking dew-point. 
710. Method of Taking the Dew-point.—Of all methods of hygro- 
metric measurement that of taking the dew-point is the most 
satisfactory. The apparatus required, Fig, 307, is a thin glass or 
silver vessel, a good thermometer, ice, and water. The operation 
consists first, in taking the temperature of the air, a small piece 
of ice is then placed in the water in the vessel, and the mixture 
stirred with the thermometer. The temperature is noted from 
time to time, and the exterior of the vessel watched for the first 
appearance of a coating of moisture or dew; the instant this is 
seen the thermometer is read, and the temperature is the dew- 
point, or that at which dew is deposited from the air. 
711. The Dew-point and Sensation of Heat.—Variation in the 
dew-point affects seriously our sensation of heat. A clear day 
on which the thermometer stands high, but the dew-point very 
low, is not as unbearable as one when it stands much lower, but 
the dew-point very high, or close upon the temperature. 
In the first case, there may be twenty degrees difference HYGROMETRY. 
587 
between the dry and wet bulb of a Mason’s hygrometer. All 
this is available for evaporation of moisture from the surface of 
the body, and this is, as we know, a cooling process. Consid- 
erable exercise can be taken on such a day without any 
unpleasant sensation of heat, for that produced in the body is 
removed by evaporation of water as fast as it arises. On 
another day, the thermometer may stand ten degrees lower, but 
the wet-bulb instrument showing that the air is saturated with 
dampness, any exertion is insufferable. There is no space for 
evaporation, the air, so to speak, cannot take up any more 
moisture, and we are drenched with perspiration if the slightest 
activity is attempted. 
712. Moisture Exhaled from the Lungs.—ln 1856 I published a 
series of experiments on this subject. They were made with a 
metallic condenser, by which the errors attending the preceding 
methods of experimentation were avoided, as the air passed 
through without obstruction. The film was one-eighth of an 
inch thick. The condenser was placed in a vessel of water and 
ice, and its temperature maintained at 32° F. At the entrance 
a thermometer registered the temperature of the breath, another 
at the exit gave that of the air escaping. The former marked 
94° F., the latter 32° F. So all the moisture between these 
points was deposited in the apparatus. The condenser wras 
weighed at the beginning and the end of each experiment, with 
the following results: 
No. of respirations in one minute, 16. 
Dew-point of breath 84° F. 
Experiment 1. 
Grains of water per minute . 
. 4.378 
Experiment 2, 
11 
It it 
. 4.539 
Experiment 3. 
U 
u u # 
. 4.329 
Experiment 4. 
ll 
u u 
. 4 418 
Average . 
. 4.416 
Experiment 1. 
Grains of water per minute 
. 3.602 
Experime.it 2. 
U 66 66 
. 3.415 
Experiment 3. 
u u U 
. 3.743 
Average . 
. 3.586 
No. of respirations per minute, 6. 
Experiment. Grains of water per minute .... 7.560 
No. of respirations per minute, 33. 
Tabulating these experiments, we obtain: 
No. of respirations 6. Grains of water per minute 
. 3.586 
u 
“ 16. “ “ “ 
. 4.416 
u 
“ 38. “ “ “ 
. 7.560 
From this we find that the quantity of water exhaled also 
depends on the rapidity of the respiratory act. 588 
HEAT 
The experiments were continued for the same period, viz,, 
twenty minutes. They were made at a temperature of 56°, 
and a dew-point of 49°. The same person was the subject, 
being a healthy adult weighing 130 pounds. 
The amount of air in each respiration was calculated from the 
amount of water deposited, with the following result: 
No. of 
Cubic inches 
respirations. 
per minute. 
6. Least amount sufficing for wants of system 
. 511 
16 Average demand ...... 
. 622 
33. Utmost extent of respiratory operation . 
. 1077 
The amount of air in each normal respiration is 38t8q cubic 
inches, the number of acts being sixteen per minute. 
this problem I constructed a balance in 1862, which, with a 
weight of 200 pounds in each pan, easily indicated the addition 
of a grain to either. With this a great number of experi- 
ments were made with the following results, in which the com- 
bined loss by lungs and skin is given: 
713. Moisture Exhaled from the Skin.—For examination of 
Insensible loss per minute. 
Temperature. 
Dew-point, 
Day rest 
. 0.79 gramme. 
55° 
46° 
Night sleep . 
. 0.47 “ 
50° 
42° 
The nocturnal loss is that which takes place during quiet, 
placid sleep, and the diurnal occurs when the body is kept in 
as perfect a state of rest as consistent with comfort, the time 
being spent either in writing, sitting, or reading in a recumbent 
posture. 
To the observant, intelligent physician, who has endeavored 
to control the condition of his patients by seeking to give them 
nervous as well as mere muscular rest, the above results explain 
the wonderful effect which sleep has, not only in restoring the 
tone of the system, but also in arresting the great loss of weight 
and emaciation which attend so many diseases during their 
restless, wakeful period, but which cease almost the moment 
that a calm night is granted to the sufferer. For during such 
a night the insensible loss continually taking place is only 
about one-half that in simple muscular rest. A sound sleep 
usually marks the beginning of the stage of convalescence in 
any disease. 
714. Effect of Exercise on Insensible Perspiration.—To determine 
this, a number of trials were made, which demonstrate that in 
health additional activity in the muscles is the chief cause of 
increase in the rate of loss by insensible perspiration; and that 
in moving the body of an adult weighing 65,000 grammes one 
mile, 44 grammes in addition to the usual amount are lost. HYGEOMETRY. 
589 
The data from which these conclusions were deduced were 
obtained by performing a series of experiments in which exer- 
cise, varying in duration and intensity, was undergone; and 
determining the increase in the rate of insensible loss. 
For 10-thousandths mile per minute motion, 1.16 gramme per minute of insensible 
loss. 
For 19-thousandths mile per minute motion, 1.67 gramme per minute of insensible 
loss. 
For 22-thousandths mile per minute motion, 1.88 gramme per minute of insensible 
loss. 
For 41-thousandths mile per minute motion, 2.40 grammes per minute of insensible 
loss. 
These examples not only bear out the statement regarding the 
increase in loss which follows active muscular exertion, but they 
also show how great an influence this has in promoting insen- 
sible perspiration; a movement of forty-one thousandths of a 
mile per minute, which is equivalent to three miles an hour, 
causing the rate of loss to rise from 80 to 240, or three times the 
original amount. Could we have indicated to us more clearly 
the true channel through which the products of waste and 
decay in the interior of the economy during violent muscular 
action are thrown off? 
While considering the evacuation of effete material in a form 
which is not appreciated by the senses, it becomes a matter of 
interest to determine whether the loss due to muscular action 
ceases as soon as exercise stops, or is continued for some time 
afterward. To answer this inquiry, I made a series of experi- 
ments in the months of February and July, 1863, The rate of 
loss before exercise was first determined. I then walked on dif- 
ferent occasions distances varying from one to five miles, and 
by weighing at once, obtained the loss during exercise. I then 
weighed at intervals of twenty minutes, to find at what time 
the rate of loss became the same as before the experiment was 
undertaken. 
The results obtained showed that the increased rate continues 
for some time after the exercise, and it is necessary that about an 
hour should elapse before the standard is regained; as illustra- 
tions, a couple of experiments are given. The average per 
minute in the state of rest was 0.79 gramme. 
Rate of loss per minute after violent exercise. 
No. 1 First (20 minutes), 1.25. Second (20 minutes), 0.91. Third (20 minutes), 
0.76 gramme. 
No. 2. First (20 minutes), 1.65. Second (20 minutes), 1.00. Third (20 minutes), 
0.90 gramme. 
Both of these show a continuance of increased rate after exer- 
cise ceased. In the first, at the close of one hour, the insen- 
sible loss had not only reached, but had fallen below the normal 
standard, 0.79; while in the second, in which it was greater, it 
had not quite reached it. 590 
HEAT 
CHAPTER XXXY. 
EBULLITION. 
Phenomena of ebullition—Variations in boiling point—lnfluence of reduced 
pressure—Elevation and boiling point—lnfluence of elevation of pressure— 
Papin's digester—Spherical slate—Effect of presence of salts—Application of 
heat in cooking. 
715. Phenomena of Ebullition.—When heat is applied to a flask 
containing water, the temperature rises, and currents are estab- 
Fig. 308. 
lished which are perfectly visible if 
the fluid is examined close at hand. 
After a while* bubbles of air escape. 
These form and rise through the liquid 
without producing any serious commo- 
tion. In their turn they are followed 
by a singing sound, caused by steam 
bubbles, which gather on the bottom 
of the flask, and rising a short distance 
are condensed by the cool water above. 
The fluid is thus thrown into vibra- 
tion and a sound emitted, well known 
as the singing of the kettle. This lasts 
for a short time, and, Anally, gives place 
to full boiling, in which the steam 
bubbles maintain their form until they break on the surface 
Ebullition. 
716. Variations in Boiling Point.—lf water is boiled in a rough- 
iron pot, violent ebullition is produced at 211° F., a degree below 
the true boiling point. If the surface is smooth, the tempera- 
ture may rise to 214° F. before it is fairly established. This is 
the result of adhesion between the molecules of the vessel and 
those of the fluid. 
Many liquids, as sulphuric acid, boil in a very irregular man- 
ner, the temperature rising a number of degrees above the true 
boiling point. There is then a sudden violent rush of vapor, 
and the temperature falls to the standard, to rise again in the 
same manner. These irregular actions cease when some object 
which affords points for the escape of vapor are thrown into 
the vessel. In the preceding case, introduce a few pieces of 
platinum into the liquid and it boils in a quiet simmering EBULLITION. 
591 
fashion, all violence is lost, and there is no further risk of 
breaking the vessel by the strength of the ebullition. 
717. Influence of Reduced Pressure.—Of all causes which in- 
fluence boiling point, that of pressure is the most profound. 
Take a flask of water boiling at ordinary pressure, pour it into a 
beaker, A, it will be cooled many degrees. Place it under the 
jar Bon the air-pump plate C, and exhaust. In a few moments 
it again begins to boil, as action of the pump continues ebullition 
becomes more and more violent, at last it ceases. If air is then 
admitted, the water will be found to have a temperature so low 
that the hand is easily borne in it. By a diminution of pres- 
sure we have lowered the boiling point to 100° F. or less. 
Fig. 309. 
Fig. 310. 
Reduced pressure. Reduced boiling point. 
Culinary paradox. 
Dependent upon this fact is a curious phenomenon known 
as the culinary paradox, in which water is boiled by application 
of cold. A flask, A, is half filled with boiling water, quickly 
corked, and placed bulb and neck in cold water, B. The liquid 
in the bulb at once begins to boil, and continues in that con- 
dition for some time. If, before it ceases, the cork is removed, 
there is a sudden inrush of air, showing that the interior was 
in a vacuous condition. 
. The explanation is simple; when the flask was placed in cold 
water, the steam filling its upper part was condensed, a vacuum 
was formed in which the fluid boiled by virtue of the law just 
demonstrated that reduction of pressure is attended by lowering 
°f boiling point. 
718. Elevation and Boiling Point.—The lowering of boiling 
point by elevation above the surface of the earth, led to its HEAT 
utilization for measurement of height. For this purpose a 
thermometer with large degrees, called an hypsometer, is used. 
It is graduated to fractions. The water must be pure, it is 
heated to boiling, and the thermometer introduced. An eleva- 
tion of about 530 feet causes a depression of 1° F. in the boiling 
point, and smaller elevations in similar proportions. 
By the diminution in the boiling point following elevation 
above the surface of the earth, a position may at last be reached 
where the temperature of ebullition is so low that the ordinary 
process of cooking as applied to coagulation of albumen fails, 
and no effect of the application of heat will succeed in producing 
the desired result. 
719. Influence of Elevation of Pressure.—Take a spherical boiler 
with three openings, the Ist for the admission of water, the 2d 
bearing a thermometer, and the 3d carrying a pressure gauge 
consisting of a tube some three feet in length which dips 
into mercury placed in the boiler. Pour in water until it rests 
on the surface of the mercury, apply heat, it soon enters into 
ebullition and steam escapes freely from the Ist opening through 
which the fluid was introduced, the thermometer marks 100° C. 
Close the stopcock by which the steam escaped, it begins to 
exert its elastic force, it presses upon the water, and this upon 
the mercury, and soon we see the latter making its appearance 
above the cap which holds the tube in place. At the same 
time we find the thermometer registers a higher degree. As 
pressure increases the temperature steadily rises until when a 
full atmosphere is reached, indicated by the mercury standing at 
thirty inches, the thermometer registers 120.6° C. The varia- 
tions of boiling-point with changes in pressure are as follows: 
Tension of the vapor of water. 
... , m ■ . .... . _ , Tension in atmospheres, 
Temperature Tension in millimetres Temperature 1 atmosphere = 760 nun 
Centigrade. of mercury. Centigrade. ‘ of mercury 
—20° 
0.927 
100.0° 
1 
—10° 
2.093 
111.7° 
1.5 
0° 
4.600 
120 6° 
2 
+5° 
6.534 
127.8° 
2.5 
10° 
9.165 
133.9° 
3 
15° 
12.699 
144,0° 
4 
20° 
17.391 
159.2° 
6 
30° 
31.548 
170 8° 
8 
40° 
54.906 
180.3° 
10 
50° 
91.982 
188.4° 
12 
60° 
148.791 
195 5° 
14 
70° 
233.093 
201.9° 
16 
80° 
354.280 
207.7° 
18 
90° 
525.450 
213.0° 
20 
100° 
760.000 
224.7° 
25 593 
EBULLITION. 
720. Papin’s Digester is a closed boiler, A, in which water is 
heated under pressure, and its boiling-point raised. With this 
rise it gains increased power of solution over all kinds of animal 
and other substances. Tendons, cartilage, and other gelatinous 
bodies placed therein under a pressure of four or five atmos- 
pheres are quickly dissolved. In this manner albuminoid sub- 
stances are now extracted from bones. 
Fig. 811. 
Fig. 312. 
Spheroidal state. 
Papin’s digester. 
721. Spheroidal State.—If a metallic vessel, A, is heated to a 
bright red and water thrown into it, instead of bursting into 
steam it quietly moves about on the surface gathering itself up 
into a sphere, and gradually disappears. The assumption of 
this form is called the spheroidal state. Though seeming to be 
in contact with the metal, it is not, but floats about on a cushion 
of steam which bears it up. Rapid evaporation from its under 
surface doubtless has a cooling effect, and if we could examine 
the temperature of the mass it is not at all improbable that it 
would be found quite cool. 
If the metal is a thin platinum capsule and we remove it 
from the source of heat, the temperature declines and when it 
reaches a point when elasticity of the steam cushion is not 
sufficient to support the wTater, it falls on the hot surface and is 
almost instantly dissipated as steam. 
722. Effect of the Presence of Salts.—Substances dissolved in 
water tend to an elevation of the boiling point, as follows: 
Water pure boils at ..••••• 
. 100° C. 
Water saturated with common salt boils at 
. 109° C. 
Water saturated with potassium nitrate boils at 
. 116° C. 
Water saturated with potassium carbonate boils at 
. 185° C. 
Water saturated with calcium chloride boils at . 
. 179° C. HEAT 
Matters merely suspended in water do not affect its boiling 
point; they must be dissolved. 
Water covered with a layer of oil may have its temperature 
raised to 120° C. without entering into ebullition, above this it 
boils suddenly with almost explosive violence. 
The temperature of vapor escaping from boiling saturated 
solutions is said by Rudberg to be the same as that of pure 
water, but this is now doubted. One thing is certain, that by 
passing steam from boiling water into a saturated salt solution, 
the temperature of the latter is raised many degrees above that 
of the former. That is, steam at 100° C. may be made to cause 
an elevation of temperature above 120° C. 
If a liquid be mingled with one of a lower boiling point, the 
point of ebullition is lower; when with one of higher it is raised. 
This, however, is not always the case, sometimes the mixture 
boils lower than either of its constituents. 
723. Application of Heat in Cooking.—The use of moist heat 
in cooking may be examined according to the object in view, 
viz., whether to prepare a soup, or merely to cook the flesh. 
In the first case we desire to extract from the meat as much 
of its soluble constituents as possible. To accomplish this it 
should be exposed to the action of water at a moderate tem- 
perature. 
An excellent formula for preparation of beef tea, which is 
the type of this group, is the following by Miss Nightingale. 
Cut a pound of beef into small pieces the size of dice or 
smaller, add a pint of cold water, and place in a saucepan on 
the fire. Bring to the boiling-point, and add a little salt, skim 
off any scum that rises. Simmer gently for one-half to three- 
fourths of an hour, removing any scum that appears. Strain 
through a hair sieve, and set aside to cool. Remove the solidified 
fat when cold, and serve hot, warming portions in a cup as re- 
quired. 
Another recipe is to place a pound of very finely minced lean 
meat in a bottle with a pint of water. Set the bottle in a kettle 
of hot water and let it simmer on the fire for an hour or so, 
adding a little salt. It is then passed through a sieve and treated 
as before. 
When meat is boiled merely as an act of cooking, the follow- 
ing method is employed. The object is to retain the savory and 
nutritious juices as far as possible. It is, therefore, heated quickly 
on the outside by plunging it into boiling hot water, the ebulli- 
tion ceases, when it recommences the pot is moved to one side 
to simmer. The albuminous substances on the exterior of the 
mass are thus coagulated, and escape of juices prevented, while CONDUCTION AND CONVECTION. 
595 
the application of moderate heat cooks the meat, without making 
it hard and indigestible. 
In boiling eggs great care should be taken to have them as 
digestible as possible, where served to a convalescent. The 
proper way is to plunge them into a vessel of boiling hot water, 
but which is not boiling—that is, it should be removed from 
the tire. Albumen coagulates at 180° F. or thereabouts. What 
is desired is to coagulate without hardening. If they are boiled, 
the albumen becomes porcelaneous and hard. If water is 
treated in the manner indicated the eggs cool it at once, and 
the cooking is accomplished by a temperature not much above 
180° F. Cooked in this manner they are simply coagulated, 
the albumen is in a tlocculent condition; not hardened and 
porcelaneous, and very digestible. 
CHAPTER XXXYI. 
CONDUCTION AND CONVECTION. 
Metals the best conductors—Different metals conduct differently—Action of gauzes 
on flames—The Davy lamp—Gas furnaces—Structure of flame—Blowpipe 
flames—Conduction by textile fabrics Liquids are poor conductors—Appli- 
cation in kerosene furnace—Convection of heat—lsothermal lines—-Island 
and continental climate—Non-conduction of dew—Gases the worst conductors. 
724. Metals the Best Conductors.—Take the apparatus known 
as the Ingenhaus’s trough, consisting of a metallic box some 
three inches square on the end, and about eight inches long. 
From the front there project rods about one-eighth of an inch 
in diameter and three in length, made of different materials— 
wood, porcelain, glass, metals. Pour melted wax on these, and 
when cool fill the box with boiling water. The wax soon begins 
to melt, and the distance to which fusion extends is the measure 
of conducting power, providing the specific heats are about the 
same. 
Another method is to attach shot to the bar by wax. As 
heat passes they drop one after another. Py both arrangements 
it is found that metals conduct heat the best, porcelain and 
wood being far behind. 
A simpler contrivance for exhibiting the same result consists 
in taking a rod of metal about one inch in diameter and six long, 596 
HEAT 
and another of wood the same size. Grip a sheet of paper once 
around the former and hold it in the flame of a spirit lamp. It 
may be held therein for some time without being scorched. 
Then grip it around the latter. It is scorched almost at once. 
In the first instance the metal conducted the heat away from 
the paper quickly, and prevented its temperature rising; in the 
second the wood could not remove the heat by conduction, con- 
sequently the paper was scorched. 
725. Different Metals Conduct Differently.—Take a wire of cop- 
per, A, one of brass, B, one of iron, C, of the same diameter and 
about twenty inches in length. On the 
end of each make close flat spirals of 
equal size. At a distance of four inches 
from this twine the wires together in- 
timately, making a ball, I), Attach the 
apparatus to the ring of a retort stand. 
On each spiral place a small piece of 
phosphorus. Under the ball of twisted 
wire put the flame of a Bunsen burner, 
or a large spirit flame, E. The air must 
be as free from motion as possible. 
After a time the heat wdll have passed 
along the copper wire and its phos- 
phorus will be ignited. In twice this 
period or longer that on the brass wire 
Fig. 313. 
Metals conduct differently. 
will catch tire. That on the iron will require a long period for 
its ignition, or may not ignite at all. Metals, therefore, con- 
duct heat with very different rates. 
Wiedemann and Franz employed a small thermo-electric pair 
for measurement of the rate of conduction. Representing that 
of silver as 100, the figures for other ordinary metals are 
Silver 
. 100 
Steel . 
. 11.6 
Copper 
. 73.6 
Lead . 
. 8.5 
Gold 
. 53.2 
Platinum . 
. 8.4 
Tin . 
. 14.5 
Pose’s alloy 
. 2.4 
Iron 
. 11.9 
Bismuth 
. 1.8 
726. Action of Gauzes on Flames.—lf a fine wire gauze, B, Fig. 
314, with meshes one-twentieth of an inch square, be lowered into 
gas flame, A, it completely obstructs its passage. This result is 
owing to the conducting power of the gauze, which conveys 
from the flame so much heat that it loses its visibility. Com- 
bustible matter, however, passes, for it can be set on fire as at C. 
Place a piece of camphor on the gauze and apply a flame 
below it. Its heavy vapor sinks through the gauze and takes fire 
beneath, but it does not ignite on the upper surface. CONDUCTION AND CONVECTION. 
597 
By means of this property we are enabled to study the char- 
acter of flames. Looking down into one thus obstructed we 
find that it consists of a luminous ring, the interior being 
perfectly dark—that is, it does not show any combustion action. 
Fig. 314. 
Wire gauze and flame. 
727. The Davy Lamp.—This property of gauzes to prevent 
passage of flame is utilized in the Davy. It consists of a flame 
surrounded by gauze in the original and 
by glass, A, in Clanny’s modification; above 
this, all direct free contact with air is cut off 
by a cylinder made of copper gauze, B. A 
lamp of this description can be lowered into 
ajar filled with illuminating gas without set- 
ting it on fire—indeed, the flame is extin- 
guished. In a mixture of air and carburetted 
hydrogen, though there may be irregular 
combustion inside the lamp, the explosive 
atmosphere on the outside is not ignited. 
Therefore, it is called the safety lamp. 
Where explosions have occurred though 
the Davy lamp was in use, they have generally 
arisen by the flame being driven against the 
gauze by a blower or strong outward current 
of gas from a fissure in the walls of the mine. 
They have also repeatedly happened by direct 
exposure of the flame. In one case a work- 
man had struck the gauze cylinder against a 
Fig. 315. 
The Davy lamp. 
nail to hang up the lamp, when it was removed the exterior 
atmosphere gained access through the opening and an explosion 
resulted. 
728. Gas Furnaces.—These consist of a chamber in which 
illuminating gas is mingled with air. The mixture is then 598 
HEAT 
passed through a wire gauze and ignited on the opposite side. 
By this device a non-luminous flame is produced useful for 
a great number of purposes in the arts. It is also commonly 
employed as a source of heat in domestic economy. 
729. Structure of Flame.—ln connection with the action of 
gauzes on flame a word is to he said regarding its structure. 
The interior is hollow, as we have learned; it is also cold, for if 
we immerse a piece of paper edgewise vertically into it, we find 
that the luminous ring has scorched its edge, leaving two burnt 
places with an untouched portion between them which repre- 
sents the central portion of the flame. 
The same fact may be shown b}7 pouring ether on water in 
a capsule some two inches in diameter. Ignite it, it gives a 
voluminous flame. Then with a metallic support introduce a 
piece of phosphorus, as it passes the luminous ring it catches 
tire, but the blaze is extinguished the moment it reaches the 
interior. Withdraw it and it is ignited, reintroduce it and it is 
extinguished. The experiment may be repeated many times. 
Hence, the centre is cold, combustion going on only in the 
bright ring which surrounds it. 
730. Blowpipe Flames.—When by means of a blowpipe, B, air 
is forced into a flame, A, its whole character is changed. As it 
is driven on one side we notice 
a sharp interior blue cone, AR, 
just beyond or at the tip of this, 
B, is the hottest part. Within 
it—that is, toward the point of 
the blowpipe—there is a reduc- 
tion effect from the excess of 
carbon present. Beyond it at 
0, there is oxidation from ex- 
cess of hot oxygen. By proper 
use of its different parts and the 
Fm. 316. 
Blowpipe flame. 
Blowpipe flame. 
employment of suitable fluxes, an analyst is enabled to discover 
the great majority of ordinary elementary bodies. Indeed, blow- 
pipe analysis, as it is called, constitutes a special and very com- 
plete system for qualitative examination of all kinds of mineral 
substances. 
731. Conduction by Textile Fabrics.—As a rule, these fibres 
conduct better along their length than across it. There is also 
great difference according as the character of fibres varies. 
Bumford made a series of experiments with linen, cotton, wool, 
and silk to determine their relative conducting power. For 
this purpose he took a flask, and having provided a good ther- CONDUCTION AND CONVECTION. 
599 
mometer its bulb was adjusted to be in the middle of that of 
the flask. The space between the thermometer bulb and the 
wall was then loosely filled with the articles in succession. The 
time required for the temperature to rise through a given num- 
ber of degrees when the flask was immersed in boiling water 
was noted. This became for each substance the index of its 
conducting power. He found that linen was the best conductor, 
next cotton, wool, silk, eider-down, and then the under fur of 
the hare. 
In these experiments it was also determined that closeness 
and looseness of package had an important effect. The tighter, 
the better the conducting power. In our domestic arts we 
find numerous illustrations of this. Blankets, for example, are 
much warmer—that is, are worse conductors—the more loosely 
they are woven. 
732. Liquids are Poor Conductors.—Take a Sanctorio’s or deli- 
cate air thermometer, A. Pass its stem through that of a funnel, 
B, with its bulb enclosed in the body of the latter. 
Make the space between the tube of the thermo- 
meter and the stem of the funnel water-tight with 
wax. Then fill the latter with water, covering 
the bulb by a layer one-eighth of an inch thick. 
The diameter of the mouth of the funnel is sup- 
posed to be about four inches. Pour on the water 
some ether. Ignite it and a powerful flame, C, four 
inches in diameter, and twenty or more in height, 
is produced. Great though the heat from this is, 
it has no effect whatever on the index liquid of the 
delicate thermometer, though separated therefrom 
by only one-eighth of an inch of water. After a 
time, it is true, a slight movement may be noticed 
by conduction of the heat downwards by the glass. 
From this experiment we learn that water is a 
very poor conductor. 
31?- 
Liquids poor 
conductors. 
733. Application in Kerosene Furnace.—The above 
property of non-conduction of heat is applied in kerosene fur- 
naces. This fluid is very vaporizable, and the stoves in which 
it is burned would easily become heated, and probably explode, 
were it not for the use of water to protect the oil. The reservoir 
is so arranged that it can be covered by a film of water half an 
inch thick. Through this the tubes bearing the wicks pass. 
The layer of liquid is, therefore, between the flames and the top 
of the vessel containing the oil. It completely cuts off the 
passage of heat, and may be used without risk. 600 
HEAT 
734. Convection of Heat.—Fill a flask three-fourths full of water, 
and drop into it a few pieces of amber. Apply a flame, B, to 
Fig. 318. 
XIL V 7 7 
the bottom. The pieces of amber rise, pass up 
through the centre of the fluid to its surface, they 
then turn outwards to the margin, and descend 
along the glass to the point of application of 
heat. The amber merely indicates the course 
which the currents are taking. At the point of 
application of the flame the liquid is warmed, it 
expands, and rises through the surrounding cold 
fluid to the surface. Thence it again passes down- 
wards to take the place of warmer portions. Thus 
a movement of rotation, or rather circulation, is 
established in the flask. Finally, all portions are 
equally warmed. 
In place of amber, ferrocyanide of copper can be 
employed. It is prepared by pouring a few drops 
Dissemination of 
heat by currents. 
of strong solution of sulphate of copper into the water in the 
flask, a little ferrocyanide of potassium is then added, when 
the dark-brown ferrocyanide of copper forms. This, after a 
time, settles to the bottom, and demonstrates the establishment 
of currents in the fluid in a most satisfactory manner when 
heat is applied. 
An ingenious illustration of the manner in which liquids are 
heated, consists in taking a large test-tube, filling it three-fourths 
full of water, and dropping into it a piece of ice weighted with 
copper or lead wire. Then hold it in an inclined position, say 
forty-five degrees. Apply a flame to the middle of the column. 
The liquid above the point of application quickly boils, while 
that below retains its original temperature, and the ice is not 
melted. Thus we have ice at the bottom, and boiling water at 
the top of the tube. The portion above is heated by the currents 
established therein, but these do not pass below that point. 
735. Isothermal Lines,—By revolution of the earth all parts 
of its surface on the same parallel should be equally heated. 
This, however, is not the case, owing to the interference of the 
great oceans, in which, by the agency of currents, there is a 
tendency to the establishment of equality of temperature in all 
its parts. If, therefore, we draw on the globe lines of equal tem- 
perature, or isothermal lines, we find that on the eastern sides 
of continents they pass much higher than on the western, the 
deflection being mainly due to oceanic currents of warm water 
which trend towards the northeast in the northern hemisphere, 
and bathing their eastern borders with warm water give a moist 
warm climate in regions far to the north. 
Many causes influence the climate of a given region of the CONDUCTION AND CONVECTION. 
601 
earth’s surface: Ist, latitude or distance from the equator. Other 
things equal, the further north we go the cooler it is. 
2d, elevation. The higher we rise above the earth’s surface the 
cooler it is. In the following table the results of Mr. Glaisher’s 
averages of reduction of temperature with increase of elevation 
for Great Britain are given. 
Height. 
Clear sky. 
Cloudy sky. 
0 to 1,000 feet. 
1° P. in 139 feet 
1° P. in 222 feet 
0 to 10,000 feet. 
1° P. in 288 feet. 
1° P. in 331 feet. 
0 to 20,000 feet. 
1° P. in 365 feet. 
1° F. in 468 feet. 
3d. Currents in the air or winds. According as prevailing winds 
set from a northern or southern direction, so is their influence 
for warmth or cold. 
4th. Currents in the ocean. These we have already considered. 
735 A. Island and Continent Climate.—The range of variation 
in temperatures is greatest in the interior of a continent, and 
smallest on islands in mid-ocean. This is best seen in the 
following tables. In both cases the temperatures are given in 
Centigrade degrees. 
Marine climaies. 
Winter. 
Summer. 
Difference. 
Faroe Islands . 
. 3.90° 
11.60° 
7.70° 
Isle of Unst (Shetland) . 
. 4.05° 
11.92° 
7.87° 
Isle of Man 
. 5.59° 
15.08° 
9.49° 
Penzance 
. 7.04° 
15.83° 
8.79° 
Helston .... 
. 6.19° 
16.00° 
9 81° 
Continental climates. 
Winter. 
Summer. 
Difference. 
St. Petersburg . 
—8.70° 
15.96° 
24.66° 
Moscow . 
—10.22° 
17.55° 
27.77° 
Kasan 
—13.66° 
17.35° 
31.01° 
Slatoust . 
—16.49° 
16.08° 
32.57° 
Irkutsk 
—17.88° 
16.00° 
33.88° 
Jakoutsk . 
—38.90° 
17.20° 
66,10° 
736. Non-conduction of Dew.—We have seen how a thin film 
of water prevents the passage of heat unless currents are estab- 
lished in the fluid. By virtue of this non-conducting power thin 
films of dew, made up largely of minute drops, become most 
important factors in protecting plants from sudden change in 
weather. When it has formed'on their leaves and other tissues, 
any further loss of heat is prevented by its non-conducting 
power. It thus acts as a guard or protection against loss of 
caloric, and the plant is enabled to resist further decline in its 
temperature. 602 
HEAT 
737. Gases the Worst Conductors.—The lack of conducting 
••-' • • • ® 
power in gases is well known. Double windows, down in birds, 
under fur in animals, all act by entrapping a layer of air and 
taking advantage of this power. Loosely woven clothing also 
utilizes the low conducting power of a film of air. Winters in 
which there is a heavy fall of snow, by the protection it affords 
to grain, are always followed by an abundant crop, the snow 
having shielded the ground from the action of frosts. 
As with liquids, gases are finally warmed throughout by the 
establishment of currents. In illustration of this, let a piece of 
phosphorus be burned in ajar of oxygen, a complete circulation 
of gas is at once seen, the course of its molecules being indicated 
by the flakes of phosphoric anhydride floating therein. 
CHAPTEE XXXYII. 
RADIATION AND TRANSMISSION. 
Radiant heat passes in straight lines—Reflection of heat—lnfluence of surface and 
color—Emission of heat not superficial—Absorption of heat—Transmission 
of heat—Theory of exchanges of heat—Formation of dew—Application of 
radiant heat in cooking. 
738. Radiant Heat Passes in Straight Lines.—lf we stand in 
front of a brightly burning fire we feel the impression of heat 
upon the face and other parts of the body exposed to its action. 
If a book or other opaque object is interposed between the face 
and the source of heat, it is completely cut off. Remove it, and 
again warmth is experienced. From this we learn that heat 
from a fire moves in straight lines like the radii of a sphere. 
Hence it is called radiant, because it escapes from the body 
equally in all directions as radii. This effect moreover is as 
well marked in vacuo as in air. Heat, like light, is the resultant 
of vibrations in the ether. 
739. Reflection of Heat.—As with light, radiant heat may be 
reflected when it falls on a polished surface, and the law is the 
same as for light. Two qiarabolic mirrors set in proper relation 
to each other, a cannon-ball, or ignited mass, placed in the focus 
of one, a small piece of phosphorus in that of the other. At a 
distance of twenty or thirty feet the phosphorus is quickly 
ignited. The rays of heat from the first mass are collected by RADIATION AND TRANSMISSION. 
603 
the mirror, sent forward from its surface as parallel rays, which, 
impinging- on the face of the second mirror, are reflected to its 
focus, and concentrated upon the object placed there. This is 
known as the Florentine experiment. 
Substances possess very different reflection powers. 
Reflecting 
Reflecting 
power. 
power. 
Silver plate 
. 97. 
Polished platinum 
80. 
Gold 
. 95. 
Steel 
. 83. 
Brass 
. 98. 
Zinc .... 
. 81. 
Speculum metal 
. 86. 
Iron .... 
. 77. 
Tin . 
. 85. 
Surfaces which are not polished diffuse the heat they receive 
in the same manner as they treat light. Each minute particle 
scatters it. Yet they seem to possess special powers in this 
respect, particularly if they are white; for example: 
Diffusive 
power. 
White lead .... 
. 82. 
Powdered silver 
. 76. 
Chromate of lead . 
. 66. 
740, Influence of Surface and Color on Eadiation.—Take a 
cubical box with faces four inches square. A, and mount it on a 
Fig. 819. 
vertical axis to allow it to turn thereon, and each of its faces 
brought in succession to the distance of ten inches from the 
blackened bulb of a differential thermometer. Each must be 
put in a different physical condition. The first polished, second 
slightly roughened, third very rough and somewhat dark, fourth 
as rough and black as possible to make it. Pour into the box 
boiling water, turning the first face towards the thermometer, 
note its effect there on reading off the number of degrees through 
Leslie’s canister. 604 
HEAT 
which the liquid moves in a given time. liepeat the experiment, 
in order, with each for the same period, pouring in fresh boil- 
ing water every time to avoid all question of irregularity of tem- 
perature. It will be found that the fourth or rough black surface 
is the best radiator, that it raises the thermometer through a 
given number of degrees in less time than any of the others. 
ISText comes the third surface, then the second, then the first. 
The instrument is known as Leslie’s canister. 
Color seems, however, to be a minor factor in producing this 
result, for a whitened surface radiated as much heat to a thermo- 
pile as a blackened one. The bulb of a thermometer coated 
with a white layer of alum absorbs radiant heat better than one 
coated with iodine'powder, which is nearly black. 
741. Emission of Heat not Superficial.—Lor examination of this 
question a Leslie canister, the surfaces equally polished, is 
taken. One remains in its normal state, the others are varnished, 
an increasing number of coats being applied to each. The can- 
ister is then experimented with as before, when it is found 
that one, two, or more coats add to the radiation power. The 
improvement continues for a dozen or more, wdien it remains 
stationary for a time, and then begins to diminish. From this 
we find that radiant heat is given off to a certain depth from the 
surface of a body and is not an absolutely superficial action. 
742. Absorption of Heat.—Bodies whose superficial condition 
enables them to radiate heat well, also absorb it well. A rough 
black substance is, therefore, a good absorber as well as radiator. 
Such bodies are bad reflectors, while good reflectors are bad 
radiators. An application of this is offered by an ordinary 
polished teapot. Its brilliant surface enables it to retain the 
temperature of the fluid for along time, the higher the polish 
the better it acts in this respect. 
Of all substances lampblack is the best absorber of heat, its 
index standing higher than that of any other body. 
743. Transmission of Heat.—While light passes through all clear 
or transparent bodies with but slight loss dependent upon their 
color and degree of opacity, it is not so with radiant heat. A 
sheet of perfectly clear glass is quite transparent or diathermous 
to the heat emitted from a red-hot cannon-ball, but opaque or 
athermous to that given off a boiling Mica, rock 
salt, and certain other substances bear the same relation to heat, 
that glass bears to light; that is, they transmit it with perfect 
facility, whether it comes from a body with a high or low 
temperature, though they may not in themselves be perfectly 
clear to light. Indeed, a black mica almost opaque to light 
transmits radiant heat of low intensity with great freedom. RADIATION AND TRANSMISSION, 
605 
744. Theory of Exchanges of Heat.—A hot substance placed in 
a room radiates its heat to surrounding bodies and these to it 
also, but the former gives it off more rapidly than the latter. 
As a consequence, it does not receive as much as it yields. Its 
temperature, therefore, declines, and finally when it reaches that 
of the others it becomes stationary, receiving as much as it dis- 
penses. 
The cooling of a substance is due first to radiation ; second, to 
conduction by the support on which it rests; and third, to con- 
duction by the currents of air which bathe its surface and rise 
therefrom in a heated condition. 
745. Formation of Dew.—ln ancient times it was supposed that 
dew either fell from the heavens, or was evaporated from the 
earth; the moon, they said, exhaled cold and caused vapors to 
rise. We now know that it is simply a condensation of moisture 
from the air. At sundown, when plants no longer receive warmth 
from the sun, they continue to radiate off their heat into space. 
After a time their temperature falls to the point at which 
moisture from the air will condense. Dew consequently forms 
on their surfaces. The coating thus produced acts as a pro- 
tection against a further decline. Other things being equal, 
deposition of moisture takes place first on surfaces dark and 
rough, and later on the smooth and light colored. 
The presence of a cloud, by radiating heat back interferes 
with this process. We do not find dew deposited on a cloudy 
night, it must be clear, to allow heat to be freely radiated oft' 
into space, and temperature sufficiently reduced to reach the 
dew-point. Anything like a screen, or which can radiate heat 
back to the plants or other objects, acts in the same manner, 
and will prevent formation of dew for a long time. 
For the theory of dew we are indebted to Dr. Wells, of 
South Carolina. It has the. merit of being simple and com- 
plete and meets every condition. It is also the natural outcome 
of the theory of exchanges of heat. 
746. Application of Radiant Heat in Cooking.—ln this the same 
object is to be attained as in the application of a boiling heat. 
The albuminous material is to be coagulated, not hardened, and 
the juices retained. The methods are: Ist, roasting; 2d, broil- 
ing; 3d, baking; 4th, frying, which may be added as an appli- 
cation of dry heat. 
In roasting, the meat is spitted (not put in an oven, that is 
baking), and placed in an open tin reflector in front of a bright 
fire. At first it is placed quite near, that coagulation of the 
exterior layers may be accomplished, the mass being turned on 
the spit until the coating is complete, it is then removed to a 606 
HEAT 
little distance, from time to time basted, and the cooking con- 
cluded at a more moderate temperature. 
In broiling the meat is treated much in the same manner as in 
roasting, an exterior coating of coagulated albumen is produced 
by a sudden strong heat, and the cooking finished at a lower 
degree. A little salt is generally dusted on the coals just before 
the meat is put on the broiler, the object being to clear the fire. 
The merits of baked funereal meats have been sung by ancient 
poets, and it is well that we should leave their consideration 
in their hands. They are inferior in every respect to those 
which are roasted. The meat is apt to be imbued with the 
melted fat in which it rests. Such fat-soaked meat is not as 
digestible as that which is roasted and from which the melted 
fat has dropped. The action of the gastric juice upon it is 
interfered with, and it passes from the stomach into the intestine 
to be digested in the colon. The flavor, moreover, is not as 
pleasant as that of roasted meat. 
In frying, meat should never be put into a cold or even cool 
pan. It should be hot and freshly greased. An immediate 
coating of the albuminoids on the exterior is thus accom- 
plished, the article should then be turned and the opposite 
side coagulated in like manner. The absorption of fat is thus 
prevented, and if the process is conducted in a proper manner 
it is a very wholesome method of cooking small quantities. 
This, however, it is not easy to do, and it was a maxim of Na- 
poleon that in armies the frying-pan killed more men than the 
bullet, by the indigestions and gastric derangements of which 
it was the cause. ANIMAL HEAT. 
607 
CHAPTER XXXYIII. 
ANIMAL HEAT. 
Source of heat in the body—Cooling process—Hot and cold blooded animals— 
Effects of exposure to cold—Distribution of plants and animals—Loss of 
heat by the body. 
747. Source of Heat in the Body.—The leading sources of heat 
are, oxidations of carbon and hydrogen. The results of these 
combinations are carbon dioxide and water. The former exists 
to a very small extent in the atmosphere, while the latter is 
present in much larger proportion. If we can prove that either 
is greatly increased during the process of respiration, we must 
arrive at the conclusion that the heat of the body arises primarily 
as a process of oxidation of these substances. 
If two hundred cubic inches of air be drawn through lime 
water, a small quantity of precipitated carbonate of lime forms. 
If through another specimen we blow two hundred cubic inches 
from the lungs, a very considerable precipitate of calcium car- 
bonate appears. We have, therefore, demonstrated that carbon 
dioxide is formed in the body to a very large extent, and that 
it is exhaled from the lungs. All processes of union of carbon 
and oxygen generate heat; we, therefore, find that the animal 
heat of our systems has its origin in oxidation of carbon. 
748. Cooling Process.—By the oxidation of carbon and hydro- 
gen contained in fats, oils, starch, and sugar, an enormous 
amount of heat is generated in the system. Some provision 
must be made for removal of the excess over and above the 
actual wants of the body. The means by which this is accom- 
plished is the evaporation of water from the raucous membrane 
of the lungs, and skin. 
Water, in its evaporation carries off no less than 1000° F. of 
latent heat (686). In the vapor arising from the body it is 
more than that. If to the 1000° of latent heat we add 212°, the 
sensible heat of steam, we find that the actual amount of heat 
in steam or vapor is 1212°. From this take the temperature 
of the latter as it escapes from the lungs, say 100° F., and we 
have 1112° as the latent heat of the vapor coming from these 
organs, and representing the cooling effect of vaporization on 608 
HEAT 
the system. To this must be added the difference between the 
temperature of the air and 100° F., to obtain the full effect. 
Anything which tends to increase the vapor in air lessens 
this action, and confines the heat generated to the system. 
Therefore, when air is loaded with it, and the dew-point stands 
high, a very profound effect is produced upon the body. Vapori- 
zation cannot take place into an air already saturated with moist- 
ure, and comfort is only found in rest as perfect as possible. 
749. Hot and Cold Blooded Animals.—Between the two pro- 
cesses of oxidation and evaporation the balance is struck in a 
healthy body, and the temperature remains at a fixed degree. 
In all hot-blooded animals or those which possess a fixed degree 
any departure from this is fraught with danger. Therefore it is, 
that the physician watches that of his patient with such zealous 
care, and when he sees a tendency for it either to rise or fall 
abnormally, does all that lies in his power to combat these con- 
ditions. 
In cold-blooded animals, on the contrary, the respiration func- 
tion is less perfect. Heat is not generated to the same extent 
as in hot-blooded mammals and birds. Their temperature rises 
and falls with that of the medium in which they live, whether 
water or air, though it is generally a few degrees higher. 
Certain animals sleep throughout the winter season. During 
this condition of hibernation, as it is called, respiration becomes 
exceedingly slow compared with its normal state. In the bat 
it falls from 200 to 30 per minute, and can hardly he detected. 
The tenrecs, though in a tropical climate, pass three months of 
the year in a torpid state. Hibernation seems to depend rather 
upon a scarcity of food than upon climatic conditions. 
750. Effects of Exposure to Cold.—The following results were 
obtained, in 1872, in an attempt to determine the quantity of 
heat passing off from the surface of the body, by finding how 
much it would elevate the temperature of a known mass of cool 
water during a given period of time. 
The manner of experimenting was as follows : Seven and a 
half cubic feet of cool water were drawn into a hath, and the 
temperature taken after careful mixing. The bath was then 
covered over for about four-fifths of its extent to prevent the 
action of currents of air, and at the close of an hour it was again 
tested. The rise of half a degree represented the amount of 
heat absorbed from the air during one hour, and was deducted 
as a normal error from the results afterwards obtained. 
During the time occupied in determining this normal error 
(viz., one hour), I lay on a sofa to bring the circulatory and 
respiratory functions into a condition similar, as regards posi- ANIMAL HEAT. 
609 
tion of the body, to that to which they would be submitted 
while in the bath.- My dress during this phase of the experi- 
ment consisted of a thin flannel summer undershirt, linen 
drawers, and cotton socks. At the completion of the hour 
these were removed with as little exertion as possible and 
I stepped into the bath, and lay down, allowing only the head 
to project above the surface. At the close of an hour the tem- 
perature of the bath was again taken. I then left it, and dry- 
ing myself, reassumed the same dress and lay down once more. 
Throughout the whole of each experiment, the dew-point, the 
temperature of the air, that of the bath, armpit, mouth, and 
temple were taken, together with the rate of respiration and the 
pulse. 
Since in these experiments two series of phenomena are 
investigated, I have for the sake of clearness of description 
separated the results in accordance therewith, and direct atten- 
tion first to the 
During rest. 
During motion. 
1st Exper. 
2d Exper. 
3d Exper. 
July 4. 
July 5. 
July 11. 
Temp, of air ...... 
90° F. 
84° F. 
83° F. 
Wet bulb thermometer .... 
78° F. 
76° F. 
74° F. 
Experiment commenced at 
11.45 A.M. 
12.10 p.m. 11.50 a.m. 
Temp, of water when drawn . . 
78|° F. - 
O 
r-l'd 
co 
75° F. 
Temp, of water at the end of an hour on 
entering the bath . . . . 
74° F. 
74° F. 
75J° F. 
Temp, of water at the close of an hour on 
78° F. 
leaving the bath ..... 
76£° F. 
76?2° F. 
Heat imparted to the water, deducting 
2° F. 
2° F. 
normal error ..... 
2° F. 
Volume of water in the bath . 
7\ cubic feet. 
Volume of the body .... 
3 cubic feet. 
Weight of the body .... 
180 lbs. 
Height of the body .... 
5 feet 5| inches 
Quantity of heat evolved from the body. 
In the first and second experiments I laid perfectly still; the 
results therefore show the quantity of heat passing off from the 
surface of the body in a state of rest. This, as the table indi- 
cates, could warm seven and a half cubic feet of water two 
degrees in one hour. The volume of the body being three 
cubic feet, it follows that if we consider its specific heat as about 
the same as that of water (which it probably is), enough heat is 
evolved in the course of one hour to warm the body itself about 
five degrees of Fahrenheit’s scale. The converse of this may 
also be considered as true, viz., that after death, the air being 
at 73°, enough is lost in the course of the first hour to cool the 
body five degrees. It is therefore a fact of considerable im- 
portance from a medico-legal point of view, especially in esti- 
mating the time a body has been immersed in water after recent 610 
HEAT 
drowning when the temperature of the water is about 73°, as 
the Croton and other streams in summer. 
In the third experiment one or other of the lower extremities 
was alternately kept in motion during the last half of the hour. 
The movement consisted in extending and flexing the leg on 
the thigh at the rate of fifty per minute, and being performed 
under the surface involved considerable muscular exertion. 
Notwithstanding this, as the table shows, there was no material 
increase in the amount of heat imparted to the water. The 
consequences flowing from this result are of great physiological 
importance, but we reserve their consideration until we have 
completed the history of our experiments. We therefore pass 
to the examination of 
The ■physiological effects of the cold hath on the body. 
Experiment of July 4,—Rest—Temp, of Bath 74° F. 
1 
Temp, be- 
fore enter- 
ing the 
bath. 
2 
Immed. 
after enter- 
ing the 
bath. 
3 
After one hour 
in the bath 
and just before 
leaving it. 
4 
Immed 
after leav- 
ing the 
bath 
5 
One hour 
after leav- 
ing the 
bath. 
6 
Two hours 
after leav- 
ing the 
bath. 
Temp, of the mouth, 
99° F. 
99° F. 
98° F. 
97° F. 
97° F. 
“ “ armpit, 
96° F. 
97° F. 
95° F. 
92° F. 
96° F. 
“ “ temple, 
96° F. 
94° F. 
Kate of respiration, . 
20 
22 
16 
13 
16 
19 
Kate of pulse, .... 
74 
73 
65 
54 
60 
72 
Note.—A chill or shock was experienced on entering, and the 
sensation of coolness remained wdiile in the water. Skin was 
dry and hot for an hour and a half after coming out. Perspira- 
tion set in and skin became cool in two hours and a half. 
Shortly after leaving the bath slept for thirty minutes. 
Experiment of July 5,—Rest—Temp, of Bath 74° F. 
1 
Temp, be- 
fore enter- 
ing the 
bath. 
2 
Immed. 
after enter- 
ing the 
bath. 
3 
After one hour 
in the bath 
and just before 
leaving it. 
4 
Immed. 
after leav- 
ing the 
hath. 
5 
One hour 
after leav- 
ing the 
bath. 
6 
Two hours 
after leav- 
ing the 
bath. 
Temp, of the month, 
99° F. 
99° F. 
98° F. 
97° F. 
97° F. 
98° F. 
“ “ armpit, 
98° F. 
97° F. 
94° F. 
94° F. 
97° F. 
97° F. 
“ “ temple, 
97° F. 
95° F. 
95° F. 
96° F. 
96° F. 
Kate of respiration, . 
17 
21 
18 
16 
16 
16 
Kate of pulse, .... 
78 
66 
64 
55 
56 
60 
Note.—Symptoms same as in experiment 1, but not as well 
marked; slept thirty minutes, as in preceding. ANIMAL HEAT. 
611 
_ If in the tables we compare column 1, representing the con- 
dition before entering, with column 4, representing that imme- 
diately after leaving, we tind that in both the exposure for one 
hour to water at a temperature of about 74° F. lowered the 
temperature of the mouth two degrees, the armpit four, and 
the temple two. The rate of respiration is also diminished in 
one case two and in the other four movements, the pulse twenty 
beats in one and twenty-three in the other. It is, therefore, 
evident that the effects of long-continued application of a 
degree of cold, as that employed, is to reduce the temperature 
of the body and the rate of respiration slightly, while it affects 
the rate of pulsation in a very profound manner. 
One of the consequences of this effect of cold on the action 
of the heart was a great reduction in the quantity of oxygen 
introduced into the system. The rate of pulsation being cut 
down nearly one-third, the quantity of oxygen conveyed into the 
interior of the body was diminished in a somewhat similar ratio. 
In a short time this began to exert its influence on the nervous 
centres, and there was an overwhelming disposition to fall asleep, 
which was unconsciously indulged in in both experiments shortly 
after leaving the bath, notwithstanding the strong desire to keep 
awake in order to record the rate of pulse and respiration at 
given periods. 
Another evident consequence of such a sluggish movement 
of the blood is the disposition to congestion of various internal 
organs, and herein we may see a partial explanation of the 
action of cold in causing inflammations, especially of those 
organs engaged in processes of secretion and excretion. 
The discussion of the results obtained has thus far been con- 
fined to the consideration of columns 1 and 4, I have followed 
this course because, while in the bath, a slight access of water 
to the armpit or to the temple causes irregularities in the ther- 
mometric indications. In the respiratory movements it is also 
very difficult to avoid affecting them in the act of counting. 
The mouth temperatures are, it is true, free from the influence 
of external agents, but the differences are too small to be per- 
fectly reliable. In the pulse determinations none of these ob- 
jections can be urged; they are considerable, and by counting 
half a minute for every record made, the error is reduced to a 
maximum of one beat The movements of the heart are, in 
addition, free from the liability to error that exists in respiration. 
Accepting the pulse determinations as being accurate and re- 
liable indications of the effects produced, while in the bath and 
out of it, we return to the consideration of the tables, and 
compare together columns 1, 8, and 4. Recollecting that 1 
represents the condition on entering, and 3 that just before 
leaving, after an immersion of one hour we find that the pulse 612 
HEAT 
was reduced nine beats' in the first experiment, and fourteen 
in the second. If now we compare 3, the condition just before 
leaving, with 4, that just after, we find that the rate of pulse 
has diminished eleven beats in the first and nine in the second 
experiment. The explanation of this extraordinary reduction 
is by no means clear. One thing is, however, very evident, 
and that is, the profound effect of the application of cold, as 
shown not only by the singular phenomenon of which we have 
just spoken, but also by the slowness with which the original 
rates of pulsation are regained, as demonstrated by columns 
5 and 6. 
The motion experiment of July 11th gave the same general 
physiological results as the rest trials of July 4th and oth. 
The difference being, that during the former the respiratory 
movements became 30 per minute and the pulse 90, both re- 
gaining the rate represented in the latter very soon after cessa- 
tion of exercise. Placing this great increase of the respiratory 
movement in juxtaposition with the failure of the exercise to 
cause any perceptible increase in the temperature of the bath, 
it is evident that the contact of cold water must put an almost 
absolute stop to the functions of the skin, and the whole duty 
of exhalation of vapor of water and consequent removal of heat 
is thrown on the lungs; hence the increased respiratory action, 
and also the special tendency of application of cold to the sur- 
face to produce inflammations of those organs by increasing the 
work they are obliged to perform, and raising the pulse-respira- 
tion ratio to that actually existing in pneumonia. 
In conclusion, it may be observed that the primary and most 
important effect of the application of cold to the whole surface 
of the body is to reduce the action of the heart. This reduction 
is still further increased on removing the cold, if the application 
has continued for a sufficient length of time; and, as a conse- 
quence, the phenomenon of stupor or sleep appears, caused 
either by deficient oxidation or by imperfect removal of car- 
bonic acid. There is also a tendency to congestion of various 
internal organs, especially of the lungs. 
751. Distribution of Plants and Animals.—Temperature exerts 
an important control over the distribution of plants. The grain 
belt, for example, in the western part of the United States runs 
far to the north. As a rule, the distribution follows closely on 
the isothermal lines anji is dependent thereon, though other 
conditions, as water supply, have a most important influence. 
On slopes of mountains in warm regions every variety of fruit 
is found in the range of a few miles. This is said to be the 
case at Quito, where tropical fruits may be cooled with ice 
brought from the mountain-top. Animals are also distributed VENTILATION AND METHODS OF WARMING. 
613 
on the earth according to thermal lines. The dog and cat as 
companions to man are perhaps more generally found than any 
other creatures. 
752. Loss of Heat by the Body.—ln cases in which life has been 
destroyed, the question of the time at which the murder was 
committed is often one of importance. The temperature of the 
body at the time of its discovery is an invaluable evidence in 
this respect, and one by no means to be overlooked. 
Many conditions are to be considered : Ist. Temperature of 
the air at the time; 2d. Character of the surface on which the 
body has lain since the crime was committed; 3d. Condition 
of the body as regards obesity. The last of these often exercises 
a wonderful effect, the temperature being retained for a very 
long time. 
CHAPTER XXXIX. 
VENTILATION AND METHODS OF WARMING. 
Action of artificial lights—Action of respiration—Object of ventilation—Re- 
moval of foul air—Ventilation of sick rooms—Warming of houses—The 
charcoal brazier—Open fireplaces—The stove—Steam-pipes in rooms—Hot- 
air furnaces—Steam furnaces—Supply of vapor—Weather strips—Joule’s 
mechanical equivalent of heat. 
753. Action of Artificial Lights.—The support of combustion 
in candles, lamps, gas, and other artificial sources of light im- 
plies the removal of oxygen from the air of the apartment, and 
the substitution of carbon dioxide in its stead. The atmos- 
phere is thus vitiated or rendered impure by a double action, 
the removal of the life-sustaining oxygen, and the substitution 
of noxious carbon dioxide. 
If combustion is from any cause incomplete, carbon mon- 
oxide is also evolved, the action of which upon the economy is 
exceedingly deleterious. 
754. Action of Respiration.—The processes of life also tend to 
vitiation of the air. We have seen that the animal heat of the 
body is the resultant of processes of oxidation or combustion. 
Carbon and hydrogen are actually burned therein. In their 614 
HEAT 
combustion we have shown that carbon dioxide or carbonic acid 
gas and water are produced. This action takes place through- 
out the system. Every cell in the course of its life is a consumer 
of oxygen and a final exhaler of carbonic acid. Air, therefore, 
in this case also suffers a double vitiation, removal of wholesome 
oxygen and evolution of toxic carbonic acid gas. 
Besides carbonic acid, other deleterious bodies are evolved. 
Ammonia in small quantity is a normal constituent of the air of 
expiration. Sulphuretted hydrogen also in minute quantity is 
given off both by skin and lungs. In addition, certain organic 
constituents are exhaled which are exceedingly deleterious. 
Their presence may be proven by breathing through colorless 
strong sulphuric acid, after a while it is darkened by action 
of the acid upon the bodies in question, their carbon being 
separated. 
755. Object of Ventilation.—To maintain the air of an apart- 
ment in which people are living in a proper state, so that foul 
ingredients are removed and a copious supply of fresh invigorat- 
ing air introduced, is the object of all processes of ventilation. 
As a rule, it is accomplished by taking advantage of the 
fact that air when heated expands, and thus gains ascensional 
power. That from an illuminating flame has a temperature 
far above 2000° F., consequently though carbonic acid, which 
is the chief product of the combustion, is heavier than air, 
in the case in question it is expanded four times its original 
volume at the moment of formation, and, therefore, has great 
ascensional power. It rapidly accumulates in the upper part of 
the room, as we can easily satisfy ourselves by placing a chair 
on a table, and mounting thereon take a few inhalations of the 
air in that region. Little by little carbonic acid by slow diffu- 
sion passes downwards, and thus at last is equally and slowly 
disseminated throughout the apartment. 
In products of expiration, it is true, the temperature may not 
be above 100° E., but the carbonic acid it contains is mingled 
with a very large proportion of air. In fact, it constitutes only 
three or four per cent, of the mixture. When cast out from 
the body the whole volume having a higher temperature than 
that of the surrounding atmosphere rises, and in like manner 
tends to accumulate in the upper part of the room. 
756. Removal of Foul Air.—The vitiated air being in the upper 
part of the apartment, it is evident that there is the proper place 
for an opening to allow its exit. Here, then, it should be ar- 
ranged, but that is not sufficient, a circulation must be estab- 
lished. To this end an aperture near the floor must be provided 
through which fresh air from the outside may enter and thus VENTILATION AND METHODS OF WARMING. 
615 
allow exit of the foul air to continue. In this way a current is 
established. Close either lower or upper opening, and at once 
the movement ceases. 
In ordinary houses flues are built to serve as the means of 
exit for foul air. As a rule, these are placed in the outside 
walls where, being in contact with the outer air, they are cold. 
Being cold, the current, such as it is, is downwards instead of 
upwards. Hold a piece of lighted paper opposite the register 
or opening of such a flue, and in place of the flame being 
drawn into it, it is driven outwards into the room. To avoid 
this reverse action, as it might be called, all flues intended for 
conveyance of foul air from an apartment should be placed in 
the chimney-stack where a fire is burning. By their vicinity to 
the smoke flue they will be heated, and containing warm air an 
upward movement will always take place when air is admitted 
at their base—that is, when they open into a room. 
In this case, as in the preceding, entrance for fresh air must 
be provided. This is generally offered by the hot-air flue which 
communicates with the furnace. 
757. Ventilation of Sick Rooms.—The provision of an ample 
supply of fresh air for a sick room is an essential condition to 
recovery of the patient. Yet it is not easy of accomplishment, 
unless at the same time we make a draught, which by suddenly 
chilling an exposed part of the body may produce serious con- 
sequences. 
When there are no flues the windows of an apartment offer 
the best means. If these are of the old-fashioned kind, which 
slide up and down, it is a very simple matter, a small opening 
at the top and another at the bottom answers. The bed must 
be placed so that no draught falls upon it, and a curtain or 
screen always put in position to shield it completely from 
any that may be established. Where the window swings upon 
hinges like a door, the action is not as satisfactory, but a slight 
opening will generally answer. It should be strongly secured in 
position to prevent change during the night. By judicious use 
of screens the bed may be protected. 
Where there are a number of windows to the room, in no case 
should those on opposite sides of the bed be opened, draughts 
would then be certainly established. One window opened in 
the manner stated will give all the ventilation required, and 
rarely do injury. 
Buildings ventilated by mechanical contrivances, as fans, 
wheels, etc., are not uncommon. When these exist, their man- 
agement is self-evident. 
758. Warming of Houses.—In cold regions some means of 
securing artificial warmth is absolutely necessary. If with this 616 
HEAT 
we can provide thorough ventilation, the best conditions for 
maintenance of life are secured. In various countries different 
means have been resorted to. Where fuel is dear it becomes 
an important object to husband it and produce the largest 
amount of heat from consumption of the smallest quantity. 
Where, on the contrary, it is abundant and cheap a greater 
degree of extravagance is allowed. 
Six methods are resorted to : Ist. Charcoal braziers; 2d. 
Open fireplaces; Bd. Stoves; 4th, Steam-pipes in rooms; sth. 
Ordinary hot-air furnaces; 6th. Steam and hot-water furnaces. 
Each of these we shall consider in its order. 
759. The Charcoal Brazier,—Throughout the south of Europe, 
where fuel is scarce, the brazier is universally employed by the 
poor. In the open air it is not objectionable, but in a room it is 
about the worst form in which heat could be obtained. It con- 
sists of a mere pan or pot in which a few embers are placed 
and partly covered with ashes. The supply of air is insufficient, 
and a leading product of the combustion is carbon monoxide, 
which is more poisonous than carbon dioxide, since it causes a 
permanent change in the blood discs and destroys their power 
to absorb oxygen. All the gases from the fire escape into, the 
room, and a more dangerous method of obtaining heat could 
hardly be devised. Indeed, when these people desire to commit 
suicide the favorite method is to shut themselves up with a 
brazier in operation, and carefully close all cracks and crevices. 
A few minutes inhalation of the gas suffices to destroy life. 
760. Open Fireplaces,—ln England the favorite method is by 
the open fireplace. This is an exceedingly cheery way of ob- 
taining heat, since the appearance of a brightly burning fire is 
enlivening and stimulating. There are, however, many objec- 
tions to its use, as well as certain advantages. 
Ist. It is very extravagant, as most of the heat goes up the 
chimney. The apartment and the articles it contains can only 
receive heat in the radiant form from the hot coal of the fire. 
2d. There is no direct contamination of the air, since all the 
products of combustion pass up the chimney, which is an 
advantage. 
3d. The air of the room is not scorched—that is, the minute 
floating particles are not charred and rendered irritating to the 
respiratory mucous membrane, as with stoves and furnaces, 
4th. The ventilation is moderately good. Of course, it is 
limited on the side of the chimney by the height of the throat 
of the fireplace. From this it extends somewhat upwards, as 
fresh air is drawn from the windows, the lower edge of the sills 
being generally about the same level as the chimney throat. VENTILATION AND METHODS OF WARMING. 
617 
sth. The draughts are bad. All air required for combus- 
tion is drawn in through the crannies and crevices about the 
room. If we come in contact with such fine currents of cold 
air, they are not only disagreeable but positively dangerous. 
More severe colds are caught by standing at a window for a 
short time exposed, to these knife-like draughts than by direct 
exposure to severe cold outside. 
Lastly, though the open fire is cheery and pleasant, in very 
cold weather it is impossible to warm one’s self in a satisfactory 
manner. One is like a joint on a spit, the side towards the fire 
is too hot and that away from it too cold for comfort. Like the 
joint, one must be in continuous revolution to warm all parts 
equally. 
761. The Stove possesses the great advantage of being the 
most economical of all methods. Not only is a larger portion 
of heat from combustion utilized from the stove itself, but by 
means of a long pipe a large percentage is secured as the pro- 
ducts pass towards the chimney. Regarding other points : 
Ist. Direct contamination is moderate. The carbon mon- 
oxide from the fire, though it does not pass through cold iron 
under the severest pressures, passes through readily when it 
is red-hot. Tests applied to the outside of a red-hot stove easily 
detect the presence of carbon monoxide and dioxide. The only 
way to avoid their filtration through the metal is to line the 
stove either with fire-brick or steatite. Direct contact is thus 
cut otf, temperature does not rise so high, and passage of noxious 
gases is prevented. At the same time, of course, a very con- 
siderable portion of heat is lost. 
2d. As air comes in contact with the red hot surface the mi- 
nute particles of floating organic matter it contains are scorched. 
At first this seems a matter hardly worth consideration, but 
when we note how numerous these are in the track of a sun- 
beam as it crosses a room, we are better prepared to understand 
how serious the objection is. 
3d. If ventilation is not perfect with the open fireplace, it 
certainly is much worse with a stove. In the latter the opening 
for the entrance of air to feed the fire is close to the floor. Ven- 
tilation, therefore, is only in the lowermost parts of the room. 
In the upper parts, and especially near the ceiling, it is very bad. 
4th. The draughts are, as with the open fire, a serious objec- 
tion. Like that, the stove is fed with air entirely from the 
apartment. It is true, it does not consume as much, and to this 
extent is less dangerous. 
A device called the ventilating stove is used in England. It is 
constructed in a manner to take foul air from the apartment for 
the maintenance of its combustion, and draw a fresh supply 618 
HEAT 
from the outside, warm it, and introduce it into the room. In 
France they are known as Caloriferes. 
762. Steam-pipes in Rooms.—This method will answer very well 
in immense stores and shops where doors which extend from 
ceiling to floor are continually being opened and shut. In a 
living apartment, or in a hospital ward, it is very objectionable. 
Ist. While there may be no direct contamination, the indirect, 
from failure to remove the respiratory products, is serious. 
2d, The air is not scorched or burned, as the floating par- 
ticles are not heated above 220 or 225° F. 
3d. The ventilation is absolutely ml The same air is warmed 
or breathed over and over again, and even in hospital wards, 
where large openings for admission of fresh supplies are pro- 
vided, patients whose beds are near these invariably stuff them 
with old clothing and other articles at night, to stop the draughts. 
763. Hot-air Furnaces are practically stoves placed in air 
chambers, in which air drawn from the outside of the building 
is heated and delivered to the rooms of the house. The hot-air 
furnace being a stove, is subject to many of the disadvantages 
which beset that apparatus. 
Ist. The direct contamination from foul gas passing through 
the heated iron is serious. Hence, the odor often remarked as 
attending their use. 
2d. The air is scorched as with the stove. 
3d. Ventilation is excellent. Volumes of cold fresh air are 
drawn from the exterior of the building and forced into the 
rooms or wards. In place of there being an exhaustion of the 
interior of these, as with the open tire and stove, there is a con- 
densation action. Air is delivered in immense quantities. In- 
stead of there being incoming currents through the crannies 
and crevices, they are in the opposite direction. They all set 
outwards, consequently there are no draughts. 
764. Steam Furnaces.—These and the hot-water arrangement 
avoid all the objections to the hot-air furnace. The air, instead 
of being heated in the chamber by a stove, is warmed by a coil 
of pipes through which either steam or hot water is passing. 
There can of course be no contamination, either direct or in- 
direct, since there is no communication between the interior of 
the pipes and the air chamber. The air is not scorched or 
burned, for the temperature does not rise high enough. Ven- 
tilation is as good as with the furnace, and there are no draughts. 
It is of all methods the best and at the same time the most ex- 
pensive. Considering the great advantage of economy which 
the stove presents, it will doubtless for the majority of people hold 
its ground against all other contrivances whatever their nature. VENTILATION AND METHODS OF WARMING. 
619 
765 Supply of Vapor.—ln all the methods we have considered 
care should be taken to provide a free supply of water for evapo- 
ration into the air of the apartment. In the 
open fire, a box A, may be readily fitted over 
the arch of the grate just under the mantle 
shelf. From this a pipe, B, shaped like an 
inverted capital T, may pass down close to the 
fire, C, and receive heat sufficient to keep the 
water in the reservoir continually boiling. On 
the stove, a well-filled vessel of water should 
always be kept, from which free vaporization 
can take place. In the furnace the pans in 
the air chamber must be well charged, and 
Fig. 320. 
Vapor generator. 
in addition vessels of water at the registers should be used 
where rooms are occupied by patients or convalescents. With 
steam contrivances, the remedy is very simple, it is merely to 
allow the escape of a little steam, either continuously or as 
required. 
765 A. Weather Strips.—ln furnace-heated houses great econ- 
omy is obtained by application of weather strips to the win- 
dows and outer doors. These consist of slips of metal, which 
embrace a narrow band of rubber. They are nailed on all sides 
of the window, the rubber making a tight joint against the sash. 
In bitter cold winter weather, when a high wind fairly blows the 
heated air out of our houses, these contrivances prevent this 
action to such an extent that rooms otherwise uninhabitable be- 
come warm and comfortable. 
766. Joule’s Mechanical Equivalent of Heat.—From time to 
time we have had occasion to speak of the conversion of work 
into heat, and vice versa, of heat into work. The best determina- 
tion we have of the reciprocal value of these two forms of energy 
is that given by Joule. He constructed a fan which revolved on 
a vertical axis in a box filled with water. The paddles on the 
fan moved between stationary ones attached to the sides of the 
box, the purpose of which was to prevent, as far as possible, 
the movement of the water; the axis of the fan was then caused 
to rotate by a thread wound around it and passed over a wheel 
which ran on friction rollers to a weight. The descent of this 
represented the energy applied, the rise in the temperature of 
the water the heat developed thereby. The necessary correc- 
tions being made, it was found that the heat communicated to 
the water by the agitation amounted to one pound-degree Fah- 
renheit for every 772 foot-pounds of work spent in producing it. 
The mechanical equivalent for the Centigrade system is 1390. 
The numbers 772 or 1390, according to the scale adopted, are 
known as Joule’s equivalents, and are represented by the letter J. SECTION VIII. 
ELECTRICITY. 
CHAPTER XL. 
First observation in friction electricity—Extended to other bodies—Conductors 
HISTORY. THEORIES. LAWS, 
discovered—Du Faye’s theory—Franklin’s theory—Electric laws—Pyro- 
electricity—Electricity by pressure and cleavage. 
767, First Observation in Friction Electricity.—About the sixth 
century before Christ, Thales, of Miletus, records the observa- 
tion, that amber when rubbed attracts light bodies in its vicinity. 
Hence the name, electricity, from Ekrpov, signifying amber. 
According to the philosophy of that time, this was explained 
upon the principle that by friction the amber became ani- 
mated. Thus by a mere play upon words, men satisfied them- 
selves that they understood the phenomena observed. 
768. Extended to Other Bodies.—Under this system the obser- 
vation of Thales remained without development until the six- 
teenth century or for over two thousand years, when Gilbert, 
physician to Queen Elizabeth, found that the property in ques- 
tion was also enjoyed by glass, resin, and a number of other 
substances. All of these when submitted to friction showed 
the same power to attract light substances. 
In 1670, Boyle discovered the electric spark; closely following 
this, the so-called medicated tubes were invented. These con- 
sisted of a stout tube filled with jalap powder, or some other 
drug. It was rubbed with a silk handkerchief and the sparks 
drawn off from a knob in which it terminated at one end. 
These sparks were supposed to carry the medicinal virtues of 
the drug with which the tube was tilled. Though, of course, 
they did not possess any power over that of the spark from an 
ordinary tube, they served the purpose of extending a knowledge 
of this form of electricity throughout Europe. Very soon char- 
latans were travelling in every direction administering sparks 
from medicated tubes to persons suffering from every conceivable 
form of disease. HISTORY. THEORIES. LAWS. 
621 
769. Conductors Discovered.—ln 1729 Gray discovered con- 
ductors and non-conductors. It is related that while experi- 
menting with a medicated tube, he found that if the brass ball 
at its extremity was connected with it by a string, the electric 
virtue, as it was called, passed along that to the ball and im- 
parted a charge to it, so that it attracted light bodies. Extending 
his experiment, he found that the charge could pass along a 
string from the upper window of his house to the area, a dis- 
tance of thirty feet. 
Having satisfied himself of the correctness of his observation, 
as was the fashion, he invited a number of friends to witness 
it. When the assemblage had gathered, being willing, as he 
relates, to perform the experiment handsomely, he provided a 
silken cord in place of the common hempen string formerly used. 
Taking his station in the window, and submitting the medicated 
tube to strong fricton, he found that the pieces of paper in the 
area remained motionless. He then substituted the hempen 
string, when, without difficulty, the light bodies were attracted. 
Thus Gray stumbled upon the fact that while some bodies 
transmit the electric virtue, others fail entirely in that power. 
In short, he had discovered the existence of conductors or anelec- 
trics, and non-conductors, insulators, electrics, dielectrics, or 
idioelectrics. 
Table of Conductors. 
Conductors in their order of 'power. 
Non-conductors, insulators, or electrics, 
in their inverse order. 
Metals. 
Dry metallic oxides, including fused alka- 
Charcoal. 
lies and earthy hydrates. 
Plumbago. 
Oils, the densest the best. 
Strong acids 
Ice below 0° F. 
Soot and lampblack. 
Phosphorus. 
Metallic ores. 
Dry chalk and lime. 
Metallic oxides. 
Lycopodium. 
Dilute acids. 
Caoutchouc. 
Saline solutions. 
Camphor. 
Animal fluids. 
Minerals, non-metallic. 
Sea-water. 
Marble. 
Rain-water. 
Porcelain. 
Ice and snow above 0° F. 
Baked wood and dried vegetables. 
Living vegetables. 
Dry paper, parchment, leather. 
Living animals. 
Dry gases. 
Flame. 
Wool, hair, feathers. 
Dyed silk. 
Smoke. 
Vapor. 
Bleached silk. 
Salts. 
Raw silk. 
Rarefied air. 
Glass and vitrified bodies, including dia- 
Dry earths. 
monds and transparent crystallized 
Massive minerals. 
minerals. 
Asphaltum. 
Wax. 
Sulphur. 
Resins and gutta-percha. 
Amber. 
Shellac. 622 
ELECTRICITY. 
It must be understood that there is no such thing as absolute 
conduction and non-conduction. The terms are merely relative. 
In the table, that power gradually diminishes throughout. 
The metals, which head it, present more or less resistance to the 
passage of electricity. The substances which close it, allow a 
small amount to pass. 
770. Du Faye’s Theory.—Let a tuft of cotton or a ball of pith, 
A, be suspended by a silken cord. Then excite a glass rod, D, 
strongly with a silk handkerchief covered with a little mosaic 
Fig. 321. 
Electric pendulum. 
gold (bisulphide of tin); bring the rod in the vicinity of the 
cotton, it is at once attracted, B. Then rub the latter in various 
parts with the former, without touching it with the hand; now 
on exciting the rod the cotton is repelled, C. Substitute for the 
glass rod a roll of sulphur, excite it by friction, present it to the 
cotton, and it is at once attracted. The apparatus is known as 
the electric pendulum. 
From this experiment we learn that there are two kindsl of 
electricity, the first called vitreous or glass electricity; jxnd second 
resinous or resin electricity. A body electrified, by a charge from the 
vitreous kind is repelled by a vitreously electrified body. In like man- 
ner, the roll of sulphur would first attract a light body, and 
after it is charged repel it; in other words, bodies electrified alike 
repel each other. If, however, to the vitreously electrified ball of 
cotton, the resinously electrified sulphur is presented, the ball 
is attracted. Therefore, bodies electrified differently attract each 
other. HISTORY. THEORIES. LAWS. 
623 
771. Franklin’s Theory.—We do not have two kinds of heat, 
only one, and if that in a body is deficient in quantity we say 
it is cold. So by Franklin’s theory, there is but one kind of 
electricity. Of this all bodies have a normal or natural charge. 
If we do anything to increase this, we say it is in the positive or 
plus state. If we take away a portion, we say it is negative or 
minus. Electric conditions may, therefore, be represented by 
the + and signs. Whichever theory we accept, these signs 
are now used for both. In Du Faye’s the + sign represents 
vitreous, and the sign resinous electricity. 
While Franklin’s is the more philosophical, there are certain 
phenomena not easy to explain upon that basis, but they are 
clear at once under the operation of Du Faye’s. For example, 
the opposite passages of two charges from a Leyden vial when 
discharged through a piece of card-board. 
772. Electric laws.—lst. The general law of attraction and 
repulsion may be briefly stated as follows: Like electricities 
repel; unlike attract. 
2d. The force of repulsion between two bodies electrified 
alike is inversely as the square of their distances. 
3d. At a given distance the attractive and repulsive forces of 
electrified bodies are as the product of the quantities of free 
electricity they contain. 
Bodies giving vitreous electricity if rubbed ivith the one that follows it, and resinous 
if rubbed with the one that precedes it. 
1. Catskin. 
2. Diamond. 
3. Flannel. 
4. Ivory. 
5. Eock crystal. 
6. Wood. 
7. Glass. 
8. Cotton. 
9. Linen. 
10. White silk. 
11. Dry hand. 
12. Wool. 
13. Sealing-wax. 
14. Colophony. 
15. Amber. 
16. Sulphur. 
17. Caoutchouc. 
18. Gutta-percha. 
19. Prepared paper. 
20. Collodion. 
21. Gun-cotton. 
773. Pyro-electricity.—Electricity of the same nature as fric- 
tional may be developed by heat in the tourmaline, cane sugar, 
and other bodies. The former should be suspended horizontally 
by a silken thread in a glass cylinder placed on a metal plate, 
which can be heated. The phenomena are only developed at 
temperatures between 10° and 150° C. As the plate is heated, 
the crystal becomes charged with electricity. An electrified 
glass rod presented to one end repels it, to the opposite attracts 
it. As it cools, it first loses its charge, the poles then reverse, 
that which was positive becoming negative, and negative 
positive. 
The name analogous pole is given to that end which is positive 
while the temperature is rising, and antilogous to that which is 
negative. 624 
ELECTRICITY. 
774. Electricity by Pressure and Cleavage.—lf a disk of wood 
covered with oiled silk, and a metal disk, each provided with 
insulated handles, are pressed firmly together, and then separated 
suddenly, the latter is found to be electrified. A crystal of 
Iceland spar pressed between the fingers becomes positively 
electrified; cork, rubber, and a number of substances exhibit 
the same property if insulated. Sudden separation of bodies 
develops the best effects. 
Cleavage also produces electric disturbance; mica, paper, and 
all poor conductors, if suddenly separated in the dark give a 
flash of phosphorescent electric light. If glass handles are fitted 
on each side of a piece of mica, and it is suddenly torn asunder, 
one piece shows positive, and the other negative disturbance. 
A stick of sealing-wax, if broken, shows different electric con- 
ditions in its two ends. 
Other sources of electricity, such as chemical action and mag- 
netism, exist. 
CHAPTER XLI. 
MACHINE AND EXPERIMENTAL ILLUSTRATIONS. 
Parts of electric machines—Cleaning and preparing the plate—The spark in air— 
The broken spark—Electric aura—Discharge in vacuo—Charging the body— 
Attraction and repulsion illustrated—Electric bells—Electric vane—Conduc- 
tion illustrated—The electrophorus—Hydro-electric machine. 
775. Parts of Electric Machines.—For the advantageous study 
of our subject, it is necessary that we describe the electric ma- 
chine, though there are certain matters involved therein, in- 
cluding the action of points, which for the present we must take 
for granted. 
In the early days of electricity machines were constructed of 
cylinders of sulphur, of glass, and plates of glass. The former 
were mounted on an axis revolved by a winch, while the hand 
acted as a rubber. Electricity was collected by a row of points 
on the opposite side, which communicated with the prime con- 
ductor. These machines are very apt to burst under influence 
of friction, and their low conducting power for heat. They have 
gone out of use. 
The next, the glass cylinder, a reproduction of the sulphur, 
has also passed away. MACHINE AND EXPERIMENTAL ILLUSTRATIONS. 
625 
The third or plate form is the only one now in use. Of its 
parts we give a description. They are four in number: Ist, 
the plate or electric; 2d, the insulators; 3d, the rubber or ex- 
citor; 4th, the prime conductor and points. 
The plate or electric A is mounted on an axis on which it 
revolves by agency of a winch supported by two columns fixed 
Fig. 322. 
firmly into the base of the machine. The plate may be all the 
way from a few inches to six feet in diameter. It is glass or 
Electric machine. 
hard rubber. 
Opposite its circumference, and a few inches therefrom, are 
the two insulators B B, which are stout glass supports fixed 
firmly into the base of the apparatus, and intended to carry, one 
the rubber, the other the prime conductor. 
The rubber C varies in size with the instrument. It is sup- 
ported by one of the insulators and occupies the position of a 
horizontal radius to the axis of revolution on one side of the 
plate. It consists of two pieces which should grasp the plate 
on opposite sides at its circumference, and extend from the 
margin about half way to the axis. It must be well padded, 
and grasp firmly. When used its parts should be coated with 
mosaic gold or amalgam, which greatly promote development 
of electricity. By means of a screw, the grip of the rubber is 
increased or diminished. 
The prime conductor D is supported by the insulator on the 
opposite side of the plate. This is placed at a distance there- 
from, and carries the former on its top. From the prime con- 
ductor an arm projects, extending horizontally to a point midway 
between the circumference of the plate and its axis. The inner 
surface of this presents a series of points towards the plate. 
These take otf the charge developed by the rubber, and store it 
upon the prime conductor, from which it cannot escape, as it is 
mounted on an insulating support. 626 
ELECTRICITY. 
lii the machine thus described the rubber and prime con- 
ductor are insulated; in this condition it would give very feeble 
results. If vigorous action is desired, and a development of 
positive electricity, the rubber ball must be put in free electric 
communication with the earth. Then on revolving the plate a 
torrent of positive sparks is obtained. If we desire negative 
electricity,'the prime conductor is put in communication with 
the earth. The rubbers are insulated. On throwing the in- 
strument into action sparks are taken from the ball attached to 
the rubbers. It will, therefore, give positive or negative elec- 
tricity, according as the prime conductor or the rubbers are con- 
nected to earth. 
776. Cleaning and Preparing the Plate.—Differences in the hy- 
groraetric character of glass produces variation in the character 
and power of the plate. The latter should always be made of a 
non-hygrometic glass. The supports or insulators must also 
be non-hygrometic. Before the instrument is used the insulators 
and plate should be wiped with a clean, dry, warm silk hand- 
kerchief, to remove all dust and moisture. The plate may be 
cleansed by a thorough washing, the last materials used being 
pure ammonia and ether. 
777. The Spark in Air .—No phenomenon in nature can be con- 
founded with the electric spark. Its light, its snap, its course, 
Fig. 323. 
are perfectly characteristic. If the machine is put in action, 
and the knuckle presented to the prime conductor at a short 
distance therefrom, a short straight spark passes from the ball 
Electric spark. MACHINE AND EXPERIMENTAL ILLUSTRATIONS. 
627 
to the finger, or it may be received upon another ball, as at A. 
As the distance is increased its character changes. It becomes 
zig-zag in its course. If still further increased, projections of 
light from each angle are produced, as in the lower figure. At 
last the limit is reached and it ceases. 
As each spark passes, it is attended by a snapping or crackling 
sound, which, when it takes place between eight-inch spherical 
insulated balls connected with a powerful induction coil, is as 
loud as the discharge of a pistol. 
778. The Broken Spark.—lf small disks of tinfoil are pasted on 
a glass tube, with a small interval between them, and the latter 
Fig. 324. 
presented to an excited prime conductor, the spark jumps from 
piece to piece of the foil, and is thus subdivided into a hundred 
or more smaller ones. The added length of these is not quite 
equal to the original single spark which the machine will give. 
In this manner, various devices can be traced on glass plates 
which, on being brought into communication with the machine, 
are suddenly lighted up and yield a very pleasing efiect. 
Broken spark. 
779. Electric Aura.—If a point is attached to the machine and 
the instrument thrown into action, the electricity escapes there- 
Fig. 325. 
Electric aura. 628 
ELECTRICITY. 
from in the form of a brush. If the hand is approached to the 
point it gives a sensation as though some one was breathing 
upon its surface. In a dark room the aura is seen as a diffuse 
light escaping from points and spreading out in a brush-like 
form. As the hand is approached towards the point the aura 
at last disappears, and is succeeded by short pungent sparks, 
which cause an irritating effect upon the skin. If the elec- 
tricity is positive, an extensive brush is formed; it negative, a 
brilliant point. . 
The ozone or electric odor so commonly perceived in the 
vicinity of a machine in full action, is stronger with the aural 
than with the spark discharge. 
780. Discharge in Vacuo.—lf the electric terminals pass into the 
interior of a tube which is exhausted by an air-pump, the dis- 
tance through which the spark can pass is greatly increased. 
With an ordinary machine it may easily be made to reach 
four or five feet. Its character also undergoes a change, the 
snapping sound disappears, and it takes the form of a waving or 
straight rod of light extending from one terminal to the other. 
By changing the gas contained in the tube—that is, having 
the residue air, hydrogen, carbonic acid, etc.—the color of the 
discharge varies. 
The electric egg is an oval or egg-shaped vessel of glass, 
which can be rarefied in the interior. Its terminals brought 
into connection with the machine, give a variety of forms of 
discharge dependent upon the degree of rarefaction and strength. 
781. Charging the Body.—lf a person is insulated by standing 
on a thick sheet of glass, or on a stool with glass legs, and the 
hand laid on the prime conductor, when the machine is thrown 
into action the body becomes charged. The hair stands out, 
every one repelling its neighbor, tinder this condition if an- 
other person approaches his hand to the charged individual, a 
very strong spark passes which affects both alike, producing 
involuntary contraction of the muscles in the vicinity of the 
parts between which it passed. 
782. Attraction and Repulsion Illustrated.—lf two balls of pith 
are connected by a linen thread ten inches or a foot in length, 
and the latter suspended by its centre from the knob of the 
prime conductor, on exciting the machine the1 former are at 
once repelled. Present an excited glass rod, and it repels them. 
Present a piece of excited sulphur, and they are attracted. In a 
jar which stands upon a metallic plate, place a number of gilt 
pith balls. Let a knob in communication with the machine 
project therein to a distance of three or four inches from the 
plate closing its mouth. Exciting the machine the balls are MACHINE AND EXPERIMENTAL ILLUSTRATIONS. 
629 
alternately attracted, and repelled with violence by the knob. 
The experiment is known as that of electric hail. 
Place a piece of gold leaf an inch square between circular 
plates of tin ten inches in diameter; the upper in communica- 
tion with the machine, and the lower with the earth. Make 
the distance between the plates four or live inches. Excite 
the machine and at once the gold leaf rises, becomes erect, and 
takes on a graceful dancing movement between the two plates. 
The vigor of gyration depends on the degree of excitation. 
783. Electric Bells.—Take a rod of metal and attach it to the 
machine so that it occupies a horizontal position. From the 
centre suspend a bell by a silken cord, and 
put it in communication with the ground by 
a chain ; from each extremity suspend others 
by good conductors. The bells should hang 
some two or three inches apart. To the cen- 
tre of each space between the points of sus- 
pension, attach a silken thread which carries 
a button at its lower extremity, the length 
must be adjusted to have the buttons hang 
opposite the rims of the bells; throw the 
machine into action, the electricity passes 
down the chains to the outer bells. These 
are excited and attract the buttons, which 
Fig. 826. 
Electric chimes. 
strike them, producing a ringing sound. Becoming charged 
they are repelled to the central bell, they strike it, discharge 
their electricity into the ground, and are again attracted by the 
outer bells. Thus a continued ringing is produced, 
which is an illustration of electric attraction and 
repulsion. The experiment is known as the electric 
chimes. 
Fiq. 327. 
784. Electric Vane.—Take six pieces of brass wire 
some six inches long, sharpen their ends to a fine 
point, bend them as in Fig. 327. Then attach the 
blunt ends to the rim of a button as radii at equal 
distances with the points all looking the same way. 
The button is then mounted upon an insulated 
vertical axis, so the whole arrangement can revolve 
freely thereon. Now connect the vane to the raa- 
Electric vane. 
chine, and throw the latter into action. At once electricity 
escapes from the points in a brush-like form, and their recoil 
sets the apparatus in rotation. 
785. Conduction Illustrated.—Take a secondary conductor, Fig, 
328, which is of the general form of the primary conductor, and, 
like it, is insulated. Place it five feet from the machine; sus- 630 
ELECTRICITY. 
Fig. 328. 
pend a pair of cork balls at each end; 
stretch between the prime and second- 
ary conductor a brass rod some six feet 
in length. The moment the machine 
is thrown into action the balls diverge 
trom each other, showing the passage 
of electricity. Make a solid glass rod 
the means of communication between 
the two conductors. Throw the ma- 
chine into action and there is no diver- 
gence, as glass is a non-conductor. 
Oases also possess considerable con- 
duction power, especially if hot. In illustration of this, restore 
the brass rod, and connect the secondary with the prime con- 
ductor. Excite the machine and the balls diverge. Hold a 
voluminous spirit flame under the secondary conductor, and at 
once they fall together. The heated air and products of com- 
bustion rising from the flame, have carried off the electric charge 
from the conductor. 
Secondary conductor. 
786. The Electrophorus is an instrument by which electricity 
is obtained continuously and at a minimum of expense. It 
consists of a metallic ring ten inches in 
diameter, A. It should be about half 
an inch high. In the circular space thus 
formed melted shellac is poured, and 
allowed to rest. A disk of metal, B, of 
little less diameter than the shellac is pro- 
vided; to its centre an insulating handle, 
C B, is attached. 
The shellac is excited by heating it with 
a catskin or flannel. Then lower the plate 
or cover upon it, touch the margin of the 
former and a spark escapes; separate it 
from the shellac, touch its margin and 
another is obtained. So an indefinite 
Fig. 329. 
Eleotropliorus. 
number can be drawn from the movable metallic plate by 
alternately touching it with the finger when laid on the shellac, 
and separated from it. 
787. The Hydro-electric Machine, invented by Sir William Arm- 
strong, consists of an insulated boiler in which high-pressure 
steam is generated. This is passed through a cooling box con- 
sisting of tubes surrounded by cotton which dip into water 
contained therein. By partial condensation of the steam, which 
is an essential feature, drops of water are produced. The fric- 
tion of these minute drops against the orifice from which the 
steam escapes develops the electricity. The steam merely fur- MEASUREMENT AND DISTRIBUTION. 
631 
uishes the propelling force. Opposite the jets is a metallic comb 
connected with an insulated conductor. Upon this the escaping 
steam impinges, and to it imparts the positive electricity with 
which it is charged. The jet piece is made of wood, and pas- 
sage through it is hindered by a metallic tongue around which 
the steam is obliged to pass to reach its entrance. A pressure 
of several atmospheres is required, and the water used in the 
boiler must be distilled. 
This instrument is very powerful, sparks over two feet in 
length being easily obtained. It works wrell in the open air, but 
in a room everything is quickly covered with condensed steam 
and it becomes inoperative. 
CHAPTER X Lll. 
MEASUREMENT AND DISTRIBUTION. 
Electroscopes—Electrometers—The torsion electrometer—The charge is on the 
surface—Distribution depends on form—Action of points—Dissipation of 
charge. 
788. Electroscopes are instruments for the detection of elec- 
tricity. The most delicate is the gold-leaf electroscope. It 
consists of two pieces of very thin leaf, A, about 
three-fourths of an inch wide and three long. 
These are suspended by one end so they lie 
face to face and touch each other. To protect 
them from currents of air they are placed in 
the interior of a jar or shade, B, through the 
top of which a metallic rod passes, the lower 
end hearing the leaves being within, the upper 
terminating in a ball, or plate, C, some three 
inches in diameter, which answers for a con- 
denser. Within the shade, at a distance of 
two inches from the leaves on each side, there 
is a brass wire terminating above in a little 
ball, D, and attached below to the base of the 
instrument. These afford communication with 
the earth. The air of the jar should be kept 
dry by a piece of quicklime placed in an evapo- 
rating dish. 
Fig. 330. 
Gold-leaf electroscope. 
When an electrified body is brought in the vicinity of the 
plate, though its distance from it is considerable, the gold 
leaves diverge from each other; when removed, they approach. 
If the divergence is strong enough to cause them to strike the ELECTRICITY. 
little balls, they remain divergent after the exciting cause is 
taken away. The character of the electricity with which they 
are charged may then be determined. If positive, the approach 
of an electrified glass rod will increase its divergence; that of 
sulphur will diminish it. 
A simpler apparatus for detecting an electric charge is a pair 
of cork balls connected with a conducting thread. It is not 
as sensitive as the instrument previously described, but answers 
all ordinary purposes. For delicate physiological investigations 
the gold-leaf electrometer is always employed; in it lightness 
of the foil, its admirable conducting power, extent of surfaces, 
and their closeness, make it the most sensitive instrument that 
could be devised. 
789. Electrometers are instruments for measuring the intensity 
of an electric charge. The quadrant electrometer consists of a 
rod attached to the electric machine so as to assume a vertical 
position. Above, it terminates in a knob to prevent loss of 
charge. Just below this is a graduated semicircle, to its centre 
a delicate wire is attached which carries a cork ball at its free 
extremity. 
When a charge is given to the instrument the cork ball in- 
stantly diverges from the rod, the extent of this is read in 
degrees on the scale, being the measure of its intensity. At 
best this instrument is imperfect, for theoretically its action is 
limited to 90° of divergence. Actually 
the ball will rise beyond that limit. 
Moreover, a divergence of 60° requires 
many times the amount of force to 
produce it that is able to cause one 
of 80°. It is, therefore, limited to very 
crude determinations. 
Fig. 331. 
790. The Torsion Electrometer, or elec- 
tric balance of Coulomb, consists of a 
cylinder of glass, A A, some five or 
six inches in diameter, from the upper 
part of this another much smaller, D D, 
projects. The top of the second carries 
a graduated scale, through the centre 
of which passes an axis, with an index 
attached traversing the scale. To the 
lower part of the axis a fine wire is fast- 
ened, which is carried down through 
the small cylinder to the centre of the 
large one, here it terminates in a slen- 
der rod of shellac, /, attached to it at right angles. This moves 
in a horizontal plane. On the wall of this cylinder a scale of 
Torsion electrometer. MEASUREMENT AND DISTRIBUTION. 
360° is affixed at AA. One end of the rod carries a gilt ball, 
g, which is mounted on an insulated support, and will retain any 
charge imparted to it. 
Through the top of the large cylinder another slender shellac 
rod, B passes vertically, which terminates in its interior 
in a gilt ball, g', of the same size as that on the horizontally 
suspended rod. When this is in position the ball it carries is 
exactly opposite that on the latter rod just touching it, and both 
are insulated. The former is held in position by a knob on its 
upper end. 
When the instrument is used the index on the small cylinder 
is set at o°, and the glass cover turned until the horizontally 
supported ball is exactly opposite that vertically suspended. 
The latter is then lifted out, charged, and returned as quickly 
as possible. The moment it is introduced it repels the former. 
The amount of this repulsion is read off from the scale arranged 
on the large cylinder. 
Let it be supposed that this is 36°. ISTow turn the index at 
the top of the small cylinder until the repulsion on the hori- 
zontal scale is reduced to 18°. Reading the amount through 
which the index on the small cylinder has been turned, and the 
consequent torsion on the wire to produce this result, we find 
that it is 126°, add to this the 18° of movement on the latter 
scale, and we have 144° as the amount required to reduce re- 
pulsion to one-half. 
Again, reduce the deviation to 8.5°. For this an additional 
movement of the upper index through 441° is required, add to 
this 126 + 8.5°, and we have 575.5° as the total torsion put upon 
the wire to reduce the deviation to one-quarter. 
Repulsions in the ratio of 1, J, J, require torsions respectively 
of 36°, 144°, and 575.5° to balance them. These figures show 
the relation of 1, 4, 16, to each other. They represent the 
ratio of torsions required to reduce the deviations of bodies 
charged with equal quantities of electricity respectively to 1, J, 
791. The Charge is on the Surface.—Take a metallic cylinder 
mounted on a horizontal axis, which is glass on one side termi- 
nating in a winch, and brass on the other, ending in a ball 
carrying a quadrant electrometer. Let a strip ot thick tin- 
foil be wound on the cylinder, which can be unwound by a 
silken thread, or wound by the winch. Wind the foil closely 
and charge the apparatus from the machine. The electrometer 
shows a certain divergence. As it is unwound, this diminishes, 
as it is wound, it increases. From this we see that when the 
superficies exposed is increased, the charge is distributed over 
a greater area and has less intensity. When diminished it is 634 
ELECTRICITY. 
disposed over a less area, and its intensity is increased, from 
which it is evident that the charge is distributed superficially. 
792. Distribution Depends on Form.—On a sphere a charge is 
entirely on the exterior, as shown by taking a hollow insulated 
sphere with an opening through the top, and examining its inte- 
rior with the proof plane of Coulomb’s balance. Ho charge is 
found therein. 
On the exterior of a sphere the electric density is the same for 
all parts of its surface. , 
On an ellipsoid it is greatest at the ends, and is at a minimum 
in the central regions. 
On a cylinder it is almost entirely at the extremities. 
On a fiat disk it is hardly appreciable on the faces, and in- 
creases suddenly as the margins are reached. 
793. Action of Points.—From the above, and from what has 
been previously stated regarding the electric brush, it is evident 
that the cause of the escape of electricity from points is the 
accumulation of the force upon them until the repellant power 
becomes so great that passage into the surrounding air occurs. 
Therefore, all points should be carefully rounded and made 
smooth, not only on the machine but also on all apparatus used 
therewith. 
The presentation of a point to the machine has the same effect 
as though it were attached to it. In evidence of this, charge 
with electricity a secondary conductor, to which a pair of cork 
balls are attached. They immediately undergo divergence. 
Present to the charged conductor the point of a needle, it quickly 
robs it of its charge, as shown by their falling together, and this 
without perceptible passage of electricity from it to the point. 
Connect a pointed wire to the prime conductor of the machine 
to make it look horizontally outwards from it. Then throw the 
machine into action, bring the flame of a spirit-lamp opposite 
the point, and it will be blown away by the electric brush escap- 
ing therefrom. 
794. Dissipation of Charge.—An insulated conductor left to 
itself gradually loses its charge. This takes place through the 
supports or insulators, and the air. 
The loss in the former can be diminished by decrease in 
their diameters. A long fibre of glass, or raw silk, makes an 
excellent insulator. 
As respects the air, the loss takes place in two ways: Ist, hy 
conduction, and, 2d, hy convection. Highly rarefied air, and that 
which is moist, probably act by conduction. In dry the action 
is by convection. The molecules in contact with the electric INDUCTION. 
635 
becoming charged are repelled, and new ones move in to take 
their place, these in their turn are also repelled. It is by this 
agency that escape from points is accounted for. It is a curious 
fact that charges of negative electricity are dissipated more 
rapidly than positive. 
CHAPTER XLIII. 
INDUCTION. 
Induction described—Bound electricity—Attraction and repulsion explained— 
Pail experiment—lnduction passes through glass—Specific inductive power 
—The Leyden vial—Dissected Leyden vial—Penetration of the charge. 
Kesiduum—Leyden batteries—Discharge through a card—Lichtenberg’s 
figures—Holtz machine—Condensers—Kate of passage—Duration of spark— 
Mechanical effects—Physical effects—Chemical effects—Physiological effects. 
795. Induction Described.—Take an insulated cylindrical con- 
ductor, A, arranged so that cork balls can be suspended from 
the two ends. Bring into the vicinity of one extremity a posi- 
tively excited insulated sphere, B. At once there is disturbance 
in the cylindrical conductor. The electricity it contains under- 
Fig. 332. 
Induction 
goes instantaneous decomposition, the balls at either end are 
diverged; now take a stick of sealing wax, excite it by friction, 
and present it to the cork balls at the end of the cylinder most 
distant from the sphere, they are attracted. Present it to those 
at the end nearest the sphere, and they are repelled. Excite 636 
ELECTRICITY, 
a glass rod and examine the balls with it. It attracts those 
nearest the sphere, and repels those at the further end of the 
cylinder. We, therefore, find that the normal charge of the 
latter has been decomposed in such a manner, that the positive 
electricity is driven to the end furthest from the former, and 
the negative attracted to that nearest it. 
Remove the excited sphere and at once the cork balls fall to- 
gether, The disturbed condition of the cylinder, therefore, 
only lasts while the former is in its vicinity. As it is approached 
nearer, or removed further therefrom, the disturbance varies, 
being greatest when it is nearest, and steadily diminishing as 
it is taken to a distance. 
The change described is called electric induction or influence. 
Nothing passes from the sphere to the cylinder, and the disturb- 
ance in the latter only lasts while the former is in its vicinity. 
It is an illustration of the law of attraction and repulsion. The 
sphere decomposes the normal charge of the*cylinder, attracting 
its negative, and repelling its positive electricity. In this change 
the neutral condition is not quite at the centre of the latter 
but a little on the side towards the former. This side also 
shows a stronger charge. 
796. Bound Electricity.—Not only are positive and negative 
electricities separated in the preceding experiment, but they are 
also in different conditions. While the positive charge is free to 
escape, and will pass off by any conducting channel; the nega- 
tive is bound, and cannot, even though put in electric com- 
munication with the earth. 
In illustration, repeat the preceding experiment, and while 
the cylinder is strongly under the influence of the sphere, estab- 
lish connection between its further extremity and the earth. 
The balls at that end immediately collapse, while those at the 
other are more strongly diverged. By this action the neutral 
line has been pushed back to the earth. The whole of the 
cylinder is now negatively electrified. Break the earth con- 
nection and remove the sphere from the vicinity of the cylinder. 
The latter will now be found to be strongly charged with nega- 
tive electricity, the former being positive. This method is known 
as charging by induction. 
797. Attraction and Repulsion Explained.—ln all electric attrac- 
tions and repulsions the light body exhibits induced changes. 
Its normal charge is decomposed and the negative portion 
powerfully attracted by the positively excited body—the sphere, 
for example. If sufficiently light, it moves toward the excited 
body, and, touching it, discharges the negative portion, and is INDUCTION. 
637 
then powerfully repelled, both bodies being electrified alike or 
in the + state. 
In place of a single cylinder conductor (795), use a number, 
and place them in a straight line at a slight distance from each 
other. Then bring the excited sphere in the vicinity of one 
end of the line; at once there is disturbance in the whole row. 
Remove it, and they relapse into their original condition. 
The experiment seems to explain how conduction takes place. 
The molecules of the body represent the cylinders. They are 
at a distance from each other. When the end of the row is 
acted upon by an excited body one side of each molecule be- 
comes positive and the other negative. In good conductors 
polarization is only instantaneous, being destroyed by the dis- 
charge from molecule to molecule. Good insulators, on the 
contrary, resist the tendency to discharge, and retain their 
polarized condition for a considerable time. 
798. Pail Experiment.—Take a metallic pail, A, seven inches in 
diameter and eleven in height. Connect its outside by a wire 
with a delicate gold-leaf electroscope, 
E, Fig. 333. Then take a metallic 
ball, B, insulated by a white silk thread 
some four feet in length. Charge it at 
the machine and lower it into the pail. 
As it enters, the electroscope shows a 
divergence of its leaves. On remov- 
ing it this ceases. Then lower it again, 
the divergence in the attached electro- 
scope increases until a depth of about 
three inches is reached, beyond this it 
remains stationary. Let the ball touch 
the bottom and discharge itself, no in- 
creased divergence is seen. Remove 
it, and divergence continues, while the 
ball is found completely discharged. 
From this we see that the effect 
produced by induction, as the ball en- 
tered the pail, was fully equal to that 
caused by the actual discharge of its 
electricity into it. Moreover, if a 
series of pails be placed one within 
the other, and insulated from each 
other by disks of shellac, so they do 
Fig. 833. 
Pail experiment. 
not touch in any part, and the external one is connected with 
an electroscope, when the ball is lowered into the inner, diver- 
gence of the leaves takes place in the electrometer, exactly as in 
the first instance, where only one was used. 638 
ELECTRICITY. 
799. Induction Passes Through Glass.—Restore the conditions 
of the first experiment (795), and provide in addition a sheet 
of glass. Bring the sphere near the end of the cylinder, the 
cork balls at either end of the latter show divergence. Inter- 
vene the glass between them and no change is perceptible. Re- 
move the sphere to a distance, the balls fall together. Restore 
it, they are repelled, and exactly to the same distance as when 
the glass is removed. We, therefore, find that electric induction 
or influence passes through glass with the same facility as through 
air. An experiment devised by Faraday, shows that this action 
is due to polarization of the molecules of the medium. It con- 
sisted in taking a vessel of turpentine in which filaments of silk 
were diffused. Two conductors were then plunged into the fluid, 
one connected with the machine, and the other with the ground. 
The particles of silk immediately arranged themselves end to 
end and adhered closely, showing the conditions of the molecules. 
Another experiment consisted in taking a number of plates of 
mica closely packed, the outer provided with movable metallic 
coatings. The system was then electrified, the coatings removed 
by insulated handles, when the opposite surfaces of each were 
found to be electrified, the one positive, the other negative ; 
thus showing the condition of the molecules of successive layers 
of the intervening electric. 
800. Specific Inductive Power.—Let two hollow spheres be pro- 
vided, each four inches in diameter, which like the Magdeburg 
hemispheres can be separated at the middle, or joined by a flange, 
and the interior exhausted. Through the upper half of each 
let an insulating conducting rod pass which communicates with 
a second sphere placed in the interior of the first, and separated 
from it by a space of about an inch wide in all its parts. Then 
let the inner sphere of one of the systems receive a charge, the 
outer being connected with the ground, the system acting like a 
Leyden vial. The electricity in the inner conductor is then deter- 
mined by a proof plane. Suppose it gives a torsion of 250°. The 
knob of this instrument is then touched to that of the other. 
The torsion in each is found to be 125°. The two pieces of 
apparatus being alike, and the space between the spheres in 
each filled with air, the charge is equally divided between 
them. 
Let the space in one be filled with shellac. Charge the other, 
put the knobs in communication, and test each by the proof 
plane. The charge is no longer equally divided; a portion ap- 
pears to be lost, and the shellac instrument contains more than 
the air. 
By a number of experiments Faraday arrived at the following INDUCTION. 
expressions of the specific inductive capacity of various dielectrics, 
as they are called. 
Air 
. 1 
Sulphur 
. 1.93 
Spermaceti . 
. 1.45 
Shellac . 
. 1.95 
Resin . 
. 1 76 
Paraffine 
. 1.98 
Pitch . 
. 1.80 
India rubber 
. 2.80 
Beeswax 
. 1.86 
Gutta-percha 
. 4 
Glass 
. 1.90 
Mica 
. 5 
801. The Leyden Vial consists of a wide-mouthed bottle, A, 
of about a half gallon capacity. The outside and inside are 
both coated with tinfoil to within a couple 
of inches of the top, a stopper of wood, JB, 
closes its mouth, through this a metal rod 
passes communicating with the inner coat- 
ing below, and terminating above in a knob. 
If the arrangement be put upon an in- 
sulated stand, C, and placed near the prime 
conductor D, of a machine in action, only 
three or four sparks pass to it. If a knob, 
E, in electric communication with the ground 
is then brought near the exterior coating, a 
spark passes to it. For every one passed 
from the machine to the inner coating, 
another passes from the outer to the knob. 
This continues for some time, a perfect 
torrent pouring from the machine to the vial. 
At last it ceases and the jar is fully charged. 
Examination shows that if positive electricity 
Fig, 334. 
Leyden vial. 
is communicated to the inner coating, it is positive electricity 
which escapes from the outer; but it is not the same as that 
which the inner coat received, for a time arrives at which the 
action ceases. That the electricity received by the inner coat 
is still there, may be proved by discharging the vial, when an 
exceedingly powerful spark is obtained, and a profound shock 
experienced, far exceeding in strength that of the sparks com- 
municated to it. 
The vial can be discharged without the electricity passing 
through the body by means of the arrangement, Fig. 336 A, 
which is a pair of brass rods some eight inches in length termi- 
nating at one end in balls, and joined at the other by a hinge, so 
they may be adjusted to ditferent distances. This is attached to 
an insulating handle. 
The discharge is either instantaneous or gradual. To effect 
the former, touch the outer coat of the vial with one ball of the 
discharging rod, and then approach the other to the knob com- 
municating with the inner coat, it is discharged with a brilliant 
spark and a noise like the explosion of a percussion cap. To 640 
ELECTRICITY. 
effect the latter, touch the outer and inner coatings alternately 
with a ball. 
802. Dissected Leyden Vial.—The object of this apparatus is to 
prove that the charge is on the glass. It consists of a cone- 
Fig. 335. 
shaped jar of glass, A, three inches in diameter at 
the base, five at the top, and eight high. This fits 
accurately into a tin jar, B, of the same diameter, 
but about two inches shorter. Another cone-shaped 
jar of tin fits the interior of the glass jar and is also 
about two inches shorter. When the three are 
placed within one another the glass projects about 
two inches above the tin jars. The latter act as 
coating to the glass. A vertical metallic rod, C, 
rises from the inner coating about four inches 
above the glass when all the parts are in position. 
Dissected 
Leyden vial. 
By it electric communication is had with the interior coat. 
"Place the coatings in position and charge the jar at the electric 
machine. It acts in all respects like a Leyden vial, and will yield 
a brilliant Hash. Charge it again, remove the inner coating by 
means of a glass rod, then the outer. The two may be brought 
into contact with each other, no spark passes. Replace them, 
discharge the apparatus, a brilliant spark is produced. It is, 
therefore, evident that the electricity must have been upon the 
glass. To prove that it is, again charge the jar, and remove the 
coatings. Then pass one figger on the outside of the glass below 
the line precisely occupied by the coating; with another finger 
touch the inside, instantly a shock is felt, demonstrating beyond 
a doubt that it is thereon. 
803. Penetration of the Charge. Residuum.—Rot only is the 
charge upon the glass, the molecules of the surface of which are 
polarized in opposite conditions, but it also penetrates into its 
substance for a certain distance. That this is the case is shown 
by the fact, that if a Leyden vial is charged and allowed to 
stand for a time, and then discharged and kept quiet a few 
minutes, on again applying the rod, another spark, small in 
comparison with the first, but exceedingly unpleasant to receive 
when not prepared for it, is experienced. This is the residual 
spark or charge. It is that portion which penetrated the glass 
during the first charging of the jar, and did not completely 
escape when it was discharged, as it required time to free itself. 
In the vial the thinner the glass the more powerful the charge. 
Lack of homogeneity in the latter is, however, apt to favor a 
discharge through that medium, and destruction of the apparatus 
follows. INDUCTION. 
641 
804. Leyden Batteries.—ln these a number of Leyden vials are 
arranged by connecting their outer coverings together by placing 
them on a board covered with tinfoil. The inner coatings are 
connected by rods. It gives a spark when discharged, which is 
in proportion to the size and number of jars entering into its 
formation. 
A battery of this description is charged either directly by the 
machine or charged by cascade, as it is called. The latter is 
accomplished by placing the jars on insulating supports, with 
the outer coat of one in juxtaposition to the knob of the inner 
coat of the next, the last of the series connecting with earth. A 
spark is then given to the inner coat of the first, one of the same 
nature leaves its outer coat to enter the inner of the next, and so 
on throughout the whole line. By this method the charge re- 
quired for one is made to charge the whole series. They are 
then placed in position—that is, their outer coats are connected 
in one series and their inner in another, when they are discharged 
in the ordinary manner. 
805. Discharge through a Card.—Charge a Leyden jar, and then 
intervene a card or piece of pasteboard between the ball of the 
discharging rod, A, and the outer coating. 
Approach the other ball to that of the jar, 
and discharge it. The charge forces itself 
through the card, and disrupts its tissue in 
a curious way. The aperture is not made 
by a force passing in one direction, as a 
needle driven through a substance on one 
side, and drawn out with its thread on the 
other. This would produce an indraft at 
the entrance, and a fraying out of the exit. 
This is not what we find. On the contrary, 
it is as though two needles had been forced 
through in opposite directions, B, and their 
Pig. 336. 
Discharging 
rod. 
Perforated 
card. 
threads drawn out at the same time as a shoemaker stitches. 
This frays out on both sides, and is exactly what the electric 
spark does. 
This fraying out in both directions by the passage of the elec- 
tric spark, is held as important evidence in support of the theory 
of two fluids or forces. It is easily explained on this hypothesis, 
the two passing in opposite directions at the same time to inter- 
mingle with each other. 
806. Lichtenberg’s Figures.—Take a plate of shellac, the elec- 
trophorus will' answer. Charge a Leyden vial, and holding it 
by the outer coating, trace a simple design with the knob upon 
the shellac. Place the former on an insulator, and take hold 642 
ELECTRICITY. 
by the knob and trace another design on the latter with the outer 
coating. A mixture of finely powdered red lead and flowers of 
sulphur is then shaken together to electrify it, and dusted on 
the surface. The powders immediately separate, the latter ad- 
heres to the pattern traced with the positive electricity, the 
former to the negative. Not only are they separated, but the 
figures are entirely different in nature. The sulphur particles 
Fig. 337. 
Lichtenberg’s figures. 
arrange themselves in branching lines, while the red lead tends 
to the formation of small circular spots. From this it would 
seem that positive electricity which has attracted the former 
travels along the surface more readily than the negative. The 
same effect is seen with electric brushes. These facts also sup- 
port the theory of duality in electricity. INDUCTIOJSr. 
807. Holtz Machine.—Another phenomenon of induction is 
the Holtz machine, as modified by Toepler. It consists of two 
glass plates, one fixed, A, and the other, B, capable of rapid 
rotation by a multiplying wheel and band, C. Condensers, DD, 
Fig. 338. 
Holtz machine. 
and discharging rods, E E, also form parts of the apparatus. 
The metallic brushes, F F, should touch the small brass knobs, 
but not the plate. 
The machine being ready, see that the plate revolves freely 
without striking anywhere, then place the discharging balls 
close together, and turn the wheel until sparks pass between 
them. Then separate them gradually with a piece of hard rub- 
ber. Turning the wheel rapidly, a torrent of sparks passes be- 
tween the knobs. 
The action is this: “The small brass disks on the anterior 
surface of the plate when this is revolved rub against the metallic 
brushes, a small amount of electricity is thus developed and car- 
ried around to the armatures upon the back of the large station- 
ary plate. The initial charge is thus given to this, which in its 
turn reacts upon the revolving plate. By this novel arrangement 
the old-style plate with windows is dispensed with, and the 
machine easily charged,” the action throughout being by induc- 
tion. 
By means of this machine the application of this form of elec- 
tricity for medicinal purposes is made a practical success. 
808. Condensers.—A Leyden vial is, properly speaking, a con- 
denser, but the term is usually applied to flat sheets of glass, or 
some other electric, the two surfaces of which carry metallic 644 
ELECTRICITY. 
coatings which are movable or not, and somewhat less in size 
than the sheet of glass. One of these, called the collecting 
plate, is connected with the machine; the other with the earth, 
and the glass is between them. When the machine has reached 
the limit of action, the face of the plate connected with the 
earth is covered with negative electricity drawn therefrom, and 
held by the attraction of the positive electricity of that attached 
to the machine. On the other hand, the latter not only pre- 
sents the charge which the machine could normally give it, but 
in addition that which is induced by the negative electricity of 
the plate in connection with the ground. 
By condensation we understand that there is an enormous 
increase of electrical density on a given surface without increase of 
potential. 
809. Rate of Passage.—lt is related that one of the kings of 
France, being desirous of determining the rate of passage of an 
electric current, ordered that 180 of his guards should form a 
line, each man with his hand upon the head of his neighbor. 
The outermost men were one to touch the outside coating of a 
Leyden vial, the other the knob communicating with the interior. 
It was thought that by this experiment it could be determined 
whether electricity travelled from the outer to the inner coat, or 
in the reverse direction, whichever way it went the man at the 
end of the line from which it started would first be prostrated, 
A trial being made, it was found that all the men were felled 
at the same moment. It was, therefore, concluded that the 
movement of electricity is instantaneous. 
Though not instantaneous, the rate of passage of an electric 
spark is very rapid, and depends upon a number of conditions. 
Among these is the length of the circuit. Through a distance 
of half a mile, Wheatstone found, by the use of his revolving 
mirror, and a break of the current in three places, two close to 
the coatings, and the third at a quarter of a mile distant from 
each, that there was a retardation of the latter less than one- 
millionth of a second This, by calculation, gave a velocity of 
288,000 miles in a second, the velocity of light being only 180,000 
miles in the same time. In longer circuits the rate is much 
slower, through 3000 miles of an Atlantic cable it required one 
second for the current from a Baniell battery at one end to give 
deflection in a Thomson mirror galvanometer at the other. 
The nature of the conductor, the insulation, and a number of 
other conditions, all have their effect. Other things being equal, 
the velocity of dynamic electricity is less than static. 
810. Duration of Spark.—The electric spark lasts for a very 
short interval of time. Its brevity may be illustrated by means INDUCTION. 
645 
0l?. the revolving card. On this the colors of the spectrum are 
painted radiating from centre to circumference. It is driven by 
clock-work, and may receive so rapid a rate of motion that the 
colors all blend together upon the retina, and a uniform gray 
tint is produced. If yrhile in rapid rotation a Leyden spark is 
discharged in front of it, every color stands out as sharply as 
though it was perfectly still. That is, the spark has come and 
gone before it has had time to move. 
In determinations made by Lucas and Cazin, by means of 
lines traced on a revolving disk, it was found that the electric 
spark lasts from 23 to 46 ten-millionths of a second. Its duration 
is prolonged by an increase in the number of Leyden jars in the 
battery employed, and with the striking distance between the 
balls of the discharger. 
811. Mechanical Effect.—By a powerful Leyden discharge, glass 
is perforated, wood and stone fractured, gases and liquids de- 
composed. 
If a sheet of glass is supported upon a cylinder of glass, and a 
pointed piece of brass touches it above, and another below, on 
making these the terminals of discharge from a Leyden battery, 
the sheet is perforated. 
Let two brass knobs be the terminals for an electric discharge 
in the interior of a glass tube an inch in diameter, and six inches 
long. The wires connected with the knobs must pass air-tight 
through the glass. Let a tube an eighth of an inch in diameter 
communicate with the lower part of the large tube, and be bent 
twice at right angles to it, so that its continuation is parallel to 
it. Water is then placed in the apparatus to such a height that 
the lower knob in the large tube projects above it. When sparks 
are passed between the knobs, the fluid in the small tubes is 
driven up, and the level immediately reestablished, showing 
that the movement is not due to heat but to impact of the spark. 
812. Physical Effects.—Ether, bisulphide of carbon, and a 
number of other liquids subjected to the passage of an electric 
spark are inflamed. Passed along a very fine wire the metal 
ma}7 be deflagrated, or driven off in vapor. Discharged upon 
gunpowder it is projected in all directions, but if delivered from 
a wet string the powder is ignited. The result in the latter case 
is owing to diminution in the velocity of the passage of the 
electricity. This principle has been applied to ignition of gun- 
powder for mining and engineering purposes; the apparatus 
is known as the electric fuse. Passed through sugar, eggs, 
various fruits, fluorspar, and heavy-spar, they become luminous 
in the dark. If sent through a wire wound around a glass tube 646 
ELECTEICITY. 
in which knitting needles are placed, the latter are magnetized; 
it will reverse the compass needle. 
If a person wearing dry shoes imitates the act of skating on 
the carpet of a house warmed hy a hot-air furnace, and then 
presents his knuckle to the escaping gas from a burner, it will 
be ignited. The use of a strong electric spark for instantaneous 
ignition of a great number of gas jets is well known. 
The luminous effect of the spark is owing to ignition of 
particles of matter in its course, or of an actual transportation 
of matter from one terminal to the other. If different metals 
are used as terminals, there will be a passage of metal of one 
knob to the other, which will in time show a well-marked 
covering. 
813. Chemical Effects.—Gases, such as oxygen and hydrogen, 
which act on each other, if mingled in proper proportion 
and submitted to the electric spark immediately combine. If 
either is in excess, it may require a number of sparks to secure 
complete union of the one deficient. Passed through moist air, 
its nitrogen and oxygen are forced to unite, especially in the 
presence of a solution of potassa, nitric acid being produced. 
Many compound gases, as ammonia, sulphuretted hydrogen, 
etc., are decomposed. Carbon dioxide is separated into oxygen 
and carbon monoxide. lodide of potassium is decomposed and 
its iodine freed, so that it will strike a blue color with solution 
of starch. Ordinary oxygen is converted into ozone, and a host 
of other examples might be cited. 
814 Physiological Effects on living beings, or on those recently 
deprived of life. In the first case, there is violent excitement 
the* result of action on the parts themselves, or on the nervous 
centres. In the second, muscular contractions imitating a res- 
toration to life. 
With large Leyden batteries small animals can be killed. 
Pats are killed with batteries of seven square feet of surface, 
and cats with one of five square yards of coated surface. 
Among the results of the action of powerful discharges are 
“ burns, superficial and deep, ecchymoses, stripping of the skin 
off the whole body, deafness, amaurosis, paralysis, lesions of 
the vascular system, transudations of liquids, and rapid putre- 
faction. Sometimes the hones are broken, the limbs torn and 
separated. In one instance the head of a man struck by light- 
ning was crushed as by a powerful blow. On the other hand, 
strokes of less intensity have cured old diseases. Among other 
singular effects are the more or less complete stripping off the 
clothing.” ATMOSPHERIC ELECTRICITY. 
647 
CHAPTER XLIY. 
ATMOSPHERIC ELECTRICIT 
Lightning identical with machine electricity—Electric state of atmosphere 
Variation in amount and character—Origin of atmospheric electricity 
Lightning—Thunder—Return shock—Lightning-rod-Aurora borealis. 
815, Lightning Identical with Machine Electricity.—For this dis- 
covery we are indebted to Franklin, who had made proposals to 
parties in France for the demonstration in question. While 
waiting for the erection of a steeple in Philadelphia, by which 
he proposed to prove the truth of his hypothesis, and fearing 
lest he might be anticipated, he determined to resort to the use 
of a kite whenever a promising thunderstorm appeared. 
For this purpose he armed the sticks of a kite with needles, 
and established electric communication between these and the 
hempen string by which it was raised. On a day when clouds 
indicated the approach of a storm he sallied out with his 
little son, to give color, as he to the expedition, and 
taking with him the kite, the front door key of his house, 
and a pair of cork balls connected by thread, they went to 
some adjacent fields. Here the kite was raised, and the string 
passed through the handle of the key, which served as a prime 
conductor. It was insulated by means of a silken cord. A 
promising cloud approached and he presented his knuckle to the 
key but failed to get a spark. After a few failures, and just as 
he was about to give up the experiment, a few drops of rain fell, 
and he remarked that the fibres of the string were repelling 
each other and standing out from it. Presenting his knuckle to 
the key he received a pretty sharp spark. Suspending the cork 
balls to the lower part of the key, they strongly repelled each 
other. Thus by exceedingly simple contrivances, Franklin 
demonstrated the identity of the spark of the machine with the 
lightning flash, and showed that the apparent difference be- 
tween them was only one of intensity and not of quality. 
816. Electric State of Atmosphere.—Electricity exists in the air 
not only in clouds, but a difference may always he found be- 
tween a given station and a point above it. Various methods 
have been resorted to for the demonstration of such electric dis- 
turbances. Among these we may mention the projection of a 
ball into the air, the discharge of arrows, kites, captive balloons, 648 
ELECTRICITY. 
the projection of an iron rod, which is, however, a dangerous 
plan and cost one experimenter his life. Finally, the appa- 
ratus of Sir W. Thomson, which consisted of a small tank of 
water placed on the sill of a window, from this an insulated 
tube projected into the air on the outside, and from it the water 
was allowed to drip slowly. These appliances served for the 
collection of atmospheric electricity, the means for examination 
were electroscopes, either straw, pith balls, or gold leaf. 
A gold-leaf electrometer with a rod four or five feet in length 
vertically projecting from it, will, in the open air, easily detect 
the difference in electric condition between the stratum in which 
it is placed and that reached by the point of the rod, Peltier used 
a gold-leaf electroscope on the top of which was a copper globe. 
Such an instrument raised a foot or two shows the variation in 
electric condition between the two strata. 
817. Variation in Amount and Character.—By means of the con- 
trivances mentioned in the last paragraph, the presence of free 
electricity in the atmosphere is invariable detected. When the 
air is perfectly clear it is always positive, varying in amount 
with the height of the locality and the time of day. It is not 
found in houses, streets, or under trees, but in the vicinity of 
bridges and docks, and other open spaces. On fiat land it is 
usually perceptible about five feet above the ground. 
At sunrise the charge is feeble, it increases up to 11 o’clock, 
it then decreases until just before sunset, and reaches a second 
maximum a few hours after the sun passes below the horizon. 
These variations follow closely upon those of the barometer, and 
the finer the weather the better they are marked. 
With a clouded sky the electricity is sometimes positive, 
sometimes negative. It often changes in this respect several 
times in the course of the day. 
818. Origin of Atmospheric Electricity.—Though our knowledge 
is not positive, it is generally conceded that it originates in the 
evaporation of water. An essential condition seems to be, that 
the water must contain a saline body in solution; that distilled 
does not show any disturbance in its evaporation. 
Becquerel considers that the earth is an immense reservoir 
of electricity. He has shown that when earth and water come 
in contact, it is produced, the former taking either positive or 
negative, and the latter the opposite. He made his examina- 
tions with platinum plates immersed in, different moist locali- 
ties, or in earth and in water, and connected with a multiplier. 
Evaporation from either source would carry the electricity of 
the region into the air, and thus account for its presence therein. 
Clouds are all electrified, some positively, some negatively. ATMOSPHERIC ELECTRICITY. 
649 
The positive condition is usually found in those formed from 
vapors set free from the ground and condensed in the upper 
regions of the air. Negative are thought to result from fogs 
which have obtained their charge from the earth. 
It is not at all improbable that the source of electricity of the 
air is the friction of solid and liquid particles against each other 
or against the earth as they are driven by wind. The strong 
electric excitement present when dry snow is driven by wind, 
strongly supports this theory of its origin. 
819. Lightning is the discharge of a charged cloud. In lower 
regions it is white, but in upper rarefied strata it is violet. The 
flashes are often between points several leagues apart, and gen- 
erally in a zigzag course. This is attributed to the resistance of 
air to its passage. 
Lightning is of different kinds. Ist. The zigzag or linear, 
which moves with exceeding velocity. 2d, Sheet, filling the 
entire horizon and without distinct shape; this is the more 
common form, and seems to envelop the cloud as though it were 
a brush-like discharge. 3d. Heat lightning is without the' appear- 
ance of clouds and without sound. This absence of noise is 
probably due to its great distance. 4th, Globe lightning, wherein 
the discharge takes the form of a globe of tire. The movement 
is comparatively slow, being often in view for ten seconds as it 
descends. It sometimes rebounds on reaching the ground, and 
often explodes with a deafening noise ; this form is rare. 
The course of the discharge is usually from the cloud to the 
earth. The latter by induction becomes charged with the op- 
posite electricity, when their tension exceeds the resistance of 
air the two combine, the spark passing. Ascending lightning 
is occasionally observed. In this case the clouds are probably 
electrified negatively, the earth then having a positive charge, 
it passes upwards, since the latter passes through air more 
readily than a negative charge. 
During a vicinity to trees, elevated buildings, 
and metallic masses should be avoided. Lightning discharge 
striking a sandy soil melts the silica and produces fulgurites or 
glassy tubes, often thirty to forty feet in length. 
820. Thunder is the report which follows a lightning discharge. 
The two are produced simultaneously, the time required by 
sound to travel through air makes the thunder seem to fol- 
low the lightning. The rate of movement is about 1100 feet 
per second, therefore, the distance of the flash can be easily 
calculated by observing the time between it and the peal. 
When lightning strikes near at hand, the thunder is one terrific 
deafening crash. At a distance it takes on a rolling character, 650 
ELECTRICITY. 
as the reports are heard in succession. If increased to fifteen 
miles, the discharge is no longer heard though the flash is seen. 
821. Return Shock is experienced by persons at a distance 
from the locality where lightning strikes. It is a result of in- 
duction. They are charged with induced electricity of the 
opposite sign to that of the cloud; when the latter is discharged 
induction ceases, and the persons reverting rapidly from the 
charged to a neutral state the return shock is the result. 
_ It ip less violent than the direct, yet many cases might be 
cited in which it has killed men and animals. 
822. The Lightning-rod was invented by Franklin, in 1755. It 
consists of a copper or iron rod, which passes the electricity 
from the ground to the excited cloud, uniting the two in a 
harmless manner. The essentials in a rod are: 
Ist. The terminal point must be perfect. 
To secure this, the points should be platinized or gilt to pro- 
tect them from the action of damp air. 
2d. Projection to a sufficient distance. 
The rod should project from six to ten feet above the ad- 
jacent parts of the building. It must also offer a perfect metallic 
communication from point to termination in the earth. Its sec- 
tion should be at least half an inch square, so it will not melt 
if lightning discharges upon it. 
3d. Connection with extended metallic surfaces. 
All metallic objects of any extent in the building must be 
connected with it, otherwise there is danger of lateral dis- 
charges. 
4th. Perfect communication with wet earth below. 
There should be the most complete communication between 
the rod and wet earth. It must never terminate under a veran- 
dah or piazza, but in the country it is better to lead it to a 
well, spring, or some other permanently wet spot. If no such 
place is near by, a hole six or seven yards deep may be dug, and 
the conductor divided into three or four strips and led into it, 
and the space filled with powdered coke. In the city it can 
communicate with the water pipes. 
823. Aurora-borealis, or northern lights, is an electric phenom- 
enon, sometimes of great beauty, seen at either pole. It consists 
of streamers or bars of light, which in the finest displays con- 
stitute a complete cupola. These are agitated by an undulatory 
movement, and from time to time exhibit great variations in 
brilliancy. Convergence of the streamers is to a point indicated 
by the northern end of the dipping needle in the northern hemi- 
sphere. Their color varies through red, green, and yellow. ATMOSPHERIC ELECTRICITY. 
651 
In north polar regions, 150 auroras were observed in 200 
days, nights without one were an exception to the rule. Their 
extent is sometimes wonderful, the same display having been 
observed at Moscow, Warsaw, Rome, and Cadiz. Their height 
is from 90 to 460 miles. 
Their action on the magnetic needle proves that they are due 
to electric currents in the higher regions!- They frequently 
interfere seriously with the working of telegraphs. Their spec- 
trum gives five lines in the green, a faint one in the blue, and 
a red; these are probably due to nitrogen. SECTION IX. 
DYNAMIC ELECTRICITY. 
CHAPTER XLY. 
THE VOLTAIC CELL. 
Electrodynamics defined—First observations—Yolta’s pile—Origin of voltaic 
electricity—The simple cell—The electric current—Electromotive force— 
Quantity and intensity—Bnfeeblement and local action. 
824. Electrodynamics Defined.—Machine electricity, which has 
thus far been the subject of our study, is electricity in the static 
state or condition of rest. It is that of tension. To under- 
stand more clearly its nature and the difference between it and 
the form we are about to examine, it is convenient that we re- 
gard it as a fluid according to the original hypothesis. As we 
study fluids first in their stationary condition under the science 
of hydrostatics, and afterwards in movement, as hydrodynamics, 
so with electricity, we may examine it first in the electrostatic, 
and then in the electrodynamic, or condition of movement. 
825. First Observations.—ln 1750 Sulzer observed, that if two 
metals were placed, one on the tongue and the other beneath it, 
when portions projecting from the mouth were touched to each 
other, a strong metallic taste was perceived. If one was placed 
upon the conjunctiva, and the other upon the tongue, and then 
brought together, a brilliant flash of light was seen. These 
results were attributed to a development of electricity. 
In 1770, Galvani made his famous experiment with frogs’ legs. 
At the time, he was studying the effect of atmospheric electricity 
upon these animals. For this purpose he had attached a pair of 
legs by a copper hook to an iron balcony. Each time that the 
wind pushed them against the iron violent contractions were 
produced. A further examination of the phenomena showed, 
that when communication was made between a nerve and a THE VOLTAIC CELL. 
653 
muscle by a single metal, contraction of the latter followed. If 
made by two metals, as zinc and copper twisted together at one 
end, and the other ends applied, one to the nerve, the other to 
the muscle, the contractions were more violent. Glalvani ex- 
plained the phenomena upon the hypothesis of two electricities, 
one in the muscle, the other in the nerve, and regarded the 
metal as acting the part of a discharging rod. 
Close upon this came the experiment of Volta, who believed 
that electricity was the result of contact between two metals. 
Though Volta was mistaken as regards its origin, his work was 
of great value, since it resulted in the production of Volta’s pile, 
which was the tirst electric battery. 
826. Volta’s Pile.—ln this the principle of an increase in in- 
tensity of the electric disturbance by an additional number of 
elements is recognized. The apparatus consists 
of several disks of zinc, cloth wet with sul- 
phuric acid, and copper. These are built up in 
a vertical pile, beginning at C, in the order zinc, 
cloth, copper, zinc, cloth, copper, the substances 
being laid on in that series until a pile of thirty 
to fifty sets is made. Wires are then attached, 
one to C at the lower end, and the other to Z at 
the upper. Through these the effects are trans- 
mitted ; they are called poles, polar wires, terminals 
and electrodes. In ordinary batteries that con- 
nected with the copper, or platinum element, is 
called the anode, positive, +, copper, or platinum 
Fig. 339- 
Voltaic pile. 
pole. That to the zinc, the cathode, negative, minus, —, or zinc 
pole. In the arrangement, Fig. 339, the terminal metals really act 
as collectors. Their character in this respect, therefore, is reversed. 
When the polar wires are brought in communication then 
separated, a minute spark is seen, which in all respects except 
that of size is a perfect counterpart of the machine spark. The 
snapping sound is also heard when contact is broken. If ex- 
amined by the gold-leaf electroscope the leaves are repelled. In 
all respects, therefore, this resembles the ordinary machine 
electricity, except in its tension, or the distance through which 
it can strike from one conductor or polar wire to another. 
Bodies which convey machine electricity well are good con- 
veyors of this form; those which conduct it poorly are likewise 
poor conductors for this variety. 
To electricity produced by Volta’s pile the name of Voltaic 
is given. Since Galvani had antedated him in his observations 
on its character his admirers called it Galvanic. It is also 
known as battery and primary. 654 
DYNAMIC ELECTRICITY. 
827. Origin of Voltaic Electricity is in chemical action gener- 
ally between a solid and fluid, in which the former is attacked 
or dissolved. It has been amply demonstrated by Becquerel, 
Faraday and many others, that when this is initiated, and while 
it lasts, there is development of electricity; when it ceases, the 
electricity ceases. Many experiments might be advanced in 
support of this hypothesis, among them we cite the following : 
Ist. Take a plate of pure zinc to which a polar wire is at- 
tached, also one of platinum with its polar wire. Plunge the 
two in a vessel containing dilute sulphuric acid (water 20, acid 1), 
keeping them at a distance from each other. While they con- 
tinue apart there is no chemical action on either. How let the 
polar wires touch, and it at once begins. The zinc slowly dis- 
solves, and hydrogen gas escapes from the surface of platinum. 
Separate them, an electric spark is seen, and at once all action 
ceases. 
The establishment of a communication between the two 
metals of a battery is called closing the circuit; the opposite act, 
breaking or opening it. 
2d. Solder two golden wires to the extremities of a conductor 
and plunge it into nitric acid, which does not act on gold: there 
is no electric action. How pour hydrochloric acid into the 
vessel: the gold is at once acted upon by the aqua regia, and a 
current is produced. 
828. The Simple Cell.—In the construction of galvanic bat- 
teries it is not easy to procure pure zinc. The ordinary zinc of 
Eig. 340. 
commerce is acted on by dilute sulphuric acid. 
This difficulty is surmounted by using that which 
has been amalgamated, or bears a coating of 
mercury. 
Amalgamation of zinc. Cleanse the surface thor- 
oughly with dilute sulphuric acid (one of acid to ten 
or fifteen of water). When perfectly clean pour 
mercury over it, this at once unites with it, and 
gives a clean, brilliant, metallic coating. If there 
are any spots which do not coat well, the action 
may be hastened by friction and fresh application 
of acid. Amalgamating fluids are recommended, 
but they evolve an irritating odor in their use. 
If the process we have described is properly man- 
Simple cell. 
aged, it can be accomplished very quickly. 
The zinc having been amalgamated, it is attached to a wire 
by means of an arrangement of binding screws, and set in a 
glass vessel that is to contain the fluid with which the cell is 
to be charged. A plate of copper the same size as the zinc, THE VOLTAIC CELL. 
655 
with a wire attached by a binding screw, is then placed in the 
cell. Dilute sulphuric acid (1 of acid to 15 or 20 of water) is 
poured into the vessel. 
While the circuit is not established there is no action, but when 
it is closed there is electric disturbance, the zinc being dissolved, 
and hydrogen escaping from the copper surface. At the first 
moment of closing the electric action is very strong, but it in- 
stantly falls very low, owing to formation of bubbles of hydrogen 
on the copper, which reduce enormously the extent of contact 
between that metal and the fluid, and cut down the chemical 
action in proportion. 
To avoid this reduction by gas formed on the copper various 
devices are resorted to, among them is the use of double fluid 
batteries. 
829. The Electric Current.—So long as chemical action con- 
tinues, and the circuit is closed, there is a continuous flow of 
electricity through the wire connecting the two metals. There- 
fore, it is called dynamic, in contradistinction to the static 
variety. The tension of this current is, moreover, exceedingly 
feeble, which is an essential difference between this and machine 
electricity. 
It is not necessary that one of the metals should not be acted 
upon at all by the liquid, only that one should be more sus- 
ceptible than the other. 
The metal upon which the action is most energetic is the 
generating plate, or metal of higher 'potential; the other the col- 
lecting, or plate of lower potential. Direction of the current 
is determined by the positive metal. The current commences 
on it, passes through the liquid to the negative plate, thence by 
the polar wire to the positive, completing the circuit. Its 
direction is always in relation to the positive electricity. 
Voltaic electricity arises whenever two metals are placed in 
a liquid which acts more, strongly on one than on the other. 
They have, therefore, been arranged in tables, which express 
their relations to each other in this respect. These are called 
electromotive series. The electropositive are at one end, the 
electronegative at the other, the intermediate being arranged 
according to their relative value. Any two of the following 
metals placed in dilute acid, the current will pass from the 
lower to the higher. Iron, for example, is electronegative to 
zinc and electropositive to silver. 
1. Zinc. 
2. Cadmium. 
3. Tin. 
4. Lead. 
5. Iron. 
6. Nickel. 
7. Bismuth. 
8. Antimony. 
9. Copper. 
10. Silver. 
11. Gold. 
12. Platinum. 
13. Graphite. 656 
DYNAMIC ELECTRICITY. 
830. Electromotive Force is that by virtue of which electric 
effects are produced in a circuit, consisting of a liquid and two 
metals acting unequally upon it. The electromotive force is 
greater in proportion as the metals are distant from each other 
in the series. Indeed, it is the sum of the electromotive forces 
between all the intervening metals. Condition of the metal 
influences it; rolled zinc is negative to cast zinc. Concentration 
of the liquid, and its nature also have their influence. 
The following table exhibits the effects of different solutions: 
Caustic potassium. 
Zinc. 
Tin. 
Cadmium. 
Antimony. 
Lead. 
Bismuth. 
Iron. 
Copper. 
Nickel. 
Silver. 
Hydrochloric acid. 
Zinc. 
Cadmium. 
Tin. 
Lead. 
Iron. 
Copper. 
Bismuth. 
Nickel. 
Silver. 
Antimony. 
Sulphide of potassium. 
Zinc. 
Copper. 
Cadmium. 
Tin. 
Silver. 
Antimony. 
Lead. 
Bismuth. 
Nickel. 
Iron. 
831. Quantity and Intensity.—The larger the size of the metal 
plates employed, the greater the quantity of electricity developed. 
In Hare’s deflagrator very extensive surfaces of copper and zinc 
were used, the action of which when they were suddenly im- 
mersed in acidulated water was so great, as instantly to dissipate 
polar wires of small diameter. Tension or intensity, on the 
other hand, depends upon the number of cells or cups in the 
circuit. The greater their number the more intense the tension, 
until with batteries of five hundred an electric arc of several 
inches length is obtained. For ordinary purposes fifty make a 
very serviceable battery. 
832. Enfeeblement and Local Action.—The principal causes of 
decrease in the action of a battery, are: Ist. Gradual neutrali- 
zation of the acid and its conversion into sulphate of zinc. 
This is remedied by addition of acid. 2d. Formation of small 
closed circuits on the zinc, whereby it is corroded without 
yielding anything to the current traversing the polar wires. 
This is called local action ; it is rectified by reamalgamating the 
zinc. 3d. Formation of a layer of hydrogen on the copper plate, 
reducing contact between the copper and liquid. This is called 
polarization of the plate. 4th. Hydrogen reacting on the zinc 
sulphate formed in the solution causes it to be precipitated 
upon the copper, hence, in place of having two metals with dif- 
ferent relations to the liquid, this lessens, and in extreme cases 
is entirely lost. sth. Production of inverse electromotive action, 
which either partially or entirely neutralizing the original cur- 
rent. BATTERIES AND THEIR PHYSICAL EFFECTS. 
657 
CHAPTER XLYI. 
BATTERIES AND THEIR PHYSICAL EFFECTS. 
Single fluid batteries—Double fluid batteries—Care of batteries—Measurements of 
electricity—Methods of coupling—Dry piles—Faure’s accumulator—The 
spark—The arc—lgnition effects—Deflagration. 
833. Single Fluid Batteries.— Oruikshank’s consists of a wooden 
trough separated into cells b}7 plates of copper and zinc soldered 
together. These are tilled with dilute sulphuric acid (1 of acid 
to 15 or 20 of water). By inclining the trough on one side, the 
fluid can be passed along the edge and the cells all filled to the 
same level, with least loss of time. Polar wires are then attached 
to the metals at the ends. 
Wollaston’s. Liquid, dilute sulphuric acid, is placed in sepa- 
rate jars. Each is provided with copper and zinc elements. 
These are double-coppered—that is, the copper is bent to be 
opposite both sides of the amalgamated zinc surface. The metals 
are then attached to a frame, so they can be simultaneously low- 
ered into the jars of acid. 
Smee’s. Liquid, dilute sulphuric acid. Metals, amalgamated 
zinc and platinum, or platinized silver, to favor escape of hy- 
drogen. 
Walker’s. Liquid, dilute sulphuric acid; elements, amalga- 
mated zinc and platinized carbon: is equal to the Smee, and 
cheaper. 
Simple cupric sulphate. Liquid, strong solution 
of cupric sulphate; metals, non-amalgamated zinc 
and copper. 
Grenet or bichromate. Liquid, electropoion, L, 
which consists of sulphuric acid and potassium 
bichromate, each one pound, water twenty pounds. 
Elements, amalgamated zinc, Z, and carbon, C. 
Fig. 341. The former should be raised out of the 
liquid by the button B, when not in use. This 
is the ordinary battery now supplied with small 
magnetoelectric coils for medical purposes. It 
has great electromotive force, and resistance is 
small. If air is blown through the cells, or if the 
fluid or elements are agitated, action is improved. 
Fig. 341. 
Grenet battery. 
Leclanche. Liquid, saturated solution of ammonium chloride 
Electropositive metal, amalgamated zinc. Electronegative ele 658 
DYNAMIC ELECTRICITY. 
ment, a porous cell occupied by a carbon plate, the remainder 
being tilled with oxide of manganese, in coarse powder, and 
small pieces of gas carbon. Works a long time, requires water 
to make up loss by evaporation. 
Colland’s gravity. Elements, a plate of copper, C, Fig. 342, 
connected to an insulated wire. This is placed in the bottom of 
ajar, and covered with crystals of cupric sul- 
phate. The jar is then filled with water, and 
the zinc element, Z, suspended therein. The 
zinc sulphate which forms floats on the sur- 
face of the cupric sulphate, S. Is very 
constant if loss by evaporation is replaced. 
Pulvermacher’s chain consists of small cyl- 
inders of wood on which zinc and copper 
wires are spirally coiled, each being in- 
sulated from its neighbor. It is thrown 
into action by dipping into acidulated water. 
Is not constant. 
Fig. 342. 
Colland’s gravity battery. 
834. Double Fluid Batteries.—Darnell’s. 
Elements, amalgamated zinc, Z, and copper, 
C. Fig. 343. A glass cell containing satu- 
O O 
rated cupric sulphate, S. Inside of the copper cylinder tits a 
porous cell containing sulphuric acid, A, and into this the zinc, 
Z, dips. Is very constant. Serves as a standard. 
Fig. 343. 
Fig. 844. 
Mendinger’s. Elements, amalgamated zinc and copper. Strong 
solution of magnesium sulphate containing the zinc, and crystals 
of cupric sulphate cover the copper. Ho porous cell, is a 
gravity battery and very constant. 
Grove’s. Elements, amalgamated zinc and platinum. Dilute 
sulphuric acid is placed in a glass cup, S, Fig. 344, in this the 
Daniell’s cell. 
Grove’s cell. BATTERIES AND THEIR PHYSICAL EFFECTS. 
659 
zinc, Z, is put; then a porous earthenware jar, IST, filled with 
nitric acid into which the platinum, P, of the next cell dips. 
Tyndall’s. Elements as in the last, and fluids the same. In 
place of glass, rectangular cups of rubber; the porous cells the 
same shape, and only half an inch wide. Has great power, and 
well adapted for lecture-room experiments. Packs into small 
space. 
Bunsen’s. Elements, amalgamated zinc and carbon. Vessels, 
a glass jar and porous cup. Liquids, dilute sulphuric and strong 
nitric acid. 
Bichromate. Same as Bunsen’s, but charged with electropoion 
in place of nitric acid. 
835. Care of Batteries.—ln those only used at considerable in- 
tervals, the porous cups must be well cleansed before they are 
put away. Soaking for two or three days in water, changed 
three or four times, suffices. If this is not done, they deteriorate 
very rapidly, and their usefulness is impaired. Forms in which 
carbon is employed should also be carefully cleaned, the carbon 
remaining in water for three days, and the latter repeatedly 
changed. By attending to the cleansing of a battery, it can be 
used for many years, otherwise it is soon destroyed. 
836. Measurements of Electricity.—The following table repre- 
sents the electromotive force of some of the ordinary batteries 
in use. The unit of comparison is a Danieli’s cell: 
Daniell’s element .... 
1.00 
Leclanche’s “ 
1.32 
Bunsen’s “ .... 
1.77 
Grove’s “ 
.... 1.82 
The greatest electromotive force was obtained by Beetz from 
elements consisting of potassium amalgam in caustic potash, 
with manganese dioxide in solution of potassium permanganate. 
It possessed three times the strength of the Daniell. 
The standard of electromotive force is the Volt, it is a little 
less than that of a Daniell’s cell, which may be taken as 1,12 Volt. 
The unit of current is a Weber, which is equal to an electro- 
motive force of one Volt working through an Ohm, the unit of 
resistance. 
The Ohm is the famous B. A, (.British Association) unit, and is 
represented by a column of mercury 104.81 centimetres long, 
one square millimetre in section, maintained at a temperature 
of 0° Cent. 
837. Methods of Coupling.—Cells may be coupled for quantity 
or intensity. Suppose a battery of 40 cups, and it is desired to 
get the largest quantity therefrom. All the zincs would be 660 
DYNAMIC ELECTRICITY. 
united for one pole, and the carbons for the opposite. The 
intensity would be that of a single cell, but the quantity equal 
to 40. Now, if required to obtain the greatest intensity, the 
cells would be coupled alternately; in a Grove battery it would 
be zinc, sulphuric acid, nitric acid, platinum; zinc, sulphuric 
acid, nitric acid, platinum, and so on for 40 variations. In this 
case the theoretical value of the result would be quantity 1, 
intensity 40. 
Again, a battery might be coupled in two series of twenty 
each, giving quantity 2, intensity 20; or four, giving quantity 4, 
intensity 10; or the opposite, viz., quantity 10, intensity 4. 
It is understood that full values are never obtained in prac- 
tice, resistance and other causes reducing them materially. 
838. Dry Piles.—ln these, paper replaces the liquid of a bat- 
tery. That of Zamboni consists of paper coated with tin on one 
side, and binoxide of manganese on the other, and cut into disks 
half an inch in diameter. One or two thousand are packed 
away in a glass tube with the tin of one always in contact with 
the manganese of the next. The tube has a knob and rod at 
each end, one of the latter has a screw thread cut on its surface, 
and is used to press the disks together. The manganese is the 
positive, the tin the negative, element. 
Dry piles sometimes retain their power for years, it is the 
result of slow oxidation of the metals. 
839. Faure’s Accumulator consists of two strips of sheet lead 
about seven inches wide and several feet in length. These are 
coated with red lead, covered with canton flannel, and bent 
backwards and forwards in contact with each other, and packed 
in a lead-lined box. They are close together, but there is no 
metallic contact between them, the canton flannel acting as the 
insulator. The box is charged with dilute sulphuric acid, and 
its polar terminations brought in connection with a dynamo- 
electric machine. After some hours of action the Faure’s cell 
is stored. If it is now separated from the dynamo, and its poles 
used in the same manner as those of any ordinary battery, it 
gives out its electricity gradually. 
Under the title of storage batteries or accumulators, the 
Faure’s cells are coming into general use for many purposes. 
840. The Spark,—Use a Grove battery of six cells, coupled 
alternately for intensity, with copper poles. 
The poles are touched, on separating them the voltaic spark 
is seen. It is a green color, owing to the presence of copper. 
If the current is weak from a smaller battery, the discharge 
is seen better by bringing one pole in communication with one BATTERIES AND THEIR PHYSICAL EFFECTS. 
end of a file, and drawing the other rapidly over its surface, a 
spark appears as contact is made and broken. 
Establish connection between mercury and one pole, with the 
other make and break contact, a spark appears each time of 
breakage. 
841. The Arc.—Use fifty cells of a Grove battery coupled for 
intensity. Between two terminals of carbon when touched 
light is produced which con- 
tinues when the poles are separ- 
ated for a short distance, de- 
pending on the strength of the 
battery. The continuous pas- 
sage of electricity between the 
carbons is called the arc. The 
light is exceedingly intense. If 
a gas flame intervenes between 
the arc and a screen, it casts a 
shadow thereon. The unbroken 
flow from one pole to the other 
demonstrates its dynamic char- 
acter. 
Fig. 345. 
Place the carbon terminals 
under water in a glass globe, 
and establish communication 
with the battery. At once the 
arc is seen, though somewhat 
diminished in brilliancy. 
Various contrivances, called 
regulators, are used to keep the 
distance between the carbon 
electrodes such that the current 
can bridge it over. The light 
consequently shows a wavering 
character, very trying to the 
eyes. By recent improvement 
in dynamo machines, electric 
lights of many thousands can- 
dles brilliancy are obtained. 
842. Ignition Effects.—Pass the 
current along a slender plati- 
num wire, it is immediately 
raised to a bright white heat, 
known as incandescence. If the current is sufficiently strong, 
it is fused. This is the principle involved in the Edison light. 
It requires much less intensity than the arc. It is, therefore, 
Arc between carbon points. 662 
DYNAMIC ELECTEICITY. 
less dangerous. As platinum undergoes a change by the pas- 
sage of the current, Edison prepares it by slow heating in 
vacuo. 
The carbon incandescent light consists of a U-shaped filament 
of carbon cut from a card and charred. It is enclosed in a small 
glass vessel which is vacuous. The passage of the current 
gives a very satisfactory light. The difficulty of obtaining ma- 
terial yielding a carbon perfectly homogeneous, has been sur- 
mounted by evaporating collodion in shallow vessels, passing the 
residue between steel rollers, cutting the product thus obtained 
in the proper form, and carbonizing it without access of air. 
843. Deflagration.—lf one of the poles of a battery consists of 
a cup-like cavity in gas carbon, and in this sodium or potassium 
is placed, on bringing a pointed pole to bear thereon, the metal 
is fused and volatilized. In this manner, the most refractory 
may be deflagrated or driven off in vapor. Gold is volatilized 
without difficulty, and metals held in the escaping vapor are 
gilded. 
Metals used as terminals are also volatilized in the arc of 
electricity which passes from pole to pole. If submitted to 
examination by the spectroscope, the lines characteristic of the 
spectrum of each are seen. By comparing these with the re- 
versed lines of the solar spectrum, the presence of the different 
metals in the atmosphere of the sun has been demonstrated. 
Magnetic effects produced by the voltaic current will be dis- 
cussed under the head of electromagnetism. 
CHAPTER XLYII. 
VOLTAIC DECOMPOSITIONS. 
Decomposition of water—The voltameter—Decomposition of cupric sulphate— 
Decomposition of sodium chloride—Electrochemical theory—Polarization of 
electrodes—Electrometallurgy—Electroplating. 
844. Decomposition of Water.—Two English chemists were 
attempting to determine the conducting power of various sub- 
stances. Among liquids the first they experimented with was 
water. They had enclosed it in a tube the ends closed by corks 
through which the polar wires of a battery passed. These could VOLTAIC DECOMPOSITIONS 
663 
be approached nearer to, or drawn further 
from each other. The wires were of copper, 
and they expected to determine the effect of 
intervening; columns of various lengths of 
O O 
liquid between the polar terminations. The 
apparatus being in order, and connections 
made with the battery, they found to their 
surprise that at one pole gas was evolved, 
while at the other a pale blue material grad- 
ually accumulated in the lower part of the 
tube. Various explanations were given of 
the phenomena, at last its true nature was 
revealed by analysis. The blue material 
proved to be hydrated oxide of copper. 
They had, therefore, decomposed water, 
which up to that time was supposed an ele- 
mentary body, and had separated it into hy- 
drogen and oxygen; the former was set free 
in the gaseous state while the latter with the 
copper had formed a hydrate of copper. 
Improvements in the apparatus soon 
substantiated the truth of this explanation, 
for bending a tube into a U form, and allow- 
ing the battery to terminate in platinum 
poles, + and —, Fig. 346, which are not acted 
on by water, one in each arm, gas was evolved 
Pig. 346 
Decomposition of water, 
from both poles. At one hydrogen, at the other pure oxygen. 
The quantities, moreover, bore a definite relation to each other. 
There was always twice as much of the former as the latter. 
It was, therefore, demonstrated that water is a compound body, 
formed of hydrogen and oxygen, in the proportion expressed by 
the formula H2O. 
845. The Voltameter.—Previous to the discovery of the com- 
pound character of water, many futile attempts had been made 
to test the value of electric currents, but no reliable method had 
been devised. The decomposition of water by strong currents 
of electricity was soon advanced as giving a satisfactory means 
of determining the value of such currents. The apparatus was 
called the Voltameter. It consisted of a tube graduated to 
cubic centimetres, or to cubic inches and fractions. Platinum 
or gold terminals of a battery passed through the bottom of 
a cup, and were arranged face to face in its interior, a moderate 
distance intervening between them. On establishing communi- 
cation with a battery, gas was evolved from the terminals, and 
the time required to collect a given quantity of the mixed gases 
represented the power of the battery. This method still con- 
stitutes one means for obtaining the value of strong currents. 664 
DYNAMIC ELECTRICITY. 
846. Decomposition of Cupric Sulphate.—Let the polar wires of 
a battery terminate in a strong solution of sulphate of copper. 
The cathode a conducting surface of any kind, the back and 
sides coated with any non-conducting material, as wax. The 
anode a plate of copper. A current of suitable strength from 
a small Smee battery is then passed through the liquid. After 
a time the cathode is removed, when it will be found coated 
over with metallic copper, if the strength of the battery has 
been properly adjusted. The action of the current has been to 
cause a deposit of copper on the cathode. As fast as this takes 
place the sulphuric acid disengaged upon the anode attacks 
it, and restores the metal to the solution. This conveyance of 
copper from anode to cathode continues as long as the former 
lasts or the battery retains sufficient power. 
847. Decomposition of Sodium Chloride.—Take a vessel shaped 
like the chimney of a kerosene lamp, A, Fig. 347. Close the 
Pig. 347. 
lower mouth with a layer of goldbeater’s 
skin, tying it on firmly. Prepare a tolerably 
strong solution of sodium chloride, add to it 
sufficient red litmus water to give it a strong 
tint. Pour half into the vessel, let it rest in 
a goblet, B, and pour the other half into this. 
Pass into the former the platinum terminal 
of the cathode: into the latter plunge the 
anode. Make connection with the battery. 
Gas bubbles appear at both poles, but the 
liquids are prevented from intermingling by 
the intervening septum of goldbeater’s skin. 
At the cathode sodium is set free, which in- 
stantly attacking the becomes con- 
verted into sodium oxide, and its alkaline 
reaction is exhibited by turning the red litmus 
blue. At the anode chlorine is evolved, as 
Sodium chloride decomposed. 
shown by bleaching of the litmus. The sodium chloride has, 
therefore, undergone decomposition, the sodium appearing at 
the cathode, and the chlorine at the anode. 
848. Electrochemical Theory.—A number of illustrations of 
this, so-called, sliding decomposition might be given. We may, 
however, sum up the results in a table, as follows: 
To anode or -f pole. 
To cathode or — pole. 
Oxygen, 
Hydrogen. 
Chlorine, bromine, etc. 
Metals. 
Acids. 
Bases. 
Electronegatives. 
Electropositives. VOLTAIC DECOMPOSITIONS. 
665 
The bodies attracted by the anode or positive pole are electro- 
negatives. Those attracted to the cathode or negative pole are 
electropositives. It is understood that the terms electronega- 
tive and electropositive are relative, and refer to the relation 
of the two substances under the conditions which they are sub- 
mitted to examination. 
To this decomposition by electric action the name of electro- 
lysis is given. The bodies subjected to the action of the current 
are called electrolytes. The substance which appears at the 
cathode is called the katione, that at the anode the anione. 
849. Polarization of Electrodes.—Let a current pass from pla- 
tinum electrodes through water for a time. Interrupt it, and 
connect the electrodes with a galvanometer. They will be 
found to give a tolerably strong flow of electricity which passes 
in the opposite direction to that of the battery. The explana- 
tion lies in the fact, that oxygen has been condensed on the 
anode, and hydrogen on the cathode. The effect of this is to 
produce a current opposed in its action to the original. 
On this principle batteries of one element may be con- 
structed, consisting of platinum poles separated by moistened 
cloth. These are connected with a battery and charged. They 
are then separated, and being attached to a galvanometer, give 
a current in the opposite direction to the original. They are 
called secondary batteries. Plante’s battery, which was the 
original of Faure’s accumulator, is of this description. 
850. Electrometallurgy, or galvanoplastics, is the application 
of voltaic electricity to copying medals, type, and other objects. 
The operation consists first, in securing an accurate mould of 
the object, upon which copper or some other metal can be 
deposited by an electric current. Various methods are resorted 
to for making the cast. One consists in softening gutta-percha 
in water, pressing it against the object, and, when cold, detach- 
ing it. The process usually employed is that followed in electro- 
typing. A mixture of wax, tallow, and turpentine, of proper 
proportions, is melted and poured into shallow pans. When 
set, it is brushed over with finely powdered graphite. While 
still soft the form of type is pressed on its surface, and an 
accurate copy obtained. This is suspended from the negative 
pole of a battery in a solution of copper, a plate of the same 
metal being attached to the positive pole, when a deposit forms 
on the cast. 
The batteries employed are usually either Daniell’s or Smee’s. 
Currents from magnetoelectric machines of special construction 
are used when a large amount of work is to be done. 
In all such operations a number of conditions govern the 666 
DYNAMIC ELECTRICITY. 
character of the deposit. Among them, the power of the 
current of the battery, the strength of the solution used for 
electrotyping, and its temperature. If the conditions are cor- 
rect, a tenacious, flexible metallic, or reguline, deposit is ob- 
tained. If the current is too strong, the deposit becomes pul- 
verulent and black; if too weak, it is brittle and crystalline. 
The object of the electrometallurgist is to adjust them to obtain 
the reguline deposit. 
The application of this principle to the preparation of forms 
for printing, makes the issuing of enormous editions of the 
great daily papers possible in the few hours available for that 
purpose. The type is set and corrected, a number of impres- 
sions of these forms in wax are then taken, they are electro- 
plated. The electroplates, each a perfect copy of the original, 
are separated from the wax, and melted metal poured into them. 
All are reduced to a uniform thickness, and mounted in a 
printing machine. Thus, in place of printing from a single 
form, ten, fifty, or even a hundred sets of copies of the original 
are all doing work at the same time. 
851. Electroplating differs from the preceding in that it is an 
exceedingly thin deposit of gold, silver, iron, nickel, or other 
metal on the surface of some composition or alloy. The prepa- 
ration of the objects is usually by two stages: Ist. The fatty 
matter, with which their surfaces are covered, is destroyed by 
heat. 2d. The oxide formed in the preceding operation is 
removed by immersion while still hot in very dilute nitric'acid. 
They are then rubbed with a hard brush in pure water, dried 
in hot sawdust, and attached to the negative pole of a battery, 
the positive bearing a plate of gold in the solution. 
There is considerable variety in the composition of the solu- 
tions or electrobaths for gilding. The ordinary one is: 
Auric chloride ..... 
I part. 
Potassium cyanide .... 
10 parts. 
Water ...... 
. 200 “ 
In electrosilvering the composition of the bath is as follows: 
Argentic cyanide .... 
2 parts. 
Potassium cyanide .... 
2 “ 
Water 
. 250 “ 
A plate of silver or gold is suspended from the positive elec- 
trode, the properly cleansed articles from the negative. 
The bath for deposition of iron is prepared by attaching a 
large sheet of iron to the positive pole in a vessel filled with 
saturated solution of ammonium chloride. A small strip of 
iron is attached to the negative pole. The current being THERMOELECTRICITY. 
667 
passed, it is dissolved, while hydrogen escapes from the small 
negative element. When the bath is changed an engraved plate 
of copper may be substituted for the small strip of iron, a 
bright deposit forms 'at once, the plate taking on the appearance 
of polished steel. The process is called steeling the acierage. In 
the course of half an hour it is sufficiently thick, and of ex- 
ceeding hardness, an immense number of impressions can be 
struck off. 
The bath for nickel is prepared in the same manner, or by 
directly mixing salts of ammonia and nickel, either chloride 
or sulphate of the metal with chloride of ammonium. The 
deposit tends to form irregularly and strip off. This is coun- 
teracted by repeatedly removing it, repolishing it, and return- 
ing it. 
Aickelplating is now extensively resorted to for coating sur- 
faces of all kinds of surgical and obstetrical instruments and 
apparatus. It resists ordinary corrosives, and air has no action 
upon it. 
CHAPTER XLYIII. 
THERMOELECTRICITY. 
Heat in obstructed conductors—Thermoelectric batteries—Thermoelectric series— 
Other batteries. 
852. Heat in Obstructed Conductors.—Wrhen a current of elec- 
tricity is passed along a conductor of too small a section to 
permit its free transit, the temperature of the latter rises, and it 
may fuse though composed of the most refractory metal. The 
converse of this is also true: if we warm a conductor along which 
heat fails to pass freely, by virtue of a strain upon its molecules, 
electricity is developed which is readily detected by a galvano- 
meter. 
In illustration, take a copper wire and tie a knot in it, to 
strain or put tension upon its molecules. Connect its ends 
with the pole of a galvanometer, then apply a spirit flame near 
the knot. The torsion of the wire affords an obstacle to the 
passage of heat, and the needle of the galvanometer shows an 
instantaneous movement from the electricity developed. To 
this the name of thermoelectricity is given. 668 
DYNAMIC ELECTRICITY. 
853, Thermoelectric Batteries. While only a single metal 
may be forced to show thermoelectric properties, the pheno- 
mena are much better developed where two are used. Take, 
for example, a small bar of antimony, A, and one of bismuth, 
B, solder them together as in Fig. 348. To the free extremi- 
ties connect polar wires, by which the apparatus may be attached 
to the galvanometer. Connect it and apply cold to the junction 
of the two metals, the needle at once shows the production of 
Fig. 348. 
Thermopile, 
a current. Apply heat thereto, and the swing of the needle 
is reversed, showing that direction of the current is changed. 
A number of such elements, of antimony and bismuth 
soldered together at their alternate ends, the order of alterna- 
tion being carefully preserved, and the bars being insulated 
elsewhere, constitutes a thermoelectric battery. The number 
of pairs increases the intensity of the current. The ordinary 
number is forty-nine, arranged in seven rows of seven. This 
gives an end-section about an inch square, C, and is known as 
Aobili’s thermoelectric pile. In connection with a galvanometer 
it forms the thermoelectric multiplier of Melloni, which is one 
of our most delicate instruments for measurement' of tempera- 
ture. 
854. Thermoelectric Series.—After many experiments, the 
thermoelectric relations of various substances to each other 
were carefully determined, and are set forth in the following table. 
The value of any pair may be found by subtracting the figures THERMOELECTRICITY. 
669 
from each other, if they have the same sign, or adding them if 
the signs are different: 
Bismuth . 
. +25 
Gas coke . 
. —0.1 
Cobalt 
9 
Zinc . 
0.2 
Potassium 
5.5 
Cadmium . 
0.3 
Nickel . 
6 
Strontium . 
2.0 
Sodium . 
3 
Arsenic 
3.8 
Lead 
1.03 
Iron . 
5.2 
Tin 
1 
Bed phosphorus 
9.6 
Copper . 
1 
Antimony . 
9.8 
Platinum 
0.7 
Tellurium . 
. 179.9 
Silver 
1.0 
Selenium . 
. 290.0 
Compared with hydroelectric currents, these are quite feeble. 
The electromotive force of a bismuth copper element with a 
difference of 100° C. in the temperature of their junctions, is, 
according to one authority -g and to another that °f a 
Daniell’s element. 
855. Other Batteries.—Becquerel discovered that artificial sul- 
phide of copper combined with copper had an electromotive 
force nearly ten times as great as that of a bismuth copper pair. 
Since this sulphide only melts at over 1000°, very high tempera- 
tures may be employed. 
Clamond’s battery has been applied to telegraphing and 
plating. The negative metal is an alloy of two parts antimony, 
and one zinc. The positive a thin strip of tinplate. Heating 
is effected by a Bunsen flame, so applied that only the hot air 
from it touches the elements. The temperature should not rise 
above 200°. SECTION X. 
MAGNETISM. 
CHAPTER XLIX. 
HISTORY. LAWS. DISTRIBUTION. 
Natural magnets—Artificial magnets—Compound magnets—Polarity law of at- 
traction and repulsion—Magnetic distribution—Magnetic metals—Magnetic 
induction. 
856. Natural Magnets were known in Europe more than 2000 
years ago. The Chinese have used them since 600 B, C. They 
were portions of lodestone, native oxide of iron, having the com- 
position Fe304. It was first found at Magnesia, in Asia Minor. 
A small portion freely suspended by a thread, sets itself with its 
long axis north and south. It is, as a rule, very free from admix- 
ture with other minerals, and when smelted yields a remarkably 
pure iron. 
While we mark the north end, the Chinese mark the south 
end. They used magnets as iron needles to guide them across 
the deserts of Asia. In French works the end pointing north 
is called the austral or southern pole; that south the boreal or 
northern pole. The English call that which points to the north, 
the north pole; to the south, the south pole. 
The awkward form of most native magnets makes them less 
advantageous for illustrating their properties than those which 
are artificial. We shall, therefore, pass at once to a description 
of the latter, and it is understood that their use is always im- 
plied unless otherwise stated. 
857. Artificial Magnets are either straight or horseshoe shaped 
bars of steel, which have been rubbed on natural or electro- 
magnets. If freely suspended, they point FT. and S, 
If placed in wrought-iron filings, Fig. 349, these arrange them- HISTORY. LAWS. DISTRIBUTION. 
671 
selves in curved lines about both ends, 17 S, and not at all about 
the central regions, E. Hence, the two extremities are called the 
poles, and the central portions the 
neutral line. Sometimes a magnet 
will show intermediate poles be- 
tween the true terminal ones. Such 
are abnormal. 
Fig. 349. 
The shortest line joining the two 
poles is called the axis of the mag- 
net. The plane at right angles to 
this, and passing through the neutral 
line, is called the equator. 
In a horseshoe magnet, Eig. 849, 
the axis is in the line of its keeper, K, 
or small piece of soft iron, in contact 
with the poles H S. The keeper 
should always remain in contact 
with the poles, as it reacts upon 
them, and enables the instrument 
to preserve its properties. 
As a rule, the north pole is marked 
H., and the south S. In some the 
former is colored red, the latter 
Straight and horseshoe magnet. 
blue; hence, the use of the terms red and blue magnetism, as 
equivalent for north and south. 
858. Compound Magnets.—ln place of making a magnet of 
a single piece, it is found that better effects are gained by 
combining a number of thin sheets of steel, Fig. 
350, A, magnetizing each, and then binding them 
together by screws. For a given weight of metal 
a more powerful action is obtained. 
This form, constructed as a horseshoe, is gener- 
ally employed in various magnetoelectric instru- 
ments. From the nearness of its poles it gives a 
stronger result, and presents the advantage of 
the preservation of its power by the keeper B. 
Fig. 350. 
859. Polarity Law of Attraction and Repulsion.— 
It has been seen in the preceding article that soft 
iron tilings are attracted by the magnet. If, for 
Compound magnet. 
these, a small bar of soft iron is substituted, and presented to a 
freely suspended magnet, it will attract it equally by either 
extremity. If in place of the soft iron bar we use a magnetized 
steel one, its north pole will be found to attract the south pole 
needle, and repel its north pole. 
Hence, we deduce the following law of the action of magnetic 672 
• MAGNETISM. 
poles on each other. Attention is directed to its similarity to 
the law of electric attractions and repulsions : Unlike 'poles attract; 
like repel. 
The intervention of a sheet of glass between the bar of steel 
and the suspended needle in no way interferes with these move- 
ments. The magnetic influence, therefore, passes freely through glass. 
860, Magnetic Distribution—The magnetic influence in a steel 
bar is not confined to the extremities, but is distributed through- 
out. In evidence of this fact, let it be broken at the middle. 
Examination will show that each fragment is a true magnet 
endowed with perfect polarity, Freely suspended it points 'N. 
and S., one end attracts the north pole of a magnetic needle, 
the other repels it. 
Break it again and again with the same result. We, there- 
fore, conclude that the magnetic influence is distributed through- 
out the bar, and the neutral line, as it is called, is merely that 
portion in which the magnetisms neutralize each other. Ac- 
cording to theory, every molecule shows polarity. The distribution 
may, therefore, be examined either in respect to the molecules, 
or to the whole bar as a system. 
From the latter point of view, the poles are not at the ex- 
treme ends, but at a small distance within. They are not per- 
manent, but change in position slightly whenever its condition 
is disturbed by the approach of a magnetic substance. 
This is the principle upon which the telephone is founded. 
861. Magnetic Metals.—These are iron, cobalt, and nickel. All 
bodies under the influence of exceedingly powerful magnets 
yield to their influence, but these, with magnetism of the ordi- 
nary intensity, exhibit magnetic properties—that is, are at- 
tracted, or show polarity. 
A distinction is made between magnetic substances and mag- 
nets. The former attract either end of a suspended magnetic 
needle. The latter exhibit polar attractions and repulsions 
when brought in its vicinity and also of each other. Soft or 
wrought iron is an example of the former, a magnetized steel 
wire of the latter. 
Many compounds of iron are magnetic bodies; some, how- 
ever, are notable exceptions. The mineral limonite, an hy- 
drated oxide of iron, does not show the property unless intensely 
heated on charcoal. Persulphide of iron is also non-magnetic 
until heated. 
862. Magnetic Induction.—Bring a small cylinder of soft iron 
in contact with a bar magnet. It is attracted, and if in com- METHODS OF MAGNETIZING. 
673 
munication with its north pole the end nearest to it takes on 
the opposite magnetic state, the further end becoming north. 
Thus bar after bar of soft iron may be attached until the limit 
of its power is reached, Fig. 351. Each piece shows polarity at 
Fig. 851. 
Magnetic induction. 
its extremities. The near end is south magnetism, the further 
north. Separate the bars, and remove them from the influence of 
the magnet. At once all polarity is lost. They become inert, 
their magnetism was temporary. 
CHAPTER L. 
METHODS OF MAGNETIZING. TEEEESTEIAL MAGNETISM. 
Magnetizing by single touch—Magnetizing by separate touch—Magnetizing by 
double touch—Magnetizing by the earth’s action—The power of magnets— 
Mayer’s floating magnets—Medical application of magnets—The earth’s action 
directive—Declination—The compass—Astatic needle—Dipping needle. 
863. Magnetizing by Single Touch,—ln this method one pole of 
a powerful magnet is passed from end to end over the bar. The 
operation is repeated a number of times. Its neutral condition 674 
MAGNETISM. 
is thus decomposed throughout. The end last touched has the 
opposite polarity. .For this operation, natural or artificial mag- 
nets and electromagnets are used. The disadvantage is that 
consequent or intermediate poles may be developed, and the 
power is not very strong. 
864. Magnetizing by Separate Touch consists in taking two com- 
pound magnets of equal power, A B, Fig, 352, and placing their 
opposite poles upon the centre of the bar to be magnetized. 
They are then moved to the opposite ends, a b, at the same time 
and with the same rate. They are then returned to the centre, 
Fig. 352. 
Magnetizing steel bars. 
and drawn to its opposite ends again. This operation is repeated 
a number of times, on both faces, until it is fully charged. The 
magnets by some are held vertically: by others, at an angle of 
twenty or twenty-five degrees. The method gives very regular 
results. 
864 A. Magnetizing by Double Touch,—The two magnets are 
placed on the centre of the bar with their opposite poles nearly 
touching, a small piece of wood between them. They are then 
moved simultaneously to one end, then to the opposite. This is 
repeated a number of times, each half receiving the same num- 
ber of movements over its surface. 
The process may be improved in this and the preceding 
method by supporting the ends, a b, upon powerful magnets, 
A B, the pole on either side being of the same name as the 
movable magnet of that side. A horseshoe shape with close 
poles may be substituted for the movable pair. This is apt to 
develop consequent poles. The magnetism is very strong. 
865. Magnetizing by the Earth’s Action.—When a bar of soft 
or wrought iron is held in the magnetic meridian parallel to the 
inclination, it becomes immediately a temporary magnet, the 
lower being the north pole for our vicinity. Reversing it, the 
opposite end becomes the north pole. If, while held in the 
proper position, a few blows are struck with a hammer, it 
retains its magnetism for a short time. If it is twisted, only a 
feeble charge is developed. METHODS OF MAGNETIZING. 
675 
Various articles of iron, both wrought and cast, if kept per- 
manently in this position, acquire a certain amount of magnet- 
ism, the north pole always being downwards. 
866. The Power of Magnets.—A magnet which has received 
its full development of force is said to be saturated. Among the 
causes which produce variation in strength, is tempering of the 
steel employed. A bar tempered at dull redness, and magnetized 
to saturation, made ten oscillations in ninety-three seconds. 
The same bar at a cherry red, took only sixty-three seconds to 
make ten oscillations. It, therefore, follows that the harder the 
steel the greater its coercive force. It is more difficult to mag- 
netize, but it retains the charge better. The property of a 
magnet is also dependent upon the percentage of carbon con- 
tained in the steel. This also causes a variation in the degree of 
heat at which it should be tempered. Compass needles are 
generally tempered at a blue, which is about 300° C. 
Increase of heat diminishes intensity of magnetism in a bar; 
heated to a bright red it completely loses it, and it is not regained 
with return to original temperature. 
Hammering a steel bar while being magnetized increases its 
power. If, on the contrary, a magnet is allowed to fall, or struck 
a strong blow, it is in part demagnetized. 
867. Mayer’s Floating Magnets consist of magnetized steel 
needles, the points being north, and the eyes south poles. 
Fig. 353. 
Mayer’s floating magnets. 
These are passed through cork disks with the eyes just pro- 
jecting. When placed on water they float, the needles being in 
the vertical position. 676 
MAGNETISM. 
If a strong magnet is brought in the vicinity of several of 
these needles floating on water, they immediately arrange them- 
selves in figures, which vary according to their number. Two 
form a line; three a triangle; four a square; five a pentagon, 
or a square with one in the centre; six a pentagon with one in 
the centre, or a triangle with curved sides, and so on. Through 
8 a, b, c, 18 a and b, a shock will often cause one figure to pass 
into another more stable. 
868. Medical Application of Magnets.—When the cornea has 
been wounded by minute particles of iron driven into its sub- 
stance with considerable force, they are sometimes extracted 
with a magnet. There does not appear to be any evidence that 
they possess medicinal or other influence on the human body. 
869. The Earth’s Action Directive.—From observations made 
in various regions of the earth, it has been likened to an im- 
mense magnet, the poles not far from the terrestrial poles. The 
influence which it exerts upon the magnetic needle is directive 
only, it neither attracts nor repels it. 
If a bar of steel is weighed before and after magnetization, 
there is no change. Therefore, the vertical component is zero. 
If suspended by a long fine thread, the course of the latter is 
vertical. If then magnetized, the thread remains the same. 
The horizontal component is, therefore, zero. Floated on a 
cork on water, the needle oscillates for a time, and finally sets 
itself FT. and S., but does not move in a north direction. On the 
approach of a magnet, the needle moves toward it, but in the 
case of the earth it is equally attracted by both poles practically 
at an infinite distance; neither can exert greater power than the 
other, consequently it is not attracted, but merely sets itself in 
relation to their directive action. 
870. Declination is the angle which the axis of a magnetic 
needle makes with the geographical meridian of a place. It is 
said to be east or west, according as its north pole is east or west 
of this meridian. 
At present the declination is to the west in Europe and Africa, 
but to the east in Asia and North and South America. It shows 
variations either annual or diurnal, regular or irregular—the 
latter are called magnetic storms. 
At London, in 1580, the declination was to the east 11° 36', 
in 1663 it was at zero. Since then it has gradually moved to 
the west, reaching the maximum of 24° 4F in 1818; thence 
slowly worked its way eastward, and in 1879 was at 18° 40' west. 
871. The Compass is a declination needle used in navigating 
ships. It consists of a case mounted AB, to keep the compass METHODS OF MAGNETIZING. 
677 
in a horizontal position in spite of the ship’s movements. From 
the bottom of the box a vertical axis rises, terminating above in 
a point which works in an agate cup attached to the centre of 
the needle, K. To the latter a disk of mica is attached, on 
which a star with thirty-two branches is traced. This gives the 
Fig. 354. 
Compass. 
eight points with halves and quarters. The ray marked with 
the small star and the letter IST indicates the position of the 
north pole of the needle under the mica. 
872. Astatic Needle.—This is a combination of two needles of 
the same strength, joined parallel to each other with their poles 
in opposite directions. A combination in this state is free to 
obey any other force, and is used in constructing a galvano- 
meter. 
meter, 
Fig. 356. 
Fig. 355. 
Astatic combination 
Dipping needle. 
873. Dipping Needle, also called the inclination compass. It 
moves in a vertical instead of horizontal plane. When this 
coincides with the magnetic meridian, the angle which it makes 678 
MAGNETISM. 
with the horizon is called the dip or inclination. This differs in 
various parts of the earth. At the equator it is zero, the needle 
being horizontal, passing from the equator northward it in- 
creases, its north pole inclining downwards, until at the pole it is 
vertical. Passing southwards from the equator, its south pole 
dips downwards, until at that pole it is vertical. 
The magnetic equator is the line which joins all places where 
there is no dip; it is sinuous, and inclined to the terrestrial at 
an angle of about twelve degrees. 
CHAPTEE LI. 
ELECTROMAGNETISM. 
Oersted’s experiments Galvanometers Rheostats The long compensator 
Wheatstone’s bridge Electromagnets Electromagnetic motors Cost of 
magnetic motors—Electric hells and clocks—The Morse telegraph—The needle 
telegraph—Reactions of currents upon currents and magnets—Solenoids— 
Why the compass needle points north—Paramagnetism Diamagnetism 
Diamagnetic illustrations—Action of magnet on polarized light. 
874. Oersted’s Experiments.—lt had long been known that when 
buildings were struck by lightning, all small objects of steel or 
Eig. 357. 
cast-iron contained therein showed more 
or less of a magnetic property. In 1819, 
Oersted, a Danish philosopher, submitted 
these phenomena to examination, and 
found, that if the wire in which a voltaic 
current is passing is placed over a freely 
suspended magnetic needle in the same 
vertical plane, the latter is instantly de- 
flected, and sets itself at right angles to 
the current, its north pole, we will sup- 
pose, being turned to the east. If it 
is then placed beneath the needle in the 
same vertical plane, the current still pass- 
Oersted’s experiments. 
ing in the same direction, it is also deflected, but now the 
north pole turns to the west. 
If in place of using a straight wire, it is bent in the form of a 
rectangle, and placed in the same vertical plane as the needle, 
and surrounds it, when a current is sent through the conductor, 
in traversing the lower limb its direction is the reverse of what ELECTROMAGNETISM. 
679 
it is in the upper. The action of the former, therefore, assists 
that of the latter, and the influence over the needle is increased. 
The stronger the current of voltaic electricity, the greater its 
effect. The nearer it is to the needle the greater the power it 
possesses over it. 
By Oersted’s discovery the intimate relationship between elec- 
tricity and magnetism was established. This finally resulted in 
giving satisfactory explanations of the source of the latter, and 
why the compass points to the north. 
875. Galvanometers.—lf in place of passing the current around 
the needle once, we cause it to pass twenty or a hundred times, 
A, Fig. 358, its influence is increased, 
though not in the same proportion. This is 
the principle involved in the galvanometer, 
multiplier, or rheometre. 
The delicacy of a galvanometer depends 
upon the facility with which its needle will 
turn. This is greater as the directive force 
of the earth upon it is diminished. There- 
fore, two with their poles reversed as in the 
astatic system are used. The directive force 
of the earth’s magnetism is thus reduced to a 
very low point, and a feeble current will 
produce movement. The insulated wire is 
passed a number of times, A, around the 
Fig. 358. 
The galvanometer. 
lower needle of the system; it is usually wound around a flat 
spool of bone or ivory, with the lower needle in the interior 
and the upper above it. A current passed through this arrange- 
ment affects the former powerfully, and provides a very delicate 
instrument for the detection, not only of the presence of electric 
disturbance but its direction. The latter is varied by means of 
the commutator, which, by the turning of a button, changes the 
connections and consequently the course of the current. 
Galvanometers are constructed either for measuring intensity 
or quantity. In the first case the current having considerable 
tension, the number of turns may be hundreds or thousands 
(that of Du Bois-Beymond made 27,000 turns), and the wire ex- 
ceedingly fine. In the other, the wire must have a much greater 
diameter to give the least possible resistance, and make only a 
few turns around the needle. If beyond fifteen or twenty, the 
influence of the current on the needle is diminished. 
The wire must be absolutely pure, and free from every trace 
of iron, otherwise it will interfere with the action of the current. 
The insulating material must be white silk, not green, as the 
latter contains iron. 
The needles are suspended by a filament of silk, and the 680 
MAGNETISM. 
whole arrangement protected from dust and currents in the air 
by a glass shade. 
The combination of a galvanometer with a thermoelectric pile con- 
stitutes a very delicate means of measuring minute changes in 
temperature (853). 
A shunt, by which the amount of current passing through is 
regulated, is usually supplied with each instrument. 
In Thomson’s galvanometer the needles are very small, and con- 
nected by a wire of aluminium astatically. This bears a slightly 
concave mirror about a quarter inch in diameter, needles and 
mirror weighing about one grain. The scale is placed hori- 
zontally about two or three feet distant. A slit below it, illu- 
minated by a lamp, allows a narrow beam of light to fall upon 
the galvanometer mirror which reflects it back upon the scale, 
and thus gives accurate indications of the movements. 
Wiedemann’s boussole. In this a magnetized ring is suspended 
in the interior of a hollow thick cylinder of copper, an alu- 
minium wire attached to it bears a mirror by which its move- 
ments are indicated. The coils through which the currents pass 
are arranged on each side of the copper chamber. The latter 
acts as a damper by reason of the currents set up in it by 
movements of the needle. By means of an accessory magnet 
the needle is made astatic. The advantage of this instrument 
is that the current slowly swings the needle to its maximum 
deflection, where it rests without oscillation. 
Thomson’s galvanometer and Wiedemann’s boussole are pro- 
vided with two coils, in which currents can be made to traverse 
in the same or opposite directions; in the latter case the results 
are differential—that is, two currents may be compared re- 
garding their strength. 
876. Rheostats are instruments for measurement of resistance 
to the electric current, and are essential in investigating prob- 
lems in electrophysiology. 
One of the simplest forms is Wheatstone’s rheostat. It consists 
of two cylinders, one of brass, the other wood, with a similar 
spiral groove on each, carrying a fine brass wire forty yards long, 
arranged to wind from one cylinder to the other. The brass 
being a good and the wooden a bad conductor, the turns of wire 
on the latter are insulated from each other, and thus as more or 
less is wound thereon a varying and known resistance, corre- 
sponding to the number of turns therein, is introduced into the 
circuit. 
When greater resistances are introduced the resistance box 
is employed. It consists of a series of bobbins of insulated 
wire, a greater or less number of which may be thrown into ELECTROMAG XETISM. 
681 
circuit by means of thick brass plugs. When all are in there 
is the least resistance, with all out the greatest. 
For greater resistances, tube rheostats containing distilled water 
are used, the wires passing into it through stoppers at each end’ 
A column of water one metre long and one millimetre in diam- 
eter, offers as much resistance to an electric current as a copper 
wire of the same diameter and long enough to make 167 turns 
around the earth. 
For the following descriptions of the long compensator and 
Wheatstone’s bridge we are indebted to Robertson’s work. 
877. The Long Compensator consists practically of a single uni- 
form wire of brass two metres long, and 1.75 mm. in diameter. 
It is stretched on a piece of wood between two brass plates, 
fitted with binding screws, A and B. On it is a slider, S, 
which can be moved from one end to the other and makes con- 
tact all the way. It also carries a binding 
screw. From a constant element, E, a 
wire is led to A, and another to B. A key 
may be interposed on the way. From A 
and S wires are led to the side cups of the 
commutator which has the cross in, and 
from end cups they go to G, the galvano- 
meter. Flow, the current from E will pass 
to A, and may here branch into two cir- 
cuits, the long circuit by the commutator 
to G, and back through it to S, then on 
to B and back to E; and the short circuit 
straight along the wire A B, and back to 
E. If the slider Sis close to A, it is 
easy to see that all the current will be 
short-circuited, and none will go through 
Fig. 359. 
Long compensator, 
the galvanometer. If, however, it is moved away, then a small 
amount will find its way through G, and this increases the 
further Sis removed from A. In fact, the amount sent through 
G will be proportional to the distance AS, Thus its strength 
can be varied at pleasure, and measured. Further, it can be 
sent in either direction through G by means of the commutator. 
If this is down towards 1, it will pass in the direction of the 
continuous arrow; if towards 2, it will traverse G following the 
dotted arrow. 
878. Wheatstone’s Bridge is shown in diagram in Fig. 360. 
At e is a Daniell’s element; and AB is the platinum wire of 
a long compensator, of which sis the slider. From e the posi- 
tive electrode goes to A, the negative to B. From A a wire 
passes to r, the body whose resistance is to be measured, from 682 
MAGNETISM . 
which again a wire is carried to one binding screw of Re, a re- 
sistance box, from whose other binding screw a wire makes con- 
nection with the end Bof the compensator wire. To the same 
binding screw c of the resistance box 
Re, by which r is connected with it, 
another wire leads to the galvano- 
meter G, and the other terminal of 
G is attached to the slider s of the 
long compensator. When the cur- 
rent reaches A it will split into two 
branches, one passing along the long 
compensator to B, and the other to 
r, c, and Re. But at s and c these 
Fig. 860. 
Wheatstone’s bridge. 
will also split, part of r c, Re, passing down to the galvano- 
meter, part of As, B, passing up to G. These two currents 
being in opposite directions, will deflect the needle in contrary 
ways. If one is in excess, it will deflect the needle in one 
direction; if the other, in the opposite; if both are equal, they 
neutralize one another, and it will remain at zero; or, to put it 
more accurately, wdaen the potential at s is equal to that at c, no 
current will pass through the galvanometer. 
As already explained, the strength of the current in the two 
branches depends on the resistances therein, and can be altered 
by the position of the slider s. Consequently, all that is neces- 
sary to secure equal potentials at c and s is to move the slider 
one way or the other, until the needle returns to zero, this indi- 
cating the desired equality, How, it can be shown, that when 
no current traverses the galvanometer, the resistance of r is to 
that of Ke, as the resistance of Asis to that of sB; thus: 
r:Re:; As:sß 
Put in another way, this is: 
r As 
ITs ~ s~B’ 
and, therefore, 
x) , , .A, s 
r = Re X —tv 
8 13 
How r is the resistance to be measured, Re is that in the box, 
which is read off at once according to the number of plugs out, 
and A s and s B are those of the lengths of the compensator 
wire on each side of the slider, which are also known. Thus, r, 
that to be measured, is given in terms of Re, A s, and s B, 
resistances that are known. The box is used, because by pulling 
out or inserting plugs its resistance can be varied at pleasure. 
According to that thrown in by it will be the position of the 
slider, and thus, by varying it, it becomes easier to adjust that 
properly. ELECTROMAGNETISM. 
683 
879. Electromagnets.—lf an insulated copper wire -j is 
wound in a helix around a rod of soft iron, A, and a voltaic cur- 
rent passed through the former, the core of 
the latter at once becomes powerfully mag- 
netized. It attracts other masses of iron with 
far greater force than an ordinary magnet. 
It exhibits polarity, having a north and south 
pole, HS. Brought into the vicinity of others, 
or of electromagnets, it shows attraction and 
repulsion. The moment the current is broken, 
or opened, magnetism ceases. The instant it 
is closed it reappears in its original intensity. 
The magnetism is, therefore, the product of the 
action of the electric current upon the soft iron 
core, lasting while it lasts, ceasing when it 
ceases. 
pIG< 36i. 
Electromagnet. 
By bending the soft iron into the form of a horseshoe, as in 
ordinary artificial magnets, Fig, 361, and winding the wire to 
have it bear the same relation to the core as though straight, 
the approximation of the poles increases the magnetic effect. 
Care must be taken that there is no reversion in the winding, 
or the effect will be diminished in the same proportion. 
Other things being equal, an increase in the number of turns 
up to a certain point, adds to the effect. After that, distance of 
the circuit becomes too great to affect the core, and increased 
resistance causes diminution. 
The greater the diameter of the wire, the stronger the mag- 
netism produced, especially with currents of feeble intensity. 
The larger the elements of the battery the greater the mag- 
netic effect. A sufficient number of elements to drive the current 
freely through the wire is, of course, essential. 
The iron used should be as pure as possible, otherwise it will 
not gain and lose its magnetism suddenly with the closing and 
opening of the circuit. That which remains in the core is called 
the residual charge. With large magnets this may be broken up 
by a very sudden reversal of poles. 
Projection of the core beyond the ends of the coils of wire 
gives a stronger magnetic effect. 
Providing the core has sufficient thickness for the develop- 
ment of magnetic effects, it does not seem to matter whether it 
is solid or hollow. 
For a given weight of iron, a bundle of wires will give a better 
effect than the same weight in the form of a single bar. 
880. Electromagnetic Motors.—Various plans for the adaptation 
of electromagnetism to the construction of motors have been 
devised. Among these machines one of the early forms con- 684 
MAGNETISM. 
sisted of a coil of wire around a hollow case of pasteboard. In 
the interior of this there was a rod of soft iron six or eight inches 
longer than the core. The arrangement being placed with this 
rod in the vertical position its top just above the coil, on passing 
a current it was raised, on breaking it fell, so a reciprocating 
motion was obtained, which by a crank could easily be converted 
into one of rotation. 
Another method was to use a horseshoe electromagnet, the 
keeper attached to a crank movement of a wheel. The instru- 
ment made and broke the circuit itself. The circuit being made 
the keeper was attracted; the moment it nearly reached the 
magnet the former was broken, magnetism was lost, and the 
momentum gained by the wheel carried the latter to the oppo- 
site limit of movement, when the circuit was again closed and 
the keeper attracted—thus a movement of rotation was estab- 
lished. 
In modern machines a number of electromagnets are arranged 
upon the circumference of a wheel. Each of these acts through 
a very small distance, but the deficiency in this respect is made 
up by their number. 
The exceedingly small distance through which magnetic at- 
tractions exert their greatest efficiency has been the chief diffi- 
culty in the way of the application of electromagnetism as a 
motor. 
881. Cost of Magnetic Motors.—Until quite recent times, the 
cost of producing electricity by oxidizing zinc in a battery has 
prevented the use of this agent as a motor. At present, how- 
ever, improvements in its development from motion, and also in 
electromotors, render it quite possible that we are on the eve of 
its application as the motor on our elevated railways, and for 
numerous purposes in the arts and manufactures. 
Even at present, where small mechanical effort is required, or 
the production of effects at a distance, as in the telegraph, elec- 
tromagnetism cannot be supplanted. 
882. Electric Bells and Clocks consist in the adaptation of an 
electromagnet to the mere sounding of an alarm by the rapid 
making and breaking of a current; or to the regular make and 
break as in the beat of seconds; or to controlling the move- 
ment of the pendulum by currents from a clock at a central 
station. In some instances signals are transmitted at regular 
intervals, and the minute hand moves over two or three minutes 
at once. 
A continuous circuit from a gravity battery is found to work 
the best, the signal being given by breaking the current. ELECTROMAGNETISM. 
685 
883. The Morse Telegraph.—Though the discussion of the tele- 
graph is properly outside of the limits of a work on medical 
physics, yet its universal use makes it necessary that we should 
say a few words regarding the principles and facts involved in 
the Morse system. 
It consists, Ist, of a battery audits circuit of wire. The battery 
varies in different countries, some form of the Daniell is perhaps 
best. The wire is of galvanized iron, suspended by insulated 
glass supports on poles or posts. But one wire is required, the 
return current at both distant and near stations being delivered 
into the earth, which acts the part of a common reservoir. 
2d. A communicator for sending the signals, consists of a hori- 
zontal lever by which the circuit is closed and opened, and 
signals at the distant station produced. These consist of dots 
and dashes. If the lever gives only momentary contact, a dot is 
formed; prolonged for a time, a dash is the result. By a com- 
bination of these the letters of the alphabet are made up, as 
follows: 
A 
B C 
D 
E 
F G 
H I 
J 
K 
L 
M X 
0 
P 
Q 
R 
S T 
U 
Y W 
X 
Y 
Z & 
1 
2 
3 
4 
5 
6 
7 
8 
9 
0 
PERIOD. 
COMMA, 
SEMICOLON 
QUOTATION “ ” 
EXCLAMATION ! 
! INTERROGATION ? PARENTHESIS ( ) PARAGRAPH 
3d. The relay or secondary battery, which receives the signals 
and imparts to them additional force, enabling them to work the 
indicator. 
4th. The indicator, which receives signals from the relay and 
records them upon a strip of paper passing under the point of 
its pencil. 686 
MAGNETISM . 
sth. The sounder, by which the clicking or noise caused by 
the movement of the keeper of the electromagnet is increased, 
has now come into general use, and replaced the indicator on 
many lines. In this case the message is read by sounds alone. 
884. The Needle Telegraph is virtually a vertical galvanometer 
with an astatic needle, or a single one formed of several pieces 
of strongly magnetized steel. This works within a bobbin of 
wire, and carries a light index outside indicating its movements. 
These are made by passing the current through the multiplier 
in different directions by means of a commutator. The deflec- 
tions are to the right or left, thus producing the letters. 
885. Reactions of Currents upon Currents and Magnets were first 
investigated by Ampere. Their consideration properly belongs 
to dynamic electricity, but since their application is chiefly in 
explanation of the action of the compass needle, we have deferred 
their examination to this point. 
The apparatus used for demonstration of these laws consists 
of wires bent in rectangular and circular forms. One is sus- 
pended to move freely, while the other is placed in any required 
fixed position. Also of magnets freely suspended, or fixed, as 
the case may be. 
The leading facts are as follows: 
Ist, Two currents parallel, and in the same direction, attract 
one another. 
2d. Two currents parallel, but in contrary directions, repel 
each other. 
3d. A finite movable current, approaching a fixed infinite 
current, is acted on to move in a direction parallel and opposite 
to that of the latter; if the former tends from the fixed current, 
it is acted on to move parallel to it and in the same direction. 
4th. The earth exerts a directive action on, closed currents 
movable about a vertical axis; the current places itself in a 
plane perpendicular to the magnetic meridian, so, for an observer 
looking at the north, it is descending on the east of its axis of 
rotation, and ascending on the west. 
sth. A magnet movable and the current fixed, the former 
sets itself at right angles to the latter. 
886. Solenoids,—A wire wound in a long spiral around a bar 
of soft iron imparts magnetism to it when a voltaic current 
passes. If the spiral coil alone is taken without the core, and 
the wire conveying the current passes down the centre of the 
helix, the.arrangement being freely suspended, it will take up a 
north and south position, and exliibit true polarity. This ar- ELECTROMAGNETISM. 
687 
rangement is called a solenoid, S. It may be defined as a com- 
bination of a sinuous with a rectilinear current. 
If the north pole of one solenoid is presented to that of 
another, they repel each other. If a north to a south, they 
Fig. 362. 
The solenoid. 
attract. In like manner, if the north pole of a magnet be pre- 
sented to that of a solenoid, it is repelled; if to the south, it is 
attracted. 
887. Why the Compass Needle Points North.—As the culmina- 
tion of his work on electric currents, Ampere gives the following 
theory of the magnetic needle, and the reason it points to the 
north. The process of reasoning is as follows: 
Ist. The molecules of all magnetic substances are traversed 
by closed electric currents, free to move about their centres. 
2d. When the substance is magnetized these are all coercecl 
into a parallel direction, the stronger the force the more perfect 
their parallelism. When all are completely parallel the sub- 
stance is said to be saturated. 
3d. The effect of the preceding action is as though a single 
strong current traversed the exterior of the magnet, which may 
now be regarded as the equivalent of a solenoid. 
4th. The presentation of various parts of the equatorial re- 
gions of the earth’s surface in succession to action of the sun, 
develops in its surface thermoelectric currents which circulate 
around the globe from east to west, very nearly in the course 
of the equator. 
sth. These exert a directive force upon magnetic needles, for 
they come to rest if freely suspended, when the currents on their 688 
MAGNETISM. 
under surface are parallel to the terrestrial. Since the axis of 
the needle is at right angles to its currents, it, therefore, points 
to the north. 
888, Paramagnetism.—lron, cobalt, and nickel are, properly 
speaking, the three magnetic bodies, when submitted to the 
action of an ordinary artificial magnet. But, if in place of an 
artificial, a powerful electromagnet is used, we then find that 
a great number of substances will, like iron, set themselves in 
the line of the two poles. These are called paramagnets. Those 
which do not are nevertheless acted upon, and set themselves 
across this line, or equatorially. They are diamagnetics. 
Among those included in the paramagnetic group are iron, 
cobalt, nickel, manganese, platinum, cerium, osmium, and pal- 
ladium. Glass, according to its composition, may be paramag- 
netic or diamagnetic. Also, many kinds of paper, sealing-wax, 
fluorspar, graphite, charcoal, etc. 
Among liquids are solutions of iron, cobalt, nickel, etc. Tubes 
containing these set themselves axially between the poles when 
a current is passed. 
The effect of magnets on these liquids is seen by placing them 
in thin watch-glasses between the poles, and directing a beam 
of light upon them. According as their form changes, the light 
is converged or dispersed. 
Among gases, Faraday found that oxygen was magnetic under 
ordinary circumstances. 
The condition under which a body is examined affects its 
relations. Oxygen, for example, becomes diamagnetic if its 
temperature is raised. A substance paramagnetic in vacuo, 
may be diamagnetic in air. 
889. Diamagnetism.—All bodies which set themselves equa- 
torially to the line connecting the poles of the magnet are 
included in this group. 
Among metals are bismuth, antimony, zinc, tin, mercury, 
lead, silver, copper, gold, and arsenic. Their action is in the 
order given, arsenic being most feeble. In addition, are rock 
crystal, alum, glass, phosphorus, iodine, sulphur, sugar, and 
bread. 
Among liquids, are water, blood, milk, alcohol, ether, oil of 
turpentine, and most saline solutions. 
All flames or heated gases are diamagnetic. Faraday mingled 
gases with visible vapor, and allowed them to ascend between 
the poles of a magnet and observed their deflections. He 
found that while oxygen was paramagnetic, nitrogen was dia- 
magnetic, and hydrogen most diamagnetic. lodine also shows 
the latter reaction well marked. FARADAIC OR INDUCED CURRENTS. 
689 
890. Diamagnetic Illustrations.—A copper rod freely suspended 
sets itself at once equatorially between the poles. A copper 
cube set in rapid rotation between the latter, ceases to move the 
moment electricity is sent through the bobbins. A circular 
thin disk of copper, set in motion on an axis by a suitable 
system of cog-wheels, stops when the current passes. The flame 
of a piece of resin or camphor placed beneath the pointed poles 
is thrust aside the moment the circuit in the electromagnet is 
closed. It looks as though it were blown down upon from 
above, so strongly is it driven away. 
891. Action of Magnet on Polarized Light.—Two powerful elec- 
tromagnets are placed with their axes in the same straight line. 
The centres of their iron cores are perforated. A source of light 
is placed opposite the opening at the end of one, and in this a 
ISTicol prism is inserted. A beam of polarized light is thus intro- 
duced into the apparatus; between the poles of the magnets a 
block of ordinary or flint glass is placed, and in the opening at 
the further end of the second magnet a ISTicol analyzer. The two 
ISTicol prisms are crossed so that light does not pass. The cur- 
rent is then sent along the wires, when at once colored light 
passes through the apparatus, the tint changing as the analyzer 
is turned. 
Faraday assumed that this action was the result of the effect 
of magnetism on the polarized ray; while Becquerel attributes 
it to action of the magnet upon the molecules of the body 
placed between the poles. 
CHAPTER LII. 
FARADAIC OR INDUCED CURRENTS. 
Currents induced by magnets—Currents produced by electromagnets—lnduc- 
torium—Experiments with inductorium—Geissler’s tubes—The telephone— 
Dynamoelectrie machines. 
In 1832, Faraday discovered that instantaneous currents of 
electricity are produced in wires placed, Ist, under the mo- 
mentary influence of metallic conductors traversed by electric 
currents; 2d, under the influence of powerful magnets; 3d, the 
action of the earth itself. 690 
MAGNETISM. 
892. Currents Induced by Magnets.—Conceive that we have a 
hollow coil of wire connected with a galvanometer. If into 
the interior of this a strong magnet is suddenly introduced, a 
momentary current is produced, as shown by the needle of the 
galvanometer moving and instantly returning to zero. When 
this ends the current ceases. On suddenly withdrawing the 
magnet it is again produced, but this time in an opposite 
direction to the first experiment. Again it only lasts while the 
magnet is moving, and is strongest when the latter moves 
quickly. 
In the previous experiment an oscillating motion is employed, 
but in practice a more satisfactory way of producing the result 
is adopted. Take a powerful compound horseshoe magnet, A, 
and let two keepers, B, be arranged to revolve rapidly opposite 
Fig. 363. 
Medical magnetoelectric machine. 
one side of its poles by means of the winch and multiplying 
wheels WW W. When one is opposite the north pole of the 
magnet, that end will have strong south magnetism induced in 
it. When opposite the south it will in like manner have strong 
induced north magnetism. The same will be the case with the 
other keeper, as they are mounted on the same axis. By rapid 
revolution they are alternately magnetized, demagnetized, and 
reversed. If around each a coil of tine insulated wire is placed, 
the magnetization and demagnetization of the soft iron core 
will have the same result as though a magnet was suddenly 
introduced into the coil, and as quickly withdrawn—that is, 
currents will be induced therein, and they will alternately run 
in opposite directions. 
Though each is exceedingly feeble, and will scarcely give 
either a spark or shock, yet when they follow each other with FAR ADAIC OR INDUCED CURRENTS. 
691 
great rapidity they cause very profound physiological effects, 
and are employed for medical purposes. 
In the primitive form of the apparatus we have here de- 
scribed, the direction of the current is continually alternating. 
By means of suitable contrivances called commutators, these 
may be made to take the same course, and yield a uniform cur- 
rent in a fixed direction. 
893. Currents Produced by Electromagnets.—ln this case the 
apparatus consists of the following parts : Ist, a battery and cir- 
cuit; 2d, an interrupter; 3d, the primary coil; 4th, the secondary 
coil. 
The battery employed is usually a Grenet, worked by the 
electropoion fluid. 
From this the wires pass to a small magnet called the inter- 
rupter, the function of which is to open and close the circuit. 
When the keeper is attracted, the circuit is opened. The mag- 
netism being then lost, a spring raises it, and the circuit is closed, 
when again the keeper is attracted and it is broken. Some- 
times this motion is accomplished by an inverted pendulum, 
which has the advantage of giving very slow movement, or an 
exceedingly rapid one. 
From the interrupter the wire from the battery or the primary 
current passes to the electromagnet, where it is wound spirally 
in an insulated coil around a soft iron core, consisting of a 
bundle of iron wires. Whenever the circuit is closed, the bundle 
becomes a powerful magnet; when opened, the magnetism is 
lost. It is introduced, or withdrawn partially, or wholly at 
pleasure; a slight introduction gives feeble magnetism, com- 
plete, strong magnetism and a powerful current. 
Outside of this primary circuit and its enclosed iron core, an- 
other insulated coil of exceedingly fine wire, several hundreds 
yards in length, is wound. When that in the interior is mag- 
netized by the primary circuit, a current is instantly established 
in the outer coil. When magnetism ceases another instantaneous 
current runs in the opposite direction in the latter. 
This is the induced, magnetoelectric, or- Faradaic current. As ex- 
plained, it continually alternates as regards its course. It is 
employed for medical purposes, and the power of its action may 
be made to differ, either by variation in the rate of oscillation of 
the keeper, or by the extent to which the core of the magnet is 
introduced. 
894. Induetormm.—The apparatus described (893) will scarcely 
yield a visible spark, though it gives very powerful physiological 
results. By an improved form, sparks of considerable length are 
obtained, and its power vastly increased. Such an arrangement 
is called an inductorium or Rhumkorff coil. 692 
MAGNETISM. 
The great increase of power in the incluctorium is due, Ist, to 
the introduction of a condenser, C, into the primary current; 2d, 
to the manner in which the secondary coil S is wound; 3d, to 
its careful insulation; and, 4th, to the method by which the cur- 
rent in the primary circuit from the battery is broken. 
The battery employed for a coil capable of giving a ten inch 
spark, is half a dozen large sized electropoion cells, its zincs 
Fig. 364. 
Incluctorium. 
six by eight inches, and at least two in each cell. A Bunsen 
battery, with elements of the largest size, may be employed. 
From the battery the current passes through the interrupter 
I, through the coil of the magnet H , and the condenser C. 
The latter consists of a great number.of sheets of tinfoil and 
paper soaked with resin. These are laid in alternate layers, 
with the tin sheets insulated from each other by the paper. The 
ends of the alternate layers of tinfoil project first on the right 
and then the left of the pile, when completed. The former 
are connected with one wire from the battery, the latter with 
the other. Each sheet of tin presents a surface of about half a 
square foot. In the largest coils the condenser presents a total 
surface of some seventy-five square yards. Its action is to re- 
ceive the extra current produced each time the circuit is broken, 
and utilize it in an instantaneous demagnetization of the bundle 
of soft iron wire. For the best effect—that is, production of the 
longest spark—the contact is broken by a stroke of a small 
hammer. It is also interrupted by an electromagnet, where 
sparks in rapid succession are required. The surfaces at which 
contact is broken are of platinum. 
The secondary coil sometimes contains as much as 280 miles 
of very fine wire, which is not only itself carefully insulated, but 693 
FARAD AIC OR INDUCED CURRENTS. 
each coil therein is separated from the next by a layer of shellac. 
Between the secondary and the primary there is a glass cylinder, 
making the insulation as perfect as possible. 
895. Experiments with Inductorinm.—Induced currents are pro- 
duced in the coil each time the circuit is opened and closed. 
That on opening is short in duration, hut of high potential. 
That of closing, of longer duration, and lower potential. The 
actions are physiological, chemical, calorific, luminous, and 
mechanical. The physiological effects are sufficiently intense to 
prostrate a person. A large coil worked by two Bunsen ele- 
ments will kill a rabbit, and doubtless with a larger number 
would destroy a man. 
The calorific properties may be shown by intervening a very 
fine iron wire between the two polar connections of the induced 
currents. It is instantly melted. If two fine wires are attached 
to these poles and then touched to each other, the negative 
alone melts. 
The chemical effects vary according to the shape and direction 
of the platinum poles from each other, and the degree of acidity 
of the water. Luminous effects with or without decomposition 
appear. In the latter mixed gases are present at either or both 
poles. Passed through air its nitrogen and oxygen combine. 
The luminous effects also vary. In air the longest spark thus 
far obtained is forty-two inches. This is greatly intensified when 
a secondary condenser is put upon the induction current. In 
vacuo, experiments with the electric egg are very beautiful, espe- 
cially as regards stratification of the electricity. The positive 
pole is the most brilliant, its light is a fiery red; while the 
negative is a feeble violet, and extends along the length of the 
negative rod. 
The mechanical effects consist in piercing glass plates, some- 
times as much as two inches thick. This is accomplished by a 
series of sparks, not by a single one. 
896. Geissler’s Tubes.—These are tubes which have been filled 
with various gases and vapors, and then exhausted. Through 
their extremities platinum poles pass. The residual gas gives 
color to the electric discharge as it passes. The striation ob- 
tained is sometimes very beautiful. Different kinds of glass and 
liquids also impart to "the electric light varying colors. The 
spectra of these colored electric discharges are also very charac- 
teristic, so that each gas, as hydrogen, oxygen, nitrogen, carbon 
dioxide, is recognized by the lines of its special spectrum. 
Light from these tubes has been employed to illuminate the 
interior of different cavities in the body. 694 
MAGNETISM. 
897. The Telephone consists of a steel magnet, some four inches 
long and half an inch in diameter. Opposite one end is a 
diaphragm of thin iron. When spoken to, this is thrown into 
vibration by the voice, and its vibrations cause a rapid shifting 
in position of the pole of the magnet. Around the latter a coil 
of wire is wound, the changing of the pole causing a current of 
electricity therein. This is received by another similar con- 
trivance at a distance, where the operation is reversed, and the 
rapidly alternating current from the first instrument produces 
vibrations in the soft iron disk, or diaphragm, and sounds like 
those received at the other are emitted. 
898. Dynamoelectric Machines.—The principle involved in these 
is somewhat similar to that of the ordinary magnetoelectric 
machine, and illustrates the conversion of motion or force into 
electricity. There are many different forms, which we cannot 
give space to consider. They are operated by steam power, 
and are made to give light equivalent to many thousands of 
candle power. They are now extensively used to furnish the 
currents employed in street lights. These have great intensity, 
and if, perchance, they pass through the human body, instant 
death is the consequence. 
Another application is in electroplating. In that case the 
current is manipulated until the positive and negative poles are 
uniform and fixed. SECTION 11. 
ELECTROBIOLOGY. 
CHAPTER LIII. 
ELECTEOPHY'SIOLOGrY. 
Electricity in plants Electric fishes Apparatus for investigating muscle 
currents—Muscle currents at rest—The frog galvanoscope—Active muscle 
currents—Nerve currents. 
Electrobiology is the study of electricity in relation to living 
creatures, whether plants or animals, and examination into the 
effects of electricity upon them. It may be divided into electro- 
physiology, which deals with their normal electric conditions, 
and electrotherapy, or the effects of electricity upon them, and 
its medical application. 
899. Electricity in Plants.—Donne, Du Bois-Reyraond, Bec- 
querel, and others, have proved, that if one platinum terminal of 
a galvanometer is inserted into a fruit near the stem, and the 
other into the opposite part, a current will be obtained. In 
fruits with pips, as apples and pears, its course is from the stem 
to the hud; in stone fruits, as peaches and plums, it is in the 
opposite direction. Prof. Buff has pursued these investigations, 
and finds that the roots and all parts of the interior of plants 
filled with sap, are constantly negative; whereas, on the con- 
trary, the humid or moistened interior of the green twigs, 
leaves, flowers, and fruits, are in a state of permanent positive 
electrification. 
The discovery of these facts led to numerous trials regarding 
the application of electricity in the culture of plants, but with- 
out satisfactory result. 
900. Electric Fishes.—The gymnotus or electric eel of South 
America, the torpedo or electric ray of the Mediterranean, and 696 
ELECTROBIOLOGY. 
the silurns of the Nile, possess the power of giving very strong 
electric discharges. This is entirely voluntary, and employed 
for offence and defence. Faraday says, that the shock given 
by the gymnotus is equal to that of a Leyden battery of 15 jars, 
exposing a surface of 25 square feet. The first discharge is 
the strongest, each succeeding one becoming weaker until the 
creature is exhausted. 
In the torpedo, the electric organ is on each side of the head 
between the pectoral fins and gills. It consists of a series of 
membranous prismatic tubes parallel to each other, and sub- 
divided by horizontal diaphragms into cells filled with albumi- 
nous liquid. Its structure recalls that of the voltaic pile. In 
all there are from one to two thousand. They are connected 
with a special lobe of the brain, called the electric lobe. 
In the gymnotus the structure of the organ is similar, the 
prismatic tubes are arranged along the axis of the animal, ex- 
tending from head to tail. 
901. Apparatus for Investigating Muscle Currents.—The requis- 
ites are a delicate galvanometer and electrodes which do not 
become polarized, and will not give a current when placed in 
contact with tissues, nor in any way alter them while in use. 
These conditions are met by the electrodes of Du Bois-Eeymond. 
They consist of a glass tube drawn down at one end, and stopped 
by a pellet made by moistening white clay with a solution of 
table salt. Saturated solution of zinc sulphate is placed therein, 
into this an amalgamated zinc wire dips, the other end connected 
with the galvanometer. Amalgamated zinc in zinc sulphate 
does not become polarized, and wet clay does not affect muscle. 
In addition to these there are various instruments for opening 
the circuit called keys, as the mercurial, spring, and friction keys, 
Pfiueger’s trip-hammer and the metronome interrupter, a commutator 
rheotrope or gyrotrope for reversing direction of current at pleas- 
ure ; a rheocord, for varying its strength by increasing the re- 
sistance. These are some of the apparatus with which the 
electrophysiologist must supply himself to conduct his experi- 
ments properly. 
902. Muscle Currents at Rest.—The surface of the muscle is 
called the natural longitudinal section ; the tendon, the natural trans- 
verse section. Cuts made longitudinally or transversely are arti- 
ficial longitudinal and transverse sections. The clay of one electrode 
being placed on the natural surface of a living muscle from a 
recently killed frog, and the other upon its tendon, the galvano- 
meter will at once show a current passing from the one to the 
other, indicating that the former is positive to the latter. Test- 
ing the muscle thus in various positions, it is found that— ELECTROPHYSIOLOGY. 
697 
Ist. Any longitudinal is positive to any transverse section. 
2d. A point of a given longitudinal section nearer to the cen- 
tre of the muscle is positive to one further off. 
3d. A point of a given transverse section near the periphery 
is positive to one near the centre. 
4th. The current between two points in any given section is 
weaker than that between any two in different sections. 
sth. Points in the same section at an equal distance from the 
centre do not give a current. 
6th. The smallest fragment that can be used will give the 
results. 
7th. The strongest current is between the centres of the 
natural longitudinal and the artificial transverse sections. 
These facts are explained upon the hypothesis that each 
muscle consists of regularly arranged electromotor elements, the 
sides charged with positive, and the ends with negative elec- 
tricity, enveloped in a conducting medium. 
The current is better marked after the muscle has been ex- 
posed, but ceases entirely when it is dead. It is, therefore, a 
phenomenon of life. 
903. The Frog Galvanoscope.—A galvanometer is not required 
for exhibiting these experiments. They may be shown by using 
another nerve and muscle. For example, if a living muscle be 
detached, with as long a portion of its nerve as possible attached 
to it, and the latter is dropped upon another living muscle 
coming in contact with a longitudinal and transverse section, 
the former will instantly contract, showing that a current passes 
between the two sections. 
904. Active Muscle Currents.—If a muscle is forced to contract, 
its normal current at rest is diminished. The effect is so instan- 
taneous that it requires a number of rapidly succeeding con- 
tractions to show it; in other words, it must be tetanized. In 
this condition the galvanometer needle moves to zero, and, 
finally, takes its position between its original position and that 
point. 
The same result is obtained from warm-blooded animals, 
though not so easily, on account of the difficulty in keeping 
these organs alive after removal from the body. 
905. Nerve Currents.—Similar effects, though on a much smaller 
scale, may be obtained from nerves, showing that they have a 
natural current which, like that of muscle, is diminished by 
activity in the organ. 698 
ELECTROBIOLOGY. 
CHAP TEE LIY. 
ELECTROTHERAPY. 
General effects of electricity—Static electricity—Constant primary current— 
Galvanocautery— Electrolysis Galvanopuncture—Nerve stimulation by 
constant current—lntermittent primary current—Alternating secondary or 
Earadaic current—Faradization localized—Eleclrotonus—Application for re- 
suscitation—Application in diagnosis. 
Electrotherapy is the study of the action of different forms 
of electricity upon the body, and their application in therapeutics. 
906. General Effects of Electricity.—When the electrodes of a 
powerful battery are taken in the hands, a violent shock is felt, 
which is greatly increased if they are moistened. If the battery 
contains 200 Bunsen cells, the shock is very dangerous. 
Protoplasm, the basis of all vegetable and animal life, is power- 
fully affected by action of the electric current, and is forced 
to contract. If a current of moderate strength is passed 
through an amoeba, it instantly withdraws its processes and con- 
tracts into an inactive ball. When this ceases, it resumes its 
activity and ever-changing form. 
When a fresh frog muscle is included in a voltaic current, no 
effect is apparent while the current is passing, but every time 
it is opened or closed there is contraction. 
By a rapidly interrupted current a state of tetanus is pro- 
duced, the muscle not being able to regain its quiescent state 
before a new contraction comes on. The amount of shortening 
shown under these conditions, in a general way, increases with 
increase in the current. 
The action of the electric current upon a living nerve is to 
add to its activity, whatever its function may be. If it goes 
to a muscle, it will be forced to contract. If to the eye, the sen- 
sation of light is produced, If to the tongue, that of taste, and 
so on, the manifestations taking place when it is closed or 
opened. 
The forms to be considered : Ist, static electricity; 2d, the 
continuous battery current; 3d, the intermittent primary or 
battery current; 4th, the Earadaic secondary or magnetoelectric 
current. 
907. Static Electricity.—Electricity first employed in medicine 
wras entirely of this form. The difficulty in the wTay of making ELECTROTHERAPY. 
699 
the apparatus work in clarap weather, caused this method to 
yield place to currents obtained from the magnetoelectric ma- 
chine. The recent introduction of the Holtz machine has, how- 
ever, brought static electricity into use again for certain purposes. 
Electricity from the Holtz, Fig. 338, is applied by bringing 
the hand in contact with one of its poles, and then by means 
of an insulated conductor placing the other pole in juxtaposition 
with other parts of the body. The character of the discharge 
varies according to the manner of application. 
Ist. The aura. A single point or a number of points being 
made the movable terminal, Figs. 325, 376 F, when this is 
brought in the vicinity of the surface of the skin it feels as 
though a gentle breeze were playing upon the part. Such a 
discharge is very pleasant, and would doubtless be exceedingly 
grateful in many forms of superficial inflammation. 
2d. Sparks from points. Bringing the point, Fig. 375 C, in 
closer proximity to the surface until visible sparks pass, these 
possess a pungent irritating character, which after a time be- 
comes intolerable, Rnd, if continued, cause local inflammations. 
3d. Sparks from knobs, Figs, 323, 376 DE. These are an inch 
or more in length; they produce spasmodic contraction in the 
parts upon which they are delivered. 
4th. Leyden vial sparks, Fig. 334, have in a general way the 
same action as the preceding, though exaggerated. From a 
battery of sufficient size they can be made sufficiently effective 
to prostrate the person receiving them. 
908. Constant Primary Current.—This is a continuous current 
from any form of voltaic battery. It should consist either of 
two cells of large size employed for cauterizing, or of twenty or 
thirty for electrolj’sis. The large cells can be stowed away in 
smaller space by subdividing the zincs, and its action made 
more constant by agitating the.elements in the electropoion. 
A current of dynamic electricity may be used, Ist, for cautery; 
2d, for electrolysis; 3d, as a nerve stimulant; 4th, as an inter- 
mittent current. The electrodes are commonly known as rheo- 
phores, the term being applied to the terminations of the wires 
for conveying the current. 
909. Galvanocautery.—The apparatus consists of a platinum 
wire about one millimetre thick, bent into a close loop, and 
flattened to form a knife edge L, Fig. 365. The current from 
two large cells sent through "this readily raises it to a red heat. 
It is useful for drawing lines along the skin, to destroy granu- 
lations, to open abscesses and fistulas, to cauterize prolapsus 
recti. The current is turned on and off the wire by pressure of 
the thumb upon a button, R. 700 
ELECTROBIOLOGY, 
The pain during the application is severe, especially if the in- 
strument is moved slowly. After the operation it is slight, 
Fig. 365. 
secondary hemorrhage never occurs if it is properly 
performed. Cicatrization is rapid. 
Adjust the current to make the wire white-hot in 
air, stop the current, apply it cold, and then increase 
it a little beyond the first adjustment, to make up 
for loss of heat by action of the tissues. The heat 
must not exceed a bright white, or the wire becomes 
enveloped in hydrogen, its styptic action on the 
blood is lost, and secondary hemorrhage is apt to 
follow, this also happens if the galvanocautery is 
moved too fast over the surface. 
Figs. 866 to 370, inclusive, represent different 
forms of platinum wires flattened and bent, which 
can be attached to the staff, Fig. 365. 
The galvanomoxa is a very thin porcelain capsule, 
around which a thin platinum wire is wound spirally; 
or a spiral of flattened platinum wire, Fig. 371. 
The galvanocaustic loop for removal of poljqmid 
growths is a thin platinum loop, Fig. 372, the ends 
passing through an insulating handle. Its size can be 
increased or diminished. It is admirably adapted for 
removing pedunculated tumors from the rectum or 
vagina. The current is adjusted by operating upon 
a piece of raw meat, of equal size of that operated 
upon. It can be introduced cold, and when all ad- 
justments are made the current is turned on. 
Galvanocautery 
holder. 
Fig. 3G6. 
Fig. 367. 
Fig. 368. 
Fig. 369. 
Fig. 370. 
Fig. 371. 
Fig. 372. 
Galvanocaustic loops. ELECTROTHERAPY. 
701 
Dr. Harrison Allen1 gives the following description of his 
improved galvanocautery and wire snare for removing polvpoid 
growths from the nasal cavity and larynx. 
Tig. 373. 
The galvanocautery snare described in the text: 
1. The cable of the battery. 
2. The canula (which is not shown in full length). 
3. The platinum wire. 
4. The vulcanite carriage, with screws holding the ends of the platinum wire in metallic contact with 
the hinge-connections, by which the current is transmitted from the battery. 
5. A slotted barrel of aluminium. 
6. A movable nut on the screw. 
7. A small portion of the screw disengaged from the slotted barrel. 
8. Milled stationary screw-head. 
It is well known that a loop of wire steadily narrowed has 
great powder in severing the attachment of tumors and other 
growths. When of a large size, it is sufficiently powerful to 
pass through bony structures, as well as softer parts of the body. 
The principle of the snare has been employed in the throat, ear, 
and nose; hut when attention was first directed to this subject 
the forms available were too large and heavy for the delicacy of 
manipulation demanded in removing small tumors lodged in the 
narrower recesses of the nose. Moreover, no snare constructed 
at that time would permit a galvanic current to pass through 
the loop wffiile it was being narrowed. It became necessary to 
devise an instrument which would be light, of small size, and 
yet sufficiently powerful to remove that class of hypertrophied 
tissues and polypoid growths that are of frequent occurrence in 
the nasal chambers. The instrument Fig. 373 combines these 
qualifications, and satisfactorily performs this service. The only 
feature of an essential character which may he said to be novel 
is that the platinum wire forming the snare is covered with a 
copper coat, excepting that portion forming the loop, which is 
bare. The current from the battery is conducted through a 
double eanula by means of the copper. The length of the in- 
strument is about nine and a half inches, and its weight less 
than half an ounce. It has the advantage of securing a rapid 
and painless operation, without hemorrhage. Sessile (pyramidal) 
or resilient growths are removed by first burning a groove 
1 A System of Practical Medicine, by American authors, vol. iii. pp. 56, 57. 702 
ELECTBOBIOLOGY. 
of any depth into them, after which the loop is drawn while the 
current is passing. It is evident that failure to remove at least 
a portion of the growth attacked is an event exceedingly unlikely 
to occur. Hypertrophies of the inferior turbinated bone can in 
this way be treated; and if cocaine is freely applied before the 
operation, it constitutes the most speedy and least painful of any 
Eig. 374. 
Double battery. The two sets of plates are united by a liat band of metal. The case which encloses the 
two batteries opens in front, displaying the cells, the plates (pendent over them), and the treadle. 
means by which such conditions can be reduced. By using a 
canula with curved end it is easy to snare growths situated on 
the posterior portion of the inferior turbinated bone. The cur- 
rent passing through the battery, Fig. 874, to the instrument 
can be interrupted by any of the numerous devices with which 
the practical electrician is familiar; or the treadle can be de- 
pressed and locked by the lever-catch, and interruption of the 
current determined by pressure of the finger on the knob of the 
handle. This is under all circumstances desirable, as the weight 
of the cells is sufficient to demand considerable force to be 
exerted by the foot—always enough to destroy delicacy of 
manipulation. 
910. Electrolysis is applied for disintegrating urinary calculi 
in the bladder. The latter is first filled with a solution of nitrate 
of potash. An instrument resembling a lithotrite, the jaws of 
which can be separated to grasp the calculus, is then introduced. ELECTROTHERAPY. 
703 
The two parts of this apparatus contain an insulated platinum 
wire, its extremities only bare. Between these the calculus is 
gripped, and the current from a strong battery sent through 
the wire. The nitrate of potash is decomposed, nitric acid 
liberated at one pole attacks the calculus, and disintegrates it. 
Having done its work, it is neutralized by the potash set free at 
the other. The bladder should be moderately full of fluid, and 
the calculus kept during the operation as near its centre as 
possible. 
After a perforation has been secured by the acid in o-ne place, 
the calculus should be gripped by a fresh diameter, and another 
made. According to condition of the patient, the operation must 
be repeated from time to time, until it is completely honey- 
combed, it can then be readily crushed, by a lithotrite, and 
removed. 
911. Galvanopuncture is the application of electrolysis to treat- 
ment of aneurisms. It consists in decomposing the blood by 
a constant current, coagulating the albumen, and furnishing 
a nucleus upon which fibrin may be deposited. The battery 
required is twenty to thirty cells of Daniell, or fifteen Grove, 
The anode consists of a fine platinum needle insulated nearly to 
its point with a uniform covering of ebonite. With this the 
tumor is pierced. The cathode is a large metallic plate covered 
with wet sponge. This is placed on the thoroughly moistened 
skin, as near as possible to the aneurism. The artery must be 
compressed below the tumor, so the clot is not carried off, and 
the current opened and closed gradually. If it is too strong, 
bubbles of gas are set free, and the clot is loose and lacks neces- 
sary consistency. The operation is continued until pulsation 
ceases, or gas is detected. The cure is generally effected by 
inflammation, which sets in immediately or after a day or two. 
912. Nerve Stimulation by Constant Current.—The muscles and 
motor nerves are not affected unless the current is very strong, 
or its density varies. The sensitive nerves, on the contrary, 
are strongly acted upon, particularly at the cathode, causing 
cutis anserina, attended by a burning or prickling. It produces, 
first, anaemia, then hypercemia. In diseased conditions there is a 
difference between the action of the continuous and Faradaic 
currents. 
Remak asserts that the constant current exerts an antiphlogistic 
action, 'paralyzing the walls of the capillaries of the inflamed part, and 
so facilitating circulation and resorption. He recommends its use 
in acute, chronic, traumatic, or rheumatic inflammations of 
joints; chronic rheumatism of joints, muscles, tendons, perios- 
teum, and nerves; cramps; inflammation of spinal cord, attended 704 
ELECTROBIOLOGY. 
by hemiplegia; inflammation of cerebrum attended by tremors 
and convulsions; and for painful and inflamed tumors. The 
cathode is placed on the inflamed part, and the anode near by. 
If there is water exudation, the application is reversed. Other 
authors deny that the constant current is superior to the induced 
in these cases. 
913. Intermittent Primary Current.—We have the following 
forms of paralysis to be subjected to treatment: 
Ist. That in which neither the will nor either form of electric 
current can act on the irritability of muscle or nerve. 
2d. When the action of the will is preserved in part, and yet 
neither current can affect either muscle or motor nerve. 
3d. Where the will has lost all power, yet both forms of elec- 
tric current act, though with diminished force. 
4th. Where both the will and the induction current are power- 
less, while the intermittent constant current acts. 
In the last condition we find: 
A. During absence of motility. 
Ist. The constant currents are so effective, that those too feeble 
to have any action on normal muscles give strong contraction. 
2d. During treatment this power rapidly reaches a maximum, 
then diminishes. 
3d. In many cases contraction is obtained not by stimulating 
the motor nerve, but the muscle itself. 
B. Motility returning. 
Irritability for constant currents diminishes, as that for the 
will, and induced currents rises. 
The intermittent primary current is of especial use in modify- 
ing the irritability of muscles and nerves. The simplest rule to 
follow in the use of this and other currents is, employ that hav- 
ing the best effect. 
914 Alternating Secondary or Earadaic Current.—The parts be- 
tween the poles are all traversed by currents which converge to 
the point of application of the poles. 
The quantity of electricity at all cross-sections of the part 
traversed is the same. Convergence at the points of application 
causes greater intensity of action and sensation, owing to the 
termination of the nerves of sensation in the skin. To avoid 
undue stimulation of the latter, we must enlarge the size of the 
electrode. 
A¥hen the skin is dry, the current passes almost entirely 
through sweat glands. 
According as a larger or smaller extent of surface is included 
in the electric current, the electrodes represented Fig, 375 are 
employed; A large sponge, B small sponge, C pointed and 
gilded. ELECTROTHERAPY. 
705 
Other forms, Fig. 376, are also employed; they are, D small 
knob gilded, E large knob gilded, F wire brush. 
To excite cutaneous nerves alone, the large electrode of wet sponge 
must be applied to the moist skin, and the wire brush drawn 
gently over the dry skin of the part treated. 
Fig. 875. 
Fig. 376. 
Electrodes. 
Knob and brush electrode. 
To excite a muscle alone, place the large sponge over the belly 
of the organ, then press the small point firmly over the entrance 
of the motor nerve into the muscle. The patient should be 
recumbent. 
915. Faradization Localized.—The following detailed directions 
are from Morgan’s work; 
Head. The trunk of the facial nerve is stimulated by placing 
the anode on the point seen inside the ear-shell, or concha, and 
the result is the entire face; half is drawn toward that side, the 
skin thrown into countless wrinkles, the eye shut, and the nose 
and mouth drawn obliquely downwards. The stimulation of 
the auriculo-posterior branch of the facial nerve, at a point in front 
of the mastoid process of the temple bone, is very painful, 
and causes contraction of the retrahens and attollens auriculae, 
drawing the scalp downwards, and raising the concha back- 
wards and upwards. The muscles of the ear are too unim- 
portant in man to detain us any further. The branch of the 
facial going to the stylo-hyoid and digastric m. is rarely reach- 
able, save in very emaciated persons; and, if reached, the result 
is the movement of the os hyoides outwards, backwards, and 706 
ELECTROBIOLOGY. 
upwards. The frontalis m. can he stimulated by itself extra- 
muscularly, the branch it gets from the facial nerve being very 
superficial, and, in contracting, it throws the brow into hori- 
zontal wrinkles, curved somewhat downwards in the median 
line. The corrugator supercilii m. is also stimulated extramus- 
cularly, and flattens and depresses the eyebrow, and draws 
its base inwards and downwards. The orbicularis 'palpebrarum 
m., stimulated extramuscularly, shows the eye and wrinkles 
up the eyelids. The zygomatic major m., stimulated extramus- 
cularly, draws the angle of the mouth outwards and upwards, 
and produces on the cheek deep wrinkles, radiating outwards, 
from this angle. The zygomaticus minor m. requires intramus- 
cular stimulation; is painful, and marked by the drawing of 
the upper lip upwards and somewhat outwards. The levator 
labii superioris proprius is difficult to reach, even intramus- 
cularly; the upper lip rises almost vertically, uncovering the 
teeth. The levator labii superioris alceque nasi is easily reached, 
but with pain, and lifts the upper lip and the wing of the nose. 
The compressor nasi and pyramidalis nasi must be stimulated 
together, giving on the nose wrinkles parallel with the back of 
the latter, and at the root short, thick, horizontal, or slightly 
oblique wrinkles, while the eyebrow is drawn downwards and 
inwards. The dilator narium anterior and posterior are very 
rarely of any significance. The orbicularis oris m. has four 
motorpoints; and, hence, to be thoroughly stimulated, would 
need four electrodes; its mode of action is self-evident. The 
buccinator m., when it contracts, draws the cheek against the 
teeth, and shortens the upper and lower lip half. The triangu- 
laris menti m., when it contracts, draws the angle of the mouth 
downwards and strongly outwards, lengthening the opening 
between the lips, but not causing them to separate from one 
another. The quadratus menti m. draws the corresponding lip 
half downwards, and somewhat outwards, and presses it firmly 
against the teeth. The levator menti m., stimulated extramus- 
cularly, pushes the lower lip forwards. The masseter m. is 
stimulated by placing the electrode in the incisura semilunaris, 
between the coronoid and condyloid processes of the lower 
jaw; and the temporal m., by placing one electrode on the pos- 
terior and the other on the anterior segment of the muscle, and 
the result is, the lower jaw presses up against the upper one 
with great force. The tongue stimulated on one side, shortens 
and curves towards it, and, if stimulated on its under surface, 
is drawn quickly into the mouth again. Using two electrodes, 
the velum palati is drawn backwards and upwmrds. The azygos 
uvulae m. is stimulated by placing the fine-pointed electrode 
gently at the root of the uvula, and the latter disappears almost 
from sight. The superior, middle, and inferior constrictor of the 
pharynx are also within reach. 707 
ELECTROTHERAPY, 
Neck. In examining this region, the patient’s face must he 
made to look towards one shoulder, and its position should be 
the same at every sitting. 
The subcutaneous colli m., or platysma myoides, requires the 
anode to be set near the middle of the inner margin of the sterno- 
cleido-mastoid muscle and the cathode on the subcutaneous colli 
branch of the facial nerve, and, drawing on the lower lip and 
jaw, it may uncover the teeth, etc. Thenervus accessorius Willisii 
is easily reached, since, on emerging posteriorly from the sterno- 
cleido-mastoid (to which it here gives off a branch), it is, until it 
enters the trapezius m., very superficially situated; and, both 
these contracting simultaneously, the neck is bent, the lower 
jaw, protruded, the head twisted toward the shoulder, which 
is strongly raised and drawn backwards and inwards. The 
sterno-cleido-mastoid m., on being stimulated by itself by placing 
the electrode somewhat lower down, draws the head down so 
that the ear faces the shoulder, whilst the face looks somewhat 
upwards, backwards, and to the opposite side. The trapezius 
m. is best acted on by placing the anode on the nerve, en- 
tering the muscle about a half inch below the accessorius 
Willisii nerve, and we get either a raising of the shoulder back- 
wards, with drawing of the scapula towards the spine, or a 
pulling of the head backwards and outwards, or both motions, 
according to the action of the antagonists of the trapezius muscle 
on the head or shoulder. The isolated stimulation of the levator 
anguli scapulae is followed by the drawing of the internal angle of 
the scapula upwards, inwards, and forwards, whilst the acromion, 
fixed by the weight of the arm and the action of the antagonists, 
does not move to any special extent. The hypoglossal nerve may 
be reached just above the cornu major of the os hyoides, just 
in front of the hyo-glossus m,, but its effect is uncertain. The 
omo-hyoid m., when it contracts, draws the os hyoides downwards 
and outwards. The actions of the sterno-thyroid. and hyo-thyroid 
are too evident to need description. The stimulation of the 
phrenic nerve (there is no danger in the simultaneous stimulation 
of both, nor is it painful) for the production of artificial respira- 
tion requires quite strong currents and large electrodes, and the 
anode must be pressed gently, but fixedly, against the outer 
margin of the sterno-cleido-mastoid, near the omo-hyoid. The 
result is rapid contraction of the diaphragm, bulging out of the 
abdomen, and forcible entry of air into the trachea, giving rise 
to a sobbing sound. 
The isolated stimulation of the separate muscles of the larynx 
is very difficult, and those interested in this subject will do 
well to consult the works of Yoltolini, Mackenzie, and other 
specialists. 
The motor nerves of the shoulder and thorax, arising from 708 
ELECTROBIOLOGY. 
the supraclavicular portion of the brachial plexus, are sometimes, 
but rarely, reachable for the purposes of isolated stimulation. 
The posterior thoracic or dorsalis scapulae nerve, when stimu- 
lated, causes the rhomboid m. and the serratus posticus superior m. 
to contract and draw the scapula upwards toward the spinal 
column and feebly to lift the upper ribs. The isolated stimula- 
tion of the lateral thoracic, or external respiratory nerve, causes 
the serratus anticus major ra. to contract vigorously, thereby 
raising the acromial angle of the scapula, and pushing this bone 
very far outwards and forwards, and lifting the clavicle some 
distance out from the thorax. The subscapular m. is most easily 
stimulated, directly, or else by acting on the subclavian nerves 
in the posterior part of the axilla. The stimulation of the 
anterior thoracic nerve causes the pectoralis major m. to draw the 
arm far towards the median line. 
Upper Extremity. On placing the electrode just above the 
clavicle towards its outer extremity, the deltoid m. is caused to 
contract. The stimulation of the musculo-cutaneous nerve at its 
emergence from the coracobrachial m., in the groove between 
the latter and the biceps muscle, or at the point between the 
two heads of the latter, is painful, though it causes the simul- 
taneous contraction of the biceps rn., and the brachialis internus 
m. The isolated contraction of the biceps m. is effected by the 
use of the motorpoint between its two heads. The stimulation 
of the brachialis internus requires the anode to be placed at the 
point where the lower half or third of the biceps muscle begins 
(pushing with the fingers the median nerve aside to save it), 
whilst the cathode rests on the outer edge of the other muscle. 
The median nerve, though easily reached at any point along the 
sulcus bicipitalis, is best stimulated at the lowmr third of the 
humerus, where it can ho, fixed against the bone. The stimula- 
tion of this nerve excites peculiar pain in its sensitive cutaneous 
branches on the hand and fingers, and causes contraction of 
the pronator teres and quadratus, radialis internus, palmaris longus, 
flexor digitor sublimus and profundus, etc., producing strong prona- 
tion of the forearm, flexion of the hand towards the radial side, 
flexion of the fingers with opposition of the thumb. The stimu- 
lation of the pronator teres, by either of its twro motorpoints, is 
quite painful, in consequence of the great number of sensitive 
nerves on the flexion side of the arm, though the resulting con- 
traction is exceedingly rapid and strong. The flexor digitor sub- 
limus, as well as the prof undus, is only accessible to intramuscular 
stimulation. The branches of the median nerve going to the 
radialis internus and palmaris ra., which come off at about the 
same point from the nerve trunk, also enter their respective 
muscles at about the same distance from the elbows on their ulnar 
margins. The pronator quadratus, and flexor pollids longus, need ELECTROTHERAPY. 
709 
intramuscular stimulation. The motorpoints of the abductor 
pollicis brevis, opponens pollicis, and flexor pollicis brevis, are super- 
ficial and easy to find; this is true in general of the other 
muscles of the hand and fingers. Though the ulnar nerve 
may be reached at any point from the axilla to the elbow, still 
the best place to stimulate it is at the groove, between the 
olecranon and the internal condyle of the humerus, and the 
result is pain along the course of its palmaris longus and digital 
branches on the dorsal side of the hand, and contraction of the 
ulnaris internus, flexor digitor profundus, palmaris brevis, interossei, 
lumbricoides quartos, and adductor pollicis. The ulnaris internus m., 
when stimulated isolatedly, directly or indirectly, flexes the hand 
towards the ulnar side of the arm. The ulnar, like the median 
nerve-branch, going to the flexor digitor profundus m., is not 
susceptible of isolation. 
The radial nerve is best reached at the point between the 
insertion of the deltoid muscle and the external condyle of the 
humerus, somewhat to the outside of the latter. The branches 
it gives to the triceps, brachialis internus, and supinator longus 
are not within reach, so that these muscles must be stimulated 
directly—i. e., intramuscularly. When the supinator longus m. con- 
tracts, it flexes the forearm on the arm in a position between 
pronation and supination, and only really supinates when the 
forearm is strongly pronated; thus it is in truth a flexor muscle. 
The radialis externus longus m. only reacts when stimulated 
intramuscularly; as is also the case with the supinator brevis and 
radialis externus brevis. Both the branches the extensor communis 
digitorum receives from the radial nerve should be stimulated 
simultaneously, to give rise to a complete contraction of this 
muscle; or, as the skin is not very sensitive here, the com- 
ponent bundles may be acted upon separately, placing, of course, 
the two electrodes upon the muscle itself. Direct stimulation is 
also necessary for the ulnaris externus ra., and the result is, ex- 
tension of the hand towards the ulnar side of the arm. The 
motorpoints of the abductor pollicis, extensor digiti minim, propr., 
extensor indicis propr., extensor pollicis longus and brevis m., are easily 
found by reference to any anatomy. 
Trunk. The muscles of the trunk receive each several nerves, 
and, hence, cannot be caused to contract generally, nor is it 
necessary that they should do so. 
Of* the muscles of the back, some have been mentioned in 
treating of the neck; of the others, the only ones that can be 
reached are: the splenius capitis, the latissimus dor si, the teres major 
and minor, and the serratus posticus inferior. 
Lower Extremity. The stimulation of the crural nerve causes 
much pain along the track of the saphenus major, minor, and cuta- 
neous femoris, anterior and median, and on the front and inner side 710 
ELECTROBIOLOGY. 
of the thigh, the knee, and the leg down to the big toe, along 
with powerful contraction of the muscles of the leg. In ema- 
ciated persons, it is often possible to stimulate the chief branch 
of the crural nerve, which goes to the quadriceps extensor cruris, and 
this excites not only that muscle, but also the extensors on the 
front of the thigh. The rectus femoris m. has a motorpoint four 
to five inches from the anterior superior spinous process of the 
ilium. 
The vastus externus m. has two motorpoints two to three 
inches apart; and it is best to act simultaneously on both with 
the two electrodes. The stimulation of this muscle is easily 
effected; but to lessen the pain, it is necessary to push the 
handle of the electrode towards the other thigh, pressing the 
nerve of this muscle outwards. The sartorius muscle receives 
several nerves, but it is most advantageous to place the cathode 
on the upper motorpoint, and the anode on the lower, or on 
the lower half of the muscle. The tensor fasciae latoe ra. receives 
a branch from the glutceus superior, and another from the crural 
nerve, both within easy reach. The stimulation of the Muratov 
nerve requires the electrode to be firmly pressed on the part, 
and is very painful, although it gives rise to an exceedingly 
energetic adduction of the thigh. The pectineus and the adductor 
brevis are best stimulated intramuscularly. The adductor longus 
and the gracilis are readily reached extramuscularly, and the 
adductor magnus has a very available motorpoint at the inner 
and posterior part of the thigh. The glutceus superior and inferior, 
and the sciatic nerves, are rarely within reach, and always need 
strong currents and pressure. Each head of the biceps femoris m. 
has a motorpoint. 
The motorpoints of the remaining muscles may be easily 
found by reference to any anatomy. 
Many of the more important points for application of elec- 
trodes are given in Eig, 377, in which the left side presents a 
face view of the body, and the right a back view. From Bar- 
tholow’s “Electrotherapeutics.” The stimulation of the bladder 
or uterus is readily effected by introducing in the one case an 
electrode into the viscus, and in the other applying it to the en- 
trance, and holding a large sponge-electrode against the abdomi- 
nal wall, or passed up the rectum, or resting against the sacrum. 
916. Electrotonus.—ln a living nerve, certain parts on thd sur- 
face are positive to other parts, and will give a current through 
the galvanometer when intervened in the course of a wire con- 
necting them. Suppose this connection made, then let another 
portion of the same nerve be included in a voltaic circuit, and 
let the current pass in the same direction as the proper nerve 
current. The latter is at once increased though none of that ELECTROTHERAPY. 
711 
Fig. 377. 
Points for application of electrodes. 712 
ELECTROBIOLOGY. 
1. Seventh or facial nerve filament supplying the frontal muscle, 
2. Seventh or facial nerve filament supplying tire levator lahii superioris alseque nasi 
3. Seventh or facial nerve filament supplying the zygomaticus minor. 
4. Seventh or facial nerve filament supplying the orbicularis oris and quadratus menti. 
5 
Phrenic nerve supplying 
the diaphragm. 
6. 
Musculocutaneous nerve “ 
biceps, brachialis, etc. 
7. 
Musculo-cutaneous nerve “ 
brachialis internus. 
8 
Ulnar nerve “ 
nmscles of forearm and hand. 
9. 
Kaclial nerve 
flexors of thumb and fingers. 
10. 
Ulnar nerve “ 
palmaris brevis, abductor digitor. min., opponens digitor 
min., etc. 
11. 
Obturator nerve “ 
sartorius, adductor longus, etc. 
12. 
Crural nerve 
adductor longus, vastus internus, etc. 
13. 
Crural nerve “ 
vastus externus. 
14. 
Musculo-cutaneous nerve 
flexor digitorum com. long. 
15. 
Occipital nerve 
posterior neck muscles. 
1G 
Circumflex nerve “ 
triceps, etc. 
17. 
Intercostales nerve “ 
lumbar muscles. 
18. 
Gluteus nerve “ 
adductor magnus, etc. 
19. 
Popliteal nerve “ 
gastrocnemius externus. 
20. 
Popliteal nerve “ 
soleus. 
from the battery passes into it. This change in the normal 
electromotive state of the whole nerve by the passage of a 
constant current through a portion, is called the electrotonic state, 
and is most intense near the exciting current. It lasts while 
this is passing. The excitability of the nerve is increased. 
The part through which it is passing is called the intrapolar 
region. The condition near the positive pole is called anelec- 
trotonus; that near the negative pole kathelectrotonus. 
The excitability of the nerve is diminished in the anelectro- 
tonic region, in the kathelectrotonic region it is increased. Its 
power to convey a stimulus is also lessened in the first and 
Increased in the second. If, therefore, it is required to diminish 
the excitability of the sensory nerves in any part, the current 
should be so passed as to throw them into the anelectrotonic 
state, and vice versa. 
317. Application for Resuscitation.—A powerful electric current 
passed through the body of a killed animal produces strong con- 
tractions of the muscles. In like manner, a Faradaic current will 
often restore functions impeded in ajohonia and asthma. Even 
the respiratory function may be restored in asphyxia from 
chloroform, or opium poisoning, by faradization of the phrenic 
nerves. This is accomplished by placing one electrode over the 
scalenus anticus muscle, behind the sterno-mastoid at the root 
of the neck, while the other is brought in contact with the sixth 
or seventh intercostal space. 
918. Application in Diagnosis is admirably summed up as fol- 
lows, by J. McGregor Robertson, who says: The electric current 
is employed, (1) to detect alterations of irritability or sensi- ELECTROTHERAPY. 
713 
bility, (2) to aid in distinguishing between forms of paralysis, 
(3) to detect the presence in the tissues of foreign metallic 
bodies, (4) to unmask malingerers, (6) as a final test of death. 
(1) To test irritability of muscle or nerve, use an induction cur- 
rent, and apply well-moistened electrodes to the part, the skin 
over which is also moist. This insures the current traversing 
the latter without affecting it. Graduate its intensity by adjust- 
ing the secondary coil or altering the extent of surface of plates 
in action in the cell. Begin with the healthy side, and find the 
feeblest current that will produce a response on the part of the 
muscle or group tested. Compare the result obtained with that 
of a similar experiment on the suspected side, taking care that 
the experiment is repeated under precisely similar conditions. 
If both sides are suspected, then a healthy standard must be 
obtained elsewhere, and the physician must compare his results 
with an average obtained from healthy individuals. 
For testing sensibility the skin must be acted on, and not the 
tissues beneath. Therefore, the electrodes must be dry (a wire 
brush), and the former well dried and dusted. Then find what 
strength of current just begins to be painful on the healthy side 
of the patient, and compare this with the diseased side. 
(2) For electrical diagnosis paralysis is considered due either 
to a central or peripheral lesion, and the value of electricity is in 
the aid it gives in distinguishing between these. A central 
lesion is one which separates the muscles from the higher centres, 
a peripheral one that cuts them off from their lower centres. Thus 
those of the legs are in nervous communication with centres in 
the spinal cord, their lower centres; but these are subservient 
to centres in the brain, their higher centres. Now these muscles 
may be cut oft' from their higher centres, their lower being left 
intact, by a lesion in the brain, or one in the cord above the 
seat of their lower centres; and in each the lesion would be 
called central. If, however, it is in the cord, affecting the centre 
from which the nerves supplying the muscles come off, or in 
the nerves, cutting off communication between the cord and the 
muscles themselves, it is called peripheral. Thus central paralysis 
is dependent upon disease in the brain, or in the cord, higher 
up than the place of origin of the nerves for the affected mus- 
cles, while peripheral paralysis is due to disease in the cord 
affecting the centres connected with the paralyzed muscles, or to 
disease of the nerves; and this would include injury to them— 
e. g., cutting, bruising, thus depriving them of nervous con- 
tinuity. 
This being explained, the main fact, stated broadly, is that 
nerves and muscles paralyzed by a central lesion have their irritability 
unaffected, ivhile those by a peripheral have it rapidly diminished and 
finally abolished. 714 
ELECTROBIOLOGY. 
In the centrhl lesion the nerves and muscles still retain their 
connection with the centres in the spinal cord. They are only 
removed from the influence of the will, so that voluntary motion 
is in abeyance, but the nourishment of nerves and muscles re- 
mains, and no sign of any impaired function ought, therefore, 
to be present. Of course, volition being suspended, their duties 
are no longer performed. They fall into disuse, and since, in 
course of time, enfeeblement always attends disease, after an 
interval, diminished irritability will be perceived. This is, how- 
ever, directly the result of disuse, and only indirectly a result of 
the lesion. The irritability can be restored by faradization, 
which affords an artificial stimulus, and causes the paralyzed 
muscles to work. So the rule remains that irritability is unaf- 
fected by the lesion. There is an exception, however. It occa- 
sionally happens that it is apparently increased. This will occur 
when the lesion in the brain or upper part of the spinal cord 
is an irritative one, and affects the ends of the fibres which it 
has cut off from their centres. In the absence of any ground 
for supposing this, a physiological explanation would be that 
the moderating influence of the higher centres had been re- 
moved, and the response of the lower was, therefore, more 
easily elicited. 
In the peripheral lesion communication has been cut off with 
the centres in the cord. These are not only reflex, but trophic; 
the nerves, therefore, degenerate, and the retrograde changes 
will in time also affect the muscles. The rapid loss of irrita- 
bility, then, is due to degeneration. Here a curious circumstance 
arises, that is difficult to explain. What has been said refers to 
electricity used as induced currents, applied by moistened elec- 
trodes. It is found that in some peripheral lesions, where, as is 
expected, response to the induced or Faradaic current is entirely 
absent, the muscles will respond to the galvanic current if it is 
slowly interrupted, and those of the paralyzed side will often re- 
spond vigorous!}7 to one so weak that it has no effect on the 
sound side. Further, in such cases the nature of the response 
is altered. Nominally, excitability is greater in the neighbor- 
hood of the cathode on closing, and the anode on opening the 
circuit; but in these cases it is contraction at the cathode on 
opening and at the anode on closing that is marked. It is 
difficult to explain these facts. That offered by Erb and corrob- 
orated by Ziemssen is that nerve and muscle respond differ- 
ently to an electric current; that, while the former responds 
readily to currents of very short duration, the latter responds 
more to currents of longer duration, like those obtained by in- 
terruptions of the constant current. Consequently, when the 
irritability of nerve and muscle to faradization has disappeared, 
the response of the latter to galvanism may still be elicited. ELECTROTHERAPY. 
715 
In time, however, if degeneration proceeds, galvanism also fails 
to elicit contraction. The cases which show these degenerative 
reactions, are rheumatic paralysis, facial palsy((due. g~ to cold— 
i. e., not hemiplegia), lead palsy, paralysis due to injury of nerve 
trunks, and others. To sum up, then, in central paralysis irrita- 
bility is unaffected, in peripheral it rapidly disappears, but in 
some cases irritability of the muscle to galvanism is increased, 
and thereafter disappears. 
(3) To detect foreign metallic bodies—e.g., a bulletin the tissues, 
the constant current is employed. What is required is a battery 
sufficiently powerful to ring an alarm bell, and in the same cir- 
cuit a probe of particular construction. This should be of insu- 
lating material, having embedded in it, and insulated from one 
another, two copper wires. Their ends are exposed at the end 
of the probe. If they are put in the circuit of the battery and 
bell, the latter will not ring, because contact is broken between 
the two wires. If, however, the probe be pushed into a wound 
and come in contact with a bullet, then, both wires touching the 
lead, the circuit is completed, and ringing the bell gives the in- 
dication, Instead of a bell, a galvanometer is used (not one of 
sensitive construction), its deflection intimating metallic contact. 
(4) As a means of detecting malingerers, electricity must, of 
course, be used with caution. If a strong induced current fail 
to induce contraction, paralysis is evident, for contraction set 
up by electricity is beyond voluntary control. Though it is 
produced, it does not follow that nothing is amiss. Faradiza- 
tion of the dry skin with the wire brush, if strong enough, is 
very painful, but can, without danger, be employed. 
(5) Within, at most, two or three hours after death induced 
currents of electricity fail to provoke a response from the 
muscles. Failure in this is, therefore, a sure sign of death. 
Moistened electrodes must be employed in the test, and the skin 
well saturated with warm salt water. IN RE X. 
4 SERRATION, chromatic, 455 
Abnormal sounds in chest, 344 
Abnormal spectra, 550 
Abscissas, axis of, 249 
Absolute vacuum-tube, 226 
zero, 565 
Absorbent media, 398 
spectra, 544 
by colored liquids, 548 
by colorless liquids, 548 
Absorption in animals, 306 
in plants, 306 
lines of spectrum, 383 
of gases by liquids, 295 
of liquids, 284 
Accommodation of eye, 470 
Accumulator, electric, 660 
Acetic acid, 514 
Achromatic condensers, 499 
Alcoholometer, 104 
Alembic, 584 
Algae, 515 
Algebra, 88 
Alloy, 73 
I Alterative waters, 96 
i Alternating current, 704 
Altitude and boiling point, 591 
Amalgamation of zinc, 654 
Amianthus, 79 
Amici prism, 499 
Amoeboid movements, 293 
Amorphous bodies, 70 
Ampere currents, 686 
Amplifyer of microscope, 494 
Amplitude of vibi-ation, 312 
Anaemia, 209 
treatment of, 208 
Anaerobies, 206 
Analogous pole, 623 
Analysis, 434 
of colored lights, 441 
of sounds, 360 
Analyzing mirror, 524 
Anamorphosis, 420 
An atmosphere of pressure, 175 
Anelectrotonus, 712 
Anemometers, 559 
Aneroid and altitude 189 
Aneroids, 188 
Aneurisms, treatment of, bv electricity, 
703 
lens, 456 
objective, 480 
prism, 435 
Acids, decanting of, 123 
Acoustic attraction and repulsion, 369 
Acoustics, 311 
Actinic rays, 436 
Adhesion, 240 
of solid and gas, 245 
of solids and liquids, 248 
plates, 243 
Pollan harp, 321 
Aerobics, 206 
Aero-therapeutical establishment, 208 
Air, absorption of light by, 399 
buoyant power of, 165 
composition of, 157 
condensed, respiration of, 201 
in caves, 200 
introduction into the lungs, 164 
rate of movement into vacuum, 170 
I Angle of aperture, 481 
of deviation, 424-428 
of incidence, 424 
of polarization, 524 
of refraction, 424 
Aniline dyes, 513 
Animal heat, 607 
Animals, distribution of, affected by 
heat, 612 
Anione, 665 
Annealing, 73, 571 
Anode, 653 
Anterior chamber of eye, 469 
Anthrax bacilli, 517 
Antilogous pole, 623 
Aplanatic lenses, 455 
i Aqueous humor, 468 
' \rapor in air, 158 
resistance to moving bodies, 169 
vibrating columns of, 340, 341 
vitiated by stoves, 302 
Air-pump exhaustion, 152 
Ajutage, 107 
Alcohol, 514 
freezing and boiling point, 562 
in wine and beer, 104 
percentage in Avines, 98 
post-mortem determination, 104 718 
INDEX 
Arc, electric, 390, 661 
Archimedes, principle of, 66 
screw, 118 
Area, unit of, 252 
Argand burner, 895 
Argentic nitrate, 514 
Artesian wells, 96 
Artificial horizon, 414 
illumination, 391 
| Barometer and death rate, 182 
and winds, 181 
aneroid, 189 
construction of, 173 
Fortin’s, 177 
glycerine, 178 
in mines, 190 
siphon, 177 
wheel, 178 
| Barometric height, 180 
readings, errors in, 179 
variations, 179 
cause of, 180 
in weather, 181 
relation to natural history, 211 
I Barometry, 172 
j Baroscope, 165 
; Bath experiment, 608 
Bathybius, 212 
j Batteries, care of, 659 
i Battery, thermoelectric, 668 
Baume’s hydrometer, 100 
I Beam of light, 400 
! Beck lens, 481, 482 
i Beef tea, preparation of, 594 
Bell-jar, 144 
Bells, 338 
electric, 684 
Bert, Paul, experiments, 195 
rarefaction cylinders, 199 
resume of his results, 214 
Biaxial crystals, 521 
Bichromate battery, 659 
Bile spectrum, 550 
! Binocular microscope, 508 
vision, 475 
Blackburne’s pendulum, 367 
i Black pigment of eye, 469 
| Blood, composition of, 193 
corpuscles, 194 
spectra, 549 
Blowpipe flames, 598 
Blue light, 438 
Body, charging with electricity, 628 
cooling, process in, 607 
loss of heat from, 613 
of microscope, 495 
| Boiling point of saline mixtures, 593 
variations in, 590 
Bones of ear, function of, 375 
Boyle’s law, 183 
Breast wheel, 126 
Breguet’s thermometer, 566 
Brick, osmosis through, 301 
Bright-lined spectra, 542 
Broiling, 606 
Broken spark, 627 
Bronchitis, chronic, treatment of, 208 
Brownian movement, 508 
Bude light, 397 
Building materials, 79 
Bullet, reflection of, 262 
Asphalt varnish, 242 
lights, action of, on air, 613 
Asbestos, 79 
Aspirator, 149 
Astatic needle, 677 
Asthma, treatment of, 208 
Astigmatism, 473 
Atmosphere, height of, 158 
pressure of, 159, 175 
Atmospheric electricity, 647 
origin of, 648 
lights, 387 
spectrum lines, 547 
Atom, centre of force, 50 
defined, 41 
hard, 49 
nature of, 49 
origin of idea of, 42 
vortex, 50 
Atomic attraction, 238 
and motion, 56 
Attraction, acoustic, 369 
electric, 628 
explained, 636 
Atwood’s machine, 258 
Audiphone, 377 
Auditory canal, 375 
Aural speculum, 421 
Auric chloride, 514 
Aurora borealis, 650 
Auroras, 387 
Auscultation, 327 
Axes, coordinate, 249 
Axial illumination, 498 
Axis of rotation, 265 
Axle and winch, 117 
Bacilli, 517 
Bacteria, 515 
Baking, 606 
Balance, 58 
essentials in, 60 
hydrostatic, 66 
of Coulomb, 78 
wheel, 264 
Balloons, 166 
ascents, 168 
sickness, 198 
traffic, 168 
Banded spectra, 390, 544 
Barometer, action of, illustrated, 174 
and altitude, 189 INDEX 
719 
Bullet, electric test for, 715 
Bull’s-eye condenser, 501 
Bunsen’s battery, 659 
burner, 392 
filter pump, 107, 155 
Buoyancy, centre of, 92 
of liquids, 91 
Chemical action in spectrum, 436 
effects of inductorium, 693 
focus, 456 
microscope, 508 
testing of microscope objects, 514 
Chemistry, 238 
relation to physics, 36 
Chest notes, 371 
Chicken cholera bacilli, 518 
Chimes, electric, 629 
Ohladni’s figures, 339 
Chlorides in spectrum analysis, 543 
Chlorophyl spectrum, 548 
Choroid, 469 
Chromatic aberration, 455, 478 
Chromatics, 437 
Chromatic scale, 356 
Chromic acid, 510 
Chromosphere, 382 
Chronograph, 254 
Ciliary muscle, action of, 472 
processes, 469 
Circuit, closing and opening, 654 
Circular polarization, 531, 532 
vibration, 314 
Circulation of blood, 307 
theories of, 307, 308 
CAESIUM, spectrum of, 543 
Caissons, 151, 209 
Calcium light, 389 
spectrum, 543 
Calorescence, 389 
Calorie, 569 
Calorific effects of inductorium, 693 
Calorimeters, 568 
Camera lucida, 460 
obscura, 460 
photographic, 461 
Campani’s eyepiece, 492 
Camphor vapor, condensation of, 578 
Cannon report, 170 
Capillaries, continuous flow in, 295 
Capillarity, 279 
and chemism, 802 
causes and laws of, 282 
Capillary tube, condition of interior, 281 
Carbolic acid solution, 514 
Carbonic acid gas, 210 
tension of, 207 
Cirrus, 582 
Clack valve, 121 
Clamond’s battery, 669 
Cleansing slides and covers, 509 
Cleavage, 71 
produces electricity, 624 
Clepsydra, 258 
Climate, 601 
and latent heat, 572 
Cistern barometer, 176 
Carbon dioxide in air, 158 
light, 662 
monoxide, 210 
Carcel lamp, 395 
Cardiograph, 114 
Carmine liquid, 513 
Cartesian diver, 92 
Cascade, charging by, 641 
Casella aneroid, 189 
Cathelectrotonus, 712 
Cathode, 658 
Catoptric instruments, 519 
telescope, 421 
Caustics, 419 
Caves, air of, 200 
Celestial telescope, 519 
Cellar floors, preparation of, 301 
Celsius scale, 564 
Cement pipes, 128 
Cements, 240 
Centigrade scale, 564 
Centric rotation, 265 
and vapors, 576 
Clocks, electric, 684 
Cloudlight illumination, 503 
Clouds, 582 
Cochlea, 376 
Coddington lens, 478 
Coefficients of expansion of solids, 556 
of liquids, 557 
of gases, 558 
Cohesion, 42, 240 
Cold bath, physiological effects of, 610 
Cold, effects of exposure to, 608 
Cold-blooded animals, 608 
Cold in decompression, 210 
Colland’s gravity battery, 658 
Collimator, 537 
Collision, 259 
balls, 260 
Centrifugal force, applications of, 267 
motion, 266 
pump, 127 
Chain pump, 117 
Chalybeate waters, 96 
Charcoal, absorptive power, 288 
brazier, 616 
filters, 286, 287 
Chemical action a mode of vibration,437 
Colloids, 72, 293 
Color, 79 
and musical pitch, 444 
Coloration, 404 
by rotatory polarization, 534 
Color-blindness, 443 
images, accidental, 442 720 
INDEX 
Color, influence of, on radiation of heat, 
603 
Convection of heat, 600 
Convergent lenses, 446 
Convex lens, action of, explained, 447 
and convergent rays, 450 
meniscus in tubes, 280 
mirrors, 418 
Cornea, 455, 467 
Corpuscles of blood, 194 
Corti, organ of, 876 
Cotton, absorbent, 285 
Coulomb, balance of, 632 
Cover adjustment of objective, 484 
Covers for microscope, 509 
Cream tube, 98 
Critical angle, 426 
Crookes’s argument for radiant matter 
217 
Colored lights, methods of mixing, 441 
mixtures of, 440 
Colored rings from polarized light, 529 
Colors, complementary, 442 
of spectrum, 482 
Combustion, 391 
Comets, 386 
hydrocarbons in, 387 
Communicator, electric, 685 
Commutator, electric, 679 
Comparison prism, 538 
Compass needle, 676 
action of, explained, 687 
Compensation bar hygrometer, 585 
plate, 536 
stripes, 560 
Complementary colors, 442 
Compound deflned, 46 
balance-wheel, 560 
microscope, 479 
Compressed air, hygienic management 
of, 209 
impurities in, 210 
therapeutical uses of, 207 
Compressed charcoal filters, 286 
oxygen, action of, on germs, 205 
in water, 212 
kinetic theory of gases, 218 
Crossed lenses, 454 
Cruikshank’s battery, 657 
Cryophorus, 580 
Crystalline lens, 468 
Crystallization, 572 
dry method, 70 
moist method, 70 
Crystallized bodies, 70 
Crystalloids, 72, 293 
Culinary paradox, 591 
Cumulus, 582 
Cupping-glass, 162 
Cupric sulphate battery, 657 
electric decomposition of, 664 
Curvature of field, 457 
Cutting implements, 273 
Cylindrical mirrors, 420 
Compressibility, 63 
of liquids, 81 
Compression air-pump, 150 
manometer, closed, 186 
open, 185 
Concave meniscus in tubes, 280 
lens, action of, explained, 448 
mirrors, parts of, 415 
Concha, 375 
Concordant sounds, 856 
Condensed air, respiration of, 201 
oxygen, respiration of, 201 
Condenser of inductorium, 692 
Condensers, achromatic, 499 
electric, 643 
Condensing air-chamber, 151 
Conduction, 595 
electric, 629 
of electricity, 621 
of heat by textile fabrics, 598 
by liquids, 599 
of sound, 326 
Conical valve, 121 
Conjugate foci, 416, 449 
Contagion spores, 130 
Continental climates, 601 
Continuous forces, 239 
spectra, 542 
Contractility, 76 
Cooking, application of heat in, 594 
by radiant heat, 605 
Conservation of energy, 234 
Consonants, 373 
DAMMAR cement, 242 
Daniell’s battery, 658 
Dark space tube, 220 
Davy lamp, 597 
Daylight illumination, 502 
Death, electric test for, 715 
from diminished pressure, 200 
from increased pressure, 206 
rate and barometer, 182 
Declination, magnetic, 676 
Decomposition apparatus, 148 
by heat, 555 
Decompression accidents, treatment of, 
211 
effects of, 210 
Defining power of objective, 483 
Deflagration by electricity, 662 
Degradation of energy, 235 
Densimeter, 103 
Density, 60 
of air, therapeutical effects of, 193 
of gases determined, 139 
Dentals, 373 
Depolarization, 528 
Deviation, angle of, 424, 428 INDEX 
721 
Deviation by rotation of mirror, 412 
minimum, 429 
Devices for raising water, 116 
Dew, formation of, 605 
non-conducting power for heat, 601 
point, determination of, 586 
Dialysis, 298 
application of, 299 
Dialyzer, 298 
Diamagnetism, 688 
illustrated, 689 
Diapason, 364 
Diaphanous bodies, 899 
Diaphragms, 458 
of microscope, 494 
Diatomic scale, 356 
EAR in lower creatures, 373 
in man, 374 
Earth’s action on magnets, 674, 676 
Ebullition, 590 
Edison light, 661 
Effects of illumination, 500 
Effervescent saline waters, 96 
Efflux, 290 
form and quantity of, 106 
Effusion, 290 
Eggs, boiling of, 595 
Elasticity, 63 
limit of, 76 
of compression, 77 
of flexure, 77 
of solids, 75 
of torsion, 76, 78 
Elder-pith, 512 
Electric, 625 
arc, 661 
aura, 627, 699 
batteries, double fluid, 658 
single fluid, 657 
charge, dissipation of, 634 
penetration of, 640 
chimes, 629 
condition of atmosphere, 647 
current, 655 
enfeeblement of, 656 
reactions of, 686 
discharge through card, 641 
egg, 628 
fishes, 695 
induction, 635 
lights, 390 
machine, cleaning of, 626 
machines, parts of, 624 
pail, 637 
pendulum, 622 
residuum, 640 
Differential thermometer, 562 
Diffraction, 459, 522 
spectra, 482, 523 
Diffused light, 409 
Diffusion between liquids, 291 
of gases, 294 
through barriers, 300 
Diminished pressure, death from, 200 
effects of, 196 
Diminution of intensity of sounds, 346 
Dioptric instruments, 519 
Diplopy, 474 
Dipping needle, 677 
Direct vision spectroscope, 540 
Discharging rod, 641 
Disease germs, 96, 515 
Disinfectant action of charcoal, 288 
Dispersion, abnormal, 432 
and deviation, 432 
normal, 431 
Dissipation of energy, 236 
of sound, 326 
Dissociation, 555 
Dissonance, 352 
Distillation, 583 
Distilled water, 514 
Distribution, magnetic, 672 
Divergent lenses, 446 
Diving-bell, 151 
Dobereiner’s lamp, 289 
Double refracting prisms, 526 
refraction, 520 
Draper’s theory of circulation, 308 
Draw tube of microscope, 494 
Dromograph, 114 
Drops, 244 
Drowning, death by, 94 
Drum, 375 
Dry objective, 480 
Dry pile battery, 660 
Ductility, 74 
Du Faye’s theory, 622 
Duhamel, graphic method, 354 
Duplex burners, 394 
Dynamic electricity, 652 
Dynamoelectric machine, 694 
spark, 660,699 
chemical effects of, 646 
duration of, 644 
in air, 626 
mechanical effects of, 645 
physical effects of, 645 ! 
physiological effects of, 646 
tension, 656 
vane, 629 
Electricity, 620 
action on animals, 698 
a physiological test, 712 
bound, 636 
by cleavage and pressure, 624 
conductors of, 621 
distribution of, 631 
induced by magnet, 690 
in diagnosis, 712 
in plants, 695 
influence of points on, 634 
intensity of, 656-659 
laws of, 622, 623 722 
INDEX 
Electricity, measurement of, 631, 659 
quantity of, 656, 659 
rate of passage, 644 
superficial distribution of, 633, 634 
Electrobiology, 695 
Exhaustion air-pump, 152 
manometer, 186 
Exosraosis, 297 
Expansion and pressure, 185 
by heat, 555 
Electrochemical theory, 664 
Electrodes, 653, 696 
of gases, 558 
of liquids, 557 
Electrodynamics, 652 
Electrolysis, 665, 702 
Electrolytes, 665 
Electromagnet, 683 
and induced currents, 691 
Electromagnetic motors, 683 
Electromagnetism, 678 
Electrometallurgy, 665 
Electrometer, 632 
Electromotive force, 656 
series, 655 
Electronegatives, 665 
Electrophorus, 630 
Electrophysiology, 695 
Electroplating, 666 
Electropositives, 665 
Electroscopes, 631 
Electrotherapy, 698 
Electrotonus, 710 
Electrotyping 665 
Element, 41 
defined, 46 
hydrogen, the original, 49 
Elliptical polarization, 531, 533 
vibration, 814 
Emission theory, 380 
Emmetropy, 473 
Emphysema, treatment of, 208 
Emulsions, 291 
Endolymph, 376 
Endoscope, 412 
Endosmometer, 296 
of solids, 556 
Expiration, act of, 164 
Extraordinary ray, 521 
Extremity, upper, electricity applied to 
muscles of, 708 
lower, electricity applied to, 709 
Eyes, 466 
care of, with microscope, 505 
Eye lens, 492 
Eyepiece, 479, 492 
FAHRENHEIT’S scale, 564 
Falling bodies, 257 
stream, form of, 108 
Falsetto notes, 371 
Faraday discovered radiant matter, 216 
tube receiver, 145 
Faradaic current, 689, 691, 704 
Faradization localized, 705 
Faure’s accumulator, 660 
Fenestra ovale, 375 
Field, curvature of, 457 
lens, 492 
Filter pump, Bunsen, 155 
Filtration, 285, 286, 287 
Fire-damp and barometer, 190 
Fireplaces, 616 
Fish, destruction of, 213 
Fishes, electric, 695 
Fixed alkalies, 514 
Flagella, 515 
Flames, constitution of, 396 
from fluids, 394 
from solids, 395 
Endosmosis, 297 
Energy, 38 
conservation of, 234 
degradation of, 235 
dissipation of, 236 
measurement of, 255 
representation of, 251 
subdivisions of, 237 
transformations of, 233 
Enteric fever bacilli, 517 
Eosin color, 513 
Erect images, 410 
Erector of microscope, 494 
Erysipelas micrococci, 518 
Ether, 514 
character of, 381 
defined, 45 
luminiferous, 380 
vibrations, rate of, 381 
Eustachian tube, 375 
Evaporation in vacuo, 575 
Excentric rotation, 265 
Exercise and insensible perspiration, 588 
sensitive, 343 
singing, 342 
structure of, 598 
Flatness of field, objective, 484 
Flexible siphon, 120 
Floating bodies and capillarity, 284 
equilibrium of, 92 
stability of, 92 
Flotation, influence of sex and obesity 
on, 94 
Fluids of different densities, equilibrium 
of, 97 
resistance to moving objects, 113 
Fluorescence, 388 
Focus, depth of, 457 
determination of, 450 
Focussing apparatus of microscope, 496 
Foetus, lungs of, 98 
Fog, 581 
Foot pound, 255 INDEX 
723 
Force, 38 
Gases have weight, 137 
hypothetical constitution, 138 
reunite behind dividing solid, 187 
transpiration of, 290 
washing and drying of, 148 
Gas-sphygmoscope. 115 
Gauze, action of, on flame, 566 
Geissler’s tubes, 155, 544, 693 
Generation of gas, 143 
Geometry, 88 
Germs, 96 
and compressed oxygen, 205 
collection of, 193 
English unit of, 254 
ideas regarding, 238 
measure of, 254 
pump, 122 
Forces, parallelogram of, 253 
representation of, by lines, 252 
Fortin’s barometer, 176, 177 
Foucault’s prism, 527 
Foul air, removal of, 614 
Fractional distillation, 584 
Fragility, 73 
Franklin’s theory of electricity, 623 
Fraunhofer’s lines, 545 
Freezing mixtures, 572 
Fresnel’s rhomb, 532 
Friction, 276 
cause of, 240 
conveyance by air, 191 
destruction of, 192 
filtration of, from air, 191 
Giffard’s injector, 107 
Gilding, 666 
Globe lightning, 649 
Glycerine, 514 
barometer, 178 
jelly, 515 
Gmelin’s test, spectrum of, 550 
j Gradient, barometric, 182 
Graphic method, 252 
Duhamel’s 354 
electricity, 620 
laws of, 277 
Frog galvanoscope, 697 
Frying, 606 
Fulgurites, 649 
Fundamental colors, 442 
tone, 358 
Furnaces, 618 
heat and vaporization, 577 
supply of vapor to, 619 
Fusion, laws of, 570 
Graphite, 72 
Gratings, 523 
Grating spectroscope, 540 
Grove’s battery, 658 
Gravity, 56, 239 
GALILEO, theory of action of pump 
172 
Galvanic electricity, 653 
centre of, 56 
influence of, on falling bodies, 257 
specific, 60 
Gregorian telescope, 421 
Grenelle artesian well, 97 
Grenet battery, 657 
Gridiron pendulum, 559 
Gutturals, 373 
Gymnotus, 696 
Gyroscope, 267 
Galvanocaustic loop, 700, 701 
Galvanocautery, 699, 700 
battery, 702 
Galvanometer, 679 
Galvanoplastics, 665 
Galvanopuncture, 703 
Gamut, 356 
Gas-burners, forms of, 393 
Gas, 139 
compressibility of, 141 
elastic force, 141 
ll4 
Hamiadynamometer, 114 
Haematachometer, 114 
elasticity of, 142 
expansibility of, 141 
generation of, 143 
flame, 391 
furnaces, 597 
pouring of, 146, 147, 148 
relation of density and combining 
equivalent, 140 
Gaseous matter, 135 
Gases, absorption of, by liquids, 295 
by solids, 287 
arrange themselves according to 
density, 146 
collection by displacement, 148 
conduction power for heat, 602 
diffusion of, 294 
form not fixed, 136 
Hsematoxylin, 513 
Haemoglobin, 194 
spectrum of, 194 
Hail, 583 
j Hair, elasticity of, 78 
hygrometer, 585 
Hand-glass, 163 
I Hardening, 510 
Hardness, 72 
i Harmonics, 358 
| Harvey’s theory, 307 
objections to, 307, 308 
Head, electricity applied to muscles, 705 
Heart sounds, 345 
Heat, absorption of, 604 
convection of, 600 724 
INDEX 
Heat, effects on composition, 554 
on physical properties, 553 
on measures of quantity, 559 
on measures of time, 569 
emission of, 604 
evolved from body, 609 
from exercise, 610 
in prismatic spectrum, 436 
lightning, 649 
measurement of, 561 
mechanical equivalent of, 619 
source of, in bodies, 607 
sources of, 552 
theories of, 551, 552 
theory of exchanges of, 605 
transmission of, 604 
Heliograph, 413 
Helioslat, 413 
Helmholtz’s resonators, 360 
Hepatic waters, 96 
Herschelian telescope, 421 
Heterogeneous liquids, arrangement of, 
98 
i Illumination in microscope, 498, 499 
500, 502, 503 
| Illuminating flames, 392 
I Images by concave lenses, 453 
by convex lenses, 451 
by spherical mirrors, 418 
fixation of, 509 
formation of, 401, 460 
from plane mirrors, 410 
lateral inversion of, 411 
Imbibition of liquids, 284 
j Immaterial, 38 
Immersion objective, 486 
Impact, 260 
Impulse, transmission of, 260 
I Incandescence, 389 
[ Incandescent light, 661 
spectra, 545 
Inclined plane, 272 
surfaces, capillary action of, 283 
| Increased pressure, effect of, 200 
j Incus, 375 
! Index of refraction, 425 
India rubber and osmosis, 302 
Indicator, electric, 685 
Indium, spectrum of, 543 
| Induced currents of electricity, 689 
i Induction, charging by, 636 
coil in spectrum analysis, 543 
electric, 635 
passes through glass, 638 
magnetic, 672 
Inductive power, 638 
Inductorium, 691 
experiments, 693 
j Inertia, 61 
i Infra-red spectrum, 546 
j Injection, 512 
Inorganic bodies, 64 
| Insensible perspiration and exercise, 588 
Inspiratory act, 164 
i Instruments, 269 
care of, 273 
Insulator, 625 
Intensities of light, relative, 408 
laws of, 404 
Intensity of sounds, 346 
Interference of light, 521 
of sounds, 351 
spectrum, 523 
| Intermittent light develops sound, 322 
siphon, 121 
: Internal ear, 376 
Interstice, 43 
actual size of, 45 
relative size of, 44 
Intramolecular movements, 265 
Hibernation, 608 
Hollow prisms, 539 
Holtz electric machine, 643 
in spectrum analysis, 544 
Homogeneous immersion objective, 487 
Hot-air furnaces, 618 
Hot-blooded animals, 608 
Hot-water furnaces, 618 
Houses, warming of, 615 
Humors of eye, 468 
Huyghen’s eyepiece, 492 
Hyaloid membrane, 468 
Hydraulic engineering, materials for, 127 
friction, 107 
press, 87, 88 
ram, 124 
tourniquet, 109 
Hydraulics defined, 115, 116 
Hydrocarbons in comets, 387 
Hydrodynamics, 105 
Hydroelectric machine, 630 
Hydrogen, 209 
osmose power of, 301 
the original element, 49 
Hydrometer, 100 
Nicholson’s, 67 
Hydrostatic bed, 88 
test for steam boilers, 89 
in infanticide, 93 
Hydrostatics, 86, 87 
Hygiene and osmose of gases, 301 
Hygrometric bodies, weighing of, 59 
Hypermetropy, 473 
Hygrometry, 585 
Iridescence, 438 
Iris, 469 
diaphragm, 459, 498 
Iron deposit by electricity, 666 
ICE flowers, 554 
machines, 576 
Ignus-fatui, 387 
occlusion power of, 289 INDEX 
725 
Iron, osmosis through, 302 
water pipes, 128 
Irradiation, 472 
Irrigation, 117 
Island climates, 601 
Isothermal lines, 600 
Life and the atmosphere, 166 
Lift-pump, 122 
explained, 161 
Light and life, 397 
and motion, 391 
composition of, 430, 433 
decomposition of, 434 
electromagnetic theory of, 380 
for spectroscope work, 539 
propagation of, 399 
qualities of, 403 
recomposition of, 434 
• sources of, 382 
theories and sources of, 379 
theory of origin, 383 
units of, 407 
velocity of, 402 
Lightning, 387, 649 
identical with electricity, 647 
flash, 172 
rod, 650 
Limpidity, 85 
I Lines of spectrum, wave lengths, 546 
Lint, absorption action of, 285 
I Liquefaction, 579 
Liquid matter, 81 
thermometers, 562 
Liquids, conduction power of, for heat, 
598 
JEWELLERS’ cement, 241 
Joule’s mechanical equivalent of 
heat, 619 
Jourdanet, theory of, 198 
Kaleidoscope, 266, 415 
Katione, 665 
Kellner’s eyepiece, 498 
Kerosene furnace and explosion, 599 
Kilogrammetres, 255 
Kinematics, 38 
Kinetic energy, 232, 238, 247 
theory, 218 
of gases, 138 
Konig’s resonator, 361 
stethoscope, 328 
Kymographion, 114 
T ABIALS, 373 
JL Labyrinth, 376 
Lactometer, 102 
Lamina spiralis, 376 
Lamplight illumination, 503 
Landslides, 91 
Lantern, photoelectric, 465 
Laryngoscope, 412, 421 
Larynx, 370 
Latent heat, 571 
densities, 83 
downward pressure, 90 
elasticity, 82 
equilibrium in communicating ves- 
sels, 95 
falling, 257 
form not fixed, 81 
hypothetical constitution of, 84 
lateral pressure, 91 
movements in tubes, 107 
porosity, 82 
resist compression, 81 
reunite behind dividing solids, 84 
spheroidal state, 85 
transpiration of, 290 
upward pressure, 91 
warming of, 602 
Liquidity, 84 
Lissajou’s figures, 366 
method, 365, 366 
Lithium, spectrum of, 543 
Local action in batteries, 656 
Long circuit, 681 
compensator, 681 
Longitudinal impulse, 261 
vibration, 313 
Longsightedness, 473 
Loops and nodes, 337 
Lovers’ telegraph, 326 
Low-pressure engine, 580 
Lubricating materials, 277 
Lugol’s solution, 514 
Luminosity, 893 
Law of movement, 249 
Laws of capillarity, 282 
of transverse vibrations of sound, 
Lead in water, 128 
Lead-pipe, insoluble lining, 128 
Leaves, 305 
Leclancbd battery, 657 
Ledger lines, 357 
Lens, aperture of, 446 
change in curvature, 471 
Lenses, 445 
Leslie’s canister, 603 
Levers, law of, 271 
three orders of, 269 
Leyden battery, 641 
vial, 639 
dissected, 640 
spark, 699 
Lichtenberg’s figures, 641 
Lieberkiihn, 421 
condenser, 501 
Liebig’s condenser, 584 
Life and rarefied air, 153 726 
INDEX 
Luminous effects of inductorium, 693 
Lungs, flotation of, 93 
moisture exhaled from, 587 
Lycopodium, absorption action of, 285 
Matter, extensibility of, 55 
impenetrability, 55 
indestructibility of, 54 
inertia of, 61 
mobility of, 61 
omnipresence of, 45 
physical forms of, 64 
porosity of, 62 
properties of, 35 
relation to rotation, 52 
structure of, 44 
Machines, 209 
Magdeburg hemispheres, 160 
Magenta color, 513 
Magical orchestra, 327 
Magic lantern, 461 
Magnesian light, 389 
phosphate, action on water, 133 
Magnet, artificial, 670 
action on high vacuum-tube, 225 
on low vacuum-tube, 224 
induces electricity, 690 
power of, 675 
Magnetic keeper, 671 
motors, cost of, 684 
needle, 676 
polarity, laws of, 671 
storms, 676 
Magnetizing, methods of, 673 
Magnetism, 670 
Magnetoelectric machine, 690 
Magnifying power, augmentation of, 
504 
subdivision of, 39 
theory of oneness of, 46 
transmigration, 54 
Maximum density, 558 
Maxwell’s theory of light, 380 
Mayer’s floating magnets, 675 
Mean free path, 218 
in radiant matter, 220 
Meat, boiling of, 594 
Meatus, 375 
Mechanical action of radiant matter, 224 
effects of inductorium, 693 
mechanism of eye, 466 
Mechanics, 238 
of blood circulation, 114 
relation to physics, 36 
Medical magnetoelectric machine, 690 
physics, domain and application of, 
36 
measurement of, 504 
of microscope, 478 
Malaria, 111 
and marshes, 133 
Malarial germs, action of trees on, 192 
Mai des Montagues, 196 
explanation of, 198 
symptoms of, 197 
Malingerers, electric test for, 715 
Malleability, 73 
Malleable glass, 78, 571 
Malleus, 875 
Manometer, compression, closed, 186 
open,lBs 
equality, 187 
exhaustion, 186 
Manometric flames, 361, 362, 363 
Marey, tambour of, 254 
Marine glue, 242 
Mariotte’s law, 183 
Marloyl’s harp, 338 
Marsh draining and malaria, 133 
Mason’s hygrometer, 586 
Mass, unit of, 252 
Mastic cement, 241 
Mathematics, relation to physics, 35 
defined, 36 
Matter, 38 
chemical divisions of, 64 
compressibility of, 63 
defined, 38 
effect of heat on, 42 
effect of pressure on, 42 
thermometers, 564 
Megascope, 465 
Melloni’s multiplier, 668 
Membrana tympani, 375 
Membranes, vibrating, 339 
Membranous labyrinth, 376 
Mendinger’s battery, 658 
Meniscus, 447 
Menstruum, 245 
Mercurial pendulum, 560 
Mercury, freezing and boiling point, 
562 
pump, 153 
| Metals, conducting power for heat, 595 
magnetic, 672 
osmosis of gases through, 802 
| Metaphysics, relation to physics, 35 
Metronome, 263 
interrupter, 696 
Miasm, 583 
Mica films, 529 
Micrococci, 515 
Micrococcus tetragenus, 518 
| Microscope, 418, 477 
care of, 605 
errors, 506 
mirror, 421 
projection, 465 
solar, 462 
Micrometre screw, 275 
Microscopic preparations, cements for, 
elasticity of, 63 INDEX 
727 
Microtome, simple, 511 
Middle ear, 375 
Milk tester, centrifugal, 267 
Mineral waters, 96 
Minims, 244 ' 
Minimum deviation, 429 
Mirage, 426 
Mirrors, 410 
aperture of, 416 
elements of, 416 
pole of, 416 
Mixed powders, colors of, 440 
Mixture, 290, 291 
Mobile, 247 
Mobility, 61 
Modern microscope, parts of, 480 
Mohr’s scale, 72 
Moisture exhaled from lungs, 587 
from skin, 588 
Muscle, irritability of, 713 
Musical notation, 356 
’ pitch and color, 444 
Myographion, 254 
Myopy, 473, 
VTASAL speculum, 421 
iM speech, 373 
J Natural philosophy, 35 
| Nearsightedness, 478 
| Nebular spectra, 544 
i Neck, electricity applied to muscles of, 
707 
: Needle, telegraph, 686 
for microscope work, 510 
Negative electricity, 622 
pole, 653 
Nerve current, 697 
Newtonian telescope, 421 
Newton’s laws of motion, 250 
Nickelplating, 667 
Nicol’s prism, 527 
; Nimbus, 582 
; Nitric acid, 514 
| Nobert’s test-plates, 489 
j Nodes and loops, 337 
! Noise, 319 
| Normal spectra, 523 
■ Norremherg’s apparatus, 525 
I Nose-piece to microscope, 492 
| Notation, musical, 856 
Notes, 359, 371 
Numerical aperture, 481 
Molar attraction, 238 
and motion, 56 
illustrated, 239 
motion, varieties of, 256 
Molecular attraction, 238 
and motion, 56 
kinds of, 240 
change and polarized light, 530 
motion, varieties of, 278 
divisions of, 279 
Molecule, 41 
actual size, 45 
defined, 41 
do not touch, 48 
motion among, 43 
movement of, in propagation of 
sound, 325 
relative size of, 44 
the true matter, 226 
vibration of, 44 
Momentary forces, 239 
Momentum, 254, 259 
Monas crepisculum, 40 
Monochord, 336 
Monochromatic light, 437 
Monsoons, 559 
Morse telegraph, 685 
Mosaic gold, 622 
Motion, 38, 247 
non-vital, 508 
Newton’s laws of, 250 
ABJECTIVE, 47.9 
' / care of, 505 
Objects, preparation of, 510 
Obsidian, 537 
Occlusion, 288 
Octave, 356 
(Ersted’s experiments, 82, 678 
Ohm, 659 
j Oil of cedarwood, 487 
of fennel, 487 
Opacity, 79 
I Opalescent bodies, 399 
| Opaque bodies, color of, 438 
| Opera-glass, 519 
Ophthalmoscope, 421 
Optic angle, 470 
Optical centre of lens, 451 
Optical mechanism of eye, 467 
I Optic axis of crystals, 521 
of eye, 470 
centre of lens, 470 
Optics, 379 
Orbital rotation, 265 
i Ordinary ray, 521 
| Ordinates, axis of, 249 
I Organic bodies, 65 
reciprocating, 262 
reflection of, 262 
and light, 391 
of fluid in capillary tube, 303 
of mouth in speech, 372 
Motor, electromagnetic, 683 
Movement, law of, 249 
kinds of, 250 
Multiple images, 411 
prism spectroscope, 539 
Multiplier, 679 
Muscle current, 696, 697 728 
INDEX 
Organic matter in water pipes, 130 
molecules, 266 
Organisms, minute living, 40 
Organized bodies, 65 
Oscillation, amplitude of, 263 
Oscillating motion, 262 * 
Osmic acid, 510 
Osmosis, 297, 300 
Osteomyelitis micrococci, 518 
Otolithic sac, 374 
Overshot water wheel, 126 
Overtones, 358 
Ovum, structures evolved from, 48 
Oxygen and life, 158 
high tension of, 204 
poisoning by, 205 
respiration of, 201 
tensions, 196 
tension of, in air, 213 
therapeutical effects of, 207 
Oxycalcium light, 462 
Oxyhtemoglobin, 195 
Oxyhydrogen flames, character of, 397 
lantern, 462 
lights, 389 
Oxymagnesium light, 463 
Oxyzirconium light, 463 
Ozone and malarfa, 134 
Phosgenic action of radiant matter 
221 
Phosphorescence, 387 
Photometers, 405 
Photophone, 321, 377 
Photosphere, 382 
Physical phenomena perceived, 37 
: Physics, 238 
defined, 35 
divisions of, 37 
of respiration, 310 
Physiological effects of inductorium, 
693 
Picro-carmine liquid, 513 
Piezometrd, 82 
Pigments, 438 
Pinna, 374 
Pipette, 161 
Pitch, 359 
of sounds, 352 
Plane mirrors, applications of, 412 
Planes of pelvis, 273 
Planetary spectra, 547 
Planets, 385 
Plants, absorption in, 306 
distribution influenced by heat, 612 
electricity of, 695 
! Plaster, osmosis through, 301 
| Plateau’s experiment, 85 
Plates, vibrating, 338 
| Platinum and osmosis, 302 
occlusion power, 289 
Pliancy, 78 
I Plucker’s tubes, 544 
Pneumatics defined, 135 
Pneumatic apparatus, 143 
trough, 144 
Pneumonia micrococci, 518 
Podura scale, 490, 491 
Points, action on electric machines, 634 
Poisons dialyzed, 299 
Polarized illumination, 502 
light, action of magnet on, 689 
interference of, 528 
theory of, 527 
Polarization by double refraction, 525 
by reflection, 524 
by single refraction, 525 
projection, 465 
of electrodes, 665 
of light, 524 
of sound, 335 
; Polarizing apparatus, 525 
mirror, 524 
Poles, electric, 653 
| Pores, physical, 62 
sensible, 62 
Porosity, 62 
; Position defined, 38 
stability of, 56 
in animals, 57 
; Positive electricity, 622 
PALLADIUM occlusion power of, 289 
Paper-pulp filters, 287 
Papin’s digester, 593 
Parabolic illuminator, 499 
mirrors, 419 
speculum, 501 
Parachute, 170 
Parallelogram of forces, 253 
Paralysis, electricity a test for, 713 
Paramagnetism, 688 
Paraplegia in decompression, treatment 
of, 211 
Particle defined, 40 
Pascal’s experiment, 174 
law, 87 
action of, in body, 89 
Pedesis, 508 
Pencil of light, 400 
Pendulum, 263 
Penetrating power, 255 
of objective, 483 
wounds, 55 
Penumbra, 400 
Percussion, 350 
Perilymph, 876 
Period of vibration, 312 
Periscopic glasses, 474 
Permanganate of potash spectrum, 548 
Persian wheel, 118 
Pettenkoffer’s test, spectrum of, 550 
Phonautaugraph, 368 
Phonograph, 368 INDEX 
729 
Positive pole, 658 
Posterior chamber of eye, 469 
Potassium spectrum, 543 
Potential electric, 655 
energy, 231, 238 
Presbyopy, 473 
Preservative media, 514 
Pressure and solubility of gas, 190 
eifect on boiling point, 591 
equality of, in fluids, 87 
on bottom of a vessel, 98 
physiological effects of, 195 
produces electricity, 624 
Primary color sensations, 442 
current, constant, 699 
intermittent, 704 
electricity, 653 
Prime conductor, 625 
Principal focus, 416, 449 
Prism, 428 
achromatic, 435 
in spectroscope, 538 
reflecting, 430 
Prismatic spectrum, 430 
chemical action in, 436 
heat in, 436 
maxima of energies in, 436 
Projectiles, trajectory of, 258 
Projection lantern, 464 
Protoplasm, 305, 698 
structures evolved from, 48 
Rainbow, 433 
Rain water, 96 
Rarefaction cylinders, 199 
Rarefied air and life, 153 
Rate of passage of electricity, 644 
Ray, 400 
Real focus, 417 
Real images, 411, 462 
Reaumur’s scale, 564 
Reciprocating motion, 262 
Rectilinear motion, 256 
Red light, 438 
Reed instruments, 341 
Reflected illumination, 500 
Reflecting prism, 430 
Reflection, laws of, 408 
of heat, 602 
of motion, 262 
of sound from plane surfaces, 332 
from curved surfaces, 333 
total, 426 
Eefracting media, 423 
Eefraction, 422 
atmospheric, 426 
index of, 425 
law of, 427 
of sound, 334 
power of, 424 
single laws of, 424 
Eegistering hygrometer, 585 
thermometers, 665 
Eeguline deposits, 666 
Eeinforcement of sounds, 348, 349 
Eelay battery, 685 
Eepose, 247 
acoustic, 369 
electric, 628 
explained, 636 
Eesidual charge, magnetic, 683 
Eesinous electricity, 622 
Eesistance box. 680 
Eesolving power of objective, 483 
Eesonance, 849, 350 
box, 357 
Pulley, 275 
wells, 117 
Pulse glass, 580 
Pulverization, 40 
Pulvermaeher’s chain, 658 
Pumps, 121 
Pupil, 469 
Putrefaction, influence on flotation, 94 
Pyroelectricity, 623 
Pyrometers, 566 
Quadrant, 414 
Quality, 359 
Resonators, 360, 361 
Respiration, action on air, 613 
physics of, 310 
Resuscitation by electricity, 712 
Retaining siphon, 120 
Retina, 409 
Rheocord, 696 
Rheometre, 679 
Rheostats, 680 
Rheotrope, 696 
Rhinoscope, 421 
Rigor mortis, 76 
Ring cells, 510 
diaphragm, 498 
Roasting 605 
Rolling friction, 276 
Root tips, 305 
Rope pump, 118 
Radiation, 602 
Radiant heat and cooking, 605 
Radiant heat, course of, 602 
matter, 216 
action on solids, 223 
best conditions for, 218 
course of movement, 222 
deflected by magnet, 224 
exerts mechanical action, 224 
interception of, 223 
phosgenic action of, 221 
produces heat, 225 
Radiometer, action of, explained, 219 
Railway tube, 224 
Rain, 582 730 
INDEX. 
Eolation, 265 
Eotatory polarization, theory of, 533 
power of liquids, 534 
Eubber, electric, 625 
Eubidium, spectrum of, 543 
Euby tube, 221 
Eupert’s drops, 73 
Silvering, 666 
Simple diffusion, 292 
electric cell, 654 
microscope, 478 
Singing flame, 342 
Single vibration, 312 
Siphon,ll9 
barometer, 177 
Siren, 353 
QACCHAEIMETEES, 534 
U Saccule, 376 
Salicylic acid, solution of, 514 
Salimeter, 102 
Saline waters, 96 
Salt water, flotation power of, 94 
Sanctorio’s thermometer, 561 
Sand-glass, 258 
Sap, movement in trees, 303 
Satellites, 385 
Saturation, 291 
Savart’s wheel, 352 
Scales in spectroscope, 539 
thermometric, 564 
Scalpels, 273 
Scattered light, 409 
Schizomycetes, 515 
Sclerotic, 467 
Screw, an inclined plane, 274 
Screws, drunkenness of, 275 
Scud, 582 
Seasickness, cause of, 57 
Sea water, gases in, 213 
waves, 112 
Secondary axes of lenses, 451 
coil, 691 
conductor, 629 m 
* current, 704 
Section cutting for microscope, 510 
Sediments, transferance of, 162 
Seeds, germination of, 204 
Selenite films, 529 
Semicircular canals, 376 
Skin, moisture exhaled from, 588 
sensibility of, 713 
Slides for microscope, 509 
Sliding friction, 276 
Slit for spectroscope, 537 
Smee’s battery, 657 
Snow, 583 
Soapstone in stoves, 302 
Society, screw of, microscope, 
Sodium chloride, decomposition of, 664 
spectrum, 542 
Solar action, energy of, 383 
microscope, 462 
spectrum, 545 
lines as a scale, 547 
Soldering, 243 
Soleil’s saccharimeter, 536 
Solenoids, 686 
Solid and gas, adhesion of, 245 
and liquid, adhesion of, 243 
Solidification, laws of, 570 
Solid matter, 64 
in urine, estimation of, 102 
Solids, adhesion of, 240 
changed by radiant matter, 223 
density of, 66 
divided do not reunite, 70 
fixity of forms, 65 
hypothetical constitution of, 80 
resist compression, 66 
Solution, 290, 291 
explained, 244 
Solvent, 245 
50ng,370 
Sonometer, 336 
Sonorous bodies, 335 
Sound, analyzer, 364 
analysis of, 360 
conduction of, 326 
dissipation of, 326 
from inanimate nature, 320 
Sensitive flames, 343 
Septicaemia bacilli, 518 
Sequoia Wellingtonia, 304 
Sewage, 96, 110 
disposal of, 111 
in houses, 129 
leakage, osmosis of, 301 
utilization of, 133 
Sextant, 414 
Shadow, 400 
Shearing, 75 
Sheaves, 275 
Sheet lightning, 649 
Shellac cement, 242 
general properties of, 319 
increase in intensity, 348 
intensity of, 346 
interference of, 351 
length of wave, in air, 360 
origin of, 320 
phases, 317 
polarization of, 335 
propagation of, 323, 324 
reinforcement of, 348 
reflection from plane surfaces, 332 
from curved surfaces, 333 
Shoals, 110 
Short circuit, 681 
Shunt, 680 
Sick rooms, ventilation of, 615 
Silt, 110 
Silurus, 696 INDEX 
731 
Sound, refraction of, 834 
special properties of, 346 
synthesis of, 364 
transmission of, in tubes, 317 
velocity of, in gas, 329 
in liquids, 330 
in solids, 331 
Sounder, electric, 686 
Sounding tube, 341 
Sound waves, characters of, 359 
length of, 371 
reflection of, 318 
Soups, preparation of, 594 
Sources of light, 379 
Space, 88 
unit of, 251 
Spark, electric, 660 
Specific gravity, 60 
bottle, 83 
of bodies lighter than water, 68 
of liquids, 83, 84 
of solids, 69 
of soluble bodies, 68 
of powders, 68 
volumetric method, 67 
heat, 567 
determination of, 569 
Spectacles, 474 
Spectra of stars and planets, 385 
Spectroscope, 536 
Spectrum, 430 
analysis, 542 
colors, 432 
Stereoscope, 476 
Stethoscope, 827 
Still, 584 
Stomata, 305 
Stops, 454, 458 
Stoves, vitiation of air by, 802 
warming by, 617 
Strangulated hernia, reduction of, 208 
Stratus, 582 
Stream, form of falling, 108 
from lateral opening, 105 
from vertical opening, 106 
Strontium, spectrum of, 543 
Student lamp, 395 
Stupor from cold, 612 
Subdivision, by solution, 40 
chemical, 41 
mechanical, 39 
Subdivisions of energy, 237 
Sub-stage of microscope, 499 
Suckers, 159 
and animal life, 161 
Sulphuretted hydrogen, 111 
Sun, 382 
Sunlight illumination, 502 
Surface influence on radiation of heat, 
tension of liquids, 281 
Swimming bladder, compression of, 212 
of fishes, 92 
Sympathetic vibrations, 343 
Synthesis, 434 
of sounds, 360, 364 
projection, 465 
Speech, 372 
Spherical aberration, 419, 453, 478 
Spherical lenses, forms of, 446 
parts of, 445 
Spheroidal state, 85 
of liquids, 593 
Sphygmograph, 115 
Sphygmophone, 115 
Spiral canal, 376 
Spirilla, 517 
Spirit-level, 99 
Spongy iron, 287 
Sprengel’s air-pump, 153 
Springs, superficial and deep, 95 
Staining microscope objects, 513 
Stage of microscope, 495 
Stanhope’s eyepiece, 493 
lens, 479 
Stapes, 375 
Stars, 385 
Static electricity, 698 
Stave, 356 
Steam engines, 578, 580 
exhaust for filtration, 286 
rpAMTAM metal, 72 
x Telegraph, 685 
Telephone, 694 
Telescope, 421, 519 
in spectroscope, 539 
Temperature and dew point, 686 
effect on solution, 245 
of body and vaporization, 608 
remarkable, 566 
Tempering, 72 
Tenacity, 75 
Tension of oxygen, 196 
Tents, hygienic advantages of, 301 
Terrestrial telescope, 519 
Testing objectives, 488 
Textile fabrics, conduction power of, for 
heat, 598 
Thallium, spectrum of, 543 
Theories of light, 379 
Thermal unit, 569 
Thermoelectricity, 667 
Thermoelectric series, 668 
Thermometer, 661 
Thermometric scales, 563 
Thermopile, 668 
Thin films and polarized light, 529 
Thomson’s galvanometer, 680 
gauge, 189 
furnaces, 618 
pipes, warming by, 618 
Stellar spectra, 547 732 
INDEX 
Thunder, 170, 649 
Timbre, 359 
Time, 38 
Unit of weight, 252 
Urinometer, 101 
rules for reading, 101, 102 
Utricle, 376 
unit of, 251 
Tin-lined lead pipes, 129 
Tissues and oxygen, 206 
Toepler-Holtz electric machine, 643 
Tolle’s amplifyer, 494 
Tone, 352 
TTACUUM, 153 
Y by chemical agents, 155 
electric discharge in, 628 
imperfection of, 45 
limit of, 155 
Torricellian, 173 
tube, 226 
Yalves, 121 
Yane, electric, 629 
Yapor, 139 
defined,l39 
vibrations of, 357 
Torpedo, 696 
Torricelli’s experiment, 172 
theorem of, 105 
vacuum, 173 
Torsion, 75 
electrometer, 632 
Tourmaline, 526 
pincette, 529 
Trajectory, 249 
of projectiles, 268 
Transformation of energy, 283 
Translatory molecular motion, 278 
Translucent bodies, 399 
Transmigration of matter, 54 
Transparency, 79 
Transparent bodies, color of, 439 
media, 398 
diffusion of, 295 
elastic force of, 578 
instantaneous condensability of, 579 
of water, tension of, 592 
properties of, 574 
supply of, to rooms, 619 
temperature of formation of, 573 
Vaporization, 573 
a cooling process, 575 
causes influencing, 574 
Velocities, table of, 248 
Velocity, 247 
of sound in gases, 329 
in liquids, 330 
in solids, 331 
mirror, 415 
Transpiration, 290 
Transverse vibration, 313 
Treble stave, 357 
Trees, ascent of sap in, 303 
Triangle, musical, 338 
Trituration, 40 
Trunk, electricity applied to muscles, 709 
Tubercle bacilli, 517 
Tube receiver, 145 
rheostats, 681 
Tubes, calibering of, 562 
inclined, movements of fluids in, 108 
Tuning-fork, 338 
in opera houses, 357 
Turbine, 126 
Vena contracta, 106 
Venomous serpents, bites of, 163 
Ventilation, object of, 614 
of sewage pipes, 131 
Ventriloquism, 373 
Vertical illumination through objective, 
502 
Vestibule, 376 
Vibrating columns of air, 340 
plates and bells, 338 
rods, 337 
Vibrations, amplitude of, 382 
described, 311 
Twilight, 409, 427 
Tympanic cavity, 374 
Tympanitis, 209 
Tyndall’s battery, 659 
illustrated, 325 
limits of perception of, 355 
red light, 381 
sympathetic, 343 
to a tone, 357 
violet light, 381 
Vibriones, 517 
Vibrios, first appearance of, 213 
Vinometer, 102 
Virtual focus, 417 
of lens, 450 
Virtual images, 411 
by convex lens, 452 
Viscosity, 84 
Viscous liquids, 85 
Vision, 466 
ULTRA-GASEOUS state, 226 
Ultra-violet spectrum, 546 
Undulation, graphic representation of, 
315, 316 
in space, 316 
in tubes, 317 
relation to vibration, 312 
Undulatory theory, 380 
Undershot water wheels, 126 
Unguents, 276 
Uniaxial crystals, 521 
Unit of space, 251 
of time, 251 
binocular, 475 INDEX 
733 
Visual angle, 470 
distance, 472 
focus, 456 
Vitreous electricity, 622 
humor, 468 
Vocal chords, 371 
Voice, 370 
Volt, 659 
Voltaic decompositions, 662 
electricity, origin of, 653 
Voltameter, 663 
Volta’s electric pile, 653 
Volume, change of, in fusing and solid! 
fying, 570 
unit of, 252 
Waves, molecular formation of, 316 
reflection and interference, 318 
Wax candles, 396 
Weather and barometer, 181 
strips, 619 
Weber, 659 
Wedge, its action, 273 
Weighing, 58 
method by double, 60 
Weight, 56 
unit of, 252 
Weights, 58 
attachment in drowning, 94 
Welding, 74 
Wells, 95 
variation in liquids, 83 
and sewage, 96 
in solids, 66 
Vortex atoms, 237 
rings, 51 
structure of, 53 
Vowels, 372 
first form of, 117 
Wheatstone’s bridge, 681 
rheostat, 680 
Wheel and axle, 271 
barometer, 178 
Whirling table, 267 
Whisper, 373 
White corpuscles, 194 
Wide angle objective, 482 
Wiedemann’s boussole, 680 
Wind, 558 
and barometer, 181 
Windmill, 191 
Wollaston’s battery, 657 
Wood-cells, circulation in, 304 
Work, British unit of, 255 
French unit of, 255 
Working distance of objective, 483 
Worm of still, 584 
artesian, 96 
WALKEE’S battery, 657 
Warming of houses, 615 
Washing bottle, 149 
Waste pipes, 109 
Water, conveying and storing, 127 
decomposition of, 662 
development of power from, 125 
expansion of, in freezing, 571 
hammer, 171, 581 
pipes, 128 
superficial, 96 
transmission of impulse, 261 
transporting power of, 110 
traps, 130 
valve exhaustion, 187 
valvular apparatus for raising, 121 
velocity in open channels, 110 
waves in, 112 
YELLOW light, 438 
wheels, 126 
Waves, formation of, 112 
height of, 113 
length of, 113 
length of spectrum lines, 546 
yAMBONTS battery, 650 
Li Zero, displacement of, 565 
Zig-zag lightning, 649 
Zinc, amalgamation of, 654 
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Lea Brothers & Co.’s Publications—Dictionaries. 
JDZTJYGLISOJY, MOBLEY, M. 8., 
Late Professor of Institutes of Medicine in the Jefferson Medical College of Philadelphia. 
MEDICAL LEXICON; A Dictionary of Medical Science: Containing 
a concise Explanation of the various Subjects and Terms of Anatomy, Physiology, -Pathol- 
ogy, Hygiene, Therapeutics, Pharmacology, Pharmacy, Surgery, Obstetrics, Medical Juris- 
prudence and Dentistry, Notices of Climate and of Mineral Waters, Formulae fur Officinal, 
Empirical and Dietetic Preparations, with the Accentuation and Etymology of the Terms, 
and the French and other Synonymes, so as to constitute a French as well as an English 
Medical Lexicon. Edited by Richard J. Dunglison, M. I). In one very large and 
handsome royal octavo volume of 1139 pages. Cloth, §6.50; leather, raised bands, $7.50; 
very handsome half Russia, raised bands, $B. 
The object of the author, from the outset, has not been to make the work a mere lexi- 
con or dictionary of terms, but to afford under each word a condensed view of its various 
medical relations, and thus to render the work an epitome of the existing condition of 
medical science. Starting with this view, the immense demand which has existed for the 
work has enabled him, in repeated revisions, to augment its completeness and usefulness, 
until at length it has attained the position of a recognized and standard authority wherever 
the language is spoken. Special pains have been taken in the preparation of the present 
edition to maintain this enviable reputation. The additions to the vocabulary are more 
numerous than in any previous revision, and particular attention has beep bestowed on the 
accentuation, which will be found marked on every word. The typographical arrangement 
has been greatly improved, rendering reference much more easy, and every care has been 
taken with the mechanical execution. The volume now contains the matter of at least 
four ordinary octavos. 
A book of which every American ought to be 
proud. When the learned author of the work 
passed away, probably all of us feared lest the book 
should not maintain its place in the advancing 
science whose terms it defines. Fortunately, Dr. 
Richard J. Dunglison, having assisted his father in 
the revision of several editions of the work, and 
having been, therefore, trained in the methods 
and imbued-with the spirit of the book, has been 
able to edit it as a work of the kind should be 
edited—to carry it on steadily, without jar or inter- 
ruption, along the grooves of thought it has trav- 
elled during its lifetime. To show the magnitude 
of the task which Dr. Dunglison has assumed and 
carried through, it is only necessary to state that 
more than six thousand new subjects have been 
added in the present edition.—Philadelphia Medical 
Tiines, Jan. 3, 1874. 
work has been well known for about forty years, 
and needs no words of praise on our part to recom- 
mend it to the members of the medical, and like- 
wise of the pharmaceutical, profession. The latter 
especially are in need of a work which gives ready 
and reliable information on thousands of subjects 
and terms which they are liable to encounter in 
pursuing their daily vocations, but with which they 
cannot be expected to be familiar. The work 
before us fully supplies this want.—American Jour- 
nal of Pharmacy, Feb. 1874. 
Particular care has been devoted to derivation 
and accentuation of terms. With regard to the 
latter, indeed, the present edition may be consid- 
ered a complete “Pronouncing Dictionary of 
Medical Science.” It is perhaps the most reliable 
work published for the busy practitioner, as it con- 
tains information upon every medical subject, in 
a form for ready access. and with a brevity as ad- 
mirable as it is practical.—Southern Medical Record, 
Feb. 1874. 
A valuable dictionary of the terms employed in 
medicine and the allied sciences, and of the rela- 
tions of the subjects treated under each head. It 
well deserves the authority and popularity it has 
obtained.—British Med. Jour., Oct. 31,1874. 
Few works of this class exhibit a grander monu- 
ment of patient research and of scientific lore.— 
London Lancet, May 13, 1875. 
About the first book purchased by the medical 
student is the Medical Dictionary. The lexicon 
explanatory of technical terms is simply a sine qua 
non. In a science so extensive and with such col- 
laterals as medicine, it is as much a necessity also 
to the practising physician. To meet the wants of 
students and most physicians the dictionary must 
be condensed while comprehensive, and practical 
while perspicacious. It was because Dunglison’s 
met these indications that it became at once the 
dictionary of general use wherever medicine was 
studied in the English language. In no former 
revision have the alterations and additions been 
so great. The chief terras have been set in black 
letter, while the derivatives follow in small caps; 
an arrangement which greatly facilitates reference. 
—Cincinnati Lancet and Clinic, Jan. 10, 1874. 
Dunglison’s Dictionary is incalculably valuable, 
and indispensable to every practitioner of medi- 
cine, pharmacist and dentist.— Western Lancet, 
March, 1874. 
As a standard work of reference Dunglison’s 
It has the rare merit that it certainly has no rival 
in the English language for accuracy and extent of 
references.—London Medical Gazette. 
JIOBLYX, JUCHAJII) I)., 31.13. 
A Dictionary of the Terms Used in Medicine and the Collateral 
Sciences. Revised, with numerous additions, by Isaac Hays, M. I)., late editor of 
The American Journal of the Medical Sciences. In one large royal 12mo. volume of 520 
double-columned pages. Cloth, $1.50; leather, $2,00. 
It is the best book of definitions we have, and ought always to be upon the student’s table—Southern 
Medical and Surgical Journal. 
MOD WELL, G. F., F. M. A. S., F. C. S., 
Lecturer on Natural Science at Clifton College, England. 
A Dictionary of Science: Comprising Astronomy, Chemistry, Dynamics, Elec- 
tricity, Heat, Hydrodynamics, Hydrostatics, Light, Magnetism, Mechanics, Meteorology, 
Pneumatics, Sound and Statics. Contributed by J. T. Bottomley, M. A., F. C. S., William 
Crookes, F.E.S., F.C.S., Frederick Guthrie, 8.A., Ph. D., K. A. Proctor, 8.A., F.R.A.S., 
G. F. Rodwell, Editor, Charles Tomlinson, F.R.S., F.C.S., and Richard Wornell, M.A., 
B.Sc. Preceded by an Essay on the History of the Physical Sciences. In one handsome 
octavo volume of 702 pages, with 143 illustrations. Cloth, $5.00. Lea Brothers & Co.’s Publications—Anatomy. 
5 
GUAY, HFNBY, F. B. S., 
Lecturer on Anatomy at St. George's Hospital, London. 
Anatomy, Descriptive and Surgical, The Drawings by 11. V, Carter, M. D., 
and Dr. Westmacott. The dissections jointly by the Author and Dr. Carter. With 
an Introduction on General Anatomy and Development by T. Holmes, M. A., Surgeon to 
St. George’s Hospital. Edited by T. Pickering Pick, F. Jl. C. S., Surgeon to and Lecturer 
on Anatomy at St. George’s Hospital, London, Examiner in Anatomy, Royal College of 
Surgeons of England. A new American from the tenth enlarged and improved London 
edition. To which is added the second American from the latest English edition of 
Landmarks, Medical and Surgical, by Luther Holden, F. R. C. S., author of 
“ Human Osteology,” “ A Manual of Dissections,” etc. In one imperial octavo volume 
of 1023 pages, with 564 large and elaborate engravings on wood. Cloth, $6.00 ; leather, 
$7.00 ; very handsome half Russia, raised bands, $7.50. 
This work covers a more extended range of subjects than is customary in the ordinary 
text-books, giving not only the details necessary for the student, but also the application to 
those details to the practice of medicine and surgery. It thus forms both a guide for the 
learner and an admirable work of reference for the active practitioner. The engravings 
form a special feature in the work, many of them being the size of nature, nearly all 
original, and having the names of the various parts printed on the body of the cut, in 
place of figures of reference with descriptions at the foot. They thus form a complete and 
splendid series, which will greatly assist the student in forming a clear idea of Anatomy, 
and will also serve to refresh the memory of those who may find in the exigencies of 
practice the necessity of recalling the details of the dissecting-room. Combining, as it 
does, a complete Atlas of Anatomy with a thorough treatise on systematic, descriptive 
and applied Anatomy, the work will be found of great service to all physicians who receive 
students in their offices, relieving both preceptor and pupil of much labor in laying the 
groundwork of a thorough medical education. 
Landmarks, Medical and Surgical, by the distinguished Anatomist, Mr. Luther Holden, 
lias been appended to the present edition as it was to the previous one. This work gives 
in a clear, condensed and systematic way all the information by which the practitioner can 
determine from the external surface of the body the position of internal parts. Thus 
complete, the work, it is believed, will furnish all the assistance that can be rendered by 
type and illustration in anatomical study. 
This well-known work comes to us as the latest 
American from the tenth English edition. As its 
title indicates, it has passed through many hands 
and has received many additions and revisions. 
The work is not susceptible of more improvement. 
Taking it all in all, its size, manner of make-up, 
its character and illustrations, its general accur- 
acy of description, its practical aim, and its per- 
spicuity of style, it is the Anatomy best adapted to 
the wants of the student and practitioner.—Medical 
Record, Sept. 15, 1883. 
There is probably no work used so universally 
by physicians and medical students as this one. 
It is deserving of the confidence that they repose 
in it. If the present edition is compared with that 
issued two years ago, one will readily see how 
much it has been improved in that time. Many 
pages have been added to the text, especially in 
those parts that treat of histology, and many new 
cuts have been introduced and old ones modified. 
—Journal of the American Medical Association, Sept. 
1, 1883. 
Also for sale separate— 
HOI DIN, JAJTHFR, F. U. C. S., 
Surgeon to St. Bartholomew's and the Foundling Hospitals, London. 
Landmarks, Medical and Surgical. Second American from the latest revised 
English edition, with additions by W. W. Keen, M. D., Professor of Artistic Anatomy in 
the Pennsylvania Academy of the Fine Arts, formerly Lecturer on Anatomy in the Phila- 
delphia School of Anatomy. In one handsome 12mo. volume of 148 pages. Cloth, $l.OO. 
This little book is all that can be desired within almost to learn it by heart. Ttteaches diagnosis by 
its scope, and its contents will be found simply in- external examination, ocular and palpable, of the 
valuable to the young surgeon or physician, since body, with such anatomical and physiological facts 
they bring before him such data as he requires at as directly bear on the subject. It is eminently 
every examination of a patient. It is written in the student’s and young practitioner’s book.—Phy- 
language so clear and concise that one ought sician and Surgeon, Nov. 1881. 
WILSON, FBAS3IUS, F. B. S. 
A System of Human Anatomy, General and Special. Edited by W. H. 
Gobrecht, M. D., Professor of General and Surgical Anatomy in the Medical College of 
Ohio. In one large and handsome octavo volume of 616 pages, with 397 illustrations. 
Cloth, $4.00; leather, $5.00. 
SMITH, H. JL, M. JL, and HO BMW, WM. F.,M.J)., 
Emeritus Prof, of Surgery in the Univ. of Penna., etc. Late Prof, of Anat. in the Univ. of Penna. 
An Anatomical Atlas, Illustrative of the Structure of the Human Body. In one 
large imperial octavo volume of 200 pages, with 634 beautiful figures. Cloth, $4.50. 
CLFLAND, JOHN, 31.1)., F. B, S., 
A Directory for the Dissection of the Human Body. In one 12mo. 
Volume of 178 pages. Cloth, $1.25. 
Professor of Anatomy and Physiology in Queen's College, Galway. 6 
Lea Brothers & Co.’s Publications—Anatomy. 
ALLEY, UARRISOK, M. D 
Professor of Physiology in the University of Pennsylvania. 
A System of Human Anatomy, Including Its Medical and Surgical 
Relations. For the use of Practitioners and Students of Medicine. With an Intro- 
ductory Section on Histology. By E. 0. Shakespeare, M. D., Ophthalmologist to 
the Philadelphia Hospital. Comprising SIS double-columned quarto pages, with 380 
illustrations on 109 full page lithographic plates, many of which are in colors, and 241 
engravings in the text. In six Sections, each in a portfolio. Section I. Histology. 
Section 11. Bones and Joints. Section 111. Muscles and Fascle. Section IV. 
Arteries, Veins and Lymphatics. Section V. Nervous System. Section VI. 
Organs of Sense, of Digestion and Genito-XJrinary Organs, Embryology, 
Development, Teratology, Superficial Anatomy, Post-Mortem Examinations, 
and General and Clinical Indexes. Just ready. Price per Section, each in a handsome 
portfolio, $3.50; also bound in one volume, cloth $23.00; very handsome half Russia, 
raised bands and open back, $25.00. For sale by subscription only. Apply to the Publishers. 
It is the design of this book to present the facts of human anatomy in the manner best 
suited to the requirements of the student and the practitioner of medicine. The author 
believes that such a book is needed, inasmuch as no treatise, as far as he knows, contains, in 
addition to the text descriptive of the subject, a systematic presentation of sucb anatomical 
facts as can be applied to practice. 
A book which will be at once accurate in statement and concise in terms; which will be 
an acceptable expression of the present state of the science of anatomy; which will exclude 
nothing that can be made applicable to the medical art, and which will thus embrace all 
of surgical importance, while omitting nothing of value to clinical medicine,—would appear 
to have an excuse for existence in a country where most surgeons are general practitioners, 
and where there are few general practitioners who have no interest in surgery. 
Extract from Introduction. 
It is to be considered a study of applied anatomy 
in its widest sense—a systematic presentation of 
such anatomical facts as can be applied to the 
practice of medicine as well as of surgery. Our 
author is concise, accurate and practical in his 
statements, and succeeds admirably in infusing 
an interest into the study of what is generally con- 
sidered a dry subject. The department of Histol- 
ogy is treated in a masterly manner, and the 
ground is travelled over by one thoroughly famil- 
iar with it. The illustrations are made with great 
care, and are simply superb. There is as much 
of practical application of anatomical points to 
the every-day wants of the medical clinician as 
to those of the operating surgeon. In fact, few 
general practitioners will read the work without a 
feeling of surprised gratification that so many 
points, concerning which they may never have 
thought before are so well presented for their con- 
sideration. It is a work which is destined to be 
the best of its kind in any language.—Medical 
Record, Nov. 25,1882. 
CLARKE, W. 8., 1,11. as. & LOCKWOOD, C. 8., F.R. C.S. 
The Dissector’s Manual. In one pocket-size 12mo. volume of 396 pages, with 
49 illustrations. Limp cloth, red edges, $1.50. Just ready. See Students’ Series of 
Manuals, page 3. 
Demonstrators of Anatomy at St. Bartholomew's Hospital Medical School, London. 
This is a very excellent manual for the use of the 1 
student who desires to learn anatomy. The meth- | 
ods of demonstration seem to us very satisfactory, j 
There are many woodcuts which, for the most I 
part, are good and instructive. The book is neat 
and convenient. We are glad to recommend it.— 
Boston Medical and Surgical Journal, Jan. 17,1884. 
TREVES, FREDERICK, F. R. C. S,, 
Senior Demonstrator of Anatomy and Assistant Surgeon at the London Hospital. 
Surgical Applied Anatomy. In one pocket-size 12mo. volume of 540 pages, 
with 61 illustrations. Limp cloth, red edges, $2.00. Just ready. See Students’ Series of 
Manuals, page 3. 
He has produced a work which will command a 1 
larger circle of readers than the class for which it 
was written. This union of a thorough, practical 
acquaintance with these fundamental branches, j 
quickened by daily use as a teacher and practi- 
tioner, has enabled our author to prepare a work 
which it would be a most difficult task to excel.— 
The American Practitioner Feb. 1884. 
CIRJSOW, JO UK, M. D., F. R. C. P., 
Professor of Anatomy at King's College, Physician at King's College Hospital. 
Medical Applied Anatomy. In one pocket-size 12mo. volume. Preparing. 
See Students’ Series of Manuals, page 3. 
BELLAMY, EDWARD, F. R. C. S., 
The Student’s Guide to Surgical Anatomy: Being a Description of the 
most Important Surgical Regions of the Human Body, and intended as an Introduction to 
operative Surgery. In one 12mo. volume of 300 pages, with 50 illustrations. Cloth, $2.25. 
Senior Assistant-Surgeon to the Charing-Cross Hospital, London. 
HARTSHORNE’S HANDBOOK OP ANATOMY 
AND PHYSIOLOGY. Second edition, revised. 
In one royal 12mo. volume of 310 pages, with 220 
woodcuts. Cloth, $1.75. 
HORNER’S SPECIAL ANATOMY AND HISTOL- 
OGY. Eighth edition, extensively revised and 
modified. In two octavo volumes of 1007 pages, 
I with 320 woodcuts. Cloth, $6.00. Lea Brothers & Co.’s Publications—Anat., Physics, Physiol. 
7 
DALTON, JOHN a, M. D., 
Professor Emeritus of Physiology in the College of Physicians and Surgeons, New York. 
The Topographical Anatomy of the Brain. In three very handsome quarto 
volumes comprising 178 pages of descriptive text. Illustrated with 48 full page photo- 
graphic plates of Brain Sections, with a like number of explanatory plates, as well as many 
woodcuts through the text. Price for the complete work, $36. Just ready. For sale by 
subscription. As but few of the copies reserved for this country now remain unsold, 
gentlemen desiring the work will do well to apply to the publishers at an early date. 
This is one of the most magnificent works on 
anatomy that has appeared during the present 
generation, and will not only supersede all its 
predecessors on the topographical anatomy pf the 
brain, but make any further work on the same 
lines unnecessary. It contains forty-eight ex- 
quisite illustrations of the brain en masse and in 
sections. Not only has perfect accuracy been 
secured, but one of the finest and most artistic 
works of recent times has been presented to the 
medical public. Its value as a work of reference 
is considerably increased by the very careful out- 
line sketches" which accompany the plates and 
which enable them to be easily followed and 
understood. These sketches are very complete 
and accurate, and have been reproduced from 
tracings. The descriptions by the author are clear, 
precise and accurate, and the methods by which 
the sections were made and the specimens re- 
produced are given very plainly in an introductory 
chapter, which cannot fail to be of the greatest 
value to any one desirous of making similar prep- 
arations. Criticism on such a work is super- 
fluous. We can only congratulate Dr. Dalton, his 
assistants, and the publishers on the energy they 
have shown in undertaking such a work, and the 
success with which they have overcome a task 
presenting so many mechanical difficulties. We 
1 envy our American confreres the authorship and 
j execution of so beautiful and useful an addition 
jto medical literature. Much light is thrown 
j on some obscure relations of parts of the brain 
j which have never before been seen in correct 
I juxtaposition.—London Lancet, April 18, 1885. 
Doctrines of the Circulation of the Blood. A History of Physiological 
Opinion and Discovery in regard to the Circulation of the Blood. In one handsome 
12mo. volume of 293 pages. Cloth, $2. Just ready. 
In the progress of physiological study no fact of three or four which have been written within a 
was of greater moment, none more completely few years by American physicians. It is in several 
revolutionized the theories of teachers, than the respects the most complete. The volume, though 
discovery of the circulation of the blood. This small in size, is one of the most creditable con- 
explains the extraordinary interest it has to all tributions from an American pen to medical history 
medical historians. The volume before us is one that has appeared.—Mod. & Surg. Pep., Dec. 6,1884. 
THE SAME AUTHOR. 
ELLIS, GEORGE VINER, 
Emeritus Professor of Anatomy in University College, London. 
Demonstrations of Anatomy. Being a Guide to the Knowledge of the 
Human Body by Dissection. From the eighth and revised London edition. In one very 
handsome octavo volume of 716 pages, with 249 illustrations. Cloth, $4.25 • leather, $5.25. 
ROBERTS, JOHN 8., A. M., 31. D., 
Prof, of Applied Anat. and Oper. Surg. in Phila. Polyclinic and Coll, for Graduates in Medicine. 
The Compend of Anatomy. For use in the dissecting-room and in preparing 
for examinations. In one 16mo. volume of 196 pages. Limp cloth, 75 cents. 
DRAPER, JOHN €., 31. D., LL. D., 
Professor of Chemistry in the University of the City of New York. 
Medical Physics. A Text-book for Students and Practitioners of Medicine. In 
one octavo volume of 725 pages, with 376 woodcuts, mostly original. Cloth, $4. In a few days: 
From the Preface. 
The fact that a knowledge of Physics is indispensable to a thorough understanding of 
Medicine has not been as fully realized in this country as in Europe, where the admirable 
works of Desplats and Gariel, of Robertson and of numerous German writers constitute a 
branch of educational literature to which we can show no parallel. A full appreciation 
of this the author trusts will be sufficient justification for placing in book form the sub- 
stance of his lectures on this department of science, delivered during many years at the 
University of the City of New York. 
Broadly speaking, this work aims to impart a knowledge of the relations existing 
between Physics and Medicine in their latest state of development, and to embody in the 
pursuit of this object whatever experience the author has gained during a long period of 
teaching this special branch of applied science. 
ROBERTSON, J. 3IcGREGOR, 31. A., 31. 8., 
Muir head Demonstrator of Physiology, University of Glasgow. 
Physiological Physics. In one 12mo. volume of 537 pages, with 219 illustra- 
tions. Limp cloth, $2.00. Just ready. See Students' Series of Manuals, page 3. 
The title of this work sufficiently explains the 
nature of its contents. It is designed as a man- 
ual for the student of medicine, an auxiliary to 
his text-book in physiology, and it would be particu- 
larly useful as a guide to his laboratory experi- 
j ments. It will be found of great value to the 
[ practitioner. It is a carefully prepared book of 
j reference, concise and accurate, and as such we 
| heartily recommend it.—Journal of the American 
j Medical Association, Dec. 6, 1884. 
BELL, F. JEFFREY, 31. A., 
Professor of Comparative Anatomy at King's College, London. 
Comparative Physiology and Anatomy. Shortly. See Students’ Series of 
Manuals, page 3. 8 
Lea Brothers & Co.’s Publications—Physiology, Chemistry. 
DALTON, JOHN C., M. I)., 
Professor of Physiology in the College of Physicians and Surgeons, New York, etc. 
A Treatise on Human Physiology. Designed for the use of Students and 
Practitioners of Medicine. Seventh edition, thoroughly revised and rewritten. In one 
very handsome octavo volume of 722 pages, with 252 beautiful engravings on wood. Cloth,. 
$5.00; leather, $6.00; very handsome half Russia, raised bands, $6.50. 
The merits of Professor Dalton’s text-book, his 
smooth and pleasing style, the remarkable clear- 
ness of his descriptions, which leave not a chapter 
obscure, his cautious judgment and the general 
correctness of his facts, are perfectly known. They 
have made his texhbook the one most familiar 
to American students.—Med. Record, March 4, 1882. 
more compact form, yet its delightful charm is re- 
tained, and no subject is thrown into obscurity. 
Altogether this edition is far in advance of any 
previous one, and will tend to keep the profession 
posted as to the most recent additions to our 
physiological knowledge.—Michigan Medical Newsy 
April, 1882. 
One can scarcely open a college catalogue that 
does not have mention of Dalton’s Physiology as- 
the recommended text or consultation-hook. For 
American students we would unreservedly recom- 
mend Dr. Dalton’s work.- Va. Med. Monthly, July,'B2* 
Certainly no physiological work has ever issued 
from the press that presented its subject-matter in 
a clearer and more attractive light. Almost every 
page bears evidence of the exhaustive revision 
that has taken place. The material is placed in a 
FOSTER, MICHAEL, M. D., F. R. S., 
Text-Book of Physiology. Third American from the fourth English edition, 
with notes and additions hyE. T. Reichert, M. D. In one handsome royal 12mo. volume 
of over 1000 pages, with about 300 illustrations. Cloth, $3.25; leather, $3.75. In a few days. 
A notice of the previous edition is appended. 
Professor of Physiology in Cambridge University, England. 
A more compact and scientific work on physiol- 
ogy has never been published, and we believe our- 
selves not to be mistaken in asserting that it has 
now been introduced into every medical college 
in which the Elnglish language is spoken. This 
work conforms to the latest researches into zoology 
and comparative anatomy, and takes into consid- 
eration the late discoveries in physiological chem- 
istry and the experiments in localization of Ferrier 
and others. The arrangement followed is such as 
to render the whole subject lucid and well con- 
nected in its various parts.—Chicago Medical Jour- 
nal and Examiner, August, 1882. 
FOWEB, HENRY, M. 8., E. R. C. S., 
Examiner in Physiology, Royal College of Surgeons of England. 
Human Physiology. In one handsome pocket-size 12mo. volume of 396 pages.. 
with 47 illustrations. Cloth, $1.50. See Students' Series of Manuals, page 3. 
The prominent character of this work is that of 
judicious condensation, in which an able and suc- 
cessful effort appears to have been made by its 
accomplished author to teach the greatest number 
of facts in the fewest possible words. The result 
is a specimen of concentrated intellectual pabu- 
lum seldom surpassed, which ought to be care- 
fully ingested and digested by every practitioner 
who desires to keep himself well informed upon 
this most progressive of the medical sciences. 
The volume is one which we cordially recommend 
to every one of our readers.— The American Jour- 
nal of the Medical Sciences, October, 1884. 
This little work is deserving of the nighest 
praise, and we can hardly conceive how the main 
facts of this science could have been more clearly 
or concisely stated. The price of the work is such 
as to place it within the reach of all, while the ex- 
cellence of its text will certainly secure for it most 
favorable commendation —Cincinnati Lancet and 
Clinic, Feb. 16,1884. 
CARFENTER, WM. 8., M. D., E. R. S., F. G. S., F. L. S., 
Registrar to the University of London, etc. 
Principles of Human Physiology. Edited by Henry Power, M. 8., Loud., 
F. E. G. S., Examiner in Natural Sciences, University of Oxford. A new American from the 
eighth revised and enlarged edition, with notes and additions by Francis G. Smith, M. D., 
late Professor of the Institutes of Medicine in the University of Pennsylvania. In one 
very large and handsome octavo volume of 1083 pages, with two plates and 373 illus- 
trations. Cloth, $5.50 ; leather, $6.50; half Russia, $7. 
FOWNES, GEORGE, Fh. D. 
A Manual of Elementary Chemistry; Theoretical and Practical. Re- 
vised by Henry Watts, B. A., F. R. S. New American edition. In one large royal 12mo. 
volume of over 1000 pages, with 200 illustrations on wood and a colored plate. Cloth, 
$2.75 ; leather, $3.25. In press. 
A notice of the previous edition is appended. 
The book opens with a treatise on Chemical 
Physics, including Heat, Light, Magnetism and 
Electricity. These subjects are treated clearly 
and briefly, but enough is given to enable the stu- 
dent to comprehend the facts and laws of Chemis- 
try proper. It is the fashion of late years to omit 
these topics from works on chemistry, but their 
omission is not to be commended. As was required 
by the great advance in the science of Chemistry 
of late years, the chapter on the General Principles 
of Chemical Philosophy has been entirely rewrit- 
ten. The latest views on Equivalents, Quantiva- 
lence, etc., are clearly and fully set forth. This 
last edition is a great improvemen. upon its prede- 
cessors, which is saying not a little of a book that, 
has reached its twelfth edition.—Ohio Medical Re- 
corder, Oct., 1878. 
Wohler’s Outlines of Organic Chemistry. Edited by Fittig. Translated; 
by Ira Eemsen, M. D., Ph. D. In one 12mo. volume of 550 pages. Cloth, $3. 
GALLOWAY’S QUALITATIVE ANALYSIS. New 
edition. 
LEHMANN’S MANUAL OF CHEMICAL PHYS- 
IOLOGY. In one octavo volume of 327 pages, 
with 41 illustrations. Cloth, $2.25, 
CARPENTER’S PRIZE ESSAY ON THE USE AND; 
Abuse of Alcoholic Liquors in Health and Dis- 
ease. With explanationsof scientific words. Small 
12mo. 178 pages. Cloth, 60 cents. Lea Brothers & Co.’s Publications—Chemistry. 
9 
FBANKLANB, JE., J). C.L., F. 8.5., A JAPP, Ph. £>., F. I. C., 
Professor of Chemistry in the Normal School Assist. Prof, of Chemistry in the Normal 
of Science, London. School of Science, London. 
Inorganic Chemistry. In one handsome octavo volume of 600 pages, with 51 
woodcuts and 2 lithographic plates. Cloth, $3.75; leather, $4.75. In press. 
This work on elementary chemistry is based upon principles of classification, nomen- 
clature and notation which have been proved by nearly twenty years experience in teaching 
to impart most readily a sound and accurate knowledge of the science. 
Professor of Practical Chemistry to the Pharmaceutical Society of Great Britain, etc. 
Chemistry, General, Medical and Pharmaceutical; Including the Chem- 
istry of the U. S. Pharmacopoeia. A Manual of the General Principles of the Science, 
and their Application to Medicine and Pharmacy. A new American, from the tenth 
English edition, specially revised by the Author. In one handsome royal 12mo. volume 
of 728 pages, with 87 illustrations. Cloth, $2.50 ; leather, $3.00. 
ATTFJFLT), JOMX, Ph, 8., 
A text-book which passes through ten editions 
in sixteen years must have good qualities. This 
remark is certainly applicable to Attfield’s Chem- 
istry, a book which is so well known that it is 
hardly necessary to do more than note the appear- 
ance of this new and improved edition. Itseems, 
however, desirable to point out that feature of the 
book which, in all probability, has made it so 
popular. There can be little doubt that it is its 
thoroughly practical character, the expression 
being used in its best sense. The author under- 
stands what the student ought to learn, and is able 
to put himself in the student’s place and to appre- 
ciate his state of mind.—American Chemical Jour- 
nal, April, 1884. 
It is a book on which too much praise cannot be 
bestowed. As a text-book for medical schools it 
is unsurpassable in the present state of chemical 
science, and having been prepared with a special 
view towards medicine and pharmacy, it is alike 
indispensable to all persons engaged in those de- 
partments of science. It includes the whole 
chemistry of the last Pharmacopoeia.—Pacific Medi- 
cal and Sugrical Journal, Jan. 1884. 
BLOXAM, CHABLBS L.. 
Professor of Chemistry in King's College, London. 
Chemistry, Inorganic and Organic. New American from tbe fifth Lon- 
don edition, thoroughly revised and much improved. In one very handsome octavo 
volume of 727 pages, with 292 illustrations. Cloth, $3.75; leather, $4.75. 
Comment from us on this standard work is al- 
most superfluous. * It differs widely in scope and 
aim from that of Attfield, and in its way is equally 
beyond criticism. It adopts the most direct meth- 
ods in stating the principles, hypotheses and facts 
of the science. Its language is so terse and lucid, 
and its arrangement of matter so logical in se- 
quence that the student never has occasion to 
complain that chemistry is a hard study. Much 
attention is paid to experimental illustrations of 
chemical principles and phenomena, and tbe 
mode of conducting these experiments. The book 
maintains the position it has always held as one of 
the best manuals of general chemistry in the Eng- 
lish language.—Detroit Lancet, Feb. 1884. 
The general plan of this work remains the 
same as in previous editions, the evident object 
being to give clear and concise descriptions of all 
known elements and of their most important 
compounds, with explanations of the chemical 
laws and principles involved. We gladly repeat 
now the opinion we expressed about a former 
edition, that we regard Bloxam’s Chemistry as 
one ot the best treatises on general and applied 
chemistry.—American Jour, of Pharmacy, Dec. 1883. 
SIMON, W,, Ph. I),, M. JD., 
Professor of Chemistry and Toxicology in the College of Physicians and Surgeons, Baltimore, and 
Professor of Chemistry in the Maryland College of Pharmacy. 
Manual of Chemistry. A Guide to Lectures and Laboratory work for Beginners 
in Chemistry. A Text-book, specially adapted for Students of Pharmacy and Medicine. 
In one Byo. vol. of 410 pp., with 16 woodcuts and 7 plates, mostly of actual deposits, 
with colors illustrating 56 of the most important chemical reactions. Cloth, $3.00; also 
without plates, cloth, $2.50. Just ready. 
This book supplies a want long felt by students 
of medicine and pharmacy, and is a concise but 
thorough treatise on the subject. The long expe- 
rience of the author as a teacher in schools of 
medicine and pharmacy is conspicuous In the 
perfect adaptation of the work to the special needs 
of the student of these branches. The colored 
plates, beautifully executed, illustrating precipi- 
tates of various reactions, form a novel and valu- 
able feature of the book, and cannot fail to be ap- 
preciated by both student and teacher as a help 
over the hard places of the science.—Maryland 
Medical Journal, Nov. 22,1884. 
II EMS 'EX, IBA, 31. J).9 Ph. I)., 
Professor of Chemistry in the Johns Hopkins University, Baltimore. 
Principles of Theoretical Chemistry, with special reference to the Constitu- 
tion of Chemical Compounds. Second and revised edition. In one handsome royal 12mo. 
volume of 240 pages. Cloth, $1.75. Just ready. 
The book is a valuable contribution to the chemi- 
cal literature of instruction. That in so few years 
a second edition has been called for indicates that 
many chemical teachers have been found ready 
to endorse its plan and to adopt its methods. In 
this edition a considerable proportion of the book 
has been rewritten, much new matter has been 
added and the whole has been brought up to date. 
We earnestly commend this book to every student 
of chemistry. The high reputation of the author 
assures its accuracy in all matters of fact, and its 
judicious conservatism in matters of theory, com- 
bined with the fulness with which, in a small 
compass, the present attitude of chemical science 
towards the constitution of compounds is con- 
sidered, gives itavalue much beyond that accorded 
to the average text-books of the day.—American 
Journal of Science, March, 1884. 10 
Lea Brothers & Co.’s Publications—Chemistry. 
CHARLES, T. CRANSTOVN, M. D., F, C. S., M. S., 
Formerly Asst. Prof, and Demonst. of Chemistry and Chemical Physics, Queen's College, Belfast. 
The Elements of Physiological and Pathological Chemistry. A 
Handbook for Medical Students and Practitioners. Containing a general account of 
Nutrition, Foods and Digestion, and the Chemistry of the Tissues, Organs, Secretions and 
Excretions of the Body in Health and in Disease. Together with the methods for pre- 
paring or separating their chief constituents, as also for their examination in detail, and 
an outline syllabus of a practical course of instruction for students. In one handsome octavo 
volume of 463 pages, with 38 woodcuts and 1 colored plate. Cloth, $3.50. 
The work is thoroughly trustworthy, and in- 
formed throughout by a genuine scientific spirit. 
The author deals with the chemistry of the diges- 
tive secretions in a systematic manner, which 
leaves nothing to be desired, and in reality sup- 
plies a want in English literature. The book ap- 
pears to us to be at once full and systematic, and 
to show a just appreciation of the relative import- 
ance of the various subjects dealt with.—British 
Medical Journal, November 29, 1884. 
Dr. Charles’ manual admirably fulfils its inten- 
tion of giving his readers on the one hand a sum- 
mary, comprehensive but remarkably compact, of 
the mass of facts in the sciences which have be- 
come indispensable to the physician; and, on the 
other hand, of a system of practical directions so 
minute that analyses often considered formidable 
may be pursued by any intelligent person.— 
Archives of Medicine, Dec. 1884 
HOFFMANN, F, AM, Fh.D., & ROWER F. 8., Fh.D., 
Public Analyst to the State of New York. Prof, of Anal. Chem. in the Phil. Coll, of Pharmacy. 
A Manual of Chemical Analysis, as applied to the Examination of Medicinal 
Chemicals and their Preparations. Being a Guide for the Determination of their Identity 
and Quality, and for the Detection of Impurities and Adulterations. For the use of 
Pharmacists, Physicians, Druggists and Manufacturing Chemists, and Pharmaceutical and 
Medical Students. Third edition, entirely rewritten and much enlarged. In one very 
handsome octavo volume of 621 pages, with 179 illustrations. Cloth, $4.25. 
We congratulate the author on the appearance 
of the third edition of this work, published for the 
first time in this country also. It is admirable and 
the information it undertakes to supply is both 
extensive and trustworthy. The selection of pro- 
cesses for determining the purity of the substan- 
ces of which it treats is excellent and the descrip- 
tion of them singularly explicit. Moreover, it is 
exceptionally free from typographical(errors. We 
have no hesitation in recommending it to those 
who are engaged either in the manufacture or the 
testing of medicinal chemicals.—London Pharma- 
ceutical Journal and Transactions, 1883. 
CLOWES, FRANK, D. Sc., London, 
Senior Science-Master at the High School, Newcastle-under-Lyme, etc. 
An Elementary Treatise on Practical Chemistry and Qualitative 
Inorganic Analysis. Specially adapted for use in the Laboratories of Schools and 
Colleges and by Beginners. Third American from the fourth and revised English edition. 
In one very handsome royal 12mo. volume of about 409 pages, with about 50 illustrations. 
Cloth, $2.50. In a few days. 
The d emand for four editions of this work proves the success of Professor Clowes’ effort 
to provide a simple, concise and trustworthy guide to qualitative analysis. The use and 
preparation of apparatus, and the directions for working have been so fully and clearly 
detailed that the book is admirably adapted not only to relieve the teacher of unnecessary 
labor, but also to answer all the requirements of self-instruction. 
RALFE, CHARLES H., M. 1)., F. R. C. F., 
Assistant Physician at the London Hospital. 
Clinical Chemistry. In one pocket-size 12mo. volume of 314 pages, with 16 
illustrations. Limp cloth, red edges, $1.50. See Students' Series of Manuals, page 3. 
This is one of the most instructive little works 
that we have met with in a long time. The author 
is a physician and physiologist, as well as a chem- 
ist, consequently the book is unqualifiedly prac- 
tical, telling the physician just what he ought to 
know, of the applications of chemistry in medi- 
cine. Dr. Ralfe is thoroughly acquainted with the 
latest contributions to his science, and it is quite 
refreshing to find the subject dealt with so clearly 
and simply, yet in such evident harmony with the 
modern scientific methods and spirit.—Medical 
Record, February 2,1884. 
CLASSEN, ALEXANDER, 
Professor in the Royal Polytechnic School, Aix-la-Chapelle. 
Elementary Quantitative Analysis. Translated, with notes and additions, by 
Edgar F. Smith. Ph. D., Assistant Professor of Chemistry in the Towne Scientific School, 
University of Penna. In one 12mo. volume of 324 pages, with 36 illust. Cloth, $2.00. 
It is probably the best manual of an elementary 
nature extant insomuch as its methods are the 
best. It teaches by examples, commencing with 
single determinations, followed by separations, 
and then advancing to the analysis of minerals and 
such products as are met with in applied ehemis- 
try. It is an indispensable book for students in 
chemistry.—Boston Journal of Chemistry, Oct. 1878. 
GREENE, WILLIAM 11., M. I)., 
A Manual of Medical Chemistry. For the use of Students. Based upon Bow- 
man’s Medical Chemistry. In one 12mo. volume of 310 pages, with 74 illus. Cloth, $1.75. 
Demonstrator of Chemistry in the Medical Department of the University of Pennsylvania. 
It is a concise manual of three hundred pages, 
giving an excellent summary of the best methods 
of analyzing the liquids and solids of the body, both 
for the estimation of their normal constituents and 
the recognition of compounds due to pathological 
conditions. The detection of poisons is treated 
with sufficient fulness for the purpose of the stu- 
dent or practitioner.—Boston Jl. of Chem., June, ’BO. Lea Brothers & Co.’s Publications—Pharm., Mat. Med., The rap. II 
FARRISH, EH WARE, 
Late Professor of the Theory and Practice of Pharmacy in the Philadelphia College of Pharmacy. 
A Treatise on Pharmacy: designed as a Text-book for the Student, and as a 
Guide for the Physician and Pharmaceutist. With many Formulae and Prescriptions. 
Fifth edition, thoroughly revised, by Thomas S. Wi eg and, Ph. G. In one handsome 
octavo volume of 1093 pages, with 256 illustrations. Cloth, $5; leather, $6. 
No thoroughgoing pharmacist will fail to possess 
himself of so useful a guide to practice, and no 
physician who properly estimates the value of an 
accurate knowledge of the remedial agents em- 
ployed by him in daily practice, so far as their 
miscibility, compatibility and most effective meth- 
ods of combination are concerned, can afford to 
leave this work out of the list of their works of 
reference. The country practitioner, who must 
always be in a measure his own pharmacist, will 
find it indispensable.—Louisville Medical News, 
March 29,1884. 
This well-known work presents itself now based 
upon the recently revised new Pharmacopoeia. 
Each page bears evidence of the care bestowed 
upon it, and conveys valuable information from 
the rich store of the editor’s experience. In fact, 
all that relates to practical pharmacy—apparatus, 
processes and dispensing—has been arranged and 
described with clearness in its various aspects, so 
as to afford aid and advice alike to the student and 
to the practical pharmacist. The work is judi- 
ciously illustrated with good woodcuts—American 
Journal of Pharmacy, January, 1884. 
There is nothing to equal Parrish’s Pharmacy 
in this or any other language.—London Pharma- 
ceutical Journal. 
BRUXTOX, T. LAUHER, M. I)., 
Lecturer on Materia Medica and Therapeutics at St. Bartholomew's Hospital, London, etc. 
A Text-book of Pharmacology, Materia Medica and Therapeutics. 
In one handsome octavo volume of about 1000 pages, with over 200 illustrations. Cloth 
$5.50; leather, $6.50. In press. 
It is with peculiar pleasure that the early appearance of this long expected work is 
announced by the publishers. Written by the foremost authority on its subject in Eng- 
land, it forms a compendious treatise on materia medica, pharmacology, pharmacy, and 
the practical use of medicines in the treatment of disease. Space has been devoted to the 
fundamental sciences of chemistry, physiology and pathology, wherever it seemed necessary 
to elucidate the proper subject-matter of the book. A general index, an index of diseases 
and remedies, and an index of bibliography close a volume which will undoubtedly be of 
the highest value to the student, practitioner and pharmacist. 
HERMAXX, Hr. L., 
Professor of Physiology in the University of Zurich. 
Experimental Pharmacology. A Handbook of Methods for Determining the 
Physiological Actions of Drugs. Translated, with the Author’s permission, and with 
extensive additions, by Robert Meade Smith, M. D., Demonstrator of Physiology in the 
University of Pennsylvania. In one handsome 12mo. volume of 199 pages, with 32 
illustrations. Cloth, $1.50. 
Prof. Hermann’s handbook, which Dr. Smith has 
translated and enriched with many valuable addi- 
tions, will be gladly welcomed by those engaged in 
this department of physiology. It is an excellent 
little book, full of concise information, and it 
should find a place in every laboratory. It ex- 
plains the various methods and instruments used, 
and points out what lines of investigation are to 
be pursued for studying different phenomena, 
and also how and what particularly to observe.— 
American Journal of the Medical Sciences, Jan. 1884. 
MAISCH, JOHXM., Fiiar. I)., 
Professor of Materia Medica and Botany in the Philadelphia College of Pharmacy. 
A Manual of Organic Materia Medica; Being a Guide to Materia Medica of 
tlie Vegetable and Animal Kingdoms. For the use of Students, Druggists, Pharmacists 
and Physicians. New (second) edition. In one handsome royal 12mo. volume of 550 
pages, with 242 illustrations. Cloth, $3.00. Just ready. 
This work contains the substance,—the practical 
“kernel of the nut” picked out, so that the stu- 
dent has no superfluous labor. He can confidently 
accept what this work places before him, without 
any fear that the gist of the matter is not in it. 
Another merit is that the drugs are placed before 
him in such a manner as to simplify very much 
the study of them, enabling the mind to grasp 
them more readily. The illustrations are most 
excellent, being very true to nature, and are alone 
worth the price of the book to the student. To the 
practical physician and pharmacist it is a valuable 
work for handy reference and for keeping fresh 
in the memory the knowledge of materia medica 
and botany already acquired. We can and do 
heartily recommend it.—Medical and Surgical Re- 
porter, Feb. 14,1885. 
BRUCE, J. MITCHELL, M. I)., F. R. C. F., 
Physician and Lecturer on Materia Medica and Therapeutics at Charing Cross Hospital, London. 
Materia Medica and Therapeutics. An Introduction to Rational Treat- 
ment. In one pocket-size 12mo. volume of 555 pages. Limp cloth, $1.50. Just ready. 
See Students’ Series of Manuals, page 3. 
One of the very latest works upon Materia 
Medica and Therapeutics, replete with informa- 
tion abreast of the times, we unhesitatingly 
recommend it as one of the very best for either 
medical student or practitioner of medicine 
Cincinnati Medical News, August, 1884. 
GRIFFITH, ROBERT E GLESFIELH, M. I). 
A Universal Formulary, containing the Methods of Preparing and Adminis- 
tering Officinal and other Medicines. The whole adapted to Physicians and Pharmaceut- 
ists. Third edition, thoroughly revised, with numerous additions, by John M. Maisch 
Phar. D., Professor of Materia Medica and Botany in the Philadelphia College of Pharmacy! 
In one octavo volume of 775 pages, with 38 illustrations. Cloth, $4.50; leather $5.50. 12 
Lea Brothers & Co.’s Publications—Mat. Med., Tlierap. 
STILLE, A., 31. E>., LL. D., & MA TSCJI, J. M., Rhar. J)., 
Professor Emeritus of the Theory and Prac- 
tice of Medicine and of Clinical Medicine 
in the University of Pennsylvania. 
Prof, of Mat. Med. and Botany in Phila. 
College of Pharmacy, Sec'y to the Amcri- 
can Pharmaceutical Association. 
The National Dispensatory: Containing the Natural History, Chemistry, Phar- 
macy, Actions and Uses of Medicines, including those recognized in the Pharmacopoeias of 
the United States, Great Britain and Germany, with numerous references to the French 
Codex. Third edition, thoroughly revised and greatly enlarged. In one magnificent 
imperial octavo volume of 1767 pages, with 311 fine engravings. Cloth, $7.25; 
leather, $8.00; half Russia, open back, $9.00, With Denison’s “Beady Deference Index” 
$l.OO in addition to price in any of above styles of binding. Just ready. 
In the present revision the authors have labored incessantly with the view of making 
the third edition of The National Dispensatory an even more complete represen- 
tative of the pharmaceutical and therapeutic science of 1884 than its first edition was of 
that of 1879. For this, ample material has been afforded not only by the new United 
States Pharmacopoeia, but by those of Germany and France, which have recently appeared 
and have been incorporated in the Dispensatory, together with a large number of new non- 
officinal remedies. It is thus rendered the representative of the most advanced state of 
American, English, French and German pharmacology and therapeutics. The vast amount 
of new and important material thus introduced may be gathered from the fact that the 
additions to this edition amount in themselves to the matter of an ordinary full-sized octavo 
volume, rendering the work larger by twenty-five per cent, than the last edition. The 
Therapeutic Index (a feature peculiar to this work), so suggestive and convenient to the 
practitioner, contains 1600 more references than the last edition—the General Index 
3700 more, making the total number of references 22,390, while the list of illustrations 
has been increased by 80. Every effort has been made to prevent undue enlargement of 
the volume by having in it nothing that could be regarded as superfluous, yet care has 
been taken that nothing should be omitted which a pharmacist or physician could expect 
to find in it. 
The appearance of the work has been delayed by nearly a year in consequence of the 
determination of the authors that it should attain as near an approach to absolute ac- 
curacy as is humanly possible. With this view an elaborate and laborious series of 
examinations and tests have been made to verify or correct the statements of the Pharma- 
copoeia, and very numerous corrections have been found necessary. It has thus been ren- 
dered indispensable to all who consult the Pharmacopoeia. 
The work is therefore presented in the full expectation that it will maintain the 
position universally accorded to it as the standard authority in all matters pertaining to 
its subject, as registering the furthest advance of the science of the day, and as embody- 
ing in a shape for convenient reference the recorded results of human experience in the 
laboratory, in the dispensing room, and at the bed-side. 
Comprehensive in scope, vast in design and 
splendid in execution, The National Dispensatory 
may be justly regarded as the most important work 
of its kind extant.—Louisville Medical News, Dee. 
6,1884. 
up to date. The work has been very well done, a 
large number of extra-pharmaeopoeial remedies 
having been added to those mentioned in previous 
editions.—London Lancet, Nov. 22, 1884. 
We have much pleasure in recording the appear- 
ance of a third edition of this excellent work of 
reference. It is an admirable abstract of all that 
relates to chemistry, pharmacy, materia medica, 
pharmacology and therapeutics. It may be re- 
garded as embodying the Pharmacopoeias of the 
civilized nations of the world, all being brought 
Its completeness as to subjects, the comprehen- 
siveness of its descriptive language, the thorough- 
ness of the treatment of the topics, its brevity not 
sacrificing the desirable features of information 
for which such a work is needed, make this vol- 
ume a marvel of excellence.—Pharmaceutical Re- 
cord, Aug. 15,1884. 
EARQVJIA IiSOX, ROBERT, 31. />., 
A Guide to Therapeutics and Materia Medica. Third American edition, 
specially revised by the Author. Enlarged and adapted to the U. S. Pharmacopoeia by 
Frank Woodbury, M. D. In one handsome 12mo. volume of 524 pages. Cloth, $2.25. 
Lecturer on Materia Medica at St. Marys Hospital Medical School, 
Dr. Farquharson’s Therapeutics is constructed 
upon a plan which brings before the reader all the 
essential points with reference to the properties of 
drugs. It impresses these upon him in such away 
as to enable him to take a clear view of the actions 
of medicines and the disordered conditions in 
which they must prove useful. The double-col- 
umned pages—one side containing the recognized 
physiological action of the medicine, andthe other 
the disease in which observers (who are nearly al- 
ways mentioned) have obtained from it good re- 
suits—make a very good arrangement. The early 
chapter containing rules for prescribing is excel- 
lent.—Canada Med. and Surg, Journal, Dec. 1882. 
STILLU, ALFBJED, M. />., LL. I)., 
Therapeutics and Materia Medica. A Systematic Treatise on the Action and 
Uses of Medicinal Agents, including their Description and History. Fourth edition, 
revised and enlarged. In two large and handsome octavo volumes, containing 1936 pages. 
Cloth, $10.00; leather, $12.00; very handsome half Kussia, raised bands, $13.00. 
Professor of Theory and Practice of Med. and of Clinical Med. in the Univ. of Penna. 
We can hardly admit that it has a rival in the 
multitude of its citations and the fulness of its 
research into clinical histories, and we must assign 
it a place in the physician’s library; not, indeed, 
as fully representing the present state of knowledge 
in pharmacodynamics, but as by far the most com- 
plete treatise upon the clinical and practical side 
of the question.—Boston Medical and Surgical Jour- 
nal, Nov. 5,1874. Lea Brothers & Co.’s Publications—Pathol., Histol. 
13 
COATS, JOSEPH, M. IX, F. F. F. S., 
Pathologist to the Glasgow Western Infirmary. 
A Treatise on Pathology. In one very handsome octavo volume of 829 pages, 
with 339 beautiful illustrations. Cloth, $5.50; leather, $6.50. 
The work before us treats the subject of Path- 
ology more extensively than it is usually treated 
in similar works. Medical students as well as 
physicians, who desire a work for study or refer- 
ence, that treats the subjects in the various de- 
partments in a very thorough manner, but without 
prolixity, will certainly give this one the prefer- 
ence to any with which we are acquainted. It sets 
forth the most recent discoveries, exhibits, in an 
interesting manner, the changes from a normal 
condition effected in structures by disease, and 
points out the characteristics of various morbid 
agencies, so that they can be easily recognized. But, 
not limited to morbid anatomy,it explains fully how 
the functions of organs are disturbed by abnormal 
conditions. There is nothing belonging to its de- 
partment of medicine that is not as fully elucidated 
as our present knowledge will admit.— Cincinnati 
Medical News, Oct. 1883. 
GREEN, T. HENRY, 31. IX, 
Lecturer on Pathology and Morbid Anatomy at Charing-Cross Hospital Medical School, London. 
Pathology and Morbid Anatomy. Fifth American from the sixth revised 
find enlarged English edition. In one very handsome octavo volume of 482 pages, with 
150 line engravings. Cloth, $2.50. Just ready. 
The fact that this well-known treatise has so 
rapidly reached its sixth edition is a strong evi- 
dence of its popularity. The author is to be con- 
gratulated upon the thoroughness with which he, 
has prepared this work. It is thoroughly abreast 
with all the most recent advances in pathology. 
No work in ihe English language is so admirably 
adapted to the wants of the student and practi- 
tioner as this, and we would recommend it most 
, earnestly to every one.—Nashville Journal of Medi- 
cine and Surgery, Nov. 1884. 
WOOHHEAH, G. SIMS, 31. H., F. R. C. F. E., 
Demonstrator of Pathology in the University of Edinburgh. 
Practical Pathology. A Manual for Students and Practitioners. In one beau- 
tiful octavo volume of 497 pages, with 136 exquisitely colored illustrations. Cloth, $6.00. 
It forms a real guide for the student and practi- 
tioner who is thoroughly in earnest in his en- 
deavor to see for himself and do for himself. To 
the laboratory student it will be a helpful com- 
panion, and all those who may wish to familiarize 
themselves with modern methods of examining 
morbid tissues are strongly urged to provide 
themselves with this manual. The numerous 
drawings are not fancied pictures, or merely 
schematic diagrams, but they represent faithfully 
the actual images seen under the microscope. 
The author merits all praise for having produced 
a valuable W'ork.—Medical Record, May 31, 1884. 
It is manifestly the product of one who has him- 
self travelled over the whole field and who is skilled 
not merely in the art of histology, but in the obser- 
vation and interpretation of morbid changes. The 
work is sure to command a wide circulation. It 
should do much to encourage the pursuit of path- 
ology, since such advantages in histological study 
have never before been offered.—The Lancet, Jan, 
5, 1884. 
SCHAFER, EH WARD A., F. It. S., 
Assistant Professor of Physiology in University College, London. 
The Essentials of Histology. In one octavo volume of about 300 pages, 
with about 325 illustrations. In press. 
CO It NIL, V., and RANVIER, L., 
Prof, in the Faculty of Med. of Paris. Prof, in the College of France. 
A Manual of Pathological Histology. Translated, with notes and additions, 
by E. O. Shakespeare, M. D., Pathologist and Ophthalmic Surgeon to Philadelphia 
Hospital, and by J. Henry C. Simes, M. I)., Demonstrator of Pathological Histology in 
the University of Pennsylvania. In one very handsome octavo volume of 800 pages/-with 
360 illustrations. Cloth, $5.50 ; leather, $6.50; half Russia, raised bands, $7. 
KLEIN, E., 31. 1)., F. It. 8., 
Joint Lecturer on General Anat. and Phys. in the Med. School of St. Bartholomew's Hasp., London. 
Elements of Histology. In one pocket-size 12mo. volume of 360 pages, with 181 
illus. Limp cloth, red edges, $1.50. See Students’ Series of Manuals, page 3. 
Although an elementary work, it is by no means 
superficial or incomplete, for the author presents 
in concise language nearly all the fundamental facts 
regarding the microscopic structure of tissues. 
The illustrations are numerous and excellent. We 
commend Dr. Klein’s Elements most heartily to 
the student.—Medical Record, Dec. 1,1883. 
FFFFFR, A. J,, M. JB., 31. S., F. R. C. S., 
Surgeon and Lecturer at St. Mary's Hospital, London. 
Surgical Pathology. In one pocket-size 12mo. volume of 511 pages, with 81 
illustrations. Limp cloth, red edges, $2.00. See Students’ Series of Manuals, page 3. 
It is not pretentious, but it will serve exceed- 
ingly well as a book of reference. It erhbodies a 
treat deal of matter, extending over the whole 
eld of surgical pathology. Its form is practical, 
its language is clear, and the information set 
forth is well-arranged, well-indexed and well- 
illustrated. The student will find in it nothing 
that is unnecessary. The list of subjects covers 
the whole range of surgery. The book supplies a 
very manifest want and should meet with suc- 
cess.—New York Medical Journal, May 31,1884. 
SCHAFER’S PRACTICAL HISTOLOGY. In one I 
handsome royal 12mo. volume of 308 pages, with I 
40 illustrations. 
GLUGE’S ATLAS OF PATHOLOGICAL HISTOL-1 
OGY. Translated by Joseph Leidy, M. D. In one 
volume, very large imperial quarto, with 320 
copper-plate figures, plain and colored and des- 
criptive letter-press. Cloth, $4.00. 14 
Lea Brothers & Co.’s Publications—Practice of Med. 
FLINT, AUSTIN, 31. I)., 
Prof, of the Principles and Practice of Med. and of Clin. Med. in Bellevue Hospital Medical College, N. Y. 
A Treatise on the Principles and Practice of Medicine. Designed for 
the use of Students and Practitioners of Medicine. With an Appendix on the Researches 
of Koch, and their bearing on the Etiology, Pathology, Diagnosis and Treatment of 
Phthisis. Fifth edition, revised and largely rewritten In one large and closely-printed 
octavo volume of 1160 pages. Cloth, $5.50; leather, $6.50; half Russia, $7. 
Koch’s discovery of the bacillus of tubercle gives promise of being the greatest 
boon ever conferred by science on humanity, surpassing even vaccination in its benefits to 
mankind. In the appendix to his work, Professor Mint deals with the subject from a 
practical standpoint, discussing its bearings on the etiology, pathology, diagnosis, prog- 
nosis and treatment of pulmonary phthisis. Thus enlarged and completed, this standard 
work will be more than ever a necessity to the physician who duly appreciates the re- 
sponsibility of his calling. 
A well-known writer and lecturer on medicine 
recently expressed an opinion, in the highest de- 
gree complimentary of the admirable treatise of 
Dr. Flint, and in eulogizing it, he described it ac- 
curately as “readable and reliable.” No text-book 
is more calculated to enchain the interest of the 
student, and none better classifies the multitudi- 
nous subjects included in it. It has already so far 
won its way in England, that no inconsiderable 
number of men use it alone in the study of pure 
medicine; and we can say of it that it is in every 
way adapted to serve, not only as a complete guide, 
but also as an ample instructor in the science and 
practice of medicine. The style of Dr. Flint is 
always polished and engaging. The work abounds 
in perspicuous explanation, and is a most valuable 
text-book of medicine.—London Medical Nexvs. 
This work is so widely known and accepted as 
the best American text-book of the practice of 
medicine that it would seem hardly worth while tc» 
give this, the fifth edition, anything more than a 
passing notice. But even the most cursory exami- 
nation shows that it is, practically, much more 
than a revised edition; it is, in fact, rather a new 
work throughout. This treatise will undoubtedly 
continue to hold the first place in the estimation 
of American physicians and students. No one of 
our medical writers approaches Professor Flint in 
clearness of diction, breadth of view, and, what we 
regard of transcendent importance, rational esti- 
mate of the value of remedial agents. It is thor- 
oughly practical, therefore pre-eminently the book 
for American readers.—St. Louis Clin, Eec., Mar. ’BL 
HARTSHORN!, HENRY, M. JD., LL. I)., 
Lately Professor of Hygiene in the University of Pennsylvania. 
Essentials of the Principles and Practice of Medicine. A Handbook 
for Students and Practitioners. Fifth edition, thoroughly revised and rewritten. In one 
royal 12mo. volume of 669 pages, with 144 illustrations. Cloth, $2.75; half bound, $3.00. 
Within the compass of 600 pages it treats of the 
history of medicine, general pathology, general 
symptomatology,and physical diagnosis (including 
laryngoscope, ophthalmoscope, etc.), general ther- 
apeutics, nosology, and special pathology and prac- 
tice. There is a wonderful amount of information 
contained in this work, and it is one of the best 
of its kind that we have seen.—Glasgow Medical 
Journal, Nov. 1882. 
An indispensable book. No work ever exhibited 
a better average of actual practical treatment than 
this one; and probably not one writer in our day 
had a better opportunity than Dr. Hartshorne for 
condensing all the views of em inent practitioners 
into a 12mo. The numerous illustrations will be 
very useful to students especially. These essen- 
tials, as the name suggests, are not intended to 
supersede the text-books of Flint and Bartholow, 
but they are the most valuable in affording the 
means to see at a glance the whole literature of any 
disease, and the most valuable treatment.—Chicago 
Medical Journal and Examiner, April, 1882. 
BRISTOWE, JOHN SYER, M. J)., F. R. C. F,, 
Physician and Joint Lecturer on Medicine at St. Thomas' Hospital. 
A Treatise on the Practice of Medicine, Second American edition, revised 
by the Author. Edited, with additions, by James H. Hutchinson, M.D., physician to the 
Pennsylvania Hospital. In one handsome octavo volume of 1085 pages, with illustrations. 
Cloth, $5.00; leather, $6.00; very handsome half Russia, raised bands, $6.50. 
The reader will find every conceivable subject 
connected with the practice of medicine ably pre- 
sented, in a style at once clear, interesting and 
concise. The additions made by Dr. Hutchinson 
are appropriate and practical, and greatly add to 
its usefulness to American readers.—Buffalo Med- 
ical and Surgical Journal, March, 1880. 
WATSON, SIR THOMAS, 31. JO., 
Lectures on the Principles and Practice of Physic. A new American 
from the fifth English edition. Edited, with additions, and 190 illustrations, by Henry 
Hartshorne, A. M., M. D., late Professor of Hygiene in the University of Pennsylvania. 
In two large octavo volumes of 1840 pages. Cloth, $9.00 ; leather, $ll.OO. 
Late Physician in Ordinary to the Queen. 
LECTURES ON THE STUDY OF FEVER. By 
A. Hudson, M. D., M. R. I. A. In one octavo 
volume of 308 pages. Cloth, $2.50. 
STOKES’ LECTURES ON FEVER. Edited by 
John William Moore, M. D., F. K. Q. C. P. In 
one octavo volume of 280 pages. Cloth, $2.00. 
A TREATISE ON FEVER. By Robert D. Lyons, 
K. O. C. In one Bvo. vol. of 354 pp. Cloth, $2.25. 
LA ROCHE ON YELLOW FEVER, considered in 
its Historical, Pathological, Etiological and 
Therapeutical Relations. In two large and hand- 
some octavo volumes of 1468 pp. Cloth, $7.00. 
A CENTURY OF AMERICAN MEDICINE, 1776—1876. By Drs. E. H. Clarke, H. J. 
Bigelow, 8. D. Gross, T. G. Thomas, and J. S. Billings. In one 12mo. volume of 370 pages. Cloth, $2.25. Lea Brothers & Co.’s Publications—Systems of Med. 
15 
For Sale by Subscription Only. 
A System of Practical Medicine 
AMERICAN AUTHORS. 
Edited by WILLIAM PEPPEE, M. D., LL. D., 
PEOVOST AND PROFESSOR OF THE THEORY AND PRACTICE OF MEDICINE AND OP 
CLINICAL MEDICINE IN THE UNIVERSITY OF PENNSYLVANIA, 
Assisted by Louis Staee, M. D., Clinical Professor of the Diseases of Children in the 
Hospital of the University of Pennsylvania. 
In five imperial octavo volumes, containing about 1100 pages each, with illustrations. Price per 
volume, cloth, §5; leather, $6 ; half Russia, raised bands and open back, $7. Volume I. 
(General Pathology, Sanitary Science and General Diseases) contains 1094 pages, 
vjith 24 illustrations and is just ready. Volume 11. (General Diseases [con- 
tinued] and Diseases of the Digestive System) will be ready June Ist, 
and the subsequent volumes at intervals of four months thereafter. 
The publishers feel pardonable pride in this magnificent work. For 
three years it has been in active preparation, and it is now in a sufficient state of forward- 
ness to justify them in calling the attention of the profession to it as the work in which 
for the first time American medicine is thoroughly represented by its worthiest 
teachers, and presented in the full development of the practical utility which is its 
preeminent characteristic. The most able men—from the East and the West, from the 
North and the South, from all the prominent centres of education, and from all the 
hospitals which afford special opportunities of study and practice—have united in 
generous rivalry to bring together this vast aggregate of specialized experience. 
The distinguished editor has so apportioned the work that each author has had 
assigned to him the subject which he is peculiarly fitted to discuss, and in which his views 
will be accepted as the latest expression of scientific and practical knowledge. The 
practitioner will therefore find these volumes a complete, authoritative and unfailing work 
of reference, to which he may at all times turn with full certainty of finding what he needs 
in its most recent aspect, whether he seeks information on the general principles of medi- 
cine, or minute guidance in the treatment of special disease. So wide is the scope of the 
work that, with the exception of midwifery and matters strictly surgical, it embraces the 
whole domain of medicine, including the departments for which the physician is accustomed 
to rely on special treatises, such as diseases of women and children, of the genito-urinary 
organs, of the skin, of the nerves, hygiene and sanitary science, and medical ophthalmology 
and otology. Moreover, authors have inserted the formulas which they have found most 
efficient in the treatment of the various affections. It may thus be truly regarded as a 
Complete Library of Practical Medicine, and the general practitioner possessing it 
may feel secure that he will require little else in the daily round of professional duties. 
In spite of every effort to condense the vast amount of practical information fur- 
nished, it has been impossible to present it in less than 6 large octavo volumes, containing 
about 5500 beautifully printed pages, and embodying the matter of about 15 ordinary 
octavos. Illustrations are introduced wherever they serve to elucidate the text. 
As material for the work is substantially complete in the hands of the editor, the pro- 
fession may confidently await the appearance of the remaining volumes upon the dates 
above specified. A detailed prospectus of the work will be sent to any address on appli- 
cation to the publishers. 
It Is a large undertaking, but quite justifiable in 
the case of a progressive nation like the United 
■States. At any rate, if we may judge of future 
volumes from the first, it will be justified by the 
result. We have nothing but praise to bestow 
upon the work. The articles are the work of 
writers, many of whom are already recognized in 
| this country as authorities on the particular topics 
I on which they deal, whilst the others show by the 
j way they have handled their subjects that they 
are fully equal to the task they had undertaken, 
j * * * A work which we cannot doubt will make 
j a lasting reputation for itself.—London Medical 
j Times and Gazette, May 9, 1885. 
REYNOLDS, J. RUSSELL, M. I)., 
Professor of the Principles and Practice of Medicine in University College, London. 
A System of Medicine. With notes and additions by Henry Hartshorne, 
A. M., M. D., late Professor of Hygiene in the University of Pennsylvania. In three large 
and handsome octavo volumes, containing 3056 double-columned pages, with 317 illustra- 
tions. Price per volume, cloth, $5.00; sheep, $6.00; very handsome half Russia, raised bands, 
$6.50. Per set, cloth, $l5; leather, $18; half Russia, $19.50. Sold only by subscription. 
There is no medical work which we have in ! 
times past more frequently and fully consulted | 
when perplexed by doubts as to treatment, or by j 
having unusual or apparently inexplicable symp- ' 
toms presented to us, than “Reynolds’ System of j 
Medicine.” It contains just that kind of informa- : 
tion which the busy practitioner frequently finds ' 
himself in need of. In order that any deficiencies 
may be supplied, the publishers have committed 
the preparation of the book for the press to Dr. 
Henry Hartshorne, whose judicious notes distrib- 
uted throughout the volume afford abundant evi- 
denee of the thoroughness of the revision.—Amer- 
lean Journal of the Medical Sciences, Jan. 1880. 16 
Lea Brothers & Co.’s Publications—Clinical Med., etc. 
STIFLE, ALFRED, 31. I)., LL. I)., 
Cholera: Its Origin, History, Causation, Symptoms, Prevention and Treatment. 
In one handsome 12mo. volume of about 175 pages, with a chart. Cloth, $1.25. Shortly. 
The threatened importation of cholera into the country renders peculiarly timely 
this work of an authority so eminent as Professor Stille. The history of previous epi- 
demics, their modes of propagation, the vast recent additions to our knowledge of the 
■causation, prevention and treatment of the disease, all have been handled so skilfully as 
to present with brevity the information which every practitioner should possess in ad- 
vance of a visitation. 
Professor Emeritus of the Theory and Practice of Med. and of Clinical Med. in the Univ. of Penna. 
FLINT, AUSTIN, 31. D. 
Clinical Medicine. A Systematic Treatise on the Diagnosis and Treatment of 
Diseases. Designed for Students and Practitioners of Medicine. In one large and hand- 
some octavo volume of 799 pages. Cloth, $4.50; leather, $5.50; half Russia, $6.00. 
It is here that the skill and learning of the great 
-clinician are displayed. He has given us a store- 
house of medical knowledge, excellentfor the stu- 
dent, convenient for the practitioner, the result of 
•■along life of the most faithful clinical work, col- 
lected by an energy as vigilant and systematic as 
untiring, and weighed by a judgment nolessclear 
than his observation is close.—Archives of Medicine, 
Dec. 1879. 
To give an adequate and useful conspectus of the 
extensive field of modern clinical medicine is a task 
of no ordinary difficulty; but to accomplish this con- 
sistently with brevity and clearness, the different 
subjects and their several parts receiving the 
attention which, relatively to their importance, 
medical opinion claims for them, is still more diffi- 
cult. This task, we feel bound to say, has been 
executed with more than partial success by Dr. 
Flint, whose name is already familiar' to students 
of advanced medicine in this country as that of 
the author of two works of great merit on special 
subjects, and of numerous papers exhibiting much 
originality and extensive research.— The Dublin 
Journal, Dec. 1879. 
Essays on Conservative Medicine and Kindred Topics. In one very hand- 
some royal 12mo. volume of 210 pages. Clgtli, $1.38. 
the Same Author. 
BROADBENT, W. 11., 31. J)., F. R. C. F., 
Physician to and Lecturer on Medicine at St. Mary's Hospital. 
The Pulse. In one 12mo. volume. See Series of Clinical Manuals, page 8. 
SCURF 1 TIER, DR. JOSEFH. 
A Manual of Treatment by Massage and Methodical Muscle Ex- 
ercise. Translated by Walter Mendelson, M. D., of New York. In one handsome 
octavo volume of about 300 pages, with about 125 fine engravings. Preparing. 
FINLAYSON, JAMES, 31. D., Editor, 
Physician and Lecturer on Clinical Medicine in the Glasgow Western Infirmary, etc. 
Clinical Diagnosis. A Handbook for Students and Practitioners of Medicine. 
"With Chapters by Prof. Gairdner on the Physiognomy of Disease; Prof. Stephens on 
Diseases of the Female Organs; Dr. Robertson on Insanity; Dr. Gemmell on Physical 
Diagnosis; Dr. Coats on Laryngoscopy and Post-Mortem Examinations, and by the Editor 
on Case-taking, Family History and Symptoms of Disorder in the Various Systems. In 
one handsome 12mo. volume of 546 pages, with 85 illustrations. Cloth, $2.63. 
This is one of the really useful books. It is at- 
tractive from preface to the final page, and ought 
to be given a place on every office table, because it 
contains in a condensed form all that is valuable 
in semeiology and diagnostics to be found in 
bulkier volumes; and because of its arrangement 
and complete index it is unusually convenient for 
quick reference in any emergency that may come 
upon the busy practitioner.—N. C. Med. Journ,, 
Jan. 1879. 
FENWICK, SAMUEL, 31. D., 
Assistant Physician to the London Hospital. 
The Student’s Guide to Medical Diagnosis. From the third revised and 
enlarged English edition. In one very handsome royal 12mo. volume of 328 pages, with 
87 illustrations on wood. Cloth, $2.25. 
TANNER, THOMAS HAWKES, M. D. 
A Manual of Clinical Medicine and Physical Diagnosis. Third American 
from the second London edition. Revised and enlarged by Tilbury Fox, M. D., Phy- 
sician to the Skin Department in University College Hospital, London, etc. In one small 
12mo. volume of 362 pages, with illustrations. Cloth, $1.50. 
FOTHERGLLL, J. 31., 31. D., Edin., M. R. C. P., Loud., 
The Practitioner’s Handbook of Treatment; Or, The Principles of Thera- 
peutics. New edition. In one octavo volume. Preparing. 
Physician to the City of London Hospital for Diseases of the Chest. 
STURGES’ INTRODUCTION TO THE STUDY 
OF CLINICAL MEDICINE. Being a Guide to 
the Investigation of Disease. In one handsome 
,12mo. volume of 127 pages. Cloth, $1,25. 
DAVIS’ CLINICAL LECTURES ON VARIOUS 
IMPORTANT DISEASES. By N. S. Davis 
M. D. Edited by Frank H. Davis, M. D. Second 
edition. 12mo. 287 pages. Cloth, $1.75. Lea Brothers & Co.’s Publications—Hygiene, Electr., Pract. 
17 
RICHARDSON, B. W., 31. A., M.D., EL. D., F.R.S., F.S.A. 
Preventive Medicine. In one octavo volume of 729 pages. Cloth, $4; leather, 
$5; very handsome half Russia, raised bands, $5.50. 
Fellow of the Royal College of Physicians, London. 
Dr. Richardson has succeeded in producing a 
work which is elevated in conception, comprehen- 
sive in scope, scientific in character, systematic in 
arrangement, and which is written in a clear, con- 
cise and pleasant manner. He evinces the happy 
faculty of extracting the pith of what is known on 
the subject, and of presenting it in a most simple, 
intelligent and practical form. There is perhaps 
no similar work written for the general public 
thatcontains such acornplete,reliable and instruc- 
tive collection of data upon the diseases common 
to the race, their origins, causes, and the measures 
for their prevention. The descriptions of diseases 
are clear, chaste and scholarly; the discussion of 
the question of disease is comprehensive, masterly 
and fully abreast with the latest and best knowl- 
edge on the subject, and the preventive measures 
advised are accurate, ejqfiicit and reliable.— The 
American Journal of the Medical Sciences, April, 1884. 
This is a book that will surely find a place on the 
table of every progressive physician. To the 
medical profession, whose duty is quite as much to 
prevent as to cure disease, the book will be a boon. 
—Boston Medical and Surgical Journal, Mar. 6, 1884. 
The treatise contains a vast amount of solid, valu- 
able hygienic information.—Medical and Surgical 
Reporter, Feb. 23, 1884. 
BARTIIOLOW, ROBERTS, A. 31., 31,1),, LL, />., 
Prof, of Materia Medico, and General Therapeutics in the Jefferson Med. Coll, of Phila., etc. 
Medical Electricity. A Practical Treatise on the Applications of Electricity 
to Medicine and Surgery. Second edition. In one very handsome octavo volume of 292 
pages, with 109 illustrations. Cloth, $2.50. 
The second edition of this work following so 
soon upon the first would in itself appear to be a 
sufficient announcement; nevertheless, the text 
has been so considerably revised and condensed, 
and so much enlarged by the addition of new mat- 
ter, that we cannot fail to recognize a vast improve- 
ment upon the former work. The author has pre- 
pared his work for students and practitioners—for 
those who have never acquainted themselves with 
the subject, or, having done so, find that after a 
time their knowledge heeds refreshing. We think 
he has accomplished this object. The book is not 
too voluminous, but is thoroughly practical, sim- 
ple, complete and comprehensible. It is, more- 
over, replete with numerous illustrations of instru- 
ments, appliances, etc.—Medical Record, November 
15, 1882. 
A most excellent work, addressed by a practi- 
tioner to his fellow-practitioners, and therefore 
thoroughly practical. The work now before us 
has the exceptional merit of clearly pointing out 
where the benefits to be derived from electricity 
must come. It contains all and everything that 
the practitioner needs in order to understand in- 
telligently the nature and laws of the agent he is 
making use of, and for its proper application in 
practice. In a condensed, practical form, it pre- 
sents to the physician all that he would wish to 
remember after perusing a whole library on medical 
electricity, including the results of the latest in- 
vestigations. It is the book for the practitioner, 
and the necessity for a second edition proves that 
it has been appreciated by the profession.—Physi- 
cian and Surgeon, Dee. 1882. 
THE YEAR-BOOK OF TH E A T3IEXT. 
A Comprehensive and Critical Review for Practitioners of Medi- 
cine. In one 12mo. volume of 320 pages, bound in limp cloth, with red edges, $1.25. 
This work presents to the practitioner not only a complete classified account of all 
the more important advances made in the treatment of Disease during the year ending 
Sept. 30, 1884, but also a critical estimate of the same by a competent authority. Each 
department of practice has been fully and concisely treated, and into the consideration of 
each subject enter such allusions to recent pathological and clinical work as bear directly 
upon treatment. As the medical literature of all countries has been placed under contri- 
bution, the references given throughout the work, together with the separate indexes of 
subjects and authors, will serve as a guide for those who desire to investigate any thera- 
peutical topic at greater length. 
The contributions are from the pens of the following well-known gentlemen:—J. 
Mitchell Bruce, M.D.; T. Lauder Brunton, M.D., F.R.S. ; Thomas Bryant, F.R. 
C.S.; F. H. Champneys, M.8.; Alfred Cooper, F.R.C.S.; Sidney Coupland, M.D. ; 
Dyce Duckworth, M.D.; George P. Field, M.R.C.S. ; Reginald Harrison, F.R. 
C.S.; J. Warrington Ha ward, F.R.C.S.; F. A. Mahomed, M.8.; Malcolm Morris, 
F.R.C.S., Ed.; Edmund Owen, F.R.C.S.; R. Douglas Powell, M.D.; Henry Power, 
M.8., F.R.C.S.; C. 11. Ralfe, M.D.; A. E. Sansom, M.D.; Felix Semon, M.D.; 
Walter G. Smith, M.D. ; J. Knowsley Thornton, M.8.; Frederick Treves, 
F.R.C.S.; A. de Watteville, M.D.; John Williams, M.D. 
JIABERSJIOJY, S. 0., 31. J)., 
Senior Physician to and late Lect. on Principles and Practice of Med. at Guy's Hospital, London. 
On the Diseases of the Abdomen; Comprising those of the Stomach, and 
other parts of the Alimentary Canal, (Esophagus, Caecum, I ntestines and Peritoneum. Second 
American from third enlarged and revised English edition. In one handsome octavo 
volume of 554 pages, with illustrations. Cloth, $8.50. 
DAVY’S TREATISE ON THE FUNCTION OF DI- 
GESTION; its Disorders and their Treatment. 
From the second London edition. In one octavo 
volume of 238 pages. Cloth, $2.00. 
BARLOW’S MANUAL OF THE PRACTICE OF 
MEDICINE. With additions by I). F. Co,\die, 
M. D. 1 yol. Bvo., pp. 603. Cloth, $2.50. 
TODD’S CLINICAL LECTURES ON CERTAIN 
ACUTE DISEASES. In one octavo volume of 
320 pages. Cloth, $2.50. 
HOLLAND’S MEDICAL NOTES AND REFLEC- 
TIONS. 1 yol. Bvo., pp. 493. Cloth, $3.50. 
CHAMBERS’ MANUAL OF DIET AND REGIMEN- 
IN HEALTH AND SICKNESS. In one hand- 
some octavo volume of 302 pp. Cloth, $2.75. 18 
Lea Brothers & Co.’s Publications—Throat, Limgs, Heart. 
COHEW, J. SOLIS, M. D„ 
Lecturer on Laryngoscopy and Diseases of the Throat and Chest in the Jefferson Medical College. 
Diseases of the Throat and Nasal Passages. A Guide to the Diagnosis and 
Treatment of Affections of the Pharynx, (Esophagus, Trachea, Larynx and Nares. Third 
edition, thoroughly revised and rewritten, with a large number of new illustrations. In 
one very handsome octavo volume. Preparing. 
SEILER, CAUL, M. />., 
Lecturer on Laryngoscopy in the University of Pennsylvania. 
A Handbook of Diagnosis and Treatment of Diseases of the Throat, 
Hose and Naso-Pharynx. Second edition. In one handsome royal 12mo. volume 
of 294 pages, with 77 illustrations. Cloth, $1.75. 
It is one of the best of the practical text-books 
on this subject with which we are acquainted. The 
present edition has been increased in size, but its 
eminently practical character has been main- 
tained. Many new illustrations have also been 
introduced, a case-record sheet has been added, 
and there are a valuable bibliography and a good 
index of the whole. For any one who wishes to 
make himself familiar with the practical manage- 
ment of cases of throat and nose disease, the book 
will be found of great value.—New York Medical 
Journal, June 9,1883. 
The work before is a concise handbook upon 
the essentials of diagnosis and treatment in dis- 
eases of the throat and nose. The art of laryngos- 
copy, the anatomy of the throat and nose and the 
pathology of the mucous membrane are discussed 
with conciseness and ability. The work is pro- 
fusely illustrated, excels in many essential feat- 
ures," and deserves a place in the office of the 
practitioner who would inform himself as to the 
nature, diagnosis and treatment of a class of dis- 
eases almost inseparable from general medical 
practice. With advanced students the book must 
be very popular on account of its condensed style. 
—Louisville Medical News, June 26, 1883. 
BROWWE, LEWWOX, F. JL 
C. S., Ed hi,, 
The Throat and Its Diseases. Second American from the second English edi- 
tion, thoroughly revised. With 100 typical illustrations in colors and 50 wood engravings, 
designed and executed by the Author. In one very handsome imperial octavo volume of 
about 350 pages. Preparing. 
Senior Surgeon to the Central London Throat and Ear Hospital, etc. 
ELIWT, AITSTIW, M. I>„ 
Professor of the Principles and Practice of Medicine in Bellevue Hospital Medical College, N. T. 
A Manual of Auscultation and Percussion; Of the Physical Diagnosis of 
Diseases of the Lungs and Heart, and of Thoracic Aneurism. Third edition. In one hand- 
some royal 12mo. volume of 240 pages. Cloth, $1.63. 
It is safe to say that there is'not in the English 
language, or any other, the equal amount of clear, 
exact ana comprehensible information touching 
the physical exploration of the chest, in an equal 
number of words. Professor Flint’s language is 
precise and simple, conveying without dubiety 
the results of his careful study and ample ex- 
perience in such wise that the young will find it the 
best source of instruction, and the old the most 
pleasant means of reviving and complementing 
their knowledge. American Practitioner, June, 
1883. 
Physical Exploration of the Lungs by Means of Auscultation and 
Percussion. Three lectures delivered before the Philadelphia County Medical Society, 
1882-83. In one handsome small 12mo. volume of 83 pages. Cloth, $l.OO. 
THE SAME AUTHOR. 
A Practical Treatise on the Physical Exploration of the Chest and 
the Diagnosis of Diseases Affecting the Respiratory Organs. Second and 
revised edition. In one handsome octavo volume of 591 pages. Cloth, $4.50. 
Phthisis: Its Morbid Anatomy, Etiology, Symptomatic Events and 
Complications, Fatality and Prognosis, Treatment and Physical Diag- 
nosis ; In a series of Clinical Studies. In one handsome octavo volume of 442 pages. 
Cloth, $3.50. 
A Practical Treatise on the Diagnosis, Pathology and Treatment of 
Diseases of the Heart. Second revised and enlarged edition. In one octavo volume 
of 550 pages, with a plate. Cloth, $4. 
GROSS, S. I)., M.JD., LL. />., JhC.L. Oxon., LL.JD. Cantab, 
A Practical Treatise on Foreign Bodies in the Air-passages. In one 
octavo volume of 452 pages, with 59 illustrations. Cloth, $2.75. 
PULLER ON DISEASES OP THE LUNGS AND 
AIR-PASSAGES. Their Pathology, Physical Di- 
agnosis, Symptoms and Treatment. From the 
second and revised English edition. In one 
octavo volume of 475 pages. Cloth, $3.50. 
SLADE ON DIPHTHERIA; its Nature and Treat- 
ment, with an account of the History of its Pre- 
valence in various Countries. Second and revised 
edition. In one 12mo. vol., pp. 158. Cloth, $1.25. 
WALSHE ON THE DISEASES OP THE HEART 
AND GREAT VESSELS. Third American edi- 
tion. In 1 vol. Bvo., 416 pp. Cloth, $3.00. 
SMITH ON CONSUMPTION; its Early and Reme- 
diable Stages. 1 vol. Bvo., pp. 253. Cloth, $2.25. 
LA ROCHE ON PNEUMONIA. 1 vol. 8m of 490 
pages. Cloth, $3.00. 
WILLIAMS ON PULMONARY CONSUMPTION; 
its Nature, Varieties and Treatment. With an 
analysis of one thousand eases to exemplify its 
duration. In one Byo. vol. of 303 pp. Cloth, $2.50. 
JONES’ CLINICAL OBSERVATIONS ON FUNC- 
TIONAL NERVOUS DISORDERS. Second Am- 
erican edition. In one handsome octavo volume 
of 340 pages. Cloth, $3.25. Lea Brothers & Co.’s Publications—Nerv. and Ment. Dis.,’etc. 
19 
MITCHELL, S. WEIL, M. I),, 
Physician to Orthopaedic Hospital and the Infirmary for Diseases of the Nervous System, Phila., etc. 
Lectures on Diseases of the Nervous System; Especially in Women. 
Second edition. In one 12mo. volume of 288 pages. Cloth, $1.75. Just ready. 
So great have been the achievements of the system perfected by the author for the treat- 
ment of hysterical and nervous diseases that the profession will welcome the second and 
enlarged edition of a work which gives in detail the methods of enforced rest, massage and 
systematic feeding on which this mode of treatment is based. Many of these lectures are 
original studies of well-known diseases, and others deal with subjects which have been 
hitherto slighted in medical literature or which are almost unknown to it. 
The interest lies in the keen insight into the I 
nature of the subject and in the suggestions which | 
the author manages to throw into his accounts. I 
The lectures must command the thoughtful | 
attention and careful study of all who desire to 
read what is best in medical science.—The London 
Lancet, May 16, 1885. 
HAMILTON, ALLAN McLANE, M. JD., 
Attending Physician at the Hospital for Epileptics and Paralytics, Blackwell's Island, N. Y. 
Nervous Diseases; Their Description and Treatment. Second edition, thoroughly 
revised and rewritten. In one octavo volume of 598 pages, with 72 illustrations. Cloth, $4. 
When the first edition of this good book appeared 
we gave it our emphatic endorsement, and the 
Eresent edition enhances our appreciation of the 
ook and its author as a safe guide to students of 
clinical neurology. One of the best and most 
critical of English neurological 'ournals, Brain, has 
characterized this hookas the best of its kind in 
any language, which is a handsome endorsement 
from an exalted source. The improvements in the 
new edition, and the additions to it, will justify its 
purchase even by those who possess the old.— 
Alienist and Neurologist, April, 1882. 
TIKE, DA NIEL HACK, 31. D., 
Joint Author of The Manual of Psychological Medicine, etc. 
Illustrations of the Influence of the Mind upon the Body in Health 
and Disease. Designed to elucidate the Action of the Imagination. New edition. 
Thoroughly revised and rewritten. In one handsome octavo volume of 467 pages, with 
two colored plates. Cloth, $3.00. 
It is impossible to peruse these interesting chap- 
ters without being convinced of the author’s per- 
feet sincerity, impartiality, and thorough mental 
grasp. Dr. Tuke has exhibited the requisite 
amount of scientific address on all occasions, and 
the more intricate the phenomenathe more firmly 
has he adhered to a physiological and rational 
method of interpretation. Guided by an enlight- 
ened deduction, the author has reclaimed for 
science a most interesting domain in psychology, 
previously abandoned to charlatans and empirics, 
This book, well conceived and well written, must 
commend itself to every thoughtful understand- 
ing.—New York Medical Journal, September 6,1884. 
CLOUSTON, THOMAS 8., 31. D., F. R. C. l\, L. It. C. S., 
Lecturer on Mental Diseases in the University of Edinburgh. 
Clinical Lectures on Mental Diseases. With an Appendix, containing an 
Abstract of the Statutes of the United States and of the Several States and Territories re- 
lating to the Custody of the Insane. By Charles F. Folsom, M. D., Assistant Professor 
of Mental Diseases, Medical Department of Harvard University. In one handsome 
octavo volume of 541 pages, illustrated with eight lithographic plates, four of which 
are beautifully colored. Cloth, $4. 
The practitioner as well as the student will ac- 
cept the plain, practical teaching of the author as a 
forward step in the literature of insanity. It is 
refreshing to find a physician of Dr. Clouston’s 
experience and high reputation giving the bed- 
side notes upon which his experience has been 
founded and his mature judgment established. 
Such clinical observations cannot but be useful to 
the genera! practitioner in guiding him to a diag- 
nosis and indicating the treatment, especially in 
many obscure and doubtful cases of mental dis- 
ease. To the American reader Dr. Folsom’s Ap- 
pendix adds greatly to the value of the work, and 
will make it a desirable addition to every library. 
—American Psychological Journal, July, 1884. 
108 pages. Cloth, $1.50. 
J&sgT’Dr. Folsom’s Abstract may also be obtained separately in one octavo volume of 
SAVAGE, GEORGE H., 31. JD., 
Lecturer on Mental Diseases at Guy's Hospital, London. 
Insanity and Allied Neuroses, Practical and Clinical. In one 12mo. vol- 
ume of 551 pages, with 18 typical illustrations. Cloth, $2.00. Just ready. See Series oj 
Clinical Manuals, page 3. 
As a handbook, a guide to practitioners and stu- 
dents, the book fulfils an admirable purpose. The 
many forms of insanity are described with char- 
acteristic clearness, the illustrative cases are care- 
fully selected, and as regards treatment, sound 
common sense is everywhere apparent. We re- 
peat that Dr. Savage has written an excellent 
manual for the practitioner and student.—Am- 
erican Journal of Insanity, April, 1885. 
JPLAYFAIR, W. S., M. JD., F. R. C. JP., 
The Systematic Treatment of Nerve Prostration and Hysteria. In 
one handsome small 12mo. volume of 97 pages. Cloth, $l.OO. 
Blandford on Insanity and its Treatment: Lectures on the Treatment, 
Medical and Legal, of Insane Patients. In one very handsome octavo volume. 20 
Lea Brothers & Co.’s Publications—Surgery. 
GROSS', S. 1)., 31. D., JLL. D., D. C. L. Oxon,, LL. D, 
Cantab., 
Emeritus Professor of Surgery in the Jefferson Medical College of Philadelphia. 
A System of Surgery: Pathological, Diagnostic, Therapeutic .and Operative. 
Sixth edition, thoroughly revised and greatly improved. In two large and beautifully- 
printed imperial octavo volumes containing 2382 pages, illustrated by 1623 engravings. 
Strongly bound in leather, raised bands, $l5; half Russia, raised bands, $l6. 
Dr. Gross’ System of Surgery has long been the 
standard work on that subject for students and 
practitioners.—London Lancet, May 10, 1884. 
The work as a whole needs no commendation. 
Many years ago it earned for itself the enviable rep- 
utation of the leading American work on surgery, 
and it is still capable of maintaining that standard. 
The reason for this need only be mentioned to be 
appreciated. The author has always been calm 
and judicious in his statements, has based his con- 
clusions on much study and personal experience, 
has been able to grasp his subject in its entirety, 
and, above all, has conscientiously adhered to 
truth and fact, weighing the evidence, pro and 
con, accordingly. A considerable amount of new 
material has been introduced, and altogether the 
distinguished author has reason to be satisfied 
that he has placed the work fully abreast of the 
state of our knowledge.—fifed. Record, Nov. 18,1882. 
_ His System of Surgery, which, since its first edi- 
tion in 18.59, has been a standard work in this 
country as well as in America, in “the whole 
domain of surgery,” tells how earnest and labori- 
ous and wise a surgeon he was. how thoroughly 
he appreciated the work done by men in other 
countries, and how much he contributed to pro- 
mote the science and practice of surgery in his 
own. There has been no man to whom America 
is so much indebted in this respect as the Nestor 
of surgery.—British Medical Journal, May 10,1884, 
ASH HURST, JOJIX. Jr., 
Professor of Clinical Surgery, Univ. of Penna., Surgeon to the Episcopal Hospital, Philadelphia. 
The Principles and Practice of Surgery. Fourth edition, enlarged and 
revised. In one large and handsome octavo volume of about 1100 pages, with about 575 
illustrations. In press. 
GOULD, A. PEA JtCE, M. S., 31. 8., F. 11. C. S„ 
Assistant Surgeon to Middlesex Hospital. 
Elements of Surgical Diagnosis. In one pocket-size 12mo. volume of 589 
pages. Cloth, $2.00. Just ready. See Students’ Series of Manuals, page 3. 
The student and practitioner will find the 
principles of surgical diagnosis very satisfactorily 
set forth with all unnecessary verbiage elimi- 
nated. Every medical student attending lectures 
should have a copy to study during the intervals, 
and if practitioners would devote a portion of their 
leisure to the study of it, they would receive 
immense benefit in the way of refreshing their 
knowledge and bringing it up to the present state 
of progress.—Cincinnati Medical News, Jan., 1885. 
GIBXEY, V. P., M. 1)., 
Surgeon to the Orthopaedic Hospital, New York, etc. 
Orthopaedic Surgery. For the use of Practitioners and Students. In one hand- 
some octavo volume, profusely illustrated. Preparing. 
BO BERTS, JOIIJSr 8., A. 31., 31. 1)., 
lecturer on Anatomy and on Operative Surgery, at the Philadelphia School of Anatomy. 
The Principles and Practice of Surgery. For the use of Students and 
Practitioners of Medicine and Surgery. In one very handsome octavo volume of about 500 
pages, with many illustrations. Preparing. 
BELLA3IY, EBWABD, F. B. C. 8., 
Surgeon and Lecturer on Surgery at Charing Cross Hospital, Examiner in Anatomy Royal 
College of Surgeons, London. 
Operative Surgery. Shortly. See Students’ Series of Manuals, page 3. 
BTI3TSOJST, LEWIS A., B. A., 31. 1)., 
Prof, of Pathol. Anat. at the Univ. of the City of New York, Surgeon and Curator to Bellevue Hosp 
A Manual of Operative Surgery. In one very handsome royal 12mo. volume 
of 477 pages, with 332 illustrations. Cloth, $2.50. 
This volume is devoted entirely to operative sur- 
gery, and is intended to familiarize the student 
with the details of operations and the different 
modes of performing them. The work is hand- 
somely illustrated, and the descriptions are clear 
and well-drawn. It is a e lever and useful volume; 
every student should possess one. This work 
does away with the necessity of pondering over 
larger works on surgery for descriptions of opera- 
tions, as it presents in a nutshell what is wanted 
by the surgeon without an elaborate search to 
find it.—Maryland Medical Journal, August, 1878. 
SARGENT ON BANDAGING and OTHER OPERA- 
TIONS OF MINOR SURGERY. New edition, 
with a Chapter on military surgery. One 12mo. 
volume of 383 pages, with 187 cuts. Cloth, $1.75. 
MILLER’S PRINCIPLES OF SURGERY. Fourth 
American from the third Edinburgh edition. In 
one Bvo. vol. of 638 pages, with 340 illustrations. 
Cloth, $3.75. 
PIRRIE’S PRINCIPLES AND PRACTICE OF 
SURGERY. Edited by John Neill, M. D. In 
one Bvo. vol. of 784 pp. with 316 illus. Cloth, $3.75. 
COOPER’S LECTURES ON THE PRINCIPLES 
AND PRACTICE OF SURGERY. In one Bvo. vol. 
of 767 pages. Cloth, $2.00. 
MILLER’S PRACTICE OF SURGERY. Fourth 
and revised American from the last Edinburgh 
edition. In one large Bvo. vol. of 682 pages, with 
364 illustrations. Cloth, $3.75. 
SKEY’S OPERATIVE SURGERY. In one vol. Bvo- 
of 661 pages, with 81 woodcuts. Cloth, $3.25. 
GIBSON’S INSTITUTES AND PRACTICE OF 
SURGERY. Eighth edition. In two octavo vols. 
of 965 pages, with 34 plates. Leather $6.50. Lea Brothers & Co.’s Publications—Surgery. 
21 
fricusfn, john i\ r. s., f. r. c. s., 
Professor of Surgery in University College, London, etc. 
The Science and Art of Surgery ; Being a Treatise on Surgical Injuries, Dis- 
eases and Operations. From the eighth and enlarged English edition. In two large and 
beautiful octavo volumes .of 2316 pages, illustrated with 984 engravings on wood. 
Cloth, $9; leather, raised bands, $11; half Russia, raised bands, $l2. Just ready. 
After the profession has placed its approval upon 
a work to the extent of purchasing seven editions, 
it does not need to be introduced. Simultaneous 
with the appearance of this edition a translation 
is being made into Italian and Spanish. Thus 
this favorite text-book on surgery holds its own in 
spite of numerous rivals attheendof thirtyyears. 
It is a grand book, worthy of the art in the interest 
of which it is written.—Detroit Lancet, Jan. 10,1885; 
After being before the profession for thirty 
years and maintaining during that period a re- 
putation as a leading work on surgery, there is not 
much to be said in the way of comment or criti- 
cism. That it still holds its own goes without say- 
ing. The author infuses into it his large experi- 
ence and ripe judgment. Wedded to no school, 
committed to no theory, biassed by no hobby, he 
imparts an honest personality in his observations, 
and his teachings are the rulings of an impartial 
judge. Such men are always safe guides, and their 
works stand the tests of time and experience. 
Such an author is Erichsen, and such a work is his 
Surgery.—Medical Record, Feb. 21, 1885. 
BUY ANT, THOMAS, I\ It. C. S., 
Surgeon and Lecturer on Surgery at Guy's Hospital, London. 
The Practice of Surgery. Fourth American from the fourth and revised Eng- 
lish edition. In one large and very handsome imperial octavo volume of 1040 pages, with 
727 illustrations. Cloth, $6.50; leather, $7.50; half Kussia, $B.OO. Just ready. 
The treatise takes in the whole field of surgery, 
that of the eye, the ear, the female organs, ortho- 
paedics, venereal diseases, and military surgery, 
as well as more common and general topics. All 
of these are treated with clearness and with 
sufficient fulness to suit all practical purposes. 
The illustrations are numerous and well printed. 
We do not doubt that this new edition will con- 
tinue to maintain the popularity of this standard 
work.—Medical and Surgical Reporter, Feb. 14, ’B5. 
This most magnificent work upon surgery has 
reached a fourth edition in this country, showing 
the high appreciation in which it is held by the 
American profession. It comes fresh from the 
pen of the author. That it is the very best work 
on surgery for medical students we think 
there can be no doubt. The author seems to have 
understood just what a student needs, and has 
prepared the work accordingly,—-Cincinnati Medical 
JSewn, January, 1885. 
By the same Author. 
Diseases of the Breast. In one 12mo. volume. Preparing. See Series of Clinical 
Manuals, page 3. 
FSMAIICH, Hr. FRIEDRICH, 
Professor of Surgery at the University of Kiel, etc. 
Early Aid in Injuries and Accidents. Five Ambulance Lectures. Trans- 
lated by H. R. H. Princess Christian. In one handsome small 12mo. volume of 109 
pages, with 24 Illustrations. Cloth, 75 cents. 
The course of instruction is divided into five 
sections or lectures. The first, or introductory 
lecture, gives a brief account of the structure and 
organization of the human body, illustrated by 
clear, suitable diagrams. The second teaches how 
to give judicious help in ordinary injuries—contu- 
sions, wounds, haemorrhage and poisoned wounds. 
The third treats of first aid in cases of fracture 
and of dislocations, in sprains and in burns. Next, 
the methods of affording first treatment in cases 
of frost-bite, of drowning, of suffocation, of loss of 
consciousness and of poisoning are described ; 
and the fifth lecture teaches how injured persons 
may be most safely and easily transported to their 
homes, to a medical man, or to a hospital. The 
illustrations in the book are clear and good.—Medi- 
cal Times and Gazette, Nov. 4,1882. 
TREVFS, FRFHERICK, F. R. C. S., 
Assistant Surgeon to and Lecturer on Surgery at the London Hospital. 
Intestinal Obstruction. In one pocket-size 12mo. volume of 522 pages, with 60 
illustrations. Limp cloth, blue edges, $2.00. Just ready. See Series of Clinical Manuals, 
page 3. 
A standard work on a subject that has not been 
so comprehensively treated by any contemporary 
English writer. Its completeness renders a full 
review difficult, since every chapter deserves mi- 
nute attention, and it is impossible to do thorough 
justice to the author in a few paragraphs. Intes- 
tinal Obstruction is a work that will prove of 
equal value to the practitioner, the student, the 
pathologist, the physician and the operating sur- 
geon.—British Medical Journal, Jan. 31, 1885. 
BALL, CHARLES 8., M. CJu, Huh., F. R. C. S. F., 
Surgeon and Teacher at Sir P. Dun's Hospital, Dublin. 
Diseases of the Rectum and Amts. In one 12mo. volume of 550 pages. 
Preparing. See Series of Clinical Manuals, page 3. 
BUT LIN, HENRY T., F. R. C. S., 
Assistant Surgeon to St. Bartholomew's Hospital, London. 
Diseases of the Tongue. In one 12mo. volume. See Series of Clinical 
Manuals, page 3. Shortly. 
HRUITT, ROBERT, M. R. C. S., etc. 
The Principles and Practice of Modern Surgery. From the eighth 
London edition. In one Bvo. volume of 687 pages, with 432 illus. Cloth, $4; leather, $5. 22 
Lea Brothers & Co.’s Publications—Surg'ery. 
HOLMES, TIMOTHY, M. A., 
Surgeon and Lecturer on Surgery at St. George's Hospital, London. 
yr A » Theoretical and Practical. IN TREATISES BY 
VARIOUSI AC I HORS. American EDITION, thoroughly revised and re-edited 
?• 1 ackard, M. I)., Surgeon to the Episcopal, and St. Joseph’s Hospitals, 
rhiladelphia, assisted by a corps of thirty-three of the most eminent American surgeons. 
In three large and very handsome imperial octavo volumes containing 3137 double- 
columned pages, with 979 illustrations on ivood and 13 lithographic plates, beautifully 
«°ood; , ] i?ce ; leathe3 $7.00; half Russia, $7.50. Per set, cloth, 
§lB.OO , leather, §21.00 ; half Ivussia, §22.00. Sold only by subscription, 
Volume I. contains General Pathology, Morbid Processes, Injuries in Gen- 
eral, Complications op Injuries and Injuries op Regions. 
Volume 11. contains Diseases op Organs op Special Sense, Circulatory Sys- 
tem, Digestive Tract and Genito-Urinary Organs. 
Volume 111. contains Diseases op the Respiratory Organs, Bones, Joints and 
Muscles, Diseases op the Nervous System, Gunshot Wounds, Operative and 
Minor Surgery, and Miscellaneous Subjects (including an essay on Hospitals). 
This gieat work, issued some years since in England, has won such universal confi- 
dence wherever the language is spoken that its republication here, in a form more 
thoroughly adapted to the wants of the American practitioner, has seemed to be a duty 
owing to the profession, lo accomplish this, each article has been placed in the hands of 
a gentleman specially competent to treat its subject, and no labor has been spared to brino- 
each one up to the lorempst level of the times, and to adapt it thoroughly to the practice 
of the country. In certain cases this has rendered necessary the substitution of an entirely 
new essay for the original, as in the case of the articles on Skin Diseases, on Diseases of 
the Absorbent System, and on Anaesthetics, in the use of which American practice differs 
from that ol England. The same careful and conscientious revision has been pursued 
throughout, leading to an increase of nearly one-fourth in matter, while the series of 
illustrations has been nearly trebled, and the whole is presented as a complete exponent 
o Lntish and American Surgery, adapted to the daily needs of the working practitioner. 
in order to bring it within the reach of every member of the profession, the five vol- 
umes ol the original have been compressed into three by employing a double-columned 
royal octavo page, and in this improved form it is offered at less than one-half the price of the 
original It is printed and bound to match in every detail with Reynolds’ System of Medi- 
cme. ihe work will be sold by subscription only, and in due time every member of the 
profession will be called upon and offered an opportunity to subscribe. 
The authors of the original English edition are 
men of the front rank in England, and Dr. Packard 
has been fortunate in securing as his American 
coadjutors such men as Bartholow, Hyde, Hunt 
Conner, Stimson, Morton, Hodgen, Jewell and 
their colleagues. As a whole, the work will be 
solid and substantial, and a valuable addition to 
the library of any medical man. It is more wieldly 
and more useful than the English edition, and with 
its companion work—“ Reynolds’ System of Medi- 
cine ”—will well represent the present state of our 
science. One who is familiar with those two works 
will be fairly well furnished head-wise and hand- 
wise.— The Medical News, Jan. 7, 1882. 
STIMSOJY, LEWIS A., B. A., M. 8., 
atJhe University of the City of New York, Surgeon and Curator 
to Bellevue Hospital, Surgeon to the Presbyterian Hospital, JSusw York, etc. 
-no Treatise on Fractures. In one very handsome octavo volume of 
098 pages, with 360 beautiful illustrations. Cloth, $4.75 ; leather, $5.75. 
The author has given to the medical profession 
in this treatise on fractures what is likely to be- 
come a standard work on the subject. It is certainly 
not surpassed by any work written in the English 
or, for that matter, any other language. The au- 
thor tells us in a short, concise and comprehensive 
manner, all that is known about his subject. There 
is nothing scanty or superficial about it, as in most 
other treatises; on the contrary, everything is thor- 
ough. The chapters on repair of fractures and their 
treatment show him not only to be a profound stu- 
dent, but likewise a practical surgeon and patholo- 
gist. His mode of treatment of the different fract- 
ures is eminently sound and practical. We consider 
this work one of the best on fractures; and it will 
be welcomed not only as a text-book, but also by 
ttie surgeon in fail practice.—A. O. Medical and 
Surgical Journal, March, 1883. 
The author gives in clear language all that the 
practical surgeon need know of the science of 
fractures, their etiology, symptoms, processes of 
union, and treatment, according to the latest de- 
velopments. On the basis of mechanical analysis 
the author accurately and clearly explains the 
clinical features of fractures, and by the same 
method arrives at the proper diagnosis snd rational 
treatment. A thorough explanation of the patho- 
logical anatomy and a careful description of the 
various methods of procedure make the book full 
of value for every practitioner.—Centralblatt fur 
Chirurgie, May 19, 1883. 
MARSH, HOWARD, F. R. 
a s., 
Senior Assistant Surgeon to and Lecturer on Anatomy at St. Bartholomew's Hospital, London, 
nr ■^seaseso the Joints. In one 12mo. volume. Preparing. See Series of Clinical 
AIOjThUCUSj O. 
PICK, I. PT<JKFItTKfr, F. C. S., 
Surgeon to and Lecturer on Surgery at St. George's Hospital, London. 
, an<3- Dislocations. In one 12mo. volume. Preparing. See Series 
oj Clinical Manuals, page 3. Lea Brothers & Co.’s Publications—Frac., Disloc., Oplithal, 
23 
HAMILTON, FRANK #., M. D., LL. 
Surgeon to Bellevue Hospital, New York. 
A Practical Treatise on Fractures and Dislocations. Seventh edition, 
thoroughly revised and much improved. In one very handsome octavo volume of 998 
pages, with 379 illustrations. Cloth, $5.50; leather, $6.50; very handsome half Russia, 
open back, $7.00. Just ready. 
Hamilton’s great experience and wide acquaint- 
ance with the literature of the subject have enabled 
him to complete the labors of Malgaigne and to 
place the reader in possession of the advances 
made during thirty years. The editions have fol- 
lowed each other rapidly, and they introduce us 
to the methods of practice, often so wise, of his 
American colleagues. More practical than Mal- 
gaigne’s work, it will serve as a valuable guide to 
the practitioner in the numerous and embarrass- 
ing cases which come under his observation.— 
Archives Generates de Medecine, Paris, Nov. 1884. 
This work, which, since its first appearance 
twenty-five years ago, has gone through many 
editions, and been much enlarged, may now be 
fairly regarded as the authoritative book of refer- 
ence on the subjects of fractures and dislocations. 
Each successive edition has been rendered of 
greater value through the addition of more re- 
cent work, and especially of the recorded re- 
searches and improvements made by the author 
himself and his countrymen.—British Medical 
Journal, May 9,1885. 
With its first appearance in 1859, this work took 
rank among the classics in medical literature, 
and has ever since been quoted by surgeons the 
world over as an authority upon the topics of 
which it treats. The surgeon, if one can be found 
who does not already know the work, will find it 
scientific, forcible and scholarly in text, exhaustive 
in detail, and ever marked by a spirit of wise con- 
servatism.—Louisville Medical News, Jan. 10, 1885. 
For a quarter of a century the author has been 
elaborating and perfecting his work, so that it 
now stands as the best of its kind in any lan- 
guage. _ As a text-book and as a book of reference 
and guidance for practitioners it is simply invalu- 
able.—New Orleans Med, and Surg. Journ'l, Nov. 1884. 
JELER, DEARY E., E. R. C. 8., 
Senior Ass't Surgeon, Royal Westminster Ophthalmic Hosp.; late Clinical Ass't, Moorfields, London. 
A Handbook of Ophthalmic Science and Practice. In one handsome 
octavo volume of 460 pages, with 125 woodcuts, 27 colored plates, and selections from the 
Test-types of Jaeger and Snellen. Cloth, $4.50; leather, $5.50. Just ready. 
This work is distinguished by the great num- 
ber of colored plates which appear in it for illus- 
trating various pathological conditions. They are 
very beautiful in appearance, and have been 
executed with great care as to accuracy. An ex- 
amination of the work shows it to be one of high 
standing, one that will be regarded as an authority 
among ophthalmologists. The treatment recom- 
mended is such as the author has learned from 
actual experience to be the best.—Cincinnati Medi- 
cal News, Dec. 1884. 
It presents to the student concise descriptions 
and typical illustrations of all important eye 
affections, placed in juxtaposition, so as to be 
frasped at a glance. Beyond a doubt it is the 
est illustrated handbook of ophthalmic science 
which has ever appeared. Then, what is still 
better, these illustrations are nearly all original. 
We have examined this entire work with great 
care, and it represents the commonly accepted 
views of advanced ophthalmologists. We can most 
heartily commend this book to all medical stu- 
dents, practitioners and specialists. Detroit 
Lancet, Jan. 1885. 
WELLS, J. SOELBERG, E. R. C. S., 
Professor of Ophthalmology in King's College Hospital, London, etc. 
A Treatise on Diseases of the Eye. Fourth American from the third London 
edition. Thoroughly revised, with copious additions, by Charles S. Bull, M.D., Surgeon 
and Pathologist to the New York Eye and Ear Infirmary. In one large octavo volume of 
822 pages, with 257 illustrations on wood, six colored plates, and selections from the Test- 
types of Jaeger and Snellen. Cloth, $5.00; leather, $6.00; half Russia, $6.50. 
The present edition appears in less than three 
years since the publication of the last American 
edition, and yet, from the numerous recent inves- 
tigations that have been made in this branch of 
medicine, many changes and additions have been 
required to meet the present scope of knowledge 
upon this subject. A critical examination at once i 
shows the fidelity and thoroughness with which 
the editor has accomplished his part of the work. 
The illustrations throughout are good. This edi- 
tion can be recommended to all as a complete 
treatise on diseases of the eye, than which proba- 
bly none better exists.—Medical Record, Aug. 18, ’B3. 
NETTLESDLJP, EDWARD, F. R. C. S., 
Ophthalmic Surg. and Lect. on Ophth. Surg. at St. Thomas' Hospital, London. 
The Student’s Guide to Diseases of the Eye. Second edition. With a chap- 
ter on the Detection of Color-Blindness, by William Thomson, M. D., Ophthalmologist 
to the Jefferson Medical College. In one royal 12mo. volume ot 416 pages, with 138 
illustrations. Cloth, $2.00. 
This admirable guide bids fair to become the 
favorite text-book on ophthalmic surgery with stu- 
dents and general practitioners. It bears through- 
out the imprint of sound judgment combined with 
vast experience. The illustrations are numerous 
and well chosen. This book, within the short com- 
pass of about4oo pages, contains a lucid exposition 
of the modem aspect of ophthalmic science.— 
Medical Record, June 23, 1883. 
BROWNE, EDGAR A., 
Surgeon to the Liverpool Eye and Ear Infirmary and to the Dispensary for Skin Diseases. 
How to Use the Ophthalmoscope. Being Elementary Instructions in Oph- 
thalmoscopy, arranged for the use of Students. In one small royal 12mo. volume of 116 
pages, with 35 illustrations. Cloth, $l.OO. 
LAWSON ON INJURIES TO THE EYE, ORBIT | 
AND EYELIDS: Their Immediate and Remote j 
Effects. 8 vo., 404 pp., 92 illus. Cloth, $3.50. 
LAURENCE AND MOON’S HANDY BOOK OF 
OPHTHALMIC SURGERY, for the use of Prac- 
titioners. Second edition. In one octavo vol- 
ume of 227 pages, with 65 illust. Cloth, $2.75. 
CARTER’S PRACTICAL TREATISE ON DISEAS- 
ES OF THE EYE. Edited by John Geeen, M. D. 
In one handsome octavo volume. 24 
Lea Brothers & Co.’s Publications—Otol., Urin. Dis.,Deut. 
BURNETT, CHARLES 11., A. M., 31. D., 
Pro/mor of Otology in the Philadelphia Polyclinic; President of the American Otological Society. 
for the nte ofaM Jr S Anatomy, Physiology and Diseases. A Practical Treatise 
for the use of Medical Students and I ractitioners. New (second) edition. In one handsome 
octavo volume of 580 pages, with 107 illustrations. Cloth, $4.00; leather, $5.00. Just ready 
We note with pleasure the appearance of a second 
edition of this valuable work. When it first came 
out it was accepted by the profession as one of 
the standard works on modern aural surgery in 
the English language; and in his second edition 
JJr. Eurnett has tally maintained his reputation, 
ior the book is replete with valuable information 
and suggestions. The revision has been carefully 
carried out, and much new matter added. Dr. 
. Barnett’s work must be regarded as a very valua- 
ble contribution to aural surgery, not only on 
account of its comprehensiveness, but because it 
contains the results of the careful personal observa- 
tion and experience of this eminentaural surgeon. 
—London Lancet, Feb. 21,1885. 
JPOLITZER, ADA 31, 
Imperial-Royal Prof, of Aural Therap. in the TJniv. of Vienna. 
cmpsA,,Tthe Ear and its Diseases. Translated, at the Author’s re- 
i Cassells, M. D., M. R. C. S. In one handsome octavo vol- 
ume of 800 pages, with 257 original illustrations. Cloth, $5.50. 
Tho umrlr ifcm 1 C u?a A ~ L I, ;i _ i . j ' 
the work itself we do not hesitate to pronounce 
the best upon the subject of aural diseases which 
has ever appeared, systematic without being too 
diffuse on obsolete subjects, and eminently prac- 
tical in every sense. (The anatomical descriptions 
ol each separate division of the ear are admirable 
and profusely illustrated by woodcuts. They are’ 
followed immediately by the physiology of the 
section, and this again by the pathological physi- 
ology, an arrangement which serves to keep up the 
interest of the student by showing the direct ap- 
plication of what has preceded to the study of dis- 
ease. The whole work can be recommended as a 
reliable guide to the student, and an efficient aid 
to the practitioner in his treatment.—Boston Med- 
ical and Surgical Journal, June 7, 1883. 
ROBERTS, WILLIAM, 31. I)., 
Lecturer on Medicine in the Manchester School of Medicine, etc. 
narv" T£eatl.se on Urinary and Renal Diseases, including Uri- 
naiy Deposits. Fourth American from the fourth London edition. In one hand- 
some octavo volume of about 650 pages, with 81 illustrations. Cloth, $3.50. Just ready. 
I his excellent book has now reached its fourth 
edition, and not too soon, for the third has been 
exhausted for some years, and it is one of those 
vyorks which no good physician’s or surgeon’s 
library should be without. The profession is sin- 
cerelytobe congratulated that he has been able 
amidst his many public and private duties to pre- 
sent a new edition of this standard work, 
thoroughly brought up to the present date.—Lon- 
don Medical Record, May 15,1885. 
CROSS, S. D,, 31. L>., LL, 1)., I). C. L., etc. 
of thePlir?mfrv °+w th£ Dif eases, Injuries and Malformations 
Urinary Bladder, the Prostate Gland and the Urethra. Third 
SartS y SAM"EVX: Gross> M- D- Professor of the Principles of 
S.t^ep i f? 7 Surgery in the Jefferson Medical College, Philadelphia. In one 
octavo volume of o/4 pages, with 170 illustrations. Cloth, $4.60. P 
MORRIS, 111 NR Y, M. 11., V. R. C. S., 
Surgeon to and Lecturer on Surgery at Middlesex Hospital, London. 
iapMaZl%°gefe KidUey- Preparing. See 
LUCAS, CLEMENT, M. 8., B. S., E. R. C. S., 
Senior Assistant Surgeon to Guy's Hospital, London. 
of 3Urethra- In one 12mo. volume. Preparing. See Series 
THOMPSON, SIR HENRY, 
Surgeon and Professor of Clinical Surgery to University College Hospital, London. 
third^nvlklfpdlHn'olB!6^®B «°f th? Urinary Organs. Second American from the 
t nrd English edition. In one Bvo. volume of 203 pp., with 25 illustrations. Cloth, $2.25. 
By the Same Author. 
UrinalvhEiJS^010ry of Stricture of the Urethra and 
r U }'o°m, t,e thlrd English edition. In one octavo volume of 359 
pages, with 4/ cuts and 3 plates. Cloth, $3.50. 
COLE3IAN, A., L. R. C. I\, E.R.C.S., Exam. L. 13. S., 
Semoi Pent. Surg. and Lect. on Pent. Surg. at St. Bartholomew's Hasp, and the Pent. Hasp., London 
adanffd toaHmane° fDAental Sn*Sevy and Pathology. Thoroughly revised and 
T) /fa -f? Pie,°f American Students, by Thomas C. Stellwagen, M. A., M. D 
volume of 419°1 - f Phil.adelPhia Cental College. In one handsome octavo 
volume ot 412 pages, with 331 illustrations. Cloth, $3.25. 
® G«?deMto °thelrR | 
cZl*™.W* of 304 with 2! illustration.. Lea Brothers & Co.’s Publications—Venereal, Impotence. 
25 
BTJMSTEAD, F. J., 
JjTi 1)., XLt I)., 
and 
TAYLOR, R. TV., 
A. 31., 31. L>,9 
Late Professor of Venereal Diseases 
at the College of Physicians and 
Surgeons, New York, etc. 
Surgeon to Charity Hospital, New York, Prof, of 
Venereal and Skin Diseases in the University of 
Vermont, Pres, of the Am. Dermatological Ass'n. 
The Pathology and Treatment of Venereal Diseases. Including the 
results of recent investigations upon the subject. Fifth edition, revised and largely re- 
written, by Dr. Taylor. In one large and handsome octavo volume of 898 pages with 
139 illustrations, and thirteen chromo-lithographic figures. Cloth, $4.75; leather, $5.75; 
very handsome half Kussia, $6.25. 
It is a. splendid record of honest labor, wide 
research, just comparison, careful scrutiny and 
original experience, which will always be held as 
a high credit to American medical literature. This 
is not only the best work in the English language 
upon the subjects of which it treats, but also one 
which has no equal in other tongues for its clear, 
comprehensive and practical handling of its 
themes.—American Journal of the Medical Sciences, 
Jan, 1884. 
It is certainly the best single treatise on vene- 
real in our own, and probably the best in any lan- 
guage.—Boston Medical and Surgical Journal, April 
3, 1884. 
The character of this standard work is so well 
known that it would be superfluous here to pass in 
review its general or special points of excellence. 
The verdict of the profession has been passed; it 
has been accepted as the most thorough and com- 
plete exposition of the pathology and treatment of 
venereal diseases in the language. Admirable as a 
model of clear description, an exponent of sound 
pathological doctrine, and a guide for rational and 
successful treatment, it is an ornament to the medi- 
cal literature of this country. The additions made 
to the present edition are eminently judicious, 
from the standpoint of practical utility.—Journal of 
Cutaneous and Venereal Diseases, Jan. 1884. 
HUTCHIXSOX, JOXATHAX, F. R. S., F. R. C. S., 
Consulting Surgeon to the London Hospital. 
Syphilis. In one 12mo. volume. Preparing. See Series of Clinical Manuals, page 3. 
CORXIL, V., 
Syphilis, its Morbid Anatomy, Diagnosis and Treatment. Specially 
revised by the Author, and translated with notes and additions by J. Henry C. Simes, 
M. D., Demonstrator of Pathological Histology in the University of Pennsylvania, and 
J. William White, M. D., Lecturer on Venereal Diseases and Demonstrator of Surgery 
in the University of' Pennsylvania. In one handsome octavo volume of 461 pages, with 
84 very beautiful illustrations. Cloth, $3.75. 
Professor to the Faculty of Medicine of Paris, and Physician to the IjOurcine Hospital. 
The anatomical and histological characters of the 
hard and soft sore are admirably described. The 
multiform cutaneous manifestations of the disease 
are dealt with histologically in a masterly way, as 
we should indeed expect them to be, and the 
accompanying illustrations are executed carefully 
and well. The various nervous lesions which are 
the recognized outcome of the syphilitic dyserasia 
are treated with care and consideration. Syphilitic 
epilepsy, paralysis, cerebral syphilis and locomotor 
ataxia are subjects full of interest; and nowhere in 
the whole volume is the clinical experience of the 
author or the wide acquaintance of the translators 
with medical literature more evident. The anat- 
omy, the histology, the pathology and the clinical 
features of syphilis are represented in this work in 
their best, most practical and most instructive 
form, and no one will rise from its perusal without 
the feeling that his grasp of the wide and impor- 
tant subject on which it treats is a stronger and 
surer one.— The London Practitioner, Jan. 1882. 
GROSS, SAMUEL TV., A. 31., M. J)., 
A Practical Treatise on Impotence, Sterility, and Allied Disorders 
of the Male Sexual Organs. Second edition, thoroughly revised. In one very hand- 
some octavo volume of 168 pages, with 16 illustrations. Cloth, $1.50. 
Professor of the Principles of Surgery and of Clinical Surgery in the Jefferson Medical College. 
The author of this monograph is a man of posi- 
tive convictions and vigorous style. This is justi- 
fied by his experience and by his study, which has 
gone hand in hand with his experience. In regard 
to the various organic and functional disorders of 
the male generative apparatus, he has had ex- 
ceptional opportunities for observation, and his 
book shows that he has not neglected to compare 
his own views with those of other authors. The 
result is a work which can be safely recommended 
to both physicians and surgeons as a guide in the 
treatment of the disturbances it refers to. It is 
the best treatise on the subject with which we are 
acquainted.— The Medical News, Sept. 1, 1883. 
This work will derive value from the high stand- 
ing of its author, aside from the fact of its passing 
so rapidly into its second edition. This is, indeed, 
a book that every physician will be glad to place 
in his library, to be read with profit to himself,, 
and with incalculable benefit to his patient. Be- 
sides the subjects embraced in the title, which are 
treated of in their various forms and degrees, 
spermatorrhoea and prostatorrhoea are also fully 
considered. The work is thoroughly practical in 
character, and will be especially useful to the 
general practitioner.—Medical Record, Aug. 18 
1883. *■ 
CULLFRIFR, A., & RU3ISTFAJ), F. J., 31.1 X, FF.JD., 
Surgeon to the H6pital du Midi. Late Professor of Venereal Diseases in the College of Physicians 
and Surgeons, New York. 
An Atlas of Venereal Diseases. Translated and edited by Freeman J. Bum- 
stead, M. D. In one imperial 4to. volume of 328 pages, double-columns, with 26 plates, 
containing about 150 figures, beautifully colored, many of them the size of life. Strongly 
bound in cloth, $17.00. A specimen of the plates and text sent by mail, on receipt of 25 cts. 
HILL ON SYPHILIS AND LOCAL CONTAGIOUS j 
DISORDERS. In one Svovol. of 479 p. Cloth, $3.25. i 
LEE’S LECTURES ON SYPHILIS AND SOME j 
FORMS OF LOCAL DISEASE AFFECTING 
PRINCIPALLY THE ORGANS OF GENERA- 
TION. In one Bvo. vol. of 246 pages. Cloth, $2.25. 26 
Lea Brothers & Co.’s Publications—Diseases of Skin. 
MYJDF, J, XFVLXS, A, M,, 31, 1 
A Practical Treatise on Diseases of the Skin. For the use of Students and 
Practitioners. In one handsome octavo volume of 570 pages, with 66 beautiful and elab- 
orate illustrations. Cloth, $4.25; leather, $5.25. 
Professor of Dermatology and Venereal Diseases in Bush Medical College, Chicago. 
The author has given the student and practi- 
tioner a work admirably adapted to the wants of 
each. We can heartily commend the book as a 
valuable addition to our literature and a reliable 
guide to students and practitioners in their studies 
and practice.—Am. Journ. of Med. Sci., July, 1883. 
Especially to be praised are the practical sug- 
gestions as to what may be called the common- 
sense treatment of eczema. It is quite impossible 
to exaggerate the judiciousness with which the 
formulae for the external treatment of eczema are 
selected, and what is of equal importance, the full 
and clear instructions for their use.—London Medi- 
cal Times and Gazette, July 28, 1883. 
The work of Dr. Hyde will be awarded a high 
position. The student of medicine will find it 
peculiarly adapted to his wants. Notwithstanding 
the extent of the subject to which it is devoted, 
yet it is limited to a single and not very large vol- 
ume, without omitting a proper discussion of the 
topics. The conciseness of the volume, and the 
setting forth of only what can be held as facts will 
also make it acceptable to general practitioners. 
—Cincinnati Medical News, Feb. 1883. 
The aim of the author has been to present to his 
readers a work not only expounding the most 
modern conceptions of his subject, but presenting 
what is of standard value. He has more especially 
devoted its pages to the treatment of disease, and 
by his detailed descriptions of therapeutic meas- 
ures has adapted them to the needs of the physi- 
cian in active practice. In dealing with these 
questions the author leaves nothing to the pre- 
sumed knowledge of the reader, but enters thor- 
oughly into the most minute description, so that 
one is not only told what should be done under 
given conditions but how to do it as well. It is 
therefore in the best sense “ a practical treatise.” 
That it is comprehensive, a glance at the index 
will show.—Maryland Medical Journal, July 7,1883, 
Professor Hyde has long been known as one of 
the most intelligent and enthusiastic representa- 
tives of dermatology in the west. His numerous 
contributions to the literature of this specialty 
have gained for him a favorable recognition as a 
careful, conscientious and original observer. The 
remarkable advances made in our knowledge of 
diseases of the skin, especially from the stand- 
point of pathological histology and improved 
methods of treatment, necessitate a revision of 
the older textbooks at short intervals in order to 
bring them up to the standard demanded by the 
march of science. This last contribution of Dr. 
Hyde is an effort in this direction. He has at- 
tempted, as he informs us, the task of presenting 
in a condensed form the results of the latest ob- 
servation and experience. A careful examination 
of the work convinces us that he has accomplished 
his task with painstaking fidelity and with a cred- 
itable result.—Journal of Cutaneous and Venereal 
Diseases, June, 1883. 
FOX, T., M.D., F.R. 
Physician to the Department for Skin Diseases, Physician for Diseases of the Skin to the 
University College Hospital, London. Westminster Hospital, London. 
An Epitome of Skin Diseases, With Pormulse, For Students and Prac- 
titioners. Third edition, revised and enlarged. In one very handsome 12mo. volume 
of 238 pages. Cloth, $1.25. 
C. F,, and FOX, T. C., 8.A., 31.11, C.5,, 
The third edition of this convenient handbook 
calls for notice owing to the revision and expansion 
which it has undergone. The arrangement of skin 
diseases in alphabetical order, which is the method 
of classification adopted in this work, becomes a 
positive advantage to the student. The book is 
one which we can strongly recommend, not only 
to students but also to practitioners who require a 
compendious summary of the present state of 
dermatology.—British Medical Journal, July 2,1883. 
We cordially recommend Fox’s Epitome to those 
whose time is limited and who wish a handy 
manual to lie upon the table for instant reference. 
Its alphabetical arrangement is suited to this use, 
for all one has to know is the name of the disease, 
and here are its description and the appropriate 
treatment at hand and ready for instant applica- 
tion. The present edition has been very carefully 
revised and a number of new diseases are de- 
scribed, while most of the recent additions to 
dermal therapeutics find mention, and the formu- 
lary at the end of the book has been considerably 
augmented.—The Medical News, December, 1883. 
MOBBIS, MALCOLM, M. JO,, 
Joint Lecturer on Dermatology at St. Mary's Hospital Medical School, London. 
Skin Diseases; Including their Definitions, Symptoms, Diagnosis, Prognosis, Mor- 
bid Anatomy and Treatment. A Manual for Students and Practitioners. In one 12mo. 
volume of 316 pages, with illustrations. Cloth, $1.75. 
To physicianswho would like to know something 
about skin diseases, so that when a patient pre- 
sents himself for relief they can make a correct 
diagnosis and prescribe a rational treatment, we 
unhesitatingly recommend this little book of Dr. 
Morris. The affections of the skin are described 
in a terse, lucid manner, and their several charac- 
teristics so plainly set forth that diagnosis will be 
easy. The treatment in each ease is such as the 
experience of the mosteminent dermatologists ad- 
vises.—Cincinnati Medical News, April, 1880. 
This is emphatically a learner’s book; for we 
can safely say, that in the whole range of medical 
literature there is no book of a like scope which 
for clearness of expression and methodical ar- 
rangement is better adapted to promote a rational 
conception of dermatology—a branch confessedly 
difficult and perplexing to the beginner.—St. Louis 
Courier of Medicine, April, 1880. 
The writer has certainly given in a small compass 
a large amount of well-compiled information, and 
his little book compares favorably with any other 
which has emanated from England, while in many 
points he has emancipated himself from the stub- 
bornly adhered to errors of others of his country- 
men. There is certainly excellent material in the 
book which will well repay perusal.—Boston Med. 
and Surg. Journ., March, 1880. 
WILSOX, FJIASMUS, 
The Student’s Book of Cutaneous Medicine and Diseases of the Skin 
F, JL S. 
In one handsome small octavo volume of 535 pages. Cloth, $3.50. 
JfTLLIEJi, TITO3IAS, M, 1)., 
Physician to the Skin Department of University College, London. 
Handbook Of Skin Diseases; for Students and Practitioners. Second Ameri- 
can edition. In one 12mo. volume of 353 pages, with plates. Cloth, $2.25. Lea Brothers & Co.’s Publications—I>is. of Women. 
27 
AN AMERICAN SYSTEM OF GYNAECOLOGY. 
A System of Gynaecology, in Treatises by Various Authors. Edited 
by Matthew I). Mann, M. IX, Professor of Obstetrics and Gynaecology in the Uni- 
versity of Buffalo, N. Y. In two handsome octavo volumes, richly illustrated. In active 
preparation. 
LIST OF CONTRIBUTORS. 
FORDYCE BARKER, M. I)., 
ROBERT BATTEY, M. D., 
SAMUEL C. BUSEY, M. D., 
HENRY P. CAMPBELL, M, D., 
BENJAMIN F. DAWSON, M. D., 
WILLIAM GOODELL, M. D., 
HENRY F. GARRIGUES, M. D., 
SAMUEL W. GROSS, M. D., 
JAMES B. HUNTER, M. D., 
WILLIAM T. HOWARD, M. D., 
A. REEVES JACKSON, M. D., 
EDWARD W. JENKS, M. D., 
CHARLES CARROLL LEE, M. D., 
WILLIAM T. LUSK, M. D., 
MATTHEW D. MANN, M. D., 
ROBERT B. MAURY, M. D., 
C. D. PALMER, M. D., 
WILLIAM M. POLK, M. D., 
THADDEUS A. REAMY, M. D., 
A. D. ROCKWELL, M. D., 
ALBERT H. SMITH, M. D., 
R. STANSBURY SUTTON, A. M., M. D., 
T. GAILLARD THOMAS, M. D., 
CHARLES S. WARD, M. D., 
WILLIAM H. WELCH, M. D. 
THOMAS, T. GAILLARD, M. I)., 
Professor of Diseases of Women in the College of Physicians and Surgeons, N. Y. 
A Practical Treatise on the Diseases of Women. Fifth edition, thoroughly 
revised and rewritten. In one large and handsome octavo volume of Stoppages, with 266 
illustrations. Cloth, $5.00; leather, $6.00; very handsome half Russia, raised bands, $6.50. 
The words which follow “fifth edition” are in i 
this case no mere formal announcement. The j 
alterations and additions which have been m ade are | 
both numerous and important. The attraction | 
and the permanent character of this hook lie in 
the clearness and truth of the clinical descriptions j 
of diseases; the fertility of the author in thera- j 
peutic resources and the fulness with which the | 
details of treatment are described; the definite I 
character of the teaching; and last, but not least, i 
the evident candor which pervades it. We would 
also particularize the fulness with which the his- i 
tory of the subject is gone into, which makes the | 
book additionally interesting and gives it value as 
a work of reference.—London Medical Times and i 
Gazette, July 30,1881. 
The determination of the author to keep his I 
book foremost in the rank of works on gymecology 
is most gratifying. Recognizing the fact that this | 
can only be accomplished by frequent and thor- | 
ough revision, he has spared no pains to make the I 
present edition more desirable even than the pre- j 
! vious one. As a book of reference for the busy 
i practitioner it is unequalled.—Boston Medical any 
\ Surgical Journal, April 7,1880. 
It has been enlarged and carefully revised. It is 
a condensed encyclopaedia of gynecological medi- 
cine. The style of arrangement, the masterly 
i manner in which each subject is treated, and the 
i honest convictions derived from probably the 
I largest clinical experience in that specialty of any 
i in this country, all serve to commend it in the 
highest terms to the practitioner.—Nashville Jour. 
: of Med. and Surg., Jan. 1881. 
That the previous editions of the treatise of Dr. 
Thomas were thought worthy of translation into 
1 German, French, Italian and Spanish, is enough 
'to give it the stamp of genuine merit. At home it 
! has made its way into the library of every obstet- 
rician and gynaecologist as a safe guide to practice, 
i No small number of additions have been made to 
j the present edition to make it correspond to re- 
j cent improvements in treatment.—Pacific Medical 
I and Surgical Journal, Jan. 1881. 
LOTS, ARTHUR W., M. D., Land., F.R. C. P., M.R. C.S., 
Assist. Obstetric Physician to Middlesex Hospital, late Physician to British Lying-in Hospital. 
The Diseases of Women. Including their Pathology, Causation, Symptoms, 
Diagnosis and Treatment. A Manual for Students and Practitioners. In one handsome 
octavo volume of 576 pages, with 148 illustrations. Cloth, $3.00; leather, $4.00. 
It is a pleasure to read a book so thoroughly 
good as this one. The special qualities which are 
conspicuous are thoroughness in covering the 
whole ground, clearness of description and con- 
ciseness of statement. Another marked feature of 
the book is the attention paid to the details of 
many minor surgical operations and procedures, 
as, for instance, the use of tents, application of 
leeches, and use of hot water injections. These 
are among the more common methods of treat- 
ment, and yet very little is said about them in 
many of the text-books. The book is one to be 
warmly recommended especially to students and 
general practitioners, who need a concise but com- 
plete resume of the whole subject. Specialists, too, 
will find many useful hints in its pages.—Boston 
Med. and Surg. Journ., March 2,1882. 
The greatest pains have been taken with the 
sections relating to treatment. A liberal selection 
of remedies is given for each morbid condition, 
the strength, mode of application and other details 
being fully explained. The descriptions of gynae- 
cological manipulations and operations are full, 
clear and practical. Much care has also been be- 
stowed on the parts of the book which deal with 
diagnosis—we note especially the pages dealing 
with the differentiation, one from another, of the 
different kinds of abdominal tumors. The prac- 
titioner will therefore find in this book the kind 
of knowledge he most needs in his daily work, and 
he will be pleased with the clearness and fulness 
of the information there given.— The Practitioner, 
Feb. 1882. 
BARNES, ROBERT, M. J)., F. R. C, I\, 
Obstetric Physician to St. Thomas’ Hospital, London, etc. 
A Clinical Exposition of the Medical and Surgical Diseases of Women. 
In one handsome octavo volume, with numerous illustrations. New edition. Preparing. 
WEST, CHARLES, M. D. 
Lectures on the Diseases of Women. Third American from the third Lon- 
don edition. In one octavo volume of 543 pages. Cloth, $3.75; leather, $4.75. 
CHURCHILL ON THE PUERPERAL FEVER! 
AND OTHER DISEASES PECULIAR TO WO- : 
MEN. In one 8m vol. of 464 pages. Cloth, $2.50. } 
MEIGS ON THE NATURE, SIGNS AND TREAT- 
MENT OF CHILDBED FEVER. In one Bvo. 
volume of 346 pages. Cloth, $2.00. 28 
Lea Brothers & Co.’s Publications—I>is. of Women, Midwfy. 
EMMET, THOMAS ADDIS, M. D., EE. D., 
Surgeon to the Woman's Hospital, New York, etc. 
The Principles and Practice of Gynaecology; For the use of Students and 
Practitioners of Medicine. New (third) edition, thoroughly revised. In one large and very 
handsome octavo volume of 880 pages, with 150 illustrations. Cloth, $5; leather, |6. 
(Just ready.) 
Excerpt from the Author’s Preface to the Second Edition. 
So great have been the advance and change of views during the past four years in 
Gynaecology, that the preparation of this edition has necessitated almost as much labor as 
to have rewritten the volume. Every portion has been thoroughly revised, a great deal 
has been left out, and much new matter added. 
The chapters on the relation of education and social condition to development, those 
on pelvic cellulitis, the diseases of the ovary and on ovariotomy, together with that on 
stone in the bladder, have been nearly rewritten. 
Tiie chapters on prolapse of the vaginal walls and lacerations of the vaginal outlet, 
the methods of partial and complete removal of the uterus for malignant disease, the 
surgical treatment of fibrous tumors, diseases of the Fallopian tubes, and the diseases of 
the urethra, are essentially new, with the views and experience of the author in a form 
which has not been presented to the profession before. To these chapters not less than 
one hundred and seventy-five pages of new material have been added. 
We are in doubt whether to congratulate the 
author more than the profession up°n the appear- 
ance of the third edition of this well-known work. 
Embodying, as it does, the life-long experience of 
■one who has conspicuously distinguished himself 
as a bold and successful operator, and who has 
devoted so much attention to the specialty, we 
feel sure the profession will not fail to appreciate 
the privilege thus offered them of perusing the 
views and practice of the author. His earnestness 
of purpose and conscientiousness are manifest. 
He gives not only his individual experience but 
endeavors to represent the actual state of gynre- 
cological science and art.—British Medical Jour- 
nal, May 16, 1885. 
Any work on gynaecology by Emmet must 
always have especial interest and value. He has 
for many years been an exceedingly busy prac- 
titioner In this department. Few men have had 
his experience and opportunities. As a guide 
either for the general practitioner or specialist, 
it is second to none other. No one can read 
Emmet without pleasure, instruction and profit. 
—Cincinnati Lancet and Clinic, Jan 31, 1885. 
DUNCAN, J. MATTHEWS, M.D., EL. D., E. R. S. E., etc. 
Clinical Lectures on the Diseases of Women; Delivered in Saint Bar- 
tholomew’s Hospital. In one handsome octavo volume of 175 pages. Cloth, $1.50. 
They are in every way worthy of their author ; 
indeed, we look upon them as among the most 
valuable of his contributions. They are all upon 
matters of great interest to the general practitioner. 
Some of them deal with subjects that are not, as a 
rule, adequately handled in the text-books; others 
of them, while bearing upon topics that are usually 
treated of at length in such works, yet bear such a 
stamp of individuality that, if widely read, as they 
certainly deserve to be, they cannot fail to exert a 
wholesome restraint upon the undue eagerness 
with which many young physicians seem bent 
upon following the wild teachings which so infest 
the gynaecology of the present day.—N. Y. Medical 
Journal, March, 1880. 
HODGE, HUGHE., 3E D., 
Emeritus Professor of Obstetrics, etc., in the University of Pennsylvania. 
On Diseases Peculiar to Women; Including Displacements of the Uterus. 
Second edition, revised and enlarged. In one beautifully printed octavo volume of 519 
pages, with original illustrations. Cloth, $4.50. 
the Same Author. 
The Principles and Practice of Obstetrics. Illustrated with large litho- 
graphic plates containing 159 figures from original photographs, and with numerous wood- 
cuts. In one large quarto volume of 542 double-columned pages. Strongly hound in 
cloth, $14.00. 
* * * Specimens of the plates and letter-press will be forwarded to any address, free by 
mail, on receipt of six cents in postage stamps. 
TARNIER, S., and CHANTREUIL, G. 
A Treatise on the Art of Obstetrics. Translated from the French. In 
two large octavo volumes, richly illustrated. 
RAMSBOTHAM, FRANCIS lE, M. D. 
The Principles and Practice of Obstetric Medicine and Surgery; 
In reference to the Process of Parturition. A new and enlarged edition, thoroughly revised 
by the Author. With additions by W. V, Keating, M. D., Professor of Obstetrics, etc., 
in the Jefferson Medical College of Philadelphia. In one large and handsome imperial 
octavo volume of 640 pages, with 64 full-page plates and 43 woodcuts in the text, contain- 
ing in all nearly 200 beautiful figures. Strongly bound in leather, with raised bands, $7. 
ASHWELL’S PRACTICAL TREATISE ON THE I 
DISEASES PECULIAR TO WOMEN. Third j 
American from the third and revised London 
edition. In one Bvo. vol., pp. 520. Cloth, $3.50. Lea Brothers & Co.’s Publications—Midwifery. 
29 
BLA YEA IR, W. 8., M. I)., J\ R. C. 8., 
Professor of Obstetric Medicine in King's College, London, etc. 
A Treatise on the Science and Practice of Midwifery. New (fourth) 
American edition, revised by the Author. Edited, with additions, by Egbert P. Har- 
ris, M. D. In one handsome octavo volume of about 700 pages, with 183 illustrations 
and 3 plates. Cloth, $4; leather, $5; half Eussia, $5.50. Just ready. 
A few notices of the previous edition are appended: 
If inquired of by a medical student what work 
on obstetrics we should recommend for him, par 
excellence, we would undoubtedly advise him to 
choose Playfair’s. It is of convenient but 
what is of chief importance, its treatment of the 
various subjects is concise and plain. While the 
discussions and descriptions are sufficiently elabo- 
rate to render a very intelligible idea of them, yet 
all details not necessary for a full understanding 
of the subject are omitted.—Cincinnati Medical 
News, Jan., 1880. 
It certainly is an admirable exposition of the 
science and practice of midwifery. Of course the 
additions made by the American editor, Ur. R. P. 
Harris, who never utters an idle word, and whose 
studious researches in some special departments 
of obstetrics are so wel 1 known to th e profession, are 
of great value.— The Amer. Practitioner, April, 1880. 
BARKER, EORDTCE, A. 31., 31. I)., EL. I). Ed in., 
Clinical Professor of Midwifery and the Diseases of Women in the Bellevue Hospital Medical College, 
New York, Honorary Fellow of the Obstetrical Societies of London and Edinburgh, etc., etc. 
Obstetrical and Clinical Essays. In one handsome 12mo. volume of about 
300 pages. Preparing. 
KIXG, A. F, A., 31. !)., 
Professor of Obstetrics and Diseases of Women in the Medical Department of the Columbian Univer- 
sity, Washington, D. C., and in the University of Vermont, etc. 
A Manual Of Obstetrics. New edition. In one very handsome 12mo. volume 
of 331 mares, with 69 illustrations. Cloth, 52.00. 
In a series of short paragraphs and by a con- 
densed style of composition, the writer has pre- 
sented a great deal of what it is well that every 
obstetrician should know and be ready to practice 
or prescribe. The fact that the demand for the 
volume has been such as to exhaust the first 
edition in a little over a year and a half speaks 
well for its popularity.—American Journal of the 
Medical Sciences, April, 1884. 
This little work upon obstetrics will be highly 
valued by medical students. We feel quite sure 
that it will be in great demand by them, so suited 
is it to their wants. Of a size that it can be easily 
carried, yet it contains all of the main points in 
obstetrics sufficiently elaborated to give a full and 
correct idea of them. The general practitioner 
wilt also find it very useful for reference, for the 
purpose of refreshing the mind. We can confi- 
dently assert that it will be found to be the best 
class texbbook upon obstetrics that lias been 
issued from the press.—Cincinnati Medical News, 
March, 1884. 
It must be acknowledged that this is lust what 
it pretends to be—a sound guide, a portable epit- 
ome, a work in which only indispensable matter 
has been presented, leaving out al! padding and 
chaff, and one in which the student will find pure 
wheat or condensed-nutriment.—New Orleans Med- 
ical and Surgical Journal, May, 1884. 
BARXES, EGBERT, 31. !>-, and EAXCOVRT, 31. J)., 
Phys. to the General Lying-in llosp., Lond. Obstetric Phys. to St. Thomas' Hasp., Lond. 
A System of Obstetric Medicine and Surgery, Theoretical and Clin- 
ical. For the Student and the Practitioner. The Section on Embryology contributed by 
Prof. Milnes Marshall. In one handsome octavo volume ot about 1000 pages, profusely 
illustrated. Cloth, $5 ; leather, $6. In press. 
BARXEB, EAXCOJJRT, 31. J)., 
Obstetric Physician to St. Thomas' Hospital, London. 
A Manual of Midwifery for Midwives and Medical Students. In one 
royal 12mo. volume of 197 pages, with 50 illustrations. Cloth, $1.25. 
BARVIX, TIIEOBHILJJS, 31. 8., LL. 8., 
Professor of Obstetrics and the Diseases of IWoineu and Children in the Jefferson Medical College. 
A Treatise on Midwifery. In one very handsome octavo volume of about 550 
pages, with numerous illustrations. In press. 
BARRY, JOJTX 8., 31. 8., 
Obstetrician to the Philadelphia Hospital, Vice-President 0} the Obstet. Society of Philadelphia. 
Extra - Uterine Pregnancy: Its Clinical History, Diagnosis, Prognosis and 
Treatment. In one handsome octavo volume ol 272 pages. Cloth, $2.50. 
TA XXER, TJIG3TA 8 IT A TYKES, 31. B. 
On the Signs and Diseases of Pregnancy. First American from the second 
English edition. In one handsome octavo volume of 490 pages, with 4 colored plates and 
16 woodcuts. Cloth, $4.25. 
WIXCKEL, E. 
A Complete Treatise on the Pathology and Treatment of Childbed, 
For Students and Practitioners. Translated, with the consent of the Author, from the 
second German edition, by James Eead Chadwick, M. D. In one octavo volume of 484 
pages. Cloth, $4.00. 30 
Lea Brothers & Co.’s Publications—Midwfy., Dis. Cliildn. 
LEISHMAN, WILLIAM, M. IX, 
Begins Professor of Midwifery in the University of Glasgow, etc. 
A System of Midwifery, Including the Diseases of Pregnancy and the 
Puerperal state. Third American edition, revised by the Author, with additions by 
John S. Parry, M. D., Obstetrician to the Philadelphia Hospital, etc. In one large and 
very handsome octavo volume of 740 pages, with 205 illustrations. Cloth, $4.50; leather, 
$5.50; very handsome half Russia, raised bands, $6.00. 
The author is broad in his teachings, and dis- 
cusses briefly the comparative anatomy of the pel- 
vis and the mobility of the pelvic articulations. 
The second chapter is devoted especially to 
the study of the pelvis, while in the third the 
female organs of generation are introduced. 
The structure and development of the ovum are 
admirably described. Then follow chapters upon 
the various subjects embraced in the study of mid- 
wifery. The descriptions throughout the work are 
plain’and pleasing. It is sufficient to state that in 
this, the last edition of this well-known work, every 
recent advancement in this field has been brought 
forward.—Physician and Surgeon, Jan. 1880. 
We gladly welcome the new edition of this ex- 
cellent text-book of midwifery. The former edi- 
tions have been most favorably received by the 
profession on both sides of the Atlantic. In the 
preparation of the present edition the author has 
made such alterations as the progress of obstetri- 
cal science seems to require, and we cannot but 
admire the ability with which the task has been 
performed. We consider it an admirable text- 
book for students during their attendance upon 
lectures, and have great pleasure in recommend- 
ing it. As an exponent of the midwifery of the 
present day it has no superior in the English lan- 
guage.—Canada Lancet, Jan. 1880. 
To the American student the work before us 
must prove admirably adapted. Complete in all its 
parts, essentially modern in its teachings, and with 
demonstrations"noted for clearness and precision, 
it will gain in favor and be recognized as a work 
of standard merit. The work cannot fail to be 
popular and is cordially recommended.—N. 0. 
Med. and Surg. Journ., March, 1880. 
SMITH, J. LEWIS, M. IX, 
Clinical Professor of Diseases of Children in the Bellevue Hospital Medical College, N. Y. 
A Complete Practical Treatise on the Diseases of Children, Fifth 
edition, thoroughly revised and rewritten. In one handsome octavo volume of 836 pages, 
with illustrations. Cloth, $4.50; leather, $5.50; very handsome half Russia, raised bands, $6. 
This is one of the best books on the subject with which we venture to say will be a favorable one.— 
which we have met and one that has given us Dublin Journal of Medical Science, March, 1883. 
satisfaction on every occasion on which we have There is no book published on the subjects of 
consulted it, either as to diagnosis or treatment, which this one treats that is its equal in value to 
It is now in its fifth edition and in its present form the physician. While he has said just enough to 
is a very adequate representation of the'subject it impart the information desired by general practi- 
treats of as at present understood. The important tioners on such questions as etiology, pathology, 
subject of infant hygiene is fully dealt with in .the prognosis, etc., he has devoted more attention to 
early portion of the book. The great bulk of the the diagnosis and treatment of the ailments which 
work is appropriately devoted to the diseases of he so accurately describes; and such information 
infancy and childhood. We would recommend is exactly what is wanted by the vast majority of 
any one in need of information on the subject to ( “ family physicians.”—Va. Med. Monthly, Feb. 1882. 
procure the work and form his own opinion on it, | 
KEATING, JOHNM., M. I)., 
Lecturer on the Diseases vf Children at the University of Pennsylvania, etc. 
The Mother’s Guide in the Management and Feeding of Infants. In 
one handsome 12mo. volume,of 118 pages. Cloth, |l.OO. 
Works like this one will aid the physician im- 
mensely, for it saves the time he is constantly giv- 
ing his patients in instructing them on the sub- 
jects here dwelt upon so thoroughly and prac- 
tically. Dr. Keating has written a practical book, 
has carefully avoided unnecessary repetition, and 
successfully instructed the mother in such details 
of the treatment of her child as devolve upon her. 
He has studiously omitted giving prescriptions, 
and instructs the mother when to call upon the 
doctor, as his duties are totally distinct from hers. 
—American Journal of Obstetrics, October, 1881. 
Dr. Keating has kept clear of the common fault 
of works of this sort, viz., mixing the duties of 
the mother with those proper to the doctor. There 
is the ring of common sense in the remarks about 
the employment of a wet-nurse, about the proper 
food for' a "nursing mother, about the tonic effects 
of a bath, about the perambulator versus the nurses, 
arms, and on many other subjects concerning 
which the critic might say, “ surely this is obvi- 
ous,” but which experience teaches us are exactly 
the things needed to be insisted upon, with the rich 
as well as the poor.—London Lancet, January, 281882 
A hook small in size, written in pleasant style, in 
language which can be readily understood by any 
mother, and eminently practical and safe; in fact 
a book for which we have been waiting a long 
time, and which we can most heartily recommend 
to mothers as the book on this subject.—New York 
Medical Journal and Obstetrical Review, Feb. 1882. 
OWEN, EDMUND, M. 8., E. 11. C. S., 
Surgical Diseases Of Children. In one 12mo. volume. Preparing. See Series 
of Clinical Manuals, page 3. 
Surgeon to the Children's Hospital, Great Ormond St., London. 
WEST, CHARLES, M. IX, 
Physician to the Hospital for Sick Children, London, etc. 
Lectures on the Diseases of Infancy and Ghildhood._ Fifth American 
from 6th English edition. In one octavo volume of 686 pages. Cloth, $4.50; leather, $5.50. 
On Some Disorders of the Nervous System in Childhood. In one small 
12mo. volume of 127 pages. Cloth, $l.OO. 
the Same Author. 
CONDIE’B PRACTICAL TREATISE ON THE 
DISEASES OF CHILDREN. Sixth edition, re- 
i vised and augmented. In one octavo volume of 
j 779 pages. Cloth, $5.25; leather, |6.25. Lea Brothers & Co.’s Publications—Med. Juris., Miseel. 
31 
TIDY, CHARLES MEYMOTT, M. 8., F, C. 8,, 
Professor of Chemistry and of Forensic Medicine and Public Health at the London Hospital, etc. 
Legal Medicine. Volume 11. Legitimacy and Paternity, Pregnancy, Abor- 
tion, Rape, Indecent Exposure, Sodomy, Bestiality, Live Birth, Infanticide, Asphyxia, 
Drowning, Hanging, Strangulation, Suffocation. Making a very handsome imperial oc- 
tavo volume of 529 pages. Cloth, $6.00; leather, $7.00. 
Volume I. Containing 664 imperial octavo pages, with two beautiful colored 
plates. Cloth, $6.00; leather, $7.00. 
The satisfaction expressed with the first portion 
of this work is in no wise lessened by a perusal of 
the second volume. We find it characterized by 
the same fulness of detail and clearness of ex- 
pression which we had occasion so highly to com- 
mend in our former notice, and which render it so 
valuable to the medical jurist. The copious 
tables of cases appended to each division of the 
subject, must have cost the author a prodigious 
amount of labor and research, but they constitute 
one of the most valuable features of the book, 
especially for reference in medico-legal trials.— 
American Journal of the Medical Sciences, April, 1884. 
TAYLOR, ALFRED S., M. D,, 
Lecturer on Medical Jurisprudence and Chemistry in Guy's Hospital, London. 
A Manual of Medical Jurisprudence. Eighth American from the tenth Lon- 
don edition, thoroughly revised and rewritten. Edited by Johk J. Reese, M. D., Professor 
of Medical Jurisprudence and Toxicology in the University of Pennsylvania. In one 
large octavo volume of 937 pages, with 70 illustrations. Cloth, $5.00; leather, $6.00; half 
Russia, raised bands, $6.50. 
The American editions of this standard manual 
have for a long time laid claim to the attention of 
the profession in this country; and the eighth 
comes before us as embodying the latest thoughts 
and emendations of Dr. Taylor upon the subject 
to which he devoted his life with an assiduity and 
success which made him facile princeps among 
English writers on medical jurisprudence. Both 
the author and the book have made a mark too 
deep to be affected by criticism, whether it be 
censure or praise. In this ease, however, we should 
only have to seek for laudatory terms.—American 
Journal of the Medical Sciences, Jan. 1881. 
This celebrated work has been the standard au- 
thority in its department for thirty-seven years, 
both in England and America, in both the profes- 
sions which it concerns, and it is improbable that 
it will be superseded in many years. The work is 
simply indispensable to every physician, and nearly 
so to every liberally-educated lawyer, and we 
heartily commend the present edition to both pro- 
fessions.—Albany Law Journal, March 26, 1881. 
the Same Author. 
The Principles and Practice of Medical Jurisprudence. Third edition. 
In two handsome octavo volumes, containing 1416 pages, with 188 illustrations. Cloth, $10; 
leather, $l2. Just ready. 
For years Dr. Taylor was the highest authority 
in England upon the subject to which he gave 
especial attention. His experience was vast, his 
judgment excellent, and his skill beyond cavil. It 
is therefore well that the work of one who, as Dr. 
Stevenson says, had an “enormous grasp of all 
matters connected with the subject,” should he 
brought up to the present day and continued in 
its authoritative position. To accomplish this re- 
sult Dr. Stevenson has subjected it to most careful 
editing, bringing it well up to the times.—Ameri- 
can Journal of the Medical Sciences, Jan. 1884. 
the Same Author. 
Poisons in Relation to Medical Jurisprudence and Medicine. Third 
American, from the third and revised English edition. In one large octavo volume of 788 
pages. Cloth, $5.50; leather, $6.50. 
FEEDER, AUGUSTUS J., M. S., M. 8., F. R. C. S., 
Examiner in Forensic Medicine at the University of London. 
Forensic Medicine. In one pocket-size 12mo. volume. Preparing. See Students’ 
Series of Manuals, page 3. 
LEA, HENRY C. 
Superstition and Force: Essays on The Wager of Law, The Wager of 
Battle, The Ordeal and Torture. Third revised and enlarged edition. In one 
handsome royal 12mo. volume of 552 pages. Cloth, $2.50. 
This valuable work is in reality a history of civ- 
ilization as interpreted by the progress of jurispru- 
denee. . . In “ Superstition and Force ” we have a 
philosophic survey of the long period intervening 
between primitive barbarity and civilized enlight- 
enment. There is not a chapter in the work that 
should not be most carefully studied; and however 
well versed the reader may be in the science of 
jurisprudence, he will find much in Mr. Lea’s vol- 
ume of which he was previously ignorant. The 
book is a valuable addition to the literature of so- 
eial science.—Westminster Review, Jan. 1880. 
By the Same Author. 
Studies in Church History. The Rise of the Temporal Power—Ben- 
efit of Clergy—Excommunication. New edition. In one very handsome royal 
octavo volume of 605 pages. Cloth, $2.50. 
The author is pre-eminently a scholar. He takes 
up every topic allied with the leading theme, and 
traces it out to the minutest detail with a wealth 
of knowledge and impartiality of treatment that 
compel admiration. The amount of information 
compressed into the book is extraordinary. In no 
other single volume is the development of the 
Just ready. 
primitive church traced with so much clearness, 
and with so definite a perception of complex or 
conflicting sources. The fifty pages on the growth 
of the papacy, for instance, are admirable for con- 
ciseness and freedom from prejudice.—Boston 
Traveller, May 3,1883. Allen’s Anatomy .... 
American Journal of the Medical Sciences 
American System of Gynaecology . . . 27 
American System of Practical Medicine . 15 
*Ashhurst’s Surgery . . . . .20 
Ashwell on Diseases of Women . . . 28 
Attfield’s Chemistry ... . .9 
Ball on the Rectum and Anus . . . 2L 
Barker’s Obstetrical and Clinical Essays, . 29 
Barlow’s Practice of Medicine . . .17 
6 Hodge’s Obstetrics ..... 
3 Hoffmann and Power’s Chemical Analysis 
!7 Holden’s Landmarks ..... 
15 Holland’s Medical Notes and Reflections 
!0 ♦Holmes’ System of Surgery 
18 Horner’s Anatomy and Histology 
9 Hudson on Fever .... 
!1 Hutchinson on Syphilis .... 
19 Hyde on the Diseases of the Skin . 
\1 Jones (C. Handheld) on Nervous Disorders 
Barnes’ Midwifery . . .29 
♦Barnes on Diseases of Women . . .27 
Barnes’ System of Obstetric Medicine . . 29 
Bartholovv on Electricity .... 17 
Basham on Renal Diseases .... 24 
Bell’s Comparative Physiology and Anatomy . 3,7 
Bellamy’s Operative Surgery . .3,20 
Bellamy’s Surgical Anatomy ... 6 
Blandford on Insanity . . .19 
Bloxam’s Chemistry . . . ,9 
Bowman’s Practical Chemistry ... 9 
♦Bristowe’s Practice of Medicine . . .14 
Broadbent on the Pulse . . . 3,16 
Browne on the Ophthalmoscope . . . 23 ! 
Browne on the Throat .... 18 
Bruce's Materia Medica and Therapeutics . 11 
Brunton’s Materia Medica and Therapeutics . 11 
Bryant on the Breast . . . . .3,21 
♦Bryant’s Practice of Surgery . . .21 
♦Buinstead on Venereal Diseases . . .25 
♦Burnett on the Ear . . . . .24 
Butlin on the Tongue ..... 3,21 
Carpenter on the Use and Abuse of Alcohol . 8 
♦Carpenter’s Human Physiology ... 8 
Carter on the Eye ... . .23 
Century of American Medicine . . .14 
Chambers on Diet and Regimen . . .17 
Charles’ Physiological and Pathological Chem. 10 
Churchill on Puerperal Fever . . .27 
Clarke and Lockwood’s Dissectors’Manual . 6 
Classen’s Quantitative Analysis . . .10 
Cleland’s Dissector .... 5 
Clouston on Insanity . . .19 
Clowes’ Practical Chemistry . . .10 
Coats’ Pathology . . . .13 
Cohen on the Throat ... . . 18 
Coleman’s Dental Surgery . . . .24 
fondle on Diseases of Children . . .80 
Co, Lectures on Surgery . . .20 
Conn. l>iUs . . . .25 
♦Cornil a. ’" T’-’thological Histology . 13 
Cullerier’s a eal Diseases . . 25 j 
Curnow’s Medi„. , A ty . . . 3,6 
Dalton on the Circu- (ion .... 7 
♦Dalton’s HuraanPhysiology ... 8 
Dalton’s Topographical Anatomy of the Brain 7 
Davis’ Clinical Lectures . . .16 
Draper’s Medical Physics ... 7 
Druitt’s Modern Surgery ... .21 
Duncan on Diseases of Women . . .28 
♦Dunglison’s Medical Dictionary ... 4 
Ed is on Diseases of Women .... 27 
Ellis’ Demonstrations of Anatomy . . 7 
Emmet’s Gyntecoiogy . . .28 
♦Erichsen’s System of Surgery . .21 
Esmarch’s Early Aid in Injuries and Accid’ts . 21 
Farquharson’s Therapeutics and Mat. Med. . 12 
Fenwick’s Medical Diagnosis . . .16 
Finlayson’s Clinical Diagnosis . . .16 
Flint on Auscultation and Percussion . . 18 
Flint on Phthisis . . . . .18 
Elint on Physical Exploration of the Lungs . 18 
Flint on Respiratory Organs . . .18 
Flint on the Heart . ... 18 
♦Flint’s Clinical Medicine . . .16 
Flint’s Essays . . . • . 16 
♦Flint’s Practice of Medicine . . .14 
Folsom's Laws of U. S. on Custody of Insane . 19 
Foster’s Physiology .... .8 
♦PothergilTs Handbook of Treatment . . 16 
Fownes’ Elementary Chemistry ... 8 
Fox on Diseases of the Skin . . .26 
Frank land and Japp’s Inorganic Chemistry . 9 
Fuller on the Dungs and Air Passages . . 18 
Galloway’s A nalysis . . ... 8 
Gibney’s Orthopaedic Surgery . . .20 
Gibson’s Surgery . . . . .20 
Gluge’s Pathological Histology, by Leidy . 13 
Gould’s Surgical Diagnosis . . . . 3, 20 j 
♦Gray’s Anatomy . . . . 5 
Greene’s Medical Chemistry . 10 i 
Green’s Pathology and Morbid Anatomy . 13 
Griffith’s Universal Formulary . . . 11 1 
Juler’s Ophthalmic Science and Practice' 
Keating on Infants . . . 
King’s Manual of Obstetrics .... 
Klein’s Histology .... 
La Roche on Pneumonia, Malaria, etc. . 
La Roche on Yellow Fever .... 
Laurence and Moon’s Ophthalmic Surgery , za 
Lawson on the Eye, Orbit and Eyelid . . 23 
Lea’s Studies in Church History . . .31 
Lea’s Superstition and Force . . .31 
Lee on Syphilis . ... 25 
Lehman n s Chemical Physiology' ... 8 
♦Leishman’s Midwifery . . . .30 
Lucas on Diseases of the Urethra . . .3,24, 
Ludlow’s Manual of Examinations . . 3 
Lyons on Fever ...... 14 
Maisch’s Organic Materia Medica . . .11 
Marsh on the Joints ..... 3,22 
Medical News . .... 1 
Meigs on Childbed Fever . . . .27 
Miller's Practice of Surgery . . 1 . 20 
Miller’s Principles of Surgery . . .20 
xri.nitu s rniiui|iiesiu ouigei)' . . . 
Mitchell’s Nervous Diseases of Women . . 19 
Morris on Diseases of the Kidneys . . 3,21 
Morris on Skin Diseases . , .26 
Neill and Smith’s Compendium of Med. Sci. . 3 
Nettleship on Diseases of the Eye . . . 23 
Owen on Diseases of Children . . .3,30 
♦Parrish’s Practical Pharmacy . . .11 
Parry on Extra-Uterine Pregnancy . . 29 
Parvin’s Midwifery ... . .29 
Pavy on Digestion and its Disorders . . 17 
r ftYj' uu j/igcsuun ctiui 110 uiowiuci . .1/ 
Pepper’s Forensic Medicine . . . 3,31 
Pepper’s Surgical Pathology . . . 3,13 
Pick on Fractures and Dislocations . .3,22 
Pirrie’s System of Surgery .... 20 
Playfair on Nerve Prostration,and Hysteria . 19 
♦Playfair’s Midwifery . ' . 29 
Politzer on the Far and its Diseases . . 
Power’s Human Physiology . . .3 
Ralfe’s Clinical Chemistry . . .3. 
Ramsbotham on Parturition 
Remsen’s Theoretical Chemistry . 
♦Reynolds’System of Medicine 
Richardson’s Preventive Medicine 
Roberts on Urinary Diseases . . ‘4 
Roberts’Principles and Practice of Surgery , j, 
Robertson’s Physiological Physics . .3, 
Rodwell’s Dictionary of Science 
Sargent’s Minor and Military Surgery . . 2C 
Savage on Insanity, including Hysteria . . 3,19 
Schafer’s Essentials of Histology, . . 13 
Schafer’s Histology . ... 13 
Schreiber on Massage . ... 16 
Seiler on the Throat, Nose and Naso-Pharynx 18 
Series of Clinical Manuals . . . .3 
Simon’s Manual of Chemistry ... 9 
Skey’s Operative Surgery . . . .20- 
Slade on Diphtheria . . . . .18 
Smith (Edward) on Consumption . . .18 
Smith (H. H.) and Horner’s Anatomical Atlas 5 
♦Smith (J. Lewis) on Children . . .30 
Suite on Cholera . . . . .16 
♦Stills & Maisch’s National Dispensatory , 12 
♦Stilly’s Therapeutics and Materia Medica . 12 
Stlmson on Fractures . . . . .22. 
Stimson’s Operative Surgery . .20 
Stokes on Fever . . ... .14 
Students’ Series of Manuals .... 3 
Sturges’ Clinical Medicine . . . .16 
Tanner on Signs and Diseases of Pregnancy . 29 
Tanner’s Manual of Clinical Medicine . . 16 
Tarnier and Chantreuil’s Obstetrics . . 28- 
Taylor on Poisons . . . .31 
♦Taylor’s Medical Jurisprudence . . .31 
Taylor’s Piin. and Prac. of Med. Jurisprudence 31 
♦Thomas on Diseases of Women . . .27 
Thompson on Stricture .... 24 
Thompson on Urinary Organs . . .24 
Tidy’s Legal Medicine. . . . .31 
Todd on Acute Diseases .... 17 
Treves’Applied Anatomy .... 3,6 
Treves on Intestinal Obstruction . . .3,21 
Take on the Influence of Mind on the Body . 19 
Walshe on the Heart . .... 18 
Watson’s Practice of Physic . . . .14 
UUtlllU O C Ul V POI llllllrtl J . . . 11 
Gross on Foreign Bodies in Ai'r-Passages . 18 
Gross on Impotence and Sterility . . .25 
Gross on Urinary Organs . . . 24 
♦Gross’ System of Surgery . . . 20 
Habershon on the Abdomen . . 17 
♦Hamilton on Fractures and Dislocations . 23 
Hamilton on Nervous Diseases . . .19 
Hartshorne’s Anatomy and Physiology . . 6 
Hartshorne’s Conspectus of the Med. Sciences . 3 
Hartshorne’s Essentials of Medicine . . 14 
Hermann’s Experimental Pharmacology . 11 
Hill on Syphilis . . . . ' . .25 
Hillier’s Handbook of Skin Diseases . . 26 
Hoblyn’s Medical Dictionary ... 4 
Hodge on Women ..... 28 
* Wei Is on the Eye ..... 28 
West on Diseases of Childhood . . . 30- 
West on Diseases of Women . . .27 
West on Nervous Disorders in Childhood . SO 
Williams on Consumption .... 18 
Wilson's Handbook of Cutaneous Medicine . 26 
Wilson's Human Anatomy .... 5 
Winckel on Pathol, and Treatment of Childbed 29 
Wohlers Organic Chemistry ... 8 
Wood head’s Practical Pathology . . . 13- 
Year-Book of Treatment . . . .17 
EE A BROTHERS & CO., Philadelphia. 
Books marked * are also bound in half Russia,