RESTRICTED 
DICTIONARY 
OF 
GERMAN SCIENTIFIC TERMS 
I December 1945 
MILITARY INTELLIGENCE DIVISION, WAR DEPARTMENT 
WASHINGTON, D. C. 
mmm DICTIONARY 
OF 
GERMAN SCIENTIFIC TERMS 
MILITARY INTELLIGENCE DIVISION, WAR DEPARTMENT 
WASHINGTON, D. C. MILITARY INTELLIGENCE 
SERVICE 
WAR DEPARTMENT 
Washington 25, D.C. 
1 December 1945 
MID 461 
NOTICE 
This dictionary is intended to assist U. S. military personnel and research agencies 
in interrogating German scientific personnel and in translating German scientific docu- 
ments. Most of the terms defined are not included in any standard German or German- 
English dictionary. 
Translations of the German terms are based upon information collected over a 
period of approximately 10 months by Military Intelligence Service interrogators. Defi- 
nitions of the terms have been taken from Weld’s "Glossary of Physics” and other 
standard English scientific works, except in the case of new terms for which no published 
definition was available. While every effort has been made to confirm the accuracy 
of the definitions, inaccuracies may be found. It is requested that these be brought to 
the attention of the Chief, CPM Branch, Military Intelligence Service, War Depart- 
ment, Washington 25, D. C. _A 
Abampere: abampere. The c.g.s. electromagnetic unit 
of current, viz., that current which, in a one-turn circu- 
lar conductor of 1 cm radius in a vacuum, produces a 
magnetic intensity of 2tt oersteds at the center of the 
circuit. Equal to 10 absolute amp. 
Abbau: degradation. (1) (Of energy) Any process 
whereby available energy becomes unavailable, as by 
conversion into heat. If the unavailable energy is al- 
lowed to escape, the term dissipation is more apt to be 
used. (2) (Of radiation) The transformation of radia- 
tion of given type into a form having lower frequency 
and lower quantum energy, as in the Compton effect. 
Abbe'sches Prisma: Abbe prisms. One of several 
prism combinations devised by Abbe for various pur- 
poses, e.g., those used in the prism binocular and in 
the Abbe refractometer. 
Abcoulomb: abcoulomb. The c.g.s. electromagnetic 
unit of electric charge or quantity, defined as that quan- 
tity of electricity which is carried past any point of a 
circuit in one second when the current is one abamp. 
Equal to 10 absolute coulombs. 
Aberration: aberration. An error, or deviation from 
ideal. (1) (astron.) Aberration of light is an apparent 
angular displacement of a star due to the earth’s orbital 
motion. Its maximum value, the aberration angle or 
aberration constant, is about 20.5 seconds. (2) (Geom., 
Opt.) Lack of point-to-point correspondence between 
an object and its image. Spherical aberration includes 
various faults of an optical image with monochromatic 
light, such as lack of sharpness, coma, astigmatism, cur- 
vature, lack of flatness, and distortion. (3) (Chromatic) 
The effect of dispersion upon the distinctness of optical 
images. 
Abfarad: abfarad. The c.g.s. electromagnetic unit of 
capacitance, corresponding to one abcoulomb per abvolt. 
Equal to 109f. 
Abflachung der Kugel: oblateness. In re a spheroid, 
like the earth: the fraction (E—P)/E, in which E and 
P are respectively the equatorial and the polar diame- 
ters. Value for the earth, about 1/297. 
abges+imm+e Spule: loading coil. A coil of adjusted 
inductance, introduced into certain complicated circuits 
to impart desired characteristics. 
Abhenry: abhenry. The c.g.s. electromagnetic unit of 
inductance (or mutual inductance), viz., that of a cir- 
cuit in which the variation of current at the rate of 1 
abamp-sec induces an e.m.f. of 1 abvolt. Equal to 
lO-9 henry. Because its c.g.s. dimensional value is 1 
cm, it has been called the cm of inductance. 
Ablenkungsoszillator: sweep oscillator. An oscillator 
used to deflect periodically the beam of a cathode-ray 
oscillograph or television tube so as to give a displace- 
ment which is a function of the time. The voltage ap- 
plied to the deflecting plates is the sweep voltage, and 
the amplitude of the displacement of the spot is the 
sweep amplitude. 
Abloesungsenergie: extraction energy. The energy cor- 
responding to an ionizing potential. 
Abnahme: degradation. See Abbau. 
Abohm: abohm. The c.g.s. electromagnetic unit of 
resistance; defined as the resistance of a conductor which, 
when a constant current of one abamp flows through it, 
maintains a p.d. of 1 abvolt between its terminals. Equal 
to 10-9 absolute ohm. 
Abschirmung: screening. (1) The effect of the inner 
orbital electrons of an atom upon the attraction of the 
nucleus for the outer electrons. (2) The effect of the 
outer layers of atoms in a crystal upon radiation or upon 
fields of force reaching the inner layers. (3) The effect 
of a conducting shell upon an electric field, or of an 
iron shell on a magnetic field. 
Abschirmungskonsfante: screening constant. A coeffi- 
cient, such that if the electronic charge be multiplied by 
it, the product represents the apparent amount of re- 
duction in the charge of the nucleus of an atom (as 
indicated), due to the screening effect of an inner 
electron group. With respect to corresponding X-ray 
spectrum lines, this coefficient is nearly the same for all 
elements of high atomic number. 
Abschirmungszahl: screening number. See Abschir- 
mungskonstante. 
Abschlemmen: levigation. The sorting of different- 
sized particles by virtue of the varying rate of fall of 
fluid. 
Abschweifung: straggling. The statistical variation in 
the range of different alpha particles, all of the same 
initial speed, in the same gas. The (Gaussian) dis- 
tribution corresponding to this variation is represented 
by the straggling curve, similar to the normal error 
curve. 
absolute Einheiten: absolute units. (1) A system of 
units defined in terms of phenomena of supposedly uni- 
versal occurrence, rather than in terms of the properties 
of special substances or systems. E.g., Planck’s system 
of absolute units, in which the units of mass, length, 
time, and temperature are so chosen that the gravita- 
tional constant, the velocity of light, the Planck constant, 
and the ideal gas constant all have the numerical value 
/absolute Temperatur A 
unity. (2) Dynamic units defined without reference to 
gravity, e.g., the dyne and the erg. 
absolute Temperatur: absolute temperature. Tempera- 
ture as reckoned from a zero corresponding to the en- 
tire absence of translational molecular motion, on either 
the hydrogen constant volume or the Kelvin scale. 
Absolute zero is approximately —273.2 degrees Centi- 
grade or —459.8 degrees Fahrenheit. 
Absorption: absorption. (1) A process in which a 
fluid, liquid or gaseous, passes into the interstices of a 
porous substance and is held there by absorption or 
capillarity. (2) The transformation, into other forms, 
of the energy of any emission as it passes through 
a material substance. (3) (Dielectric) The persistence 
of a measurable electric polarization exhibited by many 
dielectrics after the electric intensity responsible for the 
polarization has been reduced to zero. 
Absorp+ionsfakfor: absorption factor. (1) One minus 
the attenuation factor. (2) The ratio of the energy 
flux in a diffracted X-ray beam in the powder method 
to that which it would have without absorption by the 
powdered material. 
Absorptionsgrenze: absorption limit. The wave length 
or frequency corresponding to an abrupt discontinuity 
in the intensity of an X-ray absorption spectrum, which 
gives the appearance of a sharp "edge” in the photo- 
graph of such a spectrum. 
achromatisch: achromatic. (1) In re an optical sys- 
tem: having the same focal length for two distinct 
wave lengths, and hence approximately free from chro- 
matic aberration in this range. (2) In re a color: devoid 
of hue. Such a color is often called a gray. 
Absorptionshygrometer; absorption hygrometer. One 
of several types of hygrometer dependent upon the elon- 
gation or shrinkage of a hair or similar organic structure 
with changes of humidity. 
Absorptionsindex: absorption index. The value of the 
ratio fxX/Air n for any medium traversed by radiation 
of wave length A for which the refractive index is 
n and the absorption coefficient is p. 
Absorptionskante: absorption edge. See Absorptions- 
grenze. 
Absorptionskoeffizient: absorption coefficient. The frac- 
tional rate at which the flux density of an emission 
diminishes by absorption, in respect to the thickness 
of medium traversed; expressed by the equation 
di 
dx 
/x = 
I 
where I = flux density, x = thickness. The mass ab- 
sorption coefficient is similarly defined, except that the 
mass per unit area of medium replaces the thickness x. 
For a substance of density d, this coefficient is therefore 
equal to p/d. 
Absorptionsspektrum: absorption spectrum. The spec- 
trum of radiation which has passed through some se- 
lectively absorbing substance, e.g., of white light after 
passage through a vapor or a solution. 
Absorptionsvermoegen: absorptivity. The fraction of 
the radiant energy of a given character, normally inci- 
dent upon the surface of a body, which is absorbed by 
the substance of that body. For an ideal black body, 
its value would always be unity. 
Absorptivitaet: absorptivity. See Absorptionsvermoe- 
gen. 
Abstimmkondensator: tuning condenser. A condenser 
of variable capacitance, used to adjust the natural fre- 
quency of an oscillatory circuit. 
Abstimmspule: tuning coil. A coil of variable induc- 
tance, used to adjust the natural frequency of an oscilla- 
tory circuit. 
Abvolt: abvolt. The c.g.s. electromagnetic unit of 
electromotive force or potential; defined as that p.d. 
through which 1 erg of work is required to transfer 1 
abcoulomb of electricity. Equal to 10~8 absolute volt. 
Abwatt: abwatt. A unit of power, corresponding to 
one abamp through a potential difference of one abvolt 
and equal to 10~7 watt. 
Achsengesetz: law of axes. States that the opposite 
ends of any one of the axes of a crystal are cut by the 
same number of similar faces similarly arranged. 
Achsenverhaeltnis: axial ratio. The ratio between the 
length of the arbitrary unit of measure along one axis 
of a crystal to that used along some other axis. 
achtfach Untersetzer: scale of eight. A vacuum tube 
circuit for counting pulses, in groups of eight, from ion 
or photon counters. 
Adhaesion: adhesion. An interaction between the sur- 
faces of two closely adjacent bodies, which causes them 
to cling together, as paint or a lead-pencil mark adheres 
to a wall or to paper. 
/adiabatisch 
2  A 
adiabatisch: adiabatic. (1) A term used to character- 
ize any process which takes place without transfer of 
heat to or from the body concerned. (2) Taking place 
under conditions prescribed in the statement of the 
(quantum) adiabatic’hypothesis. (3) (n.) The graph 
representing an adiabatic process. 
adiabatische Gleichung: adiabatic equation. A char- 
acteristic equation relating the quantities which define 
the state of a body during an adiabatic change. 
adiabatische Hypothese: adiabatic hypothesis. A hy- 
pothesis of the quantum theory, set forth by Ehrenfest, 
to the effect that, if the motion of a mechanical system 
is initially adjusted in accordance with the appropriate 
quantum condition and if the motion is very gradually 
changed, it continues to operate under the same quantum 
condition with the same set of quantum numbers. 
Adsorption: adsorption. A term applied to the phe- 
nomena connected with the adherence of molecules of 
a foreign substance to the surface of a solid or a liquid. 
Adsorptionswaerme: heat of adsorption. Heat result- 
ing from the transportation of energy which takes place 
during adsorption; expressed quantitatively in calories 
per gram or per mol, or, in the case of gases, sometimes 
in calories per cm3. 
Aehnlichkeit: similitude. (1) A principle, set forth 
by R. C. Tolman, which he states as follows: "The fun- 
damental entities out of which the physical universe 
is constructed are of such a nature that from them a 
miniature universe could be constructed exactly similar 
in every respect to the present universe.” (2) A term 
used in connection with physical quantities having the 
same dimensional structure; e.g., in the expression 
VR2 + 47r2n2L2 for the impedance of an inductive 
circuit, the two terms under the radical have dimensional 
similitude. 
aeolo+ropisch: aeolotropic, eolotropic. Not isotropic; 
having different properties in different directions, as a 
crystal. 
aequatorielle Quan+enzahl: equatorial quantum num- 
ber. Syn. magnetic quantum number. 
aequipo+en+ial: equipotential. Having the same value 
of the potential throughout. E.g., a conductor in electri- 
cal equilibrium is electrically equipotential. 
aequivalen+e Absorption: equivalent absorption. In re 
any sound-absorbing object: the area of a surface of 
unit acoustic absorptivity which would absorb sound 
energy at the same rate as the given object under the 
same conditions. 
aequivalen+e Absorp+ionskraft: equivalent absorbing 
power. The thickness of any given absorbing material 
which will reduce the intensity of an emission in the 
same ratio as unit thickness of a standard substance 
(e.g., air) under specified conditions. Not to be con- 
fused with equivalent absorption. 
aequivalente Bahnen: equivalent paths. The optical 
path requiring the same time when traversed by light of 
the same frequency. 
aequivalente Elektronen: equivalent electrons. (1) (In 
atoms.) Electrons which have equal azimuthal quantum 
numbers and equal principal quantum numbers. (2) (In 
molecules.) Electrons which are identical in all orbital 
properties, except for a possible difference in sign of 
the orbital moment. 
Aequivalentgewicht: equivalent weight. That weight 
or mass of an acid, base, or salt which equals one mol 
divided by the total number of valence bonds connect- 
ing the positive and the negative ions of the molecule. 
E.g., for HQ the division is one; for Ca. (OH)2 it is 
two; for Fe2 (S04)3 it is six; etc. 
Aequivalentleitvermoegen: equivalent conductance. The 
ratio of the electric conductivity of an electrolytic solu- 
tion to the concentration in moles per centimeter3. 
Aequivalenzprinzip: equivalence principle. (1) A 
principle of the general relativity theory which points 
out that phenomena ascribed to the existence of a gravi- 
tational field may with equal validity be attributed to 
the effect of acceleration; illustrated by the sensations 
which one experiences in an elevator. (2) Equivalence 
principle of Pauli is an obsolescent synonym for exclu- 
sion principle. 
Aerodynamik: aerodynamics. That branch of dynamics 
which treats of the forces exerted by air or other gases 
upon bodies exposed to them. 
aeussere Arbeit: external work. Work done by a sys- 
tem against external forces, or upon the system by 
external forces, e.g., work done in compressing a gas, 
or by a gas during expansion against a piston. 
aeusserer Widerstand: external resistance. The re- 
sistance of that part of a circuit in which no e.m.f. is 
operative, e.g., the line connected between the terminals 
of a battery or other generator. 
Aether: ether, aether. A hypothetical medium, which 
has been supposed to pervade all space and all matter 
and assumed as the vehicle of propagation of light and 
other forms of radiation. 
Aetherverschiebung: ether drift. A hypothetical rela- 
3 
/Aggregat A 
tive motion of material bodies with respect to the ether; 
much sought for but never detected with certainty. 
Aggregat: aggregation. The collection of molecules 
composing any portion of matter. State of aggregation 
denotes the condition of the body as dependent upon 
the relative positions and the motions of the molecules, 
e.g., liquid, gaseous, etc. 
Aggregatzustand: aggregation. See Aggregat. 
agonische Linie: agonic line. The line on the earth’s 
surface, at all points of which the magnetic declination 
is zero. 
Airy'sches Experiment: Airy experiment. A celebrated 
observation by Airy (1871) to the effect that the aber- 
ration of light is independent of the medium filling the 
telescope with which the observation is made. 
Akkommodationskoeffizient: accommodation coefficient. 
The degree to which reflected or re-evaporated mole- 
cules, on the average, "accommodate” their energy to 
that of the surface which they strike; measured by the 
ratio of the observed heat loss from a surface to the 
theoretical heat loss which would take place if all the 
gas molecules came to thermal equilibrium with the 
surface. 
Akkumulationskoeffizient: accumulation coefficient. The 
ratio of the rate at which adsorbed molecules accumu- 
late on a surface to the rate at which they strike. 
Akkumulationszeit: accumulation time. In the theory 
of radiation, the time supposedly required for the ac- 
cumulation of a quantum of radiant energy, before it 
can be released. 
akkumulative Messmethode: cumulative method. A 
method of measurement in which a multiple of the un- 
known quantity is measured and the result divided by 
the multiplier; as in finding the period of a pendulum 
by timing a hundred successive swings. 
Akkumulator: accumulator. Syn. storage cell, secondary 
cell. 
Aktinium Reihe: actinium series. One of the principal 
radioactive series, beginning with actinium. 
Aktinometer: actinometer. (1) An instrument for 
measuring the actinic value of a given light or other 
radiation. (2) An instrument for measuring the flux 
density of solar radiation. 
aktiv: actinic. In re radiation: capable of producing 
chemical change, as in the photographic action of light. 
Aktivitaet: activity. (1) A measure of the intensity 
of the emission from a radioactive substance, in terms 
of observable effects. (2) An excited state in a gas, 
due to ionization. (3) Syn. power (Obs.).4. (Opt.) 
The property of producing cfptical rotation. (5) 
(Chem.) The concentration of free ions of a given 
type, e.g., hydrogen. 
akustische Impedanz: acoustic impedance. A complex 
quantity used in re the propagation of sound across 
any surface. It is a combination of a real term, the 
acoustic resistance, corresponding to internal friction 
and responsible for the dissipation of energy, and an 
imaginary component, the acoustic reactance, depending 
upon the inertia and the elasticity of the medium; both 
are expressed in acoustic ohms. 
akustische Inertanz: acoustic inertance. A quantity 
which, in the propagation of sound, enters into the 
acoustic reactance in a manner analogous to that in which 
inductance enters into electrical reactance. It is equal 
to the mass of the body of medium divided by the 
square of the cross section of the conduit in which it is 
contained. 
akustischer Strahlungsmesser: acoustic radiometer. An 
apparatus for measuring acoustic flux density. 
akustischer Widerstand: acoustic reactance, acoustic 
resistance. Corresponding to internal friction and re- 
sponsible for the dissipation of energy. 
akustisches Absorptionsvermoegen: acoustic absorp- 
tivity. The ratio of the sound energy absorbed by a 
surface to that incident upon it. 
akustisches Ohm: acoustic ohm. A unit of acoustic 
resistance, reactance, or impedance, corresponding to 1 
bar of sound pressure per cm3 per second of volume 
velocity. . 
akustisches Reflektionsvermoegen: acoustic reflectivity. 
The ratio of the flux density of the sound reflected from 
a surface to that incident upon it. 
Albedo: albedo. The reflection factor of a diffusely 
reflecting surface; esp. of a celestial object, as a planet. 
allgemeine Strahlung: general radiation. Continuous 
radiation such as white light or the background of an 
X-ray spectrum. 
allgemeine Struktur: gross structure (1) The array of 
bands in a band spectrum, each represented by its head 
or by its zero line, without attention to the individual 
lines of which the bands are composed. (2) The gen- 
eral multiple! structure of an atomic spectrum. 
/allochromatisch 
4 _A 
allochromatisch: allochromatic. A term used to char- 
acterize crystals which have photoconductivity on ac- 
count of dispersed microscopic or sub-microscopic par- 
ticles occurring naturally or as a result of exposure to 
certain radiations. 
Allotropie: allotropy, allotropism. The property, pos- 
sessed by many substances, of existing in different modi- 
fications, called allotropie forms, e.g., carbon, which 
represents itself as diamond, as graphite, or in the 
amorphous form of soot. 
Alpha, Beta, Gamma, . . . Linien: alpha, beta, gam- 
ma, . . . lines. The lines of a spectral series, arranged 
in the order of increasing frequency. E.g., the Lß line 
is the second line of the L series of an element. If the 
line is a doublet, the components are designated Lyd1, 
L/?2; etc. 
Alpha, Beta, Gamma . . . Zustand: alpha, beta gam- 
ma , . . form or state. Terms used to distinguish the 
different isomers of the same composition or different 
allotropie modifications of an element. E.g., these 
states of iron depend upon its temperature, and only 
the alpha iron is highly magnetic. 
Alpha -strahlen: alpha rays. A corpuscular emission 
from certain types of radioactive atom, each particle 
emitted consisting of a completely ionized helium atom, 
i.e., of a helium nucleus. 
Alpha-strahlen Spektrum: alpha-ray spectrum. A sepa- 
ration of alpha particles of different speeds, usually by 
the magnetic field alone, but in some cases by both 
magnetic and electric fields. 
Alternationsgesetz: alternation latv. The first of the 
Kossel-Sommerfeld (spectroscopic) laws. 
ambipolar: ambipolar. Operating in both of two op- 
posite directions at once, e.g., the current in an electro- 
lytic cell, in which there are ions moving in both di- 
rections. 
Amici'sches Prisma: Amici prism. A combination of 
three triangular prisms, viz., an isosceles flint-glass 
prism included between two equal crown-glass prisms, 
the refracting angles being such as to produce dispersion 
without deviation. Used in direct-vision spectroscopes, 
etc. 
amorph: amorphous. Devoid of regular structure, esp. 
of crystalline structure. 
Ampere: ampere. The practical unit of electric cur- 
rent. The absolute ampere is 1/10 of the abampere. 
The international ampere is the value of a steady cur- 
rent which would deposit 0.00111800 grams of silver 
per second from a solution of silver nitrate. The ratio 
of the international to the absolute ampere is about 
0.99993. 
Amperemeter: ammeter. An instrument for measur- 
nig electric currents in amperes. 
Ampere'sche Regel: Ampere law. The laws appears 
in two equivalent forms: 1. The magnetic intensity due 
to a current i (abamperes) in an element of length dl, 
at any point P distant r from it, is 
dH = ipdl/r3 — i sinödl/r2, 
in which p is the normal from the point P to the line 
of the element dl, and 6 is the angle between dl and 
the line r joining it to P. 2. The line integral of the 
magnetic intensity over any closed path in a magnetic 
field is equal to r times the total electric current i, 
in abamperes, linked with the path; so that if a unit 
magnetic pole is carried around the path, the work done 
is 4?ri (ergs). 
Ampere'scher Strom: Amperian current, A. whirl. 
An electric current in a resistanceless circuit in an atom 
or a molecule, accounting for its magnetic moment. 
Ampere'scher Wirbelstrom: Amperian whirl. See Am- 
pere’scher Strom. 
Ampere'sches Gesetz: Ampere law. See Ampere’sche 
Regel. 
Amperestunde: Ampere-hour. The quantity of elec- 
tricity which flows past any point of a conductor carry- 
ing a current of one amp, in 1 hour; equal therefore 
to 3600 coulombs. 
Amperewindung: ampere-turn. A unit of magnetomo- 
tive force corresponding to the effect of a current of 
one amp traversing one turn or winding. 
Amplitude: amplitude. One-half the complete range 
of any symmetrical vibration or periodic variation; e.g., 
a pendulum swinging through an angle of 10 degrees 
has an amplitude of 5 degrees. In an asymmetric vibra- 
tion, the amplitude usually expresses the maximum dis- 
placement from the normal or neutral state during the 
cycle. 
Analysator: analyzer. An apparatus, e.g., a Nicol 
prism, for detecting and testing the properties of polar- 
ized light. 
Analyse von positiven Strahlen: positive-ray analysis. 
The separation and measurement of the masses of atoms 
by subjecting their positive ions to deflection by electric 
or magnetic fields. 
5 
/anastigmatisch A 
anastigmatisch: anastigmatic. Free from astigmatism 
for narrow, oblique pencils. 
Anemograph: anemograph. A recording anemometer. 
The record is called an anemogram. 
Anemometer: anemometer. An instrument for measur- 
ing the velocity of the wind. 
aneroid: aneroid. Free from liquid or fluid parts, as 
an aneroid barometer, calorimeter, etc. 
Aneroidbarometer besonderer Art: statoscope. A very 
sensitive aneroid altimeter. 
angenaeherter Knotenpunkt: partial node. A region in 
a stationary wave system similar to a node, but at which 
the amplitude is a minimum without being reduced to 
zero. 
Angstroem: angstrom. A unit of length, equal to 10~8 
cm, used in expressing wave lengths of light, etc. 
Angstroemskoefficient: Angstroem coefficient. The co- 
efficient A in Angstroem’s formula for the scattering 
coefficient for dust in the atmosphere, viz., S = Aa — B 
in which A is the wave length and B ranges from 
0 to 4 for different sized particles. 
anhysteretisch: anhysteretic. Taking place without 
hysteresis; applied to magnetization under certain con- 
ditions. 
Anion: anion. One of the negative ions moving toward 
the anode in an electrolytic cell or a discharge tube. 
Anode: anode. That electrode from which positive 
ions are dispersed or toward which negative ions are 
collected, within an electrolytic cell, discharge tube, 
or similar apparatus. 
plate. The positive electrode of a thermionic 
vacuum tube. 
Anodenfall; anode drop: An abrupt fall of electric 
potential at the anode of an electrolytic cell or vacuum 
tube. 
Anodenfluessigkeit: anolyte. The solution surrounding 
the anode in an electrolytic cell. 
Anodenstrahlen: anode rays. Positively charged par- 
ticles in a vacuum tube, which have their origin in the 
anode. They are of atomic dimensions, being derived, 
apparently, from metallic salts on the anode. 
Anodenstrom: plate current. A current flowing to or 
from the anode or "plate” of a vacuum tube. 
Anolyt: anolyte. See Anodenfluessigkeit. 
anomale Dispersion: anomalous dispersion. An in- 
version of the usual change of refractive index with 
wave length in the vicinity of an absorption band. 
Anpassungsstrom: transient. A temporary component 
of the current in a circuit which is adjusting itself to 
a new condition of load or of impressed e.m.f. In the 
current-time equation for such a circuit, the transient 
component may be represented by a term which rapidly 
approaches zero. 
anregen: excite. (1) To bring (an atom or a mole- 
cule) to a higher quantum state than its normal or 
ground state of lowest energy; as by heating, by radia- 
tion, or by electron impact. (2) To magnetize, as by a 
current. 
Anregungsfunktion: excitation junction. (l)The prob- 
ability of excitation of a spectrum line due to electron 
impact, expressed as*a function of the energy of the 
electron. (2) A function which expresses the correc- 
tion necessary in comparing calculated and observed 
spectral line intensities, because of the unequal numbers 
of atoms or molecules in the different excited states. 
(3) An expression for the probability that an atomic 
nucleus will be rendered radioactive by the impact of a 
rapidly moving particle, in terms of the particle energy 
or other factors. 
Anregungsgrenze: excitation limit. The least value of 
the quantum energy of an incident, exciting electron 
which is capable of producing lines of a given spectral 
series. 
Anregungspotential: excitation potential. The critical 
potential for the excitation of a given radiation, either 
a line or a group of lines. 
Anregungswahrscheinlichkeit: excitation probability. In 
re the excitation of a gas by electronic impact: the 
number of excited atoms produced per unit electron 
current, per unit path length, per unit pressure at zero 
degree C. 
Anregungswelle: excitation wave. A term used by 
Frenkel to charactreize the process of absorption of 
radiation in a crystalline solid and its transformation 
into heat by the excitation of the atoms. 
Antikathode; anticatbode. A plate or block of metal 
placed opposite the cathode in an X-ray tube to inter- 
cept the cathode rays. 
Antinode: antinode. A point, line, or surface, between 
two nodes of a vibrating body, at which the amplitude 
has a maximum value. 
/antiparellel 
6 A 
antiparallel: antiparallel. Extending or moving in 
parallel lines but in opposite directions. 
Antiresonanz: antiresonance. A condition which, in a 
divided oscillatory circuit, is the antithesis of the reso- 
nance condition and through which the oscillation am- 
plitude is reduced to zero. 
Antizyklon: anticyclone. A rotary atmospheric dis- 
turbance, turning in the opposite direction from a cy- 
clone about a center of high pressure. 
aperiodisch: aperiodic. Devoid of periodicity or 
rhythm. 
aperiodisch-ausschwingend: deadbeat. Coming to rest 
without oscillation, as the indicator of a highly damped 
galvanometer. 
Apertur: aperture. (1) Any opening, as in a screen. 
(2) The diameter of the entrance-pupil of an objective. 
(3) (Angular.) The angle subtended at the focal point 
of an optical instrument by the diameter of the en- 
trance-pupil. (4) (Relative.) In a telescope or a cam- 
era: the ratio of the focal length of the objective to 
the diameter of the entrance-pupil; it determines the 
photographic speed of the objective. 
Aperturme+er: apertometer. A device, due to Abbe, 
for measuring the numerical aperture of microscope 
objectives. 
Aper+urwinkel: aperture angle. The angle subtended 
by the radius of the entrance-pupil of an optical instru- 
ment at the (axial) object-point. 
aplana+isch: aplanatic. (1) In re a lens: free from 
spherical aberration for a given point on the axis. 
(2) In re an optical system: free from spherical aber- 
ration as in (1) and also fulfilling the sine condition 
of Abbe. 
apochromatisch: apochromatic. In re an optical sys- 
tem: more highly corrected than an ordinary achromatic 
lens, i.e., achromatized for more than two wave lengths. 
Apsis: apse, apsis. A point on a central orbit at which 
the tangent is perpendicular to the radius vector from 
the center of force, or at which the radius vector has 
a maximum or a minimum value. 
Aragopunkt: Arago spot. A bright point which, owing 
to diffraction, appears at the center of the shadow of 
a sphere or other object casting a circular shadow in 
light from a point source. 
Arbeit: work. A physical magnitude relating to the 
transfer of energy from one body to another through 
the agency of mechanical force. Its measure is the 
scalar product of the force by the simultaneous linear 
displacement. 
Arbeitsfunktion: work junction. A general term ap- 
plied to the energy required to transfer electrons, ions, 
molecules, etc. from the interior of one medium across 
the boundary into an adjacent medium. It is of especial 
significance in photoelectric and thermionic emission,, 
sometimes referring to energy per unit charge and ex- 
pressed in ergs or joules, sometimes to energy per 
electron-volts. 
Arbeitssubstanz: working substance. A substance whose 
changes of volume and pressure figure in a thermody- 
namic process, as in the operation of a heat engine. 
Archimedes'sches Prinzip: Archimedes principle. States 
that the buoyant force of a liquid upon a partly or 
wholly submerged body is equal to the weight of the 
displaced liquid, and acts vertically upward through 
the center of displacement. 
Armatur: armature. (1) A removable part of a mag- 
netic circuit, of ferromagnetic material and usually of 
low reluctance; e.g., a bar of iron placed across the 
poles of a magnet. (2) That part of a generator or 
motor, or other electromagnetic device, upon whose 
relative motion with respect to the main magnetic field 
the operation of the device depends. 
astatisch: astatic. Coming to rest indifferently, with- 
out any particular orientation; e.g., an astatic pair, 
composed of two parallel, equally magnetized needles, 
rigidly connected, with their like poles in opposite di- 
rections. 
Astigmatismus: astigmatism. The property of being 
astigmatic, as a lens or a mirrör, i.e., having different 
focal power in different meridians. In an astigmatic 
bundle of rays, the rays do not all intersect at one 
point. Astigmatism of the eye is mainly due to lack 
of sphericity in the cornea, which has different curva- 
ture in different meridians. 
Asto'nscher Dunkelraum: Aston dark space. (1) A 
thin, nonluminous region of the discharge in a vacuum 
tube which sometimes is observed between the cathode 
glow and the cathode itself. (2) Aston also discovered 
a dark space next to the anode. 
Astrophysik: astrophysics. The physics of astronomical 
bodies and regions. 
atherman: athermanous. Opaque to infrared. 
7 
/Atmosphaere A 
Atmosphaere: atmosphere. (I) The air. (2) Any 
gaseous medium. (3) A unit of pressure, defined as 
the pressure of 76 cm of mercury at zero degrees C. 
under standard gravity. Equal to about 1,013,250 dynes/ 
cm2. 
atmosphaerisch: atmospheric. (1) (adj.) Pertaining 
to the atmosphere. (2) (n.) An electrical disturbance 
or stray produced by conditions in the atmosphere. 
atmosphaerisches Gesetz: Law of atmospheres. A law, 
first stated by Laplace, expressing the distribution of 
molecules in an ideal atmosphere subject only to gravity 
and thermal agitation. In one form, the number of 
molecules per unit volume at any altitude h is given by 
3 g 
N — N0e — — h 
TT2 
where N0 is the number at the arbitrary elevation zero. 
U2 is the mean square speed of molecular motion. 
It is a special case of the Boltzmann principle. 
atomare Anordnung: atomic domain. One of the sim- 
plest spacefilling polyhedrons which contain the con- 
tacting spheres used to represent the atoms in a crystal. 
atomarer Absorptionskoeffizient: atomic absorption co- 
efficient. The absorption coefficient of an element di- 
vided by the number of atoms per unit volume. 
atomare Refraktion: atomic refraction. The product 
of the specific refractive power of an element by its 
atomic weight. 
atomarer Streufaktor: atomic scattering factor. Syn. 
atom form factor. 
atomarer Streukoeffizient: atomic scattering coefficient. 
In re the scattering of a stream of electrons in travers- 
ing a substance: the scattered electron current per unit 
solid angle in any direction, per atom of scattering ma- 
terial, per unit incident electron current. 
atomarer Strukturfaktor: atomic structure factor. Syn. 
atom form factor. 
atomares Bremsvermoegen: atomic stopping power. In 
re the effect of different elements upon th£ motion of 
alpha particles: the quantity 
S-Z-2/3 
in which S is the stopping power relative to oxygen 
and Z, the atomic number. Its value is approximately 
0.23 for all elements. 
atomare Suszeptibilitaet: atomic susceptibility. The 
specific or mass susceptibility of an element, multiplied 
by its atomic weight. 
Atomformfaktor; atom form factor. (1) A quantity 
occurring in the expression for the intensity of an X-ray 
beam reflected by a crystal, whose value depends upon 
the varying configuration of the electrons in the crystal 
atoms relative to the center of the atom, as well as upon 
the angle of incidence and the wave length of the 
X-rays. (2) A quantity used in a manner similar to 
(1), but in reference to the scattering of either X-rays 
or electrons by gases. 
Atomfrequenz: atomic frequency. A natural frequency 
of vibration ascribed to the atoms composing a solid, 
and associated with the elastic constants of the solid. 
Atomrefraktion: atomic refraction. See atomare Re- 
fraktion. 
Atomsuszeptibllitaet: atomic susceptibility. See atomare 
Suszeptibilitaet. 
Atomvolumen: atomic volume. The volume of 1 gram 
atom of an element in the solid state. 
Atomwaerme: atomic heat. The product of the atomic 
mass of an element by its specific heat; or the thermal 
capacity of 1 gram atom of the element. 
Atomzahl: atomic number. The number assigned to 
any element in the complete series of elements, arranged 
in the order of the complexity of the atom; supposed to 
represent the number of electrons surrounding the 
nucleus. 
Audiofrequenz: audio frequency. A vibration fre- 
quency within the range of human tone perception. 
Audiooszillator: audio-oscillator. A generator of a.c.’s 
within the audible frequency range. 
Aufloesung: resolution. (1) The separation of a vector 
into its components. (2) The sharpness with which 
the images of two closely adjacent sources, two adja- 
cent spectrum lines, etc., may be distinguished. 
Aufloesungsvermoegen: resolving power. (1) Of an 
optical system: a measure of the distinctness with which 
the images of two point-sources of light may be sepa- 
rately detected. E.g., for ,a telescope, it is the least 
angular separation of the two point-sources (as stars) 
which can be recognized, and exists when the center 
of the diffraction ring system of one falls on the first 
dark ring of the other. (2) (Spectroscopic.) Of a 
grating or a prism: the value of A/AA (where A is the 
mean wave length for two close spectrum lines differing 
/Aufspaltung 
8 A 
in wave length by AA) when the principal maximum 
of one line coincides with the first minimum of the 
other, so that they are just distinguishable. 
Aufspaltung: exhaustion. In re the potential energy 
of a material system: the quantity of work which would 
be required to effect the separation of the bodies or 
particles to infinite distances apart; a term due to Kelvin. 
aufteilen in Blaetter: laminate. To divide into laminae; 
esp. the iron core of an electro-magnet, to minimize 
the effect of eddy currents. 
aufteilen in duenne Bleche: laminate. See aufteilen in 
Blaetter. 
aufteilen in duenne Schichten: laminate. See aufteilen 
in Blaetter. 
Aufteilungskoeffizient: partition coefficient. Syn. dis- 
tribution coefficient. 
Auftriebskurve: curve of buoyancy. Any vertical sec- 
tion of surface of buoyancy through the metacenter. 
Auftriebszentrum: center of buoyancy. Syn. center of 
displacement. 
augenblickliche Achse: instantaneous axis. Syn. axis 
of instantaneous rotation. 
augenblicklicher Mittelpunkt: instantaneous center. 
The point at which the instantaneous axis of a plane 
body moving in its own plane intersects that plane. 
augenblickliche Rotationsachse: axis of instantaneous 
rotation. A straight line about which any rigid body 
in motion may be regarded as rotating at any instant. 
augenblicklicher Schalldruck: instantaneous sound pres- 
sure. The actual pressure at any point of a medium 
traversed by sound waves, at any instant, minus the 
normal or static pressure. It may thus be either positive 
or negative. 
augenscheinlich; ocular. Pertaining to the eye, or to 
vision. 
Auger Effekt: Auger effect. The liberation of two 
electrons from different levels of an atom by a single 
X-ray quantum; a somewhat rare phenomenon first ob- 
served in argon. 
Aureole: aureole. The hazy, less luminous, outer por- 
tion of an electric arc, often of a different color from 
that of the core. 
aurrorale Linie: auroral line. A green line in the 
spectrum of the aurora borealis at wave length 5577 Ä, 
undoubtedly due to a "forbidden” transition in oxygen. 
The line has been produced artificially by Kaplan. 
Ausbreitungskonstante: propagation constant. In re 
the steady transmission of sound through any enclosure: 
the Napierian logarithm of the ratio of the volume 
velocity at entrance to that at exit of the wave train 
from the enclosure. 
ausdehnendes Universum: expanding universe. Refers 
to the fact that the mean distance between the bodies 
of the universe is apparently increasing; the rate of 
recession of the more remote visible galaxies, as indi- 
cated by the red shift, being several thousand miles per 
second. 
Ausdehnung: expansion. An increase in volume due to 
a change in energy. 
Ausdehnungskoeffizient: expansion coefficient. A meas- 
ure of the rate of expansion of a substance with tem- 
perature; usually defined as the ratio of the temperature 
rate of the change in length (or area, or volume), to 
the length (or area, or volume) at a chosen reference 
temperature or zero. Thus: 
Al 
C = 
Atl0 
Linear, superficial, and volume or cubical coefficients 
are thus similarly defined. 
Ausdehnungsmesser: extensometer, extensimeter. An 
instrument for measuring small changes in length, such 
as those produced by tension or in magnetostriction. 
Ausflusskoeffizient: efflux coefficient. A correction fac- 
tor for the rate of efflux from an orifice, to allow for 
friction. 
Ausgangsoeffnung: exit-port. The image of the en- 
trance-port of an optical system; or the image of the 
field stop as formed by the part of the system which 
is posterior to the field stop. If the field stop is behind 
the entire lens system, it is identical with the exit-port. 
Ausgangspupille: exit-pupil. The image of the en- 
trance-pupil of an optical instrument. It determines 
the apertures of the bundles of emergent rays. The exit- 
pupil of the eye is a little behind the actual pupil. 
ausgeglichen: balanced. (1) In re a circuit: having 
equal e.m.f.’s and equal currents in its main branches. 
(2) In re an electric network: having two conjugate 
branches, e.g., a Wheatstone bridge. (3) In re a 
9 
/ausgleichend A 
periodic variable: One whose average value is zero, 
e.g., a simple harmonic a.c. or voltage. 
ausgleichend: equilibrant. In re a system of forces: 
That single force, if such exists, which would, in co- 
operation with the given system, produce equilibrium. 
Ausgleichungslehrsatz: compensation theorem. States 
that if the impedance Zg of any branch B of a network, 
in which the current is IB, is altered by an amount A ZB, 
the resulting change Al in the current I at any point 
of the network is equal to the current which would be 
produced at that point by a counter e.m.f. —IbaZb in- 
troduced into the branch B. 
Ausgleichungs+rom: transient. See Anpassungsstrom. 
ausloeschen: quench. (1) To extinguish, as a glowing 
solid or a spark, by immersion in a liquid. (2) To 
suppress or reduce the fluorescence or phosphorescence 
of a substance by the admixture of some other substance, 
or by the action of some agency such as radiation. 
Ausschlussprinzip: exclusion principle. States that no 
two electrons in the same atomic or molecular system 
can have all their quantum numbers identical; discov- 
ered by Pauli. 
Ausschlussphaere: sphere of exclusion. The spherical 
surface drawn about any molecule, from which the cen- 
ter of any other molecule is excluded. 
ausserordentlich: extraordinary. Pertaining to that 
plane-polarized component of a ray of light which, in 
traversing a doubly refracting crystal, has its electric 
vector in the principal plane. So named because this 
component has different speeds in different directions. 
ausserordentlicher Index: extraordinary index. The re- 
fractive index for the extraordinary ray in a uni-axial 
crystal; defined as the ratio of the velocity of the light 
outside the crystal to that of the extraordinary compo- 
nent within the crystal in any direction perpendicular 
to the optic axis (in which its value differs most from 
the index for the ordinary component). 
Ausstrahlung; radiation. (1) The propagation of en- 
ergy through space or through material media in the 
form of electromagnetic waves, but subdivided in some 
manner into discrete portions or quanta. Commonly 
classified, according to frequency, as Hertzian radiation, 
infrared, (visible) light, ultraviolet, X-rays, gamma- 
rays, etc. (2) Sometimes extended to include corpuscular 
emissions, as a and ß "radiation”, or emissions of mixed 
or unknown type, as cosmic "radiation.” 
Ausstroemung: effusion. The escape of a gas through 
a small opening. 
Austausch; exchange. (1) The equalization of tem- 
perature among neighboring bodies through mutual ra- 
diation, as first pointed out by Prevost (1792). (2) An 
interaction between electrons, protons, alpha particles, 
etc., in the same or in different atoms; hence the terms 
exchange energy, e. force, etc. 
Austrittsgeschwindigkeit: velocity of escape. (1) The 
speed with which a projectile or a particle would have 
to leave the surface of the earth or other planet in 
order never to return. (2) The speed with which an 
electron or other ion escapes from a conductor in ther- 
mionic or photoelectric emission, or with which a mole- 
cule emerges from a liquid in evaporation. 
Auswahlprinzip: selection principle. An empirical rule, 
which governs the electron transitions actually occurring 
within an atom, as distinguished from those which 
might be expected, but apparently do not occur. 
Auswahlverstaerker; push-pull amplifier. A combina- 
tion of two vacuum-tube circuits so related that they 
are in phase for those frequencies which it is desired 
to amplify and out of phase for those which are to 
be eliminated. 
Au+okollimator; autocollimator. A telescope provided 
with a transparent scale in its objective focal plane, 
by means of which angles subtended by distant objects 
may be directly read. 
autophoto-elekfrisch: autphotoelectric. Relates to the 
hypothesis, due to Richardson, that thermionic emission 
is a form of photo-electric effect, in which radiation 
comes from the hot substance itself. 
Autotransforma+or: autotransformer. A transformer of 
which the primary windings, or part of them, are con- 
nected differentially in series with the secondary and 
which has the effect of stabilizing the secondary voltage 
against variations in the primary voltage. 
Avogadro'sches Gese+z: Avogadro law. States that at 
equal temperatures and pressures, equal volumes of all 
gases contain the same number of molecules. 
Avogadro'sche Zahl: Avogadro number. The number 
of atoms in a gram atom of any element, or the number 
of molecules in a mol of any pure substance. Its value 
is approximately 6.064 x 1023. 
axiale Vergroesserung: axial magnification. The ratio 
of the interval between two adjacent image-points on 
the axis of an optical instrument to the interval between 
the corresponding axial object-points. 
azeotropisch: azeotropic. In re a liquid mixture: in 
such proportion as to have a constant boiling point, the 
/Azimuth 
10 A 
distillate having the same composition as the original 
liquid. This property is known as azeotropism. 
Azimuth: azimuth. (1) Position as measured by an 
angle reckoned around some fixed point or pole, e.g , 
the azimuth of a particle moving in an orbit, or 
(astron.) of a star in the sky reckoned around the 
horizon from the south point; (2) In re elliptically 
polarized light: the direction of the vibration plane 
of the light which would result if the phase differ- 
ence corresponding to the ellipticity were reduced to 
zero without altering the amplitudes of the components. 
azimuthale Quantenzahl: azimuthal quantum number. 
A quantum number associated with angular motion, 
which must be an integer for any allowed stationary 
state of a particle moving subject to a central field. 
/Babinet'sches Absorptionsgesetz B 
Babinet'sches Absorptionsgesetz: Babinet absorption 
rule. States that positive, uniaxial crystals have greater 
absorption for the extraordinary component, negative 
crystals for the ordinary component, of the light doubly 
refracted by them. 
Babinet'sches Prinzip: Babinet principle. States that 
two diffraction screens, one of which is exactly the 
negative of the other, produce identical diffraction pat- 
terns. 
Babo'sches Gesetz: Babo law. States that the vapor 
pressure of a dilute solution of given concentration bears 
approximately a constant ratio to that of the pure sol- 
vent as the temperature changes. 
Back-Goudsmit'scher Effekt: Back-Goudsmit effect. A 
phenomenon analogous to the Paschen-Back effect but 
produced by a weak magnetic field upon the spectrum 
lines of an element having a nuclear magnetic moment. 
Bahn: orbit. (1) The path described by a particle, or 
by the centroid of the body, under the influence of a 
gravitational or other force field. (2) The hypothetical 
locus of one of the non-nuclear electrons within an 
atom. 
trajectory. The path followed by a projectile un- 
der the influence of gravity. 
bahn . . . orbital. (1) (adj.) Pertaining to an orbit 
or to motion in an orbit. (2) (n.) An orbital wave 
function pertaining to a single electron; a characteristic 
solution of the Schroedinger equation for a one-electron 
problem, excluding spin. 
Bahnelektron: orbital electron. One of those electrons 
of an atom or a molecule which are often visualized 
as moving in orbits around the nucleus or nuclei. 
Bahnmoment: orbital moment. The moment of mo- 
mentum of an atomic electron due to its orbital motion. 
Bahnumkehrprinzip: path-reversal principle. The fact 
that if light follows a given course through any optical 
system, it will, if reversed, traverse the same course in 
the opposite direction, so that a point and its real image 
are interchangeable. 
Bahnvalenz: orbital valence. An interaction between 
atoms in a molecule, ascribed to a coupling between 
orbital motions of electrons; a term introduced by 
Heitler. 
ballistisch: ballistic. (1) Pertaining to projectiles. (2) 
A term applied to an instrument which indicates the 
effect of an impact or of a sudden rush of energy; as 
a ballistic pendulum or galvanometer. 
Balmer Serie: Balmer series. A series of lines in the 
hydrogen spectrum, found by Balmer (1885) to be 
made up of frequencies progressing in proportion to the 
sequence of numbers 
— —)> p—-M. 
\ 22 32 / \22 42 / \22 521 
Over 30 lines have been identified in this series. 
Bande: band. (1) One of the broad stripes charac- 
teristic of molecular spectra. They are ready sequences 
of spectrum lines so closely spaced as to require high 
resolution to detect them. (2) Any sequence or range 
of frequencies. (3) A bright or a dark streak or stripe 
due to interference or diffraction. 
Bandenausfilterung: band elimination. In re a wave 
filter: the transmission of an entire range of frequencies 
with the exception of a limited portion, or band, having 
transmitted portions on either side of it. 
Bandendurchlaessigkeif: band-pass. In re a wave filter: 
having the property of transmitting only a certain band 
or range of frequencies. 
Bandenkante: band edge. The frequency toward which 
the lines in any one band of a band spectrum appear 
to be concentrated. 
Bandenkopf: hand head. See Bandenkante. 
Bankphotometer: bench photometer. Any one of vari- 
ous types of photometer, the parts of which are ar- 
ranged on an optical bench. 
Bar: bar, barye. The c.g.s. absolute unit of pressure, 
viz., one dyne/cm2. The megabarye or megabar is one 
million baryes, and equals about 0.987 atm. Note. Some 
writers designate 10(i baryes as a bar, and the barye as 
a microbar. 
Barkhausen Effekt: Barkhausen effect. A succession of 
abrupt changes in magnetization in a smoothly varying 
magnetizing field; discovered by H. Barkhausen. 
Barkhausen-Kurz Oszillator: Barkhausen-Kurz oscillator. 
A type of triode oscillator in which oscillations of fre- 
quencies ranging from 3xl08 to 15xl08 are generated,, 
apparently by the movements of filament electrons pass- 
ing back and forth through the positive grid and finally 
settling upon it. 
Barnett Effekt: Barnett effect. The magnetization of 
a body by rotaing it, without applied magnetic field. 
Barograph: barograph. A recording barometer. 
/Barostat 
12 B 
Barostaf: barostat. A pressure regulator, or an arrange- 
ment to maintain a constant pressure. 
Baume Skala: Baume scale. One of two arbitrary 
hydrometer scales, used, respectively, for liquids of 
specific gravity less than unity and greater than unity. 
Bea+fie-Bridgman'sche Gleichung: Beattie-Bridgman 
equation. An empirical characteristic equation for fluids, 
as follows: 
interval on a logarithmic scale. The number of bels in 
such an interval is the common logarithm of the ratio 
of the two powers compared; therefore the bei is the 
value of that interval for which the ratio is 10:1. 
Acoustically it is used to express differences in sound 
sensation level. Named for Alexander Graham Bell. 
Belflls' Bruecke: Belfils bridge. A type of resonance 
bridge used to ascertain the harmonic purity of an elec- 
tric wave train. 
Belichfung: exposure. A measure of photographic 
stimulus defined as the product of the illumination by 
the exposure time; usually expressed in meter-candle- 
seconds. 
Beleuchtungsschwerpunkt: luminous center of gravity. 
Syn, Photometric center. 
Beieuchtungsstaerke: illumination. The ratio of the 
luminous flux incident upon an element of surface to 
the area of the element. 
Beleuchtungsstaerkemesser: lumeter. A type of il- 
lumination photometer, depending upon the compari- 
son of the illuminated test area with an annular area 
illuminated by a lamp through a revolving adjustable 
diaphragm. 
Beleuchtungssstaerkenphotometer: illumination photo- 
meter, illuminometer. A portable photometer designed 
for the measurement of the illumination upon any sur- 
face, as a wall or a table. 
Bene+zungswaerme: heat of wetting. The quantity of 
heat evolved per unit mass of dry material when thor- 
oughly wet by immersion in a liquid. 
Beobachtungsgleichung: observation equation. An 
equation, admittedly only approximately true, which 
connects one or more quantities, to be experimentally 
determined, with the results of an observation upon 
some function of them. 
Bereich: domain. One of the regions in a ferromag- 
netic substance in which the atomic magnetic moments 
are parallel. These regions apparently behave as units 
during change of magnetization. Attributed to Weiss. 
Berichtigungsfaktor: correction factor. A constant co- 
efficient, multiplication by which renders a functional 
expression approximately the correct representation of a 
variable, whereas before it was only proportional to the 
variable. 
Bernoulli'sche Gleichung: Bernoulli equation. An equa- 
in which R, A, B, a, b, c are constants determined by 
experiment for each substance. 
Beau de Rochas' Kreis: Beau de Rochas cycle. The 
thermodynamic cycle of the ordinary, four-stroke, in- 
ternal combustion engine; commonly called the Otto 
cycle. 
Beckmann Thermometer: Beckmann thermometer. A 
mercurial thermometer having a very large bulb and a 
very fine bore; used for measurements of small tem- 
perature differences. 
Becquerel Effekt: Becquerel effect. An e.m.f. observed 
in a circuit having two identical electrodes immersed 
in an electrolyte, when the electrodes are unequally il- 
luminated. 
Becquerel Membran: Becquerel membrane. A semi- 
permeable membrane produced in situ by a chemical 
reaction e.g., by the contact of solutions of sodium sul- 
fide and silver nitrate. 
Becquerel Strahlen; Becquerel rays. The radio-active 
emission from uranium compounds, discovered by Bec- 
querel in 1896 and consisting of beta and gamma rays 
from parts of uranium. 
Bedingungsgleichung; equation of condition. An equa- 
tion which must be rigorously fulfilled by a set of meas- 
ured quantities, whatever other evidence may be avail- 
able as to their values. E.g., the sum of the three 
angles of a triangle is 180 degrees, and any set of 
measurements upon them must be adjusted to meet 
that condition exactly. 
Beharrungsvermoegen: inertia. A property common 
to all forms of matter and exhibited also by electrons 
and apparently by energy (quanta) ; manifested as a 
dynamic opposition to acceleration, 
Bel: bei. A unit used to express relationship between 
two amounts of power (acoustic, electric, etc.) as an 
/Beschleunigung ß 
tion which expresses the total head of a flowing liquid, 
as follows: 
bright object to appear larger than a dark one of the 
same dimensions. 
Beta-strahlen: beta rays. An emission of electrons 
from the atoms of an element in radioactive transfor- 
mation; proceeding in part directly from the nucleus 
and in part from the X-ray levels of the outer electron 
system. 
Be+a-s+rahlen Spektrum: beta-ray spectrum. A separa- 
tion of beta particles of different speeds, usually by the 
magnetic field alone, but in some cases by both mag- 
netic and electric fields. 
Beta-transformation: beta transformation. A radioac- 
tive transformation in which the atomic nucleus loses an 
electron (beta particle). 
Beta-umwand!ung: beta transformation. See Beta- 
transformation. 
Beugung: diffraction. A term applied to a variety of 
effects produced upon wave trains, such as light or 
X-rays, by the interposition of one or more obstacles, 
as a row of parallel bars in a grating or an array of 
atoms in a crystal; characterized by more or less sys- 
tematic interference phenomena, e.g., bands, halos, or 
spot patterns. 
Beugungsgitter: diffraction grating. A device for dis- 
persing light or other wave emission by ’interference 
between wave trains issuing from fine, parallel slits in 
an opaque plate or from very narrow, parallel reflecting 
surfaces made by ruling grooves on polished metal. 
Beugungswinkel: diffraction angle. The angle between 
the direction of an incident beam of light and any re- 
sulting diffracted beam. 
Beweglichkeit: mobility. (1) Fluidity, low viscosity, 
e.g., of a liquid, or of a plastic solid beyond its yield 
point. (2) Syn. mobility coefficient. 
Beweglichkeitskoeffizient; mobility coefficient. (1) 
(Electrolytic) The average speed per unit electric field 
with which ions of a given sign move in the direction 
of the field. (2) (Molecular) The average speed of 
diffusion, in the direction of the concentration gradient, 
of the molecules in a solution, at unit concentration and 
unit solution (osmotic) pressure gradient. 
Bewegungsgleichung: equation of motion. An equation 
which gives information as to the motion of a body or 
of a point in space in terms of suitable coordinates, ex- 
pressed as functions of the time. 
p V2 
e + + = H; 
dg 2g 
in which e is the elevation above an arbitrary datum, 
p is the pressure, d the density, v the speed of flow, 
g the acceleration of gravity, and H the total head. 
The Bernoulli law states that for an unimpeded flow 
this total head H is constant. The equation appears 
also in other forms adapted to various situations. 
Beschleunigung: acceleration. (1) (Linear.) The time 
rate of change of linear velocity, i.e., the derivative of 
the linear velocity with respect to time. (2) (Angular.) 
The time rate of change of angular velocity, or its de- 
rivative with respect to time. 
lead. The opposite of lag. 
Beschleunigungszen+rum: center of acceleration. A 
point in a plane body, moving in its plane, at which 
the acceleration is momentarily zero. 
beschraenken; constrain. To limit to a predetermined 
position or path. A body has constrained motion when 
restricted by material barriers to move in a given line, 
e.g., a railroad train along its track. 
besonders starke Linie: enhanced line. A spectral line, 
from a spark or other very hot source, whose intensity 
is out of proportion with that of other lines as com- 
pared with an arc or a flame spectrum. 
Bessel'sche Gleichung: Bessel equation. A linear dif- 
ferential equation of the form 
d2y dy 
x2 -f- x -j- (x2 — a2) y zz 0 
dx2 dx 
the solutions of which are expressible as power series 
in x known as Bessel’s functions or Bessel’s integrals. 
Important in problems of heat conduction, etc. 
bestrahlen: irradiate. To subject to radiation of any 
kind. 
Bestrahlung: insolation. (1) Exposure to solar radia- 
tion. (2) The intensity of the solar radiation received 
at any point on the earth’s surface. 
irradiation. (1) The process of irradiat- 
ing. (2) A quantity defined in the same manner as 
illumination, except that it refers to any kind of radia- 
tion; quantitatively expressed as the amount of radiant 
energy received per unit time per unit area of the ir- 
radiated surface. (3) A visual illusion, which causes a 
/Beziehung 
14 Beziehung; correlation. A quantitative relationship be- 
tween two variables which, while suggesting some con- 
nection between them, is not established with sufficient 
definiteness to take on a clear-cut functional character. 
An abstract number measuring the closeness of such a 
connection is called a correlation coefficient. 
Bezugssystem: frame of reference. A set of points, 
lines, or planes used as a system of reference for de- 
fining space coordinates. 
biaxial: biaxial. Having two different optic axes. 
Biegung: flexure. A strain in which particles or points, 
normally in a straight line, are displaced into a plane 
curve, called the curve of flexure or the elastic line. 
Biegungsmoment: 
Biegemoment: bending moment, bending torque, flex- 
ural moment, flexural torque. The torque which exists 
at any point in a bent elastic rod, and to which the 
bending is due. 
Bild: image. (1) A real image of an object-point is 
the point at which light, originating in the object-point, 
is finally converged after traversing an optical system. 
(2) A virtual image of an object-point is the point 
from which light, originating in the object-point, and 
having traversed an optical system, appears to be di- 
verging. (3) The image, real or virtual, of a finite 
object is the aggregate of the images of its component 
points. (4) Also used by analogy in re the reflection 
of electric waves in conducting networks. 
Bildlinie: image-line. Syn, focal line. 
Bildpunkt: image-point. The real or virtual point of 
intersection of a pencil of rays incident upon an optical 
system. 
Bildpunkskraft: image force. The attraction between a 
charge concentrated upon a small body (esp. an elec- 
tron) and its electric image in a neighboring conductor 
(as the metal plate from which the electron has 
emerged) ; important in thermionic and photoelectric 
emission. 
Bildungswaerme: heat of formation. The heat gener- 
ated by the formation of a chemical compound per 
gram or per mol. 
Bindung: linkage. (1) A mechanical arrangement of 
solid pieces connected by movable joints, used for im- 
parting motion of a desired character; e.g., in the me- 
chanism which controls the valves of a steam engine. 
(2) (Magnetic) A measure of the interlocking of a 
magnetic flux with an electric circuit, viz., the product 
of the flux by the number of turns of the circuit sur- 
rounding it, expressed in maxwell-turns. (3) A chemi- 
cal bond between atoms and molecules. 
Bindungsenergie: binding energy. A quantity of en- 
ergy supposed to be released upon the formation of an 
atom or a molecule from alpha particles, protons, elec- 
trons, etc., at the expense of the total mass. 
Bindungskraft: bonding power. A measure of the effect, 
positive or negative, contributed by a shared electron in 
a molecule to the attraction or repulsion between atoms 
in the molecule. 
Bindungsmoment: bond moment. The dipole moment 
associated with a chemical bond in a polar molecule. 
Bindungswaerme: heat of linkage. The energy required 
to break any chemical bond. It includes the heat of 
dissociation of a diatomic molecule as a special case. 
Binnendruck: internal pressure. A pressure supposed 
to exist within a fluid because of its cohesion, and which 
cooperates with the external pressure to maintain equi- 
librium against the expansive effect of heat. 
Binokularprisma: prism binocular. A type of binocular 
field glass, each telescope of which contains two right- 
angled prisms (Porro prisms) so placed as to secure 
at the time the erection of the image, a shorter tube, 
and greater stereo power than an ordinary binocular. 
Biolumineszenz: bioluminescence. The emission of light 
by living organisms, as the firefly, certain fungi, and 
many marine forms. 
Biophysik: biophysics. A term used in reference to 
the physical processes taking place in living organisms. 
Biot-Savar+'sche Krakf: Biot-Savart force. Syn. Lorentz 
electromotive force. 
Biof-Savar+'sches Gesetz: Biot-Savart law. States that 
the magnetic intensity due to a current i (abamp) in 
an infinitely long, straight wire, at a point distant p 
from the wire, is 
2i 
H = 
P 
Bipartitionswinkel: bipartition angle. The angle between 
a beam of X-rays passing through a layer of material 
and the conical surface (the bipartition cone) which 
contains paths of half the electrons ejected from the 
layer by the rays. 
Biprisma: biprism. A glass prism of almost 180 de- 
grees vertex angle, devised by Fresnel, to produce a 
677865—46 2 
15 
/bipolare Elektrode B 
virtual-image double source for Young’s interference 
experiment; applied also to similar devices for produc- 
ing double-image fields in spectrophotometers, etc. 
bipolare Elektrode: bipolar electrode. A conducting 
partition placed across an electrolytic cell, so that one 
surface acts as an anode, and the other as a cathode. 
Biquarz: biquartz. A plate made up of two semi-cir- 
cular pieces, one of dextrogyrate, the other of levogyrate 
quartz, of equal thickness, and cemented together along 
tne diameter; used for demonstrating polarization tints. 
Blackburn Pendel: Blackburn pendulum. An apparatus 
consisting of a pendulum which may swing with differ- 
ent periods in two directions at right angles. Used in 
studying harmonic motions. 
blaues Leuchten: blue glow. (1) A type of thermo- 
luminescence emitted by certain metallic oxides, e.g., 
MgO and BeO, when heated. (2) The bluish luminosity 
of the gas near the cathode in a Geissler tube, esp. 
when the gas is air. 
Blockierungspotential: stopping potential. A p.d. suffi- 
cient to stop the outward movement of photoelectrons 
or thermions, and used in the determination of the 
speed of the emission. 
Blockkondensator: stopping condenser. A condenser in 
series with some branch of a circuit, the purpose of 
which is to introduce a comparatively high impedance 
and thus cut down the direct or low-frequency current 
without materially effecting the h.-f. component. 
Bogenspektrum: arc spectrum. The spectrum of a sub- 
stance produced with light from an electric arc into 
which the substance is introduced. 
Bohr-Grotrian'sches Diagramm: Bohr-Grotrian dia- 
gram. One form of diagrammatic representation of the 
energy levels in an atom. 
Bohr'sche Frequenzregel: Bohr frequency rule. Syn. 
frequency conditions. 
Bohr'sches Atom: Bohr atom. The atom as conceived, 
by Bohr and Rutherford, to consist of a positive 
nucleus about which circulate a number of "orbital” 
electrons. 
Bolograph: holograph. A recording bolometer; or the 
photographic record produced by it. The latter has also 
been called a hologram. 
Bolometer: bolometer. A very sensitive type of me- 
/Bourdon'sches Ventil 
tallic resistance thermometer, used for measurements of 
thermal radiation. Devised by Langley. 
Bol+zmann'sche En+ropiehypothese: Boltzmann entropy 
hypothesis.. The assumption that the entropy of a system 
of material particles is proportional to the logarithm of 
the statistical probability of the distribution. 
Boltzmann'sche Konstante: Boltzmann constant. The 
(molar) ideal gas constant divided by the Avogadro 
number. Its value is about 1.371xlO~~10 erg/degree. 
Boltzmann'sche Maschine: Boltzmann engine. An ideal 
thermodynamic apparatus operating in cycles and having 
imprisoned radiation corresponding to a working sub- 
stance; visualized by Boltzmann in the theoretical de- 
duction of the Stefan-Boltzmann law. 
Boltzmann'scher Faktor: Boltzmann factor. A correc- 
tion factor applied to calculated line intensities in spectra 
due to thermal excitation. 
Boltzmann'sches Prinzip: Boltzmann principle. In re 
the equilibrium distribution of particles subject to ther- 
mal agitation in a field of force: states that the number 
of particles per unit volume at any point in the field is 
E 
N = N0e 
kT 
in which E is the potential energy of a particle at that 
point, N0 is the number where E is zero, T is the 
absolute temperature, and k is the Boltzmann constant. 
Bombenkalorime+er: bomb calorimeter. A fuel calori- 
meter in which the combustion takes place inside a 
"bomb.” 
Borda Mundstueck: Borda mouthpiece. A type of re 
entrant orifice, viz., a tube extending inward from a 
discharge orifice, which has the effect of modifying the 
conditions of flow. 
Bosanquet'sches Gesetz: Bosanquet law. States that 
the magnetic flux in maxwells, in a magnetic circuit is 
equal to the magnetomotive force, in gilberts, divided 
by the magnetic reluctance, as formerly expressed in 
oersteds. Also known as the Rowland law. 
Bose-Elnstein Statistik: Bose-E/nstein statistics. A sys- 
tem of statistical analysis of the distribution of gas 
molecules or of radiation quanta and their momenta, 
based upon the number of elementary compartments of 
ordinary space and of momentum space having each a 
given number of the respective entities. 
Bouguer Formel: Bouguer formula. A formula for the 
variation of gravity with altitude. If g0 is the sea-level 
16 B 
value at the latitude of the station, R the radius of the 
earth at that station, d the local crust density and dm 
the mean density of the earth, then the value of gravity 
at the altitude h is given by 
Bragg'sches Gesetz: Bragg law. An expression for the 
condition under which a system of parallel atomic layers 
in a crystal will reflect a beam of X-rays with maximum 
intensity. If d is the distance between the layers, ® the 
glancing angle, and A the wave length of the X-rays, 
the condition is 
2dsin® = NA; 
in which N must be a whole number. 
Bravais-Miller'scher Index: Bravais-Miller index. One 
of the four numbers (h, k, f, 1) used to designate any 
set of parallel planes in a crystal belonging to the 
hexagonal system. 
Braun'sche Roehre: Braun tube. An early type of 
cathode-ray oscillograph tube requiring a potential of 
several thousand volts for operation. 
brechbar: refrangible. Capable of being refracted, or 
measurably deviated by refraction. 
Brechbarkeit: rejractivity. The refractive index minus 
1. 
Brechkraft: focal power. In re a symmetrical optical 
system: a measure of the effect of the system upon the 
focus of a pencil of rays traversing it. If the rays are 
incident in air, the focal power is the reciprocal of the 
focal length for rays coming from the given direction; 
in general, ’it is the product of this reciprocal by the 
refractive index of the medium. 
Brechungsindex: extraordinary index. See ausserordent- 
licher Index. 
index of refraction, refractive index. 
The ratio of the speed of a refracted radiation before 
refraction to its speed after refraction. If the radiation 
passes from a vacuum into a substance, this ratio is 
termed the absolute index of the substance; if from 
one substance into another, the relative index of the two 
substances. 
Brechungswinkel: angle of refraction. The angle be- 
tween the direction of propagation of a refracted emis- 
sion and the normal to the refracting surface. 
Bremspotential: stopping potential. See Blockierungs- 
potential. 
Bremsvermoegen: stopping power. (1) The effect of 
a layer of matter upon the motion of alpha particles, 
expressed in terms of the thickness of ordinary air 
which would have the same effect. (2) The mass per 
cm2 of a given filter which is equivalent to 1 cm of air 
in reducing the speed of alpha particles. (3) For a 
gas: the ratio of the range of alpha particles in the 
given gas to that in air at N.T.P. 
/ 2h 3dh \ 
g = go + 
This formula has been criticized and amended by Faye. 
Bourdon'sches Ventil: Bourdon gauge. A pressure 
gauge depending upon the deformation of a curved tube 
of elastic metal, of elliptic cross-section to the interior 
of which the pressure is applied. 
Boyle-Charles Gesetz: Boyle-Charles law. A combi- 
nation of Boyle’s law for the pressure-volume relation 
and Charles’ law for the temperature-volume relation in 
an ideal gas, viz., 
Pv = Povo 0 + at)- 
Boyle'sches Gesetz: Boyle law. The statement, at- 
tributed to Robert Boyle (1662), that in a body of gas 
maintained at constant temperature, the volume and 
the pressure vary in inverse ratio, i.e., have a constant 
product. 
Brachistochron: brachistochrone, brachystochrone. The 
path of constraint along which a particle, under the 
action of a given force, will move from one given 
point to another given point in the least time. 
Brackett Serie: Brackett series. A spectral series in 
the infrared of the hydrogen spectrum, whose frequen- 
cies are multiples of 
f -2 — ] 
V 42 n2 / 
where n = 5, 6, 7, 
Bragg-Pierce'sches Gesetz: Bragg-Pierce law. States 
that the true atomic absorption coefficient (scattering 
omitted) of an element of atomic number Z for X-rays 
of wave length A is represented by 
IM = CZ4A5/2 
the value of C changing abruptly at wave lengths of 
absorption lines. Bragg later changed the exponent of 
A to 3. 
Bragg'sche Reflektion: Bragg reflection. The rein- 
forced reflection of X-rays from the successive atomic 
planes of a crystal, or of electrons from the grating-like 
structure of its surface. 
Bragg'scher Winkel: Bragg angle. The glancing angle 
for X-rays at the reflecting planes of a crystal. 
17 
/Brennpunkt B 
Brennpunkt: focal point. In re a symmetrical optical 
system: one of the two points on the axis which are 
conjugate to the axial points at infinity in opposite 
directions. An incident pencil of paraxial rays through 
the first focal point emerges as a cylindrical bundle, 
while an incident cylindrical bundle emerges as a pen- 
cil through the second focal point. These points may 
be real or virtual. 
Brennpunk+abstand: focal length. The distance of 
either of the two principal points of a symmetrical opti- 
cal system from the corresponding focal point. 
Brennpunktsebene: focal plane. The plane passing 
through either focal point of an optical system, perpen- 
dicular to the axis of the system. 
Brennpunktskollimator: focal collimator. A type of col- 
limator consisting of an objective lens at one end of a 
tube and a pair of cross hairs placed accurately in its 
focal plane at the other end. 
Brennpunktslinie: focal line. One of the two very short 
lines in the principal sections, i.e., sections made by the 
principal planes of a narrow astigmatic bundle of light 
rays; characterized by the fact that (according to Sturm) 
all of the rays intersect these two lines. 
Brewster'sches Gesetz: Brewster law. States that the 
polarizing angle of a reflecting dielectric for light of 
any wave length is equal to the angle whose tangent 
is the refractive index of the dielectric for that wave 
length. Discovered by Brewster in 1815. 
Brillianz: brilliance. That attribute of any color which 
permits it to be classed as equivalent to some member 
of the series of achromatic colors, or grays. Thus bright 
red is more brilliant than dark red. 
Brillouin Effekt: Brillouin effect. A pair of spectral 
satellites appearing in radiation scattered by liquids, 
one on each side of the unmodified line at a separation 
of about 0.04 Ä. Also known as the Debye-Sears effect. 
Brillouin Zone: Brillouin zone. A continuous ensemble 
of all energies and wave functions which may be ob- 
tained from one atomic energy level in a metallic- 
crystal lattice. 
Brinnell Haerfe: Brinell hardness. The hardness of a 
substance as measured by the force which must be ex- 
erted upon it by a rigid sphere of given radius to 
produce an indentation of given area. 
Britische'Waermeeinheit: British thermal unit. A unit, 
defined as that quantity of heat which is required to 
raise the temperature of one pound of water 1 degree 
Fahrenheit. Equivalent to about 252 (g) cal. 
Bronson Widerstand: Bronson resistance. A high re- 
sistance consisting of two electrodes in a gas made con- 
ducting by a constant source of ionization. 
Brown'sche Bewegung: Brownian movement. An er- 
ratic, zigzag motion exhibited by very small particles 
suspended in a liquid or a gaseous medium, due to 
thermal agitation of the molecules of the medium. Dis- 
covered by Brown (a botanist) in 1827. 
Bucldey'sches Ventil: Buckley gauge. A type of ioniza- 
tion gauge for measuring very low gas pressures. 
Bueschelentladung: brush discharge. An electric dis- 
charge in a gas, intermediate between a glow discharge 
and a spark, and composed partly of minute sparks. 
Bunsenkoeffizient: Bunsen coefficient. The solubility of 
a given gas in a given liquid at N.T.P., expressed in 
terms of volume of gas absorbed per unit volume of the 
solution. 
Bunsenschirm: Bunsen screen. A photometer screen 
consisting of a diaphragm of paper or parchment with 
a translucent central spot. 
/Callendar-Griffi+hs Bruecke 
18 c 
Callendar-Griffiths Bruecke: Callendar-Griffiths bridge. 
A type of slide-wire resistance bridge especially de- 
signed for use in resistance thermometry. 
Callendar'sche Gleichung: Callendar equation. A char- 
acteristic equation for steam, given by Callendar in the 
form 
Carnot Theoreme: Carnot theorems. See Carnot’sche 
Lehrsaetze. 
Cassegranischer Spiegel: Cassegranian mirror. A con- 
vex second mirror placed in front of the concave ob- 
jective in one form of reflecting telescope. It produces 
an image in a tube inserted at the center of the objec- 
tive mirror, where the eyepiece is located. 
Cauchy'sche Dispersionsformel: Cauchy dispersion for- 
mula. An approximate empirical formula for the refrac- 
tive index n as a function of the wave length, 
RT 
v - + b — c, 
P 
in which b is a constant and c a function of T. 
Campbell-Colpitts'sche Bruecke; Campbell-Colpitts 
bridge. A shielded a.=:c. bridge for the measurement 
of capacitance, using a substitution method. 
Candolumineszenz: candoluminescence. The lumines- 
cence of an incandescent body, as distinguished from the 
visible radiation due to temperature alone. 
Carcel Einheit: Carcel unit. A French unit of lumi- 
nous intensity, defined as one-tenth of the output of 
the Carcel lamp, which burns colza oil. It is approxi- 
mately 0.96 international candle. 
Carey-Foster'sche Bruecke: Carey-Foster bridge. A 
type of Wheatstone-bridge circuit for measuring the 
difference between two nearly equal resistances, in which 
the two ratio arms are coils connected by a slide wire. 
Carhart-Clark'sche Zelle: Carhart-Clark cell. A modi- 
fication of the Clark cell, having a lower temperature 
coefficient. 
Carnot-Clausius'sche Gleichung: Carnot-Clausius equa- 
tion. The equation <p dq/T = 0, in which dq is the 
quantity of heat taken in by a body, or a system, during 
an infinitesmal, reversible change of state and T is the 
absolute thermodynamic temperature of the system while 
it is receiving dq. The changes of the state form a 
reversible closed cycle. 
Carnot'sche Lehrsaetze: Carnot theorems. Two propo- 
sitions of thermodynamics: (1) No heat engine work- 
ing between two temperatures can have greater efficiency 
than a reversible engine working between those tem- 
peratures. (2) The efficiency of any reversible heat 
engine working between two temperatures is indepen- 
dent of the nature of the engine or of the working 
substance and depends only upon the temperatures. 
Carnot'scher Kreisprozess: Carnot cycle. A closed 
cycle of reversible changes in the state of a body, con- 
sisting of an isothermal expansion, an adiabatic expan- 
sion, an isothermal compression, and an adiabatic com- 
pression in the cyclic order stated. The concept was 
introduced by Carnot in 1824. 
B C 
n - A + + + . . . , 
A2 A4 
in which A, B, C, . . are constants depending upon 
the refracting medium. 
Cavendish'scher Versuch: Cavendish experiment. The 
measurement of the gravitation constant by means of a 
torsion balance, originally carried out by Cavendish. 
Celsius Skala: Celsius scale. The original of the centi- 
grade scale, but inverted, i.e., with freezing point at 100 
degrees and boiling point at 0 degrees. 
Cent: cent. A musical interval, or ratio between fre- 
quencies, whose value is the 1200th root of 2. It fol- 
lows that the interval between any two successive notes 
of the equally tempered scale is the 100th power of the 
cent (expressed as 100 cents). 
C. G. S.-System: c.g.s. system. The centimeter-gram- 
second system of physical units, i.e., those based upon 
these fundamental units of length, mass, and time. E.g., 
the erg is a c.g.s. unit of work. 
Chadwick-Goldhaber'scher Effekt; Chadwick-Gold- 
haber effect. The dissociation of an atomic nucleus by 
the absorption of gamma rays. 
charakteristische Flaeche: characteristic surface. The 
(three-dimensional) graph of a characteristic equation. 
charakteristische Gleichung: characteristic equation. 
An equation connecting the variables used to define the 
physical state of a body, such as volume, pressure, and 
temperature, e.g., the van der Waals equation, with 
constants characteristic of the gas. 
charakteristische Leitfaehigkeit: characteristic conduc- 
tivity. In re a photoelectric cell: the value of 
di/dE, 
i 
where E is the voltage on the cell and i is the current 
19 
/charakteristische Temperatur c 
at constant illumination; expressed as the percentage 
increase in current per volt increase in impressed e.m.f. 
charakteristische Temperatur: characteristic tempera- 
ture. The temperature at which the atomic heat of a 
simple cubic crystal attains the value 5.67 calories per 
degree. According to Einstein, it is given by the for- 
mula Td — hvm/k, in which vm is the maximum fre- 
quency in the vibration spectrum (atomic frequency), 
h is the Planck constant, and k is the Boltzmann con- 
stant. First introduced in connection with the variation 
of specific heat with temperature. 
Charles'sches Gesetz: Charles’ law. States that the 
coefficients of expansion of all perfect gases are equal, 
their common value being such as to indicate that the 
volume varies in direct proportion to the absolute tem- 
perature. First discovered by Charles in 1787. 
Chattock'scher Manometer: Chattock gauge. A type 
of differential manometer, utilizing the difference in 
pressure of two columns of liquid of nearly equal den- 
sity. 
Chemilumineszenz: chemiluminescence, chemicolumi- 
nescence. Luminescence produced by chemical action; 
e.g., the emission of light due to the slow oxidation of 
phosphorus at ordinary temperatures. 
chemisches Aequivalent: chemical equivalent. The 
atomic weight of an element, or the radicular weight 
of an ion, divided by its valence. 
Chladni'sche Platte: Chladni plate. A metal plate of 
regular form, which, when set into vibration by means 
of a violin bow or otherwise, exhibits nodal lines in 
various symmetrical patterns. 
Christiansen Filter: Christiansen filter. A device con- 
sisting of a coarse powder of some homogeneous, iso- 
tropic, transparent solid between parallel glass plates, 
the interstices being filled with a liquid whose refractive 
index is equal to that of the powder for a certain wave 
length. This wave length only is then transmitted with- 
out deviation and can be brought to a focus by a lens. 
chromatische Farbe: chromatic color. A color which 
exhibits hue. 
chromatische Skala: chromatic scale. Syn. equally tem- 
pered scale. 
Chromel: chromel. An alloy of nickel and chromium, 
of high resistivity and high melting point; used for 
resistance coils. 
Chronograph: chronograph. A mechanism for record- 
ing time signals on a revolving drum or moving tape; 
used for the precise measurement of time intervals. 
Chronoskop: chronoscope. (1) A type of chronograph 
which measures short intervals of time by comparison 
with the period of a tuning fork or similar vibrator. 
(2) Any short-interval timer, as a stop watch. 
Clairot-Helmert'sche Formel: Clairot-Helmert formula. 
A formula for the variation of gravity with latitude A: 
g - 978.00 (1 + 0.005310sin2A) 
Clapeyron'sche Gleichung: Clapeyron equation. A 
formula expressing the latent heat H of a vapor with 
the increase in volume during vaporization, in work 
units, thus: 
TSp 
H = (v - v0) 
ST 
v — v0 is the increase of volume, p and T are pres- 
sure and temperature. Also called the Clausius-CIapey- 
ron equation. 
Clark'sche Zelle: Clark cell. A standard cell for 
measurements of e.m.f., having positive and negative 
electrodes of mercury and zinc amalgam, respectively 
with zinc sulphate as electrolyte. 
Clausius-Clapeyron'sche Gleichung: Clausius-Clapey- 
ron equation. See Clapeyron’sche Gleichung. 
Clausius-Mosotti'sches Gesetz: Clausius-Mosotti law. 
A relation between the density d and the dielectric con- 
stant k of a given dielectric: 
k - 1 
= constant. 
(k + 2)d 
It is closely connected with the polarizability, and is 
allied to the Lorenz-Lorentz relation. 
Clausius'sche Gleichung: Clausius equation. (1) A 
differential equation connecting the specific heat at 
constant pressure, Cp, of a fluid body, with its volume v; 
fiM = _ (üm , 
\ 8p / @ \ 802 I p 
in which p is the pressure and 6 the (Kelvin) absolute 
temperature. An analogous and equally important re- 
lation is 
(iEi ] = - » -5 , 
V 8v j @ S®2 „ 
(2) An equation relating to equilibrium between a 
liquid and its saturated vapor: 
/ H \ 
s — s = ® j I , 
d® V 0 / 
/Cleanup 
20 c 
in which s and s' are the specific heats of liquid and 
vapor, respectively, and H is the heat of vaporization. 
(3) An empirical, characteristic gas equation, of the 
form 
tube, the distinctive feature of which is a cathode con- 
taining a hot filament to furnish cathode-ray electrons 
by thermionic emission. 
Corbino Effekt: Corbino effect. A form of the Hall 
effect in which, when a current is sent from center to 
circumference of a metal disk through a magnetic field 
normal to the disk, there is also a current flowing cir- 
cumferencially. Discovered by Corbino in 1911. 
Coriolis Beschleunigung: complimentary acceleration. 
An acceleration which must be vectorially added lo 
the sum of the acceleration of a moving particle with 
respect to a body of reference and the absolute accelera- 
tion of the body of reference, to give the absolute 
acceleration of the particle. It is equal to twice the 
vector product of the angular velocity of the body of 
reference and the linear velocity of the particle with 
respect to it (theorem of Coriolis). 
Coriolis Kraft: Coriolis force. The force corresponding 
to the complimentary acceleration to which Cariolis 
theorem refers. 
Coriolis Lehrsatz: Coriolis theorem. See Coriolis Be- 
schleunigung. 
Cornu'sche Spirale: Cornu spiral. The limiting curve 
approached by a succession of vector lines whose lengths 
and directions represent, respectively, the amplitudes 
and phases of the light vibrations reaching any point 
from successively more remote areas of a wave front. 
Cornu'sches Prisma: Cornu prism. A 60 degree quartz 
prism divided into halves, of right- and left-handed 
quartz, respectively, in order to neutralize the effect of 
optical rotation. 
Co+fon-Mou+on'scher Effekt: Cotton-Mouton effect. 
The acquisition of double refraction by some pure 
liquids when subjected to a magnetic field whose di- 
rection is transverse to the beam of light, a magneto- 
optical effect investigated by Cotton and Mouton in 
1905. 
Cotton-Mouton'sches Gesetz: Cotton-Mouton law. If 
np and ns are the refractive indices for light polarized 
in planes parallel and perpendicular, respectively, to 
the magnetic intensity H, then 
np — ns — CaH2. 
Here C is constant for any fixed temperature and any 
fixed (air) wave length A; it is called the Cotton-Mou- 
ton constant for the given substance, wave length, and 
temperature, and maye be (-j- ) or (— ). 
Cotton'sche Waage: Cotton balance. An apparatus 
[ P + 1 (v — b) = RT, 
L T(v + c)2J 
which has been found to represent the behavior of some 
gases somewhat better than either the Boyle or the van 
der Waals equation. 
Cleanup; cleanup. The gradual disappearance of gases 
from a discharge tube during its operation. 
Coehn'sches Gesetz: Coehn law. States that in the phe- 
nomenon of electric osmosis between dielectric, the sub- 
stance having the greater dielectric constant becomes 
charged to a potential higher than that of the other 
by an amount proportional to the difference in their di- 
electric constants. 
Compoundwicklung: compound-wound. In re the field 
magnet of a motor or a generator: having its windings 
partly in series and partly in parallel with the external 
or line circuit. 
Compton Effekt: Compton effect. A phenomenon of 
scattering of X-rays or gamma rays by the electrons in 
matter, in which the scattered radiation is characterized 
by a systematically smaller frequency of quantum value 
with increasing deviation from the original direction. 
A spectrum line whose frequency is less altered is called 
a modified line, while that part of the radiation of any 
frequency which is scattered without change of fre- 
quency gives rise to an unmodified line of the Compton 
spectrum. 
Compton Elektron; Compton electron. An electron 
having momentum due to the impact of a high-energy 
radiation quantum. 
Compton Gleichung: Compton equation. An expres- 
sion for the Compton shift, viz., 
h 
AA = (1 — cos ®), 
me 
in which ® is the scattering angle, m the electronic 
mass, h the Planck constant, and c the electromagnetic 
constant. 
Compton Verschiebung: Compton shift, C. wave 
length. The change in wave length of an X-ray quantum 
upon scattering by impact with an electron. 
Coolidge Roehre: Coolidge tube. A type of X-ray 
21 
/Coulomb c 
for measuring magnetic intensity. A horizontal wire 
carrying a known current is suspended, at right angles 
to the horizontal field, from one arm of a balance, and 
the resulting vertical force on the wire thus measured. 
Coulomb: coulomb. The practical unit of quantity of 
electricity. The absolute coulomb is 1/10 of the abcou- 
lomb. The international coulomb is the international 
ampere-second, i.e., that quantity of electricity whose 
transfer accompanies the electrolytic deposit of 0.001118 
g of silver from a solution of silver nitrate. The ratio 
of the international to the absolute coulomb is about 
0.99995, and either is approximately equal to 3x10° 
e.s.u. charge. 
Coulombme+er: coulombmeter, coulometer. An instru- 
ment for the measurement of a quantity of electricity 
by the amount of electrodeposition produced from an 
electrolyte. 
Coulomb'sches Feld: Coulomb field. An electric field 
due to a charge acting as if concentrated at a point, so 
that the field intensity is inversely proportional to the 
square of the radial distance from the point. 
Coulomb'sches Gesetz: Coulomb law. A law which 
expresses the attraction or repulsion between two elec- 
tric charges or two magnetic poles as proportional to the 
product of the charges or pole strengths and inversely 
proportional to the square of the distance between them. 
Coulomb'sche Torsionswaage: torsion balance. One 
of a variety of instruments which measure small torques 
by their torsional effect upon elastic filaments or wires. 
Crookes'scher Dunkelraum: Crookes dark space. Syn. 
Cathode dark space. 
Crookes'sche Roehre: Crookes tube. One of various 
early forms of vacuum tube, used by Sir William 
Crookes in his studies of electrical discharge at low 
pressures. 
Crookes'scher Strahlungsmesser: Crookes radiometer. 
An apparatus consisting of a set of vanes polished on 
one side, blackened on the other, and delicately pivoted 
to rotate by the inequality of gas pressure on opposite 
sides when exposed to radiation. 
Crookes'scher Radiometer: Crookes radiometer. See 
Crookes’scher Strahlungsmesser. 
Crova'sche Wellenlaenge: Crova wave length. That 
wave length in the spectrum of a radiator at any given 
temperature T whose intensity i* varies at the same 
relative rate as does the intensity I of the total radia- 
tion or of a specified portion of it; i.e., the value of A 
for which 
dü/dT dl/dT 
U ~~ I 
Curie: curie. A unit quantity of radium emanation or 
radon, defined as that quantity which is in equilibrium 
with 1 g Ra. Its volume at N.T.P. is about 0.63 mm3. 
Curie Punkt: Curie point. The temperature chosen to 
characterize the change from ferromagnetic to paramag- 
netic behavior, when this does not correspond to an 
allotropic transformation. It may be interpreted graph- 
ically in terms of the temperature-magnetization curve 
or as a constant temperature in the Curie-Weiss law. 
Curie'sche Konstante: Curie constant. The product of 
the atomic or molar magnetic susceptibility of a para- 
magnetic substance obeying the Curie law by the ab- 
solute temperature. 
Curie'sches Gesetz: Curie law. States that the mag- 
netic susceptibility of a paramagnetic substance varies 
inversely as the absolute temperature. (P. Curie, 1895.) 
Not generally valid. 
Curie'sche Waage: Curie balance. A torsion balance 
used to measure the force on a nonferromagnetic body 
in the non-uniform magnetic field. Devised by P. Curie 
(1895). 
Curie-Weiss'sches Gesetz: Curie-Weiss law. States 
that the magnetic susceptibility of a paramagnetic sub- 
stance varies inversely as the excess of its temperature 
above a certain fixed temperature characteristic of the 
substance, viz., the Curie point. It is valid only for 
temperatures above this point. (P. Weiss, 1907). 
/d-Elektron 
22 D 
d-Elek+ron: d-electron. An orbital electron whose en- 
ergy state is denoted by the azimuthal quantum num- 
ber 2. 
D Linien: D lines. The principal lines of the sodium 
spectrum, which form a doublet; distinguished as Dx 
(5895.93Ä) and D2 (5889.96Ä) in air. 
D-Zustand: D-state, D-level. The state of an atom 
in which the azimuthal quantum number is 2. 
Daempfungsfak+or: damping factor. The ratio of the 
amplitude of any one of a series of damping oscillations 
to that of the following one. 
Daempfungskoeffizient: damping coefficient. (1) In 
re a train of damped oscillations: the logarithmic decre- 
ment divided by the period, or multiplied by the fre- 
quency. (2) The force required, per unit speed, to 
propel a particle, an ion, an electron, etc., through a 
resisting medium. 
Daempfungskons+an+e: damping constant. A constant 
factor appearing in the exponent of the time function 
of an exponentially damped variable. E.g., the current 
in an inductive circuit after the sudden removal of a 
steady e.m.f. is 
Dampf: vapor. A gaseous substance at a temperature 
below the critical temperature. 
Dampf dichte: vapor density. (1) The density of a 
vapor in the usual mass and volume units. (2) The 
ratio of the density of a vapor or of a gas to that of 
hydrogen at the same temperature and pressure. 
Dampfdruck: vapor pressure. The pressure of the 
vapor of the liquid kept in confinement so that the 
vapor can accumulate above it. At any temperature it 
approaches a fixed maximum limit, called the maximum 
vapor pressure or saturated v.p., dependent only upon 
the liquid and the temperature. 
Dampfdruckkonstante: vapor-pressure constant. A con- 
stant term which appears in the formula for the loga- 
rithm of the vapor pressure of a liquid in terms of 
temperature in accordance with thermodynamic theory. 
Dampfdruckmesser: tensimeter. An apparatus for 
measuring vapor pressure. 
vaporimeter. An instrument for 
measuring vapor pressures of volatile liquids. 
Dampfdruckthermometer: vapor-pressure thermometer. 
A thermometer whose indications are based upon the 
maximum vapor pressure of a liquid. 
Dampfkalorimeter: steam calorimeter. A calorirneter 
in which a known quantity of heat is imparted by the 
condensation of a known mass of steam. Developed by 
Joly. 
Dampfmaschinenindikator: steam-engine indicator. An 
instrument which, connected with the cylinder of a 
steam engine, automatically draws a trace of the volume- 
pressure cycle. 
Dampftabelle: steam table. A table giving certain 
properties of steam as functions of the temperature or 
the pressure; including usually the density, specific 
volume, heat or vaporization, etc. 
Darcy'sches Gesetz: Darcy law. States that the veloc- 
ity of flow of a fluid in a porous medium, due to in- 
equality of pressure, is proportional to the pressure 
gradient. 
d'Arsonval'sches Galvanometer: d’Arsonval galvano- 
meter. A form of d.—c. galvanometer, consisting of a 
narrow, rectangular coil freely suspended so as to turn 
between the poles of a fixed, permanent magnet. 
Darwin-Ewald-Prins'sches Gesetz: Darwin-Ewald-Prins 
law. A somewhat complicated expression for the dif- 
_ 
i — i e L 
here the damping constant is R/L. 
d'AIembert'sches Prinzip: d’Alembert principle. (1) 
States that all the forces acting upon parts of a system 
form, with the inertia reactions against acceleration, an 
equilibrating set of forces on the system as a whole. 
Newton’s third law may thus be regarded as applying 
to cases in which there is acceleration, the reactions due 
to inertia functioning as opposing forces and setting up 
a condition of kinetic equilibrium. First explicitly stated 
by d’Alembert in 1742. (2) The principle that any 
displacement of a particle subject to constraints is neces- 
sarily perpendicular to the resultant of the constraining 
reactions. 
Dalton'sches Gesetz: Dalton law. States that when 
several gases which have no chemical action upon each 
other are mixed in the same enclosure, the pressure of 
the mixture is equal to the sum of the pressures which 
the gases would separately exert if each in turn were 
confined in the same space; and further, the saturated 
vapor pressure of two or more liquids exposed separately 
in the same closed space, each in equilibrium with its 
liquid, is, within limits, equal to the sum of the separate 
vapor pressures. Based upon the experiments of Dalton 
(1802). 
23 
/Davisson-Germer'sher Versuch D 
fraction pattern formed by the reflection of X-rays from 
a crystal; developed independently but in essentially 
equivalent forms by Darwin and Ewald and subse- 
quently modified by Prins. 
Davisson-Germer'scher Versuch; Davisson-Germer ex- 
periment. An experiment in which was first observed 
the diffraction of a stream of electrons at the surface 
of a metallic crystal, thus providing evidence in support 
of the wave-mechanical theory of electrons. 
de Broglie Frequenz: de Broglie frequency. The fre- 
quency associated with the energy of the moving elec- 
tric particle, and equal to that energy divided by the 
Planck constant. 
de Broglie Gleichung: de Broglie equation. An ex- 
pression for the wave length of the de Broglie wave 
associated with a moving electron; 
Debye Temperaturfak+or: Debye temperature factor. 
Syn. Debye-Waller factor. 
Debye-Waller'scher Faktor: Debye-Waller factor. See 
Debye Faktor. 
Deformation: strain. (1) The change in the relative 
positions of the particles of a substance, which accom- 
panies the deformation of the body or specimen of the 
substance in question. Strains may be analyzed into 
certain elementary types, as elongation, rectilinear com- 
pression, shear, torsion, volume expansion, and volume 
compression. (2) Syn. deformation, and applied to 
the external form rather than to the substance. 
Deformationsachsen: strain axes. Three mutually per- 
pendicular lines through any point of an elastic solid, 
which remain mutually perpendicular when the solid is 
subjected to strain. 
Deformationsdruck: stress. A quantity measured by 
the force per unit area exerted by one portion of a 
strained elastic substance upon a contiguous portion, 
and which is due to the external forces responsible for 
the deformation; e.g., tensile stress, compressive s., 
shearing s., pressure, etc. 
Deformationskraeftepaar: stress couple. A couple due 
to the integrated stress over any cross section of a bent 
elastic rod or beam; equal and opposite to the bending 
moment. 
Deforma+ionsellipsoid: strain ellipsoid. The ellipsoid 
resulting from the strain of a small portion of matter 
which, in its unstrained condition, was spherical. 
Deformierbarkeit: deformability. The electric or di- 
pole moment induced in a molecule by an electric field 
of unit intensity. 
degeneriertes System: degenerate system. (1) A vi- 
bratory physical system, one or more of whose periodic 
variables have ceased to vary through an increase of its 
period to infinity. (2) In quantum mechanics, a system 
which has several distinct wave functions corresponding 
to the same energy level. 
Dehnungswaerme: heat of elastic extension. The heat 
generated per unit mass per unit change of tensile strain 
in the stretching of an elastic solid. 
Dekadenbruecke: decade bridge. A type of Wheat- 
stone bridge in which the values of the ratio coils are 
decimal multiples of an ohm, so that when the bridge 
is balanced, the value of the unknown is a decimal 
multiple or a decimal fraction of the bridge reading. 
Dekantieren: levigation. See Abschlemmen. 
h . /150 volts 
A = = 10-8cm \ ; 
mv V 
in which V is the potential drop, in volts, necessary 
to give the electron its speed and energy, mv is the 
momentum of the electron, and h is the Planck constant. 
de Broglie Welle: de Broglie wave. A wave or wave 
group assumed in wave mechanics to be associated with 
an elementary particle (electron, proton). 
Debye Effekt: Debye effect. A selective absorption of 
Hertzian waves in certain dielectric media, due pre- 
sumably to the existence of molecular dipoles. 
Debye Faktor: Debye factor. The quantity M ap- 
pearing in the Debye relation F = fe~M between the 
F-value and the f-value of an atom in a crystal. Debye’s 
calculation of M was later modified by Waller. 
Debye Funktion: Debye function. An expression for 
the specific heat of a monatomic crystalline solid at 
absolute temperature T, viz., 
/ T \3 t Tp x4exdx 
Q = 9nk ( ) T 
V To / Jo (ex — I)2 
in which n is the number of atoms, k the Boltzmann 
constant, and To the Debye characteristic temperature. 
Debye'sche charakteristische Temperatur: Debye char- 
acteristic temperature. See charakteristische Temperatur. 
Debye-Scherrer Ring: Debye-Scherrer ring, D.-S. cir- 
cle. Syn. powder pattern, Hull ring. 
Debye-Sears Effekt: Debye-Sears effect. Syn. Brillouin 
effect. 
/Deklination 
24 D 
Deklination: declination. (1) (Mag.) The angle be- 
tween the horizontal component of the earth’s magnetic 
field at any point and the geographic meridian through 
that point, measured east or west from the north. (2) 
(Astron.) The angle made by a line from the observer 
to any celestial object, as a star, with the plane of the 
celestial equator; positive if north, negative if south. 
Deklinationsmesser: declinometer. An instrument for 
measuring magnetic declination, consisting essentially 
of a delicately suspended magnet in connection with a 
transit for obtaining the true meridian. 
Dekrement: decrement. A decrease in the value of a 
variable quantity; a negative increment. Syn., damping 
factor. 
Dekrementfaktor: decrement factor. The exponential 
factor, diminishing with time, which appears in an 
equation representing a damped oscillation. E.g., the 
discharge current of a condenser with initial charge Q 
is 
the upper and lower energy states. All frequencies in 
a row have the same value of n', all in a column the 
same value of n". 
Despretz'sches Gesetz: Despte/z law. States that the 
temperature of maximum density of water is lowered 
below 4 degree centigrade by the addition of a solute, 
by an amount proportional to the concentration of the 
solution. 
Detektor: detector. An apparatus which, acting as a 
rectifier or a relay, serves to detect or render audible 
radio-wave modulations or signals. 
Detektorverstaerkungsfaktor: detection coefficient. The 
approximately constant ratio of the intensity of a de- 
tector signal, e.g., the increase of plate current from 
a triode detector, to the square of the impressed h.-f. 
e.m.f. causing it. 
Deuteron: deuteron, diplon. The nucleus of the hy- 
drogen isotope, deuterium, of atomic weight approxi- 
mately 2. 
Dewar'sches Gefaess: Dewar flask. A flask surrounded 
by a vacuum space for the purpose of thermal insula- 
tion; a principle utilized in the thermos bottle. 
dextrogyr: dextrogyrate. Having the property of ro- 
tating the plane of polarization of a beam of transmit- 
ted, plane-polarized light in the right-handed or clock- 
wise direction, as viewed by one looking in the direc- 
tion in which the light travels. 
Dezibel: decibel. A power-interval unit equal to 1/10 
bei, therefore corresponding to the power ratio 101/10: 
1 equals 1.259. Commonly used in expressing acoustic 
sensation level differences. 
Diagrammlinie: diagram line. (1) An X-ray spectrum 
line which corresponds to one of the quantum transi- 
tions derivable from the energy-level diagram for the 
atom from which it comes; whether such transition is 
in accordance with the selection rules or not. (2) An 
X-ray spectrum line which fits into the scheme graph- 
ically represented by the Moseley curves. 
Diakaus+ik: diacaustic. A caustic produced by refrac- 
tion. 
Dialyse: dialysis. The separation of a colloid from a 
true solute by diffusion of the latter through a porous 
membrane, in a manner analogous to osmosis. The 
apparatus is called a dialyzer. 
diamagne+isch: diamagnetic. Having a negative mag- 
netic susceptibility, e.g., copper, silver, and bismuth. 
a2 + b2 
i — Qeatsin bt, 
b 
in which a and b are constants. Here eat is the decre- 
ment factor. 
Dekrementmanometer: decrement gauge. A pressure 
gauge in which the pressure or the density of a gas is 
measured by its effect in damping the movements of an 
oscillating disk or fiber. 
Dekrementmesser: decremeter. An instrument for 
measuring the logarithmic decrement of an electric oscil- 
lation. 
Delta Funktion: delta function. A function 8 (x) ar- 
bitrarily defined by Dirac as having the property of 
being zero for all values of x other than zero, and also 
the property that its definite integral from minus in- 
finity to plus infinity is unity. The operative symbol 
appears in many equations relating to modern quantum 
mechanics. 
Delta Strahlen: delta rays. The name given by J. J. 
Thomson to electrons emitted by substances when bom- 
barded with alpha particles. 
Densitometer: densitometer. A form of photometer 
used especially for measuring the density of silver de- 
posits on photographic plates or films. 
Deslandres Diagramm: Deslandres diagram. The fre- 
quency matrix of a spectrum band system, i.e., a table 
in which the frequencies are arranged according to 
ascending values of the quantum numbers n', n" of 
/dia+herman 
25 D 
diatherman: diahermanous. Highly transparent to in- 
frared.* 
diatonische Skala: just scale, diatonic scale. A musical 
scale in which the frequencies making up the chords 
have certain simple ratios. 
Dichroismus: dicbroism. (1) Pleochroism in respect 
to two axes only. (2) The property, exhibited by cer- 
tain colored transparent bodies, of showing different 
colors of transmitted light, depending upon the thick- 
ness traversed or the concentration of the coloring mat- 
ter; or of exhibiting one color by reflected and another 
by transmitted light. (3) (Circular.) The unequal 
absorption of the two circular components of plane- 
polarized light in an optically active (rotatory) medium, 
as in certain organic solutions. First observed by Cotton. 
Dichroskop: dichroscope. An instrument used in study- 
ing the dichroism (1) of crystals. 
Dichte; density. (1) The ratio of the mass of a 
specimen of a substance to the volume of the specimen. 
(2) In general, a term expressing the closeness of any 
space distribution; as electron density (number of elec- 
trons per unit volume), etc. (3) (Phot.) A term used 
to specify the light-absorbing power of the silver image 
in photographic materials; defined as the negative com- 
mon logarithm of the transmission factor. 
Dichtemesser: densitometer. See Densitometer. 
Dickfluessigkeit: viscidity. That combination of co- 
hesion and viscosity in a liquid which results in its 
being "sticky” and capable of being drawn out into 
fine threads, e.g., glue. 
Dielektrikum; dielectric. A substance capable of sus- 
taining an electric field and of undergoing electric po- 
larization. All electric insulators are dielectrics. 
dielektrische Absorption: dielectric absorption. See 
Absorption (3). 
dielektrische Kohaesion; dielectric cohesion. The force 
with which the molecules of a dielectric oppose an elec- 
tric field tending to ionize them; a term due to Bouty. 
dielectrische Konstante: dielectric constant, permittiv- 
ity. (1) The ratio k of the electric displacement to the 
electric intensity in the same region. (2) It has also 
been defined as a quantity whose measure (in c.g.s. 
e.s.u.) is 8?r times the electric energy density in the 
said region, divided by the square of the potential 
gradient in the direction of the displacement. 
dielektrische Kraft: insulating strength, dielectric 
strength. A measure of the ability of an electric in- 
sulator to withstand electric stress without breakdown; 
defined as p.d. per unit thickness of the insulator neces- 
sary to initiate a disruptive discharge through it. Usually 
expressed in volts per cm. 
dielektrische Polarisation: dielectric polarization, po- 
larisation. In re a polarized dielectric; the electric mo- 
ment per unit volume. 
dielektrischer Verlust: dielectric loss. Loss of power 
due to electric hysteresis. 
Dielektrizitaetskonstante: dielectric constant. See di- 
elektrische Konstante. 
Dieterici Gleichung: Dieterici equation. An empirical, 
characteristic gas equation: 
a 
p(v — b)eRTv = RT; 
in which a and b are the characteristic constants. 
Differenzbande: differerice band. A spectral band aris- 
ing in transition from an excited state, rather than from 
the ground state. 
Differenzialgalvanometer: differential galvanometer. A 
galvanometer having two similar, opposed coils, the 
currents in which tend to neutralize each other’s effect, 
and which gives a zero reading when the currents are 
equal. 
differenzielle magnetische Permeabilitaet: differential 
magnetic permeability. The derivative of the magnetic 
induction with respect to the magnetic intensity in the 
same region, viz., dB/dH. Here both dB and dH are 
taken as postive; if reversed the ratio may be different, 
on account of hysteresis. 
Differenzton: difference tone. A combination tone 
whose pitch corresponds to a frequency equal to the 
difference of the frequencies of the two components. 
Diffraktion: diffraction. See Beugung. 
Diffraktionsevolute: diffraction evolute. A term re- 
ferring to the law that when an object illuminated by 
a point source produces a diffraction pattern within its 
shadow, the predominant diffraction figure is the evo- 
lute of the boundary of the geometrical shadow. 
Diffraktionsgitter: diffraction grating. See Beugungs- 
gitter. 
Diffraktionswinkel: diffraction angle. See Beugungs- 
winkel. 
/diffuse Reflektion 
26 D 
diffuse Reflektion: diffuse reflection, d. refraction, d. 
transmission. Reflection, refraction, or transmission in 
all directions, not in any sharply defined path. 
diffuse Serie: diffuse series. One of several spectral 
series in the characteristic spectrum of an element; so 
called because of the relatively large half-width of the 
lines. 
Diffusion: diffusion. (1) The permeation of any re- 
gion by a fluid, due to the thermal agitation of its 
molecules. (2) Syn. scattering. 
diffusivity, diffusion coefficient, diffusion 
constant. The constant D in the Pick law of diffusion. 
Diffusionsindika+rix: diffusion indicatrix. A graph, in 
polar co-ordinates, showing the candle power of a given 
element of an illuminated diffusing surface as viewed 
from various directions in a plane perpendicular to the 
element. 
Diffusionskoeffizient: diffusion coefficient. See Diffu- 
sion. 
Diffusionskonstante: diffusion constant. See Diffusion. 
Diffusionspumpe: diffusion pump. A type of air pump 
which operates by virtue of the large momentum of 
mercury vapor or other heavy molecules, which, in a 
stream or jet, carry other gas molecules before them. 
Dilatometer; dilatometer. (1) An instrument resem- 
bling a large-bulbed thermometer, used for measure- 
ments of the expansion of liquids. (2) Any device for 
the measurement of thermal expansion. 
Dimensionsanalyse: dimensional analysis. An analysis 
of a relationship between concrete quantities with refer- 
ence to their physical dimensions. It is always of a 
partial character, and in particular does not give nu- 
merical factors. Thus, the kinetic energy of a moving 
body must be proportional to the square of the speed, 
because of the dimension formula ML2T~2 for energy; 
but the factor y2 is not thereby revealed. 
Dimensionsformel: dimension formula. In re any phy- 
sical magnitude: a symbolic representation of its defi- 
nition in terms of fundamental magnitudes; e.g., for’ 
example, area equals L2, force equals MLT~2, etc. 
Dimensionshomogenitaef: dimensional homogeneity. 
Equality of physical dimensions in the terms of a for- 
mula or physical equation. E.g., in the Einstein photo- 
electric equation. 
1/2mv2 — hv — p, 
each term represents energy and has the dimension 
formula ML2T~2. 
Dimensionskons+an+e: dimensional constant. A factor, 
the numerical value of which depends upon the funda- 
mental definitions and the size of the fundamental units, 
but not upon the particular physical system to which 
it is applied. E.g., the gravitation constant G in the 
Newtonian formula Gm,m,/r2 is dimensional; but in 
the formula for the circumference of a circle, p — -n-d, 
7r is not dimensional, as it has the same value whatever 
the unit of length used for d and p. 
dinerisch: dineric. A term descriptive of a solution 
in which there are two immiscible solvents with a single 
solute soluble in each. 
Diode: diode. A two-electrode vacuum tube. 
Diopter: diopter. A unit of focal power, correspond- 
ing to the focal length of one meter. 
Dioptrie: dioptry. See Diopter. 
Dipol: dipole. (1) A system composed of two equal 
electric charges of opposite sign, separated by a finite 
distance, e.g., the nucleus or orbital electron of a hydro- 
gen atom. (2) A similar system composed of two equal 
but opposite magnetic poles. 
Dipoimoment: dipole moment. The electric or mag- 
netic moment of a dipole. 
Dipolpolarisation: dipole polarization. The type of 
electric polarization exhibited by homogeneous polar 
dielectrics, and ascribed to the orientation of the per- 
manent molecular dipoles. 
Dirac'sche Funktion: Dirac junction. See Delta Funk- 
tion. 
Dirac'sche Gleichung: Dirac equation. (1) A formula 
based upon relativity-quantum theory which gives the 
mass absorption coefficient of a substance for radiation 
quanta in terms of their energy and of the constants re- 
lating to the atoms of the substance. (2) One of a 
set of four similar differential equations involving the 
components ipl, p2, \p3, if/4 of a four-dimensional 
vector. 
Dirac'sches Elektron: Dirac electron. The physical con- 
cept of the electron as expressed by Dirac in terms of 
relativistic wave mechanics. 
Dirichlet'sches Prinzip: Diricblet principle. States that 
there is one and only one function F of the coordinate 
variables x, y, z which fulfills the following conditions: 
(1) that F and its derivatives are continuous and single 
valued throughout a given closed space S. (2) that 
F satisfies the Laplace equation throughout this region, 
27 
/diskontinuierliche Absorption D 
and (3) that F may be made to assume any given set 
of boundary values all over the surface of S, provided 
these values are continuous over the surface. Important 
in the theory of potential. 
diskontinuierliche Absorption: absorption discontinuity. 
A discontinuity in the absorption coefficient of a sub- 
stance as a function of wave length, corresponding to 
a spectral absorption line and often associated with 
anomalies in other variables such as the refractive index. 
Dispersion: dispersion. (1) The process of separating 
or sorting an emission, in accordance with some char- 
acteristic such as frequency, wave length, or energy, 
into components which usually are given different di- 
rections; as a prism or a grating disperses white light, 
or a magnetic field sorts electrons of different speed. 
(2) Quantitatively, a general measure for any such 
dispersion is the derivative of the deviation with re- 
spect to that variable (wave length frequency, etc.) 
which is considered responsible for the separation; but 
some writers define refractive dispersion as the deriva- 
tive of the refractive index with respect to wave length 
or frequency. (3) The production of the disperse phase 
in a disperse system. 
Dispersionsformel: dispersion formula. One of a num- 
ber of equations essaying to express the refractive in- 
dex of a substance as a function of wave length or of 
frequency, e.g., the Cauchy formula. Characteristic con- 
stants in such a formula are dispersion constants for 
substance. 
Dispersionsfrequenz: dispersional frequency. The fre- 
quency corresponding to the anomalous dispersion at an 
absorption discontinuity. 
Dispersionsphase: disperse phase. That constituent of 
a disperse system which corresponds to the solute in a 
crystalloidal solution. 
Dispersionssystem: disperse system. Any colloidal so- 
lution having two phases separated by relatively large 
surfaces. 
Dispersionsvermoegen; dispersive power. In re any 
refractive medium: the value of the ratio 
Dispersoid: dispersoid. A highly dispersed colloidal 
suspension, such as an emulsion. 
Dissonanz: dissonance. (1) (Acoust.) Musical dis- 
cord. (2) (Opt.) The formation of maxima and minima 
by the superposition of two sets of interference fringes 
from light of two different wave lengths, i.e., what may 
be called stationary beats or secondary interference. 
Dissoziationswaerme: heat of dissociation. The quan- 
tity of heat evolved, in the chemical dissociation of 1 g 
or 1 mol of an electrolyte. 
Divergenz: divergence. A scalar differential operator, 
which, applied to a vector point function F, is denoted 
by the symbol A’F and read "divergence of F” or "del 
dot F’’. If Fx, F2, F3 are the magnitudes of the three 
components of F, the divergence of F is expressed by 
the equation 
8FX 8F2 8F3 
A*F - + + . 
Sx 8y 8z 
Doma: doma. A primitive crystalline form consisting 
of two plane surfaces forming a dihedral angle, which 
is bisected by a third plane surface. 
Doppelbild prisma: double-image prism. An apparatus, 
one type of which, devised by Wollaston, consists of 
two wedges of doubly refracting crystal fitted together 
to form a rectangular block or prism, and with their 
axial directions at right angles. When a narrow beam 
of unpolarized light enters normally at one surface, it 
emerges from the other in two separate beams, plane- 
polarized at right angles to each other. 
Doppelbrechung: birefringence, double refraction. A 
phenomenon observed when light traverses certain types 
of crystal or other aeolotropic medium; manifested by 
the separation of the light into two components, polar- 
ized at right angles to each other, having different ve- 
locities within the medium, and, in general, taking 
different directions. These two components are termed 
the ordinary and the extraordinary rays. 
Doppler Effekte: Doppler effects. The effects produced 
upon the frequency with which the waves of an un- 
dulatory emission reach the observer, by the motion 
of the source toward or away from the observer, or of 
the observer toward or away from the source, or both. 
Observed in the case of sound by Doppler in 1842. 
Doppler-Fizeau'sches Prinzip: Doppler-Fizeau princi- 
ple. The principle underlying the Doppler effects as 
applied by Fizeau to the shifting of the spectrum lines. 
Doppler Verbreiterung: Doppler broadening. The 
broadening of a spectrum line due to the Doppler effect 
ni - n2 
nm — 1 
in which nx and n2 are the refractive indices for the 
ends of the spectrum range considered, while nm is 
that for some arbitrarily chosen wave length, often the 
mean of nx and n2. Commonly nx and n2 are taken 
for F and C Fraunhofer lines, respectively, and nm for 
the D (sodium) line. The reciprocal of the dispersive 
power is the Abbe nu-value. 
/Doppler Verschiebung 
28 D 
of the radial component of thermal motion in the emit- 
ting particles, which gives the line a width (Doppler 
width) superimposed upon that due to other causes. 
Doppler Verschiebung: Doppler shift. The displace- 
ment of spectral lines caused by the relative radial mo- 
tion of source and observer. 
Dorn'scher Effekt: Dorn effect, sedimentation poten- 
tial. A p.d. set up by the falling of a particle through 
a liquid. 
Dosis: dosage. A measure of the time integral of ir- 
radiation, equal to the product of the intensity by the 
duration of exposure; a term used especially in radi- 
ology. 
Doublett: doublet. (1) (Electr.) The ideal limiting 
case of an electric dipole consisting of two equal, op- 
posite charges, + q, — q, when the distance d between 
the charges is diminished and the charges increased so 
as to keep the electric moment qd finite and constant; 
a concept useful in dielectric theory. (2) (Magnetic.) 
Definition similar to (1), but with opposite magnetic 
poles, + p, — p substituted for the two charges. 
Drehungsmoment: torque. Moment of a force with 
respect to any axis: the product of the perpendicular 
distance r from the axis to the line of action of the 
force by that component of the force which is per- 
pendicular to the axis and to the radius r; or the in- 
tegrated resultant of such moments, e.g., that arising 
from a system of forces equivalent to a couple. 
dreifaches Vektorprodukt: triple vector product. In 
re three vectors, p, q, r: any of the identical vector 
quantities 
the temperature-pressure diagram corresponds to this 
condition. 
Dreiphasens+rom: three-phase current. A polyphase 
current delivered through three wires, the components 
in which differ in phase successively by one-third cycle; 
each wire serving as the return for the other two. A 
three-phase generator supplies, and a three-phase motor 
is operated by, such a current. 
Drillpendel: torsion pendulum. A pendulum actuated 
by the torsion of an elastic wire. 
Drosseln: throttling, wiredrawing. The irreversible 
process of a fluid flowing through an opening from a 
higher to a lower pressure region. 
Drosselspule: choke coil. A coil of low resistance and 
comparatively small reactance, usually coreless, intro- 
duced in a circuit to retard transients. 
Drosselung: throttling. See Drosseln. 
Druckdiagram: stress diagram, s. sheet. An adapta- 
tion of the Maxwell diagram to the computation of 
stresses in a framed structure. 
Druckerniedrigung des Schmelzpunktes; regelation. 
The fusion and resolidification of ice below the normal 
freezing point, due to variations in pressure. 
Druckkoeffizient: pressure coefficient. (1) The ratio 
of the change in pressure per degree of temperature, 
in a gas kept at constant volume, to the pressure at the 
scale zero of temperature. It is very nearly equal to 
the (volume) expansion coefficient. (2) The increment 
of any quantity, which is a function of the pressure, 
due to unit change of pressure. 
Druckmodul: bulk modulus. The ratio of the pressure 
to which an elastic substance is subjected to the de- 
crease in volume per unit volume. 
stress modulus. The ratio of the stress 
to the strain for any kind of elastic deformation. 
druckop+Ischer Koeffizient: stress-optical coefficient. 
The difference, per unit stress, between the refractive 
indices for two beams of light traversing a photoelastic 
medium, one polarized in and the other perpendicular 
to the direction of stress. 
Druckverbreiterung: pressure broadening. An increase 
in the half-width of a line in the spectrum of a gas, 
when the source is under high pressure. It is often 
asymmetrical, the asymmetry being associated with a 
pressure shift. 
(p x q) X r = — r X (p x q) = 
r x (q x p) = — (q x p) x r. 
dreifach skalares Produkt: triple scalar product. In re 
three vectors p, q, r: any of the identical scalar quan- 
tities 
(p X q) • r = r * (p X q) = 
— r * (q X P) = - (q X p) • r. 
Dreikoerperproblem: three-body problem. A famous 
kinetic problem, dealing with the motions of three par- 
ticles or spherical bodies under their mutual gravita- 
tional attraction. 
Dreiphasengleichgewicht: three-phase equilibrium. The 
equilibrium which may exist, at a suitable temperature 
and pressure, among all three phases of a pure sub- 
stance, solid, liquid, and vapor. The triple point on 
29 
/Druckverschiebung D 
Druckverschiebung: pressure shift. A change in the 
wave length of the lines of a spectrum, when the source 
is under high pressure. 
Druckverstaerker: intensiver. A device for stepping up 
a high pressure, by means of a double free piston with 
two unequal areas, the larger of which is exposed to 
the lower pressure. 
Druckzen+rum: center of pressure. In re a surface ex- 
posed to pressure, e.g., when immersed in a fluid: the 
point of application of the single resultant force to 
which the effect of the pressure is equivalent. 
Duane-Hunt'sche Beziehung: Duane-Hunt law, D.-H. 
relation. States that the maximum frequency in the 
beam of X-rays issuing from a tube, multiplied by the 
Planck constant, is equal to the energy acquired by one 
of the cathode electrons in traversing the tube. The law 
is expressed by the Planck-Einstein equation. 
Duane-Hunt'sches Gesetz: Duane-Hunt law. See 
Duane-Hunt’sche Beziehung. 
Dubuat'sches Paradoxon: Duhuat paradox. Refers to 
the fact that the forces exerted by a fluid moving 
through a channel or conduit upon a body held at rest 
in it differ from those exerted when the liquid is at 
rest in the channel, and the body is moved through it 
with the same relative velocity as before. This is due 
to the effect of the irregularities of the walls of the 
channel, and of wall friction, upon the motion of the 
liquid. 
Duesenpumpe: jet pump. A type of suction pump 
dependent upon the Bernoulli principle of reduced 
pressure at a narrow constriction in a current of air 
or liquid, or upon the imprisonment of bubbles in a 
turbulent stream through a narrow tube. Filter pumps 
and aspirators are commonly of this type. 
Dulong-Petit Gesetze: Dulong-Petit laws. At least 
two well-known laws are attributed to Dulong and 
Petit: (1) The specific heats of elements are inversely 
proportional to their atomic weights. (2) The rate at 
which the temperature of the body approaches that of 
its surroundings by radiation is proportional to the dif- 
ference between two powers of the same constant whose 
exponents are, respectively, the absolute temperatures 
of the body and of its surroundings. The law is en- 
tirely empirical. 
Dumas'scher Kolben: Dumas bulb. A form of appa- 
ratus, on the principle of the pycnometer, for measur- 
ing the densities of vapors, and hence, indirectly, their 
molecular weights. 
Dunkelen+ladung: dark discharge. An electrical dis- 
charge (in a gas) which has no visible luminosity. 
Dunkelstrom: dark conduction. Residual electrical con- 
duction in a photosensitive substance when not illumi- 
nated. 
durchdringende Bahn: penetrating orbit. An outer or 
valence electron orbit which passes inside the atomic 
Rumpf. 
durchdringende Strahlung: penetrating radiation, cos- 
mic radiation, c. rays. A type of very penetrating radi- 
ation of unknown origin, apparently traversing inter- 
planetary space in all directions, and detected by the 
ionization which it produces in electroscopes, ion coun- 
ters, etc. 
Durchdringungskoeffizient: penetrance coefficient. A 
quantity which measures the tendency of a liquid to 
penetrate a given material which it wets; defined as 
half the product of the surface tension by the fluidity 
coefficient. 
Durchlaessigkeit: transmittance. The fraction of the 
radiant energy entering a layer of a medium which 
reaches its further boundary. 
Durchlaessiqkeitsfaktor: transmission factor, attenuation 
factor. A measure of transparency of a layer of absorb- 
ing medium for an emission traversing it. It is the 
ratio of the flux density I of the emergent emission to 
the flux density I0 of the incident emission. For an 
exponentially absorbed emission, the value of the fac- 
tor, for the thickness x of a medium whose absorption 
coefficient is is e Mx- 
Durchlaessigkeitsgrenze: transmission limit. A limit- 
ing wave length or frequency, above (or below) which 
a given type of radiation is practically all absorbed by 
a given medium. If the limits are sharply defined, the 
medium acts as a radiation filter. 
Durchlaesslgkel+skoeffizient: transmission coefficient. (1) 
In re the separation of radiation into parts at the in- 
terface between two media: the ratio of the amplitude 
of the transmitted radiation to that of the incident 
radiation. (2) In re the passage of radiation through 
an absorbing medium: one minus the absorption co- 
efficient. 
Durchlaessigkeltsmesser: transmissometer. An instru- 
ment for measuring the transmission factor of semi- 
transparent bodies. 
Durchlassebene: transmission plane. The plane of vi- 
bration of polarized light which will pass through a 
given polarizer, e.g., a Nicol prism. 
/Durchlassvermoegen 
30 D 
Durchlassvermoegen: transmissivity. See Durchlaessig- 
keitskoeffizient (2). 
Dyn: dyne. The absolute, c.g.s. unit of force, defined 
as the force which, acting upon the free mass of one 
gram, would impart to it an acceleration of 1 cm/sec2. 
Dynamik: dynamics. That branch of physics which 
treats of forces and their action upon material bodies. 
dynamisches Aequivalent: dynamic equivalent, me- 
chanical equivalent. The equivalent of a unit quantity 
of any form of energy in terms of the ordinary dynamic 
or work units. E.g., the mechanical equivalent of heat 
is 4.1852 x 107 ergs/cal; the mechanical equivalent 
of light is about 1.6 X 104 ergs/lumen-sec. 
dynamische Sfabilitaef: dynamical stability. A quan- 
tity whose measure is the torque, equal to the work 
necessary to produce a list or tipping of a floating body, 
divided by the angle through which it is tipped; a term 
applied especially to ships. 
Dynamometer: dynamometer. (1) An instrument for 
measuring force, such as a spring balance. (2) Syn. 
electro-dynamometer. 
Dynatron: dynatron. A triode in which the grid and 
plate potentials are so chosen that the plate current 
decreases as the plate potential increases. This charac- 
teristic is due to secondary electron emission from the 
plate, and because of it a dynatron can be used as an 
oscillator. 
dystektisch: dystectic. In re any mixture or solution: 
in such proportions as to have the maximum melting 
point of all mixtures of the same substances. 
677865—46 3 
31 
/Eagle mounting E 
Eagle mounting: Eagle mounting. A mounting for 
concave gratings, so arranged that the angles of in- 
cidence and diffraction are nearly equal. 
Earnshaw'sher Lehrsatz: Earnshaw theorem. States 
that an electric charge cannot be in stable equilibrium 
in an electric field unless acted upon by forces other 
than those due to the field. Analogous statements hold 
for magnet and gravitational fields or combinations of 
them. 
Ebene: plane. A surface, real or imaginary, in which 
if any two points are taken, the straight line that joins 
them lies wholly in that surface. 
Ebulliskop: ehulliscope, ebullioscope. An instrument 
for determining the concentration of a solution by 
means of its boiling point. 
Echelette: echelette. A coarse diffraction grating ruled 
on metal to resemble a reflecting echelon of very small 
steps. Devised by R. W. Wood. 
Echelon: echelon. A type of diffraction grating cap- 
able of producing spectra of very high order and dis- 
persion. The grating spaces are formed by building 
a minature stairway out of glass plates of exactly equal 
thickness. Devised by Michelson. 
Edison Effekt: Edison effect. A thermionic current, 
discovered (1892) by Edison, who connected a gal- 
vanometer between a terminal of one of his incan- 
descent lamp filaments and an auxiliary electrode placed 
in the bulb. 
effektive elektromotorische Kraft: effective electromo- 
tive force. The value of that constant e.m.f. which 
would yield the same average power as an actual vari- 
able e.m.f. in the same non-inductive circuit. It is equal 
to the r.m.s. of the variable e.m.f. 
effektive interferometrische Wellenlaenge; effective in- 
terferometric wave length. That monochromatic wave 
length which, on being substituted for heterochromatic 
.radiation, will give the same system of fringes in an 
interferometer. 
effektive lonenmasse: effective ionic mass. A quantity 
used to represent the ionic mass in connection with a 
heteropolar molecule. If and M2 are the masses 
of the two ions, the effective ionic mass is 
tor component of a given force whose direction is that 
of the actual motion of the point of application of the 
force in question. E.g., if a body slides down an in- 
clined plane under the action of gravity, the effective 
component of its weight is parallel to the plane. 
effektive Molekulargeschwindigkeit: effective molecular 
speed. That speed which each molecule of a pure gas 
would have, were their speeds all equal and the tem- 
perature unchanged. It is equal to the r.m.s. of the 
actual speeds, and is about 1.086 times the mean speed. 
effektive Quantenzahl: effective quantum number. A 
number appearing in spectral terms for non-hydrogen 
atoms, and analogous to the azimuthal quantum number 
for hydrogen. It is not, however, an integer, and is not 
properly a quantum number but merely a convenient 
square root of the energy. 
effektiver Durchmesser: effective diameter. In re mole- 
cules, atoms, ions, etc.: an average value of the diame- 
ters (or radii) of such particles, which, if they were of 
spherical shape, would result in the production of such 
scattering effects, mean-free-path phenomena, etc., as 
are actually observed with the type of particle in ques- 
tion. 
effektiver Schalldruck: effective sound pressure. The 
r.m.s. value of the instantaneous sound pressure during 
a complete cycle, at any point of a medium traversed 
by sound waves. Sometimes abbreviated to sound pres- 
sure. 
effektiver Stossradius: effective collision radius. See 
effektiver Durchmesser. 
effektiver Widerstand: effective resistance. The resis- 
tance of a conductor to a periodic current, as measured 
by the ratio of rate of dissipation of energy to square 
of effective current. It differs from the true (steady- 
current) resistance because of skin effect. 
effektive Temperatur: effective temperature. In re a 
source of thermal radiation: the temperature to which 
an ideal black body must be heated in order to give it 
the same emissive power as the source in question. 
effektive Wellenlaenge: effective ivave length. In re 
a beam of nonhomogenous radiation in a given medium: 
the wave length of a homogenous beam having the 
same penetration in the same medium. 
Effektivladung; effective charge. An electric charge 
such that, if multiplied by the actual distance between 
the two atoms of a heteropolar, diatomic molecule, the 
result is equal to the actual dipole moment. 
(M.M2)3/2 
M = 
(M, + M2)2 
effektive Komponente: effective component. That vec 
/Effektivstrom 
32 E 
Effektivstrom: effective current. The value of that 
constant current which would have the same average 
power as an actual variable current in the same cir- 
cuit. It is equal to the r.m.s. of the variable current. 
Ehrenfest'sche Formel: Ehrenfest formula. A modifi- 
cation of the Sackur equation for the entropy of a gas, 
in which allowance is made for the molecular symmetry 
number. 
Eigenenergie: eigenenergy. A quantity of energy just 
corresponding to an actual atomic state. Used in quan- 
tum mechanics. The term has also been used for proper 
energy. 
proper energy. The energy which, ac- 
cording to relativity theory, is equivalent to a given 
mass m, and is equal to me2, where c is the electro- 
magnetic constant. 
Eigenfeld: self-consistant field. The central field used 
by Hartree in the calculation of atomic wave functions. 
Eigenfrequenz; characteristic frequency. See Atomfre- 
quenz. 
Eigenfunkfion: eigenfunction, characteristic function. 
(1) A function which, among various possible forms, 
fulfills certain required conditions. Used in quantum 
mechanics. (2) The optical length of a ray in an opti- 
cal instrument, expressed as a function of the coordi- 
nates of its end points. 
Eigenkapazi+aet: self-capacitance. Distributed capaci- 
tance of an electric circuit due to its containing closely 
wound coils of insulated wire, the adjacent turns of 
which have a condenser effect. 
Eigenkapazitaetseffekt: proximity effect. One of the 
results of winding a wire in a coil with closely adja- 
cent turns, e.g., self-capacitance, the increase in effec- 
tive resistance for h.-f. currents, etc. 
Eigenveraenderung: individual change. Any dynamic 
process in which the attention is fixed upon the be- 
havior of a single particle, followed throughout all its 
course, changes in its motion being noted; in contra- 
distinction to local change, q.v. 
Eigenwert: eigenvalue, characteristic number, c. value. 
A particular solution satisfying specified conditions. 
Used in quantum mechanics. 
einachsig: uniaxial. Having but one optic axis. 
Einfallswinkel: incidence angle. The angle between the 
direction of an approaching emission and the normal to 
the surface upon which it is incident. 
Einflussphaere: sphere of influence. The region sur- 
rounding a gas molecule, within which its van der 
Waals force of attraction exerts an appreciable effect 
upon other molecules. 
Eingangsoeffnung: entrance-port. The image of the 
field stop of an optical system formed by the part of 
the system which is anterior to the field stop. If the 
field stop is in front of the system, it is identical with 
the entrance-port. 
Eingangspupille: entrance pupil. A real or imaginary 
stop (usually circular) which controls the apertures of 
the bundles of incident rays in an optical instrument 
for a given position of the focal plane. The entrance- 
pupil of the eye is a little in front of the actual pupil. 
einheitliche Feldtheorie: unified field theory, unitary 
f.t. A phase of the general relativity theory which seeks 
to treat gravitational, electric, and magnetic fields as 
aspects of a single entity. 
Einheitsebene: unit planes. In re a symmetrical opti- 
cal system: One of two planes perpendicular to the axis, 
such that any incident paraxial ray meets the first, and 
the same ray upon emergence meets the second, in 
points on a line parallel to the axis. The magnification 
ratio for these two planes being -f 1, they are sometimes 
called the unit planes. 
Einheitsflaechenwinkel: spheradian, steradian. The unit 
solid angle, which cuts unit area from the surface of a 
sphere of unit radius centered at its vertex. 
Einheitslcristall: unit crystal. The simplest geometric 
figure which includes all the characteristics of, and is 
repeated indefinitely to form, the lattice structure of a 
crystal. 
Einheitspol: unit pole. An ideal magnetic point pole, 
two of which, at a distance of 1 cm apart in a vacuum, 
would exert a mutual repulsion (or attraction) of 1 
dyne. Such a pole gives rise to 4tt maxwells of free 
magnetism. Actual magnetic poles are often treated 
quantitatively as if made up of a number of unit poles 
equal to the "pole strength.” 
Einheitspunkte: unit points, principal points. Two 
points at which the principal planes of a symmetrical 
optical system intersect the axis. 
Einheitszelle: unit cell, elementary cell. See Einheits- 
kristall. 
Einkristall: monocrystal. A body of appreciable size 
composed of a crystalline substance and formed with 
/einphasisch 
33 E 
eme continuous crystalline structure throughout, not as 
a mass of small crystals having various orientations. 
einphasisch: single-phase. Utilizing a single a.c., as 
a single-phase motor. 
einpolige Induktion: unipolar induction. The genera- 
tion of an e.m.f. by a continuous cutting of magnetic 
flux in one direction, without reversal or cyclic action; 
e.g., as in a metal disk rotating continuously between 
the poles of a magnet. 
Einstein-de Haas Effekt: Einstein-de Haas effect. An 
angular momentum imparted to a free body by suddenly 
magnetizing it; the converse of the Barnett effect. 
Einstein'sche photo-elektrische Gleichung: Einstein 
photoelectric equation. Expresses the kinetic energy of 
an escaped photoelectron as 
Eu - hv — p, 
in which hv is the energy quantum of the incident 
radiation and p is the photoelectric work function for 
the metal concerned. 
Einstein'sche Verschiebung: Einstein shift. A shift to- 
ward the red in the spectral lines of light which, ac- 
cording to the relativity theory, has its frequencies 
slightly reduced upon emerging from a strong gravi- 
tational field, such as that of a dense star. 
Einstein'sche Koeffizienten: Einstein coefficients. Quan- 
tities which represent the probabilities of the emission 
or of the absorption of radiation quanta by an atom 
within a unit of time. 
Einthoven Galvanometer: Einthoven galvanometer, 
string galvanometer. A type of galvanometer in which 
the current is measured by the lateral displacement of 
a wire carrying the current across a strong magnetic 
field. Devised by Einthoven. 
Eiskalorimeter: ice calorimeter. A calorimeter in which 
quantities of heat are measured by the quantity of ice 
melted. Developed by Black, Bunsen, and others. 
Eispunkt: ice point. The freezing point of water, viz., 
0 degree C. or 273.18 degrees K. 
elastische Dehnungswaerme: heat of elastic extension. 
See Dehnungswaerme. 
elastische Streuung: 'elastic scattering. Scattering by 
elastic impact, i.e., without loss of kinetic energy. 
elastischer Nacheffekt: elastic aftereffect. The per- 
sistence of a strain, though gradually diminishing, after 
the stress has been removed from an elastic body. 
elastischer Nachwirkungseffekt: elastic aftereffect. See 
elastischer Nacheffekt. 
elastischer Stoss: elastic collision, e. impact. An en- 
counter between moving bodies or corpuscles, subject 
to the ideal condition that the total kinetic energy of 
translation is the same after the impact as it was before; 
i.e., none of the energy is transformed into rotational 
or other form. 
Elastizitaet: elasticity. That property of a body or a 
substance, by virtue of which it develops stresses when 
subjected to strain, and therefore tends to resume its 
original configuration. Kelvin defines a perfectly elas- 
tic body as one in which a given state of strain always 
corresponds to the same distribution of stress, however 
prolonged or however often repeated, provided the tem- 
perature remains unchanged. 
Elastizitaetsgrenze: elastic limit, proportional limit, 
P-limit, limiting stress. The stress required to produce, 
in a given fnaterial, a permanent deformation of measur- 
able amount, and at which the Hooke law ceases to 
hold. 
Elastizitaetsmesser: elasmometer. An instrument for 
the study of Young’s modulus and other elastic con- 
stants, esp. by optical methods. 
Elastizitaetsmodul: elastic modulus. See Druckmodul, 
Young’scher Modul. 
Elektret: electret. A dielectric which exhibits dielec- 
tric absorption, i.e., still retains part of its electric polar- 
ization after the removal of the external field. 
elektrische Abschirmung: electric screening. The de- 
vice of completely surrounding any object or region by 
a closed metallic shell or casing, in order to exclude all 
extraneous electrostatic influence. 
elektrische Absorption: electric absorption. See dielek- 
trische Absorption. 
elektrische Achse: electric axis, piezo-electric axis. One 
of the directions in a crystal in which either tension or 
compression will cause it to develop piezo-electric 
charges. 
elektrische Dichte: electric density. The quantity of 
electricity per unit volume in any part of a space 
charge. 
elektrische Doppelbrechung: electric double ref rac- 
/elektrische Doppelschicht 
34 E 
tion. An electro-optical effect; viz., certain transparent, 
normally isotropic substances become doubly refracting 
when subjected to an electric field transverse to the 
beam of light. 
elektrische Doppelschicht: electric double layer, Syn. 
Helmholtz double layer. A limited region which in- 
cludes the surface of a metal in contact with an electro- 
lytic medium, and contains a layer of positive metallic 
ions in the electrolytic medium and an adjacent layer of 
negatively charged metal. The term is due to Helm- 
holtz. 
elektrische Faellung: electric precipitation. The col- 
lection of dust or other finely divided matter by means 
of the inductive action of an electric field. 
elektrische Induktion: electric induction. A redistribu- 
tion of electricity which takes place in a conductor when 
placed in an electric field. 
elektrische Konvektion: electric convection. An electric 
current consisting of electric charges carried by means 
of charged bodies of appreciable size, as by the "car- 
riers” of a static machine or by electrified drops of 
liquid. 
elektrische Kraft: electric force, e. intensity. A vector 
quantity pertaining to the electric field, the measure of 
which, at any point in a vacuum, is the force per unit 
charge which would act upon a charged particle placed 
at that point. It is closely related to electric displace- 
ment. 
elektrische Polarisation: electric polarization. (1) See 
dielektrische Polarisation. (2) (v.) To produce an 
electrical separation or orientation, esp. in the mole- 
cules of a dielectric. 
elektrischer Durchschlag: electric breakdown. An elec- 
tric discharge which takes place by reason of a trans- 
formation within the dielectric, rendering it, at least 
temporarily, a conductor; a disruptive discharge. 
elektrischer Fluss: electric flux. The surface integral, 
over any specified area, of the normal component of 
the electric displacement. 
elektrischer Hammer: interrupter. A device for rap- 
idly and periodically breaking and closing an electric 
circuit, as that of the primary of an induction coil. 
elektrischer Niederschlag: electric precipitation. See 
elektrische Faellung. 
elektrischer Vektor: electric vector. That component 
of the electromagnetic field associated with electromag- 
netic radiation which is of the nature of an electric 
field; supposed to coexist with, but to act at right an- 
gles to, the magnetic vector. 
elektrischer Wind: electric wind. A current of air 
or other gas repelled from an electrified, pointed con- 
ductor, or carried along by streams of ions moving in 
the electric field. 
elektrisches Bild: electric image. A fictitious distribu- 
tion of electricity, mathematically equivalent in its effect 
to an actual distribution induced on a conductor, and 
related to the inducing charge in a manner somewhat 
analogous to the relation of a virtual image to the source 
of light. 
elektrische Schwingung: electric oscillation. An a.c. 
having a natural frequency dependent upon the nature 
of the circuit, rather than upon the alternating char- 
acter of the impressed e.m.f. Or, in general, any h.—f. 
a.c. 
elektrisches Moment: electric moment. That vector, 
associated with a system having electric displacement, 
whose vector product by the electric intensity of the 
field in which the system is placed gives the resulting 
torque upon the same, the electric intensity considered 
being exclusive of any component contributed by the 
system itself. For a dipole with concentrated charges 
the electric moment is approximately the product of the 
magnitude of either charge by the distance between 
them, and its direction is that of the line drawn from 
the negative to the positive charge. 
elektrisches Potential: electric potential. (1) A scalar 
point function, the measure of which is the energy per 
unit charge involved in the transfer of an infinitesimal 
quantity of positive electricity, from an infinite distance 
to the point in question. More briefly: The line integral 
of the electric intensity from the point to infinity. The 
potential is positive or negative according to whether 
work must be expended to bring the positive charge 
from infinity or to carry it to infinity from the given 
point. Any arbitrary zero, as the potential of the earth, 
may, however, be used. (2) Sometimes loosely applied 
to p.d. or to e.m.f. 
elektrische Streckung: electric stress. The condition 
within a dielectric which is brought about by electric 
polarization, and under which the dielectric tends to 
recover its normal condition when the cause of the 
polarization is removed. 
elektrische Suszeptibilitaet: electric susceptibility, Syn. 
dielectric susceptibility. The ratio of the polarization 
in a dielectric to the electric intensity responsible for' it. 
35 
/elektrische Verschiebung E 
elektrische Verschiebung: electric displacement. A vec- 
tor quantity usually associated with the condition of a 
substance in an electric field. When a dielectric is 
placed in the field, the dielectric polarization and the 
electric intensity in the substance are both proportional 
to the displacement, their ratios to it depending upon 
the dielectric constant. 
elektrische Welle: electric wave. (1) A wave of vary- 
ing electric density and potential in a conductor, such 
as the telephone line. (2) Electromagnetic radiation 
produced by the oscillations of electricity in a conductor; 
e.g., radio waves. First demonstrated by Heinrich Hertz 
in 1888 and known as Hertzian radiation or Hertzian 
waves. 
elektrochemische Konstante: electrochemical constant, 
Faraday electrolytic constant. The quantity of electricity 
which, in electrolysis, is required to liberate a gram 
atom of any univalent element; viz., approximately 
96,494 international coulombs per gram equivalent. 
elektrochemisches Aequivalent: electrochemical equiva- 
lent. The mass of a substance liberated in electrolysis, 
per unit quantity (coulomb) of electricity passing 
through the electrolyte. 
Elektrode: electrode. A surface of contact between a 
metallic and a non-metallic conductor (metallic includes 
such conductors as carbon). 
elektrodenlose Entladung: electrodeless discha.rge. A 
luminous discharge in a gas confined in a closed tube 
without internal electrodes, due to subjecting the gas 
to a rapidly alternating electric field through the con- 
denser action of the tube wall or to the inductive action 
of the current in a neighboring h.—f. circuit. 
Elektrodialyse: electrodialysis. Dialysis under the in- 
fluence of an electric potential gradient; analogous to 
electroosmosis. 
Elektrodynamik: electrodynamics. That branch of phy- 
sics which deals with the forces and energy transforma- 
tions related to electric currents and the magnetic fields 
associated with them. 
Elektrodynamometer: electrodynamometer. An instru- 
ment for measuring electric current by means of the in- 
teraction between parts of a single circuit carrying the 
current. 
Elektroendosmose: electro-endosmosis. Cataphoresis, 
i.e., the movement of solid particles in liquid suspen- 
sion under the action of an e.m.f., esp. when the liquid 
component of the suspension migrates, while the solid 
remains stationary. 
elektrographisch: electrographic. A term applied to the 
effect of cathode rays on a metal surface, in which the 
metal becomes less subject to the action of corrosive 
vapors, and which may be used to produce developable 
cathode-ray images. 
Elek+rokapillari+aet: electrocapillarity. The effect of 
an electric current upon the equilibrium of the interface 
between two liquids in a capillary tube, consisting ap- 
parently in a modification of the surface tension. 
Elektrokinetik: electrokinetics. That branch of physics 
which deals with electricity in motion. 
elektrokinetisches Potential: electrokinetic potential. 
The p.d. which exists across the Helmholtz double 
layer at the interface between a solid and a surrounding 
liquid; a term due to Freundlich. Syn., zeta potential. 
Elektrolyse: electrolysis. A chemical process which oc- 
curs at the interface between an electrode and an electro- 
lyte when an unidirectional current passes from one to 
the other. 
Elektrolyt: electrolyte. (1) A conducting medium in 
which the current consists of charges borne by carriers 
of atomic or molecular dimensions (ions). (2) A sub- 
stance which conducts ionically either in the pure state 
or when dissolved in a suitable medium. 
Elektrolytgleichrichter: electrolytic valve. An electric 
current rectifier based on the nonsymmetrical resistance 
of certain electrolytic cells. 
elektrolytische Kapazitaet: electrolytic capacitance. 
The capacitance of a cell acting as an electrolytic con- 
denser. 
elektrolytischer Kondensator: electrolytic condenser. 
A polarized electrolytic cell used as a condenser of large 
capacitance. 
electromagnetische Einheit: electromagnetic unit. Any 
electric unit based primarily upon the magnetic effect of 
the electric current. The fundamental c.g.s. unit in the 
system is the abampere. 
elektromagnetische Induktion: electromagnetic induc- 
tion, magnetoelectric induction. The production of an 
e.m.f. by the cutting of magnetic flux (whether the 
moving conductor cuts the flux or vice versa), e.g., in 
an electric generator. First observed by Faraday in 1831. 
elektromagnetische Konstante: electromagnetic con- 
stant. A natural constant, having the dimensions of 
linear speed, which appears in the expressions for many 
relations between electric and magnetic quantities, and 
/elektromagnetische Masse 
36 E 
is commonly denoted by c. E.g., the abcoulomb is equal 
to c times the e.s.u. charge, c plays its most familiar 
role as the speed of electromagnetic radiation in a vacu- 
um. Its value is about 2.9977 X 1010 cm per second. 
elektromagnetische Masse: electromagnetic mass. The 
mass associated with a moving electric charge by reason 
of the fact that the energy of the magnetic field which 
it produces is proportional to the square of the speed. 
The mutual electromagnetic mass of two like charges 
moving side by side is greater than the sum of their 
separate electromagnetic masses. * 
elektromagnetisches Feld: electromagnetic field. A re- 
gion of space which is the seat of electromagnetic 
energy, by virtue of a rapidly moving electric field 
which sets up a coincident, moving magnetic field at 
right angles to the lines of electric force and to their 
direction of motion. This condition is believed to exist 
in the space traversed by electromagnetic radiation. 
elektromagnetisches Moment: electromagnetic momen- 
tum. A momentum which, according to the theories of 
Maxwell and J. J. Thomson, exists in an electromagnetic 
field, and whose magnitude per unit volume is equal 
to the product of the electric and the magnetic field in- 
tensities divided by the electromagnetic constant c. 
elektromagnetische Strahlung: electromagnetic radia- 
tion. See Ausstrahlung (1). 
elektromagnetische Waage: electromagnetic balance. 
An instrument which measures electromagnetic forces 
by balancing them against gravity, e.g., the Kelvin bal- 
ance. 
elektromagnetische Wellen: electromagnetic waves. 
Waves of electromagnetic radiation. 
Elektromagnetismus: electromagnetics. That branch of 
physics which treats of the mutual relationships existing 
between electric currents and the attendant magnetic 
fields. 
Elektromechanik: electromechanics. (1) A branch of 
electrical engineering which deals with machines pro- 
ducing or operated by electric currents, as generators 
and motors. (2) See Elektrodynamik. 
Elektrometer: electrometer. An instrument for detect- 
ing or measuring p.d. by means of electrostatic forces 
exerted between electrically charged bodies; a calibrated 
electroscope. 
elektromotorische Gegenkraft: counter electromotive 
force, back electromotive force. An e.m.f. which affects 
a circuit in the direction opposite to that of the current; 
due to such influences as self-induction, electrolytic 
polarization, etc. 
elektromotorische Kraft: electromotive force. That 
which tends to alter the motion of electricity or to 
maintain its motion against resistance. Its measure is 
the energy per unit charge imparted to the electricity 
as it traverses the region in which the e.m.f. is opera- 
tive; the units commonly employed being those of elec- 
tric potential, e.g., joules per coulomb (volts). 
elektromotorische Reihe: electromotive series. A series 
of different electrodes arranged in the order of their 
p.d.’s with normal solutions of their ions. There are 
two such series, one for positive and one for negative 
ions. 
Elektron: electron. The negative elementary charge. 
(Most writers confine the term to this, though some 
refer to both negative and positive electrons.) The 
mass of an electron at rest is approximately 9 X 10~28 g. 
ElektronenafFinitaet: electron affinity. (1) The ten- 
dency of an atom or molecule to attach free electrons 
and form negative ions. Its measure is the energy lib- 
erated upon the formation of the ion. (2) The p.d. 
corresponding to the energy necessary to separate an 
electron from a metal, as in photoelectric emission. 
Elek+ronenbande: electron band. A molecular spectrum 
band, usually in the visible or the ultraviolet, due to 
electron transitions within the molecule; as distinguished 
from rotational and vibrational transitions, which give 
bands in the infrared. 
elektronenberaubtes Atom: stripped atom. An atom 
which has in some manner lost most of its outer 
electrons. 
Elektronengas: electron gas. An aggregation of elec- 
trons to which a kinetic theory may be applied, in some 
respects similar to the kinetic theory of gases. 
Elektronenkanone: electron gun. A device for pro- 
jecting a narrow stream of electrons in any desired 
direction, e.g., a slender tube closed at one end and 
with a thermionic filament at the bottom of the bore, 
the whole being negatively charged. 
Elektronenleitung: electronic charge, Syn. elementary 
charge. The natural unit or quantum into which elec- 
tric charges, positive or negative, appear to be sub- 
divided. Its value has been found by electrical methods 
to be about 4.77 X 10~10 e.s.u.; X-ray and electron- 
wave data indicate a slightly higher value. 
Elektronenlehre: electronics. That branch of physical 
science which treats of electrons and of phenomena as 
37 
/Elektronenlinse E_ 
explained in terms of them, i.e., the electron theory; 
applied by some writers esp. to electronic vacuum-tube 
phenomena. 
Elektronenlinse: electron lens. An electric field, such 
as that about a circular opening in a charged metal 
plate, which acts upon an electron stream in a manner 
analogous to the action of a lens upon a beam of light. 
Elektronenmikroskop: electron miscroscope. A device 
for producing effects on streams of electrons, analogous 
to those produced on light rays in a microscope; a non- 
uniform magnetic or electric field being employed for 
the purpose, 
Elektronenoptik: electron optics. A system of con- 
trolling beams or rays of electrons by means of suitably 
adjusted electric or magnetic fields, the electron rays 
being thus made to imitate the rays of light in an 
optical instrument. 
elektronenoptische Blende: electro-optical shutter. A 
device for controlling or cutting off a beam of light 
by means of the Kerr electro-optical effect. 
Elektronenquantenzahl: electron quantum number. One 
of a set of numbers which serve to describe the quantum 
states of electrons within atoms and molecules or the 
state of the electron system as a whole, and including 
a variety of special types. 
Elektronenrohr: electron gun. See Elektronenkanone. 
Elektronenroehre: electron tube. A vacuum tube in 
which the motion of electrons is especially important, 
e.g., a thermionic, a photoelectric, or an X-ray tube. 
Elektronenteleskop: electron telescope. A device by 
means of which an infrared image of a distant object, 
focused upon a photosensitive cathode, gives rise to 
an enlarged electron image on a fluorescent screen. 
Elektronenuebergang: electron promotion. An increase 
in the principal quantum number of an electron, which 
may take place when the atom to which it belongs 
combines with another atom to form a diatomic mole- 
cule. Since it involves an increase in energy, such pro- 
motion renders the influence of the electron in question 
unfavorable to the union. 
Elektronvolt: electron-volt, volt electron, equivalent 
volt. A unit of energy, equal to about 1.591 X 10~12 
erg, and defined as the change in energy experienced 
by 1 electronic charge on passing through a p.d. of 1 
volt. 
Elektronenwelle: electron wave, de Broglie wave. See 
de Broglie-Welle. 
Elektrononwellenlaenge: electron wave length. The 
wave length associated with a moving electron. 
Elektronenniederschlag: electrodeposition. The depos- 
iting of a substance upon an electrode by electrolysis, 
as in electroplating. 
Elektronik: electronics. See Elektronenlehre. 
Elektronogen: electronogen. A molecule or group of 
molecules which, according to the Kowalski theory of 
luminescence, emit electrons under the influence of light. 
Elektroosmose: electric osmosis. The contact electrifi- 
cation of two dielectrics or of a dielectric and a con- 
ductor or semiconductor. 
electro-osmosis, electromosis. The move- 
ment of liquids through membranes or capillary tubes 
under the influence of an e.m.f. 
Elektrophor: electrophorus. An apparatus consisting 
of an electrified plate of some dielectric such as vul- 
canite, and, resting upon it, a metal disk provided with 
an insulating handle; used as a convenient means of 
generating, by induction, an indefinite succession of 
nearly equal electric charges. 
Elektrophorese: electrophoresis. The migration of 
particles or ions in a fluid under the influence of an 
electric field. 
Eiektrophotophorese: electrophotophoresis. A propul- 
sive effect of an intense beam of light upon very small 
particles (of the order of 1 micron in diameter) in sus- 
pension in the air; the particles moving in the either 
toward or away from the light source. The effect be- 
comes less as the pressure increases. In electrophoto- 
phoresis (photophoresis in an electric field) and in 
magnetophotophoresis (photophoresis in a magnetic 
field) the particles have a component of motion in the 
direction of the field. 
Elektroskop: electroscope. Any one of several types 
of instrument for the detection of small charges of 
electricity. 
Elektrostriktion: electrostriction. A deformation of a 
dielectric caused by subjecting it to an electric field. 
Elektrostatik: electrostatics. That branch of physics 
which treats of the properties of electricity which do 
not depend upon its motion. 
elektrostatische Analyse: electrostatic analysis. (1) 
The separation of a stream of electrified particles by 
an electric field in accordance with their mass, their 
/elektrostatische Einheit 
38 E 
charge, or their speed, as in a mass spectrograph. The 
apparatus used for this purpose is called an electrostatic 
analyzer. (2) In general, any process of separation 
or sorting by an electric field. 
elektrostatische Einheit: electrostatic unit. Any electric 
unit based primarily upon the mutual dynamic interac- 
tion of electric charges. The fundamental c.g.s. unit 
in this system is the electrostatic unit charge which, if 
concentrated upon a small sphere, would repel a similar 
charge 1 cm distant in a vacuum with a force of 1 dyne. 
elektrostatischer Generator: electrostatic generator. 
One of several recent designs of static machine, com- 
monly employing endless belts of insulating material 
which discharge inside the hollow terminals. 
elementares Wirkungsquantum: elementary quantum 
of action, Planck constant. A constant h having the 
dimensions of action (energy X time) and appearing 
in many physical formulas; approximate value, 6.547 X 
10~27 erg-sec. In particular it represents the ratio of the 
energy of any radiation quantum to its frequency. First 
recognized by Planck in 1900. 
Elementarladung: elementary charge. See Elektronen- 
ladung. 
Elementarzelle: elementary cell, unit cell, unit crystal, 
lattice unit. See Einheitszelle. 
Ellipsenzirkel: trammel. A mechanism consisting of a 
movable, straight bar, two relatively fixed points of 
which are constrained to move along grooves or tracks 
intersecting at right angles. Used for drawing ellipses, 
and in the Rowland mounting for concave gratings. 
elliptische Polarisation: elliptic polarization. Polariza- 
tion in which the cycle is an ellipse. 
Emanation: emanation. A term applied by Rutherford 
to the gaseous radioactive products formed by the ex- 
pulsion of an alpha particle from radium, from thorium 
X, or from actinium X; now internationally designated 
as radon, thoron, and actinon, respectively. 
Emissionsspektrum: emission spectrum. The spectrum 
of a substance, as displaying the radiation which it 
emits; in contrast to the absorption spectrum. 
Emissionsstaerke: emissive power, intrinsic radiance. 
The time rate of emission of radiant energy, in all 
directions, per unit surface area of a radiating body at 
a given temperature. The amount thus radiated within 
an infinitesimal wave length range dA is cxdA, in which 
e\ may be termed the monochromatic emissive power, 
as distinct from the total emissive power just defined. 
Emissionsstaerke: emissivity. The ratio of the total 
emissive power of a surface to that of a black body 
at the same temperature. If confined to the radiation 
within an infinitesimal wavelength range, it may be 
called monochromatic emissivity. It varies somewhat 
with temperature. 
Emissionsvermoegen: emissive power, radiating power. 
See Emissionsstaerke. 
Emissionswaerme: heat of emission. The additional 
heat energy that must be supplied to a surface which 
is emitting electrons, in order to maintain it at a con- 
stant temperature; analogous to heat if vaporization. 
Emission von positiven Ionen: positive-ion emission. 
Thermionic emission of positive particles; ions either 
of the metal itself or, commonly, due to some impurity. 
Empfindlichkeit: sensitiveness, sensibility, sensitivity. 
(1) A term applied to various measuring instruments, 
defined as the change in reading per unit of measured 
quantity. (2) (Phot.) The rate of chemical response 
of a photographic plate or film to light or other actinic 
emission. 
Emulsion: emulsion. (1) The photographically sensi- 
tive coating which is applied to glass or celluloid in the 
preparation of photographic plates or films. (2) A col- 
loidal solution, esp. one in which the suspended par- 
ticles are an oily liquid. 
enan+iomorph: enantiomorphic, enantiomorphous. In 
re two crystalline or molecular structures: having a bi- 
lateral symmetry with respect to each other, but incap- 
able of being superposed; after the manner of a right 
and a left shoe. 
enantio+rop: enantiotropic, monotropic. Occurring in 
two solid modifications, either of which is transformable 
into the other at a definite temperature. 
Endgeschwindigkeit: terminal velocity. The equilibri- 
um velocity attained by a body or a particle moving in 
a field of force through a resisting medium, e.g., the 
velocity finally attained by a body falling freely through 
the air, when the frictional resistance becomes equal 
to the weight of the body. 
Endkorrektion: end correction. A modification of the 
computed frequency of an organ pipe or similar acoustic 
apparatus, necessary because of the effect of the open 
end. 
Endosmose: endosmosis. The unidirectional diffusion 
of fluids through membranes or porous partitions, which 
results in osmotic pressure. The phenomenon is termed 
39 
/Endotherm E 
endosmosis when the diffusion is inward, toward the 
interior of the osmotic cell. 
endotherm: endothermic, endothermal. Involving the 
taking in of energy, esp. of heat energy, e.g., the melt- 
ing of ice. , 
Endprodukt: end product. The final, nonradioactive 
element of a radioactive series. 
Energie: energy. A physical entity, capable either of 
direct association with matter or (apparently) of inde- 
pendent existence. Energy is transferred from one body 
to another whenever the one does work on the other. 
This affords an expedient measure of energy, viz., the 
quantity of work done in the process of transfer; work 
units are thus also commonly used as energy units. 
According to the relativity theory, matter and energy 
are interconvertible in the ratio c2 absolute units of 
■energy to 1 unit of mass (c being the electromagnetic 
constant). 
Energiebande: energy band. In re a crystal: the set 
of energy values corresponding to the wave functions 
belonging to one or more of the Brillouin zones of the 
crystal. 
Energiedichte: energy density. The quantity of energy 
per unit volume in a given region. 
Energieellipsoid: energy ellipsoid, Poinsot ellipsoid. 
An ellipsoid drawn with reference to a rigid body in 
free rotation (under no external torque) about a chang- 
ing instantaneous axis, and used to illustrate the con- 
stancy of the rotational energy. 
Energiegleichung: energy equation. (1) An equation 
which expresses the energy of a system in terms of a 
system in terms of variables defining its configuration. 
(2) An integral equation connecting the variables re- 
lating to the motion of a particle, which results from 
the solution of the differential equations expressing the 
components of force acting upon the particle. 
Energieniveau: energy level, quantum state. One of 
the several discrete states in which an atom or a mole- 
cule may exist, permanently or momentarily, transitions 
between which are thought to cause the emission of 
distinct radiation frequencies and quanta, corresponding 
to lines of the spectrum. 
Energiestufe: energy level. See Energieniveau. 
Energiestufendiagramm: centroid diagram. A dia- 
grammatic scheme for the comparison of atomic electron 
energy levels in successive elements. 
Energiewall: energy wall, potential barrier. A region 
in which the electric potential is such that moving elec- 
tric charges attempting to traverse it encounter opposi- 
tion and may be turned back. 
entgasen: out gas, degas. To free from occluded or 
adsorbed gases by the application of heat. 
Entglasung: devitrification. Crystallization of a vitre- 
ous or amorphous substance upon subjection to a suit- 
able temperature; sometimes accompanied by a con- 
siderable evolution of heat. 
Enthalpie: enthalpy. A term applied by H. K. Onnes 
to the Gibbs function x — u + pv and superseding 
total heat, heat content, and heat of formation. (2) 
For a fluid system subject to no outside forces except 
a uniform, normal pressure, it is the thermodynamic 
potential for constant entropy and pressure. A process 
in which this quantity is constant is said to be isen- 
thalpic. 
Entladungskoeffizient: discharge coefficient. The cor- 
rection factor by which the theoretical rate of (volume) 
discharge through an orifice, 7rr2\/2gh, must be mul- 
tiplied to give the actual rate as determined by experi- 
ment. 
Entladungsroehre: discharge tube, vacuum tube. A 
general term applying to tubes or bulbs supplied with 
electrodes between which electric discharge takes place, 
and operated at pressures ranging from slightly below 
atmospheric to the lowest attainable Radio tubes and 
other triodes are also included. 
Entladungsschalter: discharge key. A device for sud- 
denly switching the connections of a condenser from 
the charging circuit to a circuit through which it 
discharges. 
Entladungsstrahlen: Entlagungsstrahlen, discharge rays. 
A radiation from spark discharges, which produces 
marked ionizing and thermoluminescent effects and is 
absorbed by fluorite. When produced in air at atmos- 
pheric pressure, the wave-length range extends from 
400 to 1000 Ä, with shorter wave lengths at lower 
pressures. 
Entmagnetisierungsfaktor: demagnetizing factor, de- 
magnetizing coefficient. The factor by which the mag- 
netization must be multiplied to give the oppositely di- 
rected magnetic intensity associated therewith (demag- 
netizing field). In an ellipsoid with uniform magnetiza- 
tion, this factor has the same value at every point. 
Entmagnetisierungsfeld: demagnetizing field. That 
component of the magnetic intensity in a ferromagnetic 
body which is due to the magnetization of the body 
/Entmodulator 
40 E 
itself and which depends only upon its magnetization 
and shape. 
Entmodulator: demodulator. A detector for h.—f. car- 
rier telephone signals. 
Entropie: entropy. A quantity introduced by Clausius. 
The entropy associated with an isolated physical system 
has the characteristic property that, as the system spon- 
taneously settles into a final, steady state, the entropy 
approaches a maximum. It may be regarded as a measure 
of the degree in which the energy of the system is 
unavailable. 
Entropiefunk+ion: entropy function. An expression for 
the entropy of a body as a function of the temperature. 
For a gas it takes the form of the Sackur equation. 
Eoe+voes'sche Waage: Eoetvoes balance. A form tor- 
sion balance especially designed for the detection and 
measurement of local irregularities in gravity. 
Eoetvoes-Ramsey-Shield'sches Gesetz: Eoetvoes-Ram- 
sey-Shields law. An empirical rule which states that 
the surface tension of a liquid is proportional to Tc 
—T — 6°, in which T is the absolute temperature of the 
liquid and Tc the absolute value of its critical tem- 
perature. 
Epstein'scher Apparat: Epstein apparatus. A type of 
transformer used primarily for the measurement of core 
losses. Devised by J. Epstein (1911). 
Erdlnduktor: earth inductor. A coil, the sudden rota- 
tion of which in the earth’s magnetic field causes a 
surge of electricity and thus affords a means of measur- 
ing the intensity of the field. 
Erg: erg. The absolute e.g.s. unit of energy and work, 
whose length and force factors are the centimeter and 
the dyne; i.e., the centimeter-dyne. 
Ergometer: ergometer. An apparatus for measuring 
energy as it is transferred, e.g., from one machine to 
another. It commonly takes the form of a friction brake 
and a speed indicator. 
Erg-Sekunde: erg-second. The e.g.s. absolute unit of 
action. 
Erhaltung: conservation. The preservation of a con- 
stant amount, as of mass, of momentum, or of energy. 
Erhoehen: step-up. A term relating to the increase 
of voltage by a transformer or equivalent device. 
erlaubte Abweichung: tolerance. The maximum error, 
or variation from the standard, permissible in a measur- 
ing instrument, e.g., a weight. 
Ermuedung: fatigue. The gradual decrease of some 
characteristic property due to external causes; e.g. of the 
photoelectric sensitivity of certain surfaces upon pro- 
longed exposure to light. 
Ermuedungsgrenze: fatigue limit. The range of stress 
to which an elastic material may be subjected a stated 
number of times in succession without fracture. 
Ermuedungsstaerke: fatigue strength. See Ermuedungs- 
grenze. 
Erniedrigen: step down. A term relating to the de- 
crease of voltage by a transformer or equivalent device. 
Eriometer: eriometer. An apparatus, due to Young, 
for measuring the diameters of very small objects by 
diffraction. 
Ersetzen einer Ecke oder Kante durch Flaechen: re- 
placement. The occurrence of crystal faces which de- 
velop in place of edges or apexes, thus apparently 
truncating the latter. If such a face makes equal angles 
with two adjacent faces which would otherwise form 
an edge, it is said to be a bevel face. 
erster Dunkelraum: primary dark space. A narrow, 
nonluminous region which appears between the cathode 
and the cathode glow in certain gases. 
erstes (u.s.w.) Funkenspektrum: first (etc.) spark spec- 
trum. The spectrum of a singly (doubly, etc.) ionized 
element. 
erzwungene Doppelbrechung: forced double refrac- 
tion. Double refraction produced in an otherwise iso- 
tropic medium as a result of strain. 
erzwungene Schwingung: forced vibration. A non- 
resonant vibration imposed upon a body or a system 
by some external agency, by which the frequency is 
also controlled. 
Esclangon'scher Effekt: Esclangon effect. The devia- 
tion of a ray of reflected light, due to the motion of the 
mirror in a direction oblique to its surface. 
Etalon: etalon. A type of interferometer for producing 
interference effects by means of multiple reflection be- 
tween fixed parallel, half-silvered glass plates. Devised 
by Fabry and Perot. 
Ettingshausen'scher Effekt: Ettingshausen effect. A 
difference of temperature which develops between the 
41 
/Euler'sche Formel E 
two edges of a strip of metal, in which an electric cur- 
rent is flowing longitudinally, when the plane of the 
strip is set perpendicularly across a magnetic field. 
Euler'sche Formel: Euler formula. A formula for the 
load P which an elastic column of length 1, sectional 
moment of inertia I, and Young modulus E, will sus- 
tain : viz.. 
results in osmotic pressure. The phenomenon is termed 
exosmosis when the diffusion is outward, toward the 
exterior of the osmotic cell. 
exotherm: exothermic, exothermal. Involving the giv- 
ing out of energy, esp. of heat energy; e.g., the conden- 
sation of steam. 
expandierendes Universum: expanding universe. See 
ausdehnendes Universum. 
Expansionskammer: expansion chamber, cloud cham- 
ber, jog c. A closed space containing saturated water 
vapor which, upon sudden expansion, reveals the pres- 
ence of condensation nuclei by the visible droplets 
formed upon them; or in which rapidly moving particles 
are revealed by the streaks of droplets, or tracks. 
Expansionskoeffizient: expansion coefficient, expansiv- 
ity. See Ausdehnungskoeffizient. 
Explosionsspektrum: explosion spectrum. The spectrum 
of the light produced by an explosive reaction or by 
electrically "exploding” a metallic wire or filament by 
a heavy current. 
Extinktion: extinction. (1) The decrease of intensity 
in radiation due to both absorption and scattering by 
the medium traversed. (2) Specifically, the shielding 
of inner layers of atoms in a crystal from incident X-rays 
by the outer layers. 
Extinktionskoeffizient: extinction coefficient, total ab- 
sorption coefficient. In re any type of radiation travers- 
ing a material medium: the absorption coefficient plus 
the scattering coefficient. 
Extinktionsphotometer: extinction photometer. A pho- 
tometer in which the luminous intensity of a source of 
light is judged by the thickness of a given absorbing 
material necessary to render it invisible. 
Extraktionsenergie: extraction energy. See Abloesungs- 
energie. 
extrapolieren: extrapolate. To estimate the value of 
a function for values of the variable lying outside the 
range in which values of the function are known; as by 
extending the graph of the function beyond the actually 
plotted points. 
4tt2EI 
P = 
I2 
Euler'sche Gleichungen: Euler equations. Three dif- 
ferential equations of motions of a rigid body, referred 
to the principal axes through the c.m. as coordinate 
axes (X, Y, Z). They are: 
dwx 
Ix Wy Wz (ly L) = Qx , 
dt 
dWy 
ly W. Wl (I. lx) — Qy , 
dt 
d\Vz 
Iz Wi Wy (lx ly) ZZ Qz ] 
dt 
in which I is the moment of inertia, w is the angular 
velocity component, and Q is the torque component, 
about the corresponding principal axis. 
eutektisch: eutectic. In re a mixture or a solution: 
in such proportions that all ingredients solidify or 
liquify at the same temperature; which is also the 
minimum solidification temperature for all, mixtures 
of the same substances. 
eutektoid: eutectoid. Similar to eutectic, except that 
it has reference to a solid solution, which resolves into 
separate components while in the solid state. Certain 
kinds of steel have this property. 
Eve'sche Konstante: Eve constant. The number of 
ions produced per cm3 per sec in air at N.T.P., at a 
distance of 1 cm from a source of radium C in equi- 
librium with 1 curie of radon. Its value is approxi- 
mately 3.56 X 109- 
Exosmose: exosmosis. The unidirectional diffusion of 
fluids through membranes or porous partitions, which 
/f-Elektron 
42 F 
f-Elek+ron: f-electron. An orbital electron whose 
energy state is denoted by the azimuthal quantum num- 
ber 3. 
f-VVert; f-value. The atom form factor, taken with 
reference to the center of the atom. 
F-Wer+: F-value. A symbol used by some writers for 
the atom form factor taken with reference to the lattice 
point corresponding to the atom, rather than to the 
center of the atom itself. 
F-Zusfand: F-state, F-level. The state of an atom 
in which the azimuthal quantum number is 3. 
Fabry-Perof Interferometer: Fabry-Perot interferome- 
ter. A multiple-reflection instrument of very high re- 
solving power, simpler than the Michelson type. It 
resembles an etalon, but with the distance between the 
plates variable by means of a micrometer screw. 
Fadenkreuz: reticle, reticule. A network or a single 
pair of cross hairs placed in the focal plane of an opti- 
cal instrument to serve as a reference system. 
Fadenmesser: fathometer. An instrument devised by 
H. G. Dorsey for supersonic ocean sounding. A neon 
tube, which rotates as an index around a circular dial, 
indicates the depth directly in fathoms by flashing upon 
the arrival of the echo. 
Fadenmikrometer: filar micrometer. A micrometer, the 
screw of which moves a fine wire or filament across 
the focal plane of a microscope or a telescope, and which 
can thus be used to measure the size of, or the angle 
subtended by, the object under examination. 
Faerbung: hue. That attribute of certain colors which 
permits them to be classed as reddish, yellowish, green- 
ish, or bluish. 
Fajans und Soddy'sche Gesetze: Fajans and Soddy 
laws. The radioactive "displacement laws,” which state 
that, upon the disintegration of a radioactive atom, (1) 
the emission of an alpha particle results in a new radio- 
active element with atomic number 2 units less, and 
(2) the emission of a beta particle results in a new 
element with atomic number 1 unit more, than the 
disintegrating atom. 
Fallbeschleunigung: Acceleration of gravity. The ac- 
celeration of a freely falling body due to the attraction 
of gravity, expressed as the rate of increase of velocity 
per unit of time; usually denoted by g. Its value varies 
slightly in different localities, being 980.621 cm (32.17 
feet) per second per second at the sea level in latitude 
45 degrees. 
falsche Linie: ghost. A false line appearing in a grat- 
ing spectrum, due to some defect of the grating. 
Farad: farad. A unit of capacitance corresponding to 
1 coulomb per volt and equal to 10~9 abf, named from 
Faraday. A more convenient unit is the microfarad, or 
io-6f. 
Farad'sche Bruecke: farad bridge. A capacitance bridge 
arranged to read capacitances directly in microfarads. 
Faraday: faraday, faraday electrolytic constant. Ob- 
jectionable because of its resemblance to farad. 
Faraday elektrolytische Konstante: Faraday electrolytic 
constant, Faraday electrochemical constant. The quantity 
of electricity which, in electrolysis, is required to liber- 
ate a gram atom of any univalent element; viz. approxi- 
mately 96,494 international coulombs per gram equiva- 
lent. 
Faraday'sche Gesetze: Faraday laws. Two laws of 
electrolysis, which state: (1) That the mass of any 
substance liberated by electrolytic action is in proportion 
to the quantity of electricity passing through the cell. 
(2) The masses of different substances liberated upon 
the electrolytic conduction of equal quantities of elec- 
tricity are in proportion to the combining equivalents 
of those substances. Also: (3) The law of magneto- 
electric induction, viz., the e.m.f. induced in a circuit 
by the variation of the magnetic linkage with that cir- 
cuit is proportional to the rate of variation of the 
linkage. 
Faraday'sche Konstante: Faraday constant. See elek- 
trochemische Konstante. 
Faraday'scher Dunkelraum: Faraday dark space. The 
nonluminous region separating the negative glow from 
the positive column in a Crookes tube at moderate 
pressure. 
Faraday'scher Effekt: Faraday effect, magnetic rota- 
tion, magneto-optical. A magneto-optical phenomenon, 
viz. the rotation of the polarization plane of polarized 
light by an otherwise isotropic medium subjected to a 
magnetic field coincident in direction with the beam of 
light; discovered in 1845. 
Faraday'scher Kaefig: Faraday ice pail. A hollow, 
closed or nearly closed, insulated metal receptacle, used 
to demonstrate that when a charge is communicated. to 
the inside of a hollow conductor it appears on the out- 
side. (Faraday originally used a tin ice pail for this 
purpose.) 
Faraday'sche Roehre; Faraday tube, tube of force. A 
43 
/Faraday'scher Zylinder F_ 
region in a field of force, of tubular form, having its 
lateral surface made up of lines of force, so that the 
intensity at any point of that surface is tangential to 
it, and the flux is the same through all cross sections. 
Faraday'scher Zylinder: Faraday cylinder, F. collector. 
A hollow, insulated metal cylinder, nearly closed, and 
placed so as to catch charged particles, the whole charge 
of which then appears upon its surface. 
Farbe: color. A term used in re those attributes of 
visual sensation which do not depend upon shape, size, 
or other spatial characteristics of the image. Thus if 
two uniform circular disks of equal size and at equal 
distances do not look alike, that fact is due to a differ- 
ence in one or more of the three attributes of color, 
namely, hue, saturation and brilliance. 
Farbentempera+ur: color temperature. In re a source 
of radiation: the temperature of a black body in color 
match with it. A definite color temperature can be as- 
signed only to radiators whose energy distribution does 
not differ greatly from that of a black body. 
faserig: funicular. Pertaining to, or made up of, 
rope or cord under tension; e.g., a funicular polygon. 
Fatamorgana: looming. A type of mirage in which 
images of objects below the horizon appear in dis- 
torted form. 
Fatamorganabild: mirage. An optical phenomenon 
produced by the presence of a stratum of heated air 
of varying density, across which the observer sees re- 
flections, usually inverted and distorted, of distant ob- 
jects. 
Fedorov'sche Koordinaten: Fedorov co-ordinates. The 
distances, measured along the Cartesian co-ordinate axes 
(not necessarily rectangular) to the projections of the 
given point in space upon those axes. If the axes are 
rectangular, these co-ordinates are identical with the 
Cartesian co-ordinates, otherwise not. Used in cry- 
stallography. 
Feld: field. (1) A region under the influence of some 
physical agency, e.g. gravitation, magnetism, etc. (2) 
Syn. field intensity. (3) The area or solid angle visible 
through an optical instrument. 
Feldemission: field emission, f. current, autoelectronic 
emission, cold emission. The emission of electrons re- 
sulting from the application of intense electric fields. 
Feldgleichung: field equation. One of the equations 
which specify the properties of a field of force; e.g., 
the Maxwell equations for the electromagnetic field. 
/ Fe i n sf r u ktu rq u a nte nza hi 
Feldinduktionsspule: flip coil. A coil which may be 
suddenly rotated through 180 degrees in a magnetic 
field; the resulting current surge, measured by a ballistic 
galvanometer, indicates the intensity of the field. 
Feldintensitaet: field intensity. A vector denoting the 
magnitude and the direction, at any point, of an influ- 
ence distributed through a field. 
Feldlinse: field lens. The anterior of the two lenses 
of the ocular of a telescope or a microscope, the effect 
of which is to enlarge the field of view. 
feldlose Emission: zero-field emission. The thermionic 
emission from a hot conductor surrounded by a region 
of uniform electric potential. 
Feldmagnet: field magnet. A magnet used to pro- 
duce a magnetic field in some selected region, as in a 
motor or a generator. 
Feldpunkf: field stop. An opening, usually circular, 
in an opaque screen, which determines the field of view 
of an optical instrument. 
Feldspule: field coil. One of the coils used to excite 
a field magnet. 
Feidstrom: field emission, f. current, autoelectronic 
emission, cold emission. See Feldemission. 
Fehler: fault. An interruption in the continuity or a 
defect in the insulation of an electrical conductor, such 
as a telephone line or a cable. 
Fehlergleichung: error equation. An equation express- 
ing the probability of the occurrence of an error x: 
hA 
p — e-h2x2 
\/ 7r 
h is the precision index or measure of precision, A the 
error interval, i.e., the smallest scale unit used in ex- 
pressing the results of measurement and hence in express- 
ing the errors. 
Fehlstelle: fault. See Fehler. 
Feinstruktor: fine structure. Refers to the occurrence 
of spectral lines as doublets, triplets, etc. 
Feinstrukturkonstante: fine-structure constant. The 
quantity 27re2/ch, in which e is the electronic charge, 
c the electromagnetic constant, h the Planck constant. 
The dimensions of these factors are such that the fine- 
structure constant is abstract. Its value is about 7.285 
44 F 
X 10~3 or 1/137. It plays a fundamental role in 
quantum theory and spectroscopy. 
Feinstrukturquantenzahl: fine quantum number, hyper- 
fine quantum number. The quantum number associated 
with the quantization of the resultant of nuclear and 
extranuclear angular momenta. Its name arises from 
its relation to hyperfine structure. 
Fermat'sches Gesetz: Fermat principle, F. law. A 
principle, announced by Fermat about 1665, which 
states that when light passes from a point A to another 
point B, the time required for its passage is either a 
maximum or a minimum with respect to other adjacent, 
arbitrary paths. For points in two homogeneous media 
separated by a plane surface, or for reflection in a sin- 
gle homogeneous medium by a plane surface, the time 
is a minimum, in which case the law is commonly 
known as the principle of least time. 
Fermat'sches Prinzip: Fermat principle, F. law. See 
Fermat’sches Gesetz. 
Fermi-Dirac Statistik: Fermi-Dirac statistics. Differs 
from the Bose-Einstein statistics (q.v.) in that it im- 
poses a specified upper limit to the number of mole- 
cules or quanta which may be contained in any one 
elementary compartment of the momentum space. 
Fermi-Thomas Feld: Fermi-Thomas distribution, F.-T. 
field. The approximate theoretical distribution of the 
electric potential within and about an atom, based upon 
certain physical and statistical assumptions. If the local 
density matrix is represented by plane waves, it is the 
closest approximation to this potential; otherwise Har- 
tree’s self-consistent fields is closer. 
Fermi-Thomas Verteilung: Fermi-Thomas distribution, 
F.—T. field. See Fermi-Thomas Feld. 
Fernpunkt: far point. That point on the axis of the 
eye which is at such distance as to be seen distinctly 
wnen the accommodation is completely relaxed, i.e., 
when the focal power of the crystalline lens is least. 
■ferromagnetisch: ferromagnetic. A term used to char- 
acterize substances which have, at ordinary temperatures, 
a combination of magnetic properties including the fol- 
lowing: their susceptibility is positive as in paramag- 
netic substances; but they exhibit appreciable remanence 
and hysteresis. The magnetization has a measurable 
saturation limit, ordinarily far in excess of any mag- 
netization attainable by paramagnetic substances; and 
even when unmagnetized they appear to have small re- 
gions (domains) throughout each of which there is 
definite magnetization. Iron, nickel, cobalt, gadolinium, 
and many alloys are ferromagentic. 
feste Loesung: solid angle. A portion of the whole 
of space about a given point, bounded by a conical sur- 
face with vertex at that point and measured by the 
area cut by the bounding surface from the surface of a 
sphere of unit radius centered at that point. 
Feuchtigkeit: humidity. (1) (Absolute.) The per- 
centage, by weight, of water vapor in the air. (2) 
(Relative.) The fraction of saturation of the water vapor 
in the air. 
Feuchtigkeitsmesser: Wet- and dry-bulb thermometer, 
psychrometer. A hygrometer consisting of two identical 
thermometers, the bulb of one of which is kept wet 
with water supplied by a wick. The lowering of the 
temperature by evaporation indicates the relative hu- 
midity of the air. 
Fick'sches Gesetz: Fick law. Expresses the rate of 
diffusion of a substance in solution as follows: 
dm dC 
= — Ds ; 
dt dx 
in which m is the mass diffused in time t through cross 
section s normal to the direction x, C is the concen- 
tration, and D is the diffusion coefficient. 
fiktive Ladung: fictitious charge, fictive c. A term 
used to characterize the phenomena exhibited by a di- 
electric in an electric field, in contradistinction to the 
"true’' induced charges on a conductor under the same 
conditions. 
Filter: fiter. (1) Any device which separates one or 
more of the ingredients of a mixture from the others. 
In particular: (2) (Radiation.) A selectively trans- 
parent body, which transmits only certain wave-length 
ranges. (3) (Electric.) A portion of a h.-f. circuit, 
which, by means of suitable inductances and capaci- 
tances, suppresses certain frequencies in a complex elec- 
tric wave. (4) (Acoustic.) A device which acts on a 
sound in a manner analogous to an electric wave filter, 
by cutting out certain frequencies. 
Fi+zgerald-Lorentz'sche Kontraktion; Fitzgerald-Lorentz 
contraction, Lorentz-Fitzgerald contraction, relativity 
contraction. A hypothetical shrinkage of all matter in 
the direction in which it moves through the ether, such 
that all dimensions in this direction are reduced in the 
ratio 
Vl :l; 
c2 
where u is the speed of the motion and c, the speed 
of light. 
/Fixierung 
45 F 
Fixierung: fixation. The act of orienting the eye so 
that a given point of the retinal image falls upon that 
point of the retina at which it may be most distinctly 
seen. The corresponding point of the actual object is 
the fixation point. 
Flackern: flicker. The sensation produced by a fluctu- 
ation in brightness at a rate comparable to the reciprocal 
of the period of persistence of vision. 
Flaechendichte: sutfacg density. The quantity per unit 
area of anything distributed over a surface, e.g. of an 
electric charge. 
Flaechenerhaltung: conservation of areas. A general 
principle of kinematics, illustrated by Kepler’s second 
law of planetary motion. 
Flaechenreduk+ion: reduction of area. The percentage 
ratio of the difference between the original and the 
broken area of cross section of a rod which has been 
pulled apart, to the original area. 
Flaechenpolarisation: plane polarization. Polarization 
in which the cycle is a straight line, corresponding to a 
rectilinear vibration. 
Flaechentraegheitsmoment: angular impulse. The time 
integral of a torque, esp. when applied for a short time; 
measured by the change in angular momentum which 
it would impart to a free mass if acting about a prin- 
cipal axis. 
Flaechenwinkel: interfacial angle. The dihedral angle 
between two adjacent faces of a crystal. 
flaechenzentriert: face-centered. In re a unit cell of 
crystal structure: having an atom at the center of each 
face. 
Flaechenzentrum: center of area. In re a plane figure: 
that point which corresponds to the center of mass of an 
infinitely thin, uniform plate whose boundaries coincide 
with those of the plan figure. 
Flammenbogen: flaming arc, flame a. An electric arc 
produced between carbons which have been impregnated 
with chemical salts. 
Fleming-Kennelly'sches Gesetz: Fleming-Kennelly law. 
States that the reluctivity of a ferromagnetic material 
is a linear function of the magnetic intensity, as mag- 
netic saturation is approached. Equivalent to the rela- 
tion expressed by the Froehlich equation. 
Fliehkraft: centrifugal force. The kinetic reaction ex- 
erted by a body under the influence of a force directed 
toward a fixed center. 
Fliesspunkt: yield point, y. value. A value of the ten- 
sile stress, somewhat greater than the elastic limit, for 
which a rod of elastic material under tension begins 
to exhibit plasticity and stretches irregularly. Sometimes 
applied also to the corresponding shearing stress. 
fluessiger Kristall: liquid crystal. A liquid that has 
optical anisotropy and other properties similar to those 
of a crystal, e.g., para-azoxyanisole. Such a substance 
is said to be in a liquocrystalline or mesormorphic state. 
Fluechtigkeit: fugacity. A term employed in thermo- 
dynamics to denote quantitatively the tendency of a 
substance to escape or to disappear by some chemical 
process from the phase in which it is. The ratio of 
the fugacities if a substance in two different phases may 
be measured by the excess of free energy per mol in 
the one phase over that in the other. 
Fluessigkeitsdruck: Fluid pressure. 
Fluessigkei+smanometer: piezometer. (1) A glass bulb, 
the stem of which is closed by a plug of mercury, and 
in which liquids may be placed for the purpose of 
studying their behavior under great pressure. (2) A 
simple liquid manometer. 
Fluoreszenz: fluorescence. A type of luminescence, 
characterized by the fact that it is observable only so 
long as the stimulus responsible for it is maintained. 
fluoreszenzerregender Stoff: fluorogen. A substance 
which promotes the fluorescence of another when mixed 
with it. Syn. activator. 
Fluoreszenzmesser: fluorometer. (1) An instrument 
for the measurement of fluorescence. (2) A apparatus 
for photometric measurement in the ultraviolet by 
means of the fluorescence produced by it; devised by 
Winther. 
Fluoroskop: fluoroscope. An instrument provided with 
a suitably mounted fluorescent screen, and used for 
detecting and studying X-rays or other emissions capable 
of exciting it. 
Fluss: flux. (1) A term used in connection with fields 
of force, the flow of fluids, various types of emission, 
etc., and designating in general the surface integral of 
normal field intensity, or the quantity of fluid or of 
emitted energy per unit time, over a specified area. 
(2) A substance used to facilitate the fusion of a metal 
and to protect it from oxidation while in the fused 
state. 
/Flussbrechung 
46 F 
Fiussbrechung: flux refraction. A change in the di- 
rection of the magnetic induction at the interface be- 
tween two media of different permeability, or of the 
electric displacement at the interface between two di- 
electrics of different dielectric constant. 
Flussdichte: flux density, intensity. (1) (Magnetic.) 
Syn. magnetic induction. (2) (Electric.) Syn. electric 
intensity. The flux through unit area of a surface nor- 
mal to the direction of propagation; or, for a diffuse 
emission, the flux per unit solid angle per unit area 
normal to a specified direction. 
Flusselastizltaet: fugitive elasticity. Maxwell’s con- 
ception of viscosity as the limiting case of elasticity, in 
substances just breaking down under shear and begin- 
ning to flow. 
Flussiinie: line of flow, streamline. The path followed 
by any one particle of fluid when flowing. 
Flussmesser: fluxmeter. A ballistic galvanometer hav- 
ing negligible mechanical control of the position of the 
moving system; used primarily in conjunction with a 
suitable exploring coil for the measurement of mag- 
netic flux. 
Flussroehre: tube of flow, stream tube. A portion of 
a moving fluid bounded by lines of flow. 
Flussverbindung: flux-turns, linkage, turn-flux. A 
measure of the interlocking of a magnetic flux with an 
electric circuit, viz., the product of the flux by the 
number of turns of the circuit surrounding it, expressed 
in maxwell-turns. 
Fokus: focal spot, anode spot, cathode s. The small 
area of an X-ray tube target upon which the cathode 
rays are concentrated and from which the X-rays pro- 
ceed. 
Fokusmesser: focometer. An instrument for measuring 
the focal length of a lens or of an optical system. 
Folge-Gesetz (Kossel-Somerfeld): alternation law. See 
Alternationsgesetz. 
Form (Kristallebenengruppe): form. A group of plane- 
families which, although represented by different per- 
mutations of the same Miller indices, are crystallo- 
graphically indistinguishable. E.g., in a cubic crystal, 
the (110) form is composed of the plane-families (110), 
(101), (Oil), (IlO), (lT0), and (Oil). 
Formfaktor; multiplicity factor, form factor. A fac- 
tor of the intensity of an X-ray beam reflected from 
a crystal, which depends upon the number of planes 
parallel to one face of the crystal form which are 
jointly responsible for the reflection, and hence upon 
the character of the form. 
Fortrat'sches Diagramm: Fortrat diagram. A para- 
bolic diagram by means of which the component lines 
of molecular bands may be represented graphically. 
fortschreitende Bewegung: translation. A displacement 
of a body or a figure in which the line joining any 
two points remains parallel to its original direction and 
its length remains unchanged. 
fortschreitende Reihe: progression. A set of spectral 
bands having a common upper (or lower) rotational 
state, but differing by steps of unity in the vibrational 
quantum number of the lower (or upper) state. 
Foucault Pendel: Foucault peizdulum. A pendulum 
consisting of a very heavy mass suspended by a very 
long wire, the plane of vibration of which appears to 
change gradually owing to the rotation of the earth; 
as first demonstrated by Foucault in 1851 at Paris. 
Fourier Integrale: Fourier integral. A double definite 
integral which constitutes a limiting case of the Fourier 
series, and the form of which is 
1 [ + 00 
f (X) = f (r) dr 
7r J 00 
' -f 00 
cos s(r—x)ds 
. o 
Fourier'scher Lehrsatz: Fourier theorem. States that 
any finite, periodic motion may be analyzed into com- 
ponents, each of which is a simple harmonic motion 
of definite and determinate amplitude and phase. 
Fourier'sche Reihe: Fourier series. A series of the form 
2?rX 4ttX 
f(x) — a0 + ai sin + a2 sin 
1 1 
6ttx 2ttx 
+ a3 sin + .... -f bx cos 
1 1 
4ttx 6ttx 
+ b2 cos + b3 cos + . . . . 
1 1 
in which the coefficients have the values 
1 f1 
a0 = f (x) dx, 
1 J o 
2 f 1 27rnx 
an = f (x) sin dx, 
1 J o I 
2 C 1 277-nx 
bn = ' f (x) cos dx. 
1 o I 
677865—46 4 
47 
/Franck-Condon'sches Prinzip F 
In series representing a physical function, these coeffi- 
cients may be obtained from the results of experiment. 
Franck-Condon'sches Prinzip: Franck-Condon princi- 
ple. A theoretical interpretation of the relative inten- 
sity of spectral bands of a given system on the basis 
of electronic transitions within the molecule, and the 
vibrations which result from them. 
Fraunhofer'sche Linien: Fraunhofer lines. The dark 
absorption lines of the solar spectrum, the more promi- 
nent of which were first studied by Fraunhofer in 1814 
and designated by letters A, B, , FI. 
freie Energie: free energy. (1) That part of the 
thermodynamic potential of a system which is internal, 
i.e., the thermodynamic potential at constant volume. It 
is expressed by the Gibbs function. The term is due 
to Helmholtz. (2) Syn. available energy. 
freier Kolbenmanometer: free-piston gauge. A gauge 
for high pressures, in which the unknown pressure is 
applied to a small piston, the resulting force being small 
enough to be conveniently measured. 
freier Magnetismus: free magnetism. (1) The mag- 
netic flux through an area of the surface of a body 
bounded by that closed line for which this flux is a 
maximum. On a magnet this line is the magnetic 
equator; in an electric circuit it is the outermost current 
streamline. (2) The pole strength corresponding to 
(1). 
freies Elektron: free electron. An electron within a 
substance but not permanently attached to any one atom 
and not restricted by potential gradients within the 
substance. 
Freiheitsgrad: degree of freedom. One of the inde- 
pendent ways in which a body or a system may alter 
its position, the configuration of its parts, or more gen- 
erally, its state. A system has as many degrees of free- 
dom as there are independent variables required to de- 
fine its position or condition. E.g., a system composed 
of two points has six degrees of freedom, one for each 
of the three co-ordinates of each point. 
Frequenz: frequency. (1) The number of occurrences 
of a periodic process per unit time. (2) The number 
of values of a statistical variable which lie within a 
specified range. 
Frequenzbruecke: frequency bridge. An arrangement 
resembling a Wheatstone bridge, and used for the meas- 
urement of a.-c. frequencies. 
Frequenzmesser: frequency meter. Any instrument for 
measuring the frequency of an a.c. or of electric oscil- 
lations. 
Frequenzniveau: frequency level. The logarithm to the 
base 2 of the tone interval between a given musical 
frequency and a specified keynote or reference fre- 
quency. For an interval of one octave, the frequency 
level is unity. 
Frequenzverhaeltnis: frequency ratio. The ratio of the 
frequency impressed upon a vibrating system (as a cir- 
cuit) to the natural or resonant frequency of the sys- 
tem. For perfect resonance, the ratio is unity. 
Frequenzverteilung: frequency distribution. A mathe- 
matical expression indicating the relative frequency with 
which the value of a statistical variable may be ex- 
cepted to lie within any specified interval. 
Frequenzzustand: frequency condition. The condition 
upon which an atom or a molecule may emit radiation 
of given frequency; viz., it must undergo a change of 
energy equal to that frequency multiplied by the Planck 
constant h. 
Fresnel, Einheit der Frequenz: fresnel. A unit of fre- 
quency, equal to 1012 cycles per second. 
Fresnel'sche Formel: Fresnel formula. An expression 
for the loss of light perpendicularly incident at an in- 
terface between two transparent media. If the relative 
refractive index is n, the fractional loss is 
V n + 1 / 
Fresnel'scher Mitnahmekoeffizient: Fresnel coefficient 
of drag. The ratio, according to Fresnel, of the velocity 
of the ether in a moving transparent medium to the 
velocity of the medium itself; supposed to have the 
value 
1 
1 — 
n2 
where n is the refractive index of the medium. 
Fresnel'scher Rhombus: Fresnel rhomb. A rhombic 
glass prism, so shaped that a ray of plane-polarized light 
entering by one face emerges from the opposite face 
after two internal reflections, and is thereby elliptically 
polarized. 
Fresnel'sche Spiegel; Fresnel mirrors. A pair of mir- 
rors placed side by side at a very obtuse angle, so that 
they produce two adjacent images of a point or line 
source of light from which interference bands may be 
formed. 
/Fresnel'sche Zone 
48 F 
Fresnel'sche Zone: Fresnel zone, half-period element, 
Huygens zone. One of the zone-like or annular areas, 
cut out from an advancing wave front by a succession 
of ideal, spherical surfaces concentric at any point of 
observation in the path of the oncoming wave and 
separated by radial distances each equal to one-half 
wave length; an analysis commonly employed in the 
theory of wave propagation and diffraction. 
Friktionskegel: cone of friction. A conical surface, 
within which always lies the line of the resultant of 
the friction between two surfaces and the normal force 
pressing them together. Its half-angle is the angle of 
friction. 
Friktionswinkel: angle of friction, angle of repose. (1) 
The angle whose tangent is the friction coefficient. 
(2) The angle of inclination assumed by the surface 
of a loose material, such as sand in a pile, when in 
equilibrium with gravity. 
Froehliche Gleichung: Froehlich equation. An empiri- 
cal formula for the magnetic induction in terms of 
magnetic intensity H; 
H 
B = , 
a + bH 
in which a and b are constants. Approximately valid 
as saturation is approached. 
fuenfseitiges Prisma: penta prism. A five-sided opti- 
cal prism, of which one angle is 90 degrees and the 
other four are 112 degrees 30 minutes each. A ray en- 
tering at one of the faces adjacent to the 90-degree edge 
emerges from the other, after two internal reflections, 
at right angles to its original direction. 
Fulcher'sche Banden: Fulcher hands. The first known 
regularities in the spectrum of the hydrogen molecule, 
discovered by G. S, Fulcher in 1912. 
Funkenspek+rum: spark spectrum. The spectrum of a 
substance produced with light from a spark between 
terminals composed of that substance, or in an at- 
mosphere of that substance. 
Funkenverzoegerung: spark lag. A time interval be- 
tween the attainment of the sparking voltage and the 
passage of a spark. 
49 
/g-Faktor G 
g-Faktor: g-factor, g-value, interval rule {Lande). 
States that if the levels of a spectral multiplet are ar- 
ranged in the order of their J value, the separations of 
the lines of successive pairs of adjacent components are 
proportional to the larger of the two J values for the 
respective pairs. The constant of proportionality is 
called the Lande factor, splitting f., separation f., g- 
factor or g-value. 
g-Wert; g-value. See g-Faktor. 
Galilaei'sches Teleskop: Galilean telescope. A form 
of telescope, devised originally by Lippershey (Holland) 
and improved by Galileo, which has a divergent lens 
for ocular and in which no real image is formed. Now 
used in the opera glass. 
Galitzin'sches Pendel: Gelitzin pendulum. A type of 
seismograph, the essential feature of which is a heavy 
pendulum with its axis of rotation almost vertical. 
Gal+on'sche Pfeife: Galton pipe. A small whistle with 
an adjustable resonance chamber, for producing very 
high pitches of known frequency. 
Galvanolumineszenz: galvanoluminescence. The prop- 
erty, exhibited by the anode in certain electrolytic cells, 
of emitting a feeble glow when the cell is in operation. 
galvanomagne+isch: galvanomagnetic. Pertaining to 
the influence of a magnetic field upon the movements 
of electricity within a conductor, e.g., as in the Hall 
effect. 
Galvanometer: galvanometer. One of a variety of 
instruments, whose function is to indicate and measure 
relatively small electric currents, usually in terms of an 
arbitrary scale. 
Gamma, Einheit der magnetischen Feldstaerke: gam- 
ma. A unit of magnetic intensity, viz., 10~5 oersted; 
used for very weak fields, such as those superposed on 
the terrestrial field by local or transient causes. 
Gammastrahlen: gamma rays. A component of the 
emission from radioactive substances, thought to be 
electromagnetic radiation of very short wave length 
(viz., of the order of 10~8 mm) and of nuclear origin. 
A distinction is recognized between true gamma rays 
and the X-rays produced by the readjustments of extra- 
nuclear electrons disturbed by alpha, beta, and gamma 
rays from the nucleus. 
Gammawert: gamma value, interval factor. A quantity 
relating to the angular momentum levels in the Zeeman 
effect, introduced by Lande, and denoted by y. 
Gang: pitch. The distance between the successive 
threads of a screw. 
Gangumkehrprinzip: path-reversal principle. See Bah- 
numkehrprinzip. 
Gangunterschied: path difference. The difference be- 
tween the distances traversed by two co-initial wave 
trains between the point of separation and the point 
of subsequent reunion, as in an interferometer; or, if 
in different media, the difference between their equiva- 
lent paths in a vacuum or in air. 
% 
ganzzahlige vielfache Resonanz: submultiple resonance. 
The excitation of resonance of a frequency which is 
a submultiple of that of the exciting impulses. 
Gas: gas. Matter in which the cohesion is so neg- 
ligibly small that it will diffuse throughout any enclo- 
sure in which it is placed; specifically, when the sub- 
stance is at a temperature above its critical temperature. 
Gaskonstante: gas constant, ideal gas constant. The 
constant R appearing in the equation representing the 
ideal gas law. Its value is about 8.3136 XlO7 ergs/mol 
°C 
Gasthermometer: gas thermometer. A thermometer 
the indications of which depend upon changes in the 
pressure or the volume of an enclosed gas. 
Gaswaage (bestimmter Dichtemesser fuer Gase): dasy- 
meter. A thin glass bulb used in determining the den- 
sity of gases by observing the buoyant force upon it as 
a sinker is used with liquids. 
Gauss: gauss. (1) The practical c.g.s. electromag- 
netic induction (by international agreement in 1932). 
(2) Prior to 1932, the practical c.g.s. electromagnetic 
unit of magnetic intensity, now called oersted. The 
term is still frequently used in this sense. If magnetic 
induction and magnetic intensity are taken as having 
the same dimensions, both are consistently expressed in 
gausses. If a linear conductor moves laterally with a 
speed of 1 cm/sec across a region in which the mag- 
netic induction (or intensity) is 1 gauss, and at right 
angles to the direction of the induction (or intensity) 
vector, an e.m.f. of 1 abvolt is produced in each centi- 
meter of length thereof. (3) the c.g.s. electromagnetic 
unit of magnetomotive force. 
Gauss'sche Einheit: Gaussian unit. An absolute unit of 
force, such as the dyne or the poundal, defined in terms 
of its accelerating effect upon a given mass. 
Gauss'scher Lehrsatz: Gauss theorem. States that the 
surface integral of the normal component of the gravi- 
/Gauss'sches Okular 
50 0 
tational field due to any distribution of matter, taken 
over any closed surface, is equal to 4ttG times the mass 
of that portion of the distribution which lies within 
the closed surface, and is independent of that which 
lies without. G denotes the gravitation constant. Analo- 
gous propositions may be stated in reference to electri- 
cal and magnetic fields. 
Gauss'sches Okular: Gaussian eyepiece. An eyepiece 
provided with a pair of cross hairs, illuminated by light 
from a side aperture reflected by a transparent glass 
plate extending obliquely across the axis of the instru- 
ment. The Huygens form of eyepiece is usually em- 
ployed for this purpose. 
Gauss'sche Verteilung: Gaussian distribution, normal 
distribution. A statistical distribution defined by the 
equation 
charges, as they are displaced from their initial positions 
to an infinite distance apart. It is the negative of the 
potential energy of such masses or charges in any con- 
figuration, the zero of energy being that corresponding 
to an infinite separation. 
Gegenstandspunkt: object-point. , The real or virtual 
point of intersection of a pencil of rays incident upon 
an optical system. 
Gegenteil von Stossionisation: detailed balancing. The 
process by which the energy of an ionized atom is im- 
parted to a free electron or other particle when the atom 
is neutralized and the particle is sent off with additional 
velocity; the inverse of ionization by impact. 
Geiger-Mueller Zaehler: Geiger-Mueller counter. A 
metallic cylindrical sheath with a slender wire running 
axially through it, and used in a manner somewhat simi- 
lar to the Geiger counter. 
Geiger-Nuttall Gesetz: Geiger-Nuttall law. States that 
for different radioactive elements emitting alpha rays, 
the logarithm of the range of the alpha particles and 
the logarithm of the disintegration constant bear a 
linear relation to each other. 
Geigerzaehler: Geiger counter. A type of counting 
tube, consisting of a highly charged needle inside a 
metallic cylinder. Devised by Geiger for detecting and 
counting ionizing particles in the air. 
Geissler Pumpe: Geissler pump. A type of air pump 
utilizing the principle of the Torricellian vacuum. Also 
known as the Toepler pump. 
Geissler Roehre: Geissler tube. Any two-electrode dis- 
charge tube giving a glow discharge at low pressures. 
One useful form has a narrow constriction of straight 
tubing, in which the glow is concentrated and can thus 
be brought conveniently before the slit of a spectro- 
scope. 
Gel: gel. A jelly-like substance formed by partial dry- 
ing or by cooling certain colloidal solutions, such as 
those of soap or gelatin in hot water. 
Generator: generator (electric). A machine which 
utilizes mechanical energy to produce an electric current. 
geomagnetische Breite: geomagnetic latitude, mag- 
netic latitude. Latitude reckoned from the magnetic, 
instead of from the geographic, equator. 
geometrische Optik; geometrical optics. Regards light 
simply as an emission traveling in straight lines and 
p — ce — k2x2 
in which x is the statistical variable. It is a limiting 
form approached by many statistical phenomena under 
suitable extreme conditions; hence a valuable approxi- 
mation. Accidental errors of measurement and similar 
phenomena theoretically follow this law. 
Gay-Lussac'sches Gesetz: Gay Lussac Laic, Charles 
law. But stated independently by Gay Lussac in 1802. 
States that the coefficients of expansion of all perfect 
gases are equal, their common value being such as to 
indicate that the volume varies in direct proportion to 
the absolute temperature. First discovered by Charles 
in 1787. 
Gefrierpunkterniedrigung durch Druck: regelation. See 
Druckerniedrigung des Schmelzpunktes. 
Gefrierpunktsgesetz: freezing-point law. States that 
the freezing point of any solvent is lowered below its 
normal value by an amount proportional to the quantity 
of solute present; and that the constant for any solvent 
is the same for all solutes, provided the concentration 
is expressed in mols per unit volume. Ascribed to 
Blagden (1788). 
gegenseitige Induktion: mutual inductance, mutual in- 
duction. A (not necessarily constant) characteristic of 
a pair of coupled circuits, defined like inductance; ex- 
cept that the current, constant or variable, in one cir- 
cuit (primary) and the linkage thereby produced, or 
the e.m.f. induced, in the other (secondary) are now 
referred to. The inducing of an e.m.f. in one circuit 
by the variation of the current in a neighboring circuit. 
gegenseitiges Potential: mutual potential. A quantity 
of the nature of gravitational or electric potential, which 
is represented by the work expended upon two or more 
masses, or the work done by two or more electric 
51 
/Geophysik G 
traces its course in "rays” through reflecting and refract- 
ing systems.* 
Geophysik: geophysics. That branch of science which 
deals with physical phenomena related to the earth, 
esp. those aspects studied by strictly physical methods. 
gequantelt: quantized. (I) Composed of, or associ- 
ated with, quanta of energy; e.g., quantized radiation. 
(2) Expressed in terms of the general quantum theory. 
gerader (oder ungerader) Term: even (or odd) term. 
A spectral term arising from one, two, three, . . . ., 
nuclear electrons, the sum of whose respective azimuthal 
quantum numbers 11, 12, 13, . . . ., is an even (or 
odd) number. 
geradsich+iges Prisma: direct-vision prism. See Amici’ 
sches Prisma. 
geritztes Fadenkreuz: graticule. A reticle composed of 
lines scratched upon a plate of glass, instead of the 
usual spider threads or wires. 
geritztes Gitter: echelette. See Echelette. 
Geschwindigkeit: speed, velocity. (1) The scalar time 
rate at which distance is covered by a moving point or 
body, without reference to direction. (2) (Phot.) A 
value used to specify the sensitiveness of a photographic 
material to light, and computed according to any one 
of several methods. (3) (Of an objective.) A quantity 
determining the shortness of exposure adequate for 
taking a photograph under given conditions. Its most 
appropriate measure is the inverse square of the relative 
aperture or F-number. Velocity. (1) (Linear.) A vec- 
tor quantity which denotes at once the time rate and 
the direction of a linear motion. (2) (Angular.) A 
vector quantity which denotes both the time rate and 
the direction of the axis of a rotation. Syn. rotational 
velocity. (3) A general term for time rate, e.g., the 
velocity of a chemical reaction. 
Geschwindigkeitsmesser: tachometer, tachymeter. Any 
instrument for measuring linear or angular speeds, or 
the rates of flow of liquids. 
Geschwindingkeitspotential: velocity potential. A func- 
tion associated with the motion of a fluid and such 
that when the motion is referred to three coordinate 
axes x, y, z and the respective velocity components are 
denoted by u, v, w, then 
same manner as momentum space (q.v.) but with 
velocity substituted for momentum. 
Geschwindigkeitsspektrograph: velocity spectrograph, 
v. analyzer. An apparatus for separating an emission of 
electrically charged particles into distinct streams in ac- 
cordance with their speeds, by means of magnetic or 
electric deflection. 
Gesetz des Potentialfalles: law of fall of potential. 
States that the difference in electric potential between 
points on a conductor is in proportion to the amount 
of electric energy transformed into other forms be- 
tween the points in question. For simple ohmic resis- 
tance, it is proportional to the resistance between the 
points. 
Gesetz der korrespondierenden Zustaende: law of cor- 
responding states. Expresses the approximate fact that 
if two of the thrfee reduced variables of state are equal 
for two different bodies of gas, the third will also be 
equal for these bodies. Such gaseous bodies are said 
to be in corresponding states. 
Gesetz der rationalen Indizes: rational index law, Haüy 
law. States that the parameters, and hence the Miller 
indices, of a crystal are always rational numbers. 
Getter: getter. A volatile metal, e.g., magnesium, va- 
porized in and sublimated upon the walls of a discharge 
tube to remove traces of gas. 
Gewicht: weight. (1) (n.) The force which a mass 
experiences because of being in a gravity field, esp. that 
of the earth. (2) A body of known mass, used in 
measuring the masses of other bodies by weighing. (3) 
One of the abstract numbers sometimes assigned to each 
of a set of data, such as results of measurements, to 
denote their relative importance or reliability, and taken 
into account in averaging or adjusting them. (4) (v.) 
To apply or assign a weight, e.g., a weighted float, the 
weighted mean of several measurements, etc. 
Gibbs'sches Adsorptionsgesetz: Gibbs adsorption law. 
A law relating to systems of several (n) components, 
and expressed by the differential equation 
8y = -2 (rSM); 
1 
in which y is the interfacial free energy, the fi’s are 
the partial free energies of the different components, 
and the r’s are the masses of those respective com- 
ponents which must be added, per unit increase of in- 
terface, to maintain the fi’s constant. 
Gibbs'sche Funktionen: Gibbs functions, heat func- 
8 <p 8 cp 8 <f> 
8 x 8 y 8z 
Geschwindigkeitsraum: velocity space. Defined in the 
/Gibbs-Helmholtz'sche Gleichung 
52 G 
tions. Three thermodynamic quantities, expressed as 
follows: 
to maintain a potential of the desired sign upon the 
grid of a vacuum tube. 
Gütereinheit: lattice unit, unit cell, elementary cell. 
See Einheitskristall. 
Gitterenergie: lattice energy. The energy which de- 
pends upon the configuration of the atoms in a crystal 
lattice, and which changes when any change is made 
in that configuration through mechanical stress, electric 
forces, or otherwise. 
Gitterglimmroehre: grid-glow tube. A thermionic re- 
lay similar to a thyratron. 
Gitterkondensator: grid condenser. A small condenser 
interposed between the grid terminal of a thermionic 
vacuum tube and the source of grid potential control. 
Gitterkonstante: lattice constant. The distance between 
successive planes of a specified plane-family in a crystal. 
For the (111) planes of calcite it is taken as 3.028 X 
10-8 cm. 
Gitterkonstante: grating constant, grating space. See 
Gitterabstand. 
Gitterstrom: grid current. A current flowing to or 
from the grid of a vacuum tube. 
Gittervorspannung: bias. A permanent negative poten- 
tial applied to the grid of a vacuum tube. 
Gitterwiderstand: grid leak. A very high resistance 
placed in parallel with a grid condenser to prevent an 
overaccumulation of negative charge upon the grid and 
thus to keep its mean negative potential approximately 
constant during operation. 
Gladstone-Dale'sches Gesetz: Gladstone-Dale law. 
States that the refractivity of a medium is proportional 
to its density as the latter varies under changing condi- 
tions of pressure or temperature; i.e., that the specific 
refractivity is constant. 
Glanzwinkel; glancing angle. The complement of a 
very large incidence angle; i.e., the very small angle 
between the incident emission and the surface upon 
which it is incident. 
Glan-Thompson'sches Prisma: Glan-Thompson prism. 
A form of polarizing prism of Iceland spar, resembling 
a Nicol prism but differing somewhat in design. The 
light enters and leaves this prism normal to the faces, 
and the parts are separated by a glycerine film. 
ip = u — Ts (free energy), 
X = u — pv (enthalpy), 
S = u — Ts + pv. 
In these, u is internal energy, T is temperature, v is 
volume, p is pressure, s is entropy. The quantities usu- 
ally pertain to unit mass of working substance. 
Gibbs-Helmholtz'sche Gleichung: Gibbs Helmholtz 
equation. An equation connecting the open-circuit e.m.f. 
of a reversible electrolytic cell with the heat of for- 
mation H of the compounds formed within it and with 
the absolute temperature T: 
8 E 
ErH+T 
8 T 
Gibbs'sche (thermodynamische) Oberflaeche: Gibbs 
(thermodynamic) surface. The (three-dimensional) 
graph of the equilibrium values of volume, energy, and 
entropy for a given pure substance. 
Gift: poison. A substance whose effect on a lumi- 
nescent material is the opposite of that produced by a 
phosphorogen. E.g. iron is a poison to certain phos- 
phorescent materials prepared from zinc sulphide. 
Gilbert: gilbert. The c.g.s. electromagnetic unit of 
magnetic potential or of magnetomotive force, equiva- 
lent to 5/2tr amp.—turns. 
Gilbert pro Zentimeter (Oersted, Gauss): gilbert per 
centimeter, oersted, gauss, i.e., the practical c.g.s. unit 
of magnetic intensity or magnetic potential gradient. It 
is sometimes used in analogy to the volt per centimeter 
for electric potential gradient, or to avoid the ambigu- 
ous term oested. 
Gitter: grid, lattice, grating. (1) An electrode con- 
sisting of a wire mesh placed between the cathode and 
the anode in a thermionic tube so that the thermions 
must pass through it, and used as a control of the ther- 
mionic current by means of variations in the negative 
grid potential. (2) The metallic (commonly lead) part 
of either of the electrodes of a storage cell. (3) An 
arrangement of points in space, representing the relative 
positions of corresponding atomic, molecular, or ionic 
centers in the elementary cells or structure units of a 
crystal. See also Beugungsgitter. 
Gitterabs+and: grating constant, g. space. (1) The 
distance between successive rulings of a diffraction grat- 
ing. (2) In re a crystal: syn. lattice constant. 
Gitterbat+erie: grid battery, C-battery. A battery used 
53 
/Glanzmesser 0 
Glanzmesser: glossimeter, glossmeter. An instrument 
for measuring the ratio of the light regularly or specu- 
larly reflected from a surface to the total light reflected. 
vom gleichen Moment: equimomental. In re two or 
more bodies: having equal mass and equal moments of 
inertia about corresponding axes. 
gleichfarbig: homochromatic, isochromatic, ortho chro- 
matic. In re different areas or different parts of the 
same area: having the same color, or a uniformity of 
color. Pertaining to any variation of factors in con- 
nection with radiation, in which the wave length or 
frequency is constant. A line connecting points of con- 
stant shearing stress in an elastic body; so called because 
such lines correspond to lines of uniform color in the 
photoelastic test method. 
gleichfoermiger Fluss: uniform flow. A condition of 
flow in which the cross section of every stream tube 
remains constant, each particle moving along its stream- 
line with constant speed. 
Gleichgewicht; equilibrium. (1) A condition of bal- 
ance among the forces operating upon or within a 
physical system, such that no accelerated motions exist 
among the parts of the system. The equilibrium is 
stable when a slight change in the configuration of the 
system gives rise to a condition tending to restore the 
original configuration; unstable when the change tends 
to increase; neutral when equilibrium persists regardless 
of the change. (2) The mutual state of two or more 
simultaneous, continuous processes such that their net 
result is equivalent to a constant condition; e.g., the 
evaporation and condensation at the surface between a 
liquid and its saturated vapor. 
Gleichgewichtskurve: equilibrium curve, transformation 
c, phase diagram. A graph representing the relation be- 
tween values of two variables of state, as temperature 
and pressure, for which there is equilibrium between 
two states or phases. E.g., the fusion curve follows the 
equilibrium between solid and liquid states; the vapori- 
zation or saturation c., that between liquid and saturated 
vapor states; and the sublimation c., that between solid 
and vapor. 
Gleichgewichtslehre: statics. That branch of dynamics 
which deals with bodies at rest relative to some given 
frame of reference and with the interaction of forces 
between them. 
Gleichgewichtspotential: equilibrium potential. The 
potential d. between an electrolyte and an electrode 
immersed in it, when they have come to equilibrium. 
gleichrichten: rectify. (1) To change from alternat- 
ing to unidirectional, as an electric current. Any device 
for securing this result is a rectifier. (2) To replace 
(an inverted image by one which is erect, as by the 
rectifying system in a field glass. 
Gleichrichter: valve. A controlled inlet or outlet, esp. 
one permitting only a unidirectional flow. (2) An elec- 
tric current rectifier, esp. of the electrolytic or thermionic 
type. 
Gleidchung: Equation. An expression of equality be- 
tween two magnitudes or operations, the sign = being 
placed between them. 
Gleichverte'lung der Energie: equipartition of energy, 
Maxwell-Boltzmann law. A principle, enunciated by 
Boltzmann, which states that the mean kinetic energy 
of the molecules of a gas is equally divided among the 
various degrees possessed by the molecules. The aver- 
age molecular energy' associated with any degree of 
freedom is one-half the product of the absolute tem- 
perature by the Boltzmann constant. 
Gleitebene: gliding plane, glide plane, slip surface. 
(1) A plane within a crystal along which occurs a dis- 
placement of the crystal structure, i.e., a slipping of 
one lattice layer past the adjacent layer, when the crystal 
is subjected to shear. (2) The common plane of the 
two axes of a twin crystal. (3) A surface (often ap- 
proximately plane) along which a solid under severe 
stress tends to crack or shear. The traces of such sur- 
faces at an external face of the specimen are slip lines. 
Gleitflaeche: gliding plane. See Gleitebene. 
Gleitkoeffizient: slip coefficient. A quantity connected 
with the slipping of a fluid at the surface of a capillary 
tube; defined §.s the ratio of the speed of slip to the 
transverse velocity gradient in the fluid. It is equal to 
the viscosity coefficient divided by the friction coeffi- 
cient at the surface. 
Glimmen: glow, g. discharge. The most frequent form 
of initial electric discharge in a gas, often emitting a 
hissing sound but with no distinct sparks. It sometimes 
develops into a brush discharge. 
Glimmentladung: glow, g. discharge. See Glimmen. 
Glimmpotential: glow potential. The voltage at which 
a glow discharge begins in a vacuum tube as the voltage 
is gradually increased. 
Globulif: globulite, spherolite. A microscopic crystal 
of globular shape, without definite plane faces, due ta 
strong surface tension effects at the time of formation 
of the crystal. 
/gnomonische Projektion 
54 0 
gnomonische Projektion: gnornonic projection. A 
method of geometric projection used in the interpreta- 
tion of Laue diffraction patterns. 
Goldpunkt: gold point. The melting point of gold, 
viz., about 1064 degrees C; commonly used as a refer- 
ence point in pyrometry. 
Goniometer: goniometer. An instrument for measur- 
ing the angles between the faces of crystals, prisms, etc., 
usually by utilizing beams of light reflected from those 
faces. 
grader Strahl: pencil. A homocentric bundle of rays, 
corresponding to a train of concentric waves. 
Gradeinteilung; scale. Anything graduated, esp. when 
used as a measure or rule or marked by lines at regular 
intervals. 
Gradient: gradient. The vector which represents the 
linear derivative of a scalar point function S at any 
point, in a direction normal to the surface of equal 
values of S through this point; e.g., of temperature in 
a direction normal to the isothermal surface. Denoted 
by grad S. 
. > 
Gradientmesser: gradiometer. An instrument for 
measuring the gradient of the earth’s gravity field in 
any locality. 
Gradiometer: gradiometer. See Gradientmesser. 
Graham'sches Gesetz: Graham law. States that the 
rate of efflux or of diffusion of different gases (volume 
per unit time) are, under similar conditions, inversely 
proportional to the square roots of the densities of the 
gases. 
Gramm: gram, gramme. A metric unit of mass, de- 
fined originally as the mass of 1 cm3 of pure water 
at its maximum density (4 degrees C.). But for prac- 
tical purposes it is now defined as one-thousandth of the 
mass of the standard platinum kilogram at Sevres; which 
is 1.000027 times the original, ideal value. 
Grammatom: gram atom. That mass of an element 
which, in grams, is numerically equal to the atomic 
mass of the element. The gram atom of every element 
thus contains the same number of atoms, viz., about 
6.06 X 1023 (Avogadro number). 
Gramme'scher Ring: Gramme ring. A form of electro- 
magnet in which the core is a continuous iron ring. 
Used in certain forms of generator armature. 
Grammolekuel: gram molecule. That mass of a pure 
substance which, in grams, is numerically equal to the 
molecular mass of the substance. The gram molecule 
of every pure substance thus contains the same number 
of molecules, viz., about 6.06 X 1023 (Avogadro num- 
ber). Syn. mol or mole. 
grau: gray, grey. (1) An achromatic color. (2) The 
property of a radiating surface such that, while its 
radiation has the same spectral energy distribution, its 
emissive power is less at any temperature than that of a 
black body; and such that, while not black, its absorp- 
tivity is nonselective. 
Gravitationseinheit: gravitational unit. A unit of force, 
pressure, work, power, or other magnitude, which in- 
volves in its measure the factor of terrestrial gravity 
e.g., the gram of force or the foot-pound. 
Gravlta+ionslconstante: gravitation constant, Syn. Netv- 
tonian constant. A constant G which appears in the 
expression for the Newtonian law of gravitational force 
between two concentrated masses m1} m2 separated by 
distance r: 
m1 m2 
f = G 
r2 
Approximately equal to 6.664 x 10~8 cm3 g^1 sec-2. 
Gravi+ationspoten+ial: gravitational potential, New- 
tonian potential, mass p. A point function analogous 
to electric potential, but always positive. Its value at 
any point is the line integral of the intensity of the 
gravitational field due to all matter, taken from that 
point to infinity. 
Gravi+a+ionsradius: gravitational radius. A quantity, 
having the dimensions of a length, associated in the 
relativity theory of gravitation with any particle of mat- 
ter, and equal to Gm/c2; in which m is the mass of 
the particle, G the gravitation constant, and c the elec- 
tromagnetic constant. 
Grotthus-Draper'sches Gesetz: Grotthus-Draper law. 
States that light is photochemically active only when it 
is absorbed by the material affected. 
Grundbeleuch+ung: priming illumination. A small, 
steady illumination applied to a photoelectric cell to 
render it more sensitive to the (superposed) variations 
in illumination which the cell is being used to measure 
or record. 
Grundflaeche: basal plane. A plane in a crystal paral- 
lel to the principal plane of symmetry. 
Grundform: ground form. The crystalline form of any 
crystal system which is bounded by natural faces, all of 
55 
/Grundlinie G 
which intersect the crystal axes. E.g., the ground form 
of the isometric system is the regular octahedron. 
Grundlinie: parent. A spectrum line which represents 
a normal quantum process, unaffected by such influences 
as are responsible for satellite lines, as in the Zeeman 
effect. 
Grundsatz: axiom. An established principle in some 
art or science, which though not a necessary truth, is 
universally received. 
Grundspektrum: persistent spectrum. The spectrum 
of a substance which results from only the most moder- 
ate excitation. The most persistent lines, which remain 
when all others have subsided or when the quantity of 
the substance is diminished to a trace (but which are 
not always the brightest in the complete spectrum), 
are called the "raies ultimes,” a term due to de Gramont. 
Grundton: fundamental. (1) (n.) The simple har- 
monic component of a composite vibration or musical 
tone which has the lowest frequency. (2) (adj.) Some- 
times used in connection with three-phase equilibrium; 
e.g., fundamental point, syn. triple point, etc. 
Grundzustand: ground state. That configuration of 
an atom which corresponds to the lowest energy level 
and hence has greatest stability. 
Gruppe: ensemble. A group comprising a great num- 
ber of independent systems, identical in nature but differ- 
ing in their configuration and velocity, e.g., the mole- 
cules of a pure gas. 
Gruppengeschwindigkeit: group velocity. The velocity 
of propagation of the resultant displacement maxima or 
minima constituting an interference wave form, in wave 
motion made up of two or more component wave trains 
of different frequency, i.e., a wave group. If the com- 
ponents have different individual speeds, it may be 
quite different from the velocity of propagation of any 
one component. 
Gruppenphaenomen: group phenomena. Properties of 
the crystalline state which apparently cannot be consid- 
ered as properties of single atoms, but arise from the 
agglomeration of atoms into groups, each consisting 
of a definite number of atoms (107 to 109). The sta- 
bility of the atoms thus arrayed is greater than that 
among the groups. 
Gudden-Pohl'sches Gesetz: Gudden-Pobl law. States 
that the number of electrons liberated in the photocon- 
ductive action of selenium is equal to the number of 
radiation quanta absorbed. 
Guillaume'sche Legierung: Guillaume alloy, G. metal. 
An alloy of about 66 percent Fe and - 34 percent Ni, 
which has the unusually low expansion coefficient 10-6 
per °C. 
gyromagnetisch: gyromagnetic. Pertaining to the mag- 
netic properties of rotating electric charges, esp. of elec- 
trons moving within atoms. 
gyromagnetisches Verhaeltnis: gyromagnetic ratio. The 
ratio of the magnetic moment of a specimen of a sub- 
stance to the angular momentum of its atoms. 
Gyroskop: gyroscope. An instrument resembling a 
spinning top, used to demonstrate precession, etc. 
Gyrostat: gyrostat. Syn. gyroscope, but with emphasis 
upon the stabilizing effect of rotation. 
/H-Funktion 
56 H 
H-Funktion: H function. A function of the coordinates 
describing the motion of the molecules of a gas, which 
represents the cologarithm of the probability of a given 
thermodynamic state of the gas; a concept due to Boltz- 
mann. 
H-Strahl: H-ray, H-particle. A positive hydrogen ion, 
or proton, which results from the bombardment of hy- 
drogen or a hydrogen compound by alpha rays or by 
swiftly moving positive ions of any kind, or from the 
bombardment and disintegration of certain other ele- 
ments, e.g. nitrogen, by alpha rays. First observed by 
Marsden in 1914. 
H-Teilchen: H-ray, H-particle. See H-Strahl. 
H-theorem: H-theorem. A theorem based upon the 
Maxwell-Boltzmann principle of equipartition of energy. 
States that if there are Nj molecules in one state or 
phase, N2 in another, etc., the quantity Hr=2, (N log N) 
tends to a minimum and reaches its equilibrium value 
only when the condition of equipartition of energy is 
Haarroehrchenkraft: capillarity. A class of phenomena 
dependent upon the interaction of molecular forces at 
the junction of the interface between a liquid and a gas 
or between two liquids, with a solid surface; e.g., the 
elevation or depression of a liquid in a capillary tube. 
Haerte: hardness. (1) Resistance to surface abrasion 
or indentation, as of steel or diamond. (2) in re X-rays 
or gamma rays, it denotes high penetration or low ab- 
sorption coefficient, corresponding to short wave length 
and high quantum energy. 
Haertemesser: penetrometer, sclerometer, scleroscope. 
(1) An instrument for testing the hardness of more 
or less plastic solids. (2) An instrument for indicating 
the quality or "hardness” of X-rays. (3) An apparatus 
for measuring the hardness of a substance by the re- 
bound of a hammer falling upon it from a given height. 
Haftspannung; penetration tension. In re a liquid in 
a capillary tube: the product of the surface tension of 
the liquid by the cosine of the angle of contact. 
halbdurchlaessige Membran: semipermeable membrane. 
A membrane through which osmosis can take place, 
but which prevents the free mixing of the fluids. 
Halbperiodenelement; half-period element, Huygens 
zone, Fresnel zone. See Fresnel’sche Zone. 
Halbquantenzahl: half-quantum number. One of the 
values of the angular momentum assumed for an atom 
or a molecule, each equal to a whole multiple of Yj 
(h/2ir), in which h is the Planck constant. 
Halbschatten: penumbra. That part of a shadow from 
which the light from only a portion of the source is 
excluded by the opaque obstacle. 
Halbschattenanalysator: half-shade analyzer. A de- 
vice used in polarimeters for determining the polariza- 
tion plane. It may be a Jellet-Cornu prism, a Lippich 
prism, or an opening partly covered by a half-wave 
plate. 
Halbwertsbreite: half-width (of spectrum line'), width- 
at-half-maximum. In re any line in the spectrum of a 
gas or vapor: the wave length or wave number interval 
throughout which the intensity equals or exceeds one- 
half its maximum value (value at the line peak). 
Halbwertsperiode: half-decay period, half-value pe- 
riod. The time required for any variable whose value 
undergoes decay in accordance with the exponential law 
to fall to one-half of its original value; equal numerically 
to 0.6931 divided by the decay coefficient. 
Halbswertsschicht: half-value layer. In re the ab- 
sorption of radiation by any given substance: the thick- 
ness of that substance which will reduce the intensity 
to one-half its initial value. It is equal to 0.6931 divided 
by the (linear) absorption coefficient. 
Halbzelle: half-cell. Consists of an electrode inserted 
into an electrolytic solution in order to set up a defi- 
nite, though not actually determinable, potential dif- 
ference. 
Hall'scher Effekt: Hall effect. A p.d. which develops 
between the two edges of a strip of metal, in which an 
electric current is flowing longitudinally, when the plane 
of the strip is set perpendicularly across a magnetic field. 
Discovered by Hall in 1879. 
Hall'scher Koeffizient: Hall coefficient. The transverse 
electric potential gradient produced in a conducting 
strip exhibiting the Hall effect, per unit current density 
per unit magnetic intensity. 
Halo: halo. (1) One of several different atmospheric 
phenomena, manifested by the appearance of faintly col- 
ored rings surrounding the sun or the moon, and caused 
by refraction due to minute ice crystals suspended in 
the upper air. (2) (Phot.) A ring surrounding the 
photographic image of a bright source, due to one of 
several causes. 
Hallwachs'scher Effekt: Hallwachs effect. The dis- 
charge of a negatively charged body in a vacuum due 
to the incidence of ultraviolet; discovered by Hallwachs 
in 1888. It is a type of photoelectric effect. 
57 
/Hamilton'sche Gleichungen H 
Hamilton'sche Gleichungen; Hamilton equations. A set 
of differential equations relating to a dynamic system, 
one pair for each of the n degrees of freedom corre- 
sponding to the generalized coordinates qx, q2, 
, qn and generalized momenta px, p2, p„. 
If H denotes the Hamiltonian function, each pair of 
equations has the form 
dqr 8H dpr 8H 
dt Spr dt 8qr 
(r = 1, 2, , n.) They are equivalent to the 
Legrange equations. 
8 (E* — Ep) dt = 0. 
• to 
harmonisch: harmonic. (1) (n.) An overtone or par- 
tial bearing a simple frequency ratio to the fundamental. 
(2) (adj.) Capable of being expressed in terms of 
sine or cosine functions, and hence analogous to musi- 
cal sound. 
harmonische Analyse: harmonic analysis. The expres- 
sion of a function in terms of sine and cosine terms 
involving the variables, with such coefficients as to ren- 
der the resulting series approximately equal to the given 
function for corresponding values of the variables. 
harmonischer Analysator: periodometer. A type of 
harmonic analyzer developed by C. G. Abbot for the 
study of solar radiation and meteorological data. 
harmonic analyzer. An ap- 
paratus which mechanically, electrically, or otherwise, 
evaluates the coefficient of the Fourier series correspond- 
ing to any function subject to harmonic analysis. 
harmonisches Band: harmonic band, overtone band. A 
spectral frequency which bears a relation to a given 
spectral frequency analogous to that of an acoustic over- 
tone to its fundamental. 
harmonische Bewegung: harmonic motion. A vibration 
in which the acceleration is proportional to the displace- 
ment from the mean or zero position but with opposite 
sign, as the vibration of a string; or which is the re- 
sultant of any number of such motions. If there is but 
one component, the motion is termed simple harmonic. 
harmonisches Echo: harmonic echo. An echo in which 
there is a selective action on the frequencies of the in- 
cident sound, usually resulting in the suppression of 
the fundamental and other low-frequency components. 
harmonischer Oszillator: harmonic oscillator. A par- 
ticle, esp. an electric particle, oscillating with harmonic 
motion; a concept often used in radiation theory. 
harmonische Schwingung: harmonic motion. See har- 
monische Bewegung. 
Hartley'sches Gesetz: Hartley law. States that the 
separations of the components in any one series of 
doublet or of triplet spectral lines, expressed in fre- 
quencies or in wave numbers (not in wave lengths), 
are equal. 
Hartmann'sches Test: Hartmann test. A photographic 
method of testing large lenses for spherical aberration. 
Hamilton-Jaccbi'sche Gleichung: Hamilton-]acobi 
equation. A partial differential equation used in the 
dynamics of conservative systems, in the form of a 
Hamiltonion function: 
/ «S, 8S, \ 
H ( — .... ,q1 .... qfj = E; 
V 8qx 8qr ' 
in which the q’s are generalized coordinates, S’s are 
actions, f is the number of degrees of freedom and E 
is the constant total energy of the system. 
Hamilton'sche Funktion: Hamiltonian function. A func- 
tion of the r generalized coordinates qx . . . . qr and 
generalized momenta p1 . . . . pr, defined by 
H = 2 p q — L ; 
1 
in which L is fhe Lagrangian function. H satisfies the 
differential equations 
8H 8H 
= q, = - P- 
8p Sq 
dq dp 
S = —. P = — • 
dt dt 
In many problems, H represents the energy of a con- 
servative system expressed in terms of q’s and p’s. 
Hamiltonoperator: Hamiltonian. The vector differen- 
tial operator 
8 8 8 
i + j k ; 
8x 8y Sz 
sometimes abbreviated by V- 
Hamilton'sches Prinzip: Hamilton principle. A prin- 
ciple relating to any dynamic system, the total kinetic 
energy and potential energy of which are, respectively, 
and Ep; expressed by the equation 
/Hartmann'sche Untersuchung 
58 H 
Hartmann'sche Untersuchung: Hartmann test. See 
Hartmann’sches Test. 
Hartree'sche Einheit: Hartree unit. A unit of wave 
length used in connection with the theory of diffrac- 
tion of electrons by crystals, and equal to h2/47r2me2, 
in which h is the Planck constant and m and e are 
the electronic mass and charge. Its value is about 5.3 
X 10-19 cm. 
Hartree'sche Funktion: Hartree function. A wave func- 
tion applying to a single electron in a central field, as 
developed by Hartree. 
Hauy'sches Gesetz: Haüy law, rational index law. 
States that the parameters, and hence the Miller indices, 
of a crystal are always rational numbers. 
Hauptachse: principal axis. A line so chosen with 
reference to a rigid body, that the body may rotate about 
it without developing a centrifugal torque in any plane 
containing that line. Through any point there are in 
general three such lines, which are axes of maximum 
or minimum moment of inertia. 
Hauptazimut; principal azimuth. The azimuth- of the 
elliptically polarized beam produced when plane-polar- 
ized light, with an azimuth of 45 degrees with the 
plane of incidence is reflected at the principal angle of 
incidence from a metallic surface. 
Hauptbogen: primary bow. The inner and brighter 
of the two rainbows sometimes visible. 
Hauptbrennpunkt: principal focus, focal point. See 
Brennpunkt. 
Hauptdruecke: principal strains and p. stresses. The 
components of strain, and the corresponding components 
of stress, in the directions of the strain axes at any 
point of an elastic solid under deformation. 
Hauptebene: principal plane. (1) In re a ray of 
light traversing a doubly refracting crystal: the plane 
determined by the direction of the ray and the axial 
direction of the crystal. (2) In re a symmetrical optical 
system: one of two planes perpendicular to the axis, 
such that any incident paraxial ray meets the first, and 
the same ray upon emergence meets the second, in points 
on a line parallel to the axis. The magnification ratio 
for these two planes being + 1, they are sometimes 
called the "unit planes.” 
Hauteffekt: skin effect. A concentration of current 
density toward the surface of an a.-c. conductor, due 
to selfinduced counter e.m.f., and resulting in an in- 
crease in effective resistance. The phenomenon is espe- 
cially noticeable at higher frequencies. 
Haupteinfallswinke!: principal angle of incidence. The 
angle at which a ray of planepolarized light must be in- 
cident upon a reflecting metallic surface in order that 
the components of the elliptically polarized reflected ray, 
parallel and perpendicular to the plane of reflection, 
shall differ in phase by one-quarter cycle. 
Hauptgeschwindigkeit: principal velocity. One of the 
three velocities which, taken by twos, correspond to the 
velocities of propagation of the two plane-polarized light 
waves traveling outward from a point source within a 
birefringent crystal in directions parallel to the three 
axes of dielectric symmetry. In a uniaxial crystal, two 
of the three principal velocities are equal, viz., in the 
direction of the optic axis. 
Haupt'inie: principal line. The first and strongest line 
of a spectral series. 
Hauptpunkte: cardinal points, principal points. The 
focal points, the principal points, and the nodal points 
of a lens or of a symmetrical optical instrument. (See 
also Einheitspunkt.) 
Hauptquantenzahl: principal quantum number, total 
quantum number. The sum 1 -f 1' of the azimuthal and 
the radial quantum number in the Bohr theory, or 1 + 
1' -f 1 in the new quantum mechanics (since in the 
latter 1 is one less). So called because the energy of 
a quantum state depends primarily upon it. The prin- 
cipal quantum number is usually denoted by n. 
Hauptschatten: umbra. That part of a shadow from 
which light from the source is completely excluded by 
the opaque obstacle. 
Hauptserien: principal series. A spectral series cor- 
responding to transitions from a low S-state to higher 
P-states. This gives the strong, persistent lines of the 
alkalis and alkaline earths but not, in general, of other 
elements. 
Haupttraegheitsmoment: principal moment of inertia. 
The moment of inertia of a body with respect to one 
of its principal axes. 
Hauptzuege: principal strains and p. stresses. See 
Hauptdruecke. 
Heaviside'sche Bruecke: Heaviside bridge. An arrange- 
ment somewhat resembling a Wheatstone bridge, but 
used for measuring mutual inductances. 
Heaviside-Lorentz Einheit: Heaviside-Lorentz unit, ra- 
tionalized unit. One of a system of electric and mag- 
netic units proposed by Heaviside and Lorentz for con- 
venience in theoretical discussions. 
59 
/Heaviside-Hertz'sche Gleichung H 
Heaviside-Hertz'sche Gleichung: Heaviside-Hertz 
equations. A set of electromagnetic field equations for 
a medium of dielectric constant k, permeability /x, and 
electric conductivity y, in which the magnetic intensity 
is H and the electric intensity E: 
grange-Helmholtz equation. (1) (Dioptrics.) An equa- 
tion of the form 
nx jq tan ai = n2 y2 tan a2 
expressing the relation between the linear and the an- 
gular magnification at a spherical refracting interface, 
jq, y2 are linear dimensions of object and image, a19 a2 
the angles made by focal rays and axis at object- and 
image-points, and the refractive indices of the two media. 
Helmhol+z'sches Pendel: Helmholtz pendulum. A de- 
vice, due to Helmholtz, whereby it is possible to charge 
a condenser for a definite short time, varied at will, 
or to impart varying amounts of magnetization to a 
specimen of iron. 
Helmholtz'sche Spulen: Helmholtz coils. Two equal 
circular coils placed coaxially at a distance apart equal 
to their radius, and traversed by the same current. The 
field near the axis between them is practically uniform. 
hemihedrisch: hemihedral. In re a crystal: having only 
one-half the number of faces necessary to complete a 
given type of symmetry. 
hemimorph: hemimorphic. In re a crystal: terminated 
at the two ends by dissimilar sets of faces. 
Henry: henry. The practical c.g.s. electromagnetic unit 
of inductance (or of mutual inductance), equal to 109 
abhenrys; viz., the inductance of a circuit in which the 
variation of current at the rate of 1 amp per second in- 
duces an e.m.f. of 1 volt. The millihenry is usually 
more convenient, 
Henry'sches Gesetz: Henry law. States that, at con- 
stant temperature, the solubility of a gas in a liquid 
which does not act chemically upon it is proportional 
to the pressure. 
Herpolhode: herpolhode. The path traced by the point 
of contact of the energy ellipsoid of a rigid body with 
the fixed tangent plane on which it rolls. The term is 
due to Poinsot (1834). 
Herschel Effekt: Herschel effect. A decrease in de- 
velopable density on a photographic plate produced by 
a second exposure to radiation of longer wave length. 
Herschel-Qulncke Roehre: Herschel-Quincke tube. A 
branched acoustic tube, resembling a divided or shunted 
electric conductor; used in studying acoustic interference 
phenomena. 
Hertz: hertz. A unit of frequency, equal to 1 eye per 
second. (Rare in U. S.) 
Hertzoszillator: Hertz oscillator. An arrangement of 
conductors, electric oscillations in which are capable of 
If 8E 
curl H — ( 4?ryE -f k , 
c V St 
fj. SH 
curl E — — 
c St 
div /xH = O, div kE = O. 
Heaviside Schicht: Heaviside layer, ionosphere, Ken- 
nelly-Heaviside layer. A stratum of the upper atmos- 
phere which is believed to be more highly ionized than 
that at the earth’s surface,- and because of this, to be 
capable of reflecting radio waves and thus directing their 
propagation, in a general way, parallel to the ground. 
Hefner Einheit: Hefner unit. A German unit of lumi- 
nous intensity, defined as the light output of a standard 
Hefner amyl acetate lamp in a particular direction. It 
is equal to about 0.90 of the international candle. 
Heisenberg'sche Kraefte: 
Heisenberg'sche Wechselwirkung: Heisenberg forces, 
H. interactions. Attractive forces between nuclear par- 
ticles, due to the exchange energy of the type postulated 
by Heisenberg. This energy is now regarded as a part 
of the Majorana exchange energy. 
Heliostat: heliostat. An arrangement of mirrors driven 
by clockwork, used to reflect a beam of sunlight in a 
fixed direction as the sun moves across the sky. 
Helligkeit: brightness. "The quotient of the luminous 
intensity of a surface measured in a given direction, by 
the area of this surface projected on a plane perpendicu- 
lar to the direction considered.” 
Helmert'sche Formel; Helmert formula. An empirical 
formula for the value of gravity at a given latitude 1 
and altitude h (in meters), published by Helmert in 
1901: 
g = g45 (1 — 0.002644 cos 2l + 
0.000007 cos2 21) 
— 0.0003086h; 
in which g45 is the value of g at 1 — 45 deg and h — 0. 
Helmholtz'sche Doppelschicht: Helmholtz double layer, 
electric double layer. See elektrische Doppelschicht. 
Helmholtz'sche Gleichung: Helmholtz equation, La- 
/Hertz'sche Strahlung 
60 H 
emitting electromagnetic (Hertzian) radiations; a fore- 
runner of the radio transmitting antenna circuit. 
Her+z'sche Strahlung: Hertzian radiation, H. waves. 
See elektrische Welle. 
Hertz'scher Vektor: Hertzian vector. A vector n, per- 
taining to the electromagnetic field, in terms of which 
both the electric intensity E and the magnetic intensity 
H may be specified according to the equations 
Hicks'sche Formel: Hicks formula. A modification of 
the Rydberg (spectral-series) formula, in which allow- 
ance is made for the variation of f with the number 
of the line in the series. It is somewhat similar to the 
Ritz formula. 
High-pass (Kurzwellenfilter fuer HF): high-pass. In re 
a wave filter: having the property of transmitting all 
frequencies above a certain limit and suppressing those 
below it. 
Hilfskreis: line of force. (1) An imaginary line in a 
field of force which, at each of its points, coincides in 
direction with the field intensity; a concept due to 
Faraday. (2) A unit of flux (magnetic, electric), so 
defined that the number of lines intersecting any cross 
section, per unit area, is numerically equal to the com- 
ponent of field intensity normal to the section. 
Hit+orfscher Dunkelraum: Hittorf dark space, cathode 
dark space, Crookes dark space. That portion of the 
glow discharge in a Crookes tube lying between the 
cathode glow and the negative glow; so called because 
it is nonluminous. 
Hittorf'sche Zahlen: Hittorf numbers, transference 
numbers, transport n. A term applied by Hittorf to the 
fractions of an electrolytic current carried by the anions 
and by the cations, respectively, the sum of which is 
unity. 
Hitzdrahtamperemeter: hot-wire ammeter (or volt- 
meter). An instrument for measuring current (or volt- 
age) by the heating effect upon a filament. 
Hitzdrahtanemometer: hot-wire anemometer. An in- 
strument for measuring the velocity of a current of gas 
by means of its cooling effect on an electrically heated 
wire. 
Hitzdrahtmanometer: hot-wire gauge. A pressure 
gauge which depends upon the cooling effect of the 
gas upon a hot filament. 
Hochfrequenzgenerator: circuit driver, radio-frequency 
generator. A source of h.-f. e.m.f. esp. of the vacuum- 
tube-controlled type, for experimental use. 
Hodograph: hodograph. The locus of the terminal 
point of the evector which, drawn from a fixed origin, 
continuously represents the velocity of a point moving 
along any given path. 
Hodoskop: hodoscope. An apparatus for tracing the 
paths of cosmic rays by means of an array of small 
Geiger counters, each of which is connected with a neon 
lamp which flashes as the counter is set off by the cosmic 
particle. 
1 s2n 
E - V(V • n) 
c2 8t2 
i m 
H = V x ; 
c St 
physically the equivalent of the vector of an oscillating 
dipole. 
Her+z'sche Wellen: Hertzian waves, H. radiation. See 
Hertz’sche Strahlung. 
Heterodyne: heterodyne. A coupling of oscillatory 
circuits of such relative frequency that the beats be- 
tween them come within the audible range. 
heterodyner Wellenmesser: heterodyne wave meter. A 
calibrated electrical oscillator of variable frequency, to- 
gether with a device, employing the heterodyne prin- 
ciple, for indicating the setting at which the frequency 
of the oscillator bears a known relation to that of the 
circuit under test. 
heteromorph: heteromorphic, polymorphic. Occurring 
in two or more different crystalline forms. 
he+eropolar: heteropolar, polar. Electrically nonsym- 
metrical as a molecule which, like HC1, has an effective 
electric moment. 
Heusler'sche Legierungen: Heusler alloys. A series 
of alloys of nonferromagnetic substances, chiefly copper, 
manganese, and aluminum, which, however, exhibit fer- 
romagnetic properties in a remarkable degree. De- 
veloped by F. Heusler and others about 1903. 
hexagonal: hexagonal. In re crystal structure: having 
three equal axes at angles of 120 degrees and a fourth 
at right angles to all three. 
Hibber+'scher Flusstandard: Hibbert flux standard. A 
permanent magnet with an annular air gap through 
which a coil of wire is dropped to produce a known 
and invariable change in the magnetic flux linked with 
an electric circuit including the coil. Devised by W. 
Hibbert, 1892. 
61 
/Hoehenmesser H 
Hoehenmesser: altimeter. An instrument, resembling 
an aneroid barometer, which indicates the altitude of an 
airplane above the ground station at which it was set 
at zero. 
Hof: halo. See Halo. 
Hof: corona (laymen). A spectral ring sometimes ob- 
served surrounding the sun or the moon; caused by 
the diffraction of light by suspended matter in the 
air. Not to be confused with halo. 
Hohlraum: Hohlraum {Germ., ”empty space”). A 
black-body cavity. 
Hohlraumbildung: cavitation. The formation of a par- 
tial vacuum in a liquid, due to the separation of its 
parts in the process of flow; or the separation of gases 
from the liquid, with the formation of gas-filled spaces 
or bubbles. 
Hohlraumstrahlung: cavity radiation, black-body radia- 
tion. The radiation from a black body at a given tem- 
perature. Syn. Planckian r., black r. 
holohedral: holohedral. In re a crystal: having the 
full number of faces corresponding to the development 
of the complete maximum symmetry possible to the 
crystal system in question. 
holomorph: holomorphic. In re a crystal: having the 
two ends symmetrical with each other. 
holonom: bolonomic, holonomous. In re a dynamic 
system; (1) having a number of degrees of freedom 
equal to the number of independent coordinates; (2) 
having integrable relations connecting the coordinate 
velocities. 
Holfz'sche Roehre: Holtz tube. A vacuum tube across 
which are funnel-shaped constrictions pointing in one 
direction, and through which a h.-f. discharge passes 
much more readily one way than the other. 
homogene Formaenderung: homogeneous strain. A 
strain such that all pairs of points in the strained 
body which were initially at equal distances in parallel 
directions are still at equal distances in parallel direc- 
itons; though both the distances and the directions may 
have been altered. 
homologes Feld; homologous field. A field of force 
in which the lines of force in a given plane all pass 
through one point (center of homology), e.g., the 
electric field between two coaxial charged cylinders. 
homologe Temperaturen: homologous temperatures. 
In re two or more substances, esp. metals: absolute 
temperatures which bear the same ratio to the absolute 
melting points of the respective substances; especially 
useful in discussing the properties of plastic solids. 
homoeopolar: homopolar, homoeopolar. Electrically 
symmetrical, as a molecule which, like N2, has no effec- 
tive electric moment; not polar. 
homotrop: homotropic. Having similar crystalline 
structure. 
Hooke'sches Gesetz: Hooke law. An approximate 
empirical law of elasticity, which states that the ratio 
of the stress to the strain, in the case of elongation or 
rectilinear compression, is constant. First stated by Rob- 
ert Hooke (1660). 
horizontal: horizontal. Perpendicular to the direction 
of gravity. 
Horizontalintensitaet: horizontal intensity. The inten- 
sity of the horizontal component of the earth’s magnetic 
field at any point. 
Horopter: horopter. The locus of those points in the 
field of binocular vision which are seen single, i.e., the 
images of which fall on corresponding retinal points. 
Huefner'scher Rhombus: Huefner rhomb. A rhombic 
glass prism used for the comparison of two illuminated 
surfaces in photometry. 
Hull'scher Ring: Hull ring, powder pattern, Debye- 
Scherrer ring. A pattern of parallel lines or bands of 
ferromagnetic powder deposited on the surface of a 
magnetized crystal. 
Huygen'sches Okular: Huygens eyepiece. A telescope 
eyepiece consisting of a plano-convex field lens and 
a plano-convex eye lens placed behind the field lens, 
with a stop halfway between them. 
Huygen'sches Penrelgesetz: Huygens pendulum law. 
States that any two conjugate points of a gravity pendu- 
lum have the property that the period of oscillation 
is the same when the pendulum is suspended at either; 
and that this common period is equal to that of an 
ideal simple pendulum of length equal to the distance 
between the two points. 
Huygen'sches Prinzip: Huygens principle. An impor- 
tant principle of wave propagation, the essential feature 
of which is the concept that every point on an advancing 
wave front acts as a source of disturbance and sends 
out waves, the resultant effect of which constitutes the 
propagation of the wave as a whole. 
/Huygen'sche Wellenoberflaeche 
62 H 
Huygen'sche Wellenoberflaeche: Huygens wave sur- 
face. The wave front of light traversing a doubly re- 
fracting medium. 
Huygen'sche Zone: Huygens zone, half-period element, 
Fresnel zone. See Fresnel’sche Zone. 
Hydraulik; hydraulics. The dynamics of liquids, esp. 
its technological applications. 
hydraulische Durchschnittstiefe: hydraulic mean depth, 
hydraulic radius. The quotient of the cross-sectional area 
of a stream flowing in a channel or a pipe, divided by 
the perimeter of the stream. 
hydraulischer Gradient; hydraulic gradient. The rate 
of fall of the pressure head along a conduit flowing full 
of liquid. 
hydraulische Gradientlinie: hydraulic grade line. An 
imaginary line so drawn, in reference to a conduit flow- 
ing full of liquid under pressure, that each point of 
the line lies vertically above or below the conduit, and 
at a distance from it equal to the pressure head at the 
corresponding point of the conduit. 
hydraulische Neigung: hydraulic slope. The slope of 
the hydraulic grade line at any point; numerically equal 
to the hydraulic gradient. 
Hydrodynamik: hydrodynamics. The dynamics of 
liquids. 
Hydrokinetik: hydrokinetics. That branch of physics 
which treats of the motion of liquids. 
Hydrometer: hydrometer. An instrument composed 
of a light float weighted at one end and bearing a ver- 
tical scale, which indicates the specific gravity of the 
liquid in which it is placed by the depth of its displace- 
ment when in equilibrium. 
Hydrostatik: hydrostatics. That portion of hydrody- 
namics which does not involve effects of liquid motion. 
Hygrograph: hygrograph. A recording hygrometer. 
Hygrometer, Feuchtigkeitsmesser: Hygrometer. Any 
one of several instruments for measuring the humidity 
of the atmosphere. 
Hyperfeinstruktur: hyperfine structure. The structure 
of a spectrum line which depends, upon angular mo- 
mentum in the atomic nucleus, each ordinary line being 
thereby rendered a multiplet. It is often superposed 
upon the isotope structure. 
Hyperfeinstrukturquantenzahl: hyperfine quantum num- 
ber, fine quantum number. See Feinstrukturquantenzahl, 
Hypsometer: hypsometer. An instrument for measur- 
ing the boiling points of liquids, esp. for the purpose 
of estimating elevations above sea level. 
Hysteresis: hysteresis. One of several effects resem- 
bling a kind of internal friction, accompanied by the 
generation of heat within the substance affected. Mag- 
netic h. occurs when a ferromagnetic substance is sub- 
jected to a varying magnetic intensity; electric h., when 
a dielectric is subjected to a varying electric intensity. 
Elastic h. is the internal friction in an elastic solid 
subjected to varying stress. 
Hys+eresiskonstante: hysteretic constan, Steinmetz co- 
efficient. Numerical values of the coefficient are based 
upon the measurement of the hysteresis loss in ergs per 
cubic centimeter per cycle and the maximum induction 
in gausses. 
Hys+eresiskurve: hysteresis curve, h. loop. The graph 
of the varying magnetic intensity H and the resulting 
magnetic induction B in a specimen of ferromagnetic 
material during a complete magnetization cycle. 
Hysteresismesser: hysteresis meter. An instrument for 
testing magnetic hysteresis, usually depending upon the 
torque developed on placing the specimen in a rotating 
magnetic field or rotating it in a stationary field. 
Hysteresisverlusf: hysteresis loss. A loss of power in 
the operation of electrical devices, due to magnetic 
hysteresis. 
Hysferesisschreiber: hysteresigraph. An instrument 
which automatically traces hysteresis curves for speci- 
mens of magnetic material placed in it. 
Hysteresisschleife: hysteresis loop, h, curve. See 
Hysteresiskurve. 
677865—46 5 
63 
/l-Wert ! 
l-Wert: 7 value. The value of the quantum number 
I which determines the internal angular momentum of 
an atomic nucleus. 
ideale Fluessigkeif: perfect fluid. An ideal fluid pos- 
sessing no viscosity; a concept useful in theoretical dis- 
cussions. 
ideales Gas: perfect gas, ideal gas. A gas which 
obeys Boyle’s law; not realized in physical fact. 
ideale Gaskonstante: ideal gas constant. See Gaskon- 
stante. 
ideales Gasgesetz: ideal gas latv. A law connecting 
the pressure p, molar volume v, and temperature T of 
an ideal gas; expressed by the equation pv zz RT; in 
which R is the ideal gas constant. 
idealer Kristall: perfect crystal, ideal crystal. A crystal 
having no mosaic structure and capable of X-ray reflec- 
tion in accordance with the Darwin-Ewald-Prins law. 
idealer Strahler: perfect radiator, ideal radiator, black 
body. A body whose reflectivity is zero for radiation of 
all frequencies. Only an ideal, it is approximated ex- 
perimentally by a nearly closed cavity with a small 
opening or slit. 
idiochromatisch: id.jochromatic. In re a crystal: hav- 
ing photoelectric properties characteristic of the material 
of the pure crystal itself, and not due to foreign matter. 
Impedanz: impedance. The ratio of the effective e.m.f. 
to the effective current in an a.-c. circuit. For a circuit 
of resistance R, inductance L, and (series) capacitance 
C, carrying a current of frequency n, its value is 
the coordinates x, y, z, represent components of mo- 
mentum. The momenta of the molecules of a gas, for 
example, then correspond to points of this space. 
Impulsstrahlung: impulse radiation. Any radiation that 
may result from the impacts of rapidly moving particles 
upon a body of matter, e.g., X-rays, produced by the 
impacts of electrons. 
Impulsverhaeltnls: impulse ratio. The ratio of the po- 
tential difference required to initiate a spark between 
terminals, when the voltage is suddenly applied, to that 
required for the same spark gap with a steady field; a 
term due to Peek. 
Indika+ordiagramm: indicator diagram. The graphical 
record made by a steam-engine indicator. 
Indikatrix: indicatrix. A vectorial ellipsoid, introduced 
by Fletcher to represent the relative refractive indices 
of a crystal in different directions. 
Induktion: inductance, induction. A (not necessarily 
constant) characteristic of an electric circuit, the measure 
of which is either the e.m.f. magnetoelectrically induced 
in the circuit by the variation at unit rate of the current 
flowing in it, or the magnetic linkage with the circuit 
produced by unit steady current flowing in it. The 
practical unit is the henry (for which the linkage per 
ampere is 108 Maxwell-turns). 
Induktionsbruecke: inductance bridge. An arrangement 
resembling a Wheatstone bridge, and used for the 
comparison of inductances by a somewhat similar 
method. 
Induktlonsmo+or: induction motor. An a.-c. motor, in 
which the torque on the rotating circuit, or rotor, is 
due to currents induced in it by a varying magnetic 
field excited by a.c.’s in the stationary circuit, or stator. 
Such motors are operated by single-phase, two-phase, 
three-phase, or polyphase currents. 
Induktionsmesser: inductometer. A variable inductance, 
esp. one calibrated to indicate the inductance in henrys 
or millihenrys. 
Induktometer: inductometer. See Induktionsmesser. 
Induktionsspule: induction coil. An apparatus consist- 
ing of two coupled circuits, interruptions of the current 
in one of which (the primary) induces an e.m.f., usually 
large, in another (the secondary). Used for ignition, 
for operating vacuum tubes, etc. 
Induktivitaet: inductivity, dielectric constant. See di- 
elektrische Konstante. 
VR2 + (2«L -die)2- 
Impuls: impulse. The time integral of a force, esp. 
when applied for a short time; measured by the change 
in momentum which it would impart to a free mass if 
acting in a line through the c.m. 
Impulsmoment: momentum, moment of momentum. 
(1) (Linear.) The product of the mass of a body by 
its linear velocity. (2) The angular momentum is the 
product of the moment of inertia of a rotating body, 
with respect to the (fixed) axis of rotation, by its angu- 
lar velocity in radians per unit time; or, the volume 
integral of the products of the momenta of the elements 
of mass of the body by their distance from the axis 
of rotation. 
Impulsraum: momentum space. A mathematical space 
in which the radius vector represents momentum and 
/induktiver akustischer Widerstand 
64  
induktiver akustischer Widerstand oder akustische Iner- 
tanz: acoustic inertance. See akustische Inertanz. 
Induktor: inductor. A coil or electromagnet introduced 
into a circuit to provide inductance. 
induzieren: induce. To bring about as the result of 
exposure to the influence or to the variation of a field 
of force; e.g., an induced charge, or an induced current, 
etc. 
Infrarot: infrared. A wide range of invisible radiation 
frequencies adjoining the visible red and merging into 
Hertzian radiation. 
Infraschall: infrasonic. Having a frequency below the 
audible range. 
Inklination; inclination. (1) The angle which a line, 
a surface, or any vector makes with the horizontal. (2) 
(Geom.) The angle which the direction of a vector 
or of a curve at any point makes with the axis of 
abscissas. (3) (Magnetic.) The angle which the mag- 
netic field of the earth makes with the horizontal at 
any station. Syn. magnetic dip. 
Inklinationsmesser; inclinometer. (1) Any instrument 
for measuring inclination, as of the surface of the land 
or of a rock stratum. (2) (Magnetic.) A magnetic 
needle poised in a vertical plane, used to indicate the 
magnetic inclination. Syn. dip needle. 
Inklinometer: inclinometer. See Inklinationsmesser. 
innere Arbeit; internal work. Work done by a system 
against forces operating within it or between its parts, 
or done upon the system by such forces e.g., when a 
body expands or when a liquid evaporates, work is done 
in general against the forces of cohesion between its 
molecules. 
innerer Druck: intrinsic pressure, internal pressure. A 
pressure supposed to exist within a fluid because of its 
cohesion, and which cooperates with the external pres- 
sure to maintain equilibrium against the expansive effect 
of heat. 
innere Energie: internal energy, intrinsic energy. That 
part of the energy of a system any change in which 
is equal to the algebraic sum of the mechanical work 
and the heat received by the system; provided that the 
recognizable forms of bulk energy, such as the kinetic 
energy of motion of its parts, or its electrical and mag- 
netic potential energy, remain constant throughout such 
change. The internal energy may be regarded as a scalar, 
reckoned from a zero taken at some arbitrarily chosen 
state. 
inneres Feld: intrinsic field, inner field, inner force. 
The electric field immediately surrounding any individual 
molecule in the interior of a polarized dielectric, or 
the magnetic field surrounding a molecule of a mag- 
netized substance. Its intensity is a linear function of 
the electric polarization or of the magnetization. 
innere Feldkonstante: inner field constant. The con- 
stant coefficient of the electric polarization or of the 
magnetization in the linear function representing the 
intensity of an inner field. 
innere Kraft: inner force. See inneres Feld. 
innere magnetische Induktion: intrinsic magnetic in- 
duction. That component of the magnetic induction 
which is proportional to the local magnetization. 
innerer photoelektrischer Effekt: internal photoelectric 
effect, volume photoelectric effect. True or primary 
photoconductivity, apart from the secondary effects usu- 
ally associated with it. 
inneres Potential: intrinsic potential. The constant 
amount by which, according to the theory of Frenkel, 
the potential in the interior of a body differs from 
that of its surroundings; closely associated with con- 
tact p.d. 
Innere Quantenzahl: inner quantum number. A quan- 
tum number J, associated with the quantization of the 
total angular momentum of the atom, exclusive of 
nuclear spin. It is analogous to the rotational quantum 
number J of a molecule (inclusive of electron spin) ; 
and the term is sometimes thus applied to the molecule. 
Innere Reflektion (Zurueckstrahlung): internal reflec- 
tion. Reflection of light incident upon the surface of 
a body from the inside, or at an interface, the medium 
beyond which has a lower refractive index than that 
in which the reflection occurs. 
innerer Widerstand: internal resistance. The resistance 
of the portion of a circuit occupied by sources of e.m.f. 
such as batteries or generators. 
Innere Umkehrung, innere Umwandlung: internal con- 
version. The effect upon an atom produced when a 
gamma-ray photon emerges from the nucleus and gives 
up its energy in an encounter with an extranuclear 
electron. 
in recjelmaessigen Zeitabschnitten: isochronous. In re 
a vibration: having a period independent of the ampli- 
tude. 
in Serie gewichelt: series-wound. In re a field magnet: 
65 
/Instrument zur Messung der Koerzitlvkraft I 
having its winding in series with the external or line 
circuit. 
Instrument zur Messung der Koerzitivkraft: coercime- 
ter. An instrument for measuring the coercive force of 
magnetic materials. 
Integrationsinstrument: integrator. An instrument that 
performs definite integrations or summations mechan- 
ically. 
Integrationsmesser: integrating meter. An instrument 
that sums up or integrates the electric energy used over 
a period of time, e.g., the ordinary electric light meter. 
Integrationsphotometer: integrating photometer. A 
photometer that sums or averages the intensity of a 
light source in all directions and thus gives the mean 
spherical candle power by a single observation. 
Integrationssphaere: integrating sphere. (Photom.) A 
spherical shell coated inside with a nonselective white 
paint, used with a photometer for measuring the reflec- 
tions of material without comparison with a reflection 
standard. 
In+egra+ionswuerfel: integrating cube, cube photometer. 
An integrating photometer similar in principle to the 
sphere photometer but employing a cubical instead of 
a spherical cavity. 
In+ensitaef (zum Beispiel Emission): intensity (of an 
emission), flux density. The flux through unit area of 
a surface normal to the direction of propagation; or, for 
a diffuse emission, the flux per unit solid angle per 
unit area normal to a specified direction. Syn. intensity. 
Interferenz: interference. A term applied to a variety 
of phenomena arising from the joint effects of two or 
more wave trains arriving at the same point simul- 
taneously. 
Interferenzphotometer: interference photometer. A 
photometer in which the balance is determined by the 
disappearance of superposed, complementary interfer- 
ence bands produced by the two sources in a thin film. 
Interferometer: interferometer. An apparatus used 
to produce and exhibit interference between two or more 
coherent wave trains from the same large, luminous 
area, and often to compare wave lengths with observable 
displacements of reflectors or other parts. 
Interkombinationslinie: intercombination line. A com- 
bination line between multiplet energy levels having dif- 
ferent numbers of components, as between quintet and 
triplet levels. 
intermittency effect: intermittency effect. A difference 
between the photographic density produced by an ex- 
posure separated into short flashes and that due to a 
continuous exposure of the same illumination and total 
duration. 
internationaler Radiumstandard: international radium 
standard. A standard of radioactivity, consisting of 21.99 
mg of pure radium chloride, prepared by Mme. Curie 
and preserved at the Bureau International des Poids et 
Mesures at Sevres. 
internationale Temperaturskala: international tempera- 
ture scale. A scale of temperature fixed by international 
agreement. Between — 190 and -f 660 degrees C., 
it is based upon the resistance of a standard platinum 
resistance thermometer in accordance with the following 
formulas for resistance at temperature t: 
below 0 degree C, 
Rt = R0 [1 + At + Bt2 + C (t — 100°) t3], 
above 0 degree C, 
Rt = R0 (1 + At + Bt2); 
where A, B, C are empirical constants. From -f 660 
degrees C. to the gold point it is based upon the plati- 
num-platin-rhodium thermel, and, beyond this, upon 
the optical pyrometer. 
interpolieren: interpolate. To estimate the value of a 
function for values of the variable lying between those 
for which the function is known; either graphically, or 
by a proportion or other interpolation formula. 
Interwall: interval. The ratio of the higher of two 
musical frequencies to the lower; e.g., the interval C 
sharp to C is 1.059. 
Interwallfaktor: interval factor, gamma value. A quan- 
tity relating to the angular momentum levels in the Zee- 
man effect, introduced by Lande, and denoted by y. 
Interwallregel (Lande): interval rule (Lande). See g- 
Faktor, g-Wert. 
Invar: invar. An alloy of nickel and iron (about 3<? 
percent Ni) which has the remarkably small linear ex- 
pansion coefficient 8 x 10~7 per degree C. 
invariable Ebene: invariable plane. The plane through 
the c.m. of a body or system of bodies, perpendicular 
to the vector representing its angular momentum; in- 
variable so long as the system is unaffected by external 
influences. 
Inversion: inversion. (1) A reversal of the usual di- 
rection of a process; e.g., the change in density of 
/inverser photoelektrischer Effekt I 
water at 4 degrees C. (2) The transformation of an 
optically active substance into one having the opposite 
rotatory effect, without change of chemical composition. 
inverser pho+oelek+rischer Effekt: inverse photoelectric 
effect. The transformation of the kinetic energy of a 
moving electron into radiant energy, as in the recombi- 
nation of an electron with an ion, or in the production 
of X-rays. 
inverser piezoelektrischer Effekt: inverse piezo-electric 
effect. The contraction or expansion of a piezo-electric 
crystal along an electric axis when subjected to an elec- 
tric field in that direction. 
inverse Spannung: inverse voltage. The effective volt- 
age attained in the noncurrent half of the cycle from 
an a.-c. source used with a valve rectifier, as in operat- 
ing an X-ray tube with a transformer. 
Ion: ion. (1) One of two oppositely charged carriers 
which effect electric conduction in an electrolyte. (2) 
Any part of a molecule or of an atom, dislodged from 
the rest by a suitable application of energy. (3) Any 
electrically charged particle of molecular or atomic or- 
der of magnitude. 
lonendosismesser: iontoquantimeter. A type of roent- 
genmeter, devised by Duane, and used for the measure- 
ment of X-ray intensities. 
lonengi+ter: ion lattice. The lattice of an ionic crystal. 
lonenkrlstall: ionic crystal. A crystal having chemical 
ions, rather than neutral atoms or molecules, at its lat- 
tice points; e.g., sodium chloride. 
lonenlelffaehigkeit: ionic conductivity. The conductiv- 
ity of a solution due to a given type of ions, correspond- 
ing to a given concentration of those ions in the solution. 
lonenzaehler: ion counter. A tabular ionization cham- 
ber designed by Ebert for measuring the ionization of 
the air. 
lonenzus+and: ionicness. A condition defined as being 
present in a molecule, either heteropolar or homopolar, 
when, using atomic orbitals, the wave function contains 
terms corresponding to opposite charges on the two 
atoms. 
lonisationsdruck: ionization pressure. An increase in 
the pressure within a gas-discharge tube, due to ioniza- 
tion of the gas. 
lonisa+ionsfunktion: ionization function. A coefficient 
proportional to the relative ionization produced in a 
given gas enclosed in a given ionization chamber by 
equal amounts of radiant energy of different wave 
length. 
Ionisationskammer: ionization chamber. An enclosure 
containing two oppositely charged electrodes in air or 
other gas, so arranged that when the gas is ionized, as 
by X-rays, the ions formed are drawn to the electrodes, 
thus establishing an ionization current. 
lonisationskoeffizient: ionization coefficient. The num- 
ber of ions formed by the impacts of a rapidly moving 
corpuscle in a gas, per unit length of path. Relative 
ionization coefficients are used to compare ionization 
produced by any ionizing agent in a given substance 
with that in a standard substance. 
lonisationskondensa+or: ionization condenser. An ap- 
paratus consisting of two parallel metal plates, placed 
within an ionized gas and supplied with a h.-f., a.-c. 
voltage for the purpose of testing the electrical prop- 
erties of the ionized gas. 
lonisationsmanome+er: ionization gauge. A pressure 
gauge that depends upon the quantitative relation be- 
tween pressure and ionization current in a vacuum tube. 
lonisationspotentlal: ionization potential, ionizing po- 
tential. The p.d., in volts, corresponding to the energy, 
in electron-volts, required to ionize an atom or a mole- 
cule, by the impact of an electron or otherwise. 
lonisationssaeule: columnar ionization. (1) A term 
used in re the properties of ionized gases in tubes or 
columns as differing from those of gases uniformly ion- 
ized throughout. (2) Also frequently applied to the 
ionization of gases by alpha particles. 
lonisationsstrom: ionization current. A current pro- 
duced by an electric field in an ionized gas. 
lonisationswaerme: heat of ionization, heat of dissoci- 
ation. The quantity of heat evolved in the chemical 
dissociation of 1 g or 1 mol of an electrolyte. 
lonisationswahrscheinlichkeit: ionization probability. 
One of several arbitrarily chosen expressions involving 
factors relating to the ionization of a gas by a corpuscu- 
lar emission, and used as measures of the likelihood 
or the relative frequency of the ionization of molecules. 
They are not probabilities in the usually accepted sense. 
ionisieren: ionize. To separate into ions. 
lonisierungspofenfial: ionizing potential. See lonisa- 
tionspotential. 
67 
/Ionometer I 
lonometer: ionometer. An ionization chamber used 
for measuring the intensity of an ionizing emission. 
lonosphaere: ionosphere. See Heaviside Schicht. 
irrationale Dispersion: irrational dispersion. An in- 
equality in the deviation angle for the same wave 
length, produced by two prisms of the same total dis- 
persion range but of different kinds of glass. 
isenthalpisch: isenthalpic, (enthalpy). For a fluid sys- 
tem subject to no outside forces except a uniform, 
normal pressure, it is the thermodynamic potential for 
constant entropy and pressure. A process in which this 
quantity is constant is said to be isenthalpic. 
isentropisch: isentropic. (1) (adj.) Taking place with- 
out change of entropy. (2) (n.) The graph represent- 
ing the variables in a transformation during which the 
entropy remains constant. 
Isobare: isobar. An isobaric line. 
isobarisch: isobaric. (1) Taking place without change 
of pressure. (2) Connecting points of equal pressure, 
as an isobaric line. (3) Having the same atomic weight 
but quite different chemical properties, e.g., the ele- 
ments uranium Xx and uranium X2; such elements are 
termed isobars. 
Isochore: isochor, isochore. The graph representing 
two variables involved in an isometric (constant-volume) 
thermodynamic change, e.g., pressure-temperature, tem- 
perature-entropy, etc. 
isochromatisch: isochromatic. See gleichfarbig. 
isochromatische Kurve: isochromat. A curve represent- 
ing an isochromatic relation. 
isochron: isochronous. See in regelmaessigen Zeit- 
abschnitten. 
Isodynamisch: isodynamic. A term applied to points 
on the earth’s surface at which the total magnetic in- 
tensity of the terrestrial field has the same magnitude. 
An isodynamic line is a line connecting Such points. 
isodynamischer Zustand: isodynamostacy. A condition 
of kinetic equilibrium. 
isoelektrisch: isoelectronic. Having the same number 
of electrons outside the nucleus. E.g., an atom may be 
made isoelectronic with the one below it in atomic 
number by removing one of its outer electrons. An 
isoelectronic sequence is a series of ions having the 
same number of extranuclear electrons, but successively 
increasing nuclear charge. 
isoelektrischer Punkt: isoelectric point. That critical 
condition of a colloidal suspension in an electrolytic 
medium for which the cataphoresis of the suspended 
particles reduces to zero and reverses in sign as the 
activity of the electrolyte is increased. 
isoenergetisch: isoenergic. Taking place under the 
condition that the internal energy remains constant. 
Isogam: isogam. A line of equal acceleration of 
gravity on the earth’s surface. 
isogon: isogonic. (1) Making, or pertaining to, a 
fixed angle. An isogonic line is a line on the earth’s 
surface, at all points of which the magnetic declination 
has the same value. (2) In re two crystalline substances: 
having corresponding dihedral angles of one or more 
zones equal. 
Isoklin: isoclinic, isoclinal. A term applied to points 
on the earth’s surface at which the magnetic inclina- 
tion is the same. An isoclinic line is a line connecting 
such points. 
Isola+ionsstaerke: insulating strength, dielectric strength. 
See dielectrische Kraft. 
Isoluxdiagramm: isolux diagram, isophote. A curve or 
surface of equal light intensity. 
isomerer Koerper: isomer. One of two or more sub- 
stances composed of molecules having the same kind 
of atoms and in the same proportions, but which, by 
reason of some difference in the number or arrange- 
ment of those atoms, have entirely different physical and 
chemical properties. 
< 
Isomeres: isomer. See isomerer Koerper. 
isometrisch: isometric, cubical. (1) In re crystal struc- 
ture: having three equal and mutually perpendicular 
axes. (2) Having the same volume, or involving the 
maintenance of a constant volume, e.g., an isometric 
change in a gas. (3) Represented without perspective 
convergence, i.e., as of the same size irrespective of 
distance. 
Isomorphie: isomorphism. The property, possessed by 
various groups of compounds, of being identical in cry- 
stalline form, and of having the same numbers of 
atoms, similarly arranged, within the molecule. 
Isosmotisch: isosmotic. In equilibrium as regards os- 
/isoplan 
68 I 
motic pressure; applied to solutions on opposite sides 
of a porous membrane when osmotic action ceases. 
isoplan: isoplanatic. In re an optical system: free from 
coma. 
Isophote: isophote. See Isoluxdiagramm. 
isostatisch: isostatic. In static equilibrium; esp. ap- 
plied to the hydrostatic equilibrium of the earth’s crust 
in accordance with the theory of isostasy. 
isotherm: isothermal. (1) (adj.) At the same tem- 
perature throughout. An isothermal line is a line on 
the earth's surface connecting points of equal tempera- 
ture. (2) (n) A graph representing the variables in a 
transformation during which the temperature remains 
constant. 
Isotherme: isotherm. An isothermal line. 
Isotop: isotope. One of two or more varieties of the 
same chemical element which, while they have the 
same atomic number, have different atomic masses. 
Isotopeneffekt: isotope effect, i. shift. A systematic 
difference in the position of lines in the spectra of dif- 
ferent isotopes of the same element or of molecules 
containing them. 
Isotopenverhaeltnis: isotopic ratio. The ratio between 
the number of atoms of two isotopes of the same ele- 
ment in the natural mixture, as of 016 and 018 in ordi- 
nary oxygen. 
isotrop: isotropic. Having the same properties in all 
directions. 
69 
/J-Wert, j-Wert  
J-Wert, j-Wert: / value, j value. The value of the 
inner quantum number in atoms, or of the rotational 
quantum number in molecules. 
Jellet-Cornu Prisma: Jellet-Cornu prism. A type of 
half-shade analyser in which two parts of a Nicol prism 
are ground to fit each other so that their transmission 
planes are not quite parallel. 
Jolyscher Leuchtschirm: Joly screen. A photometer 
screen devised by Joly, and apparently also in modified 
form by Elster, consisting of two slightly separated 
parallel plates of a translucent substance, e.g. paraffin 
or opal glass. When the plates are equally illuminated, 
the interface disappears. 
Joule: joule. A unit of energy or of work. The ab- 
solute joule is equal to 107 ergs. The international joule 
is defined, in electrical terms, as the work required to 
maintain a current of 1 international amp for 1 sec in 
a resistance of 1 international ohm. 
Joulescher Aequivalent: Joule Equivalent. Syn. me- 
chanical equivalent of heat. 
Joulescher Effekt: Joule effect. (1) (Magnetic.) Ex- 
tension accompanying change of magnetization. (2) 
Heating by mechanical means. (3) Generation of Joule 
heat. 
Joulesches Gesetz: Joule law. (1) Expresses the 
quantity of heat (Joule heat) generated by an electric 
current I (amp) flowing for t (sec) in a conductor of 
resistance R (ohms) as 0.2388 RI2t (cal). Since the 
rate of heat generation is proportional to RI2, energy 
lost in this way is sometimes called the RI2 loss. (2) 
States that the internal energy of a perfect gas is a 
function of its temperature only, i.e. does not depend 
upon its volume or pressure. 
Joulesche Waerme: Joule heat. Heat generated by 
an electric current and dependent only upon the resist- 
ance and the current, i.e. not including Peltier or Thom- 
son Effect. 
Joule-Thomson Effekt: Joule-Thomson effect. An ef- 
fect observed by Joule and Thomson (Kelvin) about 
1852 upon the temperature of a gas escaping from a 
higher pressure into a lower pressure through a porous 
partition, the change being either a cooling or a heating 
(the so-called porous-plug experiment). This change 
indicates the presence of molecular interactions. 
Joule-Thomson Experiment: porous-plug experiment. 
See Joule-Thomson Effekt. 
/K-Serie 
70 J< 
K-Serie: K series. A series of frequencies in the X-ray 
spectrum of an element, believed to arise from the 
transition of electrons from various higher quantum 
states to the state whose principal quantum number is 1. 
kael+eerzeugend: cryogenic. Pertaining to low tem- 
peratures or to apparatus for producing them. 
Kaleidophon: kaleidophone. A device for producing 
the Lissajous curves, consisting of an elastic strip cap- 
able of two vibrations at right angles, and having a 
small mirror mounted across one end. Devised by 
Wheatstone. 
Kaloreszenz: calorescence. The transformation of in- 
frared radiant energy into visible light, as by focusing 
infrared rays upon a thin plate of platinum until it 
becomes white hot. 
Kalorie: calorie. (1) A unit, defined as the quantity 
of heat required to raise the temperature of 1 g of 
water from 15 to 16 degrees C. (2) One thousand 
times the above unit. 
Kaloriemeter: calorimeter. Any one of several types 
of apparatus used for the purpose of measuring quanti- 
ties of heat. 
kaloriemetrische Koeffizienten: calorimetric coeffi- 
cients. Six quantities which express the rates of absorp- 
tion of heat by a body of fluid during reversible changes 
of its volume, pressure, and temperature, viz., 
a conductor near where the latter terminates in a sharp 
edge. 
Kapazitaet: capacity, capacitance. The ratio of the 
quantity of electricity q accumulated in charging a con- 
ductor to the accompanying change in its potential V, 
i.e., the value of dq/dV. 
Kapazitaetsmessbruecke: capacitance bridge. An ar- 
rangement resembling a Wheatstone bridge and used 
for the comparison of capacitances by a somewhat simi- 
lar method. See also Farad’sche Bruecke. 
Kapazitanz: capacitance. See Kapazitaet. 
Kapazitanzkoeffizient: capacitance coefficient. In re 
one of a system of neighboring conductors: the capaci- 
tance of the given conductor when all the others are 
kept at zero potential. 
Kapillarelektrometer: capillary electrometer. An elec- 
trometer whose action depends upon the effect of a p.d. 
on the surface tension at the interface between two 
liquids in a capillary tube. 
Kapillaritaet: capillarity. See Haarroehrchenkraft. 
Kapillarkonstante: capillary constant. In re two liquids 
of densities p15 p2, having the mutual surface tension T: 
the product (px — p2) Tg, in which g is gravity. 
Kapillarstroemung: transpiration. The passage of a 
gas or a vapor through a capillary, or its exhalation 
from the pores of an absorbing substance. 
Kaskade: cascade. An arrangement of condensers, 
analogous to the series arrangement of battery cells, in 
which the higher potential plate of each is connected 
to the lower of the next. 
Kaskadenroehre: cascade (X-ray) tube. A high-voltage 
vacuum tube used in the production of hard X-rays or 
of high-speed ion beams, in which the total voltage is 
divided by constructing the tube in several sections. 
Katakaustik: catacaustic. A caustic produced by re- 
flection. 
Kataphorese: cataphoresis. The movement of solid 
particles in liquid suspension under the action of an 
e.m.f. 
Katenari'sche Kurve: catenary. The curve assumed by 
a perfectly flexible, uniform chain hanging in equi- 
librium between two points of support. 
Kater'sches Pendel: Kater pendulum. One of several 
types of rigid pendulum designed by Kater for relative 
Sq T f Sq 1 f 8q f Sq 1 f Sq 1 f Sq 
8p v 8v p 8T v 8T p Sp T 8v T 
In these T is the temperature; q, quantity of heat; v, 
volume; p, pressure; and the subscripts denote that the 
corresponding quantity is to be kept constant. 
kalte Elektronenemission: cold emission. See Feld- 
emission. 
Kalte Emission: cold emission. See Feldemission. 
Kanalstrahlen: canal rays. An emission consisting of 
positive ions which have passed through openings in 
the cathode of a gas-discharge tube. 
kanonisch: canonical. In re the mathematical statement 
of a physical law: expressed in the simplest completely 
general form possible. 
KantenefFekt: edge effect. An abnormality such as 
that exhibited by the electric field due to the charge on 
71 
/Kalhetome+er K 
or absolute gravity determinations. The most familiar 
is reversible, having two adjustable knife edges and 
depending upon the Huygens pendulum law. 
Kathetometer: cathetometer. A form of comparator, 
consisting of a reading telescope or microscope mounted 
horizontally and movable along a vertical scale. 
Kathode: cathode, kathode. That electrode from which 
electrons or negative ions are dispersed, or toward 
which positive ions are collected, within an electrolytic 
cell, discharge tube, or similar apparatus. 
Kathodendunkelraum: cathode dark space, Crookes 
dark space. That portion of the glow discharge in a 
Crookes tube lying between the cathode glow and the 
negative glow; so called because it is nonluminous. 
Kathodenfall: cathode drop. An abrupt fall of electric 
potential at the cathode of an electrolytic cell or a 
vacuum tube. 
Kathodenfluessigkeit: catholyte, katholyte. The solution 
surrounding the cathode in an electrolytic cell. 
Kathodenleuchten: cathode glow. A luminosity which 
immediately surrounds the cathode in a gas-discharge 
tube when operating at moderately low pressures, and 
which increases in extent as the pressure is further re- 
duced. 
Kathodenlumineszenz: cathodoluminescence. Lumines- 
cence excited by cathode rays. 
Kathodenphosphoreszenz: cathodophosphorescence. 
Phosphorescence excited by cathode rays. 
Kathodenstrahlen: cathode rays. An emission from the 
cathode of a discharge tube, consisting of electrons sup- 
plied by the cathode itself and projected at right angles 
to its surface. The term is usually restricted to the 
emission from a cold cathode in a gas-filled tube at 
high potentials and does not include thermions or 
photoelectrons. 
Kathodenzers+aeubung: cathodic disintegration. The 
abrasion of a cathode through the ejection of its atoms 
in its bombardment by positive ions in a vacuum tube. 
Ka+hodenzerstoerung: cathodic disintegration. See 
Kathodenzerstaeubung. 
Kation: cation, kation. One of the positive ions mov- 
ing toward the cathode in an electrolytic cell or a gas- 
discharge tube. 
Kauffman'scher Versuch: Kauffman experiment. An 
/Kennelly'sches Gesetz der Magnetisierung 
experiment upon beta particles moving across magnetic 
and electric fields, which leads to the conclusion that 
the mass of an electron is entirely electromagnetic. 
Kaustik: caustic. A surface which envelops an astig- 
matic bundle of rays or of normals to the wave surface; 
as of light reflected from a curved mirror. In a turbid 
medium it becomes visible as a hollow, luminous cusp. 
kegelfoermige Refraktion: conical refraction. The 
transformation of a ray of light into a hollow cone by 
refraction, at a suitable angle of incidence, in a biaxial 
crystal. 
Keilphotometer: wedge photometer. A photometer in 
which the intensity of the light from one source or 
both sources to be compared is varied by means of a 
wedge of absorbing material pushed into the beam until 
requisite thickness has been interposed. 
Kelvin: Kelvin. See Thomson. 
Kelvin'sches elektrodynamisches Gesetz: Kelvin elec- 
trodynamic law. States that if a number of electric 
circuits carrying currents are displaced with reference 
to each other, the work thus done (whether positive 
or negative) appears as a change (positive or negative) 
in the total electromagnetic energy of the circuits. 
Kelvin'scher hydrodynamischer Lehrsatz: Kelvin hy- 
drodynamic theorem. States that the circulation around 
any closed fluid filament (stream line) is invariable in 
time, provided the impressed forces have a single-valued 
potential and the density is a function of the pressure 
alone. 
Kelvin-Skala: Kelvin scale. An ideal, absolute-tempera- 
ture scale, proposed by Lord Kelvin (1848), the equal 
intervals on which correspond to equal quantities of 
work derived from a working substance performing in 
perfect Carnot cycles between the respective isothermals. 
It closely approximates the ordinary hydrogen-pressure 
absolute scale. Syn. thermodynamic scale. 
Kelvin'sche thermoelektrische Beziehungen: Kelvin 
thermoelectric relations. Certain formulas derived by 
Lord Kelvin for the reversible heat development and 
the thermoelectromotive force in crystals. 
Kelvin'sche Waage: Kelvin balance. An instrument for 
measuring an electric current by balancing, against the 
weight of a known mass, the electrodynamic force on 
two coils, one at each end of a balance beam; the force 
on each coil being produced by two fixed coils mounted 
one above, the other below, the moving coil. 
Kennelly-Heaviside Schicht: Kennelly-Heaviside layer, 
ionosphere, Heaviside layer. See Heaviside Schicht. 
72 K 
Kennelly'sches Gesetz der Magnetisierung: Kennelly 
law (of magnetization'). States that the reluctivity in 
magnetizing a specimen of iron is a linear function of 
the magnetizing force. 
Kepler'sche Gesetze: Kepler laws. Three laws of 
satellite motion under a central inverse-square attrac- 
tion, stated as follows: (1) The orbit is an ellipse with 
the attracting center at one focus. (2) The radius vec- 
tor of the revolving satellite describes equal areas in 
equal times. (3) The squares of the periods of differ- 
ent satellites revolving about the same primary are pro- 
portional to the cubes of their mean radii vectors. First 
stated, empirically, by Kepler with reference to the 
planets; (1) and (2) in 1609, (3) in 1618. 
Kepler'sches Teleskop: Kepler telescope. A telescope 
in which the objective and the ocular are both con- 
vergent lenses, the objective forming a real image to 
be viewed by the ocular in whose first focal plane it 
lies. 
Kern: core, kernel, nucleus. (1) Core: a. A mass of 
iron or other ferromagnetic material placed within a 
coil to enhance the magnetic flux, as in an electromag- 
net. h. The inner metal base or heating element of 
a thermionic filament, which is covered with a ther- 
mionically active coating, usually of barium and stron- 
tium oxide, c. The inner portion of a nonhomogeneous 
carbon-arc electrode, d. The inner, intensely brilliant 
portion of the arc itself. (2) Kernel: a. A line with- 
in a conductor carrying a current, along which the 
magnetic intensity due to the current is zero. b. Syn. 
Rumpf core. (3) Nucleus: That part of an atom which 
is supposed to be the seat of its effective mass and to 
control the motions of its orbital electrons. Current 
atomic theory assigns to the nucleus a structure which 
involves an excess positive charge. 
Kernbildung: nucleation. The action of ions or other 
particles as centers of condensation. 
Kernmagneton: nuclear magneton. A unit of magnetic 
moment, in terms of which those parts of atomic mag- 
netic moments attributed to the atomic nuclei are sim- 
ple functions of small integers. 
Kernmoment: nuclear moment. The electric or the 
magnetic moment, or the moment of momentum, of an 
atomic nucleus; the last, called the nuclear mechanical 
moment, being usually expressed in units equal to h/27r. 
Kernverlust: core loss. Loss of power through mag- 
netic hysteresis or eddy currents. 
Kerr-Effekt: Kerr effect, electric double refraction. (1) 
(Elec.) An electro-optical effect; viz., certain transpar- 
ent, normally isotropic substances become doubly refract- 
ing when subjected to an electric field transverse to the 
beam of light. (2) (Mag.) The conversion into ellip- 
tically polarized light of plane-polarized light when it 
is reflected, even in or perpendicular to the polarizing 
plane, from the polished pole-piece of a magnet (polar 
reflection). The rotation of the elliptic major axis is 
equal to the magnetization multiplied by the Kerr mag- 
neto-optical constant. 
• 
Kerr'sches Gesetz: Kerr law. In re Kerr effect (1): 
if np and ns are the refractive indices for light polarized 
in planes respectively parallel and perpendicular to the 
electric intensity E, then np — ns = BaE2. Here B 
is constant for any fixed temperature and any fixed 
(air) wave length A, and is called the Kerr electro- 
optical constant for the given substance, wave length 
and temperature. Also expressed in the form A = 
2ttB1E2, in which A is the phase difference (in radians) 
introduced by a thickness 1 of medium. 
Kerr-Konstante: Kerr constants. The Kerr electro- 
optical constant and the Kerr magneto-optical constant.. 
Kerr Zelle: Kerr cell. An enclosure containing a small 
quantity of nitrobenzene or other transparent substance 
which exhibits electric double refraction, and used to 
demonstrate or utilize this effect. 
Kerzenstaerlce: candle. The unit of luminous intensity 
generally used. The international candle was established 
in 1909 by the national standards laboratories of the 
United States, Great Britain, and France and adopted 
in 1921 by the International Commission on Illumina- 
tion. The U. S. candle, defined in terms of a group 
of 45 carbon-fiilament lamps at the National Bureau 
of Standards, agrees with the international candle with- 
in the limits of observational error. 
Ketteler-Helmholfz Disperslons-formel: Ketteler- Helm- 
holtz dispersion formula. An approximate formula for 
the refractive index n of a substance in terms of the 
wave length A: 
Aa2 Ba2 
n = 1 + + -f . . . . 
A2 — A2! A2 — A22 
A, B, are constants and A1? A2, 
are wave lengths of absorption lines, all characteristic 
of the substance. First stated by Sellmeier and later in 
modified form by Ketteler and Helmholtz. 
Kilogramm: kilogram. The practical metric standard 
of mass and of weight; defined as the mass of a plati- 
num cylinder, known as the kilogramme des archives, 
at Sevres. 
Kilowattstunde: kilowatt-hour. A practical unit of 
electric energy, equal to 1,000 watt-hours. 
73 
/Kinematik K 
Kinematik: kinematics. That branch of physics which 
deals with motion in the abstract, i.e., of points or 
space figures, and apart from its dynamic aspects. 
kinematischer Viskositaetskoeffizient; kinematic viscos- 
ity coefficient. The ratio of the viscosity coefficient of 
a fluid to its density. 
Kinetik: kinetics. That branch of physics which deals 
with the motion of material bodies in relation to the 
forces acting upon them. 
kinetisches Gleichgewicht: kinetic equilibrium, isody- 
namostacy. Equilibrium in which the system, or parts 
of it, are in motion; e.g., a particle moving with uni- 
form speed in a straight line is in this condition. 
kinetische Energie: kinetic energy, vis viva (Lat). 
That part of the total energy of a body or system which 
is obviously associated with its motion or with the rela- 
tive motions of its parts. 
kinetisches Potential: kinetic potential. (1) In re a 
particle of rest mass m0 moving with speed u: A phy- 
sical magnitude represented by the expression 
Kippschwingungsoszillator: relaxation oscillator. See 
Kippschwingungsgeraet. 
Kippschwingungswandler: relaxation inverter. An in- 
verter, the circuit of which is based upon that of the 
relaxation oscillator. 
Kirchhoff'sche Bruecke: Kirchhoff bridge. A type of 
resistance bridge described by Heaviside, in which the 
potential differences through the known and the un- 
known resistances in series are balanced in a differential 
galvanometer. 
Kirchhoff'sche Gesetze: Kirchhoff laws. Several phy- 
sical laws are attributed to Kirchhoff; the more im- 
portant: (1) The ratio of the emissive power of a 
surface to its absorptivity for the same radiation is the 
same for all surfaces at a given temperature and is 
equal to the emissive power of a black body at the same 
temperature. (2) Certain adaptations of Ohm’s law to 
networks of conductors, treated in works on the mathe- 
matical theory of electricity. 
Kirchhoff'sche Konstante: Kirchhoff constant. The 
constant K in Kirchhoff’s formula for the velocity of 
sound in air confined in a tube, which is 
— mnc2yj t u2 
r2 
r , K . 
v = v” C1 - ävSl- 
c being the electromagnetic constant. The components 
of the momentum of the body are, in relativistic me- 
chanics, the derivatives of this quantity with respect to 
the components of the velocity. (2) Syn. Lagrangian 
function. 
kinetische Reaktion: kinetic reaction. The reaction of 
inertia in an accelerated body. If the mass is m and the 
acceleration is a, the kinetic reaction is — ma. 
kinetische Stabilitaet: kinetic stability. The stability 
of a moving body or system, which has the property 
that when its motion is slightly altered, it oscillates 
and, if left to itself, returns to its former state of mo- 
tion. Illustrated by touching a rapidly spinning top 
lightly with the finger. 
kinetische Theorie: kinetic theory. A theory, relating 
to any group of phenomena, which explains them on 
the basis of motion, e.g., the kinetic theory of gas 
dynamics. 
Kippschwingungsgeraet: relaxation oscillator. An elec- 
tric oscillator in which a condenser is charged periodi- 
cally from a d.-c. source through the primary of a trans- 
former and is discharged through a thyratron and a 
small series inductance when the condenser voltage is 
at or near its maximum. 
v0 is the velocity in the open air, r the radius of the 
tube, n the frequency; K is dependent upon the proper- 
ties of the gas. 
Kirchhoff'sches Potential: Kirchhoff potential. The 
retarded potential due to a moving charge or magnet. 
Langwellenaufzeichner; phonautograph. An early de- 
vice for recording the wave form of sounds; designed 
by Koenig and Scott. 
klassisch: classical. In accordance with long accepted 
theory; esp., the dynamics of Newton, as opposed to 
the more recent relativistic, quantum, or wave theories. 
klassische Statistik: classical statistics. A system of 
statistical analysis of the distribution of gas molecules 
or of radiation quanta and their momenta, based upon 
the number of these respective entities in any given 
elementary compartment of ordinary space or of mo- 
mentum space. 
Klein-Nishina Formel: Klein-Nishina formula. A for- 
mula expressing the scattering coefficient of a sub- 
stance for gamma radiation, assumed as due entirely 
to the Compton effect of the extranuclear electrons. 
/Klopfen 
74 K 
Thus 
Knudsen-Molekularstreugesetz: Knudsen molecular scat- 
tering law. A law of the diffuse emission or reflection 
of molecules from a solid surface, analogous to the 
cosine emission law for radiation. It states that the 
fraction dn/n of all the n molecules emitted or re- 
flected from the surface within solid angle dw making 
an angle with the normal is equal to 
2tt Ne4 (l q- a r 2 (1 -(- a) 
n = < 
m2 C4 ( a2 L 1 + 2a 
1 
log (1 + 2a) 
a 
1 1 + 3a 1 
+ log (1 + 2a) - 
2a (1 + 2a)2) 
1 
cos <p do> 
IT 
N is the number of electrons per cm3, m the electronic 
mass, e the electronic charge, c the electromagnetic con- 
stant, and 
Knudsen-Weber'sches Gesetz: Knudsen-Weher laiv. 
An experimentally established law for the resistance to 
the motion of spheres in a viscous medium. It is an 
extension of the Stokes law and reduces to it under 
appropriate limits. 
Koaggregation: coaggregation. The union of fog par- 
ticles into drops of appreciable size, as in the formation 
of rain in a cloud. 
Koch'scher Widerstand: Koch resistance. A high re- 
sistance, consisting essentially of an illuminated photo- 
electric cell used at voltages low enough to insure that 
the resistance is independent of the voltage. 
Kochen: ebullition. The familiar phenomenon of boil- 
ing, exhibited by a liquid at a temperature sufficiently 
high for the rapid formation and escape of bubbles of 
vapor. 
Koerpermittelpunkt: center of figure, c. of volume. 
In re any three-dimensional space figure: that point 
which coincides with the center of mass of a body 
formed by constructing the figure out of homogeneous 
material. 
Koerzitivkraft: coercive force, coercivity, retentivity. 
(1) The magnetic intensity required to reduce the mag- 
netic induction in a previously magnetized material to 
zero. If the material has been magnetized to satura- 
tion this quantity is called the coercivity. (2) a. The 
value of the remanence for the case of a symmetrical 
magnetic hysteresis cycle extending to practical satu- 
ration. h. The ratio of the remanence to the magnetic 
induction at saturation under these same circumstances. 
Syn. retentivity coefficient. 
Kohaerer: coherer. A cell containing a granular con- 
ductor between two electrodes, which becomes highly 
conducting only when subjected to an electric field; 
formerly used as a detector. 
Kohaerenz: coherence. A relation between two wave 
trains, such that when brought into coincidence they 
are capable of producing interference phenomena. The 
maximum path difference for which interference persists 
is the coherence length. 
hv 
a — 
me2 
where hv is the radiation quantum energy (Planck con- 
stant x frequency). 
Klopfen: hammer, hammering. The sharp pounding 
of a liquid, such as water or mercury, often observed 
when the tube containing it is devoid of air, which 
would otherwise act as a cushion. 
Knall: pulse. A single disturbance propagated as a 
wave, but not having the cyclic characteristic of a wave 
train; e.g.; the sound of an electric spark. 
Kno+en: node. (1) A point, line, or surface in a 
vibrating medium at which the amplitude of the vibra- 
tion is reduced to zero by the interference of oppositely 
directed wave trains, forming stationary waves; e.g., 
one of the stationary points on a vibrating string. (2) 
In re a wave function: A point at which the real part 
of the wave variable changes sign. 
Knotenpunkte: nodal points. In re a symmetrical opti- 
cal system: two conjugate points on the axis such that 
any paraxial ray which, before entering the system, in- 
tersects the axis at the first nodal point, will emerge 
from the system in a parallel direction and intersect the 
axis at the second nodal point. If the system is sur- 
rounded by the same medium on both sides, the nodal 
points are identical with the principal points, q.v. 
Knudsensche Gleichung: Knudsen equation. A some- 
what complicated equation for the flow of a rarefied 
gas through a cylindrical tube at very low pressures. 
Knudsen Manometer: Knudsen gauge, Knudsen abso- 
lute manometer. A gauge for measuring extremely low 
gas pressures. It operates on the principle of unequal 
bombardment of a surface by molecules of different 
energies which gives a measurable resultant force pro- 
portional to the pressure of the gas. 
75 
/Kohaesion K 
Kohaesion: cohesion. That property of a substance 
which enables it to cling together in opposition to forces 
tending to separate it into parts. 
Kohlrausches Gesetz: Kohlrausch law. States that the 
two kinds of ions of an electrolyte in solution conduct 
the current independently of each other and in propor- 
tion to their transference numbers. 
Koinzidenzmethode: coincidence method. A method 
of timing a periodic phenomenon by observing coinci- 
dences between the occurrences of the phenomenon in 
question and those of one whose period is known, e.g., 
the vibration of a pendulum. 
Kollektor: collector. (1) An exploring electrode or 
probe, esp. in a vacuum tube. (2) Syn. Faraday cylin- 
der. (3) An apparatus for measuring the vertical poten- 
tial gradient of the atmosphere. 
Kollimator: collimator. An optical apparatus, the pur- 
pose of which is to furnish a beam of parallel rays of 
light. A common form consists of a lens, having a 
small opening or slit at its principal focus. 
Kolliniationszentrum: center of collineation. That point 
through which pass all straight lines joining conjugate 
points of a spherical refracting surface or of a thin 
lens. For the former it is the center of curvature and 
for the latter, the optical center. 
Kolloid: colloid. A substance in the colloidal state. 
Typical colloids are smoke, gelatine solution, starch 
solution, albumen, and very finely divided gold in sus- 
pension. 
kolloidale Loesung: colloidal solution. A mixture which 
contains ingredients in the colloidal state; in contra- 
distinction to a true or "molecular” solution. 
kolloidaler Zustand: colloidal state. The finely divided 
state of matter dispersed in solids, liquids, or gases, 
the particles of which have diameters ranging approxi- 
mately between 10~7 cm and 10-5 cm. In liquids or gases 
the particles remain suspended indefinitely but do not 
pass through very fine filters. 
Kolorimetrie: colorimetry. The measurement of color. 
Such a measurement may be made directly in terms of 
the three attributes of color, viz., hue, saturation, and 
brilliance; or directly in terms of the physical character- 
istics of the stimulus, such as spectral energy distribu- 
tion, intensity, modal wave length, spectral purity, etc. 
Koma: coma. One of the types of spherical aberration, 
due to the asymmetry of a bundle of rays of finite 
aperture. 
Kombinationslinie: combination line. An atomic spec- 
tral line produced by a transition between two multiplet 
energy levels. 
Kombinationsprinzip: combination principle. An ex- 
pression of the fact that the existence of spectral lines 
can be predicted by calculating the quantum energy, 
and hence the frequency, resulting from the transition 
of an electron from one stable state to another. First 
stated in an empirical form by Ritz. 
Kombinationsserie: combination series. A series of 
spectral lines formed in accordance with the combina- 
tion principle of Ritz. 
Kombinationston: combination tone. A subjective tone 
produced by the simultaneous sounding of two or more 
physical tones. 
Kombinationsverbot: combination defect. A discrep- 
ancy arising from the application of the combination 
principle to certain molecular spectra, and explained on 
the assumption that the initial or the final rotational 
energy levels are close doubles. 
Kommutator: commutator. Any device for reversing 
the direction of an electric current or for interchanging 
the connections to a circuit. 
Komparator: comparator. An instrument for the ac- 
curate measurement of moderate distances, usually con- 
sisting of a telescope or a microscope arranged to move 
laterally along a scale. 
Kompensator: compensator. An apparatus, the original 
form of which was designed by Babinet, for the meas- 
urement of the phase difference between the two com- 
ponents of elliptically polarized light. 
Kompensationstheorie: compensation theorem. See Aus- 
gleichslehrsatz. 
Komplementaerfarben: complementary colors. Two 
colors which, when mixed additively in proper propor- 
tions, produce the sensation of white. 
Komplex-lon: complex ion. The result of the combina- 
tion of a positive ion with an uncharged molecule. 
Komplex-Spektrum: complex spectrum. A spectrum 
containing multiplet lines. 
Kompressibilitaet: compressibility. The reciprocal of 
the bulk modulus. Also called compressibility coeffi- 
cient. 
Kompressionswaerme: heat of compression. The heat 
generated per unit mass per unit change of pressure 
/Kondensationskoeffizient 
76 K 
or of volume, in the compression of a substance, such 
as a gas. Its value depends upon the circumstances of 
the compression. 
Kondensationskoeffizient: condensation coefficient. The 
ratio of the total volume of the molecules of a gas to 
the volume of the gas; a term due to Loschmidt. 
Kondensationspumpe: condensation pump. Any air 
pump acting on the principle which uses the impact of 
a stream of vapor to compress a gas to such a pressure 
that a force pump can take hold, the vapor being re- 
moved from the compression space by condensation. 
Kondensationswaerme: heat of condensation. See Ver- 
dampfungswaerme. 
Kondensator (elektr.): condenser. A device consisting 
of two electrical conductors, usually in the form of metal 
plates, separated by a small thickness of dielectric, which 
has the effect of largely increasing the capacitance of 
each conductor. 
Konsensor (opt.): condenser. A system of strongly con- 
verging lenses used to concentrate the light on the 
object or slide in a projector. - 
Konduktanz: conductance. (1) The reciprocal of elec- 
tric resistance. (2) Knudsen uses the term in an analo- 
gous manner as applying to the case of flow of rarefied 
gases in tubes. 
konjugierte Punkte: conjugate points. (1) (Opt.) Two 
points of an optical system such that each is the image 
of the other. (2) (Dyn.) Two points of a rigid body, 
on opposite sides of the c.m. and in line with it, such 
that if the body, when free, is given an impulse in a 
transverse line through either point, it begins to rotate 
about an axis through the other. 
konjugierte Zweige: conjugate branches. Two branches 
of an electric network, so related that an e.m.f. in one 
produces no current in the other. 
Konkavgitter: concave grating. An optical grating ruled 
on a concave, spherical, reflecting surface, which not 
only acts as a grating, but serves also to focus the image 
of the slit without the use of lenses. Such gratings were 
first constructed by Rowland. 
konkav-konvek: concavo-convex. Having two curved 
surfaces, of which one, the concave, has greater curva- 
ture than the other, which is convex; applied esp. to 
lenses. Syn. concave-meniscus. 
konservatives Feld: conservative field. A field of force 
such that, if a particle moves from one point to another 
within the field, the work done depends only upon its 
initial and its final position, and not upon the path 
which it follows. 
konservatives System: conservative system. A system 
of bodies acted upon only by forces within the system, 
so that the total dynamical energy of the system remains 
constant. 
Konstanten: constantan. An alloy of 60 percent Cu 
and 40 percent Ni, used for resistance coils because of 
its very low temperature coefficient of resistance. 
Kontaktpotentialdifferenz: contact potential difference. 
A difference of electric potential which devleops between 
two dissimilar conductors when they are placed in con- 
tact; first observed by Volta. Syn. Volta effect. 
Kontakt winke!: angle of contact. The angle which a 
liquid surface makes with the submerged part of the 
solid surface with which it is in contact, as in a capillary 
tube. 
kontinuierliches Spektrum: continuous spectrum. A 
spectrum which exhibits no structure and appears to 
represent a continuous variation of wave length from 
one end to the other, e.g., the spectrum of an incan- 
descent solid. 
Kontinuitaetsgleichung: equation of continuity. (1) 
An equation which, in physical analysis, expresses the 
fact that the rate at which the quantity of any conserved 
entity, e.g. matter, electricity, or energy, changes within 
any region is equal to the difference between the rates 
at which this entity enters and leaves that region. (2) 
An equation relating to the flow of a gaseous substance, 
which expresses the fact that the product of the cross 
section, the speed of flow, and the density remains 
constant. 
Kontrak+Ionskoeffizient: contraction coefficient. The 
ratio of its area of smallest cross section to the area of 
the orifice is the contraction coefficient. 
Kontur oder Gestalt: contour. (1) The geometrical 
form of a surface, esp. as indicated by its plane sections. 
(2) The wave-length-intensity curve for a particular 
line or band of the spectrum. 
Konvektion: convection. Circulation in a fluid of non- 
uniform temperature, due to differences of density. 
Konvergenz: convergence. (1) A negative divergence; 
e.g. for the gravitational field within a material sub- 
stance of density p it is — 4vp. (2) The increasing 
density of spacing of the lines in a spectral series as 
the series limit is approached with decreasing wave 
length. (3) (Math.) The property of converging, as 
an algebraic series. 
/Konvergenzfaktor 
77 K_ 
Konvergenzfaktor: convergence factor. The coefficient 
B in the square term of the quadratic function: 
of the inductance of B that is shared with A, the in- 
ductive coupling coefficient is the mean proportional of 
f1 and f2. The capacitative coupling coefficient is defined 
in an analogous way. (2) In general, an abstract con- 
stant entering into the equations of motion of two 
coupled systems and dependent upon the mutual effect 
of one upon the other. 
Korona (elek+r.): corona (electr.). The result of a par- 
tial electric breakdown in a gas, such as a brush dis- 
charge or a glow discharge. 
Korona (astronom.): corona (astron.). An extended, 
luminous, gaseous envelope which constitutes the outer- 
most portion of the sun. 
Koronavol+meter: corona voltmeter. An apparatus for 
the measurement of high peak voltages by the formation 
of a corona. 
Korrektionsfaktor: correction factor. See Berichtigungs- 
faktor. 
Korrelation: correlation. See Beziehung. 
Korrespondenzprinzip: correspondence principle. A 
relation assumed, in Bohr’s radiation theory, to exist 
between the observed intensities and frequencies of a 
molecular or atomic spectrum and the radiations which 
would be emitted by an oscillator in accordance with 
classical theory. 
korrespondierende Zustaende: . corresponding states. 
See Gesetz der korrespondierenden Zustaende. 
Kosinus Emissionsgesetz: cosine emission law. States 
that the rate of emission or diffuse reflection of radiant 
energy in a given direction from any element of area 
of a perfectly diffusing surface is proportional to the 
cosine of the angle of emission, measured between the 
emitted ray and the normal to the surface. For emis- 
sion it holds rigorously for black surfaces only. Syn. 
Lambert law. 
Kosinus Photometer: cosine photometer. A photometer 
in which the illumination of one surface to be compared 
is varied, in accordance with the cosine emission law, 
by varying its orientation. 
kosmische Strahlung: cosmic radiation, c. rays. A type 
of very penetrating radiation of unknown origin, ap- 
parently traversing interplanetary space in all directions, 
and detected by the ionization which it produces in 
electroscopes, ion counters, etc. 
Kossel-Sommerfeld'sche Gesetze: Kossel-Sommerfeld 
laws. (1) States that the arc spectra of elements of even 
v = v0 + AN + BN2, 
representing the frequency of the spectral line of ordinal 
number N in a rotation-vibration spectral band. v0 is 
the frequency corresponding to the zero line. 
konvex-konkav: convexo-concave. Having two curved 
surfaces, of which one, the convex, has greater curva- 
ture than the other, which is concave; applied esp. to 
lenses. Syn. convex-meniscus. 
Konzentrationszelle: concentration cell. An electrolytic 
cell whose e.m.f. is due to a difference in concentration 
between different parts of the electrolyte. 
Koordinate: coordinate. (1) One of the quantities 
specified in defining the position of a point or the value 
of a point function. (2) In general, one of a set of 
variables used to express the condition or the behavior 
of a physical system, as pressure, volume, temperature, 
entropy, time, etc. In this broader sense they are often 
termed generalized coordinates. 
Koordinationsgitter: coordination lattice. A crystal lat- 
tice in which each ion bears the same relation to the 
adjacent ions in all three coordinate directions, so that 
the identity of the molecule becomes ambiguous. 
Koordinationsregel: coordination rule. Describes the 
process whereby the magnetic sublevels of a multiple! 
(spectral line) in weak fields are co-ordinated with the 
magnetic levels of the component vectors in strong fields. 
As the field changes, the co-ordinate levels merge. Simi- 
lar rules exist also for other types of coupling. 
Kopf: bead. (1) A quantity used in relation to fluid 
motion, and having the dimension of length, which is 
in proportion to the energy of the particles of fluid. 
Three component heads are distinguished, viz., those 
corresponding to elevation, to pressure, and to speed of 
flow, respectively. (2) The edge of a spectral band or 
series. 
Kopplung: coupling. (1) A juxtaposition of two elec- 
tric circuits, such that their mutual relationship permits 
variations of current in one circuit to affect the e.m.f. 
in the other, (2) An interaction between one of the 
electrons of an atom and other parts of the atomic 
electron system. (3) In general, any interaction be- 
tween two or more systems. 
Kopplungskoeffizient: coupling coefficient. (1) An 
abstract fraction relating to the closeness of coupling 
of two circuits A, B. If ft is the fraction of the in- 
ductance of A that is shared with B, and f2 the fraction 
/Konstante der Bindungskraft 
78 K 
atomic number show odd multiplicity, and vice versa. 
Syn. alternation law. (2) States that the spectrum of a 
singly ionized element (first spark spectrum) resembles 
that of the next preceding element in the atomic-number 
table; the spectrum of a doubly ionized element (sec- 
ond spark spectrum), that of the next but one; etc. 
Syn. displacement law (2). 
Konstante der Bindungskraft; bond force constant. The 
Hooke-law force constant for infinitesimal extension or 
compression of a chemical bond in a molecule; a concept 
used in the treatment of the normal vibrations of a 
molecule. 
Kovolumen: covolume. A term sometimes used to 
denote the volume of the space throughout which a gas 
is distributed, minus the volume of the molecules them- 
selves. The factor v — b in the van der Waals equation 
may be considered as representing this quantity. 
Kraefte: forces. The cause of the change of move- 
ment of material bodies, determined by point of appli- 
cation, direction, and magnitude; the magnitude of the 
force is the product of mass and acceleration, the scien- 
tific unit of the force is the dyne, the technical unit the 
kilogram. 
Kraef+epolygon: force polygon. See Vektorpolygon. 
Kraeffevieleck: force polygon. See Kraeftepolygon. 
Kraftlinie: line of force. (1) An imaginary line in 
a field of force which, at each of its points, coincides 
in direction with the field intensity; a concept due to 
Faraday. (2) A unit of flux (magnetic, electric), so 
defined that the number of lines intersecting any cross 
section, per unit area, is numerically equal to the com- 
ponent of field intensity normal to the section. 
Kraftmesser: dynamometer. See Dynamometer. 
Kraftroehre: tube of force. See Faraday’sche Roehre. 
Kreis: circuit. (1) (Electr.) A conductor, or group 
of conductors, so arranged and connected or coupled as 
to be capable of conducting an electric current or sys- 
tem of currents when supplied with suitable e.m.f.’s. 
(2) (Magnetic.) A closed tube or multiple connected 
region, the surface of which is everywhere tangential to 
the magnetic induction; or a series of bodies approxi- 
mately filling such a region. The field magnet and 
armature core of a motor form a typical magnetic circuit. 
Kreisbahn: central orbit. An orbit traversed by a body 
under the influence of a force directed toward a fixed 
center. 
Kreis der geringsten Aberration: least circle of aberra- 
tion. The smallest cross section of a bundle of reflected 
or refracted rays forming a symmetrical caustic surface. 
Kreis der geringsten Unschaerfe: circle of least con- 
fusion. The small, round spot which, on account of 
aberration effects, constitutes the smallest image of a 
point source which can be formed by an uncorrected 
lens. 
Kreisel: gyro- The rotating part of any such device 
as a gyrostat, gyrocompass, etc., or in general, any ro- 
tating rigid body. See also Gyroskop and Gyrostat. 
Kreiseldynamik: gyrodynamics. The dynamics of rotat- 
ing bodies, esp. those affected by precession. 
Kreiselkompass: gyrostatic compass, gyrocompass. One 
of several devices utilizing the tendency of a rapidly 
spinning gyro to maintain its axis of rotation as a non- 
magnetic compass on shipboard. The arrangements for 
neutralizing various sources of error make the mechanism 
somewhat complicated. 
kreiselmagnetisch: gyromagnetic. See gyromagnetisch. 
Kreiselradius: radius of gyration. Of a rigid body with 
respect to a given axis: a distance such that, if all the 
particles of the body were at that distance from the 
given axis, its moment of inertia with respect to that 
axis would be unchanged. Syn. swing radius. 
Kristallanalyse: crystal analysis. The study of the ar- 
rangement of atoms, ions, or molecules in crystals, chiefly 
by X-ray methods, aided by the theory of space groups. 
Kristalldetektor: crystal detector. A rectifier consisting 
of a conducting crystal, e.g., of galena or silicon, against 
which presses a sharp steel point. The device has marked 
nonsymmetrical resistance. 
Kristalldiamagnetismus: crystal diamagnetism. Abnor- 
mal and anisotrop diamagnetism observed in crystals of 
a few substances; e.g.; bismuth. 
Kristallgitter: crystal grating. A crystal suitably 
mounted to serve as a diffraction grating, e.g., for 
X-rays. 
Kristallkunde: crystallography. That branch of physical 
science which deals with the geometrical form of 
crystals. 
Kristallographie: crystallography. See Kristallkunde. 
Kristallumineszenz: crystalloluminiscence. The emission 
of light upon the precipitation of crystals from a so- 
lution. 
677865—46 6 
79 
/kristalloidaler Zustand K_ 
kristalloidaler Zustand: crystalloid state. A condition 
of a substance in liquid form, in which its largest 
particles, either single molecules or polymers, are too 
small to be caught on the finest filters. Substances in 
this state are known as crystalloids. 
Kristallspektograph: crystal spectograph. An instru- 
ment for photographing the spectrum formed by using 
a crystal, e.g., calcite, as the diffracting system. 
Kristallsystem: crystal system. A group which includes 
all crystals containing the same number and kind of 
planes of symmetry. There are six crystal systems: iso- 
metric or cubical, tetragonal, orthorhombic, monoclinic, 
triclinic, hexagonal; q.v. 
Kristallwachstumflaeche: gliding plane. See Gleit- 
flaeche. 
Kristallwasser: water of crystallization. Water mole- 
cules incorporated in the structure of a crystal. 
kritischer Bereich: critical range. The range of tem- 
perature between two transitions in a metal, as iron or 
steel, e.g., between the recalescence points. 
kritische Daempfung: critical damping. The degree of 
damping which must be applied to a body, displaced 
against a potential or an elastic force, in order just to 
prevent its oscillating upon returning to its neutral con- 
dition. For a condenser circuit, the critical damping 
corresponds to the relation R2 = 4 L/C, in which R, 
L, C are resistance, inductance, and capacitance, re- 
spectively. 
kritische Frequenz: critical frequency. (1) Syn. thresh- 
old frequency. (2) The frequency of an intermittent 
illumination which is just sufficient to prevent a sen- 
sation of flicker. 
kritische Geschwindigkeit: critical speed, parabolic ve- 
locity. The speed with which a particle at any point 
in the field of a gravitational attracting center must be 
endowed in order that its orbit shall be a parabola. If 
the point is at the surface of the gravitating mass (as a 
planet), this speed is the same as the velocity of escape. 
kritischer Koeffizient: critical coefficient. The ratio 
of the critical temperature of a substance to its critical 
pressure. 
kritische Konstanten: critical constants. These are the 
critical temperature, critical pressure, and critical density 
of any one substance. 
kritische Konzentration: critical concentration. The 
relative proportion in the mutual solution of two par- 
tially immiscible liquids in the vicinity of their inter- 
face when the critical solution temperature is reached, 
but before they become mutually diffused. 
kritische Loesungstemperatur: critical solution tem- 
perature. The temperature below which each of two 
liquids is only partially soluble in the other (conjugate 
solution), but above which they are consolute. Syn. 
Consolate temperature. 
kritisches Potential: critical potential. The p.d. in 
volts, corresponding to the energy in electron-volts, re- 
quired either to excite or to ionize an atom or a mole- 
cule; i.e., either the radiation potential or the ionizing 
potential of the atom or molecule. 
kritische Stroemungsgeschwindigkeit: critical velocity 
of flow. The speed at which a smooth, streamline flow 
of a liquid or a gaseous substance breaks into a turbu- 
lent flow or eddy. 
kritische Temperatur: critical temperature. The tem- 
perature at which a fluid is in the critical state. Above 
this temperature, the fluid cannot exist as a liquid or 
as a vapor. Hence, a fluid at a temperature higher than 
its critical temperature cannot be liquefied by pressure 
alone. The critical temperature in degrees centrigrade 
is for water 365 degrees. 
kritische Wellenlaenge: critical wave length. The wave 
length corresponding to the critical or threshold fre- 
quency in a quantum process brought about by radi- 
ation. 
kritischer Winke!: critical angle. See totale Reflektion. 
kritischer Zustand: critical state. A condition of a 
substance such that the liquid and the vapor state are 
identical. For a pure substance, this occurs only at a 
particular temperature (the critical temperature) and 
pressure (the critical pressure). A substance above its 
critical temperature will not separate into two fluid 
phases, however great the pressure applied. For water 
the critical temperature is 374 degrees C., the critical 
pressure 217 atm., while the critical density is 0.329 
g/cm3. These are its critical constants. 
kryoskopisch: cryoscopic. Pertaining to the freezing 
points of liquids or to their determination. 
Kryostat: cryostat. A thermostat for use at very low 
temperatures. 
kubisch: cubical. (1) (Cryst.) Syn. isometric (1). 
(2) Having reference to volume, esp. in cubical ex- 
pansion. 
/kubischer Photometer 
80 K 
kubischer Photometer: cube photometer. An integrat- 
ing photometer similar in principle to the sphere photo- 
meter but employing a cubical instead of a spherical 
cavity. 
Kuehler: condenser. An apparatus for changing a 
vapor into the liquid state. 
kuenstliche Radioaktivitaet: induced radioactivity. (1) 
Radioactivity produced artificially, by corpuscular bom- 
bardment or otherwise. (2) Originally used by the 
Curies to denote radioactive deposit. 
Kugelabstand: sphere gap. A spark gap between two 
spherical knobs of equal diameter. From the width 
of the gap and the diameter of the knobs, it is possible 
to calculate the approximate spark potential; hence the 
gap may be used as a simple voltmeter for high po- 
tentials. 
Kuhn-Reich'sche Summenregel: Kuhn-Reiche sum rule. 
In re the quantum theory of dispersion: states that the 
factors by which the classical terms corresponding to 
the several absorption frequencies in the dispersion for- 
mula of the atom are multiplied, and which are char- 
acteristic of the respective absorption lines, have unity 
as their sum. 
Kundf'sche Konstante: Kundt constant. The Verdet 
"constant” divided by the magnetic susceptibility. In 
the case of ferromagnetic substances, having variable 
susceptibility, the Verdet factor is. not constant but is 
proportional to the susceptibility; so that it must be 
divided by the latter to give a constant value. 
Kundt'sches Rohr: Kundt tube. A long glass tube, 
like a horizontal organ pipe, inside which is sprinkled 
a quantity of fine powder, or which is provided with 
some other device to exhibit the acoustic nodes and 
antinodes when the tube is sounded. 
Kupplung: turn-flux, linkage, fluxturns. A measure of 
the interlocking of a magnetic flux with an electric 
circuit, viz., the product of the flux by the number of 
turns of the circuit surrounding it, expressed in maxwell- 
turns. 
kurze Nebelspuren: fish tracks. Short cloud tracks ter- 
minating in a collection of droplets, attributed by Wil- 
son to the scattering of X-ray quanta. 
81 
/L-Diagramm L 
L-Diagramm: Laue pattern. The photographic record 
of the diffracted beams produced when heterogeneous 
X-rays from a pinhole or slit impinge upon a single 
crystal. 
L-Entkopplung: L-uncoupling. A change that may take 
place in the quantization of a rotating molecule as the 
angular speed increases; the change being from a quan- 
tization of the electronic angular momentum L to that 
of the angular momentum of the revolving nuclei. 
L-Serie: L series. A series of frequencies in the X-ray 
spectrum of an element, believed to arise from the tran- 
sition of electrons from various higher quantum states 
to the state whose principal quantum number is 2. 
Ladung: Load. (1) The power delivered by a gener- 
tor to the line. (2) A resistance, inductance, or capaci- 
tance intentionally placed in a circuit, usually to in- 
crease or control the reactance. (3) The force sustained 
by any structural member, as a beam or a column. 
Laengendich+e: line density. The mass per unit length, 
as of a wire or a slender rod. 
Lag: lag. (1) A delay in the phase of current maxima 
behind the corresponding e.m.f. maxima in an inductive 
a.c. circuit. (2) In general, a delay in the action of any 
device, e.g. of a thermometer behind changes of tem- 
perature. 
Lagrange'sche Funktion: Lagrangian function. An ex- 
pression for the kinetic minus the potential energy in 
a conservative system. Syn. Kinetic potential. 
Lagrange'sche Gleichungen: Lagrange equations. A 
set of differential equations relating to a system of 
particles, one equation for each of the n degrees of 
freedom, corresponding to the generalized coordinates 
q15 q2 , qn. If Ek denotes the kinetic energy 
of the system, the form of each equation is 
Lambda/2-Blaeftchen; half-wave plate. A plate of 
mica or other doubly refracting crystal, of such thick- 
ness as to introduce a phase difference of 1/2 CYC be- 
tween the ordinary and the extraordinary components 
of the light traversing it. 
Lambda/4-Blae++chen: quarter-wave plate. A plate of 
mica or other doubly refracting crystal of such thick- 
ness as to introduce a phase difference of one-fourth 
cycle between the ordinary and the extraordinary com- 
ponents of the light traversing it. 
Lambdapla+fe: wave plate. See Lambda/2-Blaettchen 
and Lambda/4-Blaettchen. 
Lambda/4-Verschiebung: quadrature. A phase differ- 
ence of one-quarter cycle. 
Lambdawert: lambda value. The value of the orbital 
angular momentum of a molecule about its axis of 
figure, expressed as a multiple of the quantum number 
h/27T. 
Lambert: lambert. A unit of brightness, equal to that 
of a perfectly diffusing surface emitting or reflecting 
light at the rate of 1 lumen per cm2. Equivalent to 1/tt 
candle/cm2. 
Lambert'sches Gesetz: Lambert law. See Kosinus 
Emissionsgesetz. 
lamellar: lamellar. (1) Syn. laminar. (2) In re a 
vector point function: having a circuitation equal to 
zero. Syn. irrotational, noncircuital. 
laminar: laminar. In the form of a thin layer or 
lamina. Syn. lamellar (1). 
Lanchester'sche Regel: Lanchester rule. In re the pre- 
cessional effect on a gyroscope: view the whirling gyro 
from a point in the plane of its rotation and apply a 
torque to the axis of rotation, the axis of the applied 
torque being coincident with the line of sight; the 
immediate result is a precessional tipping of the rota- 
tion axis toward or from the observer, such that the 
gyro now appears to rotate in the same direction as the 
applied torque. 
Lande-Faktor: Lande factor. See g-Faktor. 
Landolt'sches Band: Landolt band. A dark band some- 
times appearing in the field of crossed Nicols with an 
intense source, as the sun; due to the light being not 
strictly parallel, so that it is not all extinguished at 
once. 
d j 8Ek \ 8Ek 
= Qr 
dt ' 8qr 1 8qr 
(r = 1.2, n); 
in which qr denotes dqr/dt. 
2 Qr Sqr 
j 
is the work done by the external forces in the arbitrary 
displacement Sq2, 8q„. 
Laguerre'sches polynom: Laguerre polynomial. A 
polynomial in x and ex which occurs in the radial 
factor of the quantum-mechanical solution of the hy- 
drogen atom. 
/Langevin'sche Funktion 
82 L 
first-order effect of a magnetic field upon the electronic 
orbits in an atom, as a precessional motion of the orbit' 
about an axis lying in the direction of the field, some- 
times referred to as the Larmor precession. 
Laue’sche Gleichungen: Laue equations. A set of three 
simultaneous equations which must be satisfied for any 
intensity maximum of radiation diffracted by a crystal. 
Lauf+erm: running term. One of a series of progres- 
sively different terms appearing in the energy differences 
which determine a series of spectral lines. Each line of 
the series is determined by the difference between one 
fixed term and one of the successive values of the run- 
ning term. 
Lautlehre: phonetics. That branch of acoustics which 
deals with the study of the production and the consti- 
tution of vocal sounds. 
Lautstaerke: intensity level. A term used in acoustics 
to denote the relation of one sound intensity to an- 
other, as expressed in bels or decibels; it is the common 
logarithm of their ratio. 
Le Chatelier’sches Prinzip: Le Chatelier principle. A 
form of the least-energy principle, stating that when a 
dynamic system is in stable equilibrium any change in 
its state brings about conditions opposed to further 
change in the same direction; equivalent to a definition 
of stable equilibrium. 
Lecher Oszillator: Lecher oscillator. A device for pro- 
ducing a system of standing waves in two parallel wires, 
called Lecher wires. 
Legendre’sche Gleichung: Legendre equation. A dif- 
ferential equation of the form 
Langevin'sche Funktion: Langevin function. A func- 
tion of the form 
1 
L(x) — cot x — ; 
x 
used in the kinetic theory of gases. 
Langevin'sches Gesetz: Langevin law. Expresses the 
average magnetic moment of the molecules of a gas 
as ju,2H/3kT, in which is the magnetic permeability, 
H the magnetizing field, k the Boltzmann constant, and 
T the absolute temperature. 
Langevin'sches Ion: Langevin ion. An electrified par- 
ticle in a gas, resulting from the accumulation of gase- 
ous ions upon dust particles or other nuclei. 
Langmuir'scher Dunkelraum: Langmuir dark space. A 
nonluminous .region surrounding a negatively charged 
probe inserted into the positive column of a glow or arc 
discharge. 
langwellige Grenze: long-wave limit. The quantum 
energy just sufficient to release photoelectrons from a 
given surface. The corresponding frequency is the 
threshold frequency. Syn. photoelectric threshold. 
Laplace'sches Gesetz: Laplace law. See Ampere’sches 
Gesetz. 
Laplace'sche Gleichung: Laplace equation. A linear 
differential equation of the second order which occurs 
very frequently in mathematical physics. E.g., for any 
point in an electric field at which there is no free elec- 
tricity, the potential V satisfies this equation, which in 
rectangular co-ordinates has- the form 
82V 82V 82V 
_(_ + — o 
Sx2 Sy2 8z2 
Laplace'scher Operator: Laplace Operator. The dif- 
ferential operator which occurs in the Laplace and the 
Poisson equations. In rectangular coordinates it is 
d ( dy ) 
< (1 — x2) > -f- ay — 0 
dx ( dx ) 
r 82 82 82 -i 
I + , 
L Sx2 8y2 8z2 J 
The solutions of this equation are Legendre functions 
or Legendre polynomials. 
Legendre'sches Polynom: Legendre polynomial. A 
cosine polynomial which occurs in the angular factor 
of the quantum-mechanical solution of the hydrogen 
atom. 
Lehrsatz: theorem. (1) That which is considered and 
established as a principle or law; hence, sometimes, a 
rule. (2) A general statement that has been proved 
or whose truth has been conjectured. 
Lehrsatz der reziproken Energie: reciprocal-energy 
theorem. A theorem due to Rayleigh; as follows: Let 
and is often represented by the symbol \72. Thus the 
Laplace equation may be written \t2V — 0. Syn. La- 
placian. 
La Porte'sche Regel: La Porte rule. States that in 
dipole radiation, even spectral terms combine only with 
odd, and vice versa. 
Larmor-Praezession: Larmor precession. See Larmor- 
’sches Prinzip. 
Larmor'sches Prinzip: Larmor principle. Sets forth the 
83 
/Leistung L 
an e.m.f., E1} inserted in any branch, designated as No. 
1, of a transducer produce a current I2, in any other 
branch No. 2; correspondingly, let an e.m.f., E2, in- 
serted in branch No. 2, produce a current I15 in branch 
No. 1; then, if Ohm’s law holds, 
Leuchtintensitaet: luminous intensity. In re a point 
source of light: the luminous flux emitted per unit solid 
angle (spheradian) in a specified direction. 
Leuchtstaerkenverteilungskurve: luminosity curve. A 
distribution curve showing luminous flux per element 
of wave length as a function of wave length. 
Leuchttemperatur: brightness temperature. The tem- 
perature that is obtained for nonblack bodies with an 
optical pyrometer calibrated to give the correct tempera- 
ture of a black body. It is always less than the true 
temperature. 
Leuchtwirksamkeit: luminous efficiency. The ratio of 
the luminous flux to the radiant flux for the complete 
range of an emission of radiant energy. 
Levogyr: levogyrate, laevogyrate, levorotatory. The 
opposite of dextrogyrate, i.e., producing a left-handed 
rotation in polarized light. 
Lewls-Adams'sches Verhaeltnis: Lewis-Adams relation. 
A hypothetical relationship involving the elementary 
charge e, the electromagnetic constant c, and the Planck 
constant h; viz., 
Closely related to the reciprocity theorem. 
Leistung: Power. The time rate of the doing of work; 
or energy transferred per unit time. 
Leistungsfaktor: poiver factor. The ratio of the mean 
power to the apparent power in an a.-c. circuit. If the 
e.m.f. and current are sinusoidal, the power factor is 
equal to the cosine of the phase angle. 
Leitelektron: conduction electron. One of the electrons, 
supposedly from the outer levels of the atoms, which 
are concerned with the electrical conduction in a metal. 
The energy levels in which these electrons are found 
are called conduction levels. 
Leitfaehigkeit: conductivity. (1) (Thermal.) The fa- 
cility with which heat flows through a conductor, as 
measured by the quantity of heat transmitted per unit 
time, per unit temperature gradient along the direction 
of flow, per unit cross-sectional area. (2) (Electric.) 
The facility with which a substance conducts electricity, 
as measured by the current density per unit potential 
gradient in the direction of flow. It is the reciprocal of 
the resistivity. Syn. specific conductance. 
Leiffaehigkeifsdispersion: conductance dispersion. A 
variation of the equivalent conductance of an electrolyte 
for an a.c. of varying frequency. 
Leitfaehigkei+smesser: conductimeter. An apparatus for 
measuring the electrical conductivities of substances, esp. 
of liquids. 
Lenard-Roehre: Lenard tube. A vacuum tube specially 
designed to exhibit Lenard rays; recently improved as 
the Coolidge cathode-ray tube. 
Lenard-Strahlen: Lenard rays. Cathode rays that have 
escaped from the vacuum tube through a "window” or 
thin metallic foil. Produced and studied by Lenard in 
1894. 
Lenz'sches Gesetz: Lenz law. States that whenever 
an e.m.f. is induced in a conductor by the variation of 
a magnetic field or by the relative motion of the con- 
ductor and the field, the direction of that e.m.f. is such 
as to tend to produce a current whose reaction with the 
field opposes the variation or the motion. 
I.Ei = I2E2. 
87r3e2 I 15 '/3 
ch ~ \7" / 
Lewls-Langmuir'sches Atom: Lewis-Langmuir atom. A 
concept of the nuclear atom in which the extranuclear 
electrons are assumed to occupy fixed relative positions; 
in contrast to the orbital electronic atom of Rutherford 
and Bohr. Syn. static atom. 
Lewis-Rayleigh'sches Leuchten: Lewis-Rayleigh glow. 
A yellow afterglow, most readily produced by condensed 
or electrodeless discharges in nitrogen. At ordinary tem- 
peratures, its spectrum consists of certain bands of the 
N2 system. 
Leydener Flasche: Leyden jar. The original form of 
electric condenser, in which the dielectric is a glass jar; 
credited to Muschenbroeck. 
Leydener Temperaturskala: Leyden tetnperature scale. 
A low temperature range of the centigrade scale, based 
upon the boiling point of hydrogen as — 252.74 degrees 
C. and and that of oxygen as — 182.95 degrees C.; 
from the work of Onnes at the Leyden laboratory. 
Lichtdruck: light pressure. A pressure proportional to 
the radiant energy in a unit of space, exerted by radia- 
tion on bodies upon which it impinges, and due to 
momentum. 
/lichtelektrische Zelle 
84 L 
lich+elek+rische Zelle: photocell, photoelectric cell. A 
compact arrangement of metallic electrodes to obtain 
a photoelectric current. 
Lichtenberg'sche Figur: Lichtenberg figure. A pattern 
traced on a dielectric surface, which has been nonuni- 
formly electrified, by sifting over it fine powders, such 
as a mixture of sulphur and red lead. 
Lichtfluss: luminous flux, light flux. Rate of emission 
of visible radiation, esp. as judged by its visual effect. 
Lichtintensitaetsmesser spezieller Art: flashometer. An 
apparatus for studying the time-intensity distribution of 
flashes of light. 
Lichtjahr: light-year. A unit of interstellar distance, 
equal to the distance which light travels, in a vacuum, 
in 1 year; approximately equal to 9.45988 X 1017 cm 
or 5.87837 X 1012 mi. 
Lichtmenge: light, quantity of. A measure of the time 
integral of luminous flux; commonly expressed in lu- 
menhours. 
Lichtmesser; photometer. An apparatus for measuring 
the intensity of a light source. 
LIchtmuehle: radiometer. An instrument for measur- 
ing the intensity of thermal radiation. 
lichtnegativ: light-negative. Having negative photo- 
conductivity, i.e., decreasing in conductivity under the 
action of light. Selenium sometimes exhibits this prop- 
erty* Syn. photo-negative. 
iichtpositiv: light-positive. Having positive photocon- 
ductivity, i.e., increasing in conductivity under the action 
of light. Selenium ordinarily has this property. 
Lichtquanti+aet: quantity of light. See Lichtmenge. 
Lichtquellenausbeu+e: light-source efficiency. The ratio 
of the luminous flux from a source of light to the power 
required to maintain it; usually expressed in lumens per 
watt. 
Lich+quellens+aerke: light-source efficiency. See Licht- 
quellenausbeute. 
Lich+raster: light valve. A device, either mechanical or 
electro-optical, for controlling the intensity of a beam 
of light, or for intermittently cutting it off, as a shutter. 
Lichtvek+or: light vector. The electric vector concerned 
in the propagation of electro-magnetic radiation. 
Lichtver+eilungskurve: light distribution curve. A graph 
showing the variations of luminous intensity with the 
direction of emission. If it is in polar coordinates, the 
curve is sometimes called a polar candle-power diagram. 
Linearoszillator: linear oscillator. A system composed 
of two parts so connected that they are capable of oscil- 
lating with respect to each other along the line joining 
them, e.g., two balls at the ends of a rubber cord, the 
two ions of a polar molecule, or the positive and nega- 
tive electricity in a Hertz oscillator. 
Linie gleicher Ultrastrahlin+ensi+aet: isocosm. A line 
of equal cosmic-ray intensity on the earth’s surface. 
Linienabs+and: line interval. The difference in fre- 
quency between two adjacent lines in a spectral series. 
Linieninterwall: line interval. See Linienabstand. 
Linienspektrum: line spectrum. An atomic spectrum, 
characterized by distinct lines, rather than by bands as 
in molecular spectra. 
linksdrehend: levorotatory. See Levogyr. 
Linsenmesser: lensometer. An instrument designed for 
the measurement of the optical characteristics of spec- 
tacle lenses. 
Liouville'scher Lehrsatz: Liouville theorem. States that 
for a conservative system of particles, the number of 
particles per unit volume in any representative group of 
the particles remains unaltered as the particles move. 
Lippich'sches Prisma: Lippich prisma. A type of half- 
shade analyzer consisting of a small Nicol prism cover- 
ing half the field of the polarimeter. 
Lippmann'scher Effekt: Lippmann effect. The effect 
of a p.d. upon the mutual surface tension of two con- 
ducting, inmiscible liquids, as mercury and an electro- 
lytic solution. The surface tension is greatest when 
the p.d. is zero. 
Lippmann'sche Streifen: Lippmann fringes. Interfer- 
ence maxima which may be detected photographically, 
in parallel planes, in the space in front of a mercury 
surface from which light is normally reflected; due to 
the interference of the incident with the reflected light, 
forming stationary waves. 
Lissajous'sche Kurven: Lissajous curves. A family of 
plane curves described by a point having two simple 
harmonic motions at right angles; varying with the 
relations of amplitude, frequency, and phase. 
85 
/Liter L 
Liter: liter, litre. Originally defined as 1,000 cm3 but 
for practical purposes now defined as the volume of 1 
kg of pure water at its maximum density (4 degrees 
C), and therefore equal to 1000.027 cm3. 
Lloyd'scher Spiegel: Lloyd mirror. A mirror used 
with very high incidence angle to produce by reflection 
two coherent light sources resulting in interference 
bands. 
Lochbild: pinhole image. The inverted picture formed 
by light passing from the source directly through a small 
opening and falling on a screen. 
loeschen: quench. See ausloeschen. 
Loeslichkeit: solubility. The equilibrium concentration 
of a solute in satured solution. 
loeslich in alien Verhaeltnissen: consolute. Miscible 
or mutually soluble in all proportions. 
Loesung: solution. A mixture of substances whose 
intimacy is of molecular order and the proportion of 
whose ingredients (concentration) is subject to con- 
tinuous variation over a certain range. 
Loesungsdruck: solution pressure. (1) The osmotic 
pressure of a solution of a substance in equilibrium with 
its solid phase. (2) (Electrolytic.) The electrolytic in- 
fluence which, according to Nernst’s hypothesis, urges 
positive metallic ions to break away from the metal 
and enter the solution with which it is in contact. 
Loesungswaerme: heat of solution. The quantity of 
heat absorbed or evolved per gram or per mol of a 
solute when it is dissolved in so large a volume of 
solvent that further dilution causes no further absorp- 
tion or evolution of heat. 
logarithmisches Dekrement: logarithmic decrement. 
The Napierian logarithm of a damping factor or oscil- 
lation decrement. 
logarithmisches Potential: logarithmic potential. A 
potential associated with a field of force subject to the 
inverse-first-power law instead of to the Newtonian or 
inverse-square law; so called because its value involves 
the logarithm of the distance. 
logarithmische Skala: logarithmic scale. A linear scale 
on which the actual distances of the points from the 
zero of the scale are proportional to the logarithms 
of the numbers with which these points are labeled. 
Lokalelement: local action. A chemical reaction which 
takes place in an electrolyte on the surface of an elec- 
trode at points where particles of foreign matter serve 
to complete microscope voltaic circuits, and which re- 
sults in corrosion of the electrode even when the main 
circuit of the cell is open. 
Lokalvereanderung: local change. Any dynamic proc- 
ess in which the attention is fixed upon a point of 
space, through which particles of a system pass in suc- 
cession, differences in their motions being noted; in 
contradistinction to individual change, q.v. 
longitudinale Masse: longitudinal mass. The ratio of 
force to acceleration, as given by the special theory of 
relativity, in the case of a particle that is accelerated 
in the direction of its existing velocity; not a funda- 
mental concept, since there is no law of conservation 
for this kind of mass. 
Lorentz'sche Doppelbrechung: Lorentz double refrac- 
tion. A group of optical phenomena in crystals, con- 
sisting of double refraction effects of the second order, 
not ordinarily observed and not included in the usual 
theories of crystal optics. E.g., Lorentz showed that 
even certain cubic crystals are not optically isotropic. 
Lorentz'sche Einheit: Lorentz unit. The difference in 
quantum energy corresponding to the Lorentz displace- 
ment in the normal Zeemann effect; expressed by the 
formula heH 4tt m0c, in which h is the Planck con- 
stant, e the elementary charge (in e.m.u.), c the elec- 
tromagnetic constant, m0 the rest mass of the electron, 
and H the magnetic intensity responsible for the effect. 
Lorentz'sche elektromotorische Kraft: Lorentz electro- 
motive force. A force acting upon an electric particle 
by reason of its motion relative to a magnetic field. 
Lorentz'sches Elektron: Lorentz electron. A moving 
electron which, according to the theory of Lorentz, has 
had its dimension parallel to the direction of motion 
shortened in the ratio 
I u2 
V1 : 1 ; 
c2 
in which u is the speed of the electron and c, the 
speed of light. 
Lorentz'scher Faktor: Lorentz factor. (1) The ratio 
of the intensity of an X-ray crystal-diffraction beam of 
a given order to that of the zero order, or undeflected, 
beam. (2) A factor expressing the dependence of the 
intensity upon the glancing angle, as the crystal is 
rotated. 
Lorentz-Fitzgerald'sche Kontraktion: Lorentz-Fitzger- 
ald contraction. See Fitzgerald-Lorentz’sche Kontrak- 
tion. 
/Lorentz Invarianz 
86 _L 
Lorentz Invarianz: Lorentz invariance. An attribute 
of any fundamental equation of physics which exhibits 
its agreement with the requirements of the special the- 
ory of relativity by being invariant under the Lorentz 
transformation. 
Lorenz-Lorentz'sche Beziehung: Lorenz-Lorentz rela- 
tion. A relation connecting the refractive index n of 
a dielectric with its density p: 
The total emission in all directions from such a source 
is 4tt lumens. 
Lumenmesser: lumen meter. A device for measuring 
luminous flux; specifically, a photometer designed by 
Blondel for measuring mean spherical candle power. 
Lumenophor: Lumenophor. A molecule or group of 
molecules which according to the Kowalski theory of 
luminescence, is capable of emitting light when excited 
by absorbing the energy of an incident electron. 
Lumens+unde: Lumen-hour. A unit quantity of lumi- 
nous energy, equal to the emission of 1 lumen for 1 
hour. 
Lummer-Brodhun Photometer: Lummer-Brodhun photo- 
meter. A photometer in which the comparison of the 
illuminations on opposite sides of a white screen is 
made by a method depending upon the principle of 
total reflection. 
Lummer-Gehrke Platte: Lummer-Gehrcke plate. A type 
of interferometer, based upon the interference effect of 
multiple reflections inside a glass plate with strictly 
plane and parallel faces, and capable of high resolving 
power, 
Lumineszenz: luminescence. (1) An emission of ra- 
diation, esp. visible light, by a substance as a result 
of the absorption of energy from some other emission, 
either radiant or corpuscular. (2) In general, an emis- 
sion of light by a substance from other causes than 
high temperature. 
Lux: lux. A practical metric unit of illumination, equal 
to 1 lumen per m2; or, the illumination of a surface 
at a uniform distance of 1m from a symmetrical point 
source of 1 candle. Syn. metercandle. 
Luxmesser: luxmeter. A type of illuminometer that 
measures illumination in luxes. 
Luxometer: luxometer. A portable form of cosine 
illumination photometer, depending upon the com- 
parison of the illuminated test area with an area illumi- 
nated by a lamp at an adjustable angle of incidence. 
Lyman Banden: Lyman bands. A group of spectral 
bands in the Schumann region of the hydrogen spec- 
trum between 1450 Ä and 1650 Ä. The frequencies 
are multiples of 
n2 — 1 
= C; 
(n2 + 2 )p 
in which C is a constant for the given dielectric, known 
as the specific refractive power. 
Lorentz Transformation: Lorentz transformation, Lo- 
rentz-Einstein t. The process of transforming the mathe- 
matical expression corresponding to a given physical 
concept from the independent variables x, y, z, t, used 
by a given observer, to a new set x‘, y', z', t', used by 
a second observer in uniform motion relative to the 
first; making use of the Lorentz equations for the 
transformation of space and time variables. 
Lorentz Triplet; Lorentz triplet. A spectral triplet ob- 
served with light at right angles to the magnetic field, 
in the normal Zeeman effect. The center line is polar- 
ized with the electric vector parallel to the field, the 
others perpendicular to the field. 
Lorentz'sche Verschiebunq; Lorentz displacement. The 
difference in frequency between the undisplaced line 
and either of the two outer components of a Lorentz 
triplet in the normal Zeeman effect. 
Lorenz'sehe Zahl: Lorenz number. A constant which, 
according to Lorenz, represents the product of the mo- 
bility coefficient of an ion by its radius. Its value is 
about 9.37 X 10-7 cm/ohm. 
Loschmidt'sche Zahl: Loschmidt number. The number 
of molecules per cm3 of an ideal gas at N.T.P. equal 
to about 2.705 X 1019. 
Ludwlg-Soret Effekt: Ludwig-Soret effect. The effect 
of temperature upon the concentration of one of the 
components of a mixed crystal. 
Lueckensatz: vacancy principle. States that a config- 
uration of q of the p electrons of given principal and 
azimuthal quantum numbers, required to complete a 
closed group, gives rise to spectral terms having the 
same J values as those which arise from a configuration 
of p — q of the same electrons. 
Lumen (Einheit der Beleuchtung): lumen. A unit of 
luminous flux equal to the flux through unit solid angle 
(spheradian) from a uniform point source of 1 candle. 
V I2 n2 / 
in which n = 2, 3, 4, 
Lyman Kontinuum: Lyman continuum. A continuous 
spectrum in the ultraviolet, extending from the visible 
down to 300 Ä or lower; produced by a heavy con- 
denser discharge through a capillary. 
87 
/M-Serie M 
M-Serie: M series. A series of frequencies in the 
X-ray spectrum of an element, believed to arise from 
the transition of electrons from various higher quantum 
states to the state whose principal quantum number is 
3. Discovered by Siegbahn. 
M-Wert: M value, magnetic quantum number. A 
quantum number related to the behavior of an atom 
or a molecule in a magnetic field, and equal to the 
component of the angular momentum of the system 
about the field direction as axis, expressed as a multiple 
of h/2 7r (h is the Planck constant). Used in connec- 
tion with magneto-optical phenomena, such as the Zee- 
man effect. Syn. equatorial quantum number, axial quan- 
tum number. 
Mach'sche Zahl: critical velocity ratio. The ratio of 
the velocity of a fluid to that of sound in that medium. 
Madelung'sche Konstante: Madelung constant. (1) A 
factor which occurs in the expression for the wave 
length of the residual radiation (Reststrahlen) selectively 
reflected by a given heteropolar crystal. (2) The con- 
stant k in the expression kE2/r for the potential 
energy of separation of the two unlike ions in a hetero- 
polar crystal, which have charges ± E and are a dis- 
tance r apart. 
Magnalium: magnalium. One of several alloys of 
aluminum and magnesium. That developed by Mach 
(69 percent A1 and 31 percent Mg) has high reflectiv- 
ity in the visible and the ultraviolet regions. 
magnetische Achse: magnetic axis. In re a magnet 
or an equivalent electric circuit: the vector direction of 
the magnetic moment. For a bipolar magnet with con- 
centrated poles, it is approximately the direction of the 
line drawn from the south to the north pole. 
magnetischer Aequator: magnetic equator. A line 
around the earth, approximately a great circle midway 
between the magnetic poles, and coinciding with the 
line of zero magnetic inclination. 
magnetische Analyse: magnetic analysis. (1) The 
separation of a stream of electrified particles by a mag- 
netic field in accordance with their mass, their charge, 
or their speed. (2) The study of the properties of iron 
or other magnetic bodies by magnetic methods. 
magnetische Breite: magnetic latitude. See geomag- 
netische Breite. 
magnetische Daempfung: magnetic damping. The 
damping of a mechanical motion by means of the re- 
action between a magnetic field and currents generated 
by the motion in accordance with the Lenz law. 
magnetische Doppelbrechung: magnetic double refrac- 
tion. See Cotton-Mouton’scher Effekt. 
magnetisches Element: magnetic element. (1) Syn. 
Amperian current. (2) Any group of Amperian cur- 
rents, e.g., a spinning electron, which conserves its 
magnetic moment throughout the process considered. 
(3) Any one of the quantities customarily chosen to 
specify the earth’s magnetic field at a given point; viz., 
declination, inclination, total intensity, horizontal in- 
tensity, or vertical intensity. 
magnetisches Feld: magnetic field. A region in which 
there is a magnetic intensity, as indicated by the torque 
experienced by a bipolar magnet placed in it, due to 
the influence of magnets or electric currents. 
magnetischer Fluss: magnetic flux. The surface inte- 
gral, over any specified area, of the normal component 
of the magnetic induction commonly expressed in max- 
wells or gauss-cm2. 
Magnetische Flussdichte: magnetic flux density, mag- 
netic induction. A vector quantity, usually associated 
with the condition of a substance when placed in a 
magnetic field, having the same direction as the mag- 
netizing fprce (provided the substance is isotropic), and 
having a magnitude dependent upon the magnetizing 
force and upon the nature of the substance. Its measure 
is the e.m.f. produced in an electric circuit linked with 
the induction at a definite time rate, in accordance with 
the Faraday law. The induction is normal if the sub- 
stance is not already magnetized when placed in the 
magnetic field. 
magnetische Hauptsuszeptibilitaet: principal magnetic 
susceptibility. The magnetic susceptibility of a nonfer- 
romagnetic crystal for one of the three or more direc- 
tions along which the magnetization is parallel to the 
magnetic intensity. 
magnetische Induktion; magnetic induction, magnetic 
flux density. See magnetische Flussdichte. 
magnetische Induktionsroehre: tube of magnetic in- 
duction. A magnetic circuit so bounded as to have the 
same magnetic flux, (esp. unit flux) through every cross 
section. 
magnetische Inklination: magnetic inclination. The 
angle which the magnetic field of the earth makes with 
the horizontal at any station. Syn. magnetic dip. 
magnetische Intensitaet: magnetic intensity. A vector 
quantity pertaining to the magnetic field, the measure 
of which, at any point in a vacuum, is the force per 
unit pole experienced by a free magnetic pole placed 
/magnetischer Kompass 
88 M 
at that point. It is closely related to magnetic induc- 
tion; in a vacuum proportional to it, and if in the 
same measure, even identifiable with it. 
magnetischer Kompass: magneto compass. A device 
used as a compass on airplanes, utilizing the inductive 
effect of the earth’s magnetic field to excite the field 
magnet of a small magneto or dynamo. When the in- 
strument is properly oriented, the current generated re- 
duces to zero. 
magnetischer Kreis: magnetic circuit. A closed tube or 
multiply connected region, the surface of which is every- 
where tangential to the magnetic induction; or a series 
of bodies approximately filling such a region. The field 
magnet and armature core of a motor form a typical 
magnetic circuit. 
magnetischer Kreislauf: magnetic cycle. A cycle of 
changes in the magnetic induction or the magnetization 
of a ferromagnetic substance due to an alternating mag- 
netic intensity. A symmetrical cycle may be represented 
by a hysteresis curve with its center at the origin. 
magnetische Linse: magnetic lens. An apparatus used 
to focus'beams of rapidly moving electrons or ions by 
means of the effect of a nonuniform magnetic field. 
magnetischer Meridian: magnetic meridian. The hori- 
zontal line, through any point on the earth’s surface, 
which coincides with the direction of the horizontal com- 
ponent of the earth’s magnetic field at that point. 
magnetisches Moment: magnetic moment. That vec- 
tor, associated with a magnet or an equivalent electric 
circuit, whose vector product by the magnetic intensity 
of the field, in which the magnet or the circuit is placed, 
gives the resulting torque upon the same; the mag- 
netic intensity considered being exclusive of any com- 
ponent contributed by the magnetic body itself. For a 
bipolar magnet with concentrated poles, the magnetic 
moment is approximately the product of the pole 
strength by the distance between the poles, and its di- 
rection, that of the line drawn from the south to the 
north pole. 
magnetische Nachwirkung: magnetic lag, magnetic 
aftereffect. A delay not due to eddy currents, in the 
establishment of the magnetic induction which finally 
corresponds to a given magnetic intensity in a given 
sequence of magnetic states. 
magnetisches Pendel: magnetic pendulum. A bar mag- 
net suspended so as to oscillate as a pendulum in a 
magnetic field. 
magnetisches Potential: magnetic potential. A scalar 
point function analogous to electric potential. Its value 
at any point is the line integral of the magnetic in- 
tensity taken from that point to infinity. 
magnetisches Potentiometer: magnetic potentiometer. 
A slender solenoid, used to measure magneto-motive 
forces between points in a magnetic field. Its core may 
be of flexible, nonferromagnetic material, or of a highly 
permeable alloy. 
magnetische Quantenzahl: magnetic quantum number. 
See M-Wert. 
magnetischer Resonanzbeschleuniger: magnetic reso- 
nance accelerator. See Zyklotron. 
magnetische Rotationsinvariante: invariant of magnetic 
rotation. The value of the expression 
An p 
(n2 — I)2 ’ 
in which A is the Verdet constant, n the refractive in- 
dex, and p the density, of a transparent substance; ap- 
proximately the same for different substances. 
magnetische Rotation: magnetic rotation. See Faraday- 
’ scher Effekt. 
magnetisches Rotationsspektrum: magnetic rotation 
spectrum. The absorption spectrum of a substance un- 
der the influence of a magnetic field in the direction of 
the transmitted light, which is thus subjected to the 
Faraday effect. 
magnetischer Spektrograph: magnetic spectrograph. 
A magnetic mass or velocity spectrograph. 
magnetisches Spektrum: magnetic spectrum. The rec- 
ord of a magnetic spectrograph. 
magnetische Strahlen: magnetic rays. A term applied 
by Righi to certain phenomena in a discharge tube un- 
der the influence of a strong magnetic field. 
magnetischer Vektor: magnetic vector. That compo- 
nent of the electromagnetic field, associated with elec- 
tromagnetic radiation, which is of the nature of a mag- 
netic field; supposed to coexist with, but to act at right 
angles to, the electric vector. 
magnetische Verzoegerung: magnetic lag. See mag- 
netische Nachwirkung. 
magnetische Viskositaet: magnetic viscosity. A prop- 
erty sometimes ascribed to ferromagnetic substances to 
account for magnetic lag. 
89 
/Magnetisierung M 
Magnetisierung: magnetization. (1) A vector quantity 
associated with a substance under magnetic influence, 
viz., the magnetic moment per unit volume. Divided 
by the density, it gives the specific magnetization, or 
magnetic moment per unit mass. Syn. intensity of mag- 
netization. (2) The process of increasing the magnetic 
moment of a body. 
Magnetisierungskraft: magnetizing force. The mag- 
netic intensity brought to bear upon a substance and 
effective in producing its magnetization. It is in gen- 
eral less than the magnetic intensity of the field ex- 
ternal to the substance. 
Magnetisierungskurve: magnetization curve. A graph 
on the magnetization-intensity (I-H) or the induction- 
intensity (B-H) diagram, representing successive states 
of a ferromagnetic substance. A normal magnetization 
curve is a portion of a symmetrical hysteresis loop. The 
initial or virgin magnetization curve is such a curve 
representing the first excursion from the origin, and is 
distinct from the subsequent cycles. 
Magnetisierungsstaerke: intensity of magnetization. 
See magnetische Intensitaet. 
Magnetismus: magnetics. That branch of physics 
which deals with the phenomena of magnetism. 
magnetoelastisch: magnetoelastic. Pertaining to mag- 
netostriction effects associated with elastic vibration. 
magnetoelektrische Induktion: magnetoelectric induc- 
tion. See elektromagnetische Induktion. 
Magnetogenerator: magneto generator. An a.-c. gen- 
erator in which the field is maintained by a permanent 
magnet. Often abbreviated "magneto.” 
magnetokalorischer Effekt; magnetocaloric effect. The 
reversible cooling of a ferromagnetic body, magnetized 
to saturation in a strong magnetic field, when the field 
is removed. Discovered by P. Weiss and R. Forrer in 
1924. 
Magnetometer: magnetometer. An instrument for the 
measurement of magnetic intensity, magnetic induction, 
or magnetic moment. 
magnetomotorische Kraft: . magnetomotive force. In 
re any closed path constituting a magnetic circuit: the 
line integral of the magnetizing force, or the change 
in magnetic potential, due to the magnetizing agency 
(as a coil) which acts upon the magnetic circuit. If it 
is due to the current in a coil, it is proportional to the 
number of ampere-turns. 
Magneton; magneton. (1) A unit of magnetic mo- 
ment in terms of which molar magnetic moments are 
small integers (Weiss, 1911), or simple functions of 
small integers (Bohr, 1913). The empirical Weiss mag- 
neton is 1125.0 e.m.u., the theoretical Bohr magneton 
is 555.7 e.m.u. (2) A unit of magnetic moment in 
terms of which the magnetic moments of magnetic ele- 
ments (Amperian currents) are functions of small in- 
tegers. The theoretical Bohr magneton in this sense 
is 9.158 X 10~21 c.g.s.e.m.u. 
Magnetonzahl: magneton number. An integral number 
by which, according to Sommerfeld, the Bohr magneton 
must be multiplied to give the magnetic moment of a 
given atom. 
magnetooptische Analyse: magneto-optical analysis. 
A method of chemical analysis based upon differences 
in the lag of the Faraday effect behind the magnetic 
intensity for different substances. 
magne+oop+ische Dispersion: magneto-optical disper- 
sion. Expresses the Faraday effect as the derivative, with 
respect to the wave length, of the product of the 
Verdet constant by the refractive index. 
magnetooptischer Parameter: magneto-optical parame- 
ter. A complex constant involved in the electron theory 
of the Faraday and the Kerr effect, and having a dis- 
tinctive value for each metal. 
magnetooptische Rotation: magneto-optical rotation. 
See Faraday’scher Effekt. 
Magnetophotophorese: magnetophotophoresis. See 
Photophorese. 
magnetostatischer Oszillator: magnetostatic oscillator, 
magnetostriction oscillator. An electric oscillating system 
containing as one of its elements a magnetostriction 
resonator, by which the frequency is controlled. 
Magnetostriktion: magnetostriction. A class of phe- 
nomena involving strains (magnetostrains) in a ferro- 
magnetic body when placed in a magnetic field. 
Magnetostriktionsoszillator: magnetostriction oscillator, 
magnetostrictive o. See magnetostatischer Oszillator. 
Magnetostriktionsresonator: magnetostriction resona- 
tor. A magnetostrictive body, usually in the form of a 
rod, which may be excited magnetically into resonant 
vibration at one or more frequencies. 
Magnetostriktionsuebertrager: magnetostriction trans- 
ceiver. A magnetostriction resonator applied to sending 
and receiving subaqueous signals of definite frequency, 
usually 17,000 eye per sec or higher. 
/Magnetowiderstand 
90 M 
Magnetowiderstand: magnetoresistance. An increase 
in electrical resistance of a conductor, associated with 
the application of a constant magnetic field; dependent 
upon the orientation of the conductor in the field. 
Magnetpol: magnetic pole. One of those regions of 
the surface of a magnet, just outside which the mag- 
netic intensity arising therefrom is greatest. Unless this 
intensity is everywhere zero (as may happen), a magnet 
must have at least one pole of each sign. 
Magnetpolstaerke: magnetic pole strength (unit pole, 
c.g.s. magnetic). An ideal magnetic point pole, two of 
which, at a distance of 1 cm apart in a vacuum, would 
exert a mutual repulsion (or attraction) of 1 dyne. 
Such a pole gives rise to 4?r maxwells of free magnetism. 
Actual magnetic poles are often treated quantitatively 
as if made up of a number of unit poles equal to the 
"pole strength.” 
Magnetron: magnetron. (1) A type of thermionic 
vacuum tube in which the motion of the ions is con- 
trolled by the influence of a magnetic field perpendicu- 
lar to the electric field propelling them. (2) A device 
for generating radio waves of very short wave length 
(from 75 to 150 cm). 
Magnus Effekt: Magnus effect. A lateral thrust ex- 
erted by wind upon a rotating cylinder (Magnus rotor) 
whose axis is perpendicular to the wind direction. The 
effect has been utilized in ship propulsion and in other 
devices. 
Majorana'sche Kraefte: Majorana forces, M. interac- 
tions. Attractive forces between neutrons or between 
protons and neutrons within an atomic nucleus; sup- 
posed to offset the mutual repulsion of the nuclear pro- 
tons and to produce saturation of bonds between nuclear 
particles. Of especial significance is the energy associ- 
ated with these forces, which is supposed to owe its 
origin to the exchange of position of the two interact- 
ing particles. 
Malus'sches Gesetz: Malus law. (1) States that the 
intensity of a beam of light, after two reflections from 
nonmetallic surfaces at the polarizing angle, is propor- 
tional to the square of the cosine of the angle between 
the two planes of reflection. Discovered by Malus in 
1808. A similar law applies to light passing through 
two Nicol prisms. (2) States that an orthotomic system 
of rays remains orthotomic after any number of reflec- 
tions and refractions. 
Manganin: manganin. An alloy of copper (84 per- 
cent), manganese (12 percent), and nickel (4 percent), 
used for resistance coils because of its very low tempera- 
ture coefficient of resistance. 
mannigfaltig: multiple, [parallel (in the electrical 
sense')']. Electrically connected between the same ter- 
minals, as two or more conductors or condensers. 
Mannigfaltigkeit (opt.): multiplicity. The largest num- 
ber of components possessed by any multiple term in a 
given spectral system. Multiplicities as high as 9 are 
known, but not all the terms of a system have the 
maximum number of components. 
Manokriometer: manocryometer. An instrument used 
for determining the variation of freezing point with 
pressure. Devised by de Visser. 
Manometer: manometer. A pressure gauge. 
manometrische Waage: manometric balance. An ap- 
paratus for the comparison of the magnetic susceptibili- 
ties of liquids. 
Mariotte'sche Flasche: Mariotte bottle. A pneumatic 
device by which the rate of discharge of a liquid from 
an orifice may be maintained constant for some time, 
irrespective of the level of its surface. 
Martens'scher Keil: Martens wedge. A type of quartz 
wedge rotator for polarized light, used in some polarime- 
ters to compensate and thus measure the optical rota- 
tion whose value is sought. 
Marx'scher Effekt: Marx effect. The reduction in the 
energy of a photoelectric emission by the simultaneous 
incidence of radiation of lower frequency than that pro- 
ducing the emission. Observed by E. Marx in 1930, 
and called by him the regressive effect. 
Masse: mass. A basic physical magnitude pertaining 
primarily to matter (though having an interpretation 
also, in modern physics, with reference to electricity and 
to energy) ; the measure of which is found in its rela- 
tion to inertia. In accordance with Newton’s second law, 
the masses of bodies are inversely proportional to the 
accelerations given them by the same force, as when 
two free bodies are drawn together by an elastic cord 
connecting them. 
Massenabsorptionskoeffizient: mass absorption coeffi- 
cient. See Absorptionskoeffizient. 
Massendefekt: mass defect. The amount by which 
the mass of an atom falls short of the sum of the masses 
of the particles of which it appears to be composed, as 
the latter are separately measured. 
Massenspektrograph: mass spectrograph, m. spectrome- 
ter. An apparatus for separating an emission of elec- 
trically charged particles into distinct streams in ac- 
cordance with their masses, by means of magnetic or 
91 
/Massensuszeptibilitaet M 
electric deflection, and for ascertaining their masses in 
this way. The streams of particles are often made to 
strike a photographic plate and thus render their posi- 
tions observable as "lines,” like those of a spectrum. 
Massensuszeptibilltaet: mass susceptibility. The ratio 
of the magnetization in a substance to the magnetizing 
force responsible for it. Divided by the density, it gives 
the mass susceptibility or specific susceptibility of the 
substance. 
Massenzahl: mass number. A type of atomic number 
which designates the number of protons in the nucleus 
of the atom, instead of the older, Moseley number. 
Massenzen+rum: center of mass. In re any body or 
system of bodies: a point such that if any plane be 
passed through it, the mass moments, with respect to 
it, of the portions on opposite sides of the plane are 
equal. Syn. center of inertia, centroid. 
Masson'sche Gleichung: Masson equation. An empiri- 
cal formula for the apparent molar specific volume of a 
substance in solution, viz., 
Maxwell'sche Bruecke: Maxwell bridge. (1) An ar- 
rangement resembling a Wheatstone bridge, but used 
for comparing an inductance with a capacitance. (2) 
An arrangement similarly used for comparing an in- 
ductance with a mutual inductance. 
Maxwell'scher Daemon: Maxwell demon. An imagi- 
nary intelligent being of molecular proportions, intro- 
duced by Maxwell into his arguments on the thermo- 
dynamics of gases. 
Maxwell'sches Diagramm: Maxwell diagram. A dia- 
gram made up of the vector polygons of forces corre- 
sponding to the different members of a framed struc- 
ture or truss, one polygon for each joint of the structure. 
Maxwell'sches Dreieck: Maxwell triangle. A graphical 
device for representing the trichromatic coefficients of 
the components of a three-color mixture. 
Maxwell'sche elektromagnetische Gleichungen: Max- 
well electromagnetic equations. Four relations which, 
according to Maxwell’s electromagnetic theory, describe 
the conditions at any point under the influence of vary- 
ing electric and magnetic fields, in a region in which, 
in general, there are conductors, dielectrics, and para- 
magnetic or ferromagnetic bodies. They are most con- 
cisely expressed in vector notation, and appear in vari- 
ous forms, of which the following are typical: 
in which C is the molar concentration and a and b 
are empirical constants. 
= a C1/2 + b, 
Materiewelle: matter wave. See de Broglie Welle. 
mathematisches Pendel: ideal simple pendulum. A 
particle of finite mass but infinitesimal size, suspended 
as a gravity pendulum by a weightless thread; a con- 
venient theoretical concept. 
Matrizenmechanik: matrix mechanics. The quantum 
mechanics of Heisenberg, expressed in the mathematical 
notation of matrices. 
Matteucci'scher Effekt: Matteucci effect. An e.m.f. 
developed between the ends of a twisted ferromagnetic 
wire upon change of its magnetization. Discovered by 
C. Matteucci, 1857. 
Maxwell: maxwell. The practical, e.g.s. electromag- 
netic unit of magnetic flux, equal to 1 gauss-cm2. Each 
maxwell may be represented by a "line” of (magnetic) 
force. 
Maxwell-Ampere'sches Gesetz: Maxwell-Amp ere law. 
A modification of the Ampere law, made by Maxwell 
to allow for the displacement current in the dielectric 
as well as the current in the conductor. 
Maxwell-Boltzmann'sches Gesetz: Maxwell-Boltzmann 
law. The principle of equipartition of energy. 
1 8D 4ttu 
Y X H = + , 
c 8t c 
V • B = 0, 
1 SB 
V X E = - ■ 
c8t 
V • D — 4?rp . 
In these, H — magnetic intensity, B = magnetic in- 
duction, E — electric intensity, D = electric displace- 
ment, p =. electric density, u = (conduction) current 
density, c is the electromagnetic constant. 
Maxwell'sches Gesichtsfeld: Maxwellian view. An op- 
tical arrangement in which a real image of a surface is 
formed by a lens at the pupil of the observer’s eye, 
resulting in a field of uniform brightness more intense 
than that of the surface as viewed without the lens. 
Maxwell'sche Reihenformel: Maxwell series formula. 
A formula, derived by Maxwell, which expresses the 
mutual inductance of two coaxial circular coils as the 
difference of two complicated infinite series in terms 
of the radii of the two coils and their distance apart. 
Maxwell'sche Spitze: Maxwell top. A gyroscope in 
/Maxwell'sche thermodynamische Beziehungen 
92 M 
the form of an adjustable top, whose point of support 
may be set below, at, or above the c.m. 
Maxwell'sche thermodynamische Beziehungen: Max- 
well thermodynamic relations. Four differential equa- 
tions of thermodynamic change, which connect the tem- 
perature ®, the volume v, the pressure p, and the en- 
tropy <£, as follows: 
first compressing a portion of the gas and observing the 
pressure thus "magnified”; from this the original pres- 
sure may be calculated. 
Mechanik: mechanics. Syn. dynamics; but often with 
special reference to machines or building construction. 
mechanisches Aequivalent: mechanical equivalent. See 
dynamisches Aequivalent. 
mechanischer Nutzeffekt: mechanical advantage. The 
(ideal) ratio of the force exerted by a machine to the 
force exerted on it by the operator. A more practical 
measure is the ratio of the linear displacement effected 
by the operator to the displacement produced by the 
machine, since this is independent of the influence of 
friction. 
Megohmempfindlichkeit: megohm sensitivity. The sen- 
sitivity of a galvanometer expressed as the resistance in 
megohms (millionths of an ohm) necessary to reduce 
the deflection to 1 scale division, when an e.m.f. of 1 
volt is applied to the circuit. 
mehrfach: multiple, [parallel (in the electrical sense) 
See mannigfaltig. 
Mehrfachionisa+ion: multiple ionization. The extrac- 
tion of more than one electron from an atom, e.g., by 
the impact of an electron of sufficient speed. 
Mehrfach+erm: multiple (spectral) term. A group of 
nearly equal spectral terms corresponding to a set of 
closely adjacent quantum states or energy levels. 
mehrphasisch: multiphase, polyphase. Having or util- 
izing several phases; e.g., a polyphase current or motor. 
Meissner'scher Effekt: Meissner effect. The acquisition 
of nearly complete diamagnetism = 0) by certain 
metals when cooled below the superconductivity transi- 
tion point. 
Melde'scher Versuch: Melde experiment. An experi- 
ment with a vibrating string, in which the nodes and 
antinodes are distinctly visible. 
Meniskus: meniscus. The concave or convex free sur- 
face of a liquid in a tube, due to capillary action. 
Meniskuskorrektor: 7neniscus correction. A correction 
often necessary in taking readings on liquid columns, 
as in a barometer, because the end of the column is 
not a plane surface. 
Meniskuslinse; meniscus lens. A lens whose two sur- 
faces have curvatures of the same sign, i.e., which is 
/S£\ _ /8v_\ /8<£\ / Sp \ 
* 8p / v \ 8® / <j> \Sv/@ \ S® / v 
/m _ /8v\ m\ _ /sp\ 
Up / ® \ 8® / P ’ \8v/p I s® / $ 
The subscripts denote that the corresponding quantity 
is to be kept constant. The equations may take other 
forms, those here given being in terms of independent 
variables subject to experimental control. 
Maxwell'sches Verteilungsgesetz: Maxwell distribution 
law. An expression for the statistical distribution of 
speeds or energies among the molecules of a pure gas 
free from convection currents and at a uniform tempera- 
ture. It takes various forms, of which the following 
is typical: 
dN iz Au2e — B2u2du; 
expressing the number of molecules having speeds in 
the range u — l/2 du to u + y2 du. A and B are 
constants involving the temperature and pressure. 
Maxwell-Wagner'sche Polarisation: Maxwell-Wagner 
polarization. A type of electric polarization exhibited 
by heterogeneous dielectrics, e.g., colloidal suspensions, 
and ascribed to the accumulation of charges at the di- 
electric interfaces; in contrast to the dipole polarization 
of homoegeneous polar dielectrics. 
Maxwell'sche Windung: maxwell-turn. A unit of mag- 
netic linkage, corresponding to one. line of force sur- 
rounded by 1 turn of the circuit. Syn. line-turn. 
Maupertuis'sches Prinzip: Maupertuis principle, least- 
action principle. States that if a dynamic system passes 
spontaneously and without change in total energy from 
one configuration to another, the action involved in the 
process is a minimum; ox (an equivalent statement) 
that the line integral of the momentum of each particle 
is a minimum. Enunciated by Maupertuis. 
McCoy Zahl: McCoy number. The ratio of the total 
alpha radiation from a radioactive substance to the 
alpha radiation per cm2, in a direction perpendicular to 
the surface, of a layer of uranium oxide (U3Og) of 
indefinite thickness. 
McLeod'scher Manometer: McLeod gauge. A device 
for measuring the pressure of highly rarefied gases by 
93 
/Meridian M 
either convexo-concave or concavo-convex. The former 
is called convex-meniscus, the latter concave-meniscus. 
Meridian: meridian. A line perpendicular to the axis 
of an optical system, e.g., any diameter of a circular 
lens. 
Meridianstrahl: meridian ray. Any one of a narrow 
bundle of rays in a symmetrical optical instrument which 
lies in the meridian section of the bundle, made by the 
plane containing the chief ray and the optic axis of the 
instrument. 
Mersenne'sches Gesetz: Mersenne law. States that the 
frequency of a vibrating string varies inversely as the 
length, inversely as the square root of the line density, 
and directly as the square root of the tension. 
Mesoform: meso form, m. phase. A form of a sub- 
stance which fails to exhibit optical activity because of 
a structure in which the dextrogyrate and levogyrate 
effects are balanced against each other. 
mesomorph: mesomorphic. In or pertaining to the 
liquid crystal state. Syn. smectic. 
Messerkantenversuch: knife-edge test. A method of 
testing large mirror objectives. 
metakristallner Zustand: metacrystalline state. An ar- 
rangement of molecules, due to strain or other influence, 
which, while it does not involve a true crystal structure, 
is capable of giving rise to X-ray diffraction patterns 
analogous to those produced by crystals. 
metamagnetisch: metamagnetic. Having the property 
of being either paramagnetic or diamagnetic according 
to conditions such as the intensity or the direction of 
the applied field. 
metastabiler Zustand: metastable state. (1) A kind of 
equilibrium which is not attainable indifferently from 
different directions, e.g., that of super-cooled water, 
which may be reached by cooling liquid water but not 
by warming solid ice. (2) In re an atom: an excited 
state in which, however, the atom will not emit radia- 
tion unless further stimulated by some external influence 
or disturbance, such as a collision, 
metazentrische Hoehe: metacentric height. Height of 
the metacenter above the c.m. 
Metazentrum: metacenter. That point, always above 
the c.m., of a rigid body floating in equilibrium, through 
which the buoyant force may be considered to act when 
the body is slightly tipped. In general its position de- 
pends upon the plane of tipping; a boat has a transverse 
metacenter (as it rolls) and a longitudinal metacenter 
(as it pitches). 
Meteorograph: meteorograph. An apparatus which 
records conditions of atmospheric pressure, temperature, 
and humidity. 
Meteorologie: meteorology. That branch of physical 
science which treats primarily of atmospheric phe- 
nomena. 
Meter: meter. The basic unit of the metric system, 
originally defined as 0.0000001 of the earth’s meridian 
quadrant at sea level. The actual metal standard meter 
bar at Sevres is constructed to fulfill this ideal specifi- 
cation as accurately as possible. The ratio of the meter 
to the English yard is about 1.093611. 
Meterlcerze: meter-candle, lux. A practical metric 
unit of illumination, equal to 1 lumen per m2; or, the 
illumination of a surface at a uniform distance of 1 m 
from a symmetrical point source of 1 candle. 
Meterkerzensekunde: meter-candle-second. A unit of 
photographic exposure, corresponding to an illumination 
of 1 lux for 1 sec. 
Methode der kleinsten Quadrate: method of least 
squares. A systematic procedure for the adjustment of 
observations in accordance with the principle of least 
squares. 
metrische Pferdestaerke: metric horse power, force de 
cheval. A metric gravitational unit of power, equal to 
75 m-kg of work per second, and equivalent to about 
736 watts or 0.9863 hp. 
Metrologie: metrology. That branch of science which 
deals with systems of units and methods of measure- 
ment. 
Mho: mho. A unit of electrical conductance, the re- 
ciprocal of the ohm. Thus a conductor having a resis- 
tance of 4 ohms has a conductance of 0.25 mho. Syn. 
reciprocal ohm. 
Michelson'scher Interferometer: Michelson interfero- 
meter. An interferometer, designed by A. A. Michel- 
son, which is arranged to produce interference maxima 
and minima between two wave trains, as of light, 
separated from the same original train and reunited 
after reflection from two mirrors. The phase of the 
interference is varied by moving one of the mirrors 
forward or backward, and the wave length thereby com- 
pared with the mirror displacement. 
Michelson-Morley'scher Versuch: Michelson-Morley ex- 
/Mikrochronograph 
94 M 
periment. A classic and crucial experiment, involving 
the transmission and reflection of light through the 
mirror system of an interferometer, which was intended 
to reveal the existence of an ether drift due to the 
earth’s motion, and the negative result of which was 
the starting point of the theory of relativity. First 
performed by Michelson and Morley in 1881. 
Mikrochronograph: microchronograph. A Chrono- 
graphie device for very small intervals of time, e.g., 
the period of a sound vibration or the duration of an 
electric spark. 
Mikrodensitometer; microdensitometer. A microphoto- 
meter for the measurement of the density of photo- 
graphic images. 
Mikrodichtemesser: microdensitometer. See Mikroden- 
sitometer. 
Mikrokinematograph: microcinematograph. A moving- 
picture camera for microscopic objects, such as particles 
exhibiting the Brownian movement, growing microcry- 
stals, etc. 
Mikrokristall: microcrystal. One of the small crystals 
in a finely crystallized mass, e.g., in cast iron. 
Mikromanipulator; micromanipulator. A device, con- 
trolled by compressed air or otherwise, for manipulating 
microscopic objects in any desired manner while under 
observation. 
Mikromanometer; micromanometer. An instrument for 
observing and measuring very small pressure differences 
or fluctuations. 
Mikromechanik: micromechanics. The dynamics of 
very minute bodies, such as the component parts of an 
atom or of a molecule. 
Mikrometer: micrometer. One of a class of measur- 
ing instruments in which linear displacements to be 
measured are made to correspond with the travel of a 
screw, of accurately adjusted pitch and provided with 
a large head graduated to indicate small subdivisions 
of the pitch. 
Mikron: micron. A unit of length, equal to one-mil- 
lionth of a meter, or 0.001 mm. Commonly designated 
by the symbol fi. The millimicron, or 0.001 micron, 
0.000001 mm, is designated by /xfi or mp. \ 
Mikrophotometer: microphotometer. An instrument 
for the measurement or comparison of small luminous 
intensities. 
Mikropyrometer: micropyrometer. An apparatus, de- 
vised by Burgess, for measuring the melting points of 
small specimens of refractory substances. 
Mikroradiometer: microradiometer. An instrument for 
the measurement of very feeble radiation. 
mikroskopisches Reversibilitaetsprinzip: microscopic 
reversibility principle. A principle of statistical equi- 
librium, formulated in various ways; by Richardson as 
follows: "Every isolatable process is exactly compen- 
sated in a state of statistical equilibrium by precisely 
the same process working backward.” The process of 
detailed balancing in ionized gases is an example. 
mikroskopisches Umkehrungsprinzip: microscopic rever- 
sibility principle. See mikroskopisches Reversibilitaets- 
prinzip. 
Mikrovoltempfindlichkeit: microvolt sensitivity. The 
sensitivity of a galvanometer as expressed in scale divi- 
sions per impressed microvolt. 
Mikrowaage: microbalance. (I) Any balance for 
weighing very small masses. (2) A very small differ- 
ential buoyancy balance for measuring densities of gases. 
Mikrowellen: microwaves, ultrashort waves. The short- 
est electromagnetic waves employed in radio communi- 
cation; specifically, those below 10 m in wave length 
or above 30,000 kc per second in frequency. 
Miller'sche Bruecke: Miller bridge. A type of bridge 
circuit devised by J. H. Miller for measuring the ampli- 
fication factors of vacuum tubes. 
Miller'scher Index: Miller index. One of the three 
numbers (h, k, 1) used to designate any set of parallel 
planes of atoms in a crystal, viz., the simplest integers 
proportional to the reciprocals of the intercepts of the 
planes on the crystal axes. 
Milliamperemeter: Milliammeter. Any type of gal- 
vanometer which measures small electric currents di- 
rectly in milliamperes, or thousandths of an ampere. 
Millivoltmeter: millivoltmeter. A voltmeter reading in 
millivolts, or thousandths of a volt. 
Minkowski Welt: Minkowski world. The totality of 
the four-dimensional continuum known as space-time 
and measured off in space-time co-ordinates. 
Mischkristall: mix-crystal, mixed c. A crystal composed 
of two or more different chemical substances, both of 
whose molecules or ions occupy positions in the same 
crystalline structure irrespective of the substance to 
which they belong. 
677865—46 7 
95 
/Mischungsmethode M 
Mischungsmethode: mixture method. A method of 
physical measurement in which two bodies are placed 
in communication until an equilibrium is obtained be- 
tween them. Used esp. in calorimetry, in which case 
the quantity measured is heat and the equilibrium is 
one of temperature. 
Mischungswaerme: heat of mixture. Heat evolved or 
absorbed upon the mixture of two liquids, not due to 
chemical reaction between them. 
Mittelpunkt: mean center. In re a number of points 
in space: the point which .corresponds to the centroid 
of a system of equal particles placed at the given points. 
Mittelpunktprojektion: gnomonic projection. See gno- 
monische Projektion. 
mittlere freie Wegelaenge: mean free path. The aver- 
age distance which the particles composing an ensemble, 
e.g., molecules composing a gas, travel between succes- 
sive encounters with other similar particles in the proc- 
ess of thermal agitation. 
mittlere Geschwindigkeit: drift speed. The mean speed 
with which electrons or ions progress through a medium 
where they are continually experiencing collisions. ‘ 
mittlere horizontale Kerzenstaerke: mean horizontal 
candle power. The average candle power of a light 
source, as viewed from all directions in the horizontal 
plane containing it. 
mittlere Lebensdauer: average life, decay modulus. In 
re any variable which diminishes or "decays” exponen- 
tially, e.g., radioactivity: the time required for the vari- 
able to diminish to 1/e or 36.97 percent of its original 
value. It is equal to 1.443 times the half-value period, 
and is the reciprocal of the decay coefficient. 
mittlere sphaerische Kerzenstaerke: mean spherical 
candlepower. The average candlepower of a light source, 
as viewed from all directions. It equals the total lumi- 
nous flux, in lumens, divided by 4tt. 
Mizelle: micelle. An aggregate of colloidal particles, 
associated with water molecules. 
modifizierte Linie: modified line. See Compton Effekt. 
Modul: Modulus. (1) A re<xx positive quantity, nu- 
merical or physical, that expresses the measure of some 
function, property or effect, as of elasticity strength, 
efficiency, etc., esp. under unit conditions. (2) A stand- 
ard or norm. (3) (math.) a. Absolute value, b. The- 
orem of numbers. 
Modul der Periodizitaet: periodicity, modulus of. The 
change which takes place in the action during one com- 
plete cycle of a periodic process. 
modulieren: modulate. To vary, esp. the amplitude or 
the frequency of an oscillation or a wave train, in some 
characteristic manner, as in sending radio signals or in 
broadcasting. 
Mol: mol, mole, gram molecule. That mass of a pure 
substance which, in grams, is numerically equal to the 
molecular mass of the substance. The gram molecule 
of every pure substance thus contains the same number 
of molecules, viz. about 6.06 X 1023 (Avogadro 
number). 
molar: molar. (1) Pertaining to a mol, or measured 
in mols. Syn. grammolecular. (2) Pertaining to masses 
of appreciable size; massive; bodily. 
molares Brechungsvermoegen: molar refractivity. The 
product of the specific refractivity by the molecular 
weight. 
molares freies Volumen: molar free volutne. The mo- 
lar volume of a substance at any temperature in the 
liquid state, minus its molar volume at the freezing 
point. 
molare Leitfaehigkelt: molar conductivity. The elec- 
trical conductivity of an electrolyte in solution (con- 
ductivity of solution minus that of the solvent) per 
unit concentration in mols per cm2; usually as compared 
with some standard liquid, as mercury. 
molare Polarisation: molar polarization. A quantity 
Pw pertaining to the molecules of a pure dielectric, and 
connected with the polarizability a and the dielectric 
constant k by the relation 
4 k — 1M 
Pm = —tt Na = ; 
3 k + 2p 
in which N is the Avogadro number, M the molecular 
weight, and p the density. It is also equal to the limit- 
ing value of the molar refraction, as the wave length 
increases. 
molare Refraktion: molar refraction. The product of 
the molecular weight of a substance by its specific re- 
fractive power. 
molare Rotation: molar rotatory power, m. rotation. 
Molar rotatory power is the specific rotatory power 
multiplied by the molecular (or atomic) weight. 
molare Suszeptibilitaet: molar susceptibility. The mass 
susceptibility of a pure substance multiplied by its mole- 
/Molarvolumen 
96 M 
cular weight; or the mass expressed in terms of mols 
instead of grams. 
Molarvolumen: molar volume. The specific volume of 
a substance in cm3 per mol; esp. in the liquid state at 
the boiling point (Nernst). Equal to th$ molecular 
mass divided by the density. 
molare Waerme: molar heat. The product of the 
molecular mass of a substance by its specific heat, or 
the thermal capacity of 1 mol of the substance. 
Molekuelfeld: molecular field. The electric field with- 
in a material body due to the presence of polar mole- 
cules. 
Molekuolgif+er: molecular lattice. A crystal lattice 
which may be regarded as built out of molecules as the 
units of structure. 
Molekuelkris+ali: molecular crystal. See Molekuelgitter. 
Molekuelmoment: molecular moment. The electric mo- 
ment of a polar molecule. 
Molekuelspektrum: molecular spectrum. A band spec- 
trum composed of radiation frequencies due to energy 
changes within molecules. There are three types: vibra- 
tion frequencies caused by changes in the vibration 
energy of the atoms; rotation frequencies, corresponding 
to changes in the rotation energy of the molecule; and 
electron frequencies, due to electronic transitions. Bands 
may also arise from combinations of these types. 
Molekuelstrahl: molecular ray, m. beam. A stream of 
molecules moving in nearly parallel directions, after 
emergence into a vacuum from a low-pressure reservoir 
through a succession of narrow apertures. 
Molekularmanometer: molecular gauge. A pressure 
gauge for the measurement of very low gas pressures 
by means of the viscous friction exerted on a moving 
body, as a rotating disk. 
Molekularpumpe: molecular pump. An air pump in 
which the molecules of the gas to be exhausted are car- 
ried away by the friction of a rapidly revolving disk or 
cylinder. 
Molekularstrahl: molecular ray, m. beam. See Molekuel- 
strahl. 
Moment: moment. (1) Moment of a force with re- 
spect to any axis: the product of the perpendicular dis- 
tance r from the axis to the line of action of the force 
by that component of the force which is perpendicular 
to the axis and to the radius r. Syn. torque. (2) Mo- 
ment of a mass or a volume with respect to any plane 
(or axis): the volume integral of the products of the 
elements of mass or of volume by their distances from 
the plane (or axis). (3) Moment of an area with 
respect to an axis (or a point) in its plane: the surface 
integral of the products of the elements of area by 
their distances from the axis (or point). 
Momentanachse: instantaneous axis, axis of instan- 
taneous rotation. See augenblickliche Achse. 
Monochord: monochord, sonometer. An acoustic in- 
strument consisting of one or more strings stretched on 
a resonating box; used for making measurements of 
musical pitch and for other acoustic experiments. Syn. 
monochord, esp. if only one string. 
monochromatisch: monochromatic. In re any radiation, 
esp. light; composed of wave trains of a limited range 
of frequency. 
Monochromator: monochromatic illuminator, mono- 
chromator. An instrument for producing and isolating 
a beam of monochromatic radiation. 
monodispers: monodisperse. A term used to charac- 
terize disperse systems whose particles are of sensibly 
uniform size. 
monoklin: monoclinic. In re crystal structure: having 
two of the three axes perpendicular to the third, but 
oblique to each other. 
monomolekulare Schicht: monomolecular layer, mono- 
layer. An adsorbed film or layer having a thickness of 
one molecule of the substance composing it. 
Morera Lehrsatz: morera theorem. Stated thus; "Any 
two systems, St, S2, S3 of forces acting on a system 
of particles with bonds independent of the time deter- 
mine, starting from rest, displacements generable in 
the same infinitesimal interval of time, these displace- 
ments being such that the work computed as done by 
the forces Sx through the displacements corresponding 
to the forces S2 is equal to the work computed as done 
by the forces S2 through the displacements correspond- 
ing to the forces Sr” 
Morse-Allis-Lamar'sche Verteilungsfunktion: Morse-Al- 
lis-Lamar distribution function. A function represent- 
ing the statistical distribution of the speeds of electrons 
in a gas. 
Mosaikstruktur: mosaic structure. The subdivision of 
a crystal into polyhedral blocks of microscopic dimen- 
sions, with discontinuities in the lattice structure between 
them; apparently associated with the secondary structure. 
97 
/Moseley-Gesclz M 
Moseley-Gesetz: Moseley law. States that all the 
heavier chemical elements may be arranged in a series, 
such that the square root of the frequency of a given 
line in the X-ray spectrum increases by a constant 
amount in passing from one element of the next. This 
sequence of elements is now recognized as that of their 
atomic (Moseley) numbers. 
Moseley'sche Kurve: Moseley curve, M. diagram. A 
curve which, graphically exhibits the relationship be- 
tween the atomic numbers of a sequence of elements 
and the wave lengths of their corresponding spectral 
lines. 
Moseley Zahl: Moseley number. See Atomzahl. 
Motorgenera+or: motor generator. A generator oper- 
ated by a motor esp. a d.-c. generator on the same shaft 
with an a.-c. motor, and used for obtaining d.-c. service 
from a.-c. mains. Syn. motor transformer, rotary con- 
verter. 
Motf'scher effekt: Mott effect. The partial polariaztion 
of a beam of electrons, i.e., orientation of their spin 
axes in one direction, due to scattering by the atoms 
of a target. 
Mue: mu. A vernacular term used to designate: (1) 
The micron. (2) The amplification factor of a triode, 
esp. in such phrases as "high-mu tube”, etc.; so called 
because of the common use of the symbol /i to repre- 
sent this factor. 
Mueller'sche Bruecke: Mueller bridge. A five- or six- 
decade Wheatstone bridge for precise resistance ther- 
mometry, characterized by ratio arms of relatively high 
resistance, adjustable to equality, and a third arm vari- 
able in steps of 0.0001 ohm, with dial switches for the 
five lower decades. 
Mu+arotation: mutarotation. A change of optical rota- 
tory power or a reversal of its direction, e.g., in a 
solution passing from levogyrate to dextrogyrate activ- 
ity as it is diluted. 
multipel: multiple. See mannigfaltig. 
Multiplett: multiplet. A group of lines in an atomic 
spectrum, arising from transitions between the different 
components of two multiple spectral terms and hence 
exhibiting the characteristic frequency differences of 
these terms. The number may vary from 1 to 15 or 20. 
Multivibrator: multivibrator. An electric oscillating 
system so designed that the energy is chiefly distributed 
among the harmonic partial frequencies rather than in 
the fundamental frequency. Devised by Abraham and 
Bloch. 
Muttersubstanz: parent. (1) The first or primordial 
element of a radioactive series. (2) In re any radio- 
active product: that element from whose disintegration 
it is immediately derived. E.g., the parent of radon 
is radium, while that of the whole series is uranium. 
(3) A spectrum line which represents a normal quan- 
tum process, unaffected by such influences as are re- 
sponsible for satellite lines, as in the Zeeman effect. 
/N Serie 
98 N 
N Serie: N series. A series of frequencies in the 
X-ray spectrum of an element, considered as arising 
from the transition of electrons from various higher 
quantum states to the state whose principal quantum 
number is 4. First observed by Dolejsek. 
Nachfliessen: afterflow. The persistence of plastic 
flow in a solid after the external forces primarily re- 
sponsible for it have ceased to act. 
Nachhall: reverberation. A succession of echoes, esp. 
of sound in a large room; the result of repeated re- 
flections. 
Nachhallzeit: reverberation time. The time required 
for the average acoustic energy density in a reverberat- 
ing enclosure to fall off to one-millionth of its initial, 
steady-state value, after the source has been silenced. 
It depends upon the geometrical form and equivalent 
absorption of the enclosure and upon the frequency of 
the sound. 
Nachleuchten: afterglow. (1) A luminosity which 
persists in a rarefied gas after the passage of an elec- 
trodeless discharge through it. (2) Syn. phosphores- 
cence. 
Nachlieferungskoeffizient: production coefficient. The 
rate at which primary radiation produces secondary ra- 
diations with respect to the thickness of medium tra- 
versed. If dl2 is the intensity of secondaries produced 
in thickness dx by primary radiation of intensity I1S the 
coefficient is 
Nebelspur: cloud track. A row or streak of droplets 
formed in a cloud chamber by the passage through it of 
an ionizing particle, whose path is thus revealed. 
Nebenbogen: secondary bow. A faint rainbow which 
sometimes appears outside the brighter primary bow 
and has its colors in the reverse order. 
Nebenschluss: shunt. A branch of an electric circuit 
in parallel with other parts of the same. 
nebenschlussgewickelt: shunt-wound. In re a field 
magnet: having its winding in parallel with the ex- 
ternal or line circuit. 
Nebenschlusskondensator: by-pass condenser. A con- 
denser used to provide an a.-c path of comparatively 
low impedance around a circuit element. 
Nebensonne: parhelion. One of the bright, spectrally 
colored spots, commonly called "sun dogs,” which ap- 
pear at times in cold weather on either side of and 
above and below the sun, at a distance of about 22 
degrees from it. They are due to the refraction of the 
sunlight by minute crystals of ice suspended in the air. 
negatives Energieniveau: negative energy level. One 
of the negative values for the energy levels of an elec- 
tron yielded by the Dirac equation, which has both 
positive and negative solutions. The positive values cor- 
responding to observation, but the physical significance 
of the negative values is not evident. 
negatives Energiespektrum: negative energy spectrum, 
A set of transitions involving negative energy levels. 
negative Energiestute: negative energy level. See 
negatives Energieniveau. 
negatives Glimmlicht: negative glow. A luminous re- 
gion in a Crookes tube at moderate pressure, lying be- 
tween the Crookes dark space and the Faraday dark 
space. 
negative Impedanz: negative impedance. A property 
possessed by certain electrical devices, such that when 
introduced into a circuit the current and the e.m.f. are 
in opposite directions. If there is no resultant inductance 
or capacitance effect, the property is termed negative 
resistance. 
negativer Kristall: negative crystal. A uniaxial, bire- 
fringent crystal in which the extraordinary wave has 
the greater velocity, e.g., Iceland spar. 
negativer Widerstand: negative resistance. See nega- 
tive Impedanz. 
dVdx 
ß = 
Ii 
nacktes Atom: stripped atom. See elektronenberaubtes 
Atom. 
Nagaoka'sche Formel: Nagaoka formula. A formula 
for the inductance in microhenrys of any single layer 
of a cylindrical coil or solenoid: 
0.03948 r2N2 
L - K 
1 
in which r is the radius and 1 the length of the coil, 
in cm, N is the number of turns, and K a constant 
depending upon the ratio of r to 1, tables of which 
have been published. 
Nahpunkt: near point. That point on the axis of the 
eye which is at such distance as to be seen distinctly 
with the utmost possible degree of accommodation, i.e., 
when the focal power of the crystalline lens is greatest. 
Nebelkammer: cloud chamber. See Expansionskammer. 
99 
/Neigung  
Neigung: inclination. See inklination. 
Neigungsnadel (magnetisch): dip needle, dipping n, 
inclinometer. A magnetic needle poised in a vertical 
plane, used to indicate the magnetic inclination. 
nematischer Zustand: nematic state. A stage prelimi- 
nary to the mesomorphic state, in which the molecules 
may be regarded as having a common orientation, but 
not otherwise arranged. 
Neper: neper. A unit used, like the bei, to express 
the relationship between two amounts of power (acou- 
stic, electric, etc.) as an interval on a logarithmic scale. 
The number of nepers in such an interval is the Na- 
pierian logarithm of the square root of the ratio of 
the two powers compared; therefore 1 neper is the 
value of that interval for which the ratio is e2 rr 7.389. 
The neper is equal to 0.8686 bei or 8.686 decibels. 
Nephelometer: nephelometer. A type of photometer 
used for the measurement of light transmitted or of 
light scattered by translucent substances, or of the tur- 
bidity of liquids, and for determining therefrom the 
quantity of suspended matter present. 
Nernst'sche Bruecke: Nernst bridge. A four-arm bridge 
containing condensers instead of resistances, and used 
for the measurement of capacitances at high frequencies. 
Nernst'scher Effekt: Nernst effect. A p.d. which de- 
velops between the two edges of a strip of metal, in 
which heat is flowing longitudinally, when the plane 
of the strip is placed perpendicularly across a magnetic 
field. Discovered by Ettingshausen and Nernst in 1886. 
Nernst Lampe: Nernst lamp. An electric lamp whose 
luminosity proceeds from a short, slender rod of zir- 
conium oxide (Nernst glower) heated to brilliant white 
incandescence by the current. 
Nernst'scher Waermelehrsatz: Nernst heat theorem. 
States that in the neighborhood of absolute zero, all 
physical and chemical processes are isentropic. 
Neumann'sches Dreieck: Neumann triangle. The tri- 
angle which graphically represents the equilibrium of 
the three surface tensions at a point where two im- 
miscible liquids come in contact in the air, as when a 
drop of one liquid rests on the surface of the other. 
neutrale Achse: neutral axis. The line of intersection 
of any cross section of a rod or beam with the neutral 
layer. 
neutrale Kurve: neutral curve. A graph between pres- 
sure and temperature, at all points of which the specific 
volumes of the solid and the liquid phases are equal. 
For points on one side of the curve the solid specific 
volume exceeds that of the liquid, while the reverse 
is true for points on the other side. 
neutrale Schicht: neutral layer. That longitudinal 
layer of material in a rod or beam, perpendicular to 
the plane of flexure, which is neither lengthened nor 
shortened when the rod is bent. 
Neutrino: neutrino. A type of neutron having elec- 
tronic mass or smaller. The existence of such a particle 
was suggested by Bragg. The name neutret was pro- 
posed by Langer. 
Neutrodyn: neutrodyne. An amplifier circuit contain- 
ing a capacitance for neutralizing the tendency to re- 
generate due to the internal capacitance between plate 
and grid of the amplifier tube. 
Neutron: neutron. An apparently stable particle, hav- 
ing a mass at least approximately equal to that of the 
proton, but electrically neutral. Its existence was first 
demonstrated by Chadwick in 1932. 
Newton'sches Abkuehlungsgesetz: Newton law of cool- 
ing. States that the rate of cooling of a heated body 
by radiation and convection varies directly as the excess 
of its temperature above that of its surroundings. It is 
approximately applicable only to small ranges of tem- 
perature. 
Newton'sche Gesetze der Dynamik: Newton laws of 
dynamics. Three dynamic principles which underlie the 
structure of the Newtonian mechanics. They may be 
stated as follows: (1) Every body remains in its state 
of rest or of uniform motion in a straight line, except 
as it may be caused to alter that state by the applica- 
tion of external forces. (2) Any change of momentum 
takes place in the direction of the force producing it, 
and at a rate proportional to the magnitude of the force. 
(3) To every force there is opposed an equal, reactive 
force in the same straight line. 
Newton'sche Kraft: Newtonian force. One of several 
types of mutual interaction which obey the inverse- 
square law, e.g., gravitation, electric force, magnetic 
force, etc. 
Newton'sche Mechanik: Newtonian mechanics. The 
classical mechanics based upon the Newton laws of 
dynamics, as distinct from quantum mechanics, wave me- 
chanics, or relativity. 
Newton'sche Potentialfunktion: Newtonian potential 
/Newton'sches Potential 
100 junction. An expression common to all potentials asso- 
ciated with inversesquare forces, viz., 
immersed in a normal solution of an electrolyte having 
that metal as one of its ions. 
9 
normaler Dampf: normal vapor. A vapor v/hose mole- 
cules are all of one kind, and not polymerized. 
normale Fluessigkeit: normal liquid. A liquid whose 
molecules are all of one kind, and not polymerized. 
normales Gas: normal gas. A gas whose molecules 
are all of one kind, and not polymerized. 
Normalgleichung: normal equation. One of a set of 
simultaneous equations involving a set of experimental 
unknowns, which occurs in the course of the least-square 
adjustment of a larger number of observation equations. 
normale magnetische Induktion: normal (magnetic) 
induction. See magnetische Flussdichte. 
normaler Kathodenfall: normal cathode potential drop. 
The constant value of the p.d. between the cathode 
and the negative glow in a discharge tube in which 
the cathode is not entirely covered by the cathode glow. 
normale Stromdichte: normal current density. The 
constant value of the current density over that part of 
the cathode in a discharge tube which is covered with 
the cathode glow, when this does not entirely cover 
the cathode. 
Normalisierung: normalization. The operation of mul- 
tiplying a given characteristic wave function (eigenfunc- 
tion) by a constant, called a normalization constant, 
in order that when so modified, the wave function will 
fulfil the condition that the volume integral 
S I I2 dv = 1 
Normalloesung: normal solution■ A solution in which 
the solute has a concentration of 1 equivalent weight 
per liter of solution. 
Normal+empera+ur und Normaldruck: normal tempera- 
ture and pressure (N.T.P.). The temperature 0 degrees 
C and pressure 1 atm. Syn. standard conditions. 
Normalterm: normal term. A spectral term in which 
the fine-structure level having the smallest inner quan- 
tum number lies farthest down on the energy-level 
diagram. 
Nuance: tint. A chromatic color of relatively low 
saturation and relatively high brilliance. 
Nullinie: zero line. A wave length in an absorption 
band in certain types of molecular spectrum, which cor- 
f dm 
v = (—■ 
in which m is mass (or electric charge, or magnetic 
pole strength) and r is distance from the element dm. 
The gravitational, the electric, and the magnetic poten- 
tials each contain a factor of this form. 
New+on'sches Potential: Newtonian potential. See 
Gravitationspotential. 
Newton'sche Ringe: Newton rings. The circular in- 
terference bands formed by light reflected from the 
glass-air interfaces between a convex glass surface and 
a plane glass surface in contact with it. The center of 
the ring system is the point of contact. 
I 
Newton'sche Theorien von der Kreisbewegung: New- 
ton theorem of orbital motion. States that the velocity 
of a body moving in a central orbit is inversely pro- 
portional to the normal from the center of attraction 
to the tangent to the orbit at the point occupied by 
the body. 
Nichols'sches Prisma: Nicol prism, Nicol, nicol. A 
well known device for producing planepolarized from 
unpolarized light, by means of two prismatic segments 
of Iceland spar cemented by a thin layer of Canada 
balsam interposed at such an angle that the ordinary 
component of the original light is entirely eliminated 
by total reflection at the cementing layer, while the ex- 
traordinary component passes through. 
Nichols'scher Radiometer: Nichols radiometer. An 
instrument devised by Nichols to demonstrate the pres- 
sure of light, and used to measure the intensity of radia- 
tion in the visible and infrared. 
Nichols'scher Strahlenmesser: Nichols radiometer. See 
Nichols’scher Radiometer. 
Nichtvariant: nonvariant. Having no degrees of free- 
dom, i.e., zero variance. 
Niederschlag: strike. An initial electrochemical de- 
posit; or sometimes the electrolyte from which such 
deposit is made. 
Niederschlagspotential: striking potential, deposition 
potential, sedimentation potential. The minimum p.d. 
between an electrode and the surrounding electrolyte 
required to deposit ions of a given kind. See also Dorn- 
Effekt. 
Normalelektrode: normal electrode. A metal electrode 
/Nullmethode N 
responds to a gap in the sequence of absorption lines, 
and which marks an origin or axis for the band as a 
whole. Syn. missing line. 
Nullmethode: null method, balance method, zero 
method. A method of measurement in which the quan- 
tity to be measured is by adjustment so related to the 
known quantity with which it is compared that the 
scale reading of the indicating instrument becomes zero; 
as in the use of a balance or of a Wheatstone bridge. 
Nullpunktenergie: zero-point energy. The energy pos- 
sessed by a thermodynamic system in any prescribed con- 
dition taken as a zero of reference; in particular, at 
the absolute zero of temperature. 
Nullzweig: zero branch. A series of lines in an ab- 
sorption band of a molecular spectrum, in the produc- 
tion of any one of which there is no change in the 
rotational quantum number. 
numerische Apertur: numerical aperture. In re an ob- 
jective,, esp. of a microscope: (1) The product of the 
refractive index of the medium in front of the objective 
by the sine of half the angle of the cone of rays which 
enters the objective and which thus defines the field of 
view. (2) The ratio of the diameter of the aperture 
of the objective to the focal length. 
numerische Dichte: numerical density. The number of 
particles or points per unit of space (area or volume) 
in any region. 
/O Serie 
102 o 
O Serie: O series. A series of frequencies believed 
to exist in the X-ray spectrum of an element and to 
arise from the transition of electrons from various higher 
quantum states to the state whose principal quantum 
number is 5. 
oberer Zustand: upper state. That one of the two 
energy states or levels, before and after a quantum 
transition, in which the atom or the molecule has greater 
electronic energy. 
Oberflaechenaufladungswaerme: surface heat of charg- 
ing. Heat theoretically developed when an electric charge 
is imparted to a metallic surface. 
Oberflaechenauftrieb: surface of buoyancy. The sur- 
face described by the center of displacement as a floating 
body is tipped through various angles and in various 
directions without altering the volume of displacement. 
Any vertical section of this surface through the meta- 
center is a curve of buoyancy. 
Oberflaechendichte: surface density. The quantity per» 
unit area of anything distributed over a surface, e.g. 
of an electric charge. 
Oberfiaechenenergie: surface energy. Energy which 
depends upon the surface area and configuration of a 
body, e.g., a bubble or a drop of liquid, and which 
varies when either is varied isothermally. 
Oberflaechengit+er: surface lattice. A structural pat- 
tern manifested at a natural cleavage surface of a cry- 
stal, and recognized by effects analogous to those of a 
plane grating. 
Oberflaechenin+egral des normalen Feldes; surface in- 
tegral of normal field. The surface integral of the nor- 
mal component of the field intensity over any given 
surface, i.e., the sum of the products obtained by mul- 
tiplying each element of the surface by the component 
of intensity perpendicular to the surface at the point 
occupied by the element. 
Oberflaechenpho+oelek+rischer Effekt: surface photo- 
electric effect, photoelectric emission. Pertaining to the 
electric effects of light or other radiation; esp. to the 
phenomenon (photoelectric emission), manifested by 
certain metals, of giving off electrons (photoelectrons) 
when subjected to suitable radiation. The movement of 
these electrons in an electric field imposed for the pur- 
pose is a photoelectric current. 
Oberflaechenspannung: surface tension. The peculiar 
effect of cohesion manifested at the free surface of a 
liquid, or at the interface of two immiscible liquids, 
and giving the impression of a tense, elastic skin or 
membrane. It is measured in units of force per unit 
length, e.g., dynes per centimeter, across any line on 
the surface. 
Oberflaechenwiderstand: surface resistivity. The elec- 
tric resistance of the surface of an insulator, measured 
between the opposite edges of a centimeter square of the 
surface. 
Objektiv: objective. That lens, lens combination, or 
mirror which, in an optical instrument, first receives 
the light coming from the object and gives the rays 
their first change of focus, as in the formation of a 
real image by the objective of a telescope. Syn. object 
glass. 
Objektivprisma: objective prism. A large prism placed 
before the objective of a telescope in order to produce 
spectral images of stars on a photographic plate in its 
focal plane. 
Objektpunkt: object point. See Gegenstandspunkt. 
Oeffnungswinkel: aperture angle. See Aperturwinkel. 
Oelrefraktometer: oleorefractometer. An instrument 
for comparing the refractive indices of liquids, such as 
oils, with that of a standard liquid. Devised by Amagat 
and Jean. 
Oersted: oersted. (1) Substituted by international 
agreement in 1932 for the term gauss to designate the 
practical, c.g.s., electromagnetic unit of magnetic inten- 
sity. A unit magnetic pole, placed in a vacuum in which 
the magnetic intensity is 1 oersted, is acted upon by a 
force of 1 dyne in the direction of the intensity vector. 
(2) Prior to 1932, the practical c.g.s. electromagnetic 
unit of magnetic reluctance. 
Oers+ed'scher Versuch: Oersted experiment. A classic 
experiment with a wire and a compass needle, which 
revealed the presence of a magnetic field surrounding 
an electric current. 
Ohm: ohm. The practical unit of electrical resistance. 
The absolute ohm is that resistance in which an e.m.f. 
of 1 absolute volt will maintain a constant current of 1 
absolute ampere. The international ohm is the resistance 
of a column of mercury of uniform cross section, hav- 
ing a mass of 14.4521 g and 106.3 cm in length, at 
0 degrees C. (The cross section is 1 mm2.) The ratio 
of the international to the absolute ohm is about 1.00046. 
Ohm'sches akustisches Gesetz: Ohm acoustic law. 
States that all musical tones are either simple harmonic 
or capable of analysis into simple harmonics; and that 
103 
/Ohm’sches Gesetz o 
the ear is able to distinguish the several components as 
distinct, pure tones. 
Ohm'sches Gesetz: Ohm law (of electric currents'). 
A law which connects the e.m.f., the resistance (or 
conductance), and the current in a conductor or a cir- 
cuit, and which takes different forms according to the 
circumstances in which it is applied. The usual, ele- 
mentary statement is: the steady current in a circuit is 
equal to the e.m.f. divided by the resistance of the cir- 
cuit. It does not apply to all circuits. 
Ohmmeter: ohmmeter. An instrument for measuring 
resistance directly in ohms. 
Ohm'scher Widerstand: Ohmic resistance. The term 
is used to distinguish the true resistance from the types 
of impedance which do not contribute to the heating 
of the circuit. Syn. resistance. 
Ohmzentimeter; ohm-centimeter. A unit of electric 
resistivity, viz., the resistivity of a substance of which 
a uniform rod of 1 cm2 cross section has a resistance 
of 1 ohm per cm length. 
okkludieren: occlude. To absorb, as some metals take 
up certain gases and apparently incorporate them into 
the metallic structure. 
Oktave: octave. (1) A musical interval of numerical 
value 2; i.e., a range of pitches, the highest of which 
has double the frequency of the lowest. (2) Hence, a 
ratio of 2:1 between frequencies of any type of vibra- 
tion or wave emission. 
Oktett: octet. A group of eight electrons collectively 
related in a special manner to the outer structure of an 
atom. 
Oktupol: octupole. A system consisting of two equal 
quadrupoles in parallel planes, but with their corre- 
sponding charges reversed. 
Okular: ocular, eyepiece. That part of an optical in- 
strument, as a telescope or a microscope, to which the 
eye is applied. 
Okularmikrometer: eyepiece micrometer, ocular mi- 
crometer. (1) A micrometer mounted in an eyepiece 
or ocular. (2) A microscopic scale mounted in the 
focal plane of a microscope or telescope ocular. (3) A 
finely divided scale ruled or photographed on a slip 
of transparent glass and placed in the focal plane of 
the eyepiece of a microscope, for the purpose of measur- 
ing the dimensions of objects viewed with the instru- 
ment. 
Omegawert; omega value. The value of the quantum 
number which refers to the combined spin and orbital 
angular momentum of a molecule, expressed as a mul- 
tiple of h/2ir. 
Opazimeter; opacimeter, turbidimeter. An instrument 
for measuring the turbidity of a liquid, as in water- 
purification plants. 
Opposition: opposition. A phase difference of one- 
half cycle. 
Optik: optics. That branch of physical science which 
treats of the phenomena of light and of vision. Physical 
optics deals with the theories of the mechanism of light 
and its propagation. Geometrical optics regards light 
simply as an emission traveling in straight lines and 
traces its course in "rays” through reflecting and refract- 
ing systems. Physiological optics deals with the eye and 
vision. 
optische Achse; optic axis. A direction through a 
doubly refracting crystal in which light traversing the 
crystal suffers no double refraction. Syn. axial direction. 
optische Analyse: optical analysis. The investigation 
of problems concerning stresses in materials by photo- 
elastic methods. 
optische Bahn: optical path. The path followed by 
luminous energy through an optical system. Optical 
paths are equivalent if they require the same time when 
traversed by light of the same frequency. 
optische Bank: optical bench. A horizontal track with 
a graduated scale upon which lenses or other optical 
pieces may be mounted for experiments in image for- 
mation, interference, etc. 
optische Ebene: optically plane, o. flat. Departing 
from a true plane only by distances small compared with 
the wave lengths of light. 
optische Konstanten; optical constants. A set of quan- 
tities used to specify the optical properties of a sub- 
stance; such as the refractive index, the reflectivity, and 
the absorption coefficient. 
optische Laenge: optical length. The vacuum equiva- 
lent of an optical path. For any one medium, it is equal 
to the geometrical length of the path multiplied by the 
refractive index of the medium. 
optischer Mittelpunkt: optical center. A point so lo- 
cated on the axis of a lens that any ray, which in its 
passage through the lens traverses a line passing through 
this point, has its incident and emergent parts parallel. 
/optische Pyrometer 
104 o 
optischer Pyrometer: optical pyrometer. A pyrometer 
in which the temperature of a body is indicated by the 
total brightness of its incandescence, or by the ratio 
of the brightness at two different wave lengths. 
optische Rotation: optical rotation. The effect which 
some transparent media, such as sugar solutions and 
quartz (parallel to its axis), exhibit in rotating the 
polarization cycle, whether linear or elliptical, of light 
traversing them, by a definite amount for each unit of 
thickness. Syn. rotatory polarization. 
optischer Zeiger: optical lever. A laboratory device 
for measuring angles of deflection by means of a long 
beam of light reflected from a small mirror. Syn. mir- 
ror and scale. 
Optometrie: optometry. A branch of optics dealing 
with the optical performance of the individual eye and 
with measurements upon it. 
ordentlich: ordinary. Pertaining to that plane-polar- 
ized component of a ray of light which, in traversing 
a unaxial crystal, has its electric vector at right angles 
to the principal plane. It obeys the Snell law of re- 
fraction. 
Ordnung: order. The integral number of wave lengths 
or cycles in the phase difference between two mutually 
amplifying wave trains, as in the production of inter- 
ference bands or diffraction spectra. Successive bands 
or grating spectra are of the first, second, , 
nth order. 
Ordnungszahl: ordinal number. (1) The number of a 
line in a rotation-vibration spectral band, counting 
either way from the zero line. In the R branch the 
numbers are +, in the P branch they are—. (2) An 
integer denoting the position of a term in a spectral 
series, the value for the lowest term being fixed by 
arbitrary convention. Syn. atomic number. 
Orientierung: orientation. The assignment or imposi- 
tion of a definite direction in space. 
orthobar: orthobaric. A term used to characterize the 
densities or specific volumes of the phases which are in 
thermodynamic equilibrium in any closed system; most 
commonly applied to the coexistent liquid and vapor 
phases of a one-component system. 
orthochromatisch: orthochromatic. A term which, in 
reference to photographic materials, implies equal sen- 
sitivity to all colors; a condition which is by no means 
fulfilled in fact. The term really indicates that the 
material is sensitive to green äs well as to shorter wave 
lengths. See also isochromatisch. 
orfhorhombisch: orthorhombic. In re crystal structure: 
having three mutually rectangular axes, no two of which 
are equal. 
or+hoskoplsch: orthoscopic. Free from optical dis- 
tortion. 
orthotom: orthotomic. In re a system of light rays: 
so disposed that they may all be cut at right angles 
by a suitably chosen surface. 
Osborne-Reynolds'sche Stroemung: Osborne-Reynolds 
streaming. The movement of a gas from cold to hot 
along a surface having a temperature gradient of suit- 
able magnitude. It is prominent in thermal transpira- 
tion, and also appears to be responsible for at least a 
part of the radiometric forces in gases at intermediate 
pressure. 
Osmometer: osmometer. An apparatus for measuring 
the rate of osmosis. 
Osmose: osmosis. The undirectional diffusion, of fluids 
through membranes or porous partitions, which results 
in osmotic pressure. The phenomenon is termed endos- 
mosis when the diffusion is inward, toward the interior 
of the osmotic cell; exosmosis, when it is outward. 
osmotischer Druck: osmotic pressure. See Osmose. 
Oszillograph: oscillograph. An instrument which ren- 
ders visible, or automatically traces, a curve representing 
the time variations of electric phenomena. The recorded 
trace is an oscillogram. Developed largely by Duddell 
and Braun. 
Oszilloskop: oscilloscope. An instrument similar to an 
oscillograph, and with which oscillatory phenomena are 
observed visually. 
Otto'scher Kreislauf or Otto Zyklus; Otto cycle, Beau 
de Rochas cycle. The thermodynamic cycle of the ordi- 
nary, four-stroke, internal combustion engine; commonly 
called the Otto cycle. 
Ovalzirkel; trammel. See Ellipsenzirkel. 
105 
/ p-Elektron p 
p-Elek+ron: p-electron. An orbital electron whose azi- 
muthal quantum number is 1. 
P Serie: P series. A series of frequencies believed to 
exist in the X-ray spectrum of an element and to arise 
from the transition of electrons from various higher 
quantum states to the state whose principal quantum 
number is 6. Not to be confused with p-series, some- 
times used as an abbreviation for principal series. 
P-Zustand: P-state, P-level. The state of an atom in 
which the azimuthal quantum number is unity. 
P Zweig: P branch. A set of molecular spectrum lines 
corresponding to unit increases in rotational quantum 
number. 
Paar: couple. (1) (Dyn.) A system composed of, or 
equivalent to, two equal, antiparallel forces. (2) (Elec.) 
A pair of metals placed in contact, as a voltaic couple 
or a thermocouple. 
Pachimeter: pachimeter. An instrument for measuring 
the elastic shear limit of a solid material. 
Packungsanteil; packing fraction. The ratio of the 
amount, by which the atomic weight of an isotope dif- 
fers from the nearest integral value, to that atomic 
weight; expressed in ten-thousandths of a unit. E.g., for 
berylium, of atomic weight 9-02, the packing fraction is 
m is the molecular weight, T the surface tension, and 
p and 8 the densities of liquid and vapor, respectively. 
parakristalliner Zustand: par aery stalline state. An in- 
cipient crystallization, i.e., the arrangement or arraying 
of the molecules of a substance as it approaches the 
crystallization point. 
Parallaxe: parallax. The change in the apparent posi- 
tion of an object, or in its direction from the observer, 
due to a movement of the observer. 
parallel: parallel. See mannigfaltig. 
paramagnetisch: paramagnetic. Having a magnetic 
permeability greater than unity, and susceptibility there- 
fore positive; yet not ferromagnetic. 
Parameter: parameter. (1) One of the constants en- 
tering into a functional equation and corresponding to 
some characteristic property, dimension, or degree of 
freedom. (2) The ratio of the displacement of an atom 
from its normal position within a crystal to the lattice 
constant in the direction of displacement. (3) The dis- 
tance from the origin of* the axes of a crystal to the 
intersection of any axis with a face, or a face produced, 
in terms of the arbitrary unit selected for measurement 
along that axis. 
parametrische Ebene: parametral plane. A crystal 
plane whose parameters are all unity and whose Miller 
indices are therefore (111). 
Parasit: parasite. A current in a circuit, due to some 
unintentional cause, such as inequalities of temperature 
or of composition; particularly troublesome in electrical 
measurements. 
paraxial: paraxial. In re light rays traversing an opti- 
cal system: close to and making only small angles with 
the axis. 
Pascal'sches Gesetz: Pascal law. States that such part 
of the pressure in a fluid as is due to externally applied 
forces (not to gravity, inertia, electrical potential, etc.) 
has the same value throughout the body of fluid when 
the latter is in equilibrium. 
Paschen-Back'scher Effekt: Paschen-Back effect. A mag- 
netooptical phenomenon, related to the Zeeman effect, 
but produced only in the most intense magnetic fields. 
Discovered by Paschen and Back in 1921. 
Paschen'sches Gesetz: Paschen law. States that the 
sparking potential between two given terminals in a 
given gas is a function of the product of the pressure 
by the spark length. It follows that for a given p.d., 
the spark length is inversely proportional to the pressure. 
0.02/9.02 — 22.17 X IO“4. 
PackungsefFekt: packing effect. The existence of a 
mass defect in the nucleus of an atom, attributed by 
some to an emission of energy upon the building to- 
gether of the component parts of the nucleus. 
panchromatisch: panchromatic. A term applied to 
photographic materials which are sensitive to all wave 
lengths within the visible spectrum (though not uni- 
formly so; different panchromatic materials vary con- 
siderably in the wave-length distribution of their sen- 
sitivity). 
parabolische Geschwindigkeit: parabolic velocity, p. 
speed. The speed with which a particle at any point 
in the field of a gravitational attracting center must be 
endowed in order that its orbit shall be a parabola. If 
the point is at the surface of the gravitating mass (as a 
planet), this speed is the same as the velocity of escape. 
Syn. critical speed. 
Parachor: parachor. A term due to Sugden, pertaining 
to a liquid and its saturated vapor, and denoting the 
(constant) value of the expression 
mr 1/4 
p — 8 
/Paschen Serien 
106 p 
Paschen Serien: Paschen series. A series of infrared 
spectral lines of the hydrogen spectrum, whose frequen- 
cies are multiples of 
more accurately, when arranged in the order of their 
atomic numbers (as pointed out by Moseley). An ar- 
rangement of the elements to exhibit this principle is 
called the periodic table or the periodic system. 
Periodizitaetsmodul: modulus of periodicity. The 
change which takes place in the action during one 
complete cycle of a periodic process. 
Periodogramm: periodogram. A curve or graph rep- 
resenting a periodic variation, such as the wave form 
of a complex musical sound. 
Periodometer: periodorneter. See harmonischer An- 
alysator. 
peripheres Elektron: peripheral electron. One of the 
outer electrons of an atom, to whose activity the spectral 
lines of visible light and thermal radiation are attributed, 
and which are supposed to be responsible for chemical 
combination. Syn. valence electron. 
Permalloy: permalloy. One of a series of alloys of 
nickel, iron, and sometimes small quantities of other 
metals, as chromium or molybdenum, having abnormally 
high magnetic permeability. A typical permalloy is 
composed of 78.5 percent Ni and 21.5 percent Fe. 
permanente Achse: permanent axis. An axis about 
which a free rigid body, when once set rotating, will 
continue to rotate in stable equilibrium. It is in general 
the principle axis of greatest moment of inertia through 
the c.m. 
permanentes Gas: permanent gas. A gas, such as 
hydrogen or nitrogen, whose critical temperature is far 
below normal atmospheric temperatures, and which 
therefore retains its gaseous state at all pressures. 
permanente Veraenderung: permanent set. A defor- 
mation which persists after release from stress. 
Permanenzprinzip: permanence principle. Either of two 
"sum rules” relating, respectively, to the sums of the 
Lande factors and interval factors of the components 
in the Zeemann effect; which state that the sum of 
the values of the factor in question for all the J values, 
other quantum numbers remaining constant, is indepen- 
dent of the magnetic intensity. Syn. sum rule. 
Permeabiiitaet: permeability. (1) (Magnetic.) The 
ratio of the magnetic induction to the magnetic inten- 
sity in the same region. In paramagnetic matter the 
permeability is nearly independent of the magnetic in- 
tensity; in a vacuum it is strictly so. But in ferromag> 
netic matter the relationship is definite only under fully 
specified conditions. (2) (Porous.) The volume of a 
1 1 
32 n2 
in which n - 4, 5, 6, 
passive Widerstand: passive resistance. A condition 
within a system in unstable equilibrium which keeps 
it from releasing energy and becoming stable until 
slightly disturbed, e.g., a cocked gun or a supercooled 
liquid. 
Pauli'sches Prinzip: Pauli principle. States that no two 
electrons in the same atomic or molecular system can 
have ?U their quantum numbers identical; discovered 
by Pauli, 
Peltier'scher Effetk: Peltier effect. The heating or cool- 
ing effect produced at the junction between two metals 
by a current sent across the junction (exclusive of the 
Joule heat due to resistance) ; depending upon the di- 
rection of flow. Discovered by Peltier in 1834. Heat 
so evolved or absorbed is called the Peltier heat. 
Pel+ier'sche elektromotorische Kraft: Peltier electromo- 
tive force. That component of the e.m.f. of a thermo- 
couple which corresponds to the local Peltier heats at 
the junctions between the different metals, and is added 
to the Thomson e.m.f. to make up the total (Seeheck) 
thermoelectromotive force. 
Peltier'scher Koeffizient: Peltier coefficient. The quan- 
tity of heat (Peltier heat) developed or absorbed per 
second per ampere of current at a given thermo junction 
in the Peltier effect. 
Peitier'sche Waerme: Peltier heat. See Peltier effect. 
Pentankerzenstaerke: pentane candle. A unit of inten- 
sity of a light source, equal to one-tenth of the intensity 
of the standard pentane lamp. Its value is approximately 
equal to the international standard candle. 
Penthode: pentode. A type of vacuum tube having 
five elements, viz., the filament, the plate, and three 
grids. 
Periode: period. The time interval during which a 
vibrating body completes one vibration. In this time 
the body in the reference circle makes one revolution. 
periodisches Gesetz: periodic law. The principle that 
certain properties of the elements recur in regular cycles 
when the elements are arranged in the order of their 
atomic weights (as discovered by Men dele j efj), or, 
107 
/Permeabili+ae+smesser p 
fluid of unit viscosity which, in unit time, passes through 
unit cross section of a porous medium under unit pres- 
sure gradient. 
Permeabilitae+smesser: permeameter. An instrument 
for measuring the average magnetic permeability of a 
ferromagnetic sample. 
Permeameter: permeameter. See Permeabilitaetsmesser. 
Permeanz: permeance. The reciprocal of the magnetic 
reluctance. 
Perminvar: perminvar. One of a series of alloys of 
iron, nickel, and cobalt, whose magnetic permeability 
is constant at different magnetic intensities, i.e., for 
which the induction is proportional to the magnetizing 
field. 
Permitivitaet: permittivity. See elektrische Konstante. 
PetzvaPsche Bedingung: Petzval condition. A criterion 
stated by Petzval for the flatness of an image formed by 
a refracting optical system of S surfaces. If the radius 
of curvature of the sth refracting surface through which 
the light passes is rs and its refractive index is ns, the 
condition is expressed by the summation 
Phasendiagramm: phase diagram, equilibrium curve. 
A graph representing the relation between values of 
two variables of state, as temperature and pressure, for 
which there is equilibrium between two states or phases. 
E.g., the fusion curve follows the equilibrium between 
solid and liquid states; the vaporization or saturation 
c., that between liquid and satured vapor states; and 
the sublimation c., that between solid and vapor states. 
Phasendichte: density-in-phase. The number of points, 
each of which corresponds to one of the particles of a 
system, per unit volume of the phase space used to rep- 
resent the state of the system. 
Phasengeschwindigkeit: phase velocity. A vector whose 
direction is normal to the wave front and whose magni- 
tude is the speed of propagation of a plane-wave dis- 
turbance. Syn. wave velocity. 
Phasengleichgewicht: phase equilibrium. An equi- 
librium between two or more interconvertible phases of 
a substance, as between ice, water, and water vapor, or 
between a solute and its satured solution. 
Phasenkonstante: phase constant. In re a harmonic, 
cyclic process: the constant term in that linear function 
of the time which appears as the argument of the sine 
or cosine factor in the expression for the cyclic variable. 
E.g., for an a.c. 
I = I0 cos (27rnt + A) 
A is the phase constant. 
Phasenmesser: phase meter. An apparatus for measur- 
ing phase differences between a.c.’s or electric oscil- 
lations. 
Phasenraum: phase space. An ideal, multidimensional 
space in which the coordinates represent the variables 
required to specify the state of a substance or of a 
system. Syn. extension-in-phase. 
Phasenregel: phase rule. A law of equilibrium be- 
tween phases or a chemically homogeneous mixture (as 
a solution) or of a pure substance; stated as follows: 
the number of degrees of freedom, or the variance, of 
the system is equal to the number of components in the 
mixture, minus the number of phases involved, plus 2. 
E.g., if the substance is pure and we include all three 
possible phases, there is no degree of freedom, three- 
phase equilibrium existing only at the triple point; but 
if we consider only the liquid and the vapor states, a 
pure substance has. one degree of freedom, i.e., along 
the vaporization curve. First stated in general form 
by J. W. Gibbs. 
S=s 1 r 1 1 "I 
Z “ — = °- 
s=1 rs *- ns ns—1 j 
Pferdestaerke: force de cheval (Fr.), metric horse- 
power. ( 1) A metric gravitational unit of power, equal 
to 75 m-kg of work per second, and equivalent to about 
736 watts or 0.9863 hp.. (2) An English gravitational 
unit of power based originally upon Watt’s experiments 
with horses, and now standardized ft-lb per second. 
Equivalent to about 746 watts. 
Pfund Serie: Pfund series. A series believed to exist 
in the far infrared spectrum of hydrogen, in which the 
frequencies are characterized by the factor 
1 1 
_ , n = 6, 7, 8, 
52 n2 
Phase: phase. (1) A quantity which denotes the stage 
of progress of any cyclic operation, as a vibration; often 
expressed as an angle, by analogy with rotation. Thus 
if the cycle is one-third completed, the phase is 2tt/3 
or 120 degrees, etc. (2) One of two or more dissimilar 
components of a body of matter, segregated from each 
other by interfaces dependent on their dissimilarity; 
e.g., two immiscible liquids in contact, or the solid, 
liquid, and vapor phases of one substance in three-phase 
equilibrium. 
Phasenumkehrung: phase reversal. A change of phase 
/Phasenwelle p 
equal to one-half cycle, such as may be experienced by 
light waves upon reflection under certain conditions. 
Phasenwelle: phase wave-de Broglie wave. A wave or 
wave group assumed in wave mechanics to be associated 
with an elementary particle (electron, proton). 
Phasenwinkel: phase angle. The phase difference be- 
tween the impressed e.m.f. and the current in an a.-c. 
circuit, expressed as an angle. 
Phona itogroph: phonautograph. An early device for 
recording the wave form of sounds; designed by Koenig 
and ccoct. 
Phonetik: phonetics. See Lautlehre. 
phonetisches Rad: phonic wheel. A type of syncho- 
nous motor geared to a revolution counter, which can 
be used to measure the frequency of the alternating or 
interrupted current driving it. The modern synchronous 
electric clock operates on a similar principle. Devised 
by La Cour. 
Phonometer: phonometer. An instrument for the 
measurement of the intensity of sounds. 
Phosphor: phosphor. Any substance which is phos- 
phorescent; esp. a synthetic material. 
Phosphoreszenz: phosphorescence. A form of lumines- 
cence in which the emission of light continues for a 
time after the exciting stimulus has ceased. 
Phosphorogen: phosphorogen. A substance which pro- 
motes phosphorescence in another, as manganese does 
in zinc sulphide. 
Phosphoroskop: phosphoroscope. An apparatus for ob- 
serving and measuring the decay of phosphorescence. 
Phot: phot. A unit of illumination, equal to 1 lumen 
per cm2, or 10,000 luxes. 
Phofoaktivitaef: photoactivity, photoconductivity. Elec- 
trical conductivity due to photo-ionization, e.g., in gases 
or in many nonmetallic crystals. Syn. photoactivity, pho- 
tosensitivity. 
Photoaniso+ropie: photo-anisotropy. The property of 
having different optical constants in different directions, 
possessed by many crystals, and by other substances un- 
der special anisotropic conditions. 
phofochemisch: photochemical. Pertaining to the 
chemical activity of molecules, ions, and atoms brought 
about by the absorption of radiant energy. 
photochemisches Aequivalent: photochemical equiva- 
lence. The principle, enunciated by Einstein, that in 
photochemical action each effective light quantum is 
transformed entire into chemical energy. 
Photodichtemesser: photodensitometer, Syn. densitome- 
ter. A form of photometer used especially for measuring 
the density of silver deposits on photographic plates or 
films. 
Photodissoziation: photodissociation. The dissociation 
of a chemical compound by the action of radiant energy. 
Syn. Photodisintegration. 
Photosffekt: photoeffect, Syn. photoelectriceffect. See 
oberflaechenphotoelectrischer Effekt. 
photoelastisch: photoelastic. Pertaining to the study 
of elastic phenomena in transparent solids by means of 
their effects on transmitted polarized light; esp. that 
of forced double refraction. 
photoelektrisch: photoelectric. See oberflaechenphoto- 
elektrischer effekt. 
photoelektrische Absorption: photoelectric absorption. 
The conversion of radiant energy into the energy of 
photoelectric emission. 
photoelektrisch Arbeitsfunktion: photoelectric work 
function. The work function for the emergence of 
photoelectrons from a given metal. 
ohotoelektrische Ausbeute: photoelectric emissivity, 
Syn. photoelectric yield, p. sensitivity, spectral sensitiv- 
ity. The rate of photoelectric emission from a metal 
per unit radiant flux of any given frequency. 
photoelektrischer Effekt: photoelectric effect. See Pho- 
toeffekt. 
photoelektrische Emission: photoelectric emission. See 
oberflaechenphotoelektrischer Effekt. 
photoelektrisches Emissionsvermoegen: photoelectric 
emissivity. See photoelektrische Ausbeute. 
photoelektrische Empfindlichkeit: photoelectric sensi- 
tivity, Syn. photoelectric yield. See photoelektrische Aus- 
beute. 
photoelektrisches Grenzpotential: photoelectric limit- 
ing potential. The stopping potential for the fastest elec- 
trons in a given photoelectric emission. 
photoelektrischer Grenzwert: photoelectric threshold. 
See Langwellige Grenze. 
109 
/photoelektrischer Konstante p 
photoelektrische Konstante: photoelectric constant. A 
quantity which, multiplied by the frequency of any 
radiation exciting photoemission, gives in c.g.s. units 
the p.d. corresponding to the quantum energy absorbed 
by the escaping photoelectron. Equal to h/e, where h 
is the Planck constant and e the electronic charge. 
photoelektrischer Schwellenwert: photoelectric thresh- 
old. See langwellige Grenze. 
photoelektrischer Strom: photoelectric current. See 
oberflaechenphotoelektrischer Effekt. 
photoelektromotorische Kraft: photoelectromotive 
force. An e.m.f. due to photovoltaic action. 
Photoelektron: photoelectron. See oberflaechenphoto- 
elektrischer Effekt. 
Photoemission: photoemission, Syn. photoelectric emis- 
sion. See oberflaechenphotoelektrischer Effekt. 
Photoempfindlichkeit: photosensitivity. The property 
of exhibiting any kind of photoelectric effect when 
irradiated, e.g., photoelectric emission, photoconductiv- 
ity, or photovoltaic action. 
Photogen: photogen. A substance which emits light 
by luminescence. 
Photogoniometer: photogoniometer. An apparatus for 
studying various aspects of crystal X-ray diffraction and 
X-ray spectra. May be used as an X-ray spectrograph 
or as a goniometer. 
Photoionisation: photo-ionization. Ionization in a gas 
which results from the action of radiation quanta, esp. 
those of visible light or ultraviolet. 
Photokathode: photocathode. The illuminated elec- 
trode, at a negative potential, in a photoelectric cell. 
Photokernspaltung: photodisintegration. The disinte- 
gation of an atomic nucleus by the action of radiant 
energy. 
Photoleitfaehigkeit: photoconductivity. Electrical con- 
ductivity due to photo-ionization, e.g., in gases or in 
many nonmetallic crystals. Syn. photoactivity, photo- 
sensitivity. 
Photolumineszenz: photoluminescence. Luminescence 
of which the stimulating cause is visible light or ultra- 
violet. 
photomagnetischer Effekt: photomagnetic effect. The 
direct effect of light upon the magnetic susceptibility of 
certain substances. 
Photometer: photometer. See Lichtmesser. 
Photometerkopf: photometer head. That part of a 
photometer which comprises the screen, the means of 
viewing it, and the accessories used in judging the equal- 
ity of illumination. 
photometrischer Mittelpunkt: photometric center, p. 
centroid. That point of a luminous or of an illumi- 
nated surface which bears the same relation to the dis- 
tribution of brightness or of illumination that the cen- 
troid of a thin plate bears to the distribution of its mass 
per unit area. Syn. luminous center of gravity. 
Photon: photon. An energy quantum of visible light; 
or in general, of any electromagnetic radiation. 
Photonenstoss: photo impact. The impact of a photon 
or light quantum, as in such processes as photo-ioniza- 
tion or photoelectric emission. 
Photoneutron: photoneutron. A neutron emitted as 
the result of photodisintegration. 
Photophorese: photophoresis. A propulsive effect of 
an intense beam of light upon very small particles (of 
the order of 1 micron in diameter) in suspension in 
the air; the particles moving either toward or away 
from the light source. The effect becomes less as the 
pressure increases. In electrophotophoresis (photopho- 
resis in an electric field) and in magnetophotophoresis 
(photophoresis in a magnetic field), the particles have 
a component of motion in the direction of the field. 
Pho+os+rom: photocurrent. A photoelectric or a photo- 
voltaic current. 
Pho+ostromkoeffizient: photocurrent coefficient. The 
change in the photocurrent generated by a photoelectric 
or a photovoltaic cell, per unit change in radiant flux 
producing it. 
photovoltaisch: photovoltaic. Capable of acting as a 
source of e.m.f. under the influence of light. 
Photozelle: photocell, photoelectric cell, photronic cell. 
(1) See lichtelektrische Zelle. (2) A type of photovol- 
taic cell using selenium. 
photometrisches Zentrum: photometric center, p. cen- 
troid. See photometrischer Mittelpunkt. 
physikalische Gleichung: physical equation. An equa- 
tion, each term of which represents a concrete physical 
/Pi Ebenen 
110 _p 
quantity, or which contains symbols representing such 
quantities. 
Pi Ebenen: Pi-planes. Atomic planes bounding crevices 
in the mosaic structure of a crystal. Sometimes called 
Zwicky pi-planes. 
Piezo-dielektrisch: piezo-dielectric. Pertaining to changes 
in dielectric constants resulting from mechanical stress. 
Piezo-elektrisch: piezo-electric. Characterized by the 
property, exhibited by certain crystals, of becoming elec- 
trically polarized and of developing charges of "piezo- 
electricity” when subjected to strain. 
Piezo-elektrische Achse: piezo-electric axis. See elek- 
trische Achse. 
Piezo-elektrischer Generator: piezo-electric oscillator, 
p.-e. generator. An electric oscillating system containing 
as one of its elements a piezo-electric resonator by which 
the frequency is controlled. Syn. piezo-oscillator. 
Piezo-elektrische Konstanten: piezo-electric constants. 
The constants in the linear equations expressing the elec- 
tric polarization developed in a deformed crystal in 
terms of the components of strain and the components 
of stress. 
Piezo-elektrischer Oszillator: piezo-electric oscillator, 
p.-e. generator. See Piezo-elektrischer Generator. 
Piezo-elektrischer Resonator: piezo-electric resonator. 
A plate or rod of piezo-electric crystal which may be 
excited electrically into resonant vibration at one or 
more frequencies. The term is commonly applied to 
the combination of the piezo-electric body with elec- 
trodes in a suitable mounting. Developed by W. G. 
Cady. 
Piezolumineszenz: piezoluminescence, Syn. tribolumi- 
nescence. Luminiscence caused by grinding, in such 
substances as glass and certain crystals. Tribothermo- 
luminescence refers to the same phenomenon, when heat 
is required subsequent to the grinding. 
Piezometer: piezometer. See Fluessigkeitsmanorneter. 
Pilotballon: pilot balloon. A small balloon released 
for the purpose of studying the movements of the air. 
Pirani-Manometer: Pirani gauge. A type of hot-wire 
gauge which, as improved by Hale, has a filament re- 
sembling that in an incandescent lamp. The filament 
temperature is deduced from its resistance. 
Pitot-Manometer: pitometer. An instrument, utilizing 
the principal of the Pitot tube, which makes a continu- 
ous record of the variations in velocity of a liquid 
stream. Devised by Code. 
Pitometer: pitometer. See Pitot-Manometer. 
Pitof'sche Roehre: Pitot tube. A narrow tube inserted 
in a fluid stream with its open end facing the current, 
and communicating at the other end with a manometer; 
used for measuring the speed of flow. 
Planck-Einstein Gleichung: Planck-Einstein equation. 
The equation 
hv — Ve 
11 v;nax — Y 
which is the mathematical expression corresponding to 
the Duane-Hunt law for the conversion of electron 
energy into X-ray quanta. vmax is the maximum X-ray 
frequency evoked by an electron e which has acquired 
its energy from a potential increment V; h is the Planck 
constant. An equivalent form of the relation is AV — 
1.234 x 10~4 cm-volt, in which A is the X-ray wave 
length. 
Planck'sche Farbe: Planckian color. The color or the 
wave-length-intensity distribution of the light emitted 
by a black body at a given temperature. 
Planck'sches Gesetz: Planck law. The statement that 
the value of the quanta of radiation of any frequency 
is proportional to the frequency, as expressed by the 
equation 
q = hv 
in which v is the frequency and h the Planck constant. 
First enunciated by M. Planck in 1900. 
Planck'sche Gleichung: Planck equation. A formula 
expressing the spectral energy distribution of black-body 
radiation at a given absolute temperature T in terms 
of wave length A. The emissive power of the black 
body within the wave-length range dA is given as 
dEA = 27rC2hA~5 [ 1 dA 
L eKXT _ ! J 
in which c is the electromagnetic constant, h the Planck 
constant, and k the Boltzmann constant. An alternative 
form gives the radiant energy density within the black- 
body cavity as , 
87TC2hA-5 1 1 dA. 
L eKXT — 1 J 
Planck'sche Konstante: Planck constant. A constant 
h having the dimensions of action (energy x time) 
and appearing in many physical formulas; approxi- 
mate value, 6.547 X 10“27 erg-sec. In particular it 
/Planck'scher Strahler 
677865—46 8 p 
represents the ratio of the energy of any radiation quan- 
tum to its frequency. First recognized by Planck in 
1900. Syn. elementary quantum of action. 
Planck'scher Strahler: Planckian radiator. An ideal 
black body. 
Planck'sehe Verteilung: Planckian distribution. See 
Planck’sche Gleichung. 
Planimeter: planimeter. An instrument used to meas- 
ure the area of any closed, plane figure traced on paper. 
A well known type which makes use of polar co-ordi- 
nates about a fixed pivotal point is called a polar plani- 
meter. 
plankonkav: plano-concave. Having two surfaces, one 
of which is plane and the other concave; applied esp. 
to lenses. 
plankonvex: plano-convex. Having two surfaces, one 
of which is plane and the other convex; applied esp. 
to lenses. 
) 
Plasma: plasma. That part of an electric discharge 
in a rarefied gas which contains electrons and positive 
ions in such relative numbers that their charges nearly 
neutralize one another. 
Plasmoid: plasmoid. One of a class of luminous bodies 
of various shapes which appear in highly exhausted tubes 
under excitation of very high frequency, and which are 
not as yet well understood. 
Plastimeter: plastometer, Syn. mohilometer. An ap- 
paratus for measuring the plasticity of a substance. 
Plastizitaet: plasticity. A property of some solids, by 
virtue of which they begin to exhibit continuous shear, 
or to flow, when subjected to shearing stress of sufficient 
magnitude. 
Plastometer: plastometer. An apparatus for measuring 
the plasticity of a substance. 
Piattenelektrode: plate. Any flat electrode, as of a 
storage cell or a condenser. 
Platteninterferenzspektrum: channeled spectrum. A 
spectrum containing interference bands, produced by 
light which has been reflected from two parallel sur- 
faces, such as those of a thin glass plate. 
Platinit: platinite. An alloy of nickel and iron (about 
46 percent Ni), whose expansion coefficient is nearly 
equal to that of platinum, and which may therefore be 
used to replace that metal for lead wires in vacuum 
tubes. 
Platinrhodium: platinrhodium. An alloy of platinum 
and rhodium, commonly used in thermocouples. 
Platinstandard: platinum standard. A unit of luminous 
intensity proposed by J. Violle, viz., that of 1 cm2 of 
the surface of molten platinum at its melting point. 
Syn. Violle standard. 
Pleochroismus: pleocbroism. The property, possessed 
by certain crystals, of exhibiting different absorption 
colors as viewed in the direction of the different crystal 
axes; e.g., iolite, which appears dark blue, light blue, 
and yellow with light transmitted along the respective 
axes. Syn. polychroism. 
ploetzliche Gasaufzehrung: leanup. The gradual dis- 
appearance of gases from a discharge tube during its 
operation. 
Pneumatik: pneumatics. That branch of physics which 
deals with the dynamic properties of gases. 
Poinsot'sche Bewegung: Poinsot motion. The motion 
of a rigid body having one point fixed, the resultant 
of all forces acting upon which is zero. 
Poinsot'scher Lehrsatz: Poinsot theorem. States that 
when a rigid body moves about its fixed c.m. under 
no forces, the energy ellipsoid, fixed in the body, rolls 
without slipping on a plane fixed in space (the invari- 
able plane) ; and the vector from the fixed point to the 
point of contact represents the instantaneous angular 
velocity of the body in direction and magnitude. 
Poinsot Prozession: Poinsot precession. The preces- 
sional rotation of a nonsymmetrical body, i.e., one which 
has three principal axes with different moments of in- 
ertia; as distinguished from regular precession. 
Poise: poise. A unit of viscosity, for wdiich the vis- 
cosity coefficient is equal to 1 dyne-sec/cm2. Named 
from Poiseuille. The practical unit for solutions, etc. 
is the centipoise, or 0.01 poise. 
Poiseuiüe'sches Gesetz: Poiseuille law. Expresses the 
(volume) rate of flow through a capillary as follows; 
dV 7rf4Ap 
dt 8^1 
Ap = pressure difference, r — radius, 1 = length of 
capillary, rj = viscisity coefficient of fluid. 
Poisson'sche Gleichung: Poisson’ equation. A differ - 
/Poisson'sche Klammer, P. Klammerausdruck 
112 p 
ential equation relating the potential function to the 
density at any point. For the gravitational potential 
function V it is 
V2 V zz — 4irp 
where p is the (mass) density. 
to correspond to the vibrations of the magnetic vector 
as the wave progresses. If the polarization is produced 
by reflection, it coincides with the plane of that re- 
flection. 
Poiarlsationsfarbe: polarization tint. A coloration of 
the field of a polariscope analyzer when using a white- 
light source, due to the emergence of the different wave 
lengths from the analyzer with altered relative inten- 
sities. 
Polarisationskapazitaet: polarization capacitance. The 
capacitance of the condenser formed by the two elec- 
trodes of a cell. 
Polarisationskreis: polarization cycle. A closed figure 
formed by the terminus of the vector representing the 
vibrations in a beam of radiation polarized in any given 
manner. For plane-polarized light, it is a straight line; 
for elliptically polarized light, it is an ellipse; etc. 
Polarisationsphotometer: polarization photometer. A 
photometer in which the intensity of the light from 
one or both sources is varied by the use of polarizing 
apparatus. 
Polarisationswinkel: polarizing angle. The angle at 
which light must be incident upon the surface of a di- 
electric reflector in order to experience maximum plane- 
polarization. Syn. Brewster angle. 
Polarisator: polarizer. A Nicol prism or other device 
for polarizing light, esp. one introduced into a polari- 
scope to receive the light as it enters. 
Polarisierbarkeit: polarizability. A quantity a pertain- 
ing to the molecules of a dielectric and defined as the 
molecular electric dipole moment per unit electric inten- 
sity. It is connected with the dielectric constant k 
through the relation. 
Poisson'sche Klammer, P. Klammerausdruck: Poisson 
bracket. An abbreviated notation used in mechanics. 
The Poisson bracket of Fr and Fs with respect to the 
variables p:, p2, , pM, qx, q2 , q„ is 
defined a;-. 
r -j E k=n / 8Fr 8FS 8FS 8Fr . 
tFrF-J =£ t 
Poisson'sches Verhaeitnis, Poisson'sche Verhaeltniszahl: 
Poisson ratio. The ratio of the fractional transverse con- 
traction to the fractional longitudinal extension of a 
body under tensile stress. Syn. rho ratio. 
Poisson'sche Verteilung: Poisson distribution. A sta- 
tistical distribution defined by the equation. 
ax e~a 
P = • 
x ! 
It is approximated by the Gaussian distribution when a 
is large. 
polar: polar. (1) Electrically nonsymmetrical, as a 
molecule which, like HC1, has an effective electric mo- 
ment. Syn. heteropolar. (2) In re a crystal structure: 
having an asymmetry in the location of certain sets of 
atoms. (3) Pertaining to or measured from a pole. 
polares Kerzenstaerkediagramm: polar candle-power 
diagram. See Lichtverteilungskurve. 
polares Traeghei+smoment: polar moment of inertia. 
An areal moment of inertia of a plane figure, but with 
respect to a line perpendicular to the plane instead of 
to a line lying in the plane. 
Polarime+er: polarimeter. A polariscope provided with 
circles or other equipment for making quantitative ob- 
servations upon the state of polarization. 
Polarisation: polarization. (1) (Dielectric.) In re a 
polarized dielectric: the electric moment per unit vol- 
ume. (2) (Electrolytic.) An alteration of the p.d. in 
an electrolytic cell by reason of a poorly conducting 
electrolytic deposit. (3) (Magnetic.) Syn. Magnetiza- 
tion. (Rare.). 
Polarisationsebene: polarization plane. A plane asso- 
ciated with a ray of plane-polarized radiation, believed 
3M k — 1 
a = , 
4ttN (k + 2)p 
in which M is the molecular weight, N the Avogadro 
number, and p the density. 
polarisieren: polarize. (1) To endow with poles, as 
a magnet. (2) To produce an electrical separation or 
orientation, esp. in the molecules of a dielectric. (3) To 
impress some spatial characteristic, as upon the vibrations 
identified with radiation; e.g., in elliptically polarized 
light. 
Polariskop: polariscope. An instrument for examining 
the state of polarization of light or other radiation, or 
for studying the polarizing properties of bodies. 
113 
/Polaritaet p 
Polaritaet: polarity. (1) The electrically positive or 
negative condition of a battery or generator terminal. 
(2) The magnetically positive (north) or negative 
(south) character of a magnetic pole. (3) The degree 
in which a molecule is polar. 
Polari+ae+seffekt: polarity effect. An asymmetry or in- 
equality in the current through a series of partial con- 
ductors, such as metallic sulphides or oxides, according 
to which way it is caused to flow; illustrated by crystal 
detectors. 
Poleffekt: pole effect. A discrepancy observed in the 
wave lengths of spectral lines when the light comes from 
the vicinity of the electrodes in an arc. 
Polhode: polhode. The curve which marks the inter- 
section of the energy ellipsoid and the momentum ellip- 
soid of a free rigid body. The term is due to Poinsot. 
polydispers: polydisperse. In re a disperse system: 
having particles of different sizes. 
Polykristall: polycrystal. A body made up of a number 
of small crystals in a mass. 
Polymer: polymer. (1) One of two or more isomers 
having different molecular weights, e.g., C2H2 (acety- 
lene) and C6H6 (benzene). (2) A complex molecule, 
or molecular aggregate, which may be considered as a 
multiple of some simpler molecule, e.g., H402 = 2 H20. 
Polymorphismus: polymorphism, Syn. allotropy, allo- 
tropism. But with especial reference to differences in the 
crystal structure. 
polytrop: poly tropic. Pertaining to a change during 
which the pressure and the volume vary in accordance 
with the relation pvn zz constant (the polytropic equa- 
tion), in which n has special constant values in different 
cases. E.g., for the Boyle law, n zz 1. 
Porro'sches Prisma: Porro prism. A triangular optical 
prism having one 90- and two 45-degree angles. Light 
entering perpendicular to the hypothenuse face emerges 
from the same face after two international reflections. 
Two of these are used in each telescope of the prism 
binocular. 
positiver Kristall: positive crystal. A unaxial, birefrin- 
gent crystal in which the extraordinary wave has the 
less velocity, e.g., quartz. 
positive Saeule: positive column. A striated, luminous 
region adjacent to the anode in a Crookes tube at mod- 
erate pressure. 
positive Strahlen: positive rays. A stream of posi- 
tively charged atoms or molecules, produced by a suit- 
able combination of ionizing agents, accelerating fields, 
and limiting apertures. 
Positron: positron. A positive charge having a mass 
equal to that of the electron, and electrically its counter- 
part. Its existence was first announced by Carl An- 
derson. Syn. positive electron. 
Potential: potential. A term applied to several dif- 
ferent scalar quantities, the measure of each of which 
involves energy as a function of position or of con- 
dition (potential energy). 
Potentialfunktion: potential junction. A function which 
constitutes the variable factor in the expression for any 
physical potential. 
Potentialgalvanometer: potential galvanometer. An 
instrument of the galvanometer type, having such high 
resistance as to take practically no current, so that the 
readings can be taken to indicate the p.d. between its 
terminals. 
Potentialloch: potential hole, p. well. A region toward 
which the electric potential drops abruptly and through- 
out which its value is distinctly lower than on either 
side; a term common in nuclear physics. 
Potentialschranke: potential barrier. See Energiewall. 
Potentialschwelle: potential harrier. See Energiewall. 
Potentialstroemung: potential streaming. Fluid motion 
in which the velocity is the negative of a velocity poten- 
tial gradient, so that the flow is irrotational. If the fluid 
is incompressible, the lines of flow coincide with the 
lines of a possible electric field in empty space. 
Potentialwall: potential barrier. See Energiewall. 
potentielle Energie: potential energy. Any form of 
energy which is not demonstrably kinetic. 
Potenz: Power (math.). A number multiplied by it- 
self any number of times; the result of taking any num- 
ber of times as a factor. 
Poundal (engl. Einheit): poundal. The absolute Eng- 
lish (footpound second) unit of force which, acting 
upon a free mass of 1 lb, would impart to it an accelera- 
tion of 1 ft/sec2. i 
Powell-Bande: Powell bands. Interference bands pro- 
duced by the insertion of a transparent plate into a 
hollow prism which contains a liquid and is used to 
/Poynting'scher Lehrsatz 
114 p 
produce a spectrum, when the plate, with its edge 
parallel to the prism edge, covers only one half of the 
field. 
Poynting'scher Lehrsatz: Poynting theorem. States that 
the transmission of energy in an electromagnetic field 
takes place in a direction perpendicular to both electric 
and magnetic components, and that the rate of energy 
transfer is proportional to the vector product of those 
components (electric and magnetic intensities), called 
the Poynting vector or vector radiant. 
Poynting'scher Vektor: Poynting vector. See Poynt- 
ing’scher Lehrsatz. 
Praedissozlation: predissociation. (1) A state that ex- 
ists in a diatomic or polyatomic molecule which, usually 
after the absorption of light, has a tendency to disso- 
ciate spontaneously, usually into two uncharged parts. 
The resulting absorption bands are diffuse, lacking the 
usual rotational fine structure. (2) The process of de- 
composition from the state described under (1). 
Prozession: precession. A motion of the axis of a 
symmetrical rotating body, which slowly describes a 
cone with the centroid as vertex, due to the action of 
a small torque tending to change the direction of the 
axis; illustrated by a spinning top or gyroscope. The 
axis of the cone is the precession axis. 
Primaerelektron: primary electron. (1) An electron 
belonging to a primary emission. (2) That electron 
which, after a collision of two electrons, has the greater 
energy. 
Primaeremission: primary emission. Incident emission, 
which may excite secondary emission from the irradi- 
ated matter. If it is of the nature of radiation (ultra- 
violet, X-rays, etc.), it is usually called primary ra- 
diation. 
primaerer Pho+oeffekt: volume photoelectric effect. See 
innerer photoelektrischer Effekt. 
Primaerfarben: primary colors. Additive primaries are 
three colors which, added in proper proportions, produce 
a sensation of white; those usually chosen are red, green, 
and blue. Their complementaries, blue-green, purple, 
and yellow, respectively, are substractive primaries; if 
white light is passed in succession through transparent 
screens of these colors, it is completely absorbed. 
Primaerschaliung: primary circuit. A circuit, the vari- 
ation of the current in which induces an e.m.f. in a 
coupled, secondary circuit as in a transformer. Often 
abbreviated to primary. 
Primaers+andard: primary standard. A unit directly 
and originally defined and established by some authority, 
e.g., the standard meter at Sevres. 
Primaers+ruktur: primary structure. See Sekundaer- 
struktur. 
Primaerzelle: primary cell. A battery cell whose energy 
is intrinsic in the substances originally composing it, 
and not derived from charging as in a storage (secon- 
dary) cell. 
Prinzip der geringsten Arbeit: least-work principle. 
A special case of the principle of least energy which 
states, in reference to an elastic structure having re- 
dundant bars or members, that the stresses developed in 
the members by the application of loads are such as to 
render the total internal work throughout the structure 
a minimum. 
Prinzip der geringsten Energie: least-energy principle. 
States that a dynamic system is in stable equilibrium only 
for configurations in which the potential energy of the 
system as a whole has minimum values. 
Prinzip des geringsten Interwalls: least-interval prin- 
ciple. A principle analogous to the principle of least 
time or the principle of least action, but which requires 
that any natural sequence of events take place in such 
a manner that the section of the world line connecting 
them in the space-time continuum shall be shorter than 
for any other, arbitrary sequence of events. 
Prinzip der geringsten Wirkung: least-action principle. 
States that if a dynamic system passes spontaneously and 
without change in total energy from one configuration 
to another, the action involved in the process is a mini- 
mum; or (an equivalent statement) that the line integral 
of the momentum of each particle is a minimum. Enun- 
ciated by Maupertuis. 
Prinzip der kleinsten Quadrate: least-squares principle. 
A principle of the theory of errors, based upon the 
normal law of error, which states that the best estimate 
of an experimental quantity, deducible from a number 
of observations, is that for which the sum of the 
weighted squares of the residuals is least. 
Prinzip der kuerzesten Zeit: least-time principle. For 
points in two homogeneous media separated by a plane 
surface, or for reflection in a single homogeneous me- 
dium by a plane surface, the time is a minimum, in 
which case the law is commonly known as the principle 
of least time. 
Prinzip der virtuellen Arbeit: virtual-work principle. 
States that a condition for the equilibrium of a system 
is that the total virtual work due to ail internal and 
/Prisma mit konstanter Ablenkung p 
external forces acting upon the system is zero; or in 
other words, that the potential energy of the system is 
a minimum or a maximum or a constant. 
Prisma mit konstanter Ablenkung: constant-deviation 
prism. A triangular prism so designed that the devia- 
tion of a ray of light entering it by one face and leav- 
ing it by another after internal reflection at the third 
face is always equal to the angle between the two re- 
fracting faces. 
Probespule: exploring coil. A small coil which may 
be moved about within a magnetic field in order to 
test the magnetic intensity at various points by electro- 
magnetic induction. 
Produk+ionskoeffizient: production coefficient. The rate 
at which primary radiation produces secondary radia- 
tions with respect to the thickness of medium tra- 
versed. If dl2 is the intensity of secondaries produced 
in thickness dx by primary radiation of intensity Ix, 
the coefficient is 
d.-c. power line usually near the far end, which auto- 
matically adjusts the voltage to a varying load. The 
battery discharges on heavy load and recharges when 
the load is light. 
Puffergefaess: surge chamber. A cavity connecting 
with a water pipe or other conduit and containing air, 
which acts as a cushion to shocks caused by sudden 
pressure or stoppage of the flow, e.g., in a force pump. 
Pulverdiagramm: powder pattern, Syn. Hull ring, 
Debye r., Debye-Scherrer r. Sometimes called Halo, 
esp. in connection with diffraction effects from amor- 
phous materials. A pattern of parallel lines or bands 
of ferromagnetic powder deposited on the surface of a 
magnetized crystal. Syn. Bitter pattern. 
Pulvermethode: powder method. A method of crystal 
analysis, devised independently by Hull and by Debye 
and Scherrer, in which the varied orientation of the 
particles of the finely pulverized substance produces the 
same diffraction-ring pattern as would result from giving 
a single crystal all possible orientations. 
Punkt: dot. (1) A notation, attributed to Newton, 
consisting of a dot placed over the symbol for a varia- 
ble, and signifying the derivative of that variable with 
respect to time. Such quantities as velocity and accelera- 
tion are frequently thus represented. (2) One of the 
symbols of vector multiplication; placed between the 
symbols for two vectors, it designates their scalar 
product. 
Punktfunk+ion; point function. A variable quantity 
which is a function of the position of a point in space. 
E.g., the electric potential, the temperature, the value 
of g, etc., are point functions. 
Punk+gruppe: point group, Syn. space group. A group 
of points in space which has one of the types of sym- 
metry exhibited by crystals. 
Punktpol: point pole. A sharply defined magnetic pole, 
from which the field radiates almost as if from a point. 
Syn. magnetic charge, 
Punk+symmetrie: point symmetry. The term point sym- 
metry or radial symmetry is used if the reference zero 
is a point. See also Symmetrie. 
punk+zentrisch: homocentric, Syn. stigmatic. In re a 
bundle of rays: passing through a common point, or 
traversing lines which, if produced, would pass through 
a common point. 
Pyknometer: specific-gravity bottle. A small flask with 
a perforated stopper, which may be filled completely 
dl2/dx 
ß = 
Ii 
Prometazentrum: prometacenter. The center of curva- 
ture of a curve of buoyancy at any point. 
Proton: proton. An elementary particle, of mass about 
1.66 X 10~24 g (1845 times that of the electron) and 
with a positive charge equal to that of the electron 
(4.77 X 10-10 e.s.u.). The nucleus of the ordinary 
hydrogen atom is thought to be a single proton. 
Prototyp: prototype. An accurate copy of a primary 
standard unit. Syn. secondary standard. 
Prozentbruecke: percentage bridge. A type of slide- 
wire bridge, so adjusted that a change of 0.01 percent 
in the ratio of the two resistances compared requires, 
for balancing a change of one division on the slide 
scale. Devised by H. C. Parker. 
pseudomorph: pseudomorphic. Having a definite geo- 
metrical form for the external surface, but made up 
structurally of smaller crystals of a form quite different. 
Psychrometer: psychrometer, Syn. wet-and-dry-bulb 
thermometer. A hygrometer consisting of two identical 
thermometers, the bulb of one of which is kept wet 
with water supplied by a wick. The lowering of the 
temperature by evaporation indicates the relative hu- 
midity of the air. 
Pufferspannung: floating electromotive force. The 
e.m.f. supplied by a storage battery placed across a 
/Pyranometer 
116 p 
full of a liquid for the purpose of obtaining its density 
and specific gravity by weighing. 
Pyranometer; pyranometer. An instrument which meas- 
ures the intensity of the radiation received from any 
portion of the sky. 
pyro-elektrisch: pyro-electric. Characterized by the 
property, exhibited by certain asymmetric crystals, of 
becoming electrically polarized and of developing 
charges of "pyro-electricity” upon change of tempera- 
ture. The true pyro-electric effect results directly from 
the temperature change; there is a pseudo-pyro-electric 
effect which arises from strains due to alteration of 
temperature and which is therefore an indirect piezo- 
electric effect. 
pyroelektrische Konstante: pyro-electric constant. 
Change in the electric polarization of a pyroelectric cry- 
stal per unit change in temperature. 
Pyroheliometer: pyroheliometer, pyrheliometer. An in- 
strument for measuring the total intensity of solar radia- 
tion, both direct and scattered by the surrounding at- 
mosphere. Syn, solarimeter. 
Pyrometer: pyrometer. Any instrument for the meas- 
urement of high temperatures. 
Pyroskop: pyroscope. A form of optical pyrometer, 
devised by Shore. 
/Q Zweig o 
Q Zweig: Q branch. A set of molecular spectrum lines 
corresponding to changes in vibrational energy with 
none in rotational energy. 
Quadrantenelektrometer: quadrant electrometer. An 
electrometer consisting of a light, elongated metallic 
plate suspended horizontally within a flat metallic cylin- 
der divided into quadrants. The electric reaction be- 
tween the charged plate and the charged quadrants 
causes the former to turn against the torsion of the 
suspending wire. 
quadratische Skala: squared scale. A linear scale so 
graduated and numbered as to indicate the square of 
the distance from the zero point; used on some photo- 
meter benches. 
Quadruplet!: quadruplet. A group of lines in an 
atomic spectrum, • arising from transitions between the 
different components of two multiple spectral terms and 
hence exhibiting the characteristic frequency differences 
of these terms. The number is 4. 
Quadrupel: quadrupole, quadripole. A system consist- 
ing of two equal dipoles parallel to each other, but with 
their corresponding charges reversed. 
Quadrupollinien: quadrupole lines. A type of "for- 
bidden” spectral lines, whose infrequency of occurrence 
is interpreted as due to the action of the atom as an 
electric quadrupole instead of as the more usual dipole. 
Such lines exist, however, in the spectra of nebulae and 
the aurora. 
Qualltaet: quality. (1) That characteristic of a musi- 
cal sound which is dependent upon the wave form and 
hence upon the harmonic components and their relative 
intensities. Syn. timbre, tone color. (2) In re a system 
composed of the liquid and the vapor states of a pure 
substance the ratio of the mass of the vapor to the total 
mass of both phases. Syn. dryness. 
Quant: quantum, quant. (1) A discrete portion of 
energy, of definite amount, first associated with intra- 
atomic or intramolecular processes involving changes 
among the electrons and with the corresponding radia- 
tion. (2) Any supposed smallest portion of a magni- 
tude; e.g., the electronic charge is sometimes called a 
quantum of electricity. 
Quantenausbeute: quantum efficiency. The number of 
photoelectrons emitted from a metal per quantum of in- 
cident radiation. Syn. quantum yield. 
Quantenaequivalenzprinzip; quantum equivalence prin- 
ciple. The principle that when, in a photoelectric or 
/Quarzfadenmanometer 
photovoltaic process of any kind, a quantum of radia- 
tion is "absorbed,” its entire energy reappears in some 
other definite form, such as the kinetic energy of a 
released photoelectron, or the energy of an ionized atom. 
Quantenbedingung: quantum condition. The mathe- 
matical condition which must be satisfied for any given 
quantum state of an atom or other system to be possible. 
Quantendefekt: quantum deject. The principal quan- 
tum number for the electron responsible for a spectral 
series, minus the square root of the Rydberg denominator 
for any actual spectral term of the series. It is usually, 
but not always, positive. 
Quantengewicht: quantum weight, Syn. statistical 
weight. An integer corresponding to the number of 
different levels into which a given state is subdivided 
when the degeneracy is completely removed. 
Quantenkorrektion: quantum correction. A correction 
required by any classical law or formula to bring it into 
harmony with the quantum theory. 
Quantenmechanik: quantum mechanics. (1) A gen- 
eral physical theory which seeks to deal with atomic 
structure and related problems in terms of only those 
quantities which can be actually measured, and excluding 
such putely inferential concepts as the position or the 
velocity of an electron in a supposed orbit. It embraces 
the matrix mechanics of Heisenberg, the wave mechan- 
ics of Schroedinger, and the transformation theory of 
Jordan and Dirac. (2) The mechanics of phenomena 
which are subject to quantum conditions, such as the 
processes going on within and among atoms and 
molecules. 
Quantenstoss: photo-impact. See Photonenstoss. 
Quan+uebergang: quantum transition. An abrupt re- 
adjustment which is accompanied by the emission or 
the absorption of a quantum of radiant energy. Syn. 
quantum jump. 
Quantenzahl: quantum number. An integral number 
which is characteristic of the statement of a quantum 
condition. E.g., for a hydrogen atom (disregarding rela- 
tivity and spin corrections) the energy corresponding to 
any quantum state is inversely proportional to the square 
of the (principal) quantum number. 
Quan+enzahlenvergroesserung bei Elektronen: electron 
promotion. See Elektronenuebergang. 
Quantenzustand: quantum state. See Energieniveau. 
118 .9 
Quarzfadenmanometer: quartz-fiber manometer. A 
type of manometer in which the pressure of a gas is 
measured by the damping which it offers to the vibra- 
tions of a quartz fiber. Devised by Haber and Kersch- 
bäum. 
Quincke'sche Roehre: Quincke tube. An acoustic wave 
filter consisting of a short tube with a semicircular side 
branch. 
/r Einheit 
119 R 
r Einheit: r unit. See Roentgen. 
R Zweig: R branch. A set of moelcular spectrum lines 
corresponding to unit decreases in rotational quantum 
number. 
Rabi'sche Feld: Rahi field. A magnetic field used to 
deflect particles having an intrinsic magnetic moment. 
It is a nonuniform field, the portion used being that 
in the plane midway between parallel, flat, rectangular 
pole pieces. 
Radialgeschwindigkeit: radial velocity. The component 
of linear velocity in line with the observer. 
radiale Quantenzahl: radial quantum number. A quan- 
tum number associated with radial motion, which must 
be an integer for any allowed stationary state of a par- 
ticle moving subject to a central field. 
radioaktives Element: radioelement. A radioactive ele- 
ment. 
radioaktives Gleichgewicht: radioactive equilibrium. 
A relationship between a radioactive substance and its 
parent substance, in which at any instant the rate of 
disintegration of the former is equal to its rate of for- 
mation from the latter. The equilibrium is "transient” 
if the balanced rates change rapidly, "secular” if the 
parent substance has a very long period. 
radioaktiver Niederschlag: radioactive deposit. A film 
of radioactive matter formed from the disintegration 
of a radioactive emanation (radon, thoron, actinon) 
and of the subsequent products. Such films may be 
found upon solid objects which have been in contact 
with any one of these emanations. 
radioaktives Produkt: radioactive product. A substance 
which results from the radioactive disintegration of an- 
other (parent) substance. 
radioaktive Reihen: radioactive series. A succession 
of radioactive elements, each of which is derived from 
the disintegration of the one preceding. 
Radloaktivitaet: radioactivity. A property of certain 
elements, which involves the spontaneous emission of 
alpha particles or of beta particles from the nucleus of 
the atom. Gamma rays, also of nuclear origin, may ac- 
company or immediately follow the disintegration, but 
are a byproduct of that process. 
Radioaktivitaetswaerme: heat of radioactivity. The 
heat generated per unit time by the radioactive disinte- 
gration in unit mass of a radioactive substance. 
Radioelement: radioelement. See radioaktives Element. 
Radiofrequenz: radio frequency. Any frequency, usually 
above the audible range, suitable for the transmission 
of radio signals. 
Radiogramm: Radiogram. A wireless telegraph message. 
Radiograph: radiograph. An X-ray or radium photo- 
graph, showing the nonuniform density of the structure 
through which the rays pass. 
Radiologie: radiology. (1) That branch of physics 
which deals with X-rays, radioactivity, and other h.-f. 
radiation. (2) The art of diagnosis and treatment of 
diseases by means of X-rays, radium, or ultraviolet ra- 
diation. 
Radiolumineszenz: radioluminescence. Luminescence 
stimulated by radioactive emission or by X-rays. 
Radiometeorograph: radiometeorograpb. A meteoro- 
graph which, when sent up in a balloon, automatically 
reports atmospheric conditions by radio to receiving ap- 
paratus at the ground station. 
Radiometer: radiometer. See Lichtmuehle. 
Radiomikrometer: radiomicrometer. An instrument, 
devised by Boys, consisting of a short-circuit thermo- 
couple suspended in a strong magnetic field, and sensi- 
tive to very feeble thermal radiation. 
Radiophotolumineszenz: radio-photoluminescence. Lu- 
minescence exhibited by certain minerals, as kunzite 
and fluorite, as a result, first of irradiation with beta 
and gamma rays, followed by exposure to light; first 
observed by K. Przibram. 
Radiothermolumineszenz: radio-thermoluminescence. 
Luminescence exhibited by certain vitreous and crystal- 
line substances as a result, first of irradiation with beta 
and gamma rays, or by Entladungsstrahlen, followed by 
heating; first observed by E. Wiedemann. 
Raman Effekt: Raman effect. The presence, in scattered 
light, of frequencies differing from that of the incident 
light by various values characteristic of the scattering 
substance but independent of the incident frequency. 
Discovered by C. V, Raman in 1928. The scattered or 
"modified” lines constitute the Raman spectrum of the 
scatterer. 
Raman'sche Viskosilae+sformel: Raman viscosity for- 
mula. Expresses the viscosity coefficient 77 of a liquid 
in terms of the absolute temperature T, as follows: 
JB 
rj = A'eT, 
in which A and B are constants. 
/Ramsauer Effekt 
120 R 
Ramsauer Effekt: Ramsauer effect. (1) The absorp- 
tion of slow-moving electrons by intervening matter, 
somewhat as alpha particles are absorbed by gases. 
Ramsden-Okular: Ramsden eyepiece. An eyepiece for 
optical instruments, consisting of two similar plano- 
convex lenses with their convex faces facing each’ other 
and at a distance equal to two-thirds the focal length 
of either. 
Rankine'scher Kreis: Rankine cycle. A type of thermo- 
dynamic engine cycle in which the isothermal compres- 
sion is continued until the original volume is attained, 
and the cycle is then completed by an increase of pres- 
sure at that volume. The ordinary steam engine approxi- 
mates this cycle. 
Rankine'scher Zyklus: Rankine cycle. See Rankine’scher 
Kreis. 
Raoult'sches Gesetz: Raoult law. A more specific 
form of the van’t Hoff law; viz.: the fractional lower- 
ing of the vapor pressure of a solvent by a nonvolatile 
solute is equal to the ratio of the number of molecules 
of the solute to the total number of molecules of both 
solute and solvent. 
rationalisierte Einheit: rationalized unit, Syn. Heavi- 
side-Lorentz unit. See Heaviside-Lorentz Einheit. 
Raumfunktion: space function. A quantity connected 
with a region of space in such a way that its value 
depends upon the extent and the boundaries of that 
region. The "space” referred to may be of any number 
of dimensions. The element of such a function, used 
in integration, is equal to the element of space multiplied 
by some function of the co-ordinates of the space ele- 
ment, E.g., an element of mass is equal to the density 
of the substance (which may vary from point to point) 
multiplied by the element of volume. 
Raumgruppe: space group. A group of points in 
space which has one of the types of symmetry exhibited 
by crystals. 
Raumladung: space charge. A charge of electricity 
distributed more or less continuously throughout a vol- 
ume; as in any part of the electron stream in a thermi- 
onic vacuum tube or in a photoelectric cell. 
Raumladungsgleichung: space-charge equation. An 
equation which expresses the space-charge-limited cur- 
rent between a plane cathode and a parallel plane anode 
in a gas: 
in which e and m are the electronic charge and mass, 
V is the voltage, and x the distance between electrodes. 
A similar but more complex equation holds for a cylin- 
drical cathode inside a cylindrical anode. 
Raumphotometer: sphere photometer. An integrating 
photometer in which the source of light is placed inside 
a spherical cavity with white walls, the light from 
which, reflected through a suitably placed opening, is 
used in the measurement of the mean spherical candle 
power of the source. 
Raumquantelung: space quantization, Syn. directional 
quantization. The application of quantum conditions 
to the orientation of a system in space traversed by a 
field of force; which limits, e.g., the number of possible 
orientations of an atom in a magnetic field. 
Raumverteilung: spatial distribution. A definite ar- 
rangement of particles or points in any type of space, 
usually specified by means of equations which express 
the number located in any element of space in terms 
of the’ co-ordinates of the element. 
Raumwinkel: solid angle. A portion of the whole of 
space about a given point, bounded by a conical surface 
with vertex at that point and measured by the area cut 
by the bounding surface from the surface of a sphere 
of unit radius centered at that point. 
Raumzeit: space-time. A four-dimensional continuum 
in which the four variable co-ordinates are the three 
ordinary space co-ordinates (as x, y, 2) and the time t. 
The last may be expressed with an imaginary coefficient 
in order to make the resulting mathematical expressions 
closer in form to those of ordinary geometry. A concept 
due to Minkowski. 
raumzentriert: body-centered. In re a unit cell of 
crystal structure; having an atom at its center of figure. 
Syn. space centered. 
Rauscheffekt: flicker effect. A variation in plate cur- 
rent in a radio tube, due to variations in the surface 
condition of the filament. 
Rayleigh'sches Gesetz: Rayleigh law. States thatjit 
very low values of the maximum magnetic induction, 
the hysteresis loss in a magnetic cycle is proportional 
to the cube of that induction. 
Rayleigh'sche Linie: Rayleigh line. That component of 
a spectrum line in scattered radiation which has the 
same frequency as the corresponding incident radiation, 
arising simply from ordinary or Rayleigh scattering, not 
from the Compton or the Raman effect. 
i = V2 J e VVi . 
9rr m X2 
121 
/Rayleigh-Jean'sches Gesetz R 
Rayleigh-Jean'sches Gesetz: Rayleigh-fean law. A law 
intended to express the spectral energy distribution of 
black-body radiation at a given absolute temperature T 
in terms of wave length X. The emissive power of the 
black body within the wave-length range is given as 
dE* = 27rck TA~4 dA; 
in which c is the electromagnetic constant and k, the 
Boltzmann constant. The law fails to meet the experi- 
mental facts except at long wave lengths. 
Rayleigh'sche Scheibe: Rayleigh disk. A light disk 
which, placed in a sound field, tends to set itself at 
right angles to the direction of motion of the particles 
of the medium. 
Rayleigh'sche Streuung: Rayleigh scattering. The selec- 
tive scattering of light by very small particles suspended 
in the air, such as dust or even the molecules of the air 
itself. 
razemisch: racemic. Not optically active; e.g. racemic 
quartz in which the two kinds are twinned so as to 
compensate each other. A substance having this char- 
acteristic is called a racemate, and the acquisition of the 
property is racemization. 
Reaktanz; reactance. (1) (Inductive.) That compo- 
nent of the impedance of a circuit which is due to 
inductance; expressed by 27rfiL. (2) (Capacitive.) That 
component which is due to capacitance; expressed by 
1/277-nC. Both are measurable in ohms. 
Reaumur'sche Skala: Reaumur scale. A thermometric 
scale on which the freezing point of water is 0 degrees 
and the boiling point 80 degrees. Introduced by Rene 
de Reaumur about 1730, and still largely used in Cen- 
tral Europe. 
rechtsdrehend: dextrogyrate. See dextrogyr. 
rechtwinkelig abbildend: rectilinear. In re an optical 
system: forming images without distortion, so that the 
image of a straight line is straight, etc. 
reduzierter Brennpunktabstand: reduced focal length. 
The first focal length of a spherical refracting surface, 
or of a lens, divided by the refractive index of the 
medium in which the light is incident; or the second 
focal length divided by the index of the medium into 
which the rays emerge. 
reduzierte Masse: reduced mass. In re a heteropolar 
molecule: the value of the quantity: 
in which M1 and M2 are the masses of the two ions. 
(2) In re an orbital electron: the value of 
m M 
m -f M 
in which m is the mass of the electron and M, that of 
the nucleus. 
reduzierte Zustandsvariablen: reduced variables of 
state. The values of the pressure, specific volume, and 
absolute temperature of a gas expressed (as abstract 
ratios) in terms of their critical values, i.e., the values 
of p/pt, v/v0, T/Tc. 
Reflecktionsfaktor: reflection factor. The ratio of the 
total luminous flux reflected by a given surface to that 
incident upon it. Syn. reflectance. 
Reflecktionskoeffizient: reflection coefficient. The 
square root of the reflectivity of a surface for any type 
of radiation. It is the ratio of the amplitude of the 
reflected radiation to that of the incident radiation. 
Reflecktionsmesser: reflectometer. An instrument for 
measuring the reflection factors of reflecting surfaces. 
Reflectionsvermoegen; reflecting power, Syn. reflectiv- 
ity. The fraction of the radiant energy of a given char- 
acter, normally incident upon the surface of a body, 
which is reflected by that surface. 
Reflectionswinkel: reflection, angle of. The angle be- 
tween the direction of propagation of a reflected emis- 
sion and the normal to the reflecting surface. 
Reflectometer: reflectometer. See Reflektionsmesser. 
Refraktionsindex: refractive index. See Brechungsin- 
dex. 
Refraktometer: refractometer. An instrument for 
masuring the refractive indices of liquids or of solids, 
usually by determining the critical angle. 
Regeneration: regeneration. A general term denoting 
various processes, the characteristic of which is that the 
result automatically enhances the cause, the action there- 
fore tending to build itself up to greater and greater 
intensity. E.g., in a regenerative vacuum-tube amplify- 
ing circuit, the fluctuations of the plate current, by 
means of a feedback arrangement, re-enforce the varia- 
tions in grid potential, and thus increase the fluctuations 
in the plate current itself. 
regulaere Brechung: regular refraction. Refraction in 
a definite direction, not diffused or scattered. 
M, M2 
m1 + m2 
/regulaere Durchlaessigkeif R 
regulaere Durchlaessiqkeit: regular transmission. Trans- 
mission in a definite direction, not diffused or scattered. 
regulaere Reflektion: regular reflection. Reflection in 
a definite direction, not diffused or scattered. Syn. specu- 
lar reflection. 
Reibung: friction. The rubbing together of two bodies, 
or the hindrance to motion so produced; attrition. 
Reibungskoeffizient: friction coefficient. The ratio of 
the tangential force of sliding friction between two sur- 
faces to the force, normal to the surfaces, which presses 
them together. It depends upon the nature of the two 
surfaces, and is in general greater for static than for 
kinetic friction. 
Reibungsfaktor: friction factor. A coefficient by which 
a dynamic quantity, calculated without reference to fric- 
tion, must be multiplied in order to correct for friction. 
Reichweite: range. (1) The distance to which a cor- 
puscular emission, as alpha rays, will penetrate a given 
substance before all its energy is absorbed. (2) The 
distance from its starting point, on a horizontal plane, 
at which a projectile again reaches the plane. 
Reihe: series. An arrangement of electrical conductors, 
generators, condensers, etc. in succession without any 
branching, so that each carries the whole conduction or 
displacement current. 
Reihenschaltung: series-connection. A mode of ar- 
ranging the separate parts of a circuit by connecting 
them successively end to end to form a single path for 
the current. 
reines Spektrum: pure spectrum. A spectrum of which 
each point corresponds to one and only one wave length 
or frequency of the dispersed radiation. 
Rekaleszenz: recalescence. The sudden evolution of 
heat by solid iron and some other ferromagnetic metals 
at certain high temperatures as the metal cools; prob- 
ably due to some exothermic structural transition. 
Rekombinationskoeffizient: recombination coefficient. A 
coefficient which appears in the law expressing the rate 
of recombination of ions in a gas. If n+ and n_ are 
the respective numbers of the two kinds of ions, 
faint, continuous spectrum ascribed to the recombination 
of ions in an ionized gas. 
Relais: relay. Any device used to communicate or pass 
on impulses from one system to another system. 
relative Apertur: relative aperture. In a telescope or 
a camera: the ratio of the focal length of the objective 
to the diameter of the entrance-pupil; it determines the 
photographic speed of the objective. Syn. F-number. 
relative Feuchtigkeit: relative humidity. The fraction 
of saturation of the water vapor in the air. 
relative Oeffnung: relative aperture. See relative Aper- 
tur. 
Relativitaet: relativity. A modern system of natural 
philosophy, characterized by its recognition of the in- 
terdependence of the basic entities of matter, space, 
and time; introduced and largely developed by Albert 
Einstein. 
Relativitaetskontraktion: relativity contraction, Syn. 
Lorentz-Fitzgerald contraction. A hypothetical shrink- 
age of all matter in the direction in which it moves 
through the ether, such that all dimensions in this di- 
rection are reduced in the ratio 
I u2 
■\ 1 — : 1 
c2 
where u is the speed of the motion and c, the speed 
of light. 
Relativitaetskorrektion: relativity correction. A correc- 
tion which must be applied to a formula derived or to 
a value calculated in accordance with classical theory 
in order to bring it into agreement with the relativity 
theory. 
Relaxationszahl: relaxation number. The reciprocal of 
the relaxation time (2). 
Relaxationszeit: relaxation time. (1) The time re- 
quired for the electric polarization at any point of a 
suitably charged dielectric to fall from its original value 
to 1/e of that value, due to the electric conductivity of 
the dielectric. (2) In general, the time required for an 
exponential variable to decrease to l/e of its initial 
value. (3) The time required for a gas, in which the 
Maxwell distribution of velocities has been temporarily 
disturbed, to recover that state. (4) The time required 
for the shearing stress in a flowing viscous substance 
to disappear after the flow has ceased. 
dn+ dn_ 
_ — — An+ n_ , 
dt dt 
A is the recombination coefficient. 
Rekombinationsspektrum: recombination spectrum. A 
123 
/Reluktanz R 
Reluktanz: reluctance. The ratio of the magnetomotive 
force acting upon any part of a magnetic circuit to the 
resulting magnetic flux. 
Reluktivitaet: reluctivity. The ratio of the magnetic 
intensity H to the magnetic induction B in the same 
region. If B and H are parallel, the reluctivity is the 
reciprocal of the magnetic permeability. Syn. specific 
reductance. 
remanente Magnetisierung: remanent magnetization. 
The magnetization I retained by a substance undergoing 
a symmetrical hysteresis cycle, when the magnetic in- 
tensity H is reduced to zero; represented by either inter- 
cept of the H-I hysteresis curve on the I axis. 
Remanenz: remanence. The residual magnetic induc- 
tion B in a substance undergoing a symmetrical hystere- 
sis cycle, when the magnetic intensity H is reduced to 
zero; represented by either intercept of the H-B hystere- 
sis curve on the B axis. 
Rheograph: rheograph. A type of magnetic vibration 
galvanometer or oscillograph, devised by Abraham, in 
which the effects of inertia and damping are neutralized 
by special means. 
Resonanz: resonance. A term denoting a variety of 
phenomena characterized by the abnormally large re- 
sponse of a system having a natural vibration period to 
a stimulus of the same, or nearly the same, frequency. 
Resonanzbruecke: resonance bridge. A type of a.-c. 
bridge, in one arm of which an inductance and a ca- 
pacitance are adjusted to such values that the bridge 
is in resonance; their product is then equal to l/Trrn2, 
where n is the frequency. 
Resonanzdurchdringung: resonance penetration. The 
penetration of an atomic nucleus by a charge changed 
particle whose energy corresponds to one of the energy 
levels in the nucleus. The probability of penetration by 
such a particle is comparatively large. 
Resonanzpotential: resonance potential, Syn. radiation 
potential. The p.d., in volts, corresponding to the en- 
ergy, in electron-volts, required to excite an atom or a 
molecule to emit one of its characteristic radiation fre- 
quencies. The first r.p. excites the lowest frequency, 
etc. 
Resonanzradiometer: resonance radiometer. A modi- 
fication of the thermo-relay, for relative measurements 
of small radiation intensities in infrared spectrometers. 
Resonanzschwingung: covibration. A resonant vibra- 
tion, i.e., a natural vibration of the same frequency as 
the stimulating or exciting impulses. 
Resonanzstrahlung: resonance radiation. Radiation from 
a gas or a vapor, due to states of excitation which may 
be brought about by radiation of the same frequencies; 
as in the case of sodium vapor traversed by sodium 
light. When so excited, it may be regarded as a type 
of fluorescence without degradation of frequency. First 
intensively studied by R. W. Wood. 
Resonanzzustand: resonance state. A state of excitation 
which gives rise to resonance radiation. 
Resonator: resonator. An apparatus designed to reso- 
nate, or respond as the result of resonance, to a stimu- 
lus of given frequency. 
Rest: residual. The result of a measurement upon a 
quantity, minus the most probable value of that quantity. 
Restdruck: residual stress. A stress which persists in 
a solid, due not to the existence of external forces but 
apparently to the fact that certain portions have been 
stressed beyond the elastic limit while the adjacent por- 
tions have not. 
Restionisation: residual ionization. Ionization of air 
or other gas in a closed vessel, not accounted for by 
recognizable agencies in the immediate neighborhood 
(X-rays, radioactivity, etc.). Formerly supposed to be 
an inherent property of the gas, but now attributed to 
the cosmic rays. 
Restladung: residual charge. The charge on the plates 
of a condenser, which remains temporarily bound, after 
an initial discharge, by that part of the polarization of 
its imperfect dielectric which is due to electron mi- 
gration. 
restliche magnetische Induktion: residual magnetic in- 
duction. The magnetic induction in a ferromagnetic 
body after the removal of the magnetizing force. It de- 
pends upon the material, the shape, and the previous 
history of the specimen. 
Reststrahlen: reststrahlen {Ger.), Syn. residual radia- 
tion. A nearly monochromatic infrared radiation isolated 
from the output of a white hot solid by successive 
reflections from surfaces of a given crystalline material, 
as quartz or rock salt; a method due to Rubens and 
Nichols, who termed the rays Reststrahlen. 
Reststrahlung: residual radiation. See Reststrahlem 
reversible: reversible. In re a succession of changes 
in a system: such that if the order in time of the changes 
is reversed, the only alteration in the corresponding 
changes in energy is reversal of sign. 
/reversible Maschine 
124 R 
reversible Maschine: reversible engine. A heat engine 
working in a reversible thermodynamic cycle, e.g., a 
Carnot cycle. 
reversibles Pendel: reversible pendulum. A pendulum 
provided with two pivots at conjugate points, from 
which it swings in equal times. 
Reynolds'sche Gesetze: Reynolds laws. (1) States that 
for a mobile liquid in a straight tube, the gradient öf 
the head is proportional to the speed of flow up to the 
critical velocity; whereas, at speeds above this, it is 
proportional to a higher power of the speed. Thus 
Richard'sche Regel: Richard rule. States that the ratio 
of the molar heat of fusion to the absolute temperature 
of the melting point is the same for various solids. 
Richtungsabhaengigkeif: directional derivative. Of a 
scalar point function F with respect to any direction 
in space: the scalar (dot) product of the gradient of F 
by the unit vector in the given direction. 
Richtungsquan+elung: directional quantization. The ap- 
plication of quantum conditions to the orientation of a 
system in space traversed by a field of force; which 
limits, e.g., the number of possible orientations of an 
atom in a magnetic field. Syn. space quantization. 
Righi-Leduc scher Effeld: Righi-Leduc effect. A dif- 
ference of temperature which develops between the two 
edges of a strip of metal, in which heat is flowing longi- 
tudinally, when the plane of the strip is placed perpen- 
dicularly across a magnetic field. 
Ri+z'sche Formel: Ritz formula, Rydberg-Ritz f. A 
somewhat complicated modification of the Rydberg 
(spectral series) formula, in which allowance is made 
for the variation of f with the number of the line in 
the series. 
Ritz'sches Prinzip: Ritz principle. States that every 
wave number occurring in the spectrum of a substance 
may be expressed as a difference between two of a 
much smaller group of terms characteristic of the sub- 
stance. These terms correspond to what are now recog- 
nized as quantum states, in accordance with the "com- 
bination principle” of Ritz. 
Rochon'sches Prisma: Rochon prism. A type of polar- 
izer, consisting of two Iceland-spar prisms, one with its 
axis parallel to the entering beam of light, the other 
with its axis perpendicular to that beam. Upon passage 
from one prism into the other, the extraordinary ray is 
refracted while the ordinary is not, the separation being 
further increased upon emergence from the second 
prism. 
Roehrenelektrometer: tube electrometer. An adapta- 
tion of the thermionic vacuum tube to use as an elec- 
trometer. 
Roehrenkoeffizien+en: tube coefficients. The constants 
which serve to describe the characteristics of a thermi- 
onic vacuum tube, viz., the amplification factor, the 
mutual conductance, the a.-c. filament-to-plate resistance, 
the detection coefficient, etc. 
Roehrenspannungsmesser: tube voltmeter. An adapta- 
tion of the thermionic vacuum tube to the measurement 
of small a.-c. voltages. 
dH 
= — Avn 
dx 
where n 1. (2) States that the critical velocity of a 
liquid flowing in a straight tube is inversely proportional 
to pcf>r, in which p is the density and <£ the fluidity 
coefficient of the liquid and r is the radius of the tube. 
reziproker Vlskositaetskoeffizient: fluidity coefficient. 
The reciprocal of the viscosity coefficient. 
Reziprozitae+sgese+z: reciprocity law {photographic). 
States that the time of exposure and the illumination 
required to produce a given photographic effect on a 
plate or film are in reciprocal relation to each other; 
so that exposures having the same value of the product 
It will, after the same development, result in the same 
density of image. The law is not strictly true. 
Reziprozi+ae+slehrsatz: reciprocity theorem. One of 
several analogous theorems, e.g.: (1) A principle of 
electric networks, in accordance with which the current 
in any branch A due to an e.m.f. in any other branch B 
is equal to the current B due to an equal e.m.f. in A. 
(2) In re a vibrating string; the amplitude of vibration 
at a point A due to a periodic force applied at an- 
other point B is equal to the amplitude produced at B 
by an equal periodic force of the same frequency ap- 
plied at A. 
Rheologie: rheology. That branch of physics which 
deals with the permanent or plastic deformation or the 
flow of matter. 
Richardson'sche Gleichung: Richardson equation. An 
expression for the saturation current density of thermi- 
onic emission, in terms of the absolute temperature T 
of the filament: 
_ B 
I zz ATne T. 
Richardson used n zz y2; others have found n= 2 
more accurate, B involves the thermionic work function. 
125 
/Roehrenspek+rometer R 
Roehrenspektrometer: tube spectrometer. A type of 
photographic X-ray spectrometer, devised by Siegbahn 
and Larsson. 
Roehrenvoltmeter: tube voltmeter. See Roehrenspan- 
nungsmesser. 
Roentgen: roentgen. The absolute unit of X-ray dos- 
age, viz., that obtained from the X-ray energy which, 
when the secondary electrons are fully utilized and 
secondary radiation from the wall is avoided, produces 
in 1 cm3 of air at N.T.P. such a degree of conductivity 
that the quantity of electricity measured at saturation 
current is 1 e.s.u. Syn. r unit. 
Roentgenlehre: roentgenology. That branch of science 
which deals with X-rays, esp. with their biological ef- 
fects and uses, including applications to medical diag- 
nosis and therapy. 
Roentgenmesser: roentgenmeter. An instrument of 
the ionization-chamber type for measuring the intensity 
of X-rays or gamma rays. 
Roentgenologle: roentgenology. See Roentgenlehre. 
Roentgenspektrome+er: X-ray spectrometer, x-r. spec- 
trograph. An apparatus for measuring the wave lengths 
of X-rays by means of their reflection by crystals; some- 
what analogous to a grating spectrometer for light, the 
crystal taking the place of the grating. In the spectro- 
graph form the reflected rays are photographically re- 
corded. 
Roenfgensfrahlen: Roentgen rays, Syn X-rays. A type 
of electromagnetic radiation of wave length varying 
from 10~9 to 10~7 cm, and highly penetrating; discov- 
ered by Roentgen in 1895. 
Roentgenvakuum: X-ray vacuum. A region in which 
the gas pressure has bejen reduced below 0.01 mm; so 
called because a pressure as low as this is necessary in 
an X-ray tube. 
Roentgenverfaerbung: roentgenization. The discolora- 
tion which develops in some transparent substances, 
such as glass, after prolonged irradiation with X-rays. 
Roget'sche Spirale: Roget spiral. A helix of wire 
which contracts in length when a current is sent through 
it, because of the mutual attraction of the turns. 
Rotation: rotation. A motion of a body or a figure, 
in which all the particles or points move in circles about 
the same axis with the same angular velocity. 
Rotation eines Vektors: curl. A vector differential 
operator, much used in physics, which, applied to a 
vector point function F, is denoted by the symbol V 
X F and read "curl F” or "del cross F”. If the three 
components of the vector F are iF1} jF2, kF3, then the 
operator is defined by the determinant 
i j k 
8 8 8 
V X F = 
8x 8y 82 
F, F2 F3 
Rotationsachse: rotation axis. A line within the struc- 
ture of a unit crystal cell, about which atoms are ar- 
ranged in regular plane polygons centered upon the 
axis; so that only simple rotation would be required 
to bring any atom into coincidence with another in the 
same plane. 
Rotationsanalyse: rotational analysis. (1) The analysis 
of a molecular rotation spectrum, i.e., a setting forth 
of the constants relating to the series of lines consti- 
tuting such a spectrum. (2) The analysis of the rota- 
tional fine structure of an atom spectrum, due to nuclear 
spin. 
Rotationsdiagramm: rotation diagram. The photo- 
graphic record of diffracted beams produced when a 
slender beam of homogeneous X-rays impinges upon a 
rotating single crystal. 
Rotationsdispersion: rotatory dispersion. A type of 
optical dispersion arising from the fact that the polari- 
zation plane of polarized light of different wave lengths 
is rotated at different rates by optically active substances, 
so that the light emerges from such a substance with 
different colors polarized in different planes. 
Rotationsentropie: rotational entropy. That part of 
the entropy of a body which is concerned with mole- 
cular rotation. 
rotationsfreie Bewegung: irrotational. (1) Free from 
rotatory motion; esp, in re the motion of a fluid. (2) 
In re a vector: Syn. lamellar, noncircuital. 
Rotationsintegral eines Vektors: circuitation. The line 
integral of a vector point function taken around a 
closed path. 
rotationsintegral: circuital. In re a vector point func- 
tion: having a circuitation not equal to zero; not la- 
mellar. Syn. rotational. 
Rotationspolarisation: rotatory polarization, Syn. opti- 
cal rotation. See optische Rotation. 
Rotationsquantenazhl: rotational quantum number. A 
/Rotationsspektrum 
126 _R 
quantum number which determines the total angular 
momentum of a molecule, exclusive of nuclear spin, and 
either inclusive or exclusive of electron spin (for which 
it is denoted, respectively, by J and K). 
Rota+ionsspektrum: rotation spectrum. An X-ray spec- 
trum or diffraction pattern, produced by a crystal which 
is rotated while an X-ray beam traverses it. 
Ro+ationss+ruk+ur: rotational structure. (1) The fine 
structure of an atomic spectrum supposed to be due to 
the rotation of the nucleus in conformity with quantum 
conditions. (2) The structure of a molecular rotation 
spectrum. 
Ro+a+ionstemperatur: rotational temperature. The tem- 
perature of an excited vapor as indicated by the radia- 
tion energy distribution in the rotational spectrum. This 
may be quite different from the temperature deduced 
from the translational energy distribution, i.e., from the 
true temperature as usually defined. 
Ro+a+ions+raegheit: rotational inertia, Syn. moment of 
inertia. Of a rigid body with respect to any axis: the 
volume inegral of the product of the element of mass 
by the square of its distance from the given axis. It 
represents the torque required, per unit angular accelera- 
tion in radian measure, to change the speed of rotation 
of the body about that axis. 
Ro+ationsvepmoegen: rotatory power. The amount of 
optical rotation produced in a beam of polarized light 
by an optically active substance, per unit length of path, 
in degrees per millimeter or per centimeter. Divided 
by the density, it gives the specific rotatory power. Mo- 
lar (or atomic) rotatory power is the specific rotatory 
power multiplied by the molecular (or atomic) weight. 
The Verdet constant is sometimes called specific mag- 
netic rotatory power. 
Rotations voltmeter: rotary voltmeter. A type of elec- 
trostatic voltmeter for high voltages. 
Rotationszustand: rotational state. One of the quan- 
tum states or energy levels of molecular rotation, changes 
in which are responsible for molecular rotation spectral 
lines. 
Rotator: rotator. (1) An optical apparatus, as a quartz 
plate cut perpendicular to the optic axis, which rotates 
the polarization plane of light traversing it. (2) In 
quantum theory: a point-mass endowed with uniform 
motion about a fixed center. (3) A mechanism for 
giving objects mounted upon it a motion of rotation. 
Rotor; rotator. See Rotator. 
Rotorfeld: rotary field. A magnetic field, of which the 
direction of the magnetic-intensity vecor rotates about 
an axis perpendicular to itself. Such fields are com- 
monly produced by means of magnets excited by poly- 
phase currents, e.g., in induction motors. 
Rotverschiebung: red shift. (1) A general shift of 
the lines of a spectrum in the direction of longer wave 
length, due to the Doppler or other effect. (2) In 
particular, an increase in wave length observed in the 
spectra of distant spiral nebulae or galaxies, which ap- 
pears to be progressively greater with greater distance, 
and the cause of which is not definitely known. 
Rowland'sches Gesetz: Rowland laiv. See Bosanquet’- 
sches Gesetz. 
Rowland'sche Gittermontage: Rowland mounting. A 
mounting for concave gratings, in which the slit is at 
the vertex of a right-triangular frame and the grating 
and the eyepiece or camera are at opposite ends of the 
(movable) hypothenuse. 
Rowland'scher Kreis: Rowland circle. The circle upon 
which lie the slit, grating, and line images in a Rowland 
concave grating spectrograph. 
Rowland'scher Ring: Rowland ring. A sample of mag- 
netic material, prepared in the form of a ring in order 
to test its magnetic properties by using it as the core 
of a transformer arrangement. 
Rueckkehrkoeffizient; restitution coefficient. The ratio 
of the relative speed of two elastic spheres, after a col- 
lision in their line of centers, to the relative speed before 
the collision. According to Newton’s experiments, this 
ratio is constant for the same two spheres. 
Rueckkehrungskoefflzient: restitution coefficient. See 
Rueckkehrkoeffizient. 
Rueckkopplung: feedback. An arrangement of a radio 
receiving apparatus in which the plate circuit of the 
detector tube is coupled to the grid circuit of the same 
tube, thus rendering it regenerative and very sensitive. 
Rueckstoss: recoil. The motion of an atom because 
of the emission of an alpha particle, a beta particle, 
a neutron, or (possibly) a quantum of radiation; or 
the motion of an electron because of having functioned 
in the Compton effect. Recoil rays are streams of such 
recoiling particles. 
Rueckstossfak+or: recoil factor. The ratio of the in- 
tensity of scattered X-rays modified by the Compton 
effect, as calculated on the quantum theory, to its classi- 
cal value. 
677865—46—9 
127 
/Ruhelagewinkel R 
Ruhelagewinkel: angle of friction. The angle whose 
tangent is the friction coefficient. 
Ruhemasse: rest mass. The mass of a body in the 
classical or Newtonian sense, i.e., not including the ad- 
ditional mass which, according to the relativity theory, 
the body acquires when set in motion. 
Ruhepoten+ial: rest potential. A residual p.d. between 
an electrode and the electrolyte, which remains after 
the electrode has become polarized; as distinct from 
the true electrokinetic potential developed when the 
solid and the liquid are in contact. 
Rumpf; Rumpf {Ger., "trunk”'). The very stable 
electron group which remains when a chemically active 
atom is ionized by the removal of its incomplete outer 
shell of electrons. See also Kern. 
Rumpfatom: kernel. See Kern. 
Runge'sches Gesetz: Runge law. States that the wave 
number for the first line of the second (diffuse) sub- 
sidiary series of the line spectrum of an element is equal 
to the difference between that for the common limit 
of the two subsidiary series and that for the limit of 
the fundamental or Bergmann series. 
Runge'scher Nenner: Runge denominator. The small- 
est integer r such that the positions of the lines in a 
Zeeman pattern are integral multiples of 1/r, when the 
unit used is the Lorentz unit. 
Runge'sche Regel: Runge rule. States that in the 
anomalous Zeeman effect the separation in frequency, 
or resolution, for a given line bears a simple commensur- 
able ratio (2:3, 5:3, etc.) to the separation in the 
normal Zeeman effect. 
Ruper+'sches Troepfchen: Rupert drop. A globule of 
glass which has been suddenly congealed by allowing 
the fused drop to fall into water, and in which there 
are residual stresses which will cause it to explode vio- 
lently upon a slight shock. 
Russell-Saunder'sche Kopplung: Russell-Saunders coup- 
ling. A condition in an atom in which the torques be- 
tween spins and those between orbital angular momenta 
are much stronger than the torque between the resultant 
of ail spins and the resultant of all orbital angular 
momenta. 
Ru+herford-Bohr'sches Atom: Rutherford-Bohr atom. 
See Bohr’sches Atom. 
Ru+herford'sches S+reuungsgesetz: Rutherford scatter- 
ing law. A (classical) expression for the effective cross 
section about the nucleus of an atom, which an alpha 
particle must enter in order to be scattered into a solid 
angle doj at a deviation 0 from the initial direction; 
viz., (EE'/2mv2)2 esc4 1/2 ®dw, *n which E and E' are 
the charges (in electronic units) of the nucleus and the 
alpha particle and m is the mass and v the speed of 
the alpha particle. 
Rydberg'sche Formel: Rydberg formula. An approxi- 
mate formula for the wave numbers of lines in hydro- 
gen-like atomic spectral series, viz., 
1 1 R(z + I)2 
A A« (m + f)2 
in which A» is the wave length for the series limit, 
R is (approximately) the Rydberg constant, z indicates 
the state of ionization (0 if not ionized, 1 if singly 
ionized, etc.), f is a fraction common to all the lines 
of the series, and m = 2, 3, 4, 
Rydberg-Frequenz: Rydberg fundamental frequency. 
The frequency equivalent to the wave number expressed 
by the Rydberg constant R, therefore equal to cR, in 
which c is the speed of light. Its value for hydrogen 
is 3.2878 X 10I5/sec. Note. Some authors have called 
this quantity the Rydberg constant. 
Rydberg Konstante: Rydberg constant. The coefficient 
R in the Rydberg formula for wave numbers of spectral 
lines. Its theoretical value is 
27r2 me4 
R = ; 
ch3 (1 -f- ) 
in which m and e are electronic mass and charge, M 
is the molecular mass, c is the electromagnetic constant, 
and h is the Planck constant. For hydrogen its value 
is 109677.76 cm“"1; for an infinite nuclear mass it would 
be 109737.42 cm-1. 
Rydberg'scher Nenner: Rydberg denominator. The de- 
nominator (22, 32, etc.) of a spectral term. 
Rydberg-Ritz'sche Formel: Rydberg-Ritz formula. See 
Ritz’sche Formel. 
Rydberg-Schuster'sches Gesetz: Rydberg-Schuster law. 
States that the wave number for the first line of the 
principal series of the line spectrum of an element is 
equal to the difference between that for the limit of the 
principal series and that for the common limit of the 
two subsidiary series. 
/S-Elektron 
128 s 
S-Elekfron: s-electron. An orbital electron for which 
the azimuthal quantum number is zero. 
S-Zustand: S-state, S-level. The state of an atom in 
which the azimuthal quantum number is zero. 
Sabin: sahin. A unit of (acoustic) equivalent absorp- 
tion, equal in its absorbing effect to 1 ft2 of a completely 
absorbing surface. Named for W. C. Sabine. 
Sabine'sches Gese+z: Sabine law. Expresses the re- 
verberation time of a hall or auditorium, in seconds, as 
0.164V 
T = 
aS 
in which V is the volume of the room in m3, S the 
total area of its exposed surfaces in m2, and a the mean 
acoustic absorptivity of those surfaces for vocal sounds.' 
Saccharimeter: Saccharimeter. A form of polariscope 
for measuring the rotatory power of sugar solutions and 
similarly active liquids. 
Sackur'sche Gleichung: Sackur equation. An expres- 
sion for the molar entropy of a perfect monatomic gas 
in terms of its volume v, its atomic weight w, and its 
absolute temperature T viz., 
S = R loge (vw3/2T3/2) + s0, 
in which R is the ideal gas constant. S0 is the Sackur- 
Tetrode constant, the value of which is about —11.05 
cal/mol deg. 
Sae+tigung: saturation. (1) The condition of a space 
in which the vapor pressure of some substance contained 
therein has reached the highest value possible at the 
existing temperature; or that of a solution when at 
maximum concentration for the existing temperature. 
(2) (Magnetic.) The condition of a magnetic sub- 
stance whose magnetization has reached its highest pos- 
sible value. (3) That attribute of a chromatic color 
which determines its degree of difference from an achro- 
matic color of the same brilliance. 
Saet+igungsanteil: fraction of saturation. The ratio of 
the actual pressure of a vapor to the maximum, or satu- 
rated, vapor pressure at the same temperature. 
Saet+igungsstrom: saturation current. The limit which 
the current through an ionized gas, the thermionic cur- 
rent, or the photoelectric current approaches with in- 
creasing voltage, i.e., its value when the ions are car- 
ried off as fast as they are released. 
Saeule: head. See Kopf. 
Saint-Venant'sche Gleichuny: Saint Venant equation. 
An equation relating to the adiabatic flow of a fluid, 
the form of which is 
y2(V22 - V,2) = [Pl vdp; 
P 2 
where p is pressure (in absolute units), v is specific 
volume, and V is speed of flow, corresponding to two 
points denoted by the subscripts 1 and 2. It is due to 
Saint Venant and Wantzel. 
Sammelpunkt (opt.): center of collineation. See Kol- 
lineationszentrum. 
Sammler: accumulator. See Akkumulator. 
Satellit: satellite. One of the fainter components of a 
multiple! spectral line. 
Sauerstoffpunkt: oxygen point. The equilibrium tem- 
perature between liquid and gaseous oxygen at 760 
mm pressure; a standard temperature point, taken as 
—182.97 degrees C. 
Savart'sche Platte: Savart plate. A device consisting 
of two calcite plates of equal thickness, cut parallel to 
the natural cleavage faces and mounted with correspond- 
ing edges at right angles. Used to detect the presence 
of polarized light by means of interference fringes, on 
a principle first described by Brewster. 
"Scale of eight": scale of eight. A vacuum tube cir- 
cuit for counting pulses, in groups of eight, from ion 
or photon counters. 
Schale: shell. (1) (Electronic.) A group of electrons, 
supposed to form, part of the outer structure of an atom, 
and having a common energy level. (2) A lamina of 
magnetic material in which the lines of induction are 
in the direction of its thickness. Its strength is the mag- 
netic moment per unit area. 
Schallenergiefluss: sound energy flux. The average rate 
of flow of sound energy through any specified area, 
taken over a complete period. 
Schallintensitaet: sound intensity. The sound energy 
flux per unit area of a plane or spherical sound wave 
front. 
Schallintensi+aetsmesser: phonometer. See Phonometer. 
scharfe Serie: sharp series. One of several spectral 
series in the characteristic spectrum of an element; so 
called because of the small half-widths of the lines. 
Sometimes called second subordinate series. 
/Schaffen s 
Schatten: shade. A chromatic color of relatively low 
saturation and relatively low brilliance. 
Schattierung: hue, tint. See Faerbung, Nuance. 
Schauer; shower {cosmic-ray). The production of 
from two to several associated ion pairs at the same 
instant, apparently due to cosmic rays. 
scheinbare Kerzenstaerke: apparent candle power. A 
measure of the equivalent luminous intensity of an ex- 
tended source of light at a specified distance, viz., the 
candle power of a point source which would produce 
the same illumination at the same distance. 
scheinbarer Durchmesser: apparent diameter. The an- 
gle subtended at the eye of the observer by the diameter 
of any object. Syn. angular diameter. 
scheinbare Leistung: apparent power. The product of 
the effective e.m.f. and the effective current in an a.-c. 
circuit. Multiplied by the power factor, it gives the 
average power. 
scheinbares Loesungsvolumen: apparent volume in so- 
lution. The volume of a solution minus the volume of 
the pure solvent entering into it at the same tempera- 
ture. Apparent specific volume in solution: the appar- 
ent volume in solution per unit mass (mol or gram) 
of solute. 
Scherspannung: shear. A type of strain in which ad- 
jacent laminar elements have a progressive relative dis- 
placement; so that a cube is skewed into a rhombic 
prism, etc. Its measure is the amount of relative dis- 
placement per unit thickness perpendicular to the direc- 
tion of the displacement; or, the tangent of the angle 
of shear. 
Scherungsdruck: shearing stress. The stress which ac- 
companies shear in an elastic body; measured by the 
tangential force per unit area parallel to the relatively 
displaced laminar elements. 
Scherungsgrenzenmesser: pachimeter. See Pachimeter. 
Scherungskoeffizient: rate of shear. The derivative of 
the speed of flow of a fluid with respect to distance 
measured at right angles to the relatively moving layers. 
Scherungsmodul: rigidity modulus, Syn. shear modu- 
lus. The ratio of the shearing stress in an elastic sub- 
stance to the strain (shear) which accompanies it. 
Scherungswinkel: angle of shear. The angle through 
which any plane, originally perpendicular to the dis- 
placement laminae, is skewed in the process of shear, 
and whose tangent is the measure of the shear. 
Schicht: sheath. A part of an electric discharge in a 
rarefied gas, in which there is a space charge because 
of the great predominance of particles of one sign over 
those of the other. 
target. (1) Syn. anticathode. (2) A cold 
plate placed in the path of a beam of molecular rays, 
which condense in a spot on the cold surface. 
Schirmgitterroehre: screen-grid tube. A form of am- 
plifier vacuum tube in which the plate is surrounded 
by a positively charged wire mesh, in order to prevent 
variations of plate potential from affecting the grid fila- 
ment circuit and thus causing feedback. 
schlagen: hammer, hammering. See klopfen. 
Schleife: loop. (1) Syn. antinode. (2) A graph in 
the form of a cyclic closed curve, e.g., a hysteresis loop. 
Schleifdrahtbruecke: slide-wire bridge. A bridge cir- 
cuit, one or more branches of which are controlled by 
a sliding contact whose position can be adjusted along 
a wire stretched upon a linear scale. 
Schleifenelek+rome+er: string electrometer. An elec- 
trometer consisting of a conducting fiber stretched mid- 
way between two conducting plates parallel to it. The 
field between the plates displaces the fiber laterally by 
an amount dependent'upon the p.d. 
Schleifengalvanometer; string galvanometer. See Eint- 
hoven-Elektrometer. 
Schlupf: slip. The excess of the angular speed of the 
rotating field of an induction motor over that of the 
rotor, expressed either in rpm or as a fraction or per- 
centage of the field speed. 
Schmelzkurve: fusion curve. The fusion curve follows 
the equilibrium between solid and liquid states. 
Schmelzwaerme: heat of fusion. The quantity of heat 
absorbed by a substance, per unit mass, upon passing 
from the solid to the liquid state, or released upon 
solidification; in either case without change of tem- 
perature. 
Schnecken-oder Schraubenlinie: helix. (1) A space 
curve which lies in the surface of a cylinder, and re- 
sembles a corkscrew. (2) A coil of wire wound in the 
approximate form of a geometrical helix. 
Schni+tmodul: section modulus. The ratio of the sec- 
tional moment of inertia of the cross section of a beam 
/Schni+fraegheitsmoment 
130 s 
or rod to the distance from the neutral axis to the most 
distant point of the section. 
Schnittraegheitsmoment: sectional moment of inertia. 
The areal moment of inertia of the cross section of an 
elastic beam or column with respect to the neutral axis; 
a constant which appears in formulas for the flexure of 
such members. 
Schot+ky-Effekt: Schottky effect. (1) The dependence 
of the saturation current in a thermionic vacuum tube 
upon the electric intensity E at the cathode; expressed 
by 
1.91 
I. = V E 
T 
in which T is the absolute temperature of the cathode. 
(2) Syn. shot effect. 
Schroedinger'sche Gleichung: Schroedinger equation. 
A wave equation set up by Schroedinger to represent the 
de Broglie wave. It contains the wave function in 
the form 
87r2m 
V2* + (W — V) * - 0 
h2 
in which m is the particle mass, W the total energy, 
V the potential energy, and h the Planck constant. 
Schroteffekt: shot effect. A statistical irregularity in 
the emission of thermions or photoelectrons, which, 
upon amplification, may be detected by a popping noise 
in a telephone receiver. First explained by Schottky. 
Syn. Schottky effect. 
Schueler'sche Roehre: Schueler tube. A vacuum tube 
having a hollow cathode, used for the production of 
ionized gas or vapor spectra. 
Schumann Bereich: Schumann region. A range of 
very short ultraviolet wave lengths, extending down to 
about 1200 A. 
Schumann Gebiet: Schumann region. See Schumann 
Bereich. 
Schumann Platte: Schumann plate. A type of photo- 
graphic plate, containing very little gelatin, prepared 
by V. Schumann, and especially adapted to use in the 
extreme ultraviolet and in positive-ray analysis. 
Schutzring: guard ring. An outer region A surround- 
ing any enclosure or area B in which it is desired, to 
maintain uniform conditions throughout or to avoid 
edge effects; B being shielded from nonuniformity by 
creating in A approximately the same conditions as 
those required in B. 
Schwaechung: attenuation. The falling off of the flux 
density, as of radio waves, with distance from their 
source, due to any cause. 
Schwaechungsfalc+or: attentuation factor. A measure 
of the transparency of a layer of absorbing medium for 
an emission traversing it. It is the ratio of the flux 
density I of the emergent emission to the flux density 
I0 of the incident emission, for an exponentially ab- 
sorbed emission, the value of the factor, for thickness 
x of a medium whose absorption coefficient is is 
e-ß-x. Syn, transmission factor. 
Schwankung: hunting. (1) The alternate lag and ad- 
vance of a synchronous motor with respect to the cur- 
rent, or of one of two coupled alternators with respect 
to the other. (2) A condition of instability in a control 
device, such as the thermostat or an engine governor, 
resulting in large fluctuations in the quantity which the 
device is intended to keep constant. 
Schwankungskurve: rocking curve. The graph or con- 
tour of the intensity variation of the X-ray reflection 
from a crystal with the angle of incidence in the neigh- 
borhood of a diffraction maximum. The amplitude of 
variation of the incidence angle is the rocking angle. 
Schwankungsphotometer: flicker photometer. A pho- 
tometer in which the matching of illuminations is de- 
termined by the absence of flicker when one is rapidly 
substituted for the other in the field of view. 
schwarzer Koerper: black body. See idealer Strahler. 
schwarze Koerperfunktion: black-body function. (1) 
The product a T4, representing the emissive power of a 
black body at absolute temperature T, in accordance with 
the Stefan-Boltzmann law; a being the S.-B. constant. 
(2) The function expressing the value of dEA/dA in 
the Planck equation. 
schwarze Koerperkonstante: black-body constant, Syn. 
Stefan-Boltzmann constant. The constant of proportion- 
ality in the Stefan-Boltzmann law for the emissive power 
of a black body. Its experimental value is 5.735 X 10^5 
erg cm-2 seer1 deg-4. 
schwarze Koerperstrahlung: black-body radiation, Syn. 
cavity radiation. See Hohlraumstrahlung. 
schwarze Koerpertemperatur: black-body temperature. 
The temperature of any body as indicated by a radiation 
pyrometer which has been calibrated by the use of a 
black body. 
Schwebung: beat. A maximum or minimum of inten- 
sity arising from the interference of two wave trains 
of unequal frequency. 
131 
/Schwebungston s 
Schwebungston: beat tone. A* musical tone due to 
beats, produced by the interference of two h.-f. wave 
trains, as in radio reception. 
Schwellenfrequenz: threshold frequency. See lang- 
wellige Grenze. 
Schwere: gravity. (1) The resultant effect, upon any 
body of matter belonging to the earth or other planetary 
mass, of the gravitational field of the mass and the cen- 
trifugal force of the body due to the planetary rotation. 
(2) The intensity of the effect (1), as measured by 
the force per unit mass of the body, or by the resulting 
acceleration of the body if free to move; commonly de- 
noted by g. Its standard terrestrial value is taken by 
international agreement as 980.665 cm/sec2. 
Schwerdruck: gravity force. Is the force which the 
earth exerts on a body and which is distributed evenly 
throughout that body. This force can be thought to 
be concentrated at the center of gravity. 
Schwerepotential: gravitational potential. See Gravita- 
tionspotential. 
schwerezentrisch: centrobaric. Having a true center of 
gravity. A rigid body is centrobaric if the resultant 
gravitational attraction of an external particle for it is 
equivalent to a single force which always passes through 
one point fixed relatively to the body (its center of 
mass), irrespective of its orientation and position. E.g., 
a homogeneous sphere or spherical shell is centrobaric, 
but bodies in general are not. Syn. baricentric. 
Schwerdruckzentrum: center of gravity. Is that point 
in body, at which the total weight of the body can be 
assumed to be concentrated. 
Schwerkraftkonstante: gravitation constant. See Gravi- 
tationskonstante. 
Schwerpunkt: center of gravity. The c.m. of a centro- 
baric body. Center of gravity and center of mass have 
come to be synonymous in common usage; but in a 
nonuniform gravitational field a center of gravity, in its 
true sense, exists only for centrobaric bodies. 
Schwimmflaeche: flotation plane. The plane of the 
level surface of the liquid in which a body floats. 
Schwlngzeit: period. See Periode. 
Schwingungsanalyse: vibrational analysis. The analy- 
sis of a molecular spectrum into bands, with the assign- 
ment of a definite pair of vibrational quantum numbers 
to each band, and the determination of a formula for 
all the bands in terms of these two quantum numbers. 
Schwingungsdauer: period. See Periode. 
Schwingungsgalvanometer: vibration galvanometer. A 
type of a.-c. galvanometer in which the natural oscilla- 
tion frequency of the moving element is equal to the 
frequency of the a.-c. applied to it. 
Schwingungsgenerator: circuit driver. A source of 
h.-f. e.m.f., esp. of the vacuum-tube-controlled type, 
for experimental use. Syn. radio-frequency generator. 
Schwingungsmesser: vibroscope. An apparatus, con- 
sisting of tuning forks vibrating at right angles, used 
by Lissajous for studying harmonic motions. 
Schwingungsquantenzahl: vibrational quantum number. 
A quantum number, associated with the vibration of 
the atoms about mean positions in a molecule, which 
must be an integer for any permissible stationary state 
of such vibration. 
Schwingungsspektrum: vibration spectrum. See Mole- 
kuelspektrum. 
Schwingungstransformator: oscillation transformer. A 
helix of many turns in which very high p.d.’s are pro- 
duced by means of inductive coupling with a circuit 
containing a condenser and a spark gap. A transformer 
having such a coil as its secondary, with the condenser 
and gap in the primary circuit, is called a Tesla oscilla- 
tion transformer. 
Schwingungszentrum: center of oscillation, center of 
suspension. (1) One of two conjugate points of a 
gravity pendulum, of which the other is the center of 
suspension. (2) One of two conjugate points of a grav- 
ity pendulum, of which the other is the center of oscil- 
lation. 
sechseckig: hexagonal. See hexagonal. 
Seebeck'scher Effekt: Seebeck effect, Syn. thermoelec- 
tro motive force. The e.m.f. given by two contacting 
metals and depending upon the metals and upon the 
temperature distribution in them. In a circuit of dif- 
ferent metals joined in series, the resultant e.m.f. is 
the algebraic sum of the e.m.f.’s due to the several 
conjoined pairs. Discovered by Seebeck in 1821. 
Sehachse: visual axis. The line joining the fixation 
point of the ocular field of view with the first nodal 
point of the eye. 
Sehwlnkel: visual angle. The angle formed at the 
eye by any two rays of light entering it. 
Seismograph: seismograph. An apparatus for record- 
/Sei+enband 
132 s 
ing the time, the direction, and the intensity of seismic 
disturbances (earth tremors). 
Seiten band: side band. A component of a modulated 
carrier current (or carrier wave) which comprises fre- 
quencies either above or below the carrier frequency, 
including those current (or wave) components whose 
frequencies are the sum or the difference of the carrier 
and the modulation frequencies; called the upper and 
the lower side band, respectively. 
Sekundaerelektron: secondary electron. (1) An elec- 
tron belonging to a secondary emission, as those emitted 
in various directions by substances bombarded by cath- 
ode rays. (2) That electron which, after a collision 
of two electrons, has the less energy. 
Sekundaeremission: secondary emission. An emission 
from matter which results from exposure to a primary 
emission; e.g., fluorescence or photoelectrons. If it is 
in the nature of radiation, it is usually called secondary 
radiation. 
Sekundaerfluoreszenz: sensitized fluorescence. A "sec- 
ond-hand” fluorescence, viz., the emission of radiation 
by one atom due to energy received in collision with 
another atom which has been excited by radiation. 
Sekundaerkreis: secondary circuit. The circuit in which 
an e.m.f. is induced by the variation of the current in 
another circuit, the primary, as in a transformer. 
Sekundaerspektrum: secondary spectrum. (1) The 
spectrum of the hydrogen molecule as distinct from that 
of the atom. (2) A spectrum overlapping from another 
order. (Rare or obs. in this sense.) 
sekundaerer Standard: secondary standard. See Pro- 
totyp. 
Sekundaerstandard: secondary standard. (1) A unit 
defined as a specified multiple or submultiple of a pri- 
mary standard; e.g., the centimeter and the foot, based, 
respectively, upon the standard meter and the standard 
yard. (2) Syn. prototype. 
Sekundaerstruktur: secondary structure. A regularly 
recurring variation which may exist in the atomic lat- 
tice arrangement or primary structure of a crystal by 
reason of electric or other stresses inherent in its physi- 
cal make-up and which is manifested as a distortion of 
the lattice and a variation of the lattice "constant” from 
point to point. 
Sekundaerzelle: secondary cell, Syn. storage cell. See 
Primaerzelle. 
Selbstinduktion: self-induction. An e.m.f. induced in 
a circuit, due to the change in the magnetic flux linked 
with it as a result of the variation of current in the 
circuit itself. 
Selbstionisation: auto-ionization. An automatic disso- 
ciation of a molecule, which occurs when the sum of 
its vibrational and electronic energies exceeds the energy 
necessary for dissociation. 
selbstphotoelektrisch: autophotoelectric. See autopho- 
toelektrisch. 
Selbssttransformator: autotransjormer. See Autotrans- 
formator. 
Selektanz: selectance. Any one of several measures for 
the falling off of the response of a resonance device 
with departure from resonance; e.g., the ratio of the 
amplitude of response at resonant frequency to that at 
some frequency differing from it by a specified amount. 
selektiv: selective. (1) Operating on a group of in- 
dividuals, in different degrees depending upon some 
variable attribute of the members of the group. E.g., a 
selective reflector reflects a larger proportion of some 
wave lengths than of others. (2) In re an emitter of 
radiation; yielding radiation of different spectral energy 
distribution from that of a blacl$ body at the. same tem- 
perature. 
Selektivifaet: selectivity. The degree in which any 
operation is selective, expressed in suitable measure, e.g., 
selectance, spectral resolving power, etc. 
Selenzelle: selenium cell. An arrangement in which 
is suitably mounted a thin film of selenium provided 
with electric terminals, for utilizing the photoconduc- 
tive property of that element. 
Sellmeier'sche Dispersionsformel: Sellmeier dispersion 
formula. See Ketteler-Helmholtz Dispersionsformel. 
semipermeable Membran: semipenrieable membrane. 
See halbdurchlaessige Membrane. 
senkrecht: vertical. (1) The direction of gravity. (2) 
(Geocentric.) The direction of the radius of the earth. 
The two cioncide, in general, only at the poles and at 
points on the equator. 
Serie: series. See Reihe. 
Seriengrenze: series limit. The convergence frequency 
of a series of spectral lines. No line occurs at this 
point, but a related continuous spectrum may begin just 
beyond it. 
133 
/Shenstone'scher Effekt s 
Shenstone'scher Effekt: Shenstone effect. An increase 
in the photoelectric emission of certain metals immedi- 
ately after having been traversed by an electric current. 
Shower: shower. See Schauer. 
Shunt: shunt. See Nebenschluss. 
sichtbar: ocular. See augenscheinlich. 
Sichtbarkeitsfaktor: visibility factor. For radiation of 
a given wave length: the ratio of the luminous flux at 
that wave length to the corresponding radiant flux. 
For the normal eye it has a maximum in the green, of 
about 660 lumens per watt. An expression for this 
factor in terms of wave length is called a visibility 
function. 
Sichtbarkeitsfunktion: visibility function. See Sicht- 
barkeitsfaktor. 
Sichtbarkeitsmesser: visibility meter. An instrument 
for measuring the clearness of definition with which 
an object can be seen under given circumstances. 
Sieden: ebullition. See Kochen. 
Siedepunkt: boiling point (of a liquid). The tempera- 
ture at which the maxinium vapor pressure of the liquid 
is in equilibrium with the superimposed pressure. If 
the latter is the normal atmospheric pressure (760 mm), 
this temperature is the normal boiling point. 
Siedepunktsgesetz; boiling-point law. States that the 
boiling point of a solvent is elevated by the addition 
of a nonvolatile solute in proportion to the molar con- 
centration of the solute. The boiling-point constant is 
the elevation in boiling point produced by adding 1 
mol of a solute to 1000 g of solvent. 
Siedepunktskonstante: boiling-point constant. See 
Siedepunktsgesetz. 
Sigma-Wert: sigma value. The value of the quantum 
number which quantizes the component of angular mo- 
mentum of spin about the axis of figure in a diatomic 
molecule. 
Silikastab: silica pencil. A rod of silica, electrically 
heated and used as a source of infrared. 
singender Lichtbogen: singing arc. An electric arc of 
such characteristics as to generate an oscillating current 
of audio frequency when an inductance and a con- 
denser are connected across it; e.g., the Duddell carbon 
arc or the Poulsen carbon-copper arc. Syn. oscillating 
arc. 
singende Roehre: singing tube. A pipe or resonator 
set into musical vibration by local heating. Special forms 
have been devised by Bosscha, Knipp, Rijke, and others. 
singulaerer Punkt: singular point (or line). A point 
(or line) in a field of force, at which (or along which) 
the field intensity or the potential gradient is zero. 
singulaere Temperatur: singular temperature. A tem- 
perature at which some property of a substance becomes 
discontinuous, e.g., a transition temperature at which 
the specific heat has a discontinuity. 
Sinusbedingung: sine condition. A condition, stated 
by Abbe, which is fulfilled by any aplanatic optical 
system. If n, and n2 are the refractive indices of the 
media in which the object and the image lie, if ax and 
a2 are the angles made with the axis by any ray as it 
leaves the object and as it reaches the image, and if 
y1 and y2 are corresponding linear dimensions of object 
and image, the condition is expressed by 
sin ttl _ n2y2 
sin a2 niYi 
sinusfoermig: sinusoidal. Varying in proportion to 
the sine (or the cosine) of an angle or of a time 
function. 
Sinusgalvanometer: sine galvanometer. An instrument 
resembling a tangent galvanometer, but in which the 
coil is turned until it lies in the plane of the deflected 
needle. The sine of the deflection is then proportional 
to the current. 
Sirene: siren. An acoustic instrument consisting of a 
revolving disk perforated with equally spaced holes, 
through which blasts of air escaping in rapid succes- 
sion produce a musical tone. 
skalares Produkt: scalar product. In re two vectors, 
P15 P2: the product of the magnitudes of the two vectors 
by the cosine of the angle between them. Syn. dot 
product, because of the use of a dot between the two 
vector symbols to indicate it: P1*P2. 
Skiaskop: skiascope. An instrument for studying the 
optical refraction within the eye. 
Skineffekt: skin effect. See Hauteffekt. 
Slug (engl. Masseneinheit): slug. A name proposed for 
a unit of mass in the British gravitational system; de- 
fined as the mass of a free body which, if acted upon 
by a force of 1 lb, would experience an acceleration of 
1 ft/sec2. Its value is thus about 32.17 lb. 
smetisch: smetic. See mesomorph. 
/Smith-Helmholtz'sche Formel 
134 s 
Smith-Helmholtz'sche Formel: Smitb-Helmholtz for- 
mula. An invariant relation concerning the imagery 
produced by paraxial rays in a centered system of spheri- 
cal refracting surfaces. If ©1? ®2, ©3, etc., denote the 
angles which a ray makes with the axis in the successive 
media of indices n15 n2, n3, etc. and if the magnifica- 
tion ratios at the points where the ray crosses the axis 
are JVYi. y3-Ti> etc-> then 
niYi®i = n2y2®2 = n3y3®3 = 
Snell'sches Gesetz: Snell law. The law of ordinary 
refraction of light, which states that the angles of 
incidence and of refraction have sines in a constant 
ratio to each other, and lie in the same plane. The 
constant ratio of the sines is equal to the refractive 
index. 
Sol: sol. A highly disperse colloid (Graham). 
Solarimeter: solarimeter. A pyrheliometer devised by 
L. Gorczynski for direct readings of solar radiation in- 
tensity from sun and sky. 
Solarisation: solarization. (1) An actinic effect of 
sunlight or of artificial ultraviolet upon glass, which 
results in a reduction of its transparency to ultraviolet 
and is also usually accompanied by a permanent colora- 
tion. (2) A reversal of gradation sequence in a dense 
photographic image sometimes observed when the nor- 
mal development is applied after overexposure. Still 
greater exposure may restore the original sequence, or 
may even result in a second reversal. 
Solarkonstante: solar constant. The total intensity of 
the solar radiation at the outer limit of the atmosphere, 
hence unaffected by atmospheric absorption. Its value 
is about 0.032 cal/cm2sec or 1.34 X 106 ergs/cm2 sec. 
Soleil'sche Platte: Soleil plate. A type of optical 
compensator, somewhat like that of Babinet, but so con- 
structed as to introduce the same relative phase change 
over the entire field at once, instead of varying it pro- 
gressively across the field. 
Solenoid, solenoid. A helix or cylindrical coil of wire, 
used to produce a magnetic field or to excite an electro- 
magnet. 
Sommerfeld'sche Konstante: Sommerfeld constant. A 
dimensionless constant, equal to 27re2/hc; in which e is 
the elementary charge in e.s.u., h the Planck constant, 
and c the electromagnetic constant. Its value is about 
0.007284. 
Sonnenwaermemesser: pyrheliometer, pyroheliometer. 
See Pyroheliometer. 
Soret'scher Effekt: Soret effect. An inequality of con- 
centration which develops in different parts of a solu- 
tion, initially homogeneous, when these parts assume 
different temperatures; the cooler portions becoming 
more concentrated than the warmer. 
Sorption: sorption. A term including both (molecular) 
absorption and adsorption. 
Spaltung: cleavage. The tendency of a crystalline sub- 
stance to split along definite planes, called cleavage 
planes, which correspond to the layers of atoms making 
up the crystalline structure. 
Spannung: pull; voltage, tension. (1) Electromotive 
force as measured or expressed in volts. (2) A force 
applied to a body in such a way as to produce elonga- 
tion in the direction of the force. 
Spannungsmesser: voltmeter. An instrument for meas- 
uring e.m.f., usually directly in volts or in multiples or 
submultiples thereof. 
Spannungsvervielfacher: voltage multiplier. A series 
arrangement of condensers charged by rapidly rotating 
brushes, resulting in a high d.-c. voltage. 
Spektralanalyse: spectrum analysis. The analysis of 
chemical substances by means of their spectra. 
Spektralapparat: spectroscope. Any one of various 
forms of instrument for dispersing radiation and observ- 
ing the resulting spectrum. 
Spektralbolometer: spectrobolometer. An infrared spec- 
trometer utilizing a bolometer as the receiving in- 
strument. 
spektrale Empfindlichkeit: spectral sensitivity, Syn. pho- 
toelectric yield. The rate of photoelectric emission from 
a metal per unit radiant flux of any given frequency. 
Spektralenergieverteilung: spectral energy distribution. 
The distribution of the intensity of radiation through- 
out the spectrum, i.e., of the monochromatic flux den- 
sity as a function of the wave length or frequency. Such 
distributions are commonly represented by graphs, viz., 
by spectral energy curves. 
Spektralfarbe: spectral color. The color sensation pro- 
duced by a narrow frequency range of stimulating radia- 
tion, i.e., by monochromatic light. (A similar sensation 
may, however, be produced in other ways; the eye being 
unable to make the distinction.) 
Spektralhelioskop: spectrohelioscope. An instrument 
for observing an image of the entire sun by light of 
/Spektralkomparator 
677865—46—10 
135 s_ 
one wave length. If used photographically, it is called 
a spectroheliograph. 
Spektralkompara+or: spectrocomparator. A compara- 
tor designed especially for the measurement of line 
spectra. 
Spektrallinie: spectrum line. (1) A definite wave 
length or very narrow range of wave lengths; the spec- 
trum of monochromatic radiation. It corresponds to a 
distinct image of the spectroscope slit made by the 
single wave length. (2) One of the traces made by 
a mass spectrograph, which correspond to atoms of dif- 
ferent mass. 
Spektrallinienverbreiterung durch lonen-oder Atom- 
stoss: collision damping. An effect upon the amplitude 
or phase of the radiation from an atom due to collision 
with other atoms, which results in one type of broaden- 
ing of the spectrum lines. 
Spektralphotometer: spectrophotometer. A combina- 
tion of a photometer and a monochrometer, used for 
making spectroradiometric measurements in the visible. 
Spektralphotometrische Analyse: spectrophotometric 
analysis. A quantitative analysis based upon the spectral 
energy distribution in the absorption spectrum of a sub- 
stance in solution. . 
spektralphotoelektrisch: spectrophotoelectric. Pertain- 
ing to the dependence of photoelectric or photovoltaic 
phenomena upon the wave length of the incident ra- 
diation. 
Spektralpyrheliometer: spectropyrheliometer. An in- 
strument used for the determination of the spectral 
distribution of the total solar radiation. 
Spektralradiometer: spectroradiometer. (1) An instru- 
ment for ascertaining the spectral energy distribution 
of any type of radiation, e.g., a spectrophotometer, but 
esp. in the infrared. (2) An infrared spectrometer. 
(3) An apparatus of the wavemeter type arranged to 
analyze the wave-length-intensity characteristic of the 
output from a radio transmitter. 
Spektralreihen: spectral series. A series of frequencies 
occurring in a characteristic radiation or absorption spec- 
trum, which converge, or appear at progressively shorter 
intervals, in the direction of decreasing wave length and 
in accordance with a definite numerical law. In general, 
the spectrum of an element may have several series, 
designated as principal, first subordinate or diffuse, sec- 
ond subordinate or sharp, fundamental or Bergmann, 
etc. 
Spektralschwerpunkt: spectral centroid. The wave 
length which corresponds to the center of area of the 
wave-length-intensity (spectrophotometric) curve for 
light of a given quality. 
spektrale Selektivltaet: spectral selectivity. The varia- 
tion of some property of a substance or a surface with 
the wave length or frequency of incident radiation. 
Spektralserien: spectral series. See Spektralreihen. 
Spektraltermen; spectral terms. The fractions occur- 
ring in the binomials which are proportional to the fre- 
quencies or wave numbers of a spectral series. 
Spektralthermograph: Jpectrothermo graph. A spectro- 
graph for the study of thermal radiation. 
Spektrograph: spectrograph. A spectroscope which re- 
cords a spectrum photographically. 
Spektrometer: spectrometer. A spectroscope provided 
with a graduated circle or other equipment for rneasuT 
ing the deviations, and, indirectly, the wave lengths, 
corresponding to spectral lines. 
Spektroskop: spectroscope. See Spektralapparat. 
Spektrum: spectrum. The result of separating or dis- 
persing an emission (such as light) and arranging it in 
accordance with some progressive property (as its fre- 
quency), which thus constitutes a systematic analysis. 
Spekulum (Legierung): speculum metal. An alloy of tin 
and copper, (about 33 percent Sn), capable of taking 
a very high polish; used for optical mirrors and espe- 
cially for reflecting gratings. 
Sperrschicht: blocking layer. The surface of contact 
between a metal and a semiconductor (e.g., copper and 
cuprous oxide), which acts as a rectifier and, when il- 
luminated, is the seat of a photovoltaic e.m.f. Syn. bar- 
rier layer. 
spezifische Brechbarkeit: specific rejractivity. The re- 
fractivity divided by the density. 
spezifisches Brechungsvermoegen: specific refractive 
power. See Lorenz-Lorentz’sche Beziehung. 
spezifische Elektronenwaerme: electron specific heat. 
That part of the specific heat of a metal which is due 
to the free electrons; usually negligible compared with 
that due to the atomic lattice. It becomes significant at 
very low temperatures and, for ferromagnetic metals, 
near the Curie point. 
/spezifische Energie 
136 s 
spezifische Energie: specific energy. The internal en- 
ergy per unit mass of a body. 
spezifische Entropie: specific entropy. The entropy per 
unit mass of a body. 
spezifisches Gewicht: specific gravity, specific weight. 
(1) The ratio of the density of any substance to the 
maximum density of water. (2) The weight of a sub- 
stance per unit volume; in absolute equal to the density 
multiplied by gravity. 
spezifische induktive Kapazitaet: specific inductive ca- 
pacity, Syn. dielectric constant. (1) The ratio of the 
dielectric constant of a substance to that of a vacuum. 
(2) The ratio of the capacitance of a condenser filled 
with a given dielectric to that of the same condenser 
when evacuated. See also dielektrische Konstante. 
spezifische Kohaesion: specific cohesion. A term used, 
in connection with Laplace’s theory of surface tension, 
to denote twice the ratio of the surface tension to the 
density of a liquid. 
spezifische Ladung: specific charge, Syn. charge-mass 
ratio. The ratio of the electric charge carried by an 
electrified particle or ion to the mass of the particle. 
spezifisch-magne+isches Rota+ionsvermoegen: specific 
magnetic rotary power, Syn. Verdet constant. The angle 
of optical rotation per oersted intensity per centimeter 
thickness in the Faraday effect. 
spezifische Magnetisierung: specific magnetization. See 
Magnetisierung. 
spezifische Rotationswaerme: rotational specific heat. 
That part of the specific heat of a substance which per- 
tains to the energy of molecular rotation, as distinct 
from translational motion and internal vibration. 
spezifisches Rotationsvermoegen: specific rotatory 
power. See Rotationsvermoegen. 
Sprengel'sche Pumpe: Sprengel pump. A type of mer- 
cury air pump, dependent upon the dropping of mercury 
down a tube. 
spezifische Schwingungswaemne: vibrational specific 
heat. That part of the specific heat of a substance which 
pertains to the energy of internal vibration within the 
molecule, as distinct from translational motion and 
rotation, 
spezifische Suszep+ibili+aet: specific susceptibility. See 
Suszeptibilitaet. 
spezifische Viskositaef: specific viscosity. The ratio of 
the viscosity coefficient of a fluid to that of some stand- 
ard substance, usually water at a specified temperature. 
spezifisches Volumen: specific volume. The volume of 
a substance per unit mass; the reciprocal of the density. 
spezifische Waerme: specific heat. (1) The thermal 
capacity per unit mass of a substance; usually expressed 
in cal/g°C. (2) The abstract ratio of the thermal 
capacity of any mass of a substance to that of an equal 
mass of water at 15 degrees C. 
spezifischer Widerstand: resistivity, Syn. specific re- 
sistance. rhat factor of the resistance of a conductor 
which depends upon the material and its physical con- 
dition. Its measure is the resistance of a specimen, in 
the form of a rod of unit length and unit cross section, 
to a current traversing it longitudinally. Usually ex- 
pressed in ohm-centimeters. 
spezifische Zaehigkeit: specific viscosity. See spezi- 
fische Viskositaet. 
sphaeroidaler Zustand: spheroidal state. A term ap- 
plied to the condition of a liquid in apparent contact 
with a hot solid, but with a layer of the liquid’s vapoi 
between; e.g., a drop of water on a hot plate, 
Sphaerometer: spherometer. One of several types oi 
instrument for measuring the curvature of spherical sur- 
faces, e.g., of lens surfaces. 
Spiegelungsfaktor: reflectance, Syn. reflection factot. 
The ratio of the total luminous flux reflected by a given 
surface to that incident upon it. 
Spinnkopplung: spin coupling. The interaction between 
the fields due to the spins of electrons. The energy 
differences between singlets and triplets are associated 
with differences in resultant spins. The term is also 
occasionally used for the interaction of the resultant 
electron spin with the resultant orbital angular momen- 
tum. Syn. spin-spin interaction. 
Spinnmoment: spin moment. The rotational moment 
of momentum of an electron on its own axis. 
Spinnquantenzahl: spin quantum number. The quan- 
tum number associated with the quantization of the 
angular momentum arising from the internal spin of 
the electrons. For a system containing a single electron, 
its value is Yl‘> in general, it is an odd or even multi- 
ple of l/2 according as the number of electrons is odd 
or even. 
Spinor: spinor. A two-dimensional, complex vector; 
so named because it may be used to define the spin of 
an electron. 
137 
/SpifzenefFekt s 
Spitzeneffekt: edge effect. See Kanteneffekt. 
SpreitungskoefFizient: spreading coefficient. The abso- 
lute value of the change in free energy which takes 
place when one liquid spreads on the surface of an- 
other, e.g., a drop of oil on water. 
sprunghafte Temperaturabnahme: decalescence. The 
reverse of recalescence; i.e., an abrupt decrease in the 
rate of temperature rise as heat is applied to the metal, 
indicating an endothermic structural change. 
Spule: coil. A ring or spiral formed by winding. 
Stabilitaet: stability. (1) That property of the stable 
equilibrium of a body or a system, which is measured by 
the amount of energy which must be applied to render 
it unstable. (2) The reciprocal of the sensitiveness of 
an instrument such as a balance. 
Stabilitaetsbereich; range of stability. The angle 
through which a floating body may be rotated from its 
equilibrium position without capsizing, i.e., before the 
restoring torque becomes zero. 
Staerke: strength, force. Any cause that produces, 
stops, changes, or tends to produce, stop, or change, 
the motion of a body. 
Stalagmome+er: stalagmometer, Syn. stactometer. An 
instrument for measuring the size of liquid drops, or 
for measuring the liquid by drops; esp. in the study of 
surface tension. 
Standardkapazi+aef: capacitor. A condenser of fixed 
capacitance used as a standard or as a capacitance load. 
S+ark-EfFekt: Stark effect. A somewhat complicated 
effect upon the spectral series of gaseous elements, pro- 
duced by subjecting the radiating atoms to a strong, 
transverse electric field (e.g., 100,000 v/cm) ; discov- 
ered in the case of hydrogen by J. Stark in 1913. Each 
spectral line becomes split up into polarized components. 
Stark-Lunelund'scher Effekt: Stark-Lunelund effect. The 
polarization of light emitted by a beam of moving atoms 
in the absence of a field. 
Statik: statics. See Gleichgewichtslehre. 
stationaere Schwebungen: stationary beats. See Disso- 
nanz (2). 
stationaere Welle: stationary wave. A condition of 
equilibrium at certain points or along certain lines or 
surfaces (nodes) in a medium, with regions of vibra- 
tion between them; brought about by the interference 
of similar wave trains traveling in opposite directions. 
Syn. standing wave. 
statisch: static. (1) (adj.) Pertaining to the phe- 
nomena and laws of statics. (2) (n) Radio disturbance 
due to natural causes, of whatever origin. 
Statisches Atom: static atom. See Lewis-Langmuir’- 
sches Atom. 
statische Elektrizitaet: static electricity. Electricity in 
the form of a charge in equilibrium, or considered ir- 
respective of the effects of its motion. 
statisches Gleichgewicht: static equilibrium. Equi- 
librium in which all parts of the system are relatively 
at rest. 
statische Hysteresis static hysteresis. A type of per- 
manent deformation or elastic lag in a stressed solid, 
which is independent of the rate of loading. 
statische Laenge static length. The length of a body 
in the classical or Newtonian sense, i.e., not affected 
by the Lorentz-Fitzgerald contraction. 
statische Maschine: static machine. A machine for 
generating electric charges, usually by electric induction. 
Syn. electrostatic machine, induction machine. 
stationaere Linie: stationary line. An absorption line 
in the spectrum of a star which does not exhibit the 
Doppler shift observed in the other lines, and is at- 
tributed to the existence of absorbing gas in interstellar 
space. Syn. interstellar line. 
statistisches Gewicht: statistical weight. See Quanten- 
gewicht. 
statistisches Gleichgewicht: statistical equilibrium. That 
state of a statistical variable in which all variations are 
due to a distribution of chance causes. E.g., the mole- 
cular velocities in a gas at constant volume and tem- 
perature are in state of statistical equilibrium, which is 
altered to another such state when the volume is 
changed. 
statistische Mechanik: statistical mechanics. That 
branch of physical science in which the laws describ- 
ing the gross behavior of systems composed of many 
particles (e.g., molecules) are investigated by statistical 
methods. 
statistische Variable: statistical variable. A variable 
whose observable magnitude is subject to chance, i.e., 
is under incomplete control; e.g., accidental error, the 
range of individual alpha particles in air, etc. 
/statistiche Veraenderliche 
138 _s 
sta+Is+ische Veraenderliche: statistical variable. See 
statistische Variable. 
Stafoskop: statoscope. A very sensitive aneroid al- 
timeter. 
Stefan-Boltzmann'sches Gesetz: Stefan-Boltzmann law. 
States that the total emissive power of a black body is 
proportional to the fourth power of its absolute tem- 
perature. First arrived at empirically by Stefan and later 
deduced theoretically by Boltzmann. 
Stefan-Bcltzmann'sche Konstante: Stefan-Boltzmann 
constant. See schwarze Koerperkonstante. 
stehende Welie: standing wave. See stationaere Welle. 
Steilheit: mutual conductance. In re a grid-controlled 
tube: the increment of plate current per unit change 
of grid potential. Syn. transconductance. 
Steinmetz'sche Formel: Steinmetz formula. An em- 
pirical formula for the magnetic hysteresis loss of energy 
per unit volume per cycle, viz., 
w — aBnii-6 ; 
in which Bm is the maximum induction during the 
cycle, and a a constant known as the Steinmetz coeffi- 
cient (q.v.), hysteretic constant, or hysteresis-loss con- 
stant. 
S+einmetz'scher Koeffizient: Steinmetz-coeffcient. See 
Hysteresiskonstante. 
Stellarinterferometer: stellar interferometer. An at- 
tachment for astronomical telescopes, consisting of an 
opaque cover over the objective in which are two 
parallel slits at an adjustable distance apart. Two images 
thus produced overlap and give rise to interference 
phenomena by means of which angular diameters of 
very small objects may be measured. Developed by 
Michelson. 
Stereophotometer: stereophotometer, Syn. stereoscopic 
photometer. A type of photometer in which light from 
the two sources compared falls simultaneously upon the 
same moving object. If a straight path is to appear 
straight, the two illuminations must be equal. Devised 
by Pulfrich. 
stereoskopisch: stereoscopic. Exhibiting a three-dimen- 
sional character, as in binocular vision of nearby objects. 
stereoskopischer Radius: stereoscopic radius. The great- 
est distance at which the stereoscopic effect can be per- 
ceived. For the unaided eyes, it is about 1500 ft; with 
the aid of a prism binocular, it is greater. 
Stereovermoegen: stereo power. In re a prism bi- 
nocular or similar optical system: the ratio of the dis- 
tance between objective axes to the distance between 
eyepiece axes, multiplied by the magnifying power. It 
indicates how many times the stereoscopic radius is 
increased by the instrument. 
Stern-Gerlach'sches Feld: Stern-Gerlacb field. A spe- 
cial, nonhomogeneous magnetic field used in studying 
molecular rays. It is produced by a wedge-shaped pole 
piece facing another pole in which there is a deep 
notch or channel. 
Stern-Gerlach'scher Versuch: Stern-Gerlach experiment. 
An experiment in which a stream of metallic atoms, de- 
flected by a strong, nonuniform magnetic field, is split 
into two parts, one part deflected toward the higher 
magnetic intensity, the other toward the lower. It gives 
evidence of directional quantization, and thus supports 
the quantum theory of atomic magnetic moments. 
Stern'scher Vervielfacher: Stern multiplier. A device 
due to Stern for converging a number of narrow beams 
of molecular rays at one point, thus securing an enhanced 
effect. 
stetiger Fluss: steady flow. A condition of flow such 
that the velocity of the fluid at any fixed point in the 
space occupied by the flow remains unchanged; though 
the velocity of any given particle of the fluid may be 
continually changing. 
stigmatisch: stigmatic. (1) In re a bundle of rays: 
Syn. homocentric. (2) In re an optical system; having 
equal focal power in all meridians. 
Stilb: stilb. A name proposed by Blondel for the unit 
of brightness of a luminous surface, viz., 1 candle/cm2. 
Stimmgabelsirene: tuning fork siren. An apparatus 
designed by Lord Rayleigh, having an adjustable slit 
in the side of a wind chest, the width of which is 
controlled by the vibrations of a tuning fork. When 
air emerges through the slit, the tuning fork is thereby 
maintained in vibration. 
* 
Stoerstelle: fault. See Fehler. 
Stoerstrom; parasite. See Parasit. 
Stoerung: distortion, a. A change in wave form in 
the transmission of a composite electric wave over a 
communication line, in which different component fre- 
quencies are transmitted with different speeds or with 
unequal attenuation. In a distortionless line, this effect 
is minimized by the use of certain devices, h. An im- 
677865—46 11 
139 
/Stokes'sche Gesetze s 
perfection in an optical image, due to spherical aberra- 
tion or similar defects of the optical system. 
perturbation, a. (Spect.) An irregularity 
in the spacing of the lines of a band spectrum, b. A 
deviation of the values of terms in a spectral series from 
the appropriate series formula, c. (Cryst.) The influ- 
ence of thermal agitation on the relations between 
atoms in a crystal or in a molecule. A deviation of a 
celestial body from the ideal orbital motion, due to 
some disturbing force. 
Stokes'sche Gesetze: Stokes laws. (1) States that 
the force required to propel a spherical body of radius 
r at uniform speed v through a viscous medium of vis- 
cosity coefficient -q is (2) States that the wave 
length of luminescence excited by radiation is always 
greater than that of the exciting radiation; in general 
valid, but with notable exceptions. 
Sfokes'sche Linie: Stokes line. A line of the Raman 
spectrum which is displaced toward the long-wave- 
length side of the incident light; so called by analogy 
with the Stokes law (2) of luminescence. Lines dis- 
placed to the short-wave-length side are called anti- 
Stokes lines. 
Stoss: Stoss (Germ.), collision. See Kollision. 
Stossen, stossweises Sieden: bumping. Sudden, explo- 
sive ebullition. 
Stossfluoreszenz: impact fluorescence. Fluorescence pro- 
duced in atoms of one element by collisions (of the 
second kind) with excited atoms of another. Syn. im- 
pact radiation. 
Stossparameter: impact parameter. The distance of the 
initial line of motion of a scattered particle from the 
center of the scattering field, e.g., of the path of an 
incident electron from the nucleus of the scattering 
atom. 
Stosspolarisation: impact polarization. Partial polari- 
zation detected in radiation excited by impact. 
S+osstrahlung: impact radiation, Syn. impact fluores- 
cence. See Stossfluoreszenz. 
Stosswahrscheinlichkeit: collision probability. In re 
collosions of electrons with the atoms of a gas: the 
number of collisions per unit electron current, per unit 
path length, per unit pressure at 0 degree C. 
Stosswelle: surge. (1) A highly accelerated flow, e.g., 
that due to suddenly applied pressure or voltage. (2) 
A general change of atmospheric pressure, distinct from 
local cyclonic and diurnal changes. 
Stosszentrum: center of percussion. One of two con- 
jugate points of a free body acted upon by an impulse, 
the other of which lies on the axis of instantaneous 
rotation. 
S+rahlenin+erferome+er: beam interferometer. A form 
of stellar interferometer in which the effective distance 
between the slits is increased by means of mirrors 
mounted on a rigid beam beyond the edge of the ob- 
jective. First used by Michelson to measure apparent 
diameters of stars. 
Strahlenpfeil: sagittal ray. Any one of a narrow bun- 
dle of rays in a symmetrical optical instrument which 
lies in the longitudinal section of the bundle made by 
the plane containing the chief ray and perpendicular 
to the meridian section. 
Strahlung: radiation. See Radiation. 
Strahlung des schwarzen Koerpers: cavity radiation, 
Syn. black-body radiation. See Hohlraumstrahlung. 
Strahlungsdaempfung: radiation damping. A decrease 
in the amplitude of an electric oscillation due to the 
emission of energy by radiation; distinct from that due 
to ohmic resistance. 
Strahlungsdiagramm; radiogram. An X-ray pattern 
produced by crystal diffraction. 
Strahlungsdruck: radiation pressure. A pressure ex- 
erted upon a surface exposed to light or other electro- 
magnetic radiation, the value of which is proportional 
to the radiant energy density in the space to which 
the surface is exposed. 
Strahlungsenergie: radiant energy. Energy trans- 
mitted through the agency of electromagnetic radiation. 
strahlungserzeugt: radiogenic. 
Strahlungsgleichgewicht: radiative equilibrium. The 
maintenance of a constant temperature by the absorption 
and emission of radiant energy at the same rate. 
Strahlungsintensitaet: radiant intensity. In re a point 
source of radiation: the radiant flux emitted per unit 
solid angle (spheradian) in a specified direction. 
Strahlungsmanometer: radiometric gauge. Any low- 
pressure gas manometer dependent upon the inequality 
of pressure due to molecular bombardment on opposite 
sides of a suspended vane; e.g., the Knudsen gauge. 
Strahlungsmesser: radiometer. See Lichtmuehle. 
/Strahlungspotential 
140 s 
Strahlungspotential: radiation potential. The p.d. in 
volts, corresponding to the energy, in electron-volts, 
required to excite an atom or a molecule to emit one 
of its characteristic radiation frequencies. The first r.p. 
excites the lowest frequency, etc. Syn. resonance po- 
tential. 
Strahlungspotentiometer: radiation potentiometer. An 
apparatus for studying the spectral energy distribution 
of thermal radiation, by the potentiometer comparison 
of the thermoelectric effects of radiation from limited 
spectral ranges with that of the total radiation. 
Strahlungspyrome+er: radiation pyrometer. A pyro- 
meter which gives the temperature of the heated body 
by measuring the total intensity or the spectral energy 
distribution of the thermal radiation emitted by it. 
Strahlungsrueckwirkung: radiation reaction. A force 
acting upon a body by reason of its emission of radia- 
tion, the direction of the force being opposite to that 
in which the radiation is emitted. It is the counter- 
part of force involved in radiation pressure. 
Sfrahlungsfemperafur: radiation temperature. See ef- 
fektive Temperatur. 
S+rahlungsvekfor: vector radiant. See Poynting’scher 
Vektor. 
Strahiungsvermoegen: radiant flux, r. power. Rate 
of emission of energy in the form of radiation, ex- 
pressed in watts or other power units. 
Sfrahlungswiders+and: radiation resistance. That part 
of the apparent or measured resistance of an oscillating 
circuit which is due to the loss of energy through 
Hertzian radiation. 
Sfra+osphaere: stratosphere. The atmosphere above 
the tropopause. Through its explored portion (the 
lower 20 km or so), the temperature normally changes 
but little with altitude, vertical convection is slight, and 
the winds are essentially horizontal; the term is limited 
by some to this portion. Syn. isothermal region. 
S+reckungsgrenzflaeche: limiting surface of stress. A 
surface, the rectangular coordinates of whose points 
represent the three principal stresses in an elastic sub- 
stance when its elastic behavior reaches the stage of 
plasticity. 
S+reckungslinie: line of stress—principal stress tra- 
jectory. An imaginary line extending through a stressed 
elastic substance in the direction of principal tension, 
compression, or shear. Syn. principal stress trajectory. 
Streifen: fringe. A band or stripe of maximum or 
minimum illumination, due to interference or diffraction. 
StrelfenbÜdung: striation. (1) A striped appearance of 
the positive column in a Crookes tubes at suitable pres- 
sures, consisting of transverse, alternate bright and dark 
bands. (2) One of the minute, parallel ridges some- 
times visible on the natural faces of crystals. 
streuen: scatter. To diffuse in various directions by 
reflection from molecules, atoms, electrons, or other 
particles; e.g., radiation and corpuscular emissions are 
scattered upon encountering matter. 
Streufaktor: scattering factor. The ratio S of the actual 
intensity of X-rays scattered in any direction by electrons 
to that which would exist if, in accordance with the 
classical theory of J. J. Thomson, the electrons acted 
independently. Syn. S-value. 
S+reukoeffizient: scattering coefficient. That part of 
the extinction coefficient which is due to scattering. It 
is defined in a manner similar to the absorption coeffi- 
cient and is added with it to form the total attenuation 
or extinction coefficient. Distinction must be made be- 
tween the spatial scattering coefficient (for a given 
stactering angle) and the total or spherical s.c. (includ- 
ing all angles). The mass s.c. is the s.c. divided by 
the density. 
straggling coefficient. A measure of 
the straggling observed in the range of alpha particles 
in an absorbing medium, relative to the range itself. 
Its value is approximately 2.096 times the ratio of the 
probable error of the (Gaussian) straggling distribu- 
tion to the mean range of the particles. 
Streuung: straggling. The statistical variation in the 
range different alpha particles, all of the same initial 
speed, in the same gas. The (Gaussian) distribution 
corresponding to this variation is represented by the 
straggling curve, similar to the normal error curve. 
Streuvermoegen: scattering power. The ratio of the 
total energy of scattered radiation per unit length of 
path in a scattering medium to the energy of the in- 
cident beam. 
S+reuwinkel: scattering angle. The angle between the 
original direction of an emission and its direction after 
scattering. 
Stripped Atom: stripped atom. See elektronenberaubtes 
Atom. 
Stroemungspotential: streaming potential. A p.d. pro- 
duced by the flow, under pressure, of a liquid through 
a capillary tube or a membrane. It may be regarded as 
the inverse of electro-osmosis. Syn. flow potential. 
/Strombrechung s 
Strombrechung: current refraction. A change in the 
direction of an electric current at an interface between 
two conductors of different conductivity. 
Stromdichte: current density. The magnitude of a 
current per unit cross-sectional area; in the case of the 
electric current, it is commonly expressed in amperes 
per square centimeter. 
Stromlinie: streamline. The contour of a longitudinal 
section of an object, such as a boat or an airplane, so 
shaped as to move through a fluid medium with mini- 
mum friction. Syn. line of flow. 
Stromlinienflaeche: hydrofoil. A blade or vane set in 
such a way as to experience a lateral thrust as it moves 
through the water, e.g., a rudder, or one of the blades 
of a screw propeller. 
Stromlinienkoerper or Fluegel: aerofoil. A blade or 
wing set in such a way as to experience a lifting force 
as it moves through the air, e.g., the wing of an air- 
plane. 
Stromroehre: stream tube. See Flussroehre. 
Stromstaerke fuer den Ausschlag I (Empfindlichkeit): 
figure of merit. In re a galvanometer: that current which 
will produce a deflection of one scale division. 
Stromunterbrecher: interrupter. See elektrischer Ham- 
mer. 
Strukturfaktor: structure amplitude factor, structure 
factor; Syn. atom form factor. A quantity occurring in 
the expression for the intensity of an X-ray beam re- 
flected by a crystal, whose value depends upon the vary- 
ing configuration of the electrons in the crystal atoms 
relative to the center of the atom, as well as upon the 
angle of incidence and the wave length of the X-rays. 
Stufe: pitch. That characteristic of a musical sound 
which is determined by the position to which the normal 
ear assigns it in the musical scale. 
Sublimation: sublimation. The transition of a substance 
from the solid directly to the vapor state, or vice versa. 
In the latter case, the solid formed is called a subli- 
mate, e.g., white frost. 
Sublimationsdruck: sublimation pressure. The solid 
vapor equilibrium pressure of a volatile solid at a given 
temperature. 
Sublimationskurve: sublimation curve. See Gleichge- 
wichtskurve. 
Sublimationswaerme: heat of sublimation. The heat 
liberated or absorbed, per unit mass, upon the sublima- 
tion of a substance. 
subtraktive Farbe: subtractive color. A color produced 
by the removal of some part of white light, as by 
passage through one or more filters. 
Summations+on: summation tone. A combination tone, 
heard under certain circumstances, whose pitch corre- 
sponds to a frequency equal to the sum of the fre- 
quencies of the two components. 
Summenregel: sum rule, Syn. permanence principle. 
Either of two "sum rules” relating, respectively, to the 
sums of the Lande factors and interval factors of the 
components in the Zeeman effect; which state that 
the sum of the values of the factor in question for all 
the J values, other quantum numbers remaining con- 
stant, is independent of the magnetic intensity. 
Sumptner'sches Prinzip: Sumptner principle. The prin- 
ciple, stated by Sumptner, which is employed in the 
Ulbricht sphere, viz., that when a source of light is 
placed at any point inside a sphere with perfectly dif- 
fusing walls, every part of the interior appears equally 
illuminated when viewed through an opening. 
Supraleitfaehigkeit: superconductivity, suprac. The 
greatly enhanced electrical conductivity attained by cer- 
tain metals when cooled to a sufficiently low tempera- 
ture, at which the resistance suddenly drops to a very 
low value. 
Suspension: suspension. (1) The state of a finely 
divided material sustained by thermal agitation in a 
fluid medium, as smoke particles in the air. (2) Any 
material so sustained. (3) A fine wire or filament by 
which a galvanometer coil or similar apparatus is sus- 
pended in an instrument. 
Suspensoid: suspensoid. A colloidal sol in which the 
particles do not unite with the suspending medium. 
Called by Perrin a lyophobe sol. 
Suszeptanz: susceptance. In re an a.-c. circuit having 
inductance L and capacitance C: the value of the 
quantity 
1 
— 2-n-nC, 
27rnL 
in which n is the frequency. 
Suszeptibilitaet: susceptibility. See elektrische Suszcp- 
tibilitaet. 
/Sutherland'sches Gesetz 
142 s 
Sutherland'sches Gesetz: Sutherland law. Expresses 
the viscosity coefficient 97 of a gas in terms of its abso- 
lute temperature T, as follows: 
T0 + C # T x ®/2 
v = vo ) 
T + C V T0 / 
in which C is a constant. rj0 is the value of 77 at the 
ice point T0. 
Sylphon: sylphon. A closed cell with thin, corrugated 
metal walls, resembling the bellows of an accordion; 
used in high-pressure research on fluids, and in certain 
thermostats. 
Symmetrie: symmetry. (1) An arrangement of ob- 
jects or parts of a figure with reference to a point, a 
line, or a plane so that for each particle or point on 
one side there is a corrseponding one at an equal dis- 
tance on the other side of the reference zero. If the 
reference zero is a point, the term point symmetry or 
radial symmetry is used; if a line, the symmetry is said 
to be axial; if a plane, it is bilateral. (2) (Cryst.) An 
arrangement of objects or parts of a figure such that 
they appear to be hung, either singly or in groups of 
constant configuration, on a space lattice whose structure 
regularly repeats itself in three dimensions in space. 
Symmetrieebene: symmetry plane. A plane which di- 
vides a body or a figure in such a way that any line 
perpendicular to the plane and terminated by the boun- 
daries of the object or figure is bisected by the plane. 
A principal s.p. is one having at least two other s.p.’s 
perpendicular to it, which could be interchanged with- 
out apparently altering the orientation of the object or 
figure. 
Symme+riezahl: symmetry number. The number of 
different symmetry planes of a body or a group of 
atoms. E.g., for a regular tetrahedron the number is 
12. The term was applied to molecules by Ehrenfest. 
sympathetische Schwingung: sympathetic vibration. 
Vibration due to resonance. 
Synchronophosphoroskop: synchrono-phosphoroscope. 
An apparatus for examining phosphorescence of brief 
duration. 
Synchroskop: synchroscope. A form of oscillograph 
used to test the phase difference or synchronism of two 
a.c.’s or electric oscillations. 
Szintillation: scintillation. A minute flash of light ob- 
served when an alpha particle strikes a suitable lumi- 
nescent screen in the dark. 
Szintilloskop: spinthariscope. An instrument devised by 
Crookes for conveniently viewing the scintillations of 
alpha particles upon a luminescent screen. 
143 
/Tachometer T 
Tachometer; tachometer, tachymeter. See Geschwindig- 
keitsmesser. 
Tag: day. (1) (Mean solar.) The average interval, 
during the year, between successive meridian passages 
of the sun. It is the basic unit of time used in physics. 
(2) (Sidereal.) The period of the earth’s complete 
rotation on its axis, equal to 23 h 56 m 4.09054 s mean 
solar time. (3) (Lunar.) The period between succes- 
sive meridian transits of the moon, average about 24 
h 50.5 m mean solar time. 
Tageslichtfaktor: daylight factor. The ratio of the 
daylight illumination at any point in a building to the 
simultaneous illumination under the open sky. 
Tageslichtphotometer: hemeraphotometer. A type of 
photometer used for measuring daylight factor. 
Talbot'sche Bande: Talbot bands. Interference bands 
appearing in a prism spectrum when half of the aper- 
ture is covered by a thin glass plate with the edge 
parallel to the edge of the prism. 
Taibot'sches Gesetz: Talbot law. States that when two 
or more luminous areas are presented to the eye at regu- 
lar intervals, so that each is seen in turn for a certain 
time, e.g., on a rotating color disk, there is a definite 
frequency of alteration for which the resultant color 
impression is invariable and is identical with the im- 
pression which would result if all the lights were seen 
simultaneously at their mean intensities. 
Tangen+engalvanometer: tangent galvanometer. A gal- 
vanometer with a fixed field coil, for which the tangent 
of the deflection is proportional to the current. 
Tangen+enmesser: derivator. A device for measuring 
the slope of a curve at any point and hence, indirectly, 
the value of the derivative of the corresponding func- 
tion. Syn. tangent meter. 
Target: target. See Schicht. 
Taupunkt: dew point. The temperature at which the 
condensation of the water vapor in the air begins for 
any given state of humidity, as the air is cooled. A 
dew point hygrometer indicates the dew point, from 
which the relative humidity may be calculated. 
Teilknoten: partial node. See angenaeherter Knoten- 
punkt. 
Teilton: partial, Syn. overtone. (1) One of the fre- 
quencies with which a vibrating body or system can 
freely oscillate, in addition to the lowest frequency. 
(2) A musical sound produced by a sonorous body 
vibrating with one of its higher possible frequencies. 
Teilungsmaschine: dividing machine, dividing engine, 
ruling engine. (1) A mechanism operated by a long 
micrometer screw, for marking the divisions on instru- 
mental scales. (2) A mechanism operated by a long 
micrometer screw, for ruling the equally spaced lines 
on optical gratings. Its principle is similar to that of a 
dividing machine. 
Telephotographie: telephotography. (1) Photography 
of distant objects by means of a special magnifying 
camera objective system. (2) The reproduction of 
photographs or other pictures at a distance by means of 
electric currents or radio. 
Telethermome+er: telethermometer. An apparatus in 
which temperature effects are electrically communicated 
to a measuring or recording instrument at some distance 
away; commonly a thermocouple or a resistance ther- 
mometer circuit. 
telezentrisch: telecentric. In re an optical instrument: 
having either the entrance-pupil at infinity, e.g., when 
a front stop is placed in the anterior focal plane of a 
convergent lens—a device commonly used in optical 
measurements to avoid parallax between image and 
scale. 
Temperaturfaktor: temperature factor. See Debye Tem- 
peratufaktor, Debye-Waller’scher Faktor. 
Temperaturkoeffizient: temperature coefficient. The 
increment of a quantity, which is a function of the 
temperature, due to unit change of temperature; i.e., 
the temperature rate or derivative of a quantity. E.g., 
the t.c. of a standard cell is its change in voltage per 
degree. 
Temperaturwelle: temperature wave. A progressing 
variation of temperature, such as that inaugurated by 
strongly heating one end of a long bar of cold metal. 
A succession of such waves would result from alter- 
nately heating and cooling the end of the bar. 
tempern: anneal. To stabilize the internal structure of 
a solid substance, e.g., glass or a metal, by protracted 
heating followed by slow cooling. 
Tensor: tensor. The absolute or numerical value of a 
vector. 
Tesla Spule: Tesla coil. A helix of many turns in 
which very high p.d.’s are produced by means of induc- 
tive coupling with a circuit containing a condenser and 
/tetragonal 
144 T 
a spark gap. A transformer having such a coil as its 
secondary, with the condenser and gap in the primary 
circuit, is called a Tesla oscillation transformer. 
tetragonal: tetragonal. In re crystal structure: having 
three mutually rectangular axes, two of which only are 
equal. 
Tetrode: tetrode. A vacuum tube having four elec- 
trodes, e.g., a screen-grid tube. 
Thalofid: t halo fide. A photoconductive composition 
of thallium, oxygen, and sulphur, developed by T. W. 
Case. 
Thermion: thermion. An ion, either positive or nega- 
tive, which has been emitted from a heated body. Nega- 
tive thermions are electrons (thermoelectrons). 
thermionische Arbeitsfunktion: thermionic work func- 
tion. See Arbeitsfunktion, Richardson’sche Gleichung, 
thermionische Emissionskonstante. 
thermionische Emission: thermionic emission. A stream 
of thermions emitted by a heated body. 
thermionische Emissionskonstante: thermionic emission 
constant. A constant appearing in the Richardson equa- 
tion for thermionic emission when written in the form 
I - A T2e ~ T-, 
in which w is the thermionic work function. It has the 
same value for all metals, viz., about 120 amp/cm2deg2. 
thermionischer Gleichrichter: thermionic valve. An 
electric-current rectifier based on the unidirectional char- 
acter of the thermionic current. 
thermische Analyse: thermal analysis, thermoanalysis. 
The investigation of physical transition processes or of 
chemical reactions by observing discontinuities in the 
absorption or evolution of heat, e.g., the recalescence 
transitions in iron, manifested by abrupt changes in 
temperature. 
thermische Bewegung: thermal agitation. A random 
movement of the molecules of a substance, which is be- 
lieved to give rise to the phenomena associated with 
heat and the kinetic energy of which is the usual inter- 
pretation of that term. 
Thermische Ionisation: thermal ionization. Ionization 
due to high temperature, as in the electrically conducting 
gases of a Bunsen flame. Syn. temperature ionization. 
thermische Stroemung: thermal transpiration. A pres- 
sure difference which develops between two bodies of 
gas, initially at the same low pressure but at different 
temperatures, when they are joined by a capillary tube. 
The flow is from the colder to the warmer gas. Discov- 
ered by Federsen and Reynolds. Syn. thermal effusion, 
thermodiffusion. 
Thermodynamik: thermodynamics. That branch of phy- 
sical science which treats of processes involving the 
conversion of heat into other forms of energy, and 
vice versa. 
thermodynamische Gesetze: thermodynamic laws. Two 
laws upon which rests the classical thermodynamic the- 
ory: (1) When work is expended in generating heat, 
the quantity of heat produced is proportional to the 
work expended; and, conversely, when heat is employed 
in the performance of work, the quantity of heat which 
disappears is proportional to the work done. (Joule.) 
(2) It is impossible for a self-acting machine, unaided 
by any external agency, to convey heat from a body of 
lower to one of higher temperature. (Clausius.) Or, 
it is impossible to derive mechanical work from heat 
taken from a body unless there is available a body of 
lower temperature into which the residue not so used 
may be discharged, (Kelvin.) (3) In addition to these, 
some writers refer to the following as the "third law 
of thermodynamics”: Every system has a finite, posi- 
tive entropy, but at the absolute zero of temperature, 
the entropy may become zero, and does so become in 
the case of perfect crystalline substances. This state- 
ment, formulated by Planck, is closely related to the 
Nernst heat theorem. 
thermodynamisches Gleichgewicht: thermodynamic 
equilibrium. The condition of a system whose members 
have conformed to the principle of equipartition of 
energy. 
thermodynamischer Kreis: thermodynamic cycle. A 
cyclic change of state of a body or a system which in- 
volves changes of temperature or the transmission of 
heat to or from the body or system. 
thermodynamisches Potential: thermodynamic poten- 
tial. In re any thermodynamic state of a substance: a 
mathematical expression for the work or change in 
energy per unit mass involved in bringing it to that 
state. It is, in general, a function of the variables which 
determine the state of the substance. So named by rea- 
son of the analogy to such cases as the energy of a body 
with reference to its position in a field of force. Syn. 
thermal potential, thermal head. 
thermodynamische Skala: thermodynamic scale. See 
Kelvin’sche Skala. 
thermodynamische Transformation: thermodynamic 
transformation. A change in the state of a body or 
145 
/thermodynamische Umwandlung T 
system which involves changes of temperature or the 
emission or absorption of heat, e.g., the expansion of 
a gas, with accompanying decrease of pressure and 
temperature. 
thermodynamische Umwandlung: thermodynamic trans- 
formation. See thermodynamische Transformation. 
thermodynamische Wahrscheinlichkeit: thermodynamic 
probability. The probability of a given state of dis- 
tribution and motion of the molecules of a body, as 
compared with that of some arbitrarily chosen reference 
state. It is proportional to the number of complexions 
which would result in that state. 
thermoelastisch: thermoelastic. Pertaining to the ther- 
modynamics of elastic processes, e.g., the heat generated 
by the deformation of an elastic body or the fall of 
temperature when it recovers etc. 
, * 
thermoelastische Koeffizienten: thermoelastic coeffi- 
cients. Two quantities relating to an elastic body, and 
defined by the expressions 
— v(8p/8v)T, — v(8p/8v)g. 
In these v is volume, p is pressure, T is temperature, 
s is entropy; and the subscripts denote that the cor- 
responding quantity is to be kept constant. These quan- 
tities are the reciprocals, respectively, of the isothermal 
and isentropic compressibilies. 
thermoelektrisches Element: thermocouple. A pair of 
metals forming a junction (thermojunction), considered 
as the seat of a thermoelectromotive force. 
thermoelektrische Leistung: thermoelectric power. The 
change in the thermoelectromotive force of a thermo- 
couple per degree of change in its temperature. The 
thermoelectric power of any metal is that of a couple 
composed of the given metal against some standard 
metal, usually lead. 
thermoelektrische Loetstelle; thermofunction. A pair 
of metals forming a junction (thermojunction), con- 
sidered as the seat of a thermoelectromotive force. 
thermoelektrisches Manometer: thermoelectric mano- 
meter. A manometer which depends upon the variation 
of thermoelectromotive force with pressure; devised by 
Rohn. 
Thermoelektrisches Thermometer: thermel. A term 
used to cover all forms of thermoelectric thermometer, 
whether single thermocouples or series of couples (ther- 
mopiles or multiple thermels). 
thermoelektrische Umkehrung: thermoelectric inver- 
sion. The phenomenon, exhibited by a thermocouple, 
of decreasing its e.m.f. with increasing temperature 
beyond a certain neutral point. 
thermoelektromotorische Kraft: thermoelectromotive 
force. The e.m.f. given by two contacting metals and 
depending upon the metals and upon the temperature 
distribution in them. In a circuit of different metals 
joined in series, the resultant e.m.f. is the algebraic sum 
of the e.m.f.’s due to the several conjoined pairs. Dis- 
covered by Seebeck in 1821. Syn. Seebeck effect. 
Thermoelektron: thermoelectron. See Thermion. 
Thermoelement: thermoelement. A combination of a 
thermocouple with a heating filament, used for measur- 
ing small currents. 
Thermogalvanometer: thermogalvanometer. A galvano- 
meter for the measurement of feeble h.-f. a.c.’s by their 
heating effect, detected by a sensitive thermocouple. 
Devised by W. Duddell in 1904. 
Thermograph: thermograph. A recording thermometer. 
Thermolumlneszenz: thermoluminescence. Luminescence 
exhibited by certain substances, as fluorite, when heated, 
but of wave length distinctly shorter than that of the 
incandescence corresponding to the exciting high tem- 
perature. Thus fluorite crystals heated on an iron plate 
may give off white light before the adjacent iron 
is even red hot. 
thermomagnetisch: thermomagnetic. Pertaining to the 
effects of a magnetic field upon the flow of heat or 
the temperature distribution in a conductor; e.g., in the 
Nernst effect; or to the effects of temperature upon 
the magnetic properties of a substance. 
thermomagnetische Potentialdifferenz: thermomagnetic 
potential difference. A change in the e.m.f. of a ther- 
mojunction, due to placing it in a magnetic field. 
Thermomanometer: thermogauge. A form of optical 
pyrometer, devised by Morse. 
Thermometerkorrektion: stetn correction. A correction 
applied to the reading of a liquid-in-glass thermometer 
because of the fact that the liquid in the stem is at a 
different temperature from that in the bulb. 
thermometrische Koeffizienten: thermometric coeffi- 
cients. Two quantities relating to a body of working 
substance; defined by the expressions 
1 f SP \ 1 / 8v \ 
p \8T/v’ v \ ST / p 
In these T is temperature, v is volume, p is pressure; 
/thermomotorische Kraft 
146 T 
and the subscripts denote that the corresponding quan- 
tity is to be kept constant. 
thermomotorische Kraft: thermomotive force. That 
which, in thermal phenomena, is analogous to electro- 
motive force in the corresponding electrical phenomena; 
e.g., the temperature difference developed in the Etting- 
hausen effect. 
Thermophon: thermophone. (1) A musical tone gen- 
erator composed of a thin strip of metal immersed in 
a gas or a volatile liquid and periodically heated by an 
d.c. (2) A form of teiethermometer in which a tele- 
phone receiver is used. 
Thermophosphoreszenz: thermophosphorescence. Phos- 
phorescence developed by heating after exposure to 
some exciting agency. 
Thermorelais: thermorelay. A device, due to Moll, for 
amplifying small galvanometer deflections. The gal- 
vanometer mirror reflects a bright beam of light upon a 
sensitive thermojunction in such a way that very slight 
deflections of the beam cause relatively large changes 
at the junction. A second galvanometer actuated by the 
thermocouple may thus be made to show deflections 
many times as large as the original. 
Thermosaeule: thermopile. A thermel consisting of a 
number of thermocouples in series, which amplifies the 
temperature effect. 
Thevenin'scher Lehrsatz: Thevenin theorem. States 
that when two points A and B of a circuit or network 
carrying a current (either steady or alternating) are 
connected by a shunt S, the resulting current in S is 
equal to the original p.d. between A and B, divided by 
the sum of the parallel impedances of the shunt S and 
the portion AB of the original circuit. 
Thixo+ropie: thixotropy. A phenomenon exhibited by 
some gels, which, when gently shaken, break up and 
form a fluid with all the properties of the original sol, 
but which, when left undisturbed, resume the form of a 
gel again. This process may be repeated indefinitely. 
Thomas'sche Praezession: Thomas precession. The pre- 
cession of the spin axis of an electron due to the ac- 
celeration given to the electron by the electric field of 
the nucleus. 
Thomson (Kelvin) Effekt: Thomson (Kelvin) effect. An 
effect manifested when an electric current is passed 
through a metallic conductor of nonuniform tempera- 
ture, e.g., in the simplest case, a wire on which there 
is a sharp temperature maximum. When the current 
flows, the maximum is observed to move, with the cur- 
rent in some metals, against it in others. 
Thomson'sche elektromotorische Kraft: Thomson elec- 
tromotive force. A p.d. existing between two points of 
different temperature on a metallic conductor; studied 
by William Thomson (Kelvin). 
Thomson'sche (Kelvin) Doppelbruecke: Thomson (Kel- 
vin) double bridge. A bridge having eight arms, used 
for comparing two resistance standards having both 
current and potential terminals. 
Thomson'scher Koeffizient: Thomson coefficient. The 
ratio of the Thomson e.m.f. in a metal to the corre- 
sponding difference in temperature. Syn. specific heat 
of electricity. 
Thomson'scher Polarisationsfaktor: Thomson polariza- 
tion factor. A factor to which the intensity of an X-ray 
beam reflected from a crystal is proportional and which, 
as derived by J. J. Thomson, is equal to the function 
1/2(1 + cos2 2©) 
of the glancing angle ©. 
Thomson'sche Waerme: Thomson h%at. The quantity 
of heat which must be supplied or withdrawn in order 
to maintain a unit temperature difference between two 
points of a conductor at a given mean temperature 
when unit quantity of electricity flows from one point 
to the other, and thus to neutralize the Thomson effect. 
Thomson-Whiddingfon-Bohrsches Gesetz: Thomson- 
Whiddington-Bohr law. Expresses the depth to which 
cathode electrons penetrate a material target in the 
production of X-rays as V2/b, in which V is the voltage 
and b a constant, known as the Thomson-Whiddington 
constant, depending upon the material and other cir- 
cumstances. 
Thorium Reihe: thorium series. One of the principal 
radioactive series, beginning with thorium. 
Thyratron: thyratron. An arc discharge tube contain- 
ing inert gas or vapor at low pressure, in which a grid 
is employed to control the starting of the discharge. 
Tiefenmesser: fathometer. See Fadenmesser. 
tieferer Zustand: lower state. That one of the two 
energy states or levels, before and after a quantum tran- 
sition, in which the atom or the molecule has less elec- 
tronic energy. 
Tiltometer: tiltometer. An instrument which measures 
inclination to the horizontal. 
toenender Lichtbogen: singing arc. An electric arc 
of such characteristics as to generate an oscillating cur- 
/Toepler-Holtz'sche Maschine 
147 rent of audio frequency when an inductance and a 
condenser are connected across it; e.g., the Duddell 
carbon arc or the Poulsen carbon-copper arc. Syn. oscil- 
lating arc. 
Toepler-Holtz'sche Maschine: Toepler-Holtz machnie. 
A type of static machine having one stationary and one 
rotating plate, or a number of such pairs. 
Toleranz: tolerance. See erlaubte Abweichung. 
\ 
Tonmesser: sonometer. See Monochord. 
Tonvariator: tonvariator. An adjustable resonator for 
comparison of musical pitches, the frequency of which 
is varied by means of a piston having a graduated scale. 
Designed by Stern. 
Tonveraenderer; tonvariator. See Tonvariator. 
Torricellisches Gesetz: Torricelli law. States that the 
speed of efflux of nonviscous fluid issuing from an 
orifice at a depth h below the level of the free surface 
in the container, under the influence of gravity alone, is 
v - V 2gh. 
Torricellisches Vakuum: Torricellian vacuum. A space 
evacuated by filling it with mercury and then lowering 
the reservoir more than 76 cm below the bulb, as in a 
barometer. 
Torsion: torsion. The strain due to twisting a rod, 
wire, or filament; measured by the angle of rotation 
of one cross section with respect to another at unit 
distance from it. 
Torsionskoeffizient: torsion coefficient, t. constant. The 
torque exerted in twisting an elastic rod per unit total 
angle of twist. 
Torsionskonstante: torsion constant, t. coefficient. See 
T orsionskoeff izient. 
Torsionskopf: torsion head. A rotary cap, often gradu- 
ated in degrees, atop the vertical tube supporting a tor- 
tion suspension, e.g., in a galvanometer or a magneto- 
meter. 
Torsionsmesser: torsometer. An instrument for study- 
ing the elastic behavior of solids under torsion, esp. 
by optical methods. 
Torsionsmodul: torsion modulus, Syn. shear modulus, 
rigidity modulus. The ratio of the shearing stress in 
an elastic substance to the strain (shear) which accom- 
panies it. 
Torsionspendel: torsion pendulum. A pendulum actu- 
ated by the torsion of an elastic wire. 
torische Linse: toric lens. A lens, one surface of which 
is a portion of the surface of a tore. Much used for 
spectacles. 
Totaler Absorptionskoeffizient; total absorption coeffi- 
cient, Syn. extinction coefficient. In re any type of 
radiation traversing a material medium: the absorption 
coefficient plus the scattering coefficient. 
totaler elastischer Wirkungsquerschnitt: total elastic 
cross section. In re atoms scattering electrons of given 
velocity: the number of electrons scattered per atom 
from an electron beam whose intensity is 1 electron 
per unit area per unit time. 
totales Emissionsvermoegen: total emissive power. See 
Emissionsstaerke. 
totale Quantenzahl: total quantum number, Syn. prin- 
cipal quantum number. The sum 1 + 1', of the azi- 
muthal and the radial quantum number in the Bohr 
theory, or 1 -f- 1' + 1 in the new quantum mechanics 
(since in the latter 1 is one less). So called because 
the energy of a quantum state depends primarily upon 
it. The principal quantum number is usually denoted 
by n. 
totale Retlektion: total reflection. Internal reflection 
in which the angle of incidence exceeds a value, known 
as the critical angle, whose sine is the relative refrac- 
tive index from the more to the less refractive medium; 
so called because all the radiation is reflected and none 
transmitted. 
totale Spiegelung: total reflection. See totale Reflek- 
tion. 
Totalwaerme: total heat. See Enthalpie. 
Townsend'sche Charakteristik; Townsend characteristic. 
The current-voltage characteristic curve for a photoelec- 
tric cell at constant illumination and at voltages below 
the glow potential. 
Townsend'sche charakteristische Kurve: Townsend 
characteristic. See Townsend’sche Charakteristik. 
Townsend'sche Entladung: Townsend discharge. Any 
space-charge-free electrical discharge in a gas at moder- 
ate pressure above 0.1 mm, whether self-or externally 
maintained. More loosely, Syn. coroqa. 
Townsend'sche Gleichung; Townsend equation. An ex- 
pression for the photoelectric current in a gas, as a 
/Townsend'scher Koeffizient 
148 T 
function of the distance d between plates, and having 
the form 
I = Iuead 
a is the Townsend coefficient, which may be interpreted 
as the number of new ion pairs produced by the im- 
pacts per unit length of electron path. 
Townsend'scher Koeffizient: Townsend coefficient. See 
Townsend’sche Gleichung. 
Traegheit: inertia. See Beharrungsvermoegen. 
Traegheitsellipsoid: inertia ellipsoid. An ellipsoid so 
drawn, in reference to any point of a rigid body, that 
the radius vector from the center of the ellipsoid to any 
point on its surface represents the reciprocal square root 
of the moment of inertia of the body about that vector 
as an axis. The axes of the ellipsoid coincide with the 
principal axes of the body through the given point. 
Traegheitsmomenf: moment of inertia. Of a rigid 
body with respect to any axis: the volume integral of 
the product of the element of mass by the square of its 
distance from the given axis. It represents the torque 
required, per unit angular acceleration in radian meas- 
ure, to change the speed of rotation of the body about 
that axis. Syn. rotational inertia. 
Traegheifsmomentellipsoid: momentum ellipsoid. An 
ellipsoid drawn with reference to the principal axes of 
inertia of a rigid body in free rotation (under no ex- 
ternal torque) about a changing instantaneous axis, and 
used to represent graphically the relation between the 
resultant angular velocity and the position of the in- 
stantaneous axis when the angular momentum is con- 
stant. 
Traeghei+sprodukt: product of inertia. In re any body, 
with respect to any pair of rectangular axes X and Y: 
the value of the volume integral J f f xydxdydz taken 
throughout the volume of the body. 
Traegheitszentrum: center of inertia, Syn. center of 
mass. In re any body or system of bodies: a point such 
that if any plane be passed through it, the mass mo- 
ments, with respect to it, of the portions on opposite 
sides of the plane are equal. 
Transforma+ionskons+an+e: transformation, constant, 
Syn. disintegration constant. The decay coefficient for 
radioactive disintegration. 
Transforma+ionsperiode: transformation period. The 
half-value period for the decay of the activity of a radio- 
active substance. 
Transforma+ionsverhaeltnis: transformation ratio. The 
ratio of the voltage in the secondary to that in the pri- 
mary of a transformer. 
Transformator: transformer. A device which, through 
magnetoelectric induction but without the use of mov- 
ing parts, transforms alternating or intermittent electric 
energy in one circuit into energy of similar type in an- 
other circuit, commonly with altered values of the volt- 
age and current. 
Transkonduktanz: transconductance, Syn. mutual con- 
ductance. In re a grid-controlled tube: the increment 
of plate current per unit change of grid potential. 
Translation: translation. See fortschreitende Bewe- 
gung. 
transversale Effekte: transverse effects. A term col- 
lectively applied to the Hall, Ettingshausen, Nernst, 
and Righi-Leduc effects (q.v.). 
transversale Masse: transverse Mass. The mass of a 
body measured in the relativistic sense, in a direction 
perpendicular to that of its motion relative to the 
observer; in contradistinction to its longitudinal mass 
(q.v.). 
Trennungsfaktor: separation factor. See g-Faktor. 
Trennungslinie: line of separation. The line at which 
the two streams along the curved surface of a body 
advancing through a fluid, one from the front toward 
the rear, the other from the rear toward the front, 
meet upon the surface and at which they separate from 
it. 
Trevelyanischer mechanischer Oszillator: Trevelyan 
rocker. A mechanical oscillator which depends upon 
the alternate expansion and contraction, at the points 
of contact, of a heated solid in contact with a cold one. 
triboelektrisch: triboelectric. Pertaining to electrifica- 
tion generated by friction. A triboelectric series is a 
list of substances so arranged that any one of them 
becomes positively electrified when rubbed with one 
farther down the list. 
Tribolumineszenz: triholuminescence. Luminescence 
caused by grinding, in such substances as glass and 
certain crystals. Tribothermoluminescence refers to the 
same phenomenon, when heat is required subsequent 
to the grinding. Syn. piezoluminescence. 
Tribophosphoreszenz: tribop hasp horescence. The en- 
during or phosphorescent type of triholuminescence. 
Tribolhermolumineszenz: tribothermoluminescence. See 
Tribolumineszenz. 
149 
/trichromatlscher Koeffizient T 
trichromatischer Koeffizient: trichromatic coefficient. 
The fraction of a three-color mixture which consists of 
any one of the three standard colors used to obtain a 
match for any given color, in accordance with the three- 
color method of Maxwell. 
triklin: triclinic. In re crystal structure: having three 
unequal axes intresecting at angles, not more than two 
of which are equal, and not more than one of which 
is 90 degrees. 
Triode: triode. A vacuum tube having three electrodes, 
viz., a filament, a grid, and a plate; used in radio 
and other h.-f. apparatus. Syn. radiotron, audion, 
pliotron. 
Tripelpunkt: triple point. See Dreiphasengleichgewicht. 
Triplett: triplet. A multipiet of three components. 
Troepfchen: cluster. A group of atoms held together 
by the electric attraction of a charged ion, but not in 
permanent chemical union. 
Troepfchenbildung: coaggregation. See Koaggregation. 
Troepfchenmethode: drop-weight method. A method 
of investigating surface tension and cohesion in a liquid 
by weighing its drops which fall from a tube of speci- 
fied dimensions. 
Tropfenzaehler: stalagmometer. See Stalagmometer. 
Tropie: tropism. A directional property of a substance, 
esp. a crystal, dependent upon the vector quantities 
which determine the states of the constituent atoms or 
molecules. 
Tropopause: tropopause. The upper limit of the tropo- 
sphere, in middle latitudes generally 10 to 12 km above 
the earth’s surface. 
Troposphaere: troposphere. All that portion of the 
atmosphere, next above the earth’s surface, in which 
vertical convection is frequently active and in which 
clouds usually occur. 
Trouton'sches Gesetz: Trouton law. States that the 
molar heat of vaporization of a liquid at a given tem- 
perature, divided by its absolute boiling point (the 
Trouton ratio), is approximately the same for all 
liquids. 
Trouton-Noble'scher Versuch: Trouton-Noble experi- 
ment. An attempt to detect an ether drift by the possi- 
ble electromagnetic effect of the motion of an electric 
charge as carried with the velocity of the earth. No 
effect was observed. 
Truebung: turbidity. A property of a medium which 
renders it imperfectly transparent, due to having parti- 
cles in suspension, e.g., milky or muddy water. 
Truebungsfaktor: turbidity factor. The percentage of 
reduction of solar radiation of a given wave length re- 
ceived upon the earth’s surface, because of haze or other 
type of turbidity in the atmosphere. 
Truebungskoeffizient: turbidity coefficient. See Ang- 
stroem Koeffizient. 
Truebungsmesser: turbidimeter. An instrument for 
measuring the turbidity of a liquid, as in water-purifi- 
cation plants. Syn. opacimeter. See also Nephelometer. 
Turbulenz: turbulence. Irregular motion of a moving 
fluid, caused by an impediment in the stream, by fric- 
tion, or by vortex action. Syn. sinuosity. 
Turnover: turnover. The lack of symmetry in the fila- 
ment plate current fluctuations of a vacuum tube circuit, 
due to the fact that the increase in current caused by 
a given increase in grid potential is not equal to the 
decrease in current caused by an equal decrease in grid 
potential. 
Tyndall'scher Effekt: Tyndall effect. The scattering of 
light by very small suspended particles, which was theo- 
retically investigated by Tyndall, but first described by 
Faraday. The scattered light is polarized to an extent 
which is greater, the smaller the particles. For diameters 
less that 0.1 micron the polarization is complete. 
/Uebereinstimmung 
150 u 
Uebereinstimmung: consistency. (1) The approximate 
agreement between results of measurements on the 
same quantity. External consistency refers to the agree- 
ment between final adjusted results obtained by differ- 
ent methods; internal consistency, to that between re- 
sults of repeated- single measurements of the same 
series. (2) That quality of a material which depends 
upon its viscosity, plasticity viscidity, etc. 
Ueberfuehrungszahl: transport numbers, Syn. transfer- 
ence numbers, Hittorf numbers. A term applied by Hit- 
torf to the fractions of an electrolytic current carried 
by the anions and by the cations, respectively, the sum 
of which is unity. 
Uebergangsphaenomen: transport phenomena. A 
class of phenomena due to the transfer of mass, energy, 
or momentum across any given surface or interface as 
a result of molecular or electronic agitation, in accord- 
ance with the kinetic theory. E.g., momentum may be 
so transferred from a rotating disk to an adjacent parallel 
disk by means of air molecules receiving momentum 
from the one and subsequently impinging upon the 
other. 
Uebergangsstrom: transient. See Ausgleichungsstrom. 
Uebergangswahrscheinlichkeit: transition probability. 
(1) The number of spontaneous transitions from one 
given state to another given state which a single atom 
would perform, on the average, in 1 sec, if the initial 
state were restored immediately after each transition. It 
is a function of the frequency of the radiation emitted, 
and of the atomic structure. (2) The number of in- 
duced transitions per single atom per second, as above, 
due to unit intensity of the incident radiation. It is 
likewise a function of the frequency and of the atomic 
structure. (3) (Radioactive) The probability that a 
radio-active atom of a given species will disintegrate 
within unit time. It is numerically equal to the disinte- 
gration constant. 
Uebergangswiderstand: passive resistance. See passiver 
Widerstand. 
ueberhitzen: superheat. (I) (v.) To raise the tem- 
perature of a vapor, as steam, above the saturation point. 
(2) To raise the temperature of a liquid above its boil- 
ing point at the existing pressure, without ebullition; 
facilitated by covering the surface with another, im- 
miscible liquid, as oil on water. (3) (n) The number 
of degrees by which the temperature of a vapor at a 
given pressure exceeds the temperature at which the 
vapor is saturated. 
Ueberlappung: overlapping. The coincidence of the 
long-wave end of a diffraction or interference spectrum 
with the short-wave end of the spectrum of the next 
higher order; which may give rise to confusion in 
spectroscopy. 
Ueberpo+ential: overpotential. An excess of potential, 
or p.d.; esp. the p.d. required to effect the electrolysis 
of an electrolyte, minus that of the electrodes with 
the products deposited upon them after the separation 
has taken place. Syn. overvoltage, excess v. 
Ueberschall: supersonic, Syn. ultrasonic. Having a 
frequency above that of audible sound. 
Ueberschneiden: overlapping. See Ueberlappung. 
uebersaet+Igen: supersaturate. To cause a solution to 
attain a condition of greater concentration than its nor- 
mal saturation concentration at the existing temperature, 
without initiating precipitation of the solute. This may 
sometimes be done by careful supercooling. 
Uebers+ruktur: superstructure. A regular, periodic 
spacing found in the structure of a solid solution; ex- 
hibited by certain alloys. It is due to a systematic con- 
figuration of atoms of the solute in the solvent crystal, 
and is not characteristic of the solvent. 
Ueberton: overtone. See Teilton. 
Uebertonband: overtone band. A spectral frequency 
which bears a relation to a given spectral frequency 
analogous to that of an acoustic overtone to its funda- 
mental. Syn. harmonic band. 
Uebertrager: transducer. Any device for transmit- 
ting energy from one system to another, esp. from one 
electric transmission or communication system to an- 
other, e.g., a transformer. 
uebrigbleibende Abweichung: residual. See Rest. 
uebrigbleibendes Blau: residual blue. A phenomenon 
observed by Tyndall with white light scattered by small 
particles in suspension. Viewed through a suitably ori- 
ented nicol, the scattered light appears blue. 
uebrigbleibendes Res+blau: residual blue. 
Ulbricht'sche Kugel: Ulbricht sphere. An integrating 
sphere used in a sphere photometer; so called because 
of the first adaptation of the Sumptner principle to this 
use by Ulbricht in 1900. 
Ultraionisationspotential: ultraionization potential. A 
definite electron potential which elicits a responsive ion- 
ization, but which is greater than that corresponding to 
the ordinary excitation limit. 
151 
/Ultrakurzwellen u 
Ultrakurzwellen: ultrashort waves. See Mikrowellen. 
Ultramikrometer: ultramicrometer. An instrument for 
the measurement of very small displacements, esp. by 
electrical means, e.g., by the variation of an electrical 
capacitance. 
Ultramikroskop: ultramicroscope. An arrangement con- 
sisting of a powerful microscope whose field is illumi- 
nated by a strong beam of light from one side, so that 
extremely minute objects (or the diffraction patterns 
produced by them) are visible against a dark back- 
ground. 
ultrarot: infrared. See infrarot. 
Ultraschall: ultrasonic, supersonic. See Ueberschall. 
ultraviolett: ultraviolet. A range of invisible radiation 
frequencies immediately adjoining the visible violet, and 
extending into the region of low-frequency X-rays. 
Umformer: converter. One of several types of machine 
consisting of an electric generator driven by an electric 
motor, with the purpose of changing the service in 
some respect; as from a.-c. to d.-c. (motor generator 
or rotary converter), to a different frequency (frequency 
converter), to a different number of phases (phase 
converter). 
umgekehrter photoelektrischer Effekt: inverse photo- 
electric effect. The transformation of the kinetic energy 
of a moving electron into radiant energy, as in the re- 
combination of an electron with an ion, or in the pro- 
duction of X-rays. 
umgekehrter piezo-elektrischer Effekt; inverse piezo- 
electric effect. The contraction or expansion of a piezo- 
electric crystal along an electric axis when subjected to 
an electric field in that direction. 
umgekehrte Spannung: inverse voltage. See inverse 
Spannung. 
umgekehrter Term: inverted term. A spectral term 
in which the fine-structure level having the largest inner 
quantum number lies farthest down on the energy-level 
diagram. 
umkehren (opt.): rectify. (1) To change from alter- 
nating to unidirectional, as an electric current. Any de- 
vice for securing this result is a rectifier. (2) To re- 
place (an inverted image) by one which is erect, as by 
the rectifying system in a field glass. 
Umkehrstrahlen: retrograde rays. A type of corpuscular 
rays, of atomic dimensions, like positive rays, and mag- 
netically deflected as positive rays are, but moving away 
from the cathode instead of toward it. They appear to 
be of complex character. 
Umwandler: inverter. A device for converting d.-c, 
into a.-c. 
Umwandlung: disintegration, transmutation. (1) The 
emission of an alpha or a beta particle by a radioactive 
atom. (2) The passage of a solid into a colloidal state. 
(3) A change from one chemical element into another, 
or the derivation of one element from another; sought 
for by the alchemists, and now recognized as actually 
taking place through either natural or induced radio- 
activity. 
Umwandlungselektron: disintegration electron. An elec- 
tron emitted from the nucleus of an atom upon radio- 
active disintegration, in that class of radioactive ele- 
ments which emit beta rays. 
Umwandlungsfaktor: conversion factor. A number by 
which the numerical value of a physical quantity as 
expressed in one set of units must be multiplied in order 
to obtain its numerical value as expressed in another 
similar set of units of different size. Syn. change ratio, 
Umwandlungsfunktion: transmutation function. A func- 
tion which expresses the probability of an induced 
nuclear transmutation in terms of the energy of the 
bombarding particle; the target being considered in- 
finitely thin. 
Umwandlungskoeffizient: conversion coefficient. An 
abstract fraction which represents the probability that 
a gamma-ray quantum, emitted from the nucleus of a 
radioactive atom, will give up its energy in releasing 
an electron from one of the outer levels. The K con- 
version coefficient is the probability that the release will 
take place at the K level, etc. 
Umwandlungskonstanfe: disintegration constant, Syn. 
transformation constant radioactive c. The decay coeffi- 
cient for radioactive disintegration. 
Umwandlungsperiode: transformation period. The 
half-value period for the decay of the activity of a 
radioactive substance. 
Umwandlungswaerme bei Eisen: heat of recalescence. 
Heat liberated per unit mass at certain temperatures by 
a cooling metal, due to the recalescence transformation. 
Unbeschraenkt mischbar: consolute. See loeslich in 
alien Verhaeltnissen, 
Unbestimmtheitsprinzip: indetermination principle, in- 
determinacy p., Syn. uncertainty principle. A feature 
/ungerader Term 
152 u 
of the quantum mechanics of Heisenberg, which postu- 
lates that complete information as to the mechanism 
of processes taking place on the electronic scale of 
magnitude, in terms of the usual geometrical coordinates 
and of time, is impossible. E.g., the position and the 
velocity of an electron are, according to this principle, 
in capable of simultaneous expression in terms of these 
conventions. 
ungerader Term: odd term. 
ungequantel+er Zus+and: unquantized state. A state of 
an atom in which there are electrons whose motion is 
not subject to quantum conditions, and which give 
rise to continuous spectral bands rather than lines. 
ungeradzahliges Molekuel: odd molecule. One of the 
very rare molecules having in its neutral state an odd 
number of extranuclear electrons. 
unipolare Induktion: unipolar induction. See einpolige 
Induktion. 
« 
Univariant: univariant. Having one degree of freedom, 
i.e., variance unity. 
universeller Nebenschluss: universal shunt. A type of 
shunt devised by Ayrton for use with galvanometers in 
order to increase their range, but without change of 
damping. Syn. Ayrton shunt. 
unendlich weiter Punkt: jar point. See Fernpunkt. 
Unschaerfering: blur circle, circle of diffusion. The 
circular intersection of a screen, as the retina, with a 
conical pencil of rays from a point source whose image 
does not lie exactly upon the screen. Syn. circle of 
diffusion. 
Unterdrück: negative pressure. (1) A pressure less 
than that of the atmosphere. (2) A condition of stress 
within a cohesive body which is subjected to equal 
tensions in all directions, and which is thus truly the 
opposite of pressure. 
Unterdrueckung: suppression. (1) The elimination of 
any component of an emission, as of a given frequency 
in a radio wave train. (2) The nonappearance, of a 
normally occurring natural face on a crystal, due to 
the adjacent faces coming together to a point or an 
edge. 
un+erkuehlen: supercool, undercool. To reduce the 
temperature of a liquid below its freezing point or that 
of a solution below its saturation point. 
unmodifizierte Linie: unmodijide line. See Compton 
Effekt. 
Unterniveau: sublevel. The energy level or quantum 
state of the electrons in an atomic subshell. 
Unterstufe: sublevel. See Unterniveau. 
Unterschale: subshell. A subdivision of an electron 
shell, all the electrons of which have the same azimuthal 
quantum number.* 
untersynchron: subsynchronous. Having a frequency 
which is a submultiple of the driving frequency. 
Uranreihe: uranium series, uranium-radium s. One of 
the principal radioactive series, beginning with uranium 
and including radium. 
Ursaechlichkeit: causality, causation. The doctrine that 
there necessarily exists an actual cause-and-effect connec- 
tion between related phenomena, such that the same 
conditions must always bring about the same results. 
Syn. determinism. 
Ursprung: origin. The zero line in a band spectrum. 
urspruengliche magnetische Permeabilitaet: initial 
magnetic permeability. The magnetic permeability cor- 
responding to an infinitely small, normal magnetic 
induction. 
Urspruengliche Spannung: initial stress, Syn, residual 
stress. A stress which persists in a solid, due not to 
the existence of external forces but apparently to the 
fact that certain portions have been stressed beyond the 
elastic limit while the adjacent portions have not. 
Uviolglass: uviol glass. A glass developed by Schott, 
highly transparent to ultraviolet. 
153 
/Vakuumgewichf V 
Vakuumgewicht: vacuum weight. The weight obtained 
for an object when the result of weighing is corrected 
for the buoyancy of the air, i.e., the weight in vacuo. 
Vakuumroehre: vacuum tube. See Entladungsroehre. 
Vakuumspektrograph: vacuum spectrograph. A spec- 
trograph which operates in a vacuum, so as to introduce 
no air-absorption of the emission under examination. 
Valenz: valence, valency. In re an electro-negative 
chemical ion: the number of hydrogen ions or other 
univalent ions with which it is combined or is capable 
of combining. In re a positive ion: its combining 
power as compared with hydrogen, or the number of 
hydrogen ions which it displaces in chemical combina- 
tion. Grimm defines the absolute valence of an atom 
as the number of its electrons which are engaged in 
attaching the other atoms of the molecule to it. 
Valenzelektron: valence electron, Syn. peripheral elec- 
tron. (1) One of the outer electrons of an atom, to 
whose activity the spectral lines of visible light and 
thermal radiation are attributed, and which are supposed 
to be responsible for chemical combination. (2) An 
outer electron of an atom, which does not form part 
fo a closed shell, and which apparently is concerned in 
chemical combination. 
van der Bijl'sche Gleichung: van der Bijl equation. An 
empirical equation which expresses the plate current I„ 
in a triode in terms of the plate voltage Vp and the 
grid voltage Vp: 
Ip = a(Vp + fxVg + c) ; 
in which a and c are constants and is the amplifica- 
tion factor. 
van der Waals'sche Gleichung: van der Waals equa- 
tion. An empirical, or partially empirical, characteristic 
equation, the first successful approximation of the be- 
havior of real gases: 
(p + v)(v ~ b)= RT> 
in which p is the pressure in atmospheres, v is the 
volume of the gas in terms of its volume at N.T.P. 
as the unit, and a and b are the van der Waals con- 
stants, dependent upon the gas. 
van der Waals'she Kraef+e: van der Waals forces. The 
molecular interactions in a gas, of which account is 
taken in the construction of the van der Waals equation; 
the attractive forces by the constant a and the repulsive 
forces by the constant b of that equation. 
van der Waals'sches Potential: van der Waals poten- 
tial. A term used in connection with the potential en- 
ergies corresponding to the attractive forces between 
atoms and atoms or between molecules and molecules 
in a gas, which are taken into account by the use of 
the constant a in the van der Waals equation. 
van't Hoffscher Faktor: van’t Hoff factor. A factor 
by which, according to van’t Hoff, the molecular weight 
of an electrolyte as calculated from the freezing point 
law must be multiplied to give its true molecular weight. 
van't Hoffsches Gesetz: van’t Hoff law. States that 
the vapor pressure of a solvent is lowered by the addi- 
tion of a nonvolatile solute in proportion to the molar 
concentration of the solute. Syn. Wuellner law. 
Varianz: variance. The number of degrees of free- 
dom of a system. 
Variationsprinzip: variation principle. States that if 
the kinetic energy minus the potential energy of a par- 
ticle is denoted by L, and if we assume a slightly dif- 
ferent, arbitrary path to be followed, in the time inter- 
val tj to t2, from the one actually followed under the 
forces in operation, then the resulting variation of the 
integral 
i t2 
j Ldt 
J t, 
is equal to zero. 
Variometer: variometer. (1) A variable inductance 
provided with a scale, arbitrary or otherwise. (2) A 
device for measuring or recording variations in terrestrial 
magnetism. 
Vegard'sches Gesetz: Vegard law. States that when 
two substances A and B having similar crystalline struc- 
ture form together a solid solution, the lattice constant 
of the solution divides the interval between the lattice 
constants of A and of B in proportion to the relative 
amounts of A and of B present. 
Vegard-Kaplan'sche Bande: Vegard-Kaplan bands. 
Spectral bands due to metastable nitrogen molecules; 
discovered by Vegard in the spectrum of the aurora 
borealis and by Kaplan in the nitrogen afterglow. 
Vektor: vector. A quantity which is fully specified 
when and only when there are given its magnitude and 
an associated direction in space; e.g., a velocity or a 
magnetic intensity. 
Vektorpolygon: vector polygon. A polygon (not neces- 
sarily plane) whose sides represent a number of similar 
/Vektorpotentialfunktion V 
vectors, and the completion or "closing” of which in- 
dicates that the vector sum is zero; e.g., the force 
polygon for a set of forces in equilibrium. 
Vektorpotentialfunktion: vector potential function. A 
variable vector V, so related to another variable vector 
R that R is the curl of V. V is then said to be a vector 
potential function of R. 
Vektorprodukt; vector product. In re two vectors, 
P-,, P2: a vector whose magnitude is the product of 
the magnitudes of the two vectors and the sine of the 
angle between them; and whose direction is that of 
the perpendicular to both of them, such that while look- 
ing along this direction one would have to turn the 
vector Pa clockwise to make it coincide with the vector 
P2. Designated by P4 X Pa- 
vena contrac+a: vena contracta (Lat.). The con- 
tracted jet in which a liquid emerges from an orifice. 
The ratio of its area of smallest cross section to the 
area of the orifice is the contraction coefficient. 
Venturimesser: Venturi meter. An hourglass-shaped 
constriction in a pipe carrying a fluid, by means of 
which it is possible to compute the rate of flow from 
the pressure difference between the main pipe and the 
point of least diameter, in accordance with the Bernoulli 
law. 
verallgemeinerte Koordinaten: generalized coordinates. 
See Koordinate. 
Verbindung: turn-flux, Syn. linkage, fluxturns. See 
Kupplung. 
Verbindungsaequivalent: combining equivalent. Of a 
chemical element: its atomic weight divided by its 
valence. E.g., the combining equivalent of magnesium 
is 24.32 ~ 2 = 12.16. In the case of a radical the 
radicular weight is divided by the valence; e.g., for S04, 
the combining equivalent is 96.06 — 2 — 48.03. 
Verbindungsgewicht: combining equivalent. See Ver- 
bindungsaequivalent. 
verboten: forbidden. A term applied to certain intra- 
atomic phenomena which, while they might be looked 
for in accordance with the general rules, apparently 
never or very rarely occur; e.g., some electron transi- 
tions and corresponding spectral lines. 
Verdampfungskurve: vaporization curve. See Gleich- 
gewichtskurve. 
Verdampfungswaerme: heat of vaporization. The 
quantity of heat absorbed by a substance per unit mass, 
upon passing from the liquid to the vapor state, or 
released upon condensation; in either case without 
change of temperature. It is a function of the tempera- 
ture at which the transformation takes place. Syn. heat 
of evaporation, heat of condensation (the latter if the 
vapor is condensing). 
Verdet Konstante: Verdet constant. The angle of 
optical rotation per oersted intensity per centimeter 
thickness in the Faraday effect. Syn. specific magnetic 
rotatory power. 
Verdraengungszentrum: center of displacement. In re 
a body submerged or partially submerged in a fluid: 
that point which coincides with the center of mass of 
the body of fluid thereby displaced. Syn. center of 
buoyancy. 
Verduennungswaerme: heat of dilution. The quantity 
of heat absorbed or evolved per gram or per mol of 
a solute when a solution of given concentration con- 
taining it is infinitely diluted. It is a function of the 
initial concentration. 
Vereinigungsebene: plane of union. The plane upon 
which the two components of a twin crystal are united. 
It always coincides with a possible crystal face. 
Verformbarkeit: malleability. The plasticity of a metal, 
by virtue of which it may be rolled into sheets or other- 
wise worked into permanent shape when cold. 
Verformungsarbeit; resilience. (1) The work required 
to deform an elastic body to the elastic limit. Its value 
depends upon the elastic constants and the dimensions 
of the body. (2) The ability of a material to make 
internal adjustment to rapid deformation without the 
development of excessive stress; the opposite of brit- 
tleness. 
verfuegbare Energie: available energy. That part of 
the energy of a body or of a system which is in such 
form that mechanical work may be derived from it. 
verfuegbare Waerme: motivity. That part of the 
heat energy taken in during a thermodynamic cycle 
which is transformed into external work, i.e., the avail- 
able energy of the cycle. The term is attributed to 
Kelvin. 
Vergenz: vergency. Either divergence or convergence 
of rays from a lens or a mirror, expressed as the re- 
ciprocal of the distance from lens or mirror to the 
focus of the rays. 
Vergroesserungsvermoegen: magnifying power, Syn. 
magnification. (1) Of a visual instrument (telescope. 
677865—46 12 
155 
/Verhaeltnis von Ladung zu Masse V 
microscope, etc.): the ratio of the apparent diameter 
of the object as seen in the instrument to its apparent 
diameter as seen by the unaided eye at whatever dis- 
tance it would be viewed without the instrument. (For 
a microscope, this distance is usually taken as 25 cm 
or 10 in.) (2) For a projection instrument, it is the 
ratio of any linear dimension of the projected image to 
the corresponding dimension of the object. 
Verhaeltnis von Ladung zu Masse: charge-mass ratio, 
Syn. specific charge. The ratio of the electric charge 
carried by an electrified particle or ion to the mass of 
the particle. 
Verlaengerung: elongation. (1) Any increase in 
length. (2) The type of strain which accompanies 
tension, and which is measured by the ratio of the 
increase in length to the normal, unstressed length. 
(3) The radius vector of a body or a particle moving 
in an orbit. 
Verlust (elektr., magn.) durch hohen Widerstand: leak, 
leakage. (1) A ground or cross connection of very 
high resistance, e.g., a grid leak. Electric leakage is the 
small current traversing such a leak. (2) Magnetic 
leakage is a straying of lines of magnetic induction 
from the prescribed magnetic circuit into the surround- 
ing space. 
Vermoegen: power. See Leistung. 
Vernichtungsstrahlen: annihilation radiation. Radiation 
produced by the collision and mutual annihilation of 
an electron and a positron, and usually consisting of 
two quanta for each such encounter, moving in oppo- 
site directions. 
Vernier: vernier. A device applied to the graduated 
scale on many instruments, which serves at the same 
time as an index and as a means of subdividing the 
smallest scale unit into tenths or other aliquot parts. 
Named for its inventor, Pierre Vernier. 
Verrueckung: dislocation. A disarrangement of the 
perfect configuration of the units of a crystal lattice, 
as evidenced by anomalous mechanical, optical, or mag- 
netic properties. 
Verschiebung: dislocation, displacement. See Verrueck- 
ung and elektrische Verschiebung. 
Verschiebung: masking. A term used in accoustics to 
denote the shift of the audibility threshold of one 
sound, due to the presence of another. It may be 
expressed quantitatively in decibels. 
Verschiebungsgesetz: displacement law. (1) (Radia- 
tion.) The first of the Wien laws of thermal radiation 
(q.v.). (2) (Spect.) The second of the Kossel-Som- 
merfeld spectroscopic laws (q.v.). (3) (Radioact.) 
See Fajans und Soddysche Gesetze. (4) (Chem.) A 
principle which recognizes the fact that an atom which 
has had one of its electrons removed behaves chemically 
like the one preceding it in the periodic table. 
Verschiebungsinterferometer: displacement interfero- 
meter. An optical instrument consisting of an arrange- 
ment of mirrors, and used, in conjunction with a dis- 
persive system such as a prism or a grating, for meas- 
uring small displacements. 
Verschiebungslinie: line of displacement. That which, 
in a polarized dielectric, corresponds to a line of 
electric force in a vacuum. The lines of displacement 
in a nonisotropic dielectric do not, however, necessarily 
coincide with the lines of force of the field in which 
it is placed. 
Verschiebungsroehre: tube of displacement. Defined 
in a manner similar to tube of force, with lines of 
(electric) displacement substituted for lines of force. 
Verschiebungss+rom: displacement current. A term 
introduced by Maxwell to denote the effective current 
in a dielectric or a vacuum (as between the plates of 
a condenser) corresponding to the electron current in 
a metallic conductor (as in the wires leading to the 
condenser). Maxwell regarded the time rate of change 
of the electric intensity as equivalent to the value of an 
actual current. In modern usage, the displacement cur- 
rent density is defined as the time rate of the electric 
displacement, i.e., to 
dE dP 
to + 4?r ; 
dt dt 
in which E is the intensity and P the polarization. 
verschiedenfarbig: heterochromatic. (1) Not mono- 
chromatic. (2) Not homochromatic. 
Versor: versor. That factor of a vector which deter- 
mines its geometrical direction and which is multiplied 
by the tensor to give the complete expression for the 
vector. 
Vers+aerkerschirm: intensifying screen. A fluorescent 
screen placed in close contact with a photographic plate 
used in radiographic work, the fluorescent light from 
which adds its effect to that of the invisible rays in 
producing the image on the plate. 
Verstaerkungsfak+or: amplification factor. The nega- 
tive of the ratio of any small change of plate potential, 
/Versuchsballon 
156 V 
in a triode, to the change in grid potential necessary 
to offset it and keep the plate current constant. 
Versuchsballon: sounding balloon. A free, unmanned 
balloon designed to carry instruments such as thermo- 
graphs, barographs, etc., into the upper atmosphere, for 
the purpose of obtaining meteorological or physical 
data. 
verteilte Kapazitaet: distributed capacitance. That 
part of the capacitance of an electric circuit which is 
due, not to the introduction of condensers, but to the 
insulation of the conducting wires from the ground, 
or esp. from a surrounding conducting conduit or 
sheath. 
Verteilung: distribution, dissipation (of energy'). A 
statistical tabulation of one variable in terms of an- 
other which may be related to it through a distribu- 
tion function (q.v.), e.g., frequency-energy distribution, 
velocity-angle d., etc. 
Verteilungsfunktion: distribution junction. A mathe- 
matical expression indicating the relative frequency with 
which the value of a statistical variable may be expected 
to lie within any specified interval. 
Verteilungsgesetz: distribution law, partition law. (1) 
States that in a dineric solution, the ratio of the con- 
centrations of the solute in the two solvents is inde- 
pendent of the quantity of solute. Attributed to Nernst. 
(2) The mathematical statement of statistical frequency 
as expressed by a distribution function, e.g., the Max- 
well or the Gaussian distribution law. 
Verteilungskoeffizient: distribution coefficient, d. con- 
stant, d. ratio, partition coefficient. The constant ratio 
of the concentrations of a solute dissolved in two im- 
miscible solvents which are in contact in the same con- 
tainer. See also Aufteilungskoeffizient. 
Ver+eilungskons+ante: distribution constant, d. coeffi- 
cient, d. ratio. See Verteilungskoeffizient. 
Verteilungsmodul: distribution, modulus of. A term 
used by Gibbs to denote the quantity kT (Boltzmann 
constant X absolute temperature) as it occurs in the 
probability distribution function 
e kT ; 
in which is the thermodynamic potential and e is 
the energy. 
Verteilungssystem: dissipative system. A nonconserva- 
tive system. 
Verteilungsverhaeltnis: distribution ratio, d. coefficient. 
See Verteilungskoeffizient. 
Vertex: vertex. That point of a refracting or a reflect- 
ing surface at which the axis of the optical system in- 
tersects it. 
vertikal: vertical. (1) The direction of gravity. (2) 
(Geocentric.) The direction of the radius of the earth. 
The two coincide, in general, only at the poles and 
at points on the equator. 
Vertikalintensitaet: vertical intensity. The intensity of 
the vertical component of the earth’s magnetic field at 
any point. 
Vervielfaeltiger: multiplier. A series resistance used 
in connection with a voltmeter so that it can be used 
to measure higher voltages than those indicated on the 
scale. 
Verzoegerung: lag, deceleration. See Lag. 
Verwirbelung: vorticity. A measure of the extent to 
which the motion of a fluid is rotational. Its value at 
any points is the cuti of the particle velocity, or twice 
the angular velocity of rotation of the fluid element, 
at that point; it is thus a vector quantity. 
Verzoegerungspotential: retarded potential. The elec- 
tric or magnetic potential at any point due to an electric 
or a magnetic system at a distance r and with due 
allowance for the time r/c required for the electric or 
magnetic effect to travel over that distance; c being the 
electromagnetic constant. 
Verzweigungsregel: branching rule. States that each 
term of the spectrum of a singly ionized atom gives 
rise to two groups of terms of consecutive multiplicity 
in the spectrum of the neutral atom; except the singlet 
terms, which give rise only to doublets. Formulated by 
Lande and Heisenberg. 
Verzweigungsverhael+nis: branching ratio. The ratio 
between the numbers of atoms of a radioactive element 
which undergo two different types of transformation, 
the one emitting an alpha particle, the other a beta 
particle. 
Vibrationsgalvanometer: vibration galvanometer. A 
type of a.-c. galvanometer in which the natural oscilla- 
tion frequency of the moving element is equal to the 
frequency of the a.-c. applied to it. 
Victor-Meyer'scher Apparat: Victor-Meyer apparatus. 
A volumetric apparatus for measuring vapor densities 
of volatile substances, and hence, indirectly, their mole- 
cular weights. 
Vielfaeltigkeit: multiplicity. The largest number of 
components possessed by any multiple term in a given 
/Vielgestaltigkeit 
157 V 
spectral system. Multiplicities as high as 9 are known, 
but not all the terms of a system have the maximum 
number of components. 
Vielgestaltigkeit: polymorphism. See Polymorphismus. 
Vielkristall: polycrystal. A body made up of a number 
of small crystals in a mass. 
vierdimensionale Analyse: jour-dimensional analysis. 
The space-time analysis of Minkowski. 
viereckig: tetragonal. See tetragonal. 
vierkantig: tetragonal. See tetragonal. 
Virial: virial. A quantity which appears in the general 
dynamic equation of a mass of gas molecules. It is 
half of the sum of the average products of the coordi- 
nates of the molecules by the corresponding components 
of force acting upon them, and, according to the virial 
theorem of Clausius, is equal to the negative of the 
total kinetic energy of the molecules. 
Virialkoeffizienten: virial coefficients. The coefficients 
A, B, of an inverse-power series in v repre- 
senting the product pv in the equation of state for a 
real gas: 
pv — A + B,,-1 + Qr2 
+ + 
The coeffcients are functions of the temperature. 
virtuelle Arbeit: virtual work. The quantity of work 
done during an infinitely small displacement ds under 
the action of either a constant or a variable force f. If 
the force and the displacement are at an angle <p, then 
the virtual work is dw zz f cos ds. 
virtuelles Bild: virtual image. See Bild. 
virtuelle Geschwindigkeit: virtual velocity. That com- 
ponent of the velocity (of a particle) which is in the 
direction of a given force, in any assumed displacement 
through the position of equilibrium. 
virtueller Oszillator: virtual oscillator. An ideal elec- 
tric oscillator, consisting of a charged point executing 
harmonic motion; a concept used in developing the 
classical theories of radiation. * 
virtuelle Verrueckung: virtual displacement. The pro- 
jection, on the original line of action of a force, of the 
path followed by the point of application of the force 
during an infinitely small displacement. 
Viskoelastizitaet: visco-elasticity. That property of a 
body, by virtue of which deformations are reversible 
and without dissipation of energy when produced at in- 
finitely slow rates, but not so at finite rates. 
Viskosimesser: viscometer, viscosimeter. An apparatus 
for measuring the viscosity of a fluid. 
Viskositaet: viscosity. A property of fluids, by virtue 
of which they offer a resistance to flow, and which in- 
volves their yielding to a certain amount of shearing 
stress. A fluid is said to be viscous or limpid according 
as this property is conspicuous or negligible. 
Viskositaetskoeffizient: viscosity coefficient. The shear- 
ing stress involved in maintaining the uniform flow of 
a fluid, per unit rate of shear. Syn. viscosity. 
Viskositaetsmanometer: viscosity manometer, v. gauge. 
A low-pressure manometer dependent upon the varia- 
tion of the viscosity of the gas with pressure; e.g., the 
molecular gauge. 
vizinal: vicinal. In re a crystal face: lying in a sub- 
ordinate plane, not one of the usual planes of cleavage 
or of external growth, and not in accordance with the 
Haiiy law. 
Voigt-Thomson'sche Symmetriebeziehung: Vdigt-Thom- 
son symmetry relation. An expression for the value 
of a (vector) property of a crystal in a given direction 
in terms of two principal values, one parallel to a rota- 
tion axis of symmetry and the other perpendicular there- 
to. When the relation holds, the value in a direction 
making an angle 6 with this axis is a linear function 
of cos2 6. TTie two principal values correspond to 
6 — 0 and 6 — 90 deg., respectively. 
vollkommene Abtrennung: exhaustion. See Auf- 
spaltung. 
Volt: volt. The practical unit of e.m.f. and potential. 
The absolute volt is equal to 108 abvolts. The interna- 
tional volt is that e.m.f. which, when applied to a 
resistance of 1 international ohm, maintains a current 
of 1 international amp. The ratio of the international 
to the absolute volt is about 1.00039. 
Voltameter: voltameter, Syn. coulomhmeter. An in- 
strument for the measurement of a quantity of electricity 
by the amount of electrodeposition produced from an 
electrolyte. Not to be confused with voltammeter (q.v.). 
Voltampere: volt-ampere. The practical unit of ap- 
parent power (effective volts times effective amperes) 
in a variable-current circuit. 
Voltamperemesser: volt-ammeter. An instrument which 
may be used either as a voltmeter or as an ammeter. 
Not to be confused with voltameter. 
/Voltapaar 
158 V 
Volta paar: voltaic couple. A pair of dissimilar metals 
in contact, which results in a contact p.d. 
Voltascher Effekt: Volta effect, V. potential, Syn. con- 
tact potential difference. A difference of electric poten- 
tial which develops between two dissimilar conductors 
when they are placed in contact; first observed by 
Volta. 
Voltasches Gesetz: Volta law. States that the con- 
tact p.d. of two conductors is the same, whether they 
are in direct contact or joined through one or more 
intermediate conductors. 
Voltasches Potential: Volta potential, contact potential 
contact potential difference. See Voltascher Effekt. 
Voltascher Potentialunterschied: voltaic potential dif- 
ference, Volta effect—contact potential difference. See 
Voltascher Effekt. 
Voltelektron: volt-electron, Syn. electron-volt. A unit 
of energy equal to about 1.591 X 10~12 erg, and de- 
fined as the change in energy experienced by 1 electronic 
charge on passing through a p.d. of 1 volt. 
Voltmeter: voltmeter. See Spannungsmesser. 
Voltmeterwiderstand: voltmeter resistor. A resistance 
used with a galvanometer or other current-measuring 
instrument to convert it into a voltmeter. 
Voltsekunde: volt-second, Syn. weher. The practical 
unit of magnetic flux, equal to 108 maxwells. 
Volumengeschwindigkeit: volume velocity. In re any 
flow or flux across a plane: the product of the linear 
speed of flow, or of propagation, by the cross-sectional 
area through which the flow is considered. Multiplied 
by the density (quantity per unit volume), it gives the 
flux; in case quantity is measured by volume, it equals 
the flux. 
von der gleichen Enthalpie: isenthalpic. See isenthal- 
pisch. 
von gleicher Entropie: isentropic. See isentropisch. 
von gleicher Inklination: isoclinic, isoclinal. See isoklin. 
von gleicher Neigung: isoclinic, isoclinal. See isoklin. 
vorbedingte Beobachtung: conditioned observation. 
An observation upon a quantity or upon quantities sub- 
ject to rigorous theoretical conditions. 
Vorbeleuchtung: priming illumination. See Grundbe- 
leuchtung. 
Vorpumpe: fore pump. An auxilliary air pump, used 
to create a partial vacuum, preliminary to the operation 
of another, more effective air pump. Syn. backing pump. 
Vreeland'scher Oszillator: Vreeland oscillator. A de- 
vice for producing a sinusoidal electric current by 
means of a mercury arc in a periodically varying mag- 
netic field. 
159 
/Wadsworth'scher Spiegel w 
Wadsworth'scher Spiegel: Wadsworth mirror. A 
plane mirror used in certain forms of prism spectro- 
meter in which the prism is used at minimum deviation. 
Waermeausbreitungsvermoegen; thermal diffusivity. 
The ratio of the thermal conductivity of a substance 
to the product of the density by the specific heat. Upon 
it depends the rate at which a temperature wave is 
propagated in conducting substance. 
Waermediffusion: thermodiffusion, Syn. thermal trans- 
piration, thermal effusion. A pressure difference which 
develops between two bodies of gas, initially at the 
same low pressure but at different temperatures, when 
they are joined by a capillary tube. The flow is from 
the colder to the warmer gas. Discovered by Feddersen 
and Reynolds. 
Waermefunktion: heat function. (1) A quantity re- 
lated to thermionic emission, and equal to the heat of 
emission per mol at constant pressure, minus 
5 
RT ; 
2 
in which R is the gas constant and T is temperature. 
The heat function h is related to the work function w 
by the equation 
dw 
h = w — T . 
dT 
(2) Syn. any one of the Gibbs functions. 
Waermegleichgewicht: thermal equilibrium. That 
condition of a system in which the net rate of ex- 
change of heat among its parts has become zero; a 
special feature of thermodynamic equilibrium. 
Waermeeinhalt: heat content. See Enthalpie. 
Waermeionisation: thermal ionization. Ionization due 
to high temperature, as in the electrically conducting 
gases of a Bunsen flame. Syn. temperature ionization. 
Waermekapazitaet; heat capacity, Syn. thermal ca- 
pacity. The quantity of heat required to increase the 
temperature of a body by unity, or which the body 
yields when its temperature is lowered by unity, with- 
out change of state. 
Waermeleitfaehigkeit: thermal conductivity. See Leit- 
faehigkeit. 
Waermes+rahlung: thermal radiation, Syn. temperature 
radiation, heat radiation, radiant heat. Radiation ex- 
cited by the thermal agitation of molecules or atoms, 
irrespective of other causes of excitation. Its existence 
is observable from the far infrared to the extreme ultra- 
violet. 
Waerme+od: heat death. The final state of thermo- 
dynamic equilibrium which the material universe ap- 
pears to be approaching, in accordance with the laws 
of dissipation of energy and increase of entropy. 
Waermeuebertragung: thermal elusion, Syn. thermal 
transpiration, thermodiffusion. See Waermediffusion. 
Waagerecht: horizontal. See horizontal. 
Wagner'sche Erdung: Wagner ground. A device for 
preventing false indications of the detector in a.-c. 
bridge measurements, due to capacitance effects between 
the bridge and the ground, 
Waidner-Burges'scher Standard; Waidner-Burgess 
standard. A standard of luminous intensity, designed 
to supplant the Bureau of Standards candle. Defined 
as the luminous intensity of 1 cm2 of a black body 
at the melting point of platinum. 
Walden'sches Gesetz: Walden law. States that the 
limiting equivalent conductance of a solution (at in- 
finite dilution) is inversely proportional to the viscosity 
coefficient of the solvent, the constant being the same 
for all solvents. 
wahre Energie: intrinsic energy, Syn. internal energy. 
See innere Energie. 
wahre Kontaktpotentialdifferenz: intrinsic contact po- 
tential difference. The true contact p.d. between two 
perfectly clean metals. Its value is given by Millikan 
as h(vx — v2)/e in which vx and v2 are the threshold 
photoelectric emission frequencies for the two metals, 
h is the Planck constant, and e is the elementary 
charge. 
wahre magnetische Permeabilitaet: intrinsic magnetic 
permeability. The magnetic permeability minus one. 
wahrscheinlicher Fehler: probable error. The magni- 
tude of an error that is as likely as not to be exceeded 
by a single observation, or by the mean or the adjusted 
result from a certain number of observations. It is se- 
lected with reference to the true but unknown mean 
which would theoretically be obtained from an indefi- 
nitely large number of observations, and is a statistical 
measure of precision. 
Wahrscheinllchkei+samplitude: probability amplitude. 
A wave function, commonly denoted by which satis- 
fies the Schroedinger wave equation or other similar 
equations of wave mechanics, and corresponds to a 
quantum condition actually fulfilled in nature. 
/wahrscheinlichster Verteilungswert 
160 w 
wahrscheinlichster Verteilungswert: mode. The most 
probable value of the variable in a statistical distribu- 
tion. It corresponds to the abscissa of the highest point 
on the distribution curve. Adj. modal. 
wahrscheinlichster Wert: most probable value. A hy- 
pothetical value of a measured quantity, arrived at 
through calculations upon the tabulated results of sev- 
eral measurements upon it, in accordance with the theory 
of errors. 
Wanderung: migration. The relatively slow movement 
of the ions in electrolysis, due to the applied electric 
field; or any similar movement of minute particles. 
Wanderungspo+ential: migration potential. A p.d. due 
to the settling or centrifuging of charged colloidal par- 
ticles. It may be regarded as the reverse of electro- 
phoresis. 
Wasseraequivalent: water equivalent. The mass of 
water which would have the same thermal capacity as 
a given body, such as a calorimeter cup. 
Wasserkalorimeter: water calorimeter. A calorimeter 
which measures quantities of heat by the change in 
temperature of a known mass of water. 
Wasserstoffskala: hydrogen scale. A temperature scale 
based upon the variation of pressure in hydrogen gas 
kept at constant volume. 
Watt: watt. A unit of power, defined as 1 joule of 
work per second. 
Wattmeter: wattmeter. An instrument for measuring 
electric power in watts. 
Wattstunde: watt-hour. A unit of work or energy, 
equivalent to 1 watt of power operating for 1 hr, and 
equal therefore to 3,600 joules or 3.6 X 1010 ergs. 
Weber: weber, Syn. volt-second. (1) An obsolete 
name for the coulomb. (2) An obsolete name for the 
ampere. (3) An obsolete unit of magnetic pole strength, 
equal to 108 times the (c.g.s.) unit magnetic pole. 
Weber'sche Einheit: Weber unit. An electromagnetic 
unit of electric current based on the millimeter, milli- 
gram, and second; hence equal to 0.01 c.g.s. electro- 
magnetic unit (abampere). Not to be confused with 
weber (q.v.), 
Weber'sche Energiegleichung: Weber energy equation. 
An equation developed in 1846, expressing the total 
mutual electric and magnetic energy of two moving 
charges e15 e2 at distance r apart, as follows: 
in which c is the electromagnetic constant. 
Wechselbeziehung: correlation. See Beziehung. 
Wechselrichter: inverter. See Umwandler. 
Wechselstromleitvermoegen: admittance. The recipro- 
cal, of the impedance of an electric circuit. 
Wechselwirkung zwischen Elektronenanordnungen: con- 
figuration interaction. The perturbing effect of one ar- 
rangement of electrons in the atom (as represented by 
the assigned quantum numbers) upon another such ar- 
rangement, so that the energy levels and spectral terms 
corresponding to the two arrangements are altered with 
respect to their values when no such interaction exists. 
Wehnel+'sche Kathode: Wehnelt cathode. A type of 
hot cathode consisting of a metallic core coated with 
alkaline earth oxides. 
Wehnelt'scher Unterbrecher: Wehnelt interrupter. An 
interrupter in which the current passes between a fine 
wire and an electrolytic solution, and is interrupted by 
the formation and collapse of small bubbles of vapor. 
Wellenaufzeichnungsgeraet: phonodeik. An apparatus 
which photographically records the wave form of any 
sound on a moving film, so that it may be studied and 
analyzed. Devised by D. C. Miller. 
Wellenbahnfunction: orbital wave function. An orbital 
wave function pertaining to a single electron; a char- 
acteristic solution of the Schroedinger equation for a 
one-electron problem, excluding spin. 
Wellenfilter: wave filter. See Filter. 
wellenfoermig: undulatory. Pertaining to or consisting 
of waves. 
Wellenform: wave form. A curve which graphically 
represents the magnitude of a wave variable (as ordi- 
nate) in its relation to distance along the path of propa- 
gation (as abscissa). 
Wellenfront: wave front. A surface connecting all 
points of a wave-propagating medium which are in the 
same given phase of the same order. 
Wellenfunktion; wave function. A point function com- 
monly represented by which in a wave equation 
161 
/Wellengeschwindigkeit w 
specifies the amplitude of a wave variable at any point 
of the region traversed by the waves. 
Wellengeschwindigkeit: wave velocity, Syn. phase ve- 
locity. A vector whose direction is normal to the wave 
front and whose magnitude is the speed of propaga- 
tion of a plane-wave disturbance. 
Wellengleichung: wave equation. An equation which 
gives a mathematical specification of a wave process, or 
describes the performance of a medium through which 
a wave is passing. 
Wellengruppe: wave group. The resultant of two or 
more wave trains of different frequency traversing the 
same path. 
Wellenlaenge: wave length. The distance between suc- 
cessive points in the same phase along a line in the 
direction of propagation of a wave train. 
Wellenleiter: wave guide. A dielectric of limited 
cross section, used to transmit electromagnetic waves. 
Wellenmechanik: wave mechanics. A general physical 
theory which ascribes wave characteristics to the funda- 
mental entities of atomic structure and seeks to inter- 
pret all physical phenomena in terms of hypothetical 
wave forms. Introduced by Schroedinger in 1926. 
Wellenmesser: wave meter. A calibrated electric reso- 
nator of variable frequency, used for measuring electric 
oscillation or wave frequencies. 
Wellenpaket: wave packet. (1) A group of wave 
trains so related as to wave length, velocity, phase, and 
amplitude that when they are combined the resultant 
wave is approximately a single pulse of definite ampli- 
tude advancing with a definite speed. (2) In general, 
a wave disturbance which is confined to a limited volume 
of space. 
Wellenveraenderliche: wave variable. A quantity which 
varies progressively and periodically at any point in a 
field of waves, and whose variations, moving forward, 
constitute a characteristic feature of the wave propaga- 
tion. E.g., in the case of sound, pressure is a wave 
variable. 
Wellenzahl: wave number. The reciprocal of a wave 
length, i.e., the number of waves per unit distance in 
the direction of propagation. 
Wel+linie: world line. The graph in space-time coordi- 
nates which represents any continuous sequence of events 
relating to a given particle. 
weisses Licht: white light. Any one of a variety of 
spectral energy distributions producing the same color 
sensation as average noon sunlight. 
weisse Strahlung: white radiation. Any radiation 
which produces a continuous spectrum. For X-rays 
there is a sharply defined short-wave length limit deter- 
mined by the Duane-Hunt law. 
Wertekomplex: complexion. Any specified set of 
values of the coordinates and momenta for the mole- 
cules or other particles composing a system, treated as 
a distribution of the particles among the phase-space 
elements. 
Wertheim'scher Effekt: Wertheim effect. A change in 
the helical (circular) magnetization of a ferromagnetic 
wire or rod when twisted; detected by the correspond- 
ing longitudinal e.m.f. Discovered by G. Wertheim in 
1852, and by G. Wiedemann in 1862. Syn. Wiede- 
mann effect. 
Wertigkeit: valence, valency. See Valenz. 
Weston'sche Zelle: Weston cell. A standard cell whose 
positive electrode is mercury and negative electrode 
cadmium, with a saturated cadmium sulphate solution 
as electrolyte. Mercurous sulphate is added as a de- 
polarizer. 
Wetterkunde: meteorology. That branch of physical 
science which treats primarily of atmospheric phe- 
nomena." 
Wheatstone'sche Bruecke: Wheatstone bridge. A 
branched electric circuit used for the measurement of 
resistances by a balance method. 
Widerstand: resistance. That which limits the steady 
electric current in a conductor and is expressed by the 
ratio of the applied constant e.m.f. to the current. 
Widerstandsapparat: resistor. A device, the primary 
purpose of which is to introduce resistance into an 
electric circuit. 
Widerstandsbruecke: slide-wire bridge. See Schleif- 
drahtbruecke. 
Widerstandsgeraet: resistor. See Widerstandsapparat. 
Widerstandsneutralisierung: resistance neutralization. 
The effect of a triode associated with a circuit in such 
a way as to lower the effective resistance of certain 
branches. 
Widerstandsthermometer: resistance thermometer. A 
/Wiedemann'scher Effekt 
162 w 
thermometer based upon the variation of the electrical 
resistivity of a metal, e.g., platinum, with temperature. 
Wiedemann'scher Effekt: Wiedemann effect, Syn. 
Wertheim effect. Torsional magnetostriction in a ferro- 
magnetic wire or rod; discovered by G. Wiedemann in 
1862. 
Wiedemann'sches Gesetz: Wiedemann law. States 
that the molar susceptibility of a substance in solution 
is independent of the concentration. 
Wiedemann-Franz'sches Gesetz: Wiedemann-Franz 
law. States that the ratio of the thermal conductivity 
of a metal to the product of the electrical conductivity 
by the absolute temperature (Wiedemann-Franz ratio) 
has for all metals approximately the same value, viz., 
5.345 X cal ohm/sec deg2. Known also as the 
Wiedemann-Franz-Lorenz law. 
Wien'sche Bruecke: Wien bridge. A type of capaci- 
tance bridge circuit developed by M. Wien. 
Wien'sche Verschiebungskonstante: Wien displace- 
ment constant. The constant which in accordance with 
the Wien displacement law represents the product of 
the maximum-emissivity wave length and the absolute 
temperature of the radiator. Its value is about 0.2884 
cm-deg. 
Wien'sche Waermestrahlungsgesetze: Wien laws (of 
thermal radiation). Three laws formulated by W. Wien 
in the 1890’s :(1) The wave length at which the 
monochromatic emissivity of a black body is a maxi- 
mum is inversely proportional to the absolute tempera- 
ture of the body (Wien "displacement law”). (2) The 
monochromatic emissive power for this "peak” wave 
length is proportional to the fifth power of the absolute 
temperature. (3) The spectral energy distribution of 
black-body radiation for temperature T is given by the 
formula 
_ _B_ 
dEx = Aa “5 e XT dA ; 
in which dEx is the emissive power within wave-length 
range d.A and A and R are constants. Not accurate at 
long wave lengths. 
Wilson'sche Nebelkammer: Wilson (cloud) chamber. 
An inclosure containing air supersaturated by sudden 
expansion, in which rapidly moving particles, e.g., alpha 
or beta rays, produce ionization tracks by condensation 
on the ions. These may be observed or photographed 
through a suitable window. 
Wilson'scher Versuch: Wilson experiment. An experi- 
ment of H. A. Wilson, which consisted in the rotation 
of a hollow dielectric cylinder about an axis parallel 
to a magnetic field, with arrangements for detecting 
the resulting electric polarization in the dielectric. 
Wimshurst'sche Maschine: Wimshurst machine. A 
type of static machine having two plates, or two sets 
of plates, rotating in opposite directions. 
Windmesser: wind meter, Syn. anemometer. An in- 
strument for measuring the velocity of the wind, 
Windungsfluss: turn flux, linkage (mag.) A measure 
of the interlocking of a magnetic flux wtih an electric 
circuit, viz., the product of the flux by the number of 
turns of the circuit surrounding it, expressed in max- 
well-turns. 
Windungslinie: line-turn, maxwell-turn. A unit of 
magnetic linkage, corresponding to one line of force 
surrounded by 1 turn of the circuit. 
Winkel: angle. (1) The figure, concept, or relation of 
two straight lines (sides) emanating from one point 
(the vertex) ; a corner or point. (2) In the strictest 
mathematical sense the word angle signifies that relation 
of the lines which is measured by the amount of rota- 
tion necessary to make one coincide with the other. 
This amount is commonly expressed in degrees. When 
the sides of an angle are perpendicular to each other, 
it is a right angle; when less than a right angle, an 
acute angle; when greater than a right angle, an obtuse 
angle; when the sides go out in opposite directions, a 
straight angle. Any angle not a right or straight angle 
is an oblique angle. 
Winkel an der Trennungslinie: angle of repose. (1) 
The angle of inclination assumed by the surface of a 
loose material, such as sand in a pile, when in equi- 
librium with gravity. (2) By some writers, Syn. angle 
of friction. 
Winkeldrehmoment: moment of momentum, angular 
momentum. The angular momentum is the product of 
the moment of inertia of a rotating body, with respect 
to the (fixed) axis of rotation, by its angular velocity 
in radians per unit time; or, the volume integral of 
the products of the momenta of the elements of mass 
of the body by their distances from the axis of ro- 
tation. 
Winkelimpuls: angular impulse. The time integral of 
a torque, esp. when applied for a short time; measured 
by the change in angular momentum which it would 
impart to a free mass if acting about a principal axis. 
Winkelmesser: goniometer. See Goniometer. 
Winkelveraenderliche: angle of slip. The angle be- 
tween surfaces of slip or shear and the direction of 
163 
/Winkelvergroesserung w 
stress during flow or during the plastic deformation of 
a solid. 
Winkelvergroesserung: angular magnification. The ra- 
tio of the tangent of the angle with the optic axis made 
by a ray upon emergence from an optical instrument 
to the tangent of the angle for the corresponding (con- 
jugate) incident ray; or, approximately, the ratio of the 
angles themselves. 
Wirbel: vortex. A portion of fluid which rotates 
about an axis with resulting centrifugal force and re- 
duced pressure at the axis, and which is surrounded by 
a relatively stationary portion of the same fluid. The 
strength of an ideal vortex is its integrated vorticity, 
or twice the product of its angular speed of rotation 
by its cross section. See also Rotation eines Vektors. 
Wirbelbildung: vorticity. See Verwirbelung. 
Wirbelring; vortex ring. A type of vortex motion of 
a fluid, illustrated by the familiar smoke ring. 
Wirbels+rom: eddy current. A transient and local 
electric current in a conductor, due to change in mag- 
netic induction; e.g., in the core of a generator arma- 
ture. Syn. Foucault current. 
Wirbelstromverlust; eddy current loss. The power 
loss due to eddy currents in a core, which has been ex- 
pressed by the following empirical formula: 
pe = A(nfBwl)2, 
in which n is the frequency, Bm the maximum induc- 
tion during the cycle, 1 the thickness of the laminations, 
and f a form factor. A is the eddy-current constant. 
Wirbelsturm: cyclone. See Zyklon. 
wirkliches Bild: real image. See Bild. 
wirkliche Energie; intrinsic energy, internal energy. 
See wahre Energie. 
wirksame Komponente: effective component. See effek- 
tive Komponente. 
Wirksamkeit: efficiency. The ratio of the useful energy 
derived from a dynamic system (as an engine or other 
machine) to the energy communicated to it during the 
same process or over a protracted period of operation. 
Wirkung; action. (1) A magnitude defined as twice 
the time integral of the kinetic energy of a system, 
the variable time being measured from an arbitrary 
zero up to the time in question: Thus: 
S = 2 f Ekin dt. 
J t0 
It may be interpreted as twice the mean kinetic energy 
during the interval, multiplied by the duration of the 
interval. (2) In relativity dynamics, action is repre- 
sented by the formula: 
S = f 1 (Zqp)dt 
J to 
or 
s = C <24{s)* 
' to 
in which the and p's are generalized velocities and 
generalized momenta and L the Lagrangian function, 
and the summation extends over all the degrees of 
freedom. 
Wirkungsquantum: quantum of action. See Planck’- 
sche Konstante. 
Wismuthspirale: bismuth spiral. A coil of bismuth 
wire, the magnetoresistance effect in which is used as 
a measure of the magnetic field intensity. 
Woelbung: camber. The ratio of the sagitta (maxi- 
mum ordinate) of an arc to the length of the chord; 
a term applied to the streamlined contours of aerofoils 
or similar surfaces. 
wohltemperierte Tonleiter: equally tempered scale. A 
musical scale having equal intervals, therefore with fre- 
quencies in geometrical progression. Introduced by 
Bach. Syn, chromatic scale. 
Wollaston'sches Prisma: Wollaston prism, Syn. double- 
image prism. A large, quadrilateral reflecting prism of 
glass, used for sketching. 
Wuerfel: cube. A solid bounded by six equal squares 
and having all its angles right angles. 
Wurzel; root. (1) A quantity that, taken a specified 
number of times as a factor, will give another quan- 
tity called its power; as 2 is the fourth root of 16. (2) 
The quantity that, when substituted for the unknown 
quantity in an equation satisfies the equation. 
/x-Einheit 
164 X 
x-Einheit: x-unit. A unit of wave length, equal to 
10-11 cm or 0.001 Ä; commonly used for X-rays and 
other highly penetrating radaition. 
165 
/Youngscher Interferenzversuch Y 
Youngscher Interferenzversuch: Young interference 
experiment. An epochal experiment, performed by 
Thomas Young in 1801, which demonstrated the inter- 
ference of light from two sources and thereby estab- 
lished its undulatory character. 
Young'scher Modul; Young modulus. The ratio of 
the tensile stress, or longitudinal force per unit cross 
section, in a stretched elastic solid to the change in 
length per unit length. 
/Zaehfluessigkeit 
166 z 
Zaehfluessigkeit: viscidity. See Dickfluessigkeit. 
Zaehlrohr; counting tube, tube counter. An ionization 
chamber used for counting electrons or other ionizing 
particles. 
Zahl der Freiheitsgrade: variance. The number of de- 
grees of freedom of a system. 
Zahlenkomplex: complexion. Any specified set of 
values of the coordinates and momenta for the mole- 
cules or other particles composing a system, treated as 
a distribution of the particles among the phase-space 
elements. 
Zeeman Effekt: Zeeman effect. An effect upon the 
spectral series of gaseous elements produced by subject- 
ing the radiating atoms to a strong magnetic field; dis- 
covered by Zeeman in 1896. The lines are split up into 
more or less complicated multiplets, depending upon the 
direction of the field and other circumstances; and the 
effect may be either "normal” or "anomalous”, i.e., it 
may or may not be subject to a comparatively simple 
quantum explanation. 
Zeitintegral: time integral. In re any variable f which 
is a function of the time: the definite integral of the 
product of the variable by the element of time, viz., 
Jfdt between specified limits of t. 
Zeitkonstante: time constant. In re an electric circuit: 
the ratio of the inductance to the resistance; so called 
because it may be expressed dimensionally in time units, 
and measures the relaxation time of the current when 
the e.m.f. is removed. 
Zelle verschiedener Elektrolyten: gravity cell. A pri- 
mary cell in which the electrolyte is in two parts kept 
separate by their difference in specific gravity. 
Zentimeter: centimeter. (1) 1/100 of a meter. (2) 
The e.g.s. electrostatic unit of capacitance. It is the 
capacitance of an isolated spherical conductor of radius 
1 cm; equal to about 
1.113 X 10-12 f. 
(3) Syn. abhenry. (4) A centimeter of mercury is a 
unit of pressure equal to about 1333.2 bars. 
Zentrifugalkraft: centrifugal force. The kinetic reac- 
tion exerted by a body constrained to move in a curved 
path, and due to inertia. 
Zentrifugalmoment: centrifugal moment, c. torque. 
(1) The integrated torque of the centrifugal forces of 
all the particles of a freely rotating body with respect 
to any line through its center of mass perpendicular to 
the axis of rotation. (2) In general, the torque of a 
centrifugal force with respect to any given line. 
Zentripetalkraft; centripetal force. The force which 
constrains a moving body to follow a curved path rather 
than a straight line; the equilibrant of the centrifugal 
force. 
zentrobar: centroharic. Having a true center of grav- 
ity. A rigid body is centrobaric if the resultant gravita- 
tional attraction of an external particle for it is equiva- 
lent to a single force which always passes through one 
point fixed relatively to the body (its center of mass), 
irrespective of its orientation and position. E.g.; a 
homogeneous sphere or spherical shell is centrobaric, 
but bodies in general are not. 
Zentrode: centrode. The curved trace by the instan- 
taneous center of a plane body as it moves in any 
manner in its own plane. 
Zerfallskoeffizient: decay coefficient. A constant factor 
appearing in the exponent of the time function of decay 
for such phenomena as radioactivity, which obey the 
exponential law. E.g., the intensity of a radioactive 
emission of any type is given by an equation of the 
form 
I = I0e~Xt 
in which A is the decay coefficient. 
Zerfallsmodul: decay modulus. In re any variable 
which diminishes or "decays” exponentially, e.g., radio- 
activity: the time required for the variable to diminish 
to 1/e or 36.97 percent of its original value. It is equal 
to 1.443 times the half-value period, and is the re- 
ciprocal of the decay coefficient. 
Zerreissfrequenz: shatter oscillation. An oscillation in 
a liquid of such frequency and amplitude as to break 
the continuity of the liquid. 
Zerreissfestigkeif: ultimate strength, tensile strength. 
The limiting stress for which a material completely 
breaks down, and gives way. 
Zerrelssgrenze: destruction limit. The limiting shear- 
ing stress at which a crystal begins to lose its lattice 
structure, as indicated by the change in the Laue X-rays 
pattern. 
Zerreisskegel: cone of rupture. A double conical sur- 
face along which a solid cylinder, when subjected to 
severe longitudinal compression, tends to crack and 
slip. 
Zerreissmodul: rupture, modulus of. A kind of ulti- 
mate strength of a material, intermediate between the 
ultimate tensile and compressive strengths, which per- 
tains to the breaking of a rod by flexure; defined as 
the product of the bending torque required to rupture 
167 
/Ziehbarkeit z 
by the distance of the extreme fiber from the neutral 
axis, divided by the sectional moment of inertia. 
Ziehbarkeit: ductility. A combination of properties in 
a metallic substance, including malleability and tough- 
ness, which makes it capable of being drawn into wires. 
Zirkularpolarisation: circular polarization. Polarization 
in which the cycle is a circle. 
Zirkulation; circulation. In re any closed path within 
a fluid: the line integral of the tangential component 
of the velocity of the fluid taken around the closed path. 
zonale Aberration: zonal aberration. Spherical or 
monochromatic aberration of a lens of wide aperture, 
due to the fact that the refracting power is different 
for different zones concentric at the axis. 
Zone: zone. (1) A belt of crystal faces extending 
around a crystal, the planes of which form a prismatic 
surface, e.g., the lateral facets of a quartz crystal. (2) 
A portion of the surface of a sphere included between 
two parallel circles or bounded by one circle. 
Zonenachse: zone axis, zonal axis. (1) A line through 
the origin or center of a crystal which has a zone of 
faces, the line being parallel to each of those faces. 
(2) A row of atoms, ions, or molecules, located at 
the intersection of two or more atomic planes in a 
crystal. 
Zonenpla+te: zone plate. A transparent screen placed 
in a beam of light and having photographed on it a 
series of concentric opaque rings corresponding to alter- 
nate half-period elements of the intercepted waves. 
It exhibits effects similar to those of a converging lens. 
Zuckergehal+smesser: Saccharimeter. See Saccharimeter. 
Zuendfunker: pilot spark. A feeble disruptive dis- 
charge sometimes released between close spark terminals 
in order to promote a more violent spark in an adjacent, 
wider gap. The whole arrangement is called a three- 
point gap. 
Zuendungspotential: striking potential. The p.d. neces- 
sary to start an electric arc. 
Zuendverzoegerung: spark lag. See Funkenverzoege- 
rung. 
Zufuehrung: lead. A connecting wire to or from an 
electric device. 
Zug: negative pressure. A condition of stress within 
a cohesive body which is subjected to equal tensions 
in all directions, and which is thus truly the opposite 
of pressure. 
zulaesslge Spannung: allowable stress. The maximum 
stress which will not cause a plastic or permanent defor- 
mation of the substance to which it is applied. 
zusaetzlicher Pol: consequent pole. A magnetic pole 
in excess of the usual two on a magnetized body. 
Zusammenstoss: Collision. See Stoss. 
Zustandsgesetz: law of stages. The principle that in 
the process of crystallization from the liquid state, the 
atoms arrive at their final, permanent configuration 
through successive, temporary arrangements of varying 
stability. 
Zustandsgleichung: equation of state. (1) An equa- 
tion connecting the pressure p, the density d, and the 
temperature T of a fluid as any two or all of these 
quantities vary; e.g., for an ideal gas it has the form 
p/dT = constant. 
(2) In general, an equation connecting the variables 
chosen to specify the state of a substance. 
Zustandsveraenderliche: variables of state. The varia- 
bles, e.g., pressure, volume, temperature, and entropy, 
which determine the physical state of a body, and in 
terms of which its thermodynamic transformations are 
expressed. 
Zweig: branch. (1) Part of the series of lines form- 
ing a single band in a band Spektrum; the two branches 
proceed in opposite directions from a common zero line. 
(2) One of the subdivisions of a radio-active series 
due to transformations of different types. (3) A con- 
ductor joining any two given points of an electric net- 
work. 
Zweiphasenstrom: two-phase current. (1) A current 
service delivered through two pairs of wires forming 
separate circuits in which a phase difference of one- 
quarter cycle is maintained. A two-phase generator 
supplies, and a two-phase motor is operated by, such a 
current. (2) The same as (1), except that the two 
circuits are connected and usually grounded at their 
extremities or neutral points, forming a true polyphase 
system of four components. 
Zwillingsachse: twin axis. The line perpendicular to 
both crystalline axes of a twin crystal. 
Zwillingskristall: twin crystal. A crystal composed of 
two parts having axes in different directions, usually 
at right angles. They may be juxtaposed twins, i.e.. 
/Zwischenelektrodenkapazitaet 
168 z 
merely grown together, with a plane of separation be- 
tween ; or interpenetrant twins, i.e., having their struc- 
tures intimately commingled. 
Zwlschenelek+rodenkapazi+aet: interelectrode capaci- 
tance. The capacitance of a vacuum-tube circuit due 
to the condenser action of two of the tube electrodes, 
as the filament and the plate. 
Zwischenflaechenspannung: interfacial tension. The 
surface tension at'the interface between two fluids, as 
water and oil. 
Zybo+axis: cyhotaxis. The space arrangement of mole- 
cules in a liquid, with orientation simulating crystalline 
structure but without stability or permanence at any 
point. Studied by the X-ray diffraction patterns of the 
liquid. 
Zyklon: cyclone. See Wirbelsturm. 
Zyklotron: cyclotron. An apparatus for imparting high 
speeds to electrons or ions by causing them to move 
in semi-circular paths in a magnetic field, with an ac- 
celeration and increased radius every 180 degrees due 
to an electric field alternating in synchronism with 
their motion. 
☆ U. S. GOVERNMENT PRINTING OFFICE: I94S 677865 
169