SPLINTER OF A LUCiFER MATCH MICROSCOPICAL MANIPULATION. Plate I ON 
MICROSCOPICAL MANIPULATION, 
BEING THE SUBJECT-MATTER OF 
A COURSE OF LECTURES 
DELIVERED BEFORE THE 
QUEKETT MICROSCOPICAL CLUB, 
d AN UARY —APRI L, 1869. 
BY 
W. T. SUFFOLK, F.R.M.S. 
Illustrated with Forty-Nine and Seven Lithographs. 
PHILADELPHIA: 
J. B. LIPPINCOTT AND CO. 
1870. PRINTED AT THE CHEMICAL NEWS OFFICE, 
BOY COURT, LUDGATE HILL, E.C. 
LONDON: To PHILIP LeNEVE FOSTER, M.A., F.R.M.S., 
PRESIDENT OF THE QUEKETT MICROSCOPICAL CLUB. 
Dear Sir, 
Permit me to dedicate this little volume to you, in 
remembrance of your kind aid in promoting the delivery 
of the Lectures, in 1866, which were the origin of 
the more extended course contained in the following 
pages. 
And believe me, 
Sir, 
Yours faithfully, 
W. T. SUFFOLK. CONTENTS. 
PAGE 
Description of the Plates 
Preface xiii 
CHAPTER I. 
Construction of Microscope . . . . i 
Microscope Stand, 2, 215. Properties of Light, 3. Re- 
fledtion, 3. Refradtion, 4. Lenses, 6. Formation of 
Images, 7. Simple Microscopes, 11. Compound 
Microscopes, 13. Spherical Aberration, 14. Chromatic 
Aberration, 15. Eye-Pieces, 18. Draw-Tube, ig. 
Binocular Microscope, 19. Care of Microscope, 23. 
Lamps, 24. Illuminating Apparatus, 27. Air- 
Bubbles, 29. Oil-Globules, 29. Dust, 30. 
CHAPTER II. 
Mechanical Processes 32 
Glass, 32. Cutting Glass, 33, 216. Drilling Glass, 36. 
Corundum Tools, 37. Glass Tubes, Bending and 
Working, 38. Cleaning Glass, 39. Cementing, 42. 
Troughs, 44. Growing-Slide, 46. Cells, 47. Needles, 
4g. Sharpening Cutting Instruments, 50. 
CHAPTER III. 
Mounting Objects Dry and in Balsam . . 52 
Dry Mounting, 52. Disc-Holder, 53. Open Cells, 53. 
Mounting with Cement, 54. Drying Objedts, 57. 
Canada Balsam, 5g. Air-Bubbles, 61. Finishing 
Objedts, 62. Balsam Compounds, 64, 217. Cutting 
Sedtions of Hard Substances, 64, 217. viii 
CONTENTS. 
CHAPTER IV. 
Mounting Objects in Fluid 69 
Preliminary Processes, 70. Placing Object in Cell, 71. 
Cementing, 73. Cautions in Closing Cell, 74. 
Damar Varnish, 75. Cabinets, 76. Media Used in 
Mounting, 77. Endosmosis, 78. Distilled Water, 80. 
Camphor Water, 81. Creosote Water, 81. Alcohol, 
81. Thwaites’s Fluid, 82. Chloride of Calcium, 83. 
Chloride of Sodium, 84. Glycerine, 84. Glycerine 
Compounds, 88. Staining Tissues, 91. 
CHAPTER V. 
Illuminating Apparatus 93 
Condensing Lens, 93. Lieberkuhn, 97. Parabolic 
Lieberkuhn, 99, 218. Side Reflector, 102. Vertical 
Illuminators, 103. Mirror, 105. Diaphragm Plate, 
105. White Cloud Illumination, 106. Dark-Field 
Illumination, 107. Internal Reflection, no. Achro- 
matic Condenser, 112. Webster Condenser, 1x5. 
CHAPTER VI. 
Polarised Light 119 
Undulations of Light, 120. Interference, 121, 2ig. 
Iridescence, 122. Newton’s Rings, 123. Polarisation 
by Reflection, 125. Nicol’s Prism, 127. Tourmaline, 
127. Herapathite, 127. Colours Produced by Sele- 
nite Films, 129. Apparatus Used for Polarising with 
the Microscope, 131. Polarisation with High Powers, 
136. Polarisation a Test of Double Refraction, 137. 
Conducting Observations with Polarised Light, 140. 
CHAPTER VII. 
Drawing and Micrometry 142 
Photography, 143. Free Hand Drawing, 145. Camera 
Lucida, 146. Soemmering’s Mirror, 147. Neutral 
Tint Reflector, 148. Mode of Using Drawing Instru- 
ments, 149. Illumination for Making Drawings, 152. 
Scales Attached to Drawings, 152. Estimating 
Magnifying Power, 153. Ruled Disc in Eye-piece 
Used for Drawing, 154. Micrometry, 156. Stage 
Micrometers, 157. Eye-Piece Micrometers, 158. 
Adjusting Eye-Piece Micrometers, 159. Drawing 
Materials, 163. Engraving, 166. Lithography, 170. CONTENTS. 
ix 
APPENDIX. 
Apparatus 178 
Lesson 1. On Use of Condensing Lens and Mirror . 182 
Lesson 2. Examination of Sponge Dirt . . . 186 
Lesson 3. Examination of White Powders . . 190 
Lesson 4. Structure of Wood 198 
Lesson 5. Aquatic Observations .... 201 
Lesson 6. Fibres and Textile Fabrics . . . 205 
Notes 215 
Microscope Stands, 215. Immersion Obje&ives, 215. 
Molecular Motion and Organic Matter in Air, 215, 
Cutting Glass, 216. Solution of Canada Balsam in 
Benzol, 217. Cutting Rock Sections, 217. Parabolic 
Lieberkuhn, 218. Illuminating Objects by Reflected 
Light, 218. Phenomena of Interference, 219. DESCRIPTION OF THE PLATES. 
Plate i—Frontispiece. 
Splinter of lucifer match after drawing by Richard Beck 
(pp. 169, 198). 
The elongated wood cells or fibres run from top to 
bottom of the plate, and in some places their characteristic 
tapering ends are visible; they are covered with rows of 
peculiar pitted dots already mentioned. The bands 
of cellular tissue, crossing the fibres at right angles, are 
portions of the medullary rays. This splinter is identical 
with the radial section, PI. 4, fig. 3. 
Plate 2. 
Figs. 1—6. Various Foraminifercz from Smyrna sponge 
dirt (p. 188). 
Figs. 7—11. Sponge spicules (p. 187). 
Figs. 12—14. Barbadoes Polycistince (fossil), (p. 195). 
Plate 3. 
Figs. 1—6. Starches (p. 193). 
1. Tous les mois. 2. St. Vincent arrowroot, Mar ant a 
arundinacea. 3. Barley. 4. Oat. 5. Maize (Brown 
and Poison’s corn flour). 
Fig. 7. Fibre of wool (p. 213). 
Fig. 8. The same treated with a hot alkaline solution (p. 
213)- 
Fig. 9. Silk fibres (p. 212). 
Fig. 10. The same after treatment with hot alkali (p. 212). 
This plate is a specimen of engraving on stone (p. 173), and shows the 
usual defedts of a first attempt, principally the result of fear in cutting 
the surface. Engraved lines print finer than they appear on the stone. 
Considerable practice is required to attain excellence in this mode 
of lithography. DESCRIPTION OF THE PLATES. 
xi 
Plate 4. 
Fig. x. Transverse sedtion of stem of Clematis from nature 
(p. 200). 
Figs. 2—6. Diagrams illustrating the strudture of exo- 
genous and endogenous stems. 
Exogenous Stem— 
Fig. 2. Transverse sedtion. 
Fig. 3. Radial sedtion. 
Fig. 4. Tangential sedtion. 
Endogenous Stem— 
Fig. 5. Transverse sedtion. 
Fig. 6. Longitudinal sedtion. 
a, pith; b, fibro-vascular bundles; c, medullary rays 
d, bark. 
Plate 5. 
Fresh water animals and plants (p. 201). 
Lower figures, Stephanoceros Eichornii; on conferva on 
the right, at the top Melicerta ringens (Rotiferce); entangled 
in confervae, on the left, statoblasts or buds of Plumatella 
(Polyzoa). 
Plate 6. 
Marine animals (p. 204). 
Upper group, Bowerbankia imbricata (Polyzoo). Many 
of the Polyzoa are interesting to the microscopist on 
account of their transparency permitting a good view of 
the internal organs. The digestive organs and some of 
the retradtor muscles are plainly seen in the figure. 
Lower figures, on the left, Campanulina acuminata 
(tenuis), (Hydrozoa), from drawing by C. P. Johnson; on 
left, Pedicellina Belgica ? 
Plates 4,5, and 6 are specimens of white line engraving on stone (p. 174). 
Plate 7. 
Fig. 1. Fibres of wool, refledted light (p. 206). 
Fig. 2. Fibres of jute, polarised light (p. 206). 
Fig. 3. Fibres of silk, polarised light (p. 206). 
Fig. 4. Fibres of cotton, polarised light (p. 206). 
Fig. 5. Fibres of flax, polarised light (p. 206). xii 
DESCRIPTION OF THE PLATES. 
The swelling on the right-hand portion of fig. 5 is 
characteristic of the liber fibres when injured by bending 
or crushing. 
This and Plate 2 are specimens of chalk drawing. Owing to the 
necessity of representing these objedts on a black ground, the figures 
have lost much of the delicacy of detail which they possessed before 
the stones were “ etched,” the solid black ground requiring to be 
treated with acid to an extent injurious to the more tender lithographic 
chalk. The combination of large masses of ink with chalk should 
always be avoided when possible. 
Plate 8. 
Figures illustrating interference and coalescence of waves 
(pp. 122, 219). PREFACE. 
THE ledtures forming the principal contents 
of this volume were delivered at the 
Quekett Microscopical Club at the commence- 
ment of 1868, and were prepared for publication 
in the “ Chemical News ” from the short-hand 
writer’s report. The ledture form has not been 
retained, although the chapters, with one ex- 
ception,* represent almost exadtly the course as 
delivered. 
To render the subjedt more complete, a few 
notes have been added to the earlier sheets, 
principally relating to events which have 
transpired during publication ; the later ones 
have been corrected to bring their contents as 
nearly as possible to the present time. 
With the view of making the work more useful 
to those for whom it is principally intended, a 
* For the sake of convenient demonstration, the subject 
of Chapter IV. occupied two ledlures. xiv 
PREFACE. 
few practical lessons have been added ; these 
are chiefly founded upon the demonstrations 
following the delivery of the original leCtures. 
The selection of specimens for examination has 
been made from the most easily procured sub- 
stances, rather than from those objects 
commonly examined by microscopists, and 
which have been so frequently described, that 
the student would probably commence his ob- 
servations with some pre-conceived ideas as to 
structure. 
The plates, which, with the exception of the 
frontispiece, have been executed by the author, 
are added principally as illustrations of the 
lithographic processes described in Chapter VII., 
and to show how far the art, in the hands of an 
amateur, may be rendered available for the re- 
production of microscopical drawings. 
The frontispiece, after a drawing by the late 
Richard Beck, is a fine specimen of wood 
engraving, and is introduced as an instance of 
that successful interpretation of the artist’s ideas, 
which is, unfortunately, rare. For this, many 
other wood-blocks, and permission to re-produce 
the subject of Plate 7, the author is indebted 
to the kindness of Messrs. R. and J. Beck. The 
thanks of the author are also due to Messrs. 
Churchill and Sons, Messrs. Longmans and Co., PREFACE. 
XV 
Mr. Collins, Messrs. Winsor and Newton, and 
Messrs. Cotton and Johnson for drawings kindly 
supplied to illustrate the work. 
The instruments and apparatus mentioned 
are chiefly those used at the Lectures, and by 
no means represent all procurable either in 
England or on the Continent. For full in- 
formation on this subject the reader is referred 
to “ Carpenter,” pp. 19—238. With respect to 
the introduction of the names of makers, no 
apology is needed in the case of Messrs. Powell 
and Lealand, Ross, and R. and J. Beck. Mr. 
Collins was engaged by the Ledture Committee 
to supply lamps and such apparatus as was 
needed beyond that in possession of the 
Ledturer and the gentlemen who assisted at 
the demonstrations ; and Mr. Bailey has for 
some time made such experimental apparatus 
as the author has required : this will account 
for the frequent mention of these opticians. In 
the case of other makers, omission by no means 
implies inferiority, as the author believes that 
equally good apparatus may be obtained from 
many of those of whom no mention has been 
made. ON 
MICROSCOPICAL MANIPULATION. 
THE objedt of the present series of chapters is to 
place my own practice before beginners in 
microscopical science, for although there are a vast 
number of existing works on the microscope, many of 
them are of a popular nature and addressed to those 
who seek in the microscope a means of recreation 
rather than of scientific research. My wish is to supply 
simple and practical directions to aid the student, 
giving very much in detail such processes as are but 
little mentioned in books, and which are more usually 
learned by seeing the instrument in the hands of an 
experienced person; but as this is an advantage not 
accessible to every one, it would seem that there is 
still a want, which it is my hope this and succeeding 
chapters will help to supply, and prepare the student 
to consult with profit more elaborate treatises. 
CHAPTER I. 
I have thought proper, therefore, to devote this 
chapter to the consideration of the instrument we have 2 
MICROSCOPICAL MANIPULATION. 
to work with. No workman is any the worse for a 
knowledge of the contents of his tool-chest; in fact, 
he will be far better qualified for making use of the 
appliances he possesses by knowing th'eir construc- 
tion. 
Microscopes vary much in their details of con- 
struction, each maker having an instrument for 
which he claims its own especial merit. For con- 
venience sake, the general plan of structure may be 
described as consisting of a tube containing the 
optical portion, capable of a sufficient range of motion 
to and from a support for the object to be examined, 
known as the stage, beneath which is placed a mirror, 
provided with the necessary adjustments for reflecting 
light upwards through the aperture in the stage. 
The plans employed for supporting the tube con- 
taining the lenses, or “body,” are two in number; in 
one, that adopted by Messrs. Beck and a few other 
makers, the body is supported by the greater part 
of its length, and runs in groove of peculiar form, 
which effectually prevents the detrimental movement 
known as “twist.” In the other mode, the one used 
by Messrs. Ross, Powell and Leland, and the majority 
of opticians, the body is attached to the extremity of 
the cross-arm, the rack work moving up and down in 
a tube attached to the trunnions which carry the 
instrument between the two uprights connected with 
its base. This last plan of construction involves the 
use of a greater weight of metal and a more careful 
disposition of it to secure stability than where the 
body is supported in the former manner, but when PROPERTIES OF LIGHT. 
3 
skilfully made there is no practical objection to its 
employment. 
Dr. Carpenter speaks highly of the first mode, 
which is also approved of by Dr. Bowerbank : my 
experience is decidedly in its favour, my own instru- 
ment so constructed having been exposed to more 
than ten years’ severe wear, and having had no 
substantial repairs during that period. 
The part of the microscope I wish to direCt 
attention to in the first instance, is the body and its 
contents. A combination of lenses, called the objeCt 
glass, is screwed to the bottom of the tube, and 
another called the eye-piece, is placed at the top. 
For the sake of simplicity, the binocular arrangement 
will be for the present omitted, the instrument 
being supposed to have but a single body. In order 
that the use of the glasses contained in this tube may 
be understood, I must direCt attention in the first 
place to some of the properties of light. 
A ray of light, which is a very arbitrary term, 
may be considered, for the present purpose, as a small 
cylinder of light—a thing which has no real existence 
in nature, but will serve well for the purpose of de- 
monstration. It is very much what the line is in 
mathematics. 
Should this ray of light fall upon a polished surface 
which is not capable of allowing it to go through, or, 
in other words, an opaque polished surface like a 
bright plate of metal, c, d (Fig. i), if the ray 
of light, b, a, falls upon that surface perpen- 
dicularly, it will be sent back by the same course 4 
MICROSCOPICAL MANIPULATION. 
through which it came down. On the contrary, 
should the ray of light e, a, fall obliquely, it will 
be reflected at an angle, b, a, /, equal to that 
e, a, b, at which it fell upon the reflecting medium. 
This angle of incidence, e, a, b, will be equal to the 
angle of reflection, b, a, /. Now this principle is made 
use of in our commonest means of illumination,—the 
mirror under the stage by which the light from a 
lamp or other source of light at one side or in front 
of the microscope, or in any other convenient place, 
is directed through the axis of the instrument. In 
Fig. x. 
the subsequent chapters I shall say more about the 
application of the refleCtive principle. This is the 
only instance to be noticed at present. 
Now, supposing that the ray of light falls upon a 
transparent material (a plate of glass, for example, a 
substance more dense than air), should the ray, c,f, fall 
upon this plate of glass, a, b (Fig. 2), perpendicularly, 
it passes straight through it without any alteration 
taking place; but should the ray of light, e, f, fall 
obliquely, it will no longer pass through in the same 
direction, but will be bent towards the perpendicular, 
c, d, in a greater or less degree according to the density REFRACTION. 
5 
of the medium, as at /, g, and is bent again upon 
its emergence into the rarer medium at g, towards h. 
The amount of “ refradtion,” as this bending is 
called, would be much less with water than it would 
Fig. 2. 
be with glass, and it would be greatest of all in the 
diamond, other substances refradting in intermediate 
degrees. 
The effedt of refradtion is familiarly illustrated by 
the well-known phenomenon of objedts immersed in 
water appearing to be nearer the surface than they 
Fig. 3. 
really are, a pool appearing to be only three or four 
feet deep, when in reality it is nearer six or eight. 
This may be readily demonstrated by placing a stick or 6 
MICROSCOPICAL MANIPULATION. 
other objedt in a basin of water (Fig. 3) ; the stick 
will appear bent where it enters the water; a coin or 
other objedt will appear to be at a much less depth 
than it adtually is. 
It is owing to refradtion that we are able to make use 
of lenses, which give us the power of bending rays of 
light and turning them about in any way that may 
be required. 
Lenses are circular pieces of glass or other trans- 
parent material capable of refradting light, and 
having curved surfaces, either convex or concave. 
The adtion of a lens upon a ray of light will be best 
understood by reference to Fig 4. For the sake of 
Fig. 4. 
simplicity the dotted curved lines representing the 
sedtion of the lenses may be considered as straight 
lines, as shown in the diagram. 
It has been shown (Fig 2) that when a ray falls 
obliquely it is refradted, but that when it falls at 
right angles with the refradting medium it suffers 
no refradtion. The central ray in both a and b passes 
straight through without refradtion ; in a the incli- 
nation of the surfaces is such that the rays passing FORMATION OF IMAGES. 
7 
above and below the centre line converge at a point 
called the focus. The lens, b, being thickest at the 
margin, the effeCt is just the reverse; the rays are 
dispersed, and do not come to a focus but diverge, as if 
they proceeded from a point on the opposite side of 
the lens, called the virtual focus. These concave 
lenses do not magnify, but are used in microscopes 
and other optical instruments, for purposes to be 
hereafter mentioned : the most familiar instances to 
be cited of their use are as the eye-glass of an opera- 
glass or Galilean telescope, and as spectacles for 
short-sighted persons. 
Lenses may be made with one side worked to a 
plane surface and the other either convex or concave, 
such lenses are known as plano-convex and plano- 
concave lenses; their -respective powers are about 
half those of lenses of similar and double curvatures. 
There are also lenses convex on one surface, and 
concave on the other; these are called meniscus 
lenses; the curves may be so proportioned that they 
have either the power of convex or concave lenses, 
according as they are thickest in the middle or at 
the edge; they have, moreover, some properties 
peculiar to themselves which are turned to good 
account by skilful opticians. 
The formation of images is one of the most valu- 
able properties of convex lenses, and one taken ad- 
vantage of in the construction of optical instruments. 
If a convex lens is held at the distance of its focal 
length in front of a sheet of paper or other white sur- 
face, an inverted picture more or less distinCt will be 8 
MICROSCOPICAL MANIPULATION. 
seen of objedts that may be before it, such as a window 
or candle flame. This is illustrated by the diagram 
Fig. 5, representing a candle flame on the left hand, 
from the apex of which two rays diverge, the lower 
Fig. 5. 
one reaching the lower edge of the lens and the 
upper one its centre. Rays proceed from each point 
of the flame to every part of the surface of the lens, 
but, for the sake of clearness, only two are here re- 
presented. After passing through the lens they con- 
verge ; the same takes place with the rays proceeding 
from the lower part of the flame, which also pass 
through the lens. The result is the formation of an in- 
verted image, the size of which and its distance from 
the lens are dependent upon the distance of the objedt 
and the focal length of the lens. 
The greater the distance of the objeft, or “ anterior 
focus,” the shorter will be the distance of the image, 
or “ posterior focus.” The commonest example may 
be taken from the operations of the photographer, 
who, if he wants to take a small portrait, will place 
the sitter at a great distance from the camera, if, on 
the contrary, he desires a large figure, he will bring 
his model nearer; in the former case the posterior 
focus of the camera will be shorter than in the latter, THE SIMPLE MICROSCOPE. 
9 
which is shown by the camera requiring to be 
lengthened when the model is brought near to it. 
Besides the use of lenses to form images, they are 
also employed as magnifiers, and constitute the 
simplest form of microscope. Most naturalists and 
microscopists are provided with some little con- 
trivance of this kind either attached to the watch chain 
or carried in the pocket,—either one or more lenses 
suitably mounted, or the Stanhope lens. In all these 
simple microscopes no image is formed, so that the 
principle upon which a magnified view is obtained is 
different. The idea of the magnitude of an objedt is 
formed entirely by the space which it occupies upon the 
retina of the eye. It is quite irrespective of its actual 
size; or, to express it in mathematical language, an 
object is large or small in proportion as it sub- 
tends a great or small angle with respect to the eye. 
The eye has a certain power of adjusting itself to 
view objects at different distances, but there is a 
limit to the distance of distinct vision. It varies 
from five to ten inches in different persons. An 
object cannot be distinctly seen nearer than either 
one or other of these distances, or some inter- 
mediate point. Now optical science supplies a 
means of overcoming this difficulty. An objedt 
apparently enlarged by being brought nearer to 
the eye, becomes indistindt, because the pencils of 
rays proceeding from it diverge too much to be brought 
to a focus on the retina by the lens of the eye. 
The optical instrument most closely resembling 
the eye is the camera obscura. When the rack is MICROSCOPICAL MANIPULATION. 
run out to its full extent and the body is drawn out 
as far as it will go, and the objeCt is still too near to be 
focussed distinctly, the position is precisely that of 
the eye with an objeCt too close to it for distinCt vision. 
The remedy with the camera, supposing that no 
more focussing space could be obtained, would be 
to shorten the focus of the lens ; that is, use one of 
greater refractive power. The same thing must be 
done in the case of indistinCt vision, by interposing 
a convex lens, and so increasing the convergent 
power of the lens of the eye ; the objeCt, hitherto too 
near the eye, a, b, is thus rendered visible and clearly 
defined, but with this remarkable difference, that it 
appears not to be the image of the objeCt placed near 
the eye, but of a larger objeCt, A, b, at the distance of 
distinct vision. No crossing of the rays takes place, 
and consequently the image is not inverted. 
Fig. 6. 
The hand magnifier is an extremely useful instru- 
ment, but many persons find great trouble in using it to THE HAND MAGNIFIER. 
advantage, especially when it is of short focus and 
high power. A trifling hint about its use may be of 
value. 
Hold the objedt in the left hand, either in the fingers 
or with forceps, and, placing the left hand against 
the right which is holding the lens, look through the 
magnifier and adjust the focus. The view is usually 
most distindt when the eye is in one focus of the lens 
and the objedt in the other ; the two hands being held 
in contadt move together and prevent that tremor 
which would be apparent, especially with high 
powers, if the hands were kept apart, and which un- 
steadiness prevents any accurate view of the objedt 
being obtained. Single lenses, when their diameter 
exceeds that of the pupil, possess the property of 
bringing light to the eye and rendering the objedt 
clearer than it would be without such assistance. 
This may be proved by looking at print or other 
suitable objedt in a bad light, and noticing how 
much the magnifier aids by its light-colledting 
power. 
Single lenses are mounted on stands of various 
kinds, and then they become what are called single 
or simple microscopes. The older observers had no 
other instruments. These may consist of many 
lenses, while the compound microscope may be made 
with as few as two ; but then they adt upon the 
principle that no image is formed, but the objedt is 
rendered visible at a shorter distance than it could 
be without optical aid. Single microscopes are still 
in use for dissedtion and other purposes where only MICROSCOPICAL MANIPULATION. 
A 
Fig. 7. 
B THE COMPOUND MICROSCOPE. 
13 
a low power is required. And various contrivances 
have been adopted by which both eyes may be used 
and much fatigue saved in protradted operations. 
The compound microscope differs from the simple 
instrument just mentioned in an image being formed 
and again magnified by being viewed with another 
lens or eye-piece (Fig. 7, A). 
From what has been said before respecting the 
formation of images, it is evident if a lens of short 
focus is used and an objedt placed before it, the image 
will be formed at a great distance behind it and be 
much enlarged; if instead of viewing this image 
direCtly, as in the camera obscura, it is viewed with 
a suitable lens, l, m, another enlargement takes place. 
Such an instrument might be constructed with only 
two lenses, as in the diagram Fig. 7, A, but a microscope 
so made would of course be a very imperfect instru- 
ment ; indeed it would in almost every point be 
inferior in its performance to that of a simple lens, 
principally because the eye lens magnifies all the 
imperfections of the image formed by the small lens 
or objeCt-glass. These imperfections are chiefly 
caused by the spherical and chromatic aberrations of 
the objeCt-glass, and also in some degree by those of 
the eye-piece. 
Theoretically, convex lenses bring parallel rays to a 
point called the focus, at a distance from the lens 
dependent upon the radii of their curved sides. 
Practically, this is not the case; the rays passing 
through the marginal portion of the lens come to a 
focus at a shorter distance from it than those which 14 
MICROSCOPICAL MANIPULATION. 
pass through or near its centre (Fig. 8). Those 
passing through intermediate portions converge to 
some part between these two points; the result is 
that indistindt images are formed at various points 
between f and/, Fig. 8, no well-defined figure being 
seen anywhere. Could lenses be made having an 
hyperbolic or elliptic sedtion, the spherical aberration 
would be corredted, but the difficulties of making 
lenses of such figures are so great as to be considered 
Fig. 8. 
impossible in practice. Spherical aberration maybe 
lessened by reducing the aperture of the lens, by 
cutting off the marginal portion by means of stops or 
diaphragms; but any great use of this means causes 
a loss of light very detrimental to the performance 
of the instrument. Advantage may also be taken of 
the position in which the lens is placed and also of 
its figure; the spherical aberration of some lenses, 
such as plano-convex and meniscus, is much affedted 
by the way they are placed, being much greater in 
one position than other. Much may be done by 
placing the glasses in their most favourable position 
and using suitable curves : as a striking example, take CHROMATIC ABERRATION. 
15 
to pieces a photographic lens and observe the curious 
forms adopted in its construction.. The details of 
these corrections are rather a matter for the practical 
optician, and are unsuitable for an elementary treatise 
on the microscope. 
Fig. g. 
Blue. 
Chromatic aberration is caused by the unequal re- 
fraction of the constituents of a ray of light. If a 
ray be bent by passing through a glass prism, instead 
of the ray appearing on the other side as white light 
it will be decomposed, owing to the unequal capability 
of bending which the rays possess ; the red ray is bent 
least, the yellow more, and the blue and violet most 
of all (Fig 9). This also takes place when light is 
caused to pass through a lens (Fig. 10). The blue ray 
being the most refrangible comes to a focus nearest 
to the lens at b; the red ray being the least refrangible 
will not converge until it reaches r; the yellow, green, 
&c., rays come to a focus at intermediate points, so 
that a series of images surrounded by fringes of their 16 
MICROSCOPICAL MANIPULATION. 
respective colours would be formed at various points 
between b and r, such coloured margins rendering 
the definition extremely defective. Chromatic aber- 
ration may be lessened by the use of stops, cutting off 
the marginal portion of the lens, but at the sacrifice 
of a great quantity of light and the impairing of some 
of the most valuable qualities of the glass for micro- 
scopic purposes. Fortunately, a means has been 
Fig. io. 
found of almost entirely correcting chromatic aber- 
ration. Different kinds of glass vary not only in 
their refractive power but also in the degree in which 
they disperse the coloured rays, and, by combining 
lenses of suitable forms and materials, the error of 
one lens is so neutralised by the opposite error of 
the other that the combination as a whole is nearly 
free from the production of colour, or becomes, as it is 
termed, achromatic. For the practical application of 
this valuable fact, we are indebted to the elder 
Dollond, who constructed telescopes on this principle 
towards the end of the last century. The object 
glass of the microscope was not improved until many 
years afterwards. 
Owing to the very divergent condition of the rays 
proceeding from a minute object placed near the lens THE ACHROMATIC OBJECT-GLASS. 
of a microscope, the construction of an achromatic 
objeCt-glass is much more complex than the com- 
bination employed in other optical instruments. 
High powers contain as many as three combina- 
tions of compound lenses placed behind each other, 
the careful adaptation of which requires the greatest 
skill on the part of the optician, and necessarily causes 
objectives of large aperture and great perfection to 
be very costly. A valuable series of papers by Mr. 
F. H. Wenham on the construction of objeCt-glasses 
for microscopes will be found in the Monthly Micro- 
scopical Journal, vol. i., pp. in, &c. 
So perfectly was the correction of the chromatic 
and spherical aberrations effected, that it was found 
that even the covering of the objeCt to be viewed 
with a thin plate of glass or mica rendered the image 
sensibly indistinct: fortunately the defect was no 
sooner discovered than the late Andrew Ross applied 
a simple remedy; some alteration was made in the 
disposition of the correcting media, and the front 
combination allowed a small range of motion back- 
wards and forwards, which is usually regulated by a 
graduated collar, the use of which it will be well to 
explain, as, although it is to be found in most works 
on the microscope, it seems to be generally overlooked. 
Makers differ a little in the details of their arrange- 
ment for this correction, but there will always be 
found some mark indicating when the objeCt-glass 
is corrected, for viewing an uncovered objeCt. Focus 
carefully for distinct vision, with the glass so arranged, 
and then, taking hold of the collar, turn it round until 18 
MICROSCOPICAL MANIPULATION. 
a view is obtained of dust that may be resting on the 
upper surface of the cover of the slide ; if the object is 
now focussed by the use of the fine adjustment, the cor- 
rection for the thickness ol the cover glass will be 
found to be very perfectly made, and as the 
collar is usually graduated, the number may be 
noted on the slide for future use, as it is constant 
with the same objeCt and eye-piece, and also for the 
same thickness of cover-glass. 
The eye-piece usually employed in the microscope 
in combination with achromatic objeCt-glasses is 
that invented by Huyghens, a Dutch astronomer 
(Fig. 7, B), and consists of two plano-convex lenses 
(e e and F f), with their plane sides towards the eye ; 
this eye-piece, although not achromatic, when used 
with objeCt-glasses slightly “over-correCted,” renders 
the instrument achromatic as a whole. The optical 
principles involved are far too complicated to find 
a place in the present chapter. 
The power of the instrument may be greatly varied 
by using a series of eye-pieces of different power, and 
if the corrections of the objeCt-glass are perfect, and 
its angular aperture sufficient to admit a large 
amount of light, great advantage may be derived from 
the use of a short or “ deep” eye-piece ; but as the 
magnifying power of the eye-piece exaggerates every 
defeCt of the image, it is only with good objeCt-glasses 
that this means of increasing the power is available. 
A very deep eye-piece is of value in testing the quality 
of an objective, as it causes defects which may not be 
apparent with lower powers to become very marked. THE BINOCULAR MICROSCOPE. 
19 
The power of the instrument is greatly influenced 
by the length of the tube or body, and were it not for 
the inconvenience of excessive length, this would 
probably be the least objectionable way of increasing 
the magnifying power; but a very long tube renders 
manipulation difficult, on account of its removing the 
hands to an uncomfortable distance from the stage 
and illuminating apparatus. Most microscopes have 
a sliding tube in the body known as the draw-tube, 
by which the length can be increased to the extent 
of four or six inches at pleasure. 
A description of the compound achromatic micro- 
scope can, at the present time, hardly be considered 
complete without some mention of binocular instru- 
ments. The binocular principle had been applied to 
opera glasses with great success for many years. 
More recently the invention of the stereoscope and 
its great popularity drew increased attention to the 
subjeCt of binocular vision, but until a few years ago 
no attempt seems to have been made to adapt the 
principle to microscopes. Owing to the short focal 
length of microscopical objectives, the use of two 
convergent instruments would of course be im- 
practicable ; the only resource was to divide the pencil 
proceeding from the objeCt-glass and convey half to 
each eye. The earlier attempts resulted in the 
production of pseudoscopic instruments; that is, the 
relative positions of the objeCt viewed were reversed, 
projections being represented by depressions and the 
contrary. This was found to be caused by the rays 
of light being conveyed to the wrong eyes, the right 20 
MICROSCOPICAL MANIPULATION. 
side of the image entering the right eye, and the left 
the left eye, the effeCt being that of a wrongly 
mounted stereoscopic picture. It was found neces- 
sary that the right-hand image should be conveyed 
to the left eye, and vice versa, to produce a stereoscopic 
Fig. ii 
effeCt; this was accomplished by M. Nachet of Paris, 
and Mr. Wenham by different methods, each having 
their respective merits. As Mr. Wenham’s is most 
in use in this country, I will briefly describe it. A 
four-sided prism of peculiar form (Fig. n, A) is placed THE BINOCULAR MICROSCOPE. 
21 
in thebodyof the microscope, just behind the posterior 
combination of the objeCt-glass (Fig. n, B, a), which, 
when in position, it half covers. An additional body, l, 
is joined at a slight inclination to the left-hand side of 
the instrument, and the two bodies are furnished at 
their upper extremities with draw-tubes, which supply 
the means of making an adjustment for the varying 
distance between the eyes of different persons. The 
image formed by the left-hand half of the objective 
passes up the straight tube to the right eye without 
being in anyway interfered with by the prism; the 
right-hand image falls on the prism, is twice reflected, 
and passes into the left-hand inclined tube, and in 
this simple manner the crossing of the images from 
the two sides of the objective is effected, only one- 
half of the pencil suffering any reflection at all, 
besides giving the great advantage of instantly 
converting the instrument into a monocular by 
simply withdrawing the prism. It is only due to Mr. 
Wenham to mention that he has, with most praise- 
worthy liberality, granted free and unconditional use 
of his valuable invention to the public. 
The binocular arrangement of Mr. Wenham cannot 
be used with advantage with objectives of less 
than half an inch focal length, but several arrange- 
ments have been constructed by which both eyes 
can be employed in high power observations, the 
most noteworthy of which has been brought 
forward by Messrs. Powell and Lealand. This 
instrument does not produce any stereoscopic effeCt, 
but nevertheless greatly diminishes the fatigue of 22 
MICROSCOPICAL MANIPULATION. 
protradted observations. A still more perfedt adapta- 
tion has been construdted by Mr. Wenham,in which 
the light in each tube has been more nearly equalised 
than in preceding instruments. 
The stereoscopic binocular offers many advantages 
over-the monocular instrument, not the least of 
which is the saving of the fatigue to the eyes from 
which most persons suffer in a greater or less degree 
whenusingone eye for observation. Did the binocular 
arrangement do no more than this it would be a great 
boon, but it has the valuable property of enabling 
the observer readily to estimate the amount of 
elevation and depression of the surface he is viewing, 
and accurately to determine the relative position as 
to depth of the various parts of the tissue under ob- 
servation. The discoveries which we owe to this 
improvement of the microscope have been numerous 
and valuable; among the earliest were some in- 
teresting observations on the circulating system of 
the tadpole, by Mr. W. U. Whitney (Trans. Micros. 
Soc. Lond., vol., x., 1862, p. 1 ; and vol. xv., p. 43). 
Several also by the late Richard Beck ; among them 
the re-discovery of the aperture in the fang of the 
spider figured by Leeuwenhoek (Hoole’s English 
Translation, vol. 1., PI. 2, fig. 19) (Science Gossip, 1866, 
p. 201). 
By a slight variation of the form of the prism, Mr. 
Crouch has succeeded in constructing a microscope 
which can, by merely shifting the position of the prism, 
become stereoscopic or pseudoscopic at pleasure. 
This modification of the binocular will probably be of SOURCES OF LIGHT. 
23 
value in confirming certain doubtful points of 
structure, by giving a reversal of the parts in relief. 
Further particulars respecting the construction of 
the microscope and the optical principles involved 
will be found in the “ Microscope and its Revelations,” 
by Dr. Carpenter, and “Manual of Natural Philo- 
sophy” by Mr. Charles Brooke. 
The microscope being a costly instrument, it is neces- 
sary that great care should be taken to preserve it from 
injury. When out of use it should be returned to its 
case, or may be conveniently covered with a large 
shade or bell-glass. The eye-pieces should be carefully 
cleaned, as dust upon them becomes very apparent. 
The objeCt-glasses, if kept in their boxes when out of 
use, will seldom require much cleaning; dust on the 
objeCt-glass only causes a slight loss of light, but does 
not make itself visible. The best material for cleaning 
lenses is a piece of very soft wash-leather from which all 
dust has been beaten out; it should be kept in a large 
pill-box when out of use to preserve it from dust and 
grit, and should on no account be used for any other 
purpose, such as cleaning the brass-work of the in- 
strument. Should the objeCt-glasses require any- 
thing beyond mere dusting, they should be placed in 
the maker’s hands, as they are liable to injury if taken 
to pieces by inexperienced persons. 
The sources of light for the purposes of observa- 
tion will need a few remarks. When it can be pro- 
cured, daylight is in every respeCt to be preferred to 
artificial sources of illumination, as by it alone can 
colours be perfectly seen and distinguished, and day- 24 
MICROSCOPICAL MANIPULATION. 
light observations are far less fatiguing than those 
made by lamp-light. DireCt sunlight should be 
avoided, and, if possible, the light taken from a white 
cloud. But in towns, as the sky is seldom visible, and, 
moreover, few persons have much time to observe by 
daylight, it becomes important to seek for a good 
source of artificial light. 
Gas has been used by many microscopists; it 
has the disadvantage of giving out a large amount 
of heat, and the quality of the light is inferior to 
that obtained from most other sources; its sole 
advantage is its convenience, as it is always ready 
for use, and requires no trimming, as is the case with 
lamps. 
Well constructed lamps burning colza oil give a 
light of good and pure quality, although not as intense 
as those presently to be described. The best oil lamp I 
have used was obtained from Mr. Pillischer, and was 
only abandoned for the very intense camphine lamp. 
Oil-lamps require great care in trimming and cleaning, 
otherwise they will not burn well. 
The mineral oils (paraffin, belmontine, &c.), when of 
good quality, and consumed in properly constructed 
lamps, are among the best of the microscopist’s means 
of illumination. The quality of the light is good, and 
there is very little trouble required in keepingthe lamp 
in good working order. The glasses, as in all lamps, 
should be kept clean, otherwise much light is lost, and 
to obtain the best possible effect the lamp should be 
trimmed each time of using, although it will burn 
very well two or three times without any attention. THE BOCKETT LAMP. 
25 
The best way of obtaining a good oil is to try small 
samples from various shops, and when a good one is 
found keep to its use. The burner exercises a very 
great influence upon the light, so great that in a 
series from various makers it would hardly be 
supposed that they were burning the same oil. The 
burners of American make supplied by Mr. Collins with 
Fig. 12. 
the Bockett microscope lamps (Fig. 12), are some of 
the best that I have met with. This lamp has recently- 
been improved by the adaptation of a metal chimney 
which is not liable to breakage, and also has the ad- 
vantage of protecting the eyes of the observer from 
the light. 
The best light of all for those who do not mind 26 
MICROSCOPICAL MANIPULATION. 
the slight amount of trouble attending its use is ob- 
tained from the combustion of camphine or highly 
rectified spirits of turpentine in a small lamp, especi- 
ally constructed for the purpose by Mr. W. Young. 
The light is much whiter and more intense than 
that of any other lamp; owing to this quality the 
flame can be very much reduced in size, and most of 
the heat of a large lamp avoided, a matter of im- 
portance where the lamp is often placed near and 
below the face of the observer. 
Camphine, when not used quickly, should be kept 
in small bottles, filled up to the neck, and closely 
corked, and kept in a cool place—a wine-cellar 
answers admirably. For the small consumption of 
the microscope lamp the bottles should not exceed 
four or five ounces, as the spirit rapidly deteriorates 
by exposure to the air both from evaporation and the 
absorption of oxygen, which renders it liable to clog 
the wick and reduces its illuminating power. The 
wick should be cut very exactly to a level, far more 
carefully than would be required for oil or paraffin, 
the least uneven point rendering the lamp liable to 
smoke. No more camphine than is likely to be con- 
sumed should be placed in the lamp ; if there is more 
than is needed it should be allowed to burn itself 
out, or be thrown away, and the wick allowed to 
burn dry, otherwise the lamp is liable to become 
clogged, and burn badly. Should any part of the 
lamp become incrusted with a resinous deposit, it 
must be cleaned with methylated spirit; care should 
be taken that none of the air passages are obstructed. ILLUMINATING APPARATUS. 
27 
Although these precautions may seem troublesome, 
they really are not so to persons willing to acquire 
the habits of neatness so necessary to those who 
would make good microscopists ; and the slight 
extra trouble is amply compensated by the superior 
purity and intensity of the light and its extreme 
cleanliness, it being perfedtly free from greasiness or 
disagreeable smell. As the lamp is always kept 
empty it is very convenient for carrying about when 
it is necessary to make observations away from 
home. 
The illuminating apparatus commonly supplied 
with microscopes consists of the mirror below the 
stage, and a condensing lens either attached to the 
instrument or, as is to be preferred, on a separate 
stand. Other apparatus will be described in sub- 
sequent chapters. 
The mirror is used for illuminating objedts by 
diredting light through them from beneath the stage, 
and is the usual, although not always the best, 
means of lighting an objedt, as it is one which we 
are unaccustomed to, and, without special pre- 
cautions, is likely to lead into error. The mirror is 
capable of being moved out of the axis of the instru- 
ment, and light may be diredted very obliquely upon 
the objedt, which is sometimes advantageous. 
The condensing lens is used to concentrate light 
upon the objedt from above, and, when it can be em- 
ployed, it is always preferable to commence an ob- 
servation in this way rather than by means of trans- 
mitted light, as it accords more closely with our 28 
MICROSCOPICAL MANIPULATION. 
every-day way of viewing objedts: it is not our usual 
custom to hold up a substance we wish to examine and 
try to look through it, but we generally allow the light 
to fall naturally upon it. If a plano-convex lens, or 
“ bull’s-eye, ” be used as a condenser, it is necessary 
to be careful which side is turned to the source of 
light, otherwise it may be used in a position causing 
a great amount of spherical aberration and con- 
sequent loss of light. A plano-convex condenser 
should always have its curved side turned to the 
source of light when used for concentrating light 
upon an objedt. When used for rendering divergent 
rays, such as those of a lamp, parallel, which is 
often required when using apparatus hereafter to be 
described, the bull’s-eye should be placed with its 
flat side to the lamp and at about the distance of its 
focal length.* 
The beginner is recommended to commence his 
observations by endeavouring to procure a good and 
brilliant illumination with the condensing lens, 
looking at any easily procured objedts, such as frag- 
ments of paper, feathers, sand, &c.; a humming- 
bird’s feather or wing of a butterfly is particularly 
useful, as either of them presents very different ap- 
pearances, according to the direction of the illumi- 
nating pencil, the iridescent colours of the first and 
* Each lefture was followed by a pra&ical demonstration, during 
which various objedts, &c., were examined and processes in manipu- 
lation carried on under the superintendence of the ledturer and assist- 
ants. Much of the subjedt-matter of these demonstrations will be in- 
corporated with the text; such portions as cannot be so given will be 
added at the end of the various chapters. AIR BUBBLES. 
29 
the imbricated structure of the second not being seen 
unless the light is made to fall in the proper direc- 
tion. The light should be moved or the objedt 
turned round, and the varied appearances carefully 
noted. This precaution should be adopted with all 
objects viewed by reflected light. 
In commencing observations by transmitted light, 
the student may profitably examine air-bubbles in 
water, easily procured by shaking up a little very 
weak gum-water in a bottle, and also globules of oil 
in water, of which milk furnishes a good and readily- 
procured example. A little of each of these should 
be placed on a separate slide, covered with a 
thin glass and examined by transmitted light, the 
air-bubbles with an inch objective; the milk may 
probably require a I or J. 
The leading characteristic of the air-bubble is its 
broad black margin when examined by transmitted 
light. If the laws of refraction are considered, it will 
be evident that a bubble of air in water will aCt pre- 
cisely as a double concave lens, Fig. 4, B, and by its dis- 
persive power scatter the rays of light, especially at 
the part where its power is greatest—the margin. 
The same effeCt may be produced, on a large scale, 
by holding to the light two plano-concave lenses of 
glass with their hollow sides placed together; this 
will almost exadtly represent the air-bubble in water, 
differing only in the glass having a greater refradtive 
power than the water in the microscopic slide, and 
dispersing the light rather more powerfully. 
The oil globules of the milk exhibit a brilliant spot MICROSCOPICAL- MANIPULATION. 
of light in their centre when slightly beyond the focus 
of the microscope ; this is owing to their being more 
refractive than the surrounding medium : their aCtion 
is that of double convex lenses, Fig. 4, A, and the bright 
spot is an imperfeCt image of the source of illumination, 
which is rendered visible when the focus of the 
microscope coincides with that of the globule, which 
will be when the instrument is slightly above the 
focus for distinct vision of the globule. 
These appearances should be carefully studied and 
remembered, as bubbles of air are among the most 
frequent of the instrusive substances to be met with 
during microscopical observations ; cells filled with 
oil and globules of oil are also of frequent occurrence 
in tissues. Besides these, the student should make 
himself acquainted with the microscopical appearance 
of fibres of cotton, wool, flax, &c., hair of cats and 
other animals, all of which are frequently found in 
the dust of our apartments, and of course in our 
microscopical preparations, unless more than 
ordinary care is taken to prevent their intrusion, so 
that it is well to know them that they may not be 
mistaken for characteristic portions of the substance 
under observation, a not unlikely error on the part 
of inexperienced observers. 
A sample of dust from the walls of an office in the 
Bank of England, where it had accumulated for 
more than ten years, consisted of about one-half 
cotton fibre, probably derived from abrasion of paper; 
the remainder consisted of fibres of wool and flax in 
small quantities, and soot and grit; molecular DUST. 
31 
motion was apparent when examined in water with 
a power of 400 diameters. An interesting paper “ On 
the Microscopical Examination of Dust ” was read 
by Mr. J. B. Dancer before the Literary and Philo- 
sophical Society of Manchester, January 26th, 1869. 32 
CHAPTER II. 
THE subjedt of the present chapter may be con- 
sidered rather as mechanical than microscopical; 
in fadt, it relates more to the workshop than to the 
study. It may, perhaps, seem strange to write about 
making apparatus and preparing materials in these 
days when nearly everything can be bought often 
better and more cheaply than it can be made at 
home, and when it is not as it was within the 
memory of many microscopists, who were obliged 
to cut their glass slides, or, at all events, to order a 
glazier to make them: but the more dexterous a 
person is with his fingers the better microscopist he 
is likely to make. Very often the success of an 
observation depends upon the observer being able to 
make some little contrivance to aid his researches, 
and it is for that purpose that the subjedt of the 
mechanics of the microscopical laboratory finds a 
place here. 
The first material that engages the attention is 
glass. It comes under notice in several forms—the 
plates of glass upon which objedts are mounted, the THE CUTTING DIAMOND. 
33 
thin covering glass, and glass tubing. The glass 
generally used for mounting objedts is a description 
of glass known as patent plate. Crown glass is 
sometimes used, but patent plate is perhaps the best. 
It is made from that commonly known by the name 
of cylinder glass, which is manufactured by the glass 
being blown, first of all, into a globe, then, by dex- 
terous manipulation on the part of the workman, it is 
elongated, and a cylinder formed. This cylinder is 
ripped up, and put into an annealing oven: it un- 
bends at the slit, and rolls itself out flat. In this 
state it is known as sheet or flatted glass. The 
glass then undergoes the same treatment as plate 
glass. It is ground down and polished, and then it 
becomes the patent plate. It is a thin glass, with a 
beautiful surface, so accurately worked that the 
plates will adhere together if pressed, just as good 
specimens of ordinary plate. 
The tool used for cutting glass is the well-known 
glazier’s diamond. It seems to have nothing in 
common with ordinary cutting tools: an incision or 
scratch with a diamond or other instrument, such 
as a flint or chilled-steel point, will not make the 
clean fradture we are so familiar with when the 
cutting diamond is used by a skilled hand. The 
diamond would seem rather to adt by inducing some 
molecular displacement than by any adtual penetra- 
tive power that it possesses. This view would seem 
to be supported by the appearance presented by the 
glass adjacent to a diamond cut when examined by 
the microscope with the aid of polarised light, which 34 
MICROSCOPICAL MANIPULATION. 
shows that the glass has been subjected to some 
kind of strain. Rubies and sapphires, if worked to 
the form of the natural edges of the diamond crystal, 
will cut glass, but lose the power when the curved 
edge wears away. A very interesting paper on the 
fracture of glass and the action of the diamond, by 
Mr. F. H. Wenham, will be found in the Microscopical 
Transactions for 1868, p. 105. (See also Holtzapffel, 
“ Turning, &c.,” vol. i.) 
There is some little art in using the cutting dia- 
mond : it is not any part of a diamond that will cut. 
Fig. 13. 
It is very easy, indeed, to scratch with a diamond, 
but it is only in certain directions that it will make 
the so-called cut. The glazier's diamond (Fig. 13), CUTTING GLASS. 
35 
when viewed under the binocular microscope, will 
be found to exhibit a well-defined and slightly curved 
edge, a, b. The diamond is carefully set so that this 
edge (which is a natural crystalline one) lies parallel 
with the oblong mounting, and, as the diamond 
requires to be held in an inclined position to secure 
a clean cut, the top of the setting is always bevelled 
to the proper angle. It is allowed a little play hori- 
zontally on a pivot, so that, upon placing the dia- 
mond in contaCt with a rule, it will always place 
itself in the cutting direction, and, by keeping the 
end of the setting parallel with the glass, it will be 
in a position for cutting. It is then drawn along; 
and those who have seen a glazier cut glass will 
remember the curious noise which accompanies 
the operation—something between a ringing and a 
hissing: the sound is very different from a scratch. 
The glass breaks at the place upon being bent. 
With a little practice, the cutting of glass will be 
very easy indeed; but it is not worth while, as a 
general practice, to cut slides, as they can now be 
bought at a cheap rate : it is chiefly for exceptional 
purposes that facilities for cutting glass are of value. 
Sometimes a piece of glass of extra size or unusual 
shape is required, and then time is often saved by 
being able to do the work, instead of waiting until 
the services of a glazier can be obtained. 
The other kind of glass employed in mounting 
objects is the thin glass for covers. The details of 
its manufacture are unknown to me. It is remark- 
able for its extreme brittleness. In cutting, the 36 
MICROSCOPICAL MANIPULATION. 
glazier’s diamond is not employed, but a splinter 
known as the writing diamond. The operation 
is attended with some difficulty, as the glass is 
very likely to crack and star under the diamond. 
This is best prevented by placing the thin glass to be 
cut on a piece of wet plate-glass, which affords sup- 
port, and effectually prevents splitting and cracking. 
As in the case of the 3x1 slides, it is hardly worth 
while to cut up squares and circles of thin glass, as 
it can be easily procured of the opticians already 
cut into the most useful sizes, or, if required in large 
quantities, of the wholesale glass warehouses. Of 
course pieces of unusual sizes and shapes are some- 
times required, and then the power of cutting 
becomes of value. 
The writing diamond is also used for making 
marks and writing on glass. Some persons write 
the names of their objedts on the glass instead of on 
a label: it has the advantage of durability, but is 
not so legible as an inscription on paper. 
Sometimes it is required to drill a hole in a piece 
of glass. This is a matter of no very difficult 
accomplishment. A good hard drill, if it is kept 
moistened with turpentine, will, with a small amount 
of patience and labour, eventually work its way 
through a piece of glass. Care should be taken that 
the glass rests upon a cork bed, or something soft, but 
yet firm, to give it sufficient support, or it may break 
just before the point of the drill makes its way 
through. Perhaps the best plan is to begin on the 
other side when the drill has penetrated about half- CORUNDUM TOOLS. 
37 
way. Some persons are of opinion that dilute sul- 
phuric acid, in the proportion of eight parts of water 
to one of acid, serves for moistening the drill better 
than turpentine. Of course the fluid used is the 
reverse of a lubricant: if oil were employed, the 
drill would not cut. The drills are best hardened by 
heating to redness and cooling suddenly with strong 
sulphuric acid. The edge requires working up from 
time to time upon an Arkansas stone, with oil. In 
drilling a thick piece of glass, the drill may require 
setting once or twice during the process ; but I have 
never had any difficulty in drilling through a thick 
piece of plate. 
The rough, sharp edges left on glass after cutting 
with the diamond may be removed by grinding with 
fine emery and water upon a smooth paving-stone 
or thick plate of zinc: the glass-cutters usually 
employ emery upon a “ lap ” or horizontal wheel. 
For many cutting processes, tools made of corun- 
dum and shellac are very useful; this composition, 
in the form of wheels, files, hones, &c., of several 
degrees of fineness, can be obtained of Mr. D. Lyon, 
43, St. John’s Square, Clerkenwell, E.C. These 
tools, especially the wheels, are employed by dentists, 
in cutting and shaping the semi-vitrified porcelain 
used in the manufacture of artificial teeth. The use 
of the corundum composition in this country is com- 
paratively recent, although it has been employed for 
centuries by the native jewellers of India. 
Corundum is a crystalline mineral, identical, or 
nearly so, in composition with the sapphire, ruby, 38 
MICROSCOPICAL MANIPULATION. 
topaz, and amethyst, equally hard, but wanting in 
transparency and lustre. Emery is nearly similar, 
but occurs in a granular form, and does not cut so 
well, although there are many purposes for which it 
is more serviceable than the harder corundum. 
These tools must be plentifully supplied with water 
when in use, as, unless kept cool, they soon lose 
their shape, which would be the case if used dry, 
as they would rapidly heat and melt with the 
friction of rasping and grinding a hard substance. 
Glass plates may be smoothed, and even rounded 
at the edges, with the greatest ease, with a corun- 
dum file, and almost as quickly as brass could be 
filed. A tapering tool is useful for enlarging a hole 
drilled in glass ; and the hones serve for grinding 
sections of substances too hard for the ordinary 
stones. As the material becomes better known, 
many other uses will, no doubt, be found for it. 
Glass is frequently used by the microscopist in 
another form, that of tube. It is chiefly employed in 
making the dipping tubes, with which objedts such 
as free swimming animals and deposits in water 
are taken up, and for the pointed tubes, or pipettes, 
with which small portions of fluids are removed and 
deposited where they may be needed. The manu- 
facture of these bent tubes, or pipettes, is not a 
matter of difficulty. The processes of drawing glass 
tube to points, and bending, are very frequent in the 
laboratory. The best source of heat is obtained 
from the Bunsen burner, which gives a very large 
flame without smoke and of great heating power WORKING GLASS TUBES. 
39 
by the consumption of a mixture of air and coal gas. 
It can be obtained of the chemical instrument 
makers for a very small sum ; a spirit lamp, however, 
will answer the purpose tolerably well if the wick is 
a large one. A piece of glass tube, in which it is 
intended to make a bend, should be heated to a slight 
redness, and then carefully and slowly bent to the 
required angle. If an attempt is made to bend a 
tube suddenly, it will produce a choke, or contraction, 
in the bend. It is also necessary to heat a con- 
siderable length of tube. Pieces of glass tube are 
very easily detached, by making a notch on them 
with the edge of a file, and they are then sure to 
break straight across; any length of glass tube can 
be cut off in this way. The process most frequently 
required to be performed by the microscopist is the 
drawing tubes out into pointed ends for pipettes. To 
effedt this, heat the tube in the flame ; when the tube 
has become sufficiently soft, it can be drawn out to 
any length and fineness you please. The rough edge 
at the cut ends of tubing may be taken off by heating 
the ends in the flame, which will melt the edges and 
leave them rounded. This rounding of the edges is, 
perhaps, effected more rapidly by using a blowpipe, 
which facilitates the fusion of the glass. Sometimes 
a pipette curved as well as pointed is required; 
there are many purposes for which it is extremely 
useful. This is easily made by a little variation of 
the other process ; while it is being drawn out, give 
it a skilful bend at the proper moment. Always keep 
tubes of glass revolving while they are being heated, 40 
MICROSCOPICAL MANIPULATION. 
and do not- heat them more than is absolutely 
necessary, as, when the tube is made very hot, it is 
extremely pliable, and likely to lose its shape. With 
a little ingenuity a number of useful things may be 
made out of glass tube. A variety of these pipettes 
will be found useful, and they are rather expensive to 
buy. 
Glass, whether in the form of slides or thin glass, 
always requires cleaning. The best cleaning fluid is 
methylated spirit, which, as it is not subject to duty, 
and can be obtained cheaply, may be made free use 
of for this and nearly all the operations of the micro- 
scopist in which strong alcohol is required. Care 
must, however, be taken to obtain pure methylated 
spirit, and not what is commonly known as “ methy- 
lated finish,” which contains a small portion of shellac 
in solution, and is quite useless for all microscopical 
and laboratory purposes, and which is not unfre- 
quently sold when methylated spirit is enquired for. 
I am indebted to the Rev. J. B. Reade for the history 
of this adulteration. Formerly, methylated alcohol 
was allowed to be sold without a licence ; but certain 
persons, finding that it was cheap, and not being 
particular about the flavour of methylic ether, used it 
for making grog. This faft coming to the knowledge of 
the excise authorities, its sale by unlicensed dealers 
was prohibited, unless containing shellac in solution, 
a mixture which would not spoil it for its chief use, 
that of varnish making, while, upon mixture with 
water, the gum would be precipitated, making a 
very disagreeable turbid compound. There is no CLOTHS FOR CLEANING GLASS. 
difficulty in obtaining pure methylated alcohol in 
large towns, where one or more licensed dealers are 
generally to be found. It can be obtained perfectly 
pure, either in large or small quantities, of Messrs. 
Jackson and Townson, Bishopsgate Street, and of 
most other dealers in chemicals. It should not leave 
any residue upon evaporation, or become turbid 
when mixed with water; any spirit having these 
defeats should not be used for microscopical pur- 
poses. 
Great care should be taken that the cloths used 
for cleaning glass be perfectly free from soap or 
dirt, otherwise they will leave the surfaces of the 
slide covered with striae. Old linen, or cotton cloths, 
are-to be preferred to new ones ; they should, before 
use, be boiled in water and common washing soda, to 
remove all soap left from former washings. They are 
then to be washed several times in clean water, until 
all trace of the soda is removed, and then dried, but 
not ironed, as the rough fluffy condition they will be 
left in is extremely favorable for cleaning glass. 
After the spirit is cleaned off with the cloth, any 
fibres that may be left from the cloth should be 
removed with a soft wash-leather. 
Thin cover glass is treated in a similar manner, 
but, on account of its excessive brittleness, requires 
great care in cleaning. After a little practice, it is 
quite easy to rub it with the cloth and leather between 
the thumb and finger; but, should any difficulty be 
experienced, which may be the case with the thinnest 
kinds, it will be found that it can be rubbed with 42 
MICROSCOPICAL MANIPULATION. 
considerable force, without injury, between two discs 
of wood covered with wash-leather. The great 
thing in rubbing a brittle substance is to support 
it well behind; this is the whole secret of cleaning 
thin glass between the finger and thumb. 
For joining together pieces of glass, and for 
attaching metal to glass, the cement known as 
marine glue is usually employed. It consists ot 
india-rubber, shellac, and coal naphtha, combined in 
various proportions, according to the purpose for 
which it is intended to be used. It is, I believe, 
difficult to make in small quantities ; but there is no 
trouble in obtaining it, as it is sold by most micro- 
scope makers. As this cement will only adhere to 
hot surfaces, it is necessary to have some means of 
applying a steady heat to the pieces of glass, &c., to 
be joined ; and as this cannot be done by means of 
the unprotected flame of a lamp, a hot-plate is 
generally employed. This can be obtained, ready 
made, of the opticians; but a piece of thick brass 
plate, about 6 or 7 inches long and 2 inches wide, 
placed upon one of the rings of a retort stand, will 
answer admirably; it can be heated by means of a 
spirit lamp or gas flame placed underneath. Sup- 
posing, for example, it is required to attach a ring 
of glass or metal to a glass slide, to form a cell for 
an objedt to be mounted in. The glass slide is placed 
upon the hot-plate, first of all, at the part most 
distant from the lamp, to avoid breaking it by too 
sudden heating, and then moved gradually to the 
hotter part; the ring is also heated on the plate, a CEMENTING GLASS. 
43 
piece of marine glue is held on the point of a needle 
in a handle, or other convenient holder, and rubbed 
on the heated glass over the surface to which the 
ring is to be attached. When a sufficient portion 
of glue is melted on the glass, care being taken to 
heat the glue sufficiently for free working, while 
overheating amounting to boiling is to be avoided, 
the heated ring is then lifted on with a pair of forceps, 
which, for this and all purposes where they are likely 
to be made hot, should be of brass, or else an old pair 
of steel forceps, which are to be kept for such uses. 
The ring is then to be turned round backwards and 
forwards on the glass, to the cement equally, 
and then removed from the hot-plate and pressed on 
a piece of wood, to expel superfluous glue, and allowed 
a little time to set; when set, but still warm, the greater 
part of the cement can be scraped off with a blunt 
knife, a process much more difficult if it is allowed to 
become quite cold. A number of cells can be attached 
and roughly cleaned at one time, the plate next re- 
quired being heated while the one cemented is being 
cleaned off. When quite cold, the slides can be 
thoroughly cleaned with a piece of rag and a free 
use of methylated spirit; they should then be rubbed 
bright with a clean cloth. Some persons use liquor 
potassse for cleaning off superfluous marine glue; 
it does this very effectually, but not so rapidly as 
strong alcohol, and the operation is a rather un- 
pleasant one, as the alkaline solution first softens, 
and then removes the skin from the fingers. 
The adhesion of marine glue, and other cements, 44 
MICROSCOPICAL MANIPULATION. 
to glass surfaces, is much improved by grinding, 
which gives the cement a better hold than it would 
have on a polished surface, although marine glue 
will adhere well to polished glass, provided the sur- 
face is free from grease, which may be insured by 
a cleaning with methylated spirit. The adhesion 
of two pieces of glass cemented with marine glue 
is so perfedt that they generally break in any 
place rather than at the joint. 
A very useful trough for viewing objedts in fluid 
can be made with a slight amount of trouble. Cut 
in half an ordinary 3x1 slide (Fig. 14, shaded portion 
Fig. 14. 
in centre). From this cut off the strip a, then the 
pieces b and c, and rejedt the centre piece, d. Before 
cutting, it is well to mark the adjacent edges with 
ink, as indicated in the figure, to prevent any mistake 
in putting them together afterwards. The three 
pieces a, b, and c are to be cemented with marine 
glue on the middle of a slide, and, as the cut portions, 
if replaced as directed, fit each other accurately, 
there is no occasion for grinding. The trough is 
completed by fastening an oblong piece of thin cover- 
glass on the upper surface. For this purpose it is 
better not to use marine glue, as the cover frequently ELECTRICAL CEMENT. 
45 
requires removal, as, from its thinness, it is liable to 
be broken in cleaning. It can be best secured by the 
use of the following, known as “ eledtrical cement,” 
from its having been used to fasten various portions 
of eledtrical apparatus together :—Melt together five 
parts rosin, one part bees’-wax, one part red-ochre, 
two parts Canada balsam ; mix well, and pour into 
pill-boxes of convenient size. This cement is most 
conveniently used with a miniature soldering bit, 
which is rendered more comfortable to use by its 
being balanced with a plug of lead in the handle. 
With a little pradtice, a very neat joint can be made. 
The cement is also useful for many other purposes, 
of which notice will be taken in the proper place. 
Larger troughs, having sides of plate-glass, can 
be made by those who will take the necessary trouble. 
In this case, the surfaces to be cemented must be 
Fig. 15. 
accurately ground. Such vessels are very useful in 
looking over the results of pond-hunting with a low 
power, for the purpose of selecting such objedts as 
may be required for more detailed observation. The 
troughs, of various shapes, can be purchased at 
most opticians. 
The form represented in Fig. 15 is particularly 46 
MICROSCOPICAL MANIPULATION. 
convenient, as by means of the whalebone spring,/, 
and the wedge, g, the space between the front glass, 
b, of the trough and the inclined plate, e, is capable 
of adjustment, so that an objedt can, when desired, 
be kept close to the front glass. These parts can be 
removed when a greater depth of water is required 
for larger objedts. 
A simple and useful contrivance, to be used as a 
growing-slide, has been described by Mr. C. J. Muller 
(.Monthly Microscopical Journal, vol i., p. 174). The 
objedt of a growing-slide is to keep alive any minute 
water-plant or animal, the development of which it is 
Fig. 16. 
B 
wished to observe. Many plans have been devised 
for this purpose, but none equal in simplicity or 
efficiency that now to be described. 
An ordinary 3x1 slide (Fig. 16, A) is pierced with a 
minute hole at about 3-ioths of an inch from the centre 
on one side. When an objedt under investigation is GROWING SLIDE. 
47 
put upon it immersed in water, the thin glass cover 
is so placed as to include this hole, which should 
be near its margin. When it is desired to keep 
the specimen moist while off the stage of the micro- 
scope, the slide is placed in a small flat trough (B) 
in an oblique position, objedt uppermost, with one 
end (that nearest the hole) resting against the bottom 
of the vessel on one side, and the other resting upon 
the edge of it. Sufficient water is put into the vessel 
to admit of the liquid reaching within a i or £ an 
inch of the glass cover on the uppermost side, when 
it will be found that the water on the under side 
reaches beyond the centre of the slide, and conse- 
quently beyond the hole with which it is pierced. 
In this state, the objedt will remain moist so long as 
the trough contains a sufficient quantity of water. 
When required to be placed on the stage of the 
microscope, the water is easily wiped off the slide, 
without any disturbance of the objedt. 
Mr. Muller’s original trough was made of tin-plate, 
but, as this material is liable to rust when long in 
use, Mr. F. W. Gay has had them made of pewter and 
of an improved form, which has proved an effedtual 
remedy for this defedt. Thus constructed, they are 
to be obtained of Mr. C. Baker, Holborn. 
The process of attaching cells to plates of glass 
has been given; but nothing has been said about 
the material of the rings forming the cells. When 
required of some considerable depth, rings made of 
slices cut from thick glass tubing answer admirably. 
If square or oblong cells are required, they can be 48 
MICROSCOPICAL MANIPULATION. 
cut from tubes of suitable form. Very useful cells 
are now made by Mr. Collins of pure tin of various 
thicknesses, from that of thin writing-paper up to 
that of a thick tube cell: several sizes can also be 
procured in each thickness. Tin is not adted upon 
by any of the fluids used in preserving microscopical 
objedts, and has the advantage of being much cheaper 
than glass, and at the same time equally efficient. 
Cells of unusual form can readily be cut from the sheet- 
tin with a penknife or pair of scissors, and circles can 
readily be punched. The adhesion of the cover-glass 
is improved, and the process of mounting in fluid 
much facilitated, by grinding the upper surface of the 
cell after it is attached to the slide with water upon a 
Water-of-Ayr stone, as suggested by Dr. Carpenter. 
This gives a beautiful surface, and ensures the perfedt 
fit of the cover, and renders the closing of the 
cell a matter of greater certainty than it would be if 
the natural surface of the metal were used. 
Some very useful aids to the examination of micro- 
scopical objects, and which can readily be made by 
the exercise of the smallest amount of mechanical 
ingenuity, are described by Mr. S. J. Mclntire, in 
the Transactions of the Quekett Microscopical Club, 
vol. i., p. 69. One of these is of such general appli- 
cation that it will be well to describe it. A piece of 
sound sheet cork, about 2 in. by 34, or other con- 
venient size, and of a thickness suited to the purpose 
for which it is intended, is perforated with an oval 
or circular hole ; this may easily be cut with a pen- 
knife or sharp chisel, and the edges finished with a CELLS FOR LIVE OBJECTS. 
49 
file. The cork is placed between two pieces of glass 
of similar size, the lower one being covered with a 
few layers of pink blotting paper, and the whole con- 
trivance kept together with two india-rubber rings. 
The cell so constructed is used for keeping alive 
small inseCts that inhabit damp situations, such as 
Podurce. The moisture is readily supplied by dipping 
the end of the slide into water, which is absorbed 
and retained by the blotting paper. The proper food 
of the inseCts can be placed in the cell. By the aid 
of this simple contrivance, Mr. Mclntire has been 
enabled to make some most interesting observations 
on the habits of the Podurce, which have been kept 
living in these cells for many months. This plan 
admits of modification to suit the objeCt under 
observation. In the author’s researches on the blow- 
fly, it was necessary to use thin glass, and to have 
the means of viewing the objeCt on either side; this 
was accomplished by cutting a rectangular hole in a 
suitable piece of cork, placing the thin glass on 
either side, and securing it by bending on its edges 
strips of the sheet tin used for making cells; these 
had been inserted in the cork, which effectually 
fastened the glass in a somewhat similar manner to 
that by which a stone is set by jewellers, and readily 
permitted its removal when required. 
Among the tools employed by the microscopist, 
none are more generally in request than needles of 
various sizes and forms. They are frequently re- 
quired of various curvatures ; this bending can 
readily be performed by the microscopist himself. MICROSCOPICAL MANIPULATION. 
If a needle is heated to redness in the flame of a 
spirit-lamp, and allowed to cool, it can easily be bent 
or twisted into any required form. Steel so treated, 
if heated again to redness and suddenly cooled in 
water, becomes excessively hard and brittle ; in this 
condition, it is capable of scratching glass, but is too 
fragile for dissecting instruments. The right temper 
for the dissedting needles is obtained by heating and 
cooling in tallow or oil; this, with needles, may be 
readily done in a common tallow (not composite or 
paraffin) candle. While the needle is soft, it may, by 
the exercise of a little dexterity, be hammered out so 
as to form a small knife, or lancet, which can then 
be hardened so as to take a cutting edge; many use- 
ful instruments can also be made out of small pieces 
of steel. Needles and cutting instruments are best 
sharpened upon a very hard, white stone, known at 
the tool shops as Arkansas oil-stone ; it cuts very 
rapidly, and gives an extremely fine edge. Scissors, 
when blunt, may readily be sharpened on the oil- 
stone, by opening the blades and rubbing them on 
the stone, holding them nearly upright. The burr 
produced by this operation need not be ground off, 
as it is soon removed when the blades are worked 
together; the screw is to be tightened if required. 
For delicate dissections, the steadiest cutting instru- 
ment is a kind of scissors, made almost exactly like 
a minute pair of sheep shears, and known as the micro- 
tome; in use, it feels very much as if the fingers were 
extended and armed with cutting edges. There is DISSECTING INSTRUMENTS. 
hardly any other cutting instrument so much under 
the control of the operator. 
The best handles for needles and other small 
instruments are made of cedar pen-holders, into 
which the needle, with the eye broken of, is inserted 
with a pair of pliers. Very convenient handles, 
which have the advantage of allowing the needles 
to be removed at pleasure, are to be purchased at 
fancy warehouses; they are used for holding crochet 
hooks ; they are improved by the removal of the 
ivory handle, and the substitution of one made of a 
cedar pen-holder, which can easily be attached to the 
socket with eledtrical cement, and will be found 
to be lighter and more pleasant in use. 52 
CHAPTER III. 
THE processes connected with the preparation 
and preservation of microscopical objeCts have 
always occupied a considerable space in nearly every 
work on the use of the instrument. The subjeCt is one 
of general interest, and the importance of being able to 
preserve specimens for future reference can scarcely 
be overrated. 
The simplest of these processes, and also the 
oldest, is that known as “ dry-mounting.” 
The objects suitable for mounting dry are those 
which can be preserved in air and are capable of 
being dried without injury to their structure. The 
ways of mounting are extremely numerous, and are 
principally means of protection from the great 
enemies of all natural history preparations—damp 
and dust. One of the oldest ways of mounting objects 
was upon discs punched from a compound sheet of 
card and wash-leather, through which a pin was run 
for convenience of holding in the stage forceps and 
keeping in a cork-bottomed drawer. This plan of THE DISC HOLDER. 
53 
mounting was abandoned when the lieberkuhn fell 
into disuse, but it has since been revived in a new 
form by the late Richard Beck, who invented a 
very ingenious instrument for holding the small 
Fig. 17. 
discs of metal and turning them into any required 
position. This is an extremely useful piece of 
apparatus, as it is often required to turn an 
objeCt into several positions for the thorough 
examination of its structure. So perfectly is this 
accomplished, that five out of the six sides of a 
cube may be examined by means of the revolving 
disc-holder. This instrument has supplied a want 
created by the introduction of the binocular micro- 
scope, as the greater focal depth and stereo- 
scopic effedt given by it has rendered advantageous 
frequent changes of the position of objects, for which 
this contrivance most effectually provides. For the 
keeping of the discs from the influence of dust and 
damp, he contrived a close-fitting screw-box, having 
suitable arrangements for the reception of twenty- 
four discs. 
Great use has also been made by some observers 
of open cells. These consist of a hole bored in a 
3x1 slide of wood, with a piece of card-board glued 54 
MICROSCOPICAL MANIPULATION. 
to the bottom, the objeCts being fastened with a 
little gum. This answers very well with objeCts not 
liable to injury from exposure, such as shells ; but, 
for most purposes, it is necessary to clbse up the 
objeCt, and this, in many instances, is done in a 
manner very detrimental to its preservation. Where- 
evef paper and paste or gum are used, various fungi 
and confervse are nearly sure to make their appear- 
ance, unless special precautions, such as saturating 
the paper with, and mixing in the gum, a small 
quantity of corrosive sublimate. The microscopical 
fungi are doubtless interesting plants, but, when they 
grow over valuable preparations, we feel them to be 
a nuisance, and decidedly in the way. 
Some microscopists, avoiding the use of paste, 
gum, and paper for securing the cover to the 
slide, have made use of varnishes of several kinds. 
These generally have the defeCt, if thin, of running 
in between the glass and cover and spoiling the 
objeCt, and, if thickened with a solid substance, such 
as lamp-black or vermillion, of becoming porous 
after a time. Some of the fluid medium of the 
varnish, also, is liable, in drying, to rise in vapour 
within the cell, and condense on the cover, inter- 
fering with the distinct view of the objeCt. The 
vapour of turpentine or naphtha, however, is in no 
way otherwise detrimental, as it tends rather to the 
preservation than the destruction of tissues. 
The electrical cement previously described 
(Chapter ii., p. 45) is free from this defeCt, and 
furnishes a means of rapidly mounting objeCts MOUNTING WITH CEMENT. 
55 
either with or without a cell. If the object is very 
thin and flat, it may be placed upon a slide, 
and a thin glass cover put over it. Both having 
been carefully cleaned, one of the spring clips made 
of wire and cork (which are to be procured of most 
opticians) can be used to hold the cover in place 
while the cement is being run round it with the little 
brass bit. The bit should not be made too hot, or it 
will not hold the cement. After the cover has been 
fastened down, the rough cement can be smoothed 
by passing over it a clean bit, heated rather more 
than is required for laying on the cement. The bit 
is easily cleaned by wiping while hot upon a piece of 
blotting-paper. The first attempts, no doubt, will 
be far from elegant in appearance ; but, after a little 
practice, great neatness may be attained. This 
process is also available for attaching the cover to 
cells of metal or glass, which must be used with 
dry-mounted objects whenever their thickness is 
such as to require it. This mode was formerly much 
employed, but was abandoned on account of the 
brittleness of the cement. This may be remedied 
by varnishing, when the cement has become hard, 
with gold-size, which is remarkable for the tenacity 
with which it adheres to glass and its toughness and 
non-liability to crack. Respecting the properties of 
this varnish, more will be said in the chapters re- 
lating to fluid-mounting. This system of compound 
cementing answers perfectly ; the eleCtrical cement 
having, in the first instance, no tendency to run in, 
and the gold-size effectually keeping it from separa- 56 
MICROSCOPICAL MANIPULATION. 
ting from the glass. If the natural red colour of the 
eledtrical cement is objedted to, a black finish can 
best be obtained by the use of lamp-black as pre- 
pared for water-colour painting. The best form is 
that in tubes. A little of this is pressed from the 
tube, and, if too thick, a small quantity of water 
added. With this the varnished surface is thickly 
painted, and, when dry, a few coats of gold-size will 
keep it from being washed off. The result is a dense, 
lustrous black, very superior in effedt and durability 
to that produced by a black varnish. This finish is 
equally available for fluid and balsam mountings. 
If the objedt cannot be kept in its place by. the 
pressure of the cover glass, it will require fastening. 
If the objedt will bear a slight amount of heat, a 
small spot of eledtrical cement may be placed on the 
glass, melted by holding over a lamp, and, while soft, 
the objedt fixed. Or the thick varnish composed of 
shellac and wood-naphtha, sold at most varnish- 
shops as liquid glue or “ patent knotting varnish,” 
will be found useful for this and other purposes to 
be mentioned hereafter. Care must be taken to 
allow the naphtha time to evaporate, or its vapour will 
obscure the cover. While this drying is taking 
place, the slide may be turned face downwards over 
a large pill-box, or the cover put on, and kept in 
place with a spot or two of eledtrical cement, defer- 
ring the completion until the varnish has dried. 
It is not necessary to employ any kind of black 
background for opaque objedts, the best background 
being that of the dark-well beneath the stage, formed DRYING OBJECTS. 
57 
by bringing round that part of the diaphragm-plate 
which has no hole, and so closing up the aperture. 
If a black patch is used, it prevents advantage being 
taken of various kinds of illumination from beneath, 
which are often of great service, while the mounting 
on clear glass is in no way detrimental to the view 
of an objeCt lighted from above. 
It is necessary that the objedt to be mounted 
should be perfectly dry before it is placed in the cell, 
otherwise moisture will, sooner or later, make itself 
apparent. 
Most objects can be dried by the application of a 
moderate heat. If wrapped up in a piece of paper, 
and placed inside the fender, in an hour or so they 
will be found to be effectually dried. A Seidlitz- 
powder box answers extremely well for this kind of 
drying: it can be still more effectually accomplished 
by means of the well-known hot-water oven. 
There are cases, however, where heat is inadmis- 
sible, especially with delicate tissues. The desicca- 
tion of these is best accomplished in a vacuum. The 
substance to be dried is placed under the receiver of 
an air-pump ; the air is exhausted, and, under these 
conditions, it will give off vapour at a much lower 
temperature than under ordinary atmospheric pres- 
sure. It is only necessary to provide some means 
of absorbing the watery vapour as fast as it is given 
off—such as concentrated sulphuric acid or dry lime. 
Another, and very effectual mode of drying delicate 
tissues without heat, is the process described in the 
Chemical News (vol. xiii., p. 122), translated from 58 
MICROSCOPICAL MANIPULATION. 
Zeitsch. fur Anal. Chemie. This process, which is 
quite new so far as its application to microscopical 
purposes is concerned, consists in immersing the 
substance to be dried in ether in the presence of dry 
chloride of calcium. The apparatus employed is 
simple, consisting of a wide-mouthed stoppered 
bottle, at the bottom of which is placed some 
chloride of calcium. A slice from the bowl of a 
tobacco-pipe forms a support for a Berlin crucible 
and cover, in which the substance to be dried is 
placed. The whole is then covered with ether (the 
methylated answers very well for the purpose), and 
the mouth of the bottle closed. The ether absorbs 
water from the tissue, which is again absorbed by 
the chloride of calcium, and the process goes on 
without attention until the chloride of calcium ceases 
to absorb. The results, as far as at present ascer- 
tained, have been very satisfaCtorjr. Cellular tissue 
(fresh potatoe) has been dried without any contrac- 
tion. Flies’ heads have contracted less than by 
drying in air; the eyes were in very perfeCt condition, 
and gave good results upon a section being cut; the 
striation on the muscular fibre was perfectly pre- 
served. A small spider, treated by this process, was 
dried without any shrinking of the abdomen. Those 
substances which are injuriously aCted upon by ether 
cannot, of course, be dried by this process ; but it is 
evidently a very valuable addition to the micro- 
scopist’s resources. 
When the objei5t is removed from the drying ap- 
paratus, the ether dries off in a few seconds. If it CANADA BALSAM. 
59 
is required to preserve the objedt in balsam, it can 
either be mounted at once, wet, with ether, or trans- 
ferred to benzol or turpentine. 
In the old days of microscopic manipulation, no 
means was known of preserving objects but that of 
mounting them dry. The usual plan was to mount 
about six objedts in an ivory slide, between discs of 
mica, secured with a brass ring: thin glass was un- 
known at that time. Mounting in Canada-balsam 
was, after this, hailed as a very great improvement. 
Whether the idea was suggested or not by insedts pre- 
served in amber there are no means of ascertaining. 
Very often ideas are suggested by natural occurrences, 
and it would seem likely that some attempt might 
be made to imitate these specimens of Nature’s 
mounting. Gum and various varnishes were tried, 
until, at last, Canada balsam was found to succeed. 
Canada balsam may be considered as a natural 
varnish. It is one of the substances known as oleo- 
resins, and is, according to the “ Micrographic 
Dictionary,” the produdt of Pinus Balsamea, although, 
possibly, it may be obtained from more species of 
the Conifercs than one : something nearly similar is 
found in every pine-wood—the turpentine exuding 
from many of the trees. Canada balsam, like some 
other varnishes, possesses a power of drying more 
or less readily according to circumstances. It dries 
more quickly at a moderate heat than otherwise; is 
readily soluble in ether, turpentine, and benzol; and 
possesses the advantage of being highly refradtive— 
nearly as much so as glass, thereby rendering the 60 
MICROSCOPICAL MANIPULATION. 
view of the edges of objeCts clearer when examined 
by transmitted light, by diminishing the diffraction— 
that power which light seems to have of going round 
a corner under certain circumstances, and which 
causes objeCts, under high powers, to show ill-defined 
margins when viewed in air. Canada balsam is also 
capable of soaking into tissues, and rendering them 
much more transparent than they would otherwise 
be. A much clearer view of the interior of semi- 
opaque objeCts, and, frequently, of objeCts that are 
too dense to transmit any light, can be obtained by 
its means than possibly could be without it. But, 
while it has the advantage of rendering tissues very 
transparent, and, at the same time, preserving them 
in an undoubtedly permanent manner, it is some- 
times liable to render them almost invisible by 
inducing an excessive transparency; it is, also, ap- 
plicable only to those substances that can be dried 
without injury. This, of course, prohibits its use 
with a very large class of tissues, the minute details 
of many animal and vegetable structures being 
obliterated by drying, either by ordinary desiccative 
processes, or the absorption of their water by means 
of strong alcohol;—a process which frequently in- 
duces great contraction in a substance treated with 
it, but which is sometimes taken advantage of when 
it is required to harden a soft tissue. 
The process of mounting in Canada balsam is not 
a very difficult one. The chief obstacles are the 
presence of damp and air. A few air-bubbles in a 
preparation are of little consequence ; but, if the MOUNTING IN CANADA BALSAM. 
61 
preparation should be mounted at all damp, it will 
almost invariably fail. Damp makes itself known 
by a kind of fog surrounding the objeCt. 
If the objeCt to be mounted can be dried on the 
slide, the mounting is extremely easy. Place upon 
it a drop of Canada balsam; warm gently over 
the lamp chimney until it runs, but do not let it boil; 
then place the cover glass on with the forceps, letting 
one edge touch first and bringing the cover down 
gradually, so as to expel any floating air-bubbles with 
the surplus balsam. Should there be any doubt 
about the penetration of the balsam, the objeCt may 
advantageously be moistened with turpentine, or, 
still better, camphine, if it is to be procured. ObjeCts 
especially liable to retain air should be prepared by 
a prolonged soaking in turpentine or benzol; and, 
in obstinate cases, the air-pump may be used with 
advantage to aid the saturation with the fluid. 
Small air-bubbles in a preparation need not be a 
source of anxiety, as they speedily disappear by 
absorption. 
Sometimes the objeCt may be placed upon the 
slide, the cover clipped down, and some balsam 
placed at the edge, which is then melted, and allowed 
to run in by capillary attraction. This plan has the 
advantage of causing little or no disturbance in the 
position of an objeCt, and should always be used, if 
there is any tendency to curl upon the application 
of heat. 
In some cases, the presence of air within a tissue 
is an advantage instead of a detriment. The lacunae 62 
MICROSCOPICAL MANIPULATION. 
and canaliculi in sections of bone, and the tracheal 
tubes of insedts are much better shown when they 
are, as it were, injedted with air. To retain the air, 
the treatment must be the reverse of that described. 
The balsam must be the thickest that can be pro- 
cured, and the mounting done cold, or with the 
application of the smallest available amount of heat. 
The surplus balsam around the edges of the cover 
will require to be cleaned off; but this must not be 
attempted until it has become hard and firm. The 
hardening of the balsam may be much accelerated 
by the application of heat. The inside of a fender 
is a very convenient place for drying balsam-mounted 
slides. A drying apparatus for effecting this more 
quickly is described by Mr. D. E. Goddard, in the 
Transactions of the Microscopical Society of London, 
January, 1864, p. 45. 
The simplest way of removing the surplus balsam 
is to make it very hard, and then wet the slide, and 
scrape away the balsam with a wet knife. It comes 
off very readily, and leaves the slide so clean that 
it can be easily finished with a rag and a little 
methylated spirit. Where the balsam is not very 
hard, it is better to scrape away as much as possible 
with a hot knife, and remove the remainder with 
alcohol, being very careful not to disturb the cover. 
The knife for scraping the slide should be softened 
by heating to redness and allowing it to cool, or it 
will scratch the glass. 
The forceps and needles may be cleaned from 
balsam by heating in a spirit-lamp, and wiping with COLLAPSIBLE TIN TUBES. 
63 
rag or blotting-paper. The forceps should be 
common brass ones, as steel would soon be spoiled, 
and the needles kept for this particular purpose, as 
they are useless for any other. Balsam may be 
removed from the fingers by a free use of methylated 
spirit. 
Canada balsam is best preserved for use in the 
collapsible tin-tubes used for containing oil-colours. 
As already mentioned, air is largely absorbed by 
balsam; indeed, most varnishes dry quite as much 
by the absorption of oxygen as by evaporation. The 
advantage of the tube as a receptacle is that the 
balsam is kept quite close to the top of the tube, and 
no air allowed to remain there, so the balsam may 
be preserved in a perfectly fluid state for a long 
period. Balsam has been kept for two years in 
these tubes, and been as limpid as when the tube 
was filled; while, in bottles, the balsam rapidly 
hardens, and becomes useless if long kept. The 
tubes have also the advantage of cleanliness in use : 
the supply is obtained by squeezing out the quantity 
required ; the use of a dipper, an endless source of 
dirt and introduction of foreign substances, being 
dispensed with. Should a little balsam ooze out 
around the screw-cap, it can be scraped away with 
a hot knife. These tubes also form convenient re- 
ceptacles for varnishes which are liable to injury by 
being exposed to the air—such as gold-size. They do 
not answer for varnishes made with naphtha or spirit, 
as these varnishes dry entirely by evaporation, and 
soon fasten down the cap. 64 
MICROSCOPICAL MANIPULATION. 
Solutions of balsam in various media have been 
much used by some microscopists. They have the 
advantage of allowing the mounting of an objedt to 
be effedted without the employment of heat, a great 
desideratum in many cases. Chloroform has been 
the medium hitherto employed for dissolving the 
balsam, which is previously exposed to a slow heat, 
until it is dried into a hard, resinous mass. It has 
been found, however, that objedts mounted in this 
solution have frequently become cloudy, and that 
the solution, if kept for a considerable period, becomes 
turbid. Dr. Bastian recommends the use of benzol 
as a solvent, on the ground of its greater stability. 
He has made great use of the solution as a medium 
for making preparations of nervous tissue. A de- 
tailed account of his processes will be found in the 
Monthly Microscopical Journal, vol. i., p. 94. 
The solution of balsam and benzol is most con- 
veniently kept in a wide-mouthed bottle, with a 
ground cap instead of a stopper, which will allow a 
small pipette to be kept in the bottle. Should the 
fluid become too thick from evaporation, a little 
more benzol may be added. 
Besides the use of balsam as a mounting medium, 
it is useful as a cement for a special set of purposes. 
The microscopist who makes the osseous tissues, 
rocks, or hard substances in general his particular 
study, will often require thin sections. 
The preparation of a bone section will serve very- 
well as an example of sedtion-cutting, and polishing 
in general. It is required to make a very thin CUTTING SECTIONS OF BONE, 
65 
sedtion of a recent bone, polished on both sides, to 
be mounted dry. The bone is to be cut into thin 
slices with a watch-spring saw. A level surface is 
then to be made on one side, by grinding down with 
water on a piece of blue-stone, or Water-of-Ayr, If 
the slice is very rough, time may be saved by using 
a file in the first instance, and finishing on the stone. 
The fingers may be protected from the aCtion of the 
stone by bedding the rough section in a piece of cork. 
The bone slices are to be cemented with Canada 
balsam, by their ground sides, to pieces of thick 
plate-glass; inches by f of an inch is a convenient 
size for general use. The chief art consists in using 
the balsam of the right degree of hardness'. A drop 
of balsam is to be placed on one of the slips, boiled 
on the hot plate, and allowed to cool. If, when 
cold, it is just capable of receiving a slight impres- 
sion of the thumb-nail when pressed hard, it will do. 
If too soft, it must be heated again, and allowed to 
cool, and the process repeated, if necessary, until 
the right degree is obtained. If the balsam is not 
hardened sufficiently, it will clog the stone in the 
subsequent process ; and, if too hard, it is liable to 
chip off along with the partially-finished section 
during the grinding, The piece of bone, cemented 
in its balsam bed, is to be ground down with water 
until the surface is levelled. It is then to be 
polished, so that no scratches appear upon it when 
examined under the microscope. This is done with 
putty-powder (oxide of tin, and not in any way con- 
nected with glaziers’ putty), used with water upon a 66 
MICROSCOPICAL MANIPULATION. 
wash-leather strop. When the polishing is com- 
pleted, the section is to be removed from the glass, 
which can be done by dropping it into a bottle of 
benzol, which will dissolve the hardened balsam, 
and release the section in a few minutes. A wide- 
mouthed stoppered bottle is convenient for this pur- 
pose, and the pieces of plate-glass are cut of the small 
size recommended, in order that they may be easily 
placed in and removed from the bottle. The half- 
finished seCtion is now to be cemented to another 
balsam-bed, and ground down until it is sufficiently 
thin. With practice, i-sooth of an inch may be 
attained with a tough substance like bone. The 
author has approached this thickness even with 
fossil ganoid scales from the Weald clay. At first, 
it is well not to attempt too thin a seCtion, and to 
practise on some material of which a large supply 
can be obtained. When ground sufficiently thin, 
the second surface is to be polished, and then de- 
tached as before, and afterwards washed in clean 
benzol, to remove all traces of balsam. The 
finished sections, when the benzol has dried off, are 
to be mounted dry by one of the usual processes. 
Sections to be mounted in balsam will not require 
to be polished, as the balsam fills up, and, by its re- 
fractive power, apparently obliterates the scratches 
left by the grindstone. Other hard substances are 
treated in a nearly similar manner. Fossil bones 
and teeth, from their extreme brittleness, will require 
greater care in grinding, and, from their dark colour, 
must often be mounted in balsam, instead of dry. CUTTING ROCK SECTIONS. 
67 
This is also necessary when they have a tendency 
to disintegrate. For very hard substances, such as 
teeth, the Arkansas stone would be of great service; 
but, unfortunately, it does not cut well when used 
with water, and, if oil is employed, the balsam is 
softened. A process devised by Dr. Christopher 
Johnstone about ten years ago, and published in 
Silliman's Journal, gives a process by which an oil- 
stone can be employed. The cement used is isinglass 
jelly, made with alcohol. Use is made of thin paper, 
as a guard against grinding away the sedtion—an 
accident of frequent occurrence with beginners. The 
grinding is performed upon an Arkansas stone, with 
oil, and hot water is used to detach the sedtion. The 
grease can be extradted with benzol. A detailed 
account of the process is given in the Journal of the 
Quekett Microscopical Club, 1869, p. 201. Accounts of 
the mode of cutting rock-sedtions, by J. B. Jordan, 
will be found in the same journal, p. 186, and, by 
D. Forbes, F.R.S, in the Monthly Microscopical 
Journal, vol. i., p. 240. The process of cutting sedtions 
of still harder substances, such as gems, is described 
by Mr. H. C. Sorbv in the Monthly Microscopical 
Journal, vol. i., p. 220. Grindstones and polishing 
powders of various kinds can be obtained at the 
better class of tool shops, as Holtzapffel’s, Buck’s, 
Fenn’s, &c. 
Although it is the usual custom to cover slides 
containing dry and balsam mounted objedts with 
paper, it is preferable to leave them without. A 
balsam-mounted preparation, well cleaned, and MICROSCOPICAL MANIPULATION. 
mounted on a piece of good patent plate with 
polished edges, is far neater than when covered with 
paper, which too often only serves to conceal an 
inferior quality of glass. 69 
CHAPTER IV. 
THE microscopist, in the course of his studies, will 
find a very large class of substances for which 
the processes described in the preceding chapter are 
of no avail, owing to the impossibility of drying 
them without materially affecting their structure. 
The preservation of such substances has always 
been a matter of some trouble ; and beginners are 
frequently deterred from attempting the processes 
of fluid mounting by supposing that the difficulties 
are of an insurmountable kind. 
There is also a prejudice against objects mounted 
in fluid, owing to their supposed want of durability. 
There is, no doubt, some ground for this objection if 
the ordinary fluid-mounted objects only are con- 
sidered. These are of necessity manufactured 
cheaply and in large numbers, and but little care can 
be bestowed upon their preparation. But, if the 
cabinets of our best manipulators are examined, the 
evidence will be found rather in favour of than 
against fluid mounting, provided care be taken to 70 
MICROSCOPICAL MANIPULATION. 
adopt the best processes, and carry them out care- 
fully ; the causes of failure being rather attributable 
to bad workmanship than to defedts in the mode of 
preparation. Instances are on record of objedts 
mounted in fluid as long ago as twenty years being 
still in good preservation. 
The subjedt naturally divides itself into two parts ; 
the processes connected with the enclosing of the 
objedt in its cell, and the consideration of the nature 
of the fluid media employed as preservatives. 
The object to be mounted in fluid will nearly 
always require some previous preparation, excepting 
in those cases where it is free from included air, and 
the fluids contained in its tissues are readily miscible 
with the preservative employed. This preparation 
consists in keeping the tissues required for preserva- 
tion immersed either in the fluid in which they are 
to be mounted, or some other which is capable of 
combining with it without injurious chemical change. 
This soaking will occasionally occupy a considerable 
time; but it may be materially expedited by 
making use of the air-pump, which will ensure the 
saturation of the tissue, and assist in the removal of 
air that may be held within it. The process 
is of the same kind as that adopted on the large 
scale for the preservation of railway-sleepers, by 
impregnating them with creosote; and, in another 
operation (one that more closely approaches the 
subje<5t under consideration), Manfield’s patent for 
making pickles, in which the vegetables to be treated 
are saturated in a few minutes with vinegar, by being FLUID MOUNTING. 
71 
submitted to its adtion in a vessel from which the 
air has been exhausted; a process which took so 
long a time in the ordinary way, that manufadturers, 
to save the loss of capital involved in using vinegar, 
employed brine, which was afterwards removed by 
strong acetic acid, greatly to the detriment of the 
resulting manufadture, both as to flavour and whole- 
someness. This is now obviated by the new process, 
the pickles produced by which closely resemble those 
made at home. 
Although the air-pump is useful where substances 
peculiarly liable to retain air (such as large ana- 
tomical preparations) are being operated upon, its 
use can generally be dispensed with for ordinary 
purposes, a prolonged soaking being sufficient in most 
cases. 
In mounting an object in fluid, a cell of suitable 
size and depth is to be selected, and care taken that 
it is properly cleaned. It is then filled with the 
mounting fluid, and should be rather over than under 
filled. The objedt is now placed in the cell, unless 
circumstances have rendered it advisable that this 
should be done previously. The preparation, at this 
stage, should be carefully examined, with a view to 
the detection of air-bubbles. They are especially 
liable to adhere to the lower part of the cell, where 
it joins the glass slide. They are best dislodged by 
drawing the point of a needle round the interior of 
the cell. Floating bubbles may be broken or re- 
moved by lightly touching with a pointed fragment 
of blotting-paper. MICROSCOPICAL MANIPULATION. 
The cover glass is to be placed upon the cell as 
directed in balsam mounting—letting one edge touch 
the cell first; and, as in that process care was taken 
to keep everything dry, in fluid mounting we should 
adopt the opposite course of treatment. To secure 
the adhesion of the mounting fluid to the cover, and 
lessen the chance of including an air-bubble, it is 
well to moisten the cover by breathing on it just 
before placing it on the cell. 
The surplus fluid is best removed, in the first in- 
stance, by drawing it off with a curved and sharp- 
pointed pipette, made in the form of an ordinary blow- 
pipe. The use of this contrivan ce will generally allow 
the floating cover to be brought in contact with the 
top of the cell without the risk of flooding its upper 
surface, which is nearly sure to take place when the 
cover is pressed down suddenly, and will give trouble 
to remove when viscid fluids like glycerine and oil 
are used. When as much of the fluid is removed as 
can be conveniently taken up with the pipette, the 
rest is absorbed by the careful use of fragments of 
blotting-paper. Care must be taken not to carry 
this process too far, as, if too much of the fluid is 
absorbed, an air-bubble may enter, which will neces- 
sitate the removal of the cover and a repetition of 
the operation. The moisture being cleaned off the 
outside, the cell is ready to receive its first coat of 
varnish, which is to be applied with a small brush, 
and care should be taken to fill the angle at the 
contact of the cover and cell, and to include in the 
ring of varnish a small portion of the edge of the FLUID MOUNTING. 
73 
cover. This first coat of varnish must be put on by 
hand, as the adhesion of the cover is too slight to 
bear the adtion of the turn-table; this machine, 
however, may be employed with advantage in laying 
on the second and subsequent coats, as, by its use, 
greater neatness and rapidity are attained than are 
possible by painting on the varnish by hand. 
The best and most durable cement for securing 
the covers of objects mounted in fluid is the varnish 
known as japan gold-size, the principal constituent 
of which is boiled linseed-oil. It is easily obtained 
at any varnish shop. It is best kept for use in the 
collapsible tubes recommended for holding Canada 
balsam. If kept in a bottle, it absorbs air, thickens, 
and loses, to some extent, its drying properties. 
This varnish is remarkable for its elasticity and 
toughness when dry, which may readily be proved 
by scraping a portion, which will be found to come 
away in shreds instead of chipping, as many other 
varnishes do. Glycerine and castor-oil, both valu- 
able mounting fluids, have the unfortunate property 
of dissolving gold-size; therefore, in using these 
media, it is necessary, before putting on the coatings 
of gold-size, to apply two or three coatings of 
the liquid glue previously mentioned. This varnish 
is impervious to oil and glycerine, but is too brittle 
when dry to be trusted alone. The liquid glue will 
be found effectually to protedt the gold-size, with 
which the preparation is to be finished. This pre- 
caution is not required when using media which 
do not injuriously affedt gold-size, such as weak 74 
MICROSCOPICAL MANIPULATION. 
alcohol and water, saline solutions, camphor and 
creosote water, &c. 
Some microscopists make use of asphalte or 
Brunswick black for securing the cover. They have 
the fault of being brittle, which, however, is said by 
Dr. Beale to be remedied by the admixture of a 
small portion of solution of india-rubber in naphtha. 
The author’s experience of this cement is rather un- 
favourable. It may, however, be owing to having 
used a bad specimen; as it is probable that many 
kinds of Brunswick black are manufactured, and 
they are likely to vary extremely in quality. How- 
ever, as gold-size is so reliable a cement, and so 
easily procured, there is no occasion to risk the use 
of a varnish whose properties are somewhat un- 
certain. 
Should the mounting fluid be one which leaves a 
deposit on drying (which is the case with saline 
solutions), or be difficult to clean off (like glycerine), 
after the first coat of varnish is dry, the slide should 
be washed, either by holding under a partially-open 
tap, or by means of the ordinary wash-bottle. If 
this precaution is not taken, the adhesion of the 
cement is rendered uncertain, and negleCt of this 
matter is a not unfrequent cause of leakage. If 
necessary, this washing must be repeated after the 
second coat of varnish. With oil, a somewhat dif- 
ferent treatment is needed. The cleaning is best 
effected with a camels’-hair brush, charged with tur- 
pentine or benzol. 
The slide should not be put away in the cabinet FLUID MOUNTING. 
75 
until it has received at least six or eight coats of 
gold-size. No varnish should be laid on thickly, 
otherwise it is liable to remain fluid in the interior, 
although apparently hard outside. 
In commencing the practice of fluid mounting, it 
will be advisable for the student to make his first 
trials with some such fluid as camphor-water or 
diluted alcohol, as the difficulties of cleaning, &c.’ 
are much less than with saline solutions or glycerine. 
A very ingenious process of fluid mounting forms 
the subject of a communication by Mr. T. C. White to 
the Quekett Microscopical Club (Journal of the Quekett 
Microscopical Club, vol. i., p. 147). He forms a cell 
with a thick varnish, made by dissolving gum damar 
in benzol. This is done by holding a brush charged 
with it against a slide while revolving on the turn- 
table. The cell will be ready in a few minutes, as it 
is used while half dry. The fluid and objedt are 
placed in the cell, and the cover glass put on, and 
pressed down into the cement, which adheres most 
tenaciously to wet glass. The surplus fluid is to be 
removed with blotting-paper, which may be used 
with the greatest freedom, as the glass is held very 
firmly by the damar varnish; another coat of this 
is applied by means of the turn-table, and the slide is 
completed. It would no doubt be more secure if 
finished with a few coats of gold-size. This pro- 
cess can only be used by those who are somewhat 
expert, as, should the first attempt fail, the cover 
cannot be removed and the process repeated. It is 
a very expeditious mode of mounting, and is likely, 76 
MICROSCOPICAL MANIPULATION. 
in some cases, to prove of great value. Mr. White 
states that he has had slides mounted for two years 
which are still perfedtly sound and free from air- 
bubbles. The solution of damar may also be used 
as a very efficient substitute for the mixture of balsam 
and benzol. It is, like most varnishes, rather 
troublesome to make, as, owing to the impurities 
usually contained in the gum, the varnish requires 
straining; a somewhat difficult matter with so 
volatile a solvent as benzol. 
The durability of objects, however mounted, is much 
influenced by the manner of storing them. Racked 
boxes and drawers are the worst possible receptacles, 
as from the vertical position of the slides they' are 
liable to serious injury, those in fluid being likely to 
become leaky, and the balsam specimens sliding down, 
frequently, cover and all. Arrangements should be 
made for keeping the objedts flat, which is now 
always done in well constructed cabinets ; it is also 
a great advantage to be able to see every slide, which 
is impossible in a racked box, and often causes much 
loss of time in searching for an objedt. For the con- 
venience of those for whom the usual cabinets are 
too costly, Mr. Piper has invented some very 
ingenious trays, in which slides are placed 
horizontally; besides the merit of cheapness, they 
have the advantage of being extremely convenient. 
Five or six of these trays, with a mill-board at the 
top and bottom, may be fastened together with a 
couple of India-rubber rings, and any vacant shelf 
room utilised for the storage of objedts; a similar CHOICE OF FLUID FOR MOUNTING. 
77 
bundle of two or three trays is very convenient for 
carrying a small seledtion of objedts in the pocket. 
Dr. Carpenter has used these trays placed in wooden 
cases made to resemble books, a very convenient 
way when bookshelves are vacant to receive them. 
The chief difficulty of fluid mounting will be found 
not to consist so much in the mechanical process of 
closing the objedt perfedtly in its cell, as in the 
seledtion of a fluid suitable for its preservation. 
A fluid which may be considered as a perfedt 
medium—that is, one capable of preserving substances 
for an unlimited period without change, is at present 
unknown, and it is more than doubtful whether the 
discovery of such a fluid would be altogether an ad- 
vantage, as use is frequently made of what some 
may consider the defedts of preservative fluids ; the 
alterations they induce in tissues submitted to their 
adtion often revealing fadts of great importance. 
Some media are valuable, because they soak into 
tissues and render them transparent; this is the 
case to such an extent with glycerine, that Dr. Beale 
very appropriately calls it “The Canada balsam of 
moist tissues.” Others are used for quite the oppo- 
site purpose, because they induce opacity, and very 
frequently do so partially, bringing out details some- 
what in the same manner as is done by the colouring 
of a map, and which, without such aid, would be very 
imperfedtly distinguished. Others are slightly 
corrosive, and clear away parts wished to be got rid 
of for the sake of bringing others more prominently 
into view. 78 
MICROSCOPICAL MANIPULATION. 
In mentioning some of the very numerous media 
which have been used for mounting, the results can 
only be stated generally, and no fixed set of rules can 
be given, as the whole subjedt is at present in too 
imperfedt a state. Much good might be done by 
observers mounting a series of the same objedt in 
different media, carefully labelling each slide with 
the date of mounting and the nature of the medium 
employed, and from time to time noticing and recording 
the result. 
One of the great difficulties afifedting the mounting 
of objedts in fluid, arises from endosmotic adtion. 
When two fluids of different densities are separated 
by a permeable membrane, they will pass through 
and mix at very unequal rates. Supposing some 
dense fluid, like glycerine, enclosed in a bladder 
and immersed in water, the water would flow into the 
bladder faster than the glycerine made its way out, the 
result would be the expansion of the bladder. This 
is called endosmosis: the reverse adtion is known as 
exosmosis. With a view to observing pradtically the 
result of these adtions, the student is recommended 
to obtain a specimen of some fresh-water conferva, 
such as are abundant in nearly every pond or 
aquarium. A portion of this conferva should be 
placed on a slide in a drop of water, covered with a 
thin glass, and examined with a power of fifty or 
sixty diameters. When the appearance of the plant 
is well impressed on the mind, remove the slide from 
the microscope, take off the cover glass from the 
objedt, and with a piece of blotting-paper drain off ENDOSMOTIC ACTION. 
79 
(not blot up) as much of the water as possible.* Now 
cover the conferva with some strong glycerine, re- 
place the cover quickly, and examine without loss 
of time under the microscope, and notice the change 
that has taken place. The fluid contents of the 
conferva cells have suddenly emptied themselves into 
the surrounding glycerine, leaving the whole plant 
in a shrivelled and contracted state ; in many cases 
the cells will be found to be ruptured, but those which 
have escaped injury will after a time expand and 
resume their natural appearance. In observing, 
advantage is sometimes taken of induced endosmosis, 
the tissues ruptured by this means often revealing 
points of structural detail difficult or impossible 
of demonstration by dissection. Endosmotic 
aCtion may be prevented by introducing objeCts 
which contain light fluids very gradually into denser 
ones ; for instance, an objeCt should be passed from 
water into weak glycerine and then after a time into 
stronger, till at last it might be placed in glycerine 
of full strength without any contraction taking place. 
The same phenomenon takes place if marine plants 
are immersed in fresh water. This may be familiar 
to some who have attempted to wash delicate sea 
weeds, such as Griffithsia setacea, in fresh water, 
the result being that the cells burst and stain 
the mounting paper; this may be prevented by 
washing in sea water, or water having gum or sugar 
dissolved in it, so that its specific gravity approaches 
that of sea water. An ingenious application of the 
principle of gradually increasing the specific gravity 80 
MICROSCOPICAL MANIPULATION. 
of the' mounting fluid with a view to the prevention 
of endosmosis, will be found in the method known 
as Hantzsch’s. The fluid consists of three parts 
alcohol, two of distilled water, and one of glycerine 
(Price’s), all by measure. This medium is principally 
employed in mounting' The specimen is placed 
in the cell with this fluid and the cover put on, but 
not cemented, so as to allow evaporation to take 
place ; the waste is supplied from time to time, until 
at last the cell contains nearly pure glycerine ; it is 
then to be cemented as before described. The fluid 
is of very nearly the same specific gravity as water, 
so little or no endosmotic aCtion takes place on the 
immersion of the specimen ; and as the evaporation 
process increases the strength of the solution very 
gradually, the most delicate tissues can be eventually 
mounted in strong glycerine ; doubtless this principle 
would answer equally well with a solution of chloride 
of calcium, a very valuable medium for certain 
preparations. Much valuable information respecting 
the collection and preparation of Alger, will be found 
in “The Collector’s Handy Book of Algas,” by Rev. 
W. W. Spicer, from which the above process is taken. 
Taking the preservative fluids in groups, the 
simplest consist of water, either alone or in com- 
bination with some antiseptic substances. 
Distilled water alone is capable of preserving such 
objects as the Desmidice and other Alger in tolerable 
perfection as to form, although with more or less 
loss of colour and alteration of the disposition of the 
endochrome or cell contents. Confervas are very apt PRESERVATIVE FLUIDS. 
81 
to grow in slides in which distilled water is used ; 
this is best prevented by saturating the water with 
camphor or creosote. 
Camphor water is made by placing a lump of 
camphor in a bottle of distilled water, and allowing 
it to remain a few days ; the water will then be found 
to smell very strongly, although the quantity dissolved 
is exceedingly small. Such portion as may be re- 
quired for use is to be filtered and kept in a small 
bottle ; the store bottle is to be filled up from time to 
time with distilled water. This fluid may be used 
with advantage in making and diluting all the 
preservative fluids mentioned in these papers instead 
of pure distilled water, unless an indication to the 
contrary is given in the formula. It is capable of 
preserving animal tissues as well as vegetable, but 
with the fault of most watery liquids, that it is apt 
in time to induce a granulous texture in objedts 
of this kind mounted in it. 
Creosote water is made in a nearly similar manner ; 
a few drops of creosote are poured on a quantity of 
precipitated chalk, and the whole shaken up in a 
bottle of distilled water. When the chalk has 
settled, the clear liquid may be poured off and filtered 
as required for use ; the preservative properties of 
this and also of a very diluted solution of carbolic 
acid closely resemble those of camphor water. For 
another use of carbolic acid see paper by Dr. Bastian, 
Monthly Microscopical Journal, vol. i., p. 96. 
Alcohol, diluted with water in various proportions, 
is much used for the preservation of large anatomical 82 
MICROSCOPICAL MANIPULATION. 
specimens ; portions of inje<5ted tissue to be viewed as 
opaque objects keep very well in it, also vegetable 
structures where loss of colour is not objectionable. 
The striated structure of muscular fibre is well shown 
when this medium is employed; a piece of cooked 
meat will do to experiment upon. The fibres 
should be well separated with the needles before the 
cell is closed. Many other preparations are used for 
the preservation of objects. 
Thwaites's Fluid.—Water, 16 02s.; alcohol, 1 oz. ; 
creosote and chalk, as in creosote water. Pour the 
creosote on the chalk as before, add the alcohol, stir up 
the whole, and add the water very gradually; allow the 
mixture to stand a few days, and then filter. Dr. Beale 
found that this solution was liable to become thick after 
a time, and gives the following substitute in his“ How 
to Work with the Microscope:”—“ Creosote,3 
drachms; wood naphtha, 6 ounces ; distilled water, 64 
ounces; chalk, as much as may be necessary. Mix first 
the naphtha and creosote ; then add as much prepared 
chalk as may be sufficient to form a smooth, thick 
paste ; afterwards add very gradually a small 
quantity of the water, which must be well mixed with 
the other ingredients in a mortar. Add two or three 
small lumps of camphor, and allow the mixture to 
stand in a lightly-covered vessel for a fortnight or 
three weeks, with occasional stirring. The almost 
clear supernatant fluid may then be poured off and 
filtered if necessary; it should be kept in well corked 
or stoppered bottles.” Dr. Beale states that he has 
had large preparations preserved in this fluid for PRESERVATIVE FLUIDS. 
83 
more than twelve years, and that it is still bright 
and colourless. 
Fluids are filtered by being strained through a 
conical bag made of a circular piece of porous paper 
manufactured for the purpose, folded in the usual 
manner, and supported in a glass or porcelain funnel 
of suitable dimensions. If the proper filtering paper 
is not at hand, white blotting paper will answer the 
purpose. 
Chloride of Calcium (a saturated solution in cam- 
phor water).—For making this solution, the pure 
fused salt should be used, and not the common kind 
used for drying; it should be carefully filtered before 
use; it can be diluted to any extent with camphor 
water. The saturated solution is an extremely 
valuable preservative fluid ; it soaks into objects, 
rendering them transparent, but rather less so than 
strong glycerine; it has the advantage, also, of not 
injuring calcareous tissues. Insects, viz., fleas and 
lice, mounted whole in this medium, with little or no 
compression, show the tracheal system and many of 
the internal organs remarkably well when properly 
illuminated, and are still in perfect condition ; date 
of mounting, 1866. Flax, hemp, and other similar 
fibres display their structure far better in this than 
in any other medium, the secondary deposits being 
very clearly brought out. 
Diluted, Solution.—One part of saturated solution 
to ten of camphor water answers well for the preser- 
vation of the fresh-water Alga ; the green colour is 
better preserved by it than it is in any other fluid. 84 
MICROSCOPICAL MANIPULATION. 
Chloride of Sodium (common table salt).—A satu- 
rated solution seems to preserve Entomostraca very 
well indeed; it induces a slight degree of opacity, 
which is sometimes an advantage. Specimens of 
Daphniapulex (water fleas) mounted in it in September, 
1866, show much of the internal structure; the eyes 
and bundle of optic nerves are in very perfedt condition. 
This solution is of value from its being readily pro- 
cured anywhere, and a supply of specimens which 
would otherwise be lost may be preserved in it. Sea 
water impregnated with camphor or creosote will 
preserve various delicate marine’animals and plants 
extremely well and without injury from endosmosis ; 
by taking proper precautions they may be gradually 
transferred, if necessary, to strong glycerine. 
Solution of arsenious acid in water has been used 
both alone and in combination with glycerine for 
the preservation of objedts; the latter mixture has 
answered very well in re-mounting a series ofinjedted 
preparations, which are now, after a period of about 
six years, in perfedt condition. The quantity of 
arsenic capable of being dissolved in water is ex- 
tremely small; solutions of arsenic, unless saturated 
with camphor, are especially liable to confervoid 
growths, a rather unexpedted phenomenon in so 
poisonous a fluid. 
Many other saline solutions will be found in micro- 
scopical works. The best have been given above ; a 
larger selection would tend rather to confuse than 
assist the beginner. 
Glycerine is one of the most valuable materials PRESERVATIVE FLUIDS. 
85 
ever added to the resources of the microscopist. 
We are indebted to the late Mr. Robert Warington 
for the application of this fluid to microscopical pur- 
poses. It is obtained as a waste produCt in the 
manufacture of soap, and lead plaster. The quality 
of the glycerine from these sources is very inferior, 
being both weak and impure. The best is that 
made by Price’s Patent Candle Company, and 
obtained by a distillation process. This is much 
purer and stronger than the common kind, having 
a specific gravity of about 1240, and is the only 
kind fit for use by the microscopist. The pro- 
perties of glycerine as a means of giving trans- 
parency to an objeCt have already been mentioned. 
It is a thick, syrupy, and highly refractive fluid, 
nearly colourless, and intensely but pleasantly sweet. 
Although made from fat, it is not at all greasy, but 
freely miscible with water and many other fluids ; it 
is also a solvent for a great number of substances. 
Its aCtion upon varnish has already been alluded to. 
It is stated by Dr. Carpenter that it dissolves car- 
bonate of lime readily, and quite destroyed the cal- 
careous skeleton of certain Echinodermata mounted 
in it. He suggests that, when used for such pur- 
poses, it should be saturated with carbonate of lime 
by being kept in a bottle with some fragments of 
marble (“ Microscope and its Revelations,” fourth 
edition, p. 222). One of the advantages of glycerine is 
that it never dries ; so that an objeCt can be placed in 
it, covered with a glass, and left uncemented, without 
fear of evaporation for any length of time, and after- 86 
MICROSCOPICAL MANIPULATION. 
wards mounted permanently, if desired. Owing to 
its free miscibility with other substances, it forms 
many very valuable compounds, some of which 
will presently be described. A very full account 
of its use in delicate physiological investigations 
is given in Dr. Beale’s “ How to Work with the 
Microscope,” a book of the greatest service to 
all intending to study the particular subjects upon 
which it treats. It is by the use of glycerine that 
Dr. Beale has succeeded in carrying on his elaborate 
investigations of the ultimate structure of nerve 
tissue under excessively high powers ; and his pro- 
cesses afford a remarkable illustration of the support 
afforded to a delicate tissue by immersion in a fluid 
of extreme density, the manipulation of tender sub- 
stances being comparatively easy in glycerine, when, 
in water or alcohol, it would have been impossible. 
Strong glycerine preserves nearly every kind of 
objeCt, whether animal or vegetable, with great per- 
fection, and is, perhaps, the nearest approach to an 
universal mounting-fluid yet known. Inserts and 
other objects may be put into a bottle of glycerine, 
and left until wanted ; they are even better after a 
year or two’s soaking. ObjeCts mounted in glycerine 
generally improve after a time, details often being 
visible which were not seen immediately after 
mounting. The introduction of the binocular micro- 
scope has very much influenced the style of mounting 
objects to be viewed with low and medium powers. 
For this purpose, it will be found advantageous to 
mount the objeCt with little or no compression. Of PRESERVATIVE FLUIDS. 
87 
course, for examination with high powers, thin and 
compressed specimens are absolutely necessary (see 
author’s paper, Monthly Microscopical Journal, vol. i., 
P- 33i)- 
Glycerine can be diluted to any extent, either with 
camphor or creosote water, should it be desired to 
obtain a less refractive fluid, and one which does not 
render objects so transparent as pure glycerine; 
sometimes a portion of alcohol may be added with 
advantage. This compounding of media is one 
of the greatest arts in fluid mounting, and can only 
be acquired by experience, as, at present, no definite 
diredtions can be given. Diluted fluids, as a general 
rule, make animal tissues more granulous and opaque 
after a time than the strong, dense ones. The 
author possesses an instance of a difficult mounting 
accomplished almost by chance. The subjedt was 
the Medusoid embryo of Hydra tuba, which he had 
been observing at a friend’s house. Thinking it a 
pity to lose a specimen then seen for the first time, 
he took the objedt home alive in its cell of sea- 
water, and then determined to attempt its permanent 
preservation. The course of operation was as 
follows :—The slide was placed in a saucer, which 
was quickly filled with strong alcohol (about 60 over 
proof). This fortunately killed the animal so sud- 
denly that it was but little contradted. A mounting- 
fluid, consisting of glycerine, alcohol, and sea-water, 
was then extemporised, and the objedt mounted. It 
is still in good preservation, although somewhat 
opaque. It was mounted in February, 1862. This 88 
MICROSCOPICAL MANIPULATION. 
is given as an instance of the kind of practice occa- 
sionally needed in cases of emergency, and where 
the taCt acquired by experience may be turned to 
good account. 
It is occasionally convenient to make use of a 
medium which, while it is fluid at the time the objeCt 
is mounted, will ultimately harden, and preserve the 
objeCt from injury from being shaken or moved. 
Such media are especially useful for mounting 
Diatomacea attached to other Alga. There are 
many compounds of this nature, some of the best of 
which are largely composed of glycerine. 
The earliest of these was that known as Deane's 
gelatine. It is composed of—Gelatine, i oz.; water, 
4 ozs.; honey, 5 ozs.; creosote, 6 drops ; alcohol, i oz. 
The gelatine is to be soaked in the water until 
quite soft; the honey, heated to the boiling point, is 
to be added. The whole is then to be boiled, and, 
when it has cooled a little, the creosote and alcohol, 
mixed together, are to be added, and the whole 
filtered through fine flannel. 
Glycerine jelly consists of gelatine soaked in cam- 
phor-water until it swells and becomes soft. The 
surplus water is to be poured off, the gelatine melted 
in a water-bath (a large wide-mouthed bottle placed 
in a saucepan of hot water will answer the purpose), 
and the resulting jelly strained, and, if necessary, 
clarified after the manner of confectioners with white 
of egg. To every ounce by measure of this jelly add 
i drachm of alcohol and 6 drachms of Price’s 
glycerine. PRESERVATIVE FLUIDS. 
89 
Both these media are used by melting the com- 
position by placing the bottle in hot water, just as 
glue is melted. It is then used almost precisely in 
the same way as Canada balsam, taking the pre- 
caution to prepare the objedt by a previous soaking. 
Thin objedts do not require a cell When the gela- 
tine has hardened sufficiently, the surplus portion is 
scraped off, and the slide cleaned. It should then 
be secured with a coat or two of liquid glue, followed 
by several coats of gold-size, as in moist preparations. 
A very useful medium of nearly similar properties 
is made according to the following formula of Mr. 
Farrants :—Picked gum arabic, 4 parts by weight; 
water, 4 parts ; glycerine, 2 parts. The mixture is 
to be made cold, and, if necessary, strained through 
fine muslin. It is to be used in the same manner as 
the foregoing gelatinous preparations, only without 
heat; which renders it particularly fit for objedts 
that will not bear the slight increase of temperature 
required to liquefy gelatine. 
The adtion of all the above media is nearly similar 
to that of slightly diluted glycerine, excepting that, 
when set, they keep the objedt fixed in the position 
in which it was mounted. It is necessary when using 
these preparations to guard against endosmotic 
adtion, by soaking in suitable fluids. 
Strong syrup is capable of preserving animal and 
vegetable tissues, but is, under some conditions, liable 
to crystallise. The best proof of the perfect manner 
in which vegetable substances are preserved is given 
in the condition of preserved fruits, which are in MICROSCOPICAL MANIPULATION. 
an extremely favourable state for microscopical 
examination. The samples of jam, &c., examined 
by Dr. Hassall, and reported upon in his “ Food and 
its Adulterations,” were probably among the tissues 
most easily identified, owing to their perfedt con- 
dition. 
Castor-oil will be found an excellent mounting- 
fluid ; it penetrates, and gives considerable trans- 
parency, and keeps the objedt well and for a long 
period. It is particularly successful with parasitic 
insedts ; these maybe placed in a bottle of castor-oil, 
and kept until required for mounting. As castor-oil 
is so readily procured, being in every medicine-chest, 
and to be obtained at any little village shop, it is a 
very useful medium for those who may wish to pre- 
serve insects, &c., captured while travelling, as they 
need no attention after they are immersed in it. 
Should it be desired to mount the objedts ultimately 
in some other medium, the oil can easily be removed 
by soaking in benzol. 
Mounting-fluids which are in frequent use are best 
kept in a small, wide-mouthed bottle, through the 
cork of which is passed a pipette, surmounted by a 
funnel at its upper extremity, upon which is stretched 
a piece of sheet india-rubber (Fig. 18). By this 
contrivance, a small quantity of fluid can be taken 
up, and delivered, drop by drop, upon the slide. 
Where mounting-fluids are continually required, as 
in pathological laboratories, Dr. Beale has contrived 
a little fountain on the principle of the wash-bottle, 
which answers admirably for a supply of any kind PRESERVATIVE FLUIDS. 
91 
of fluid in drops; but, for the occasional use of the 
student, the pipette-bottle is to be preferred. 
Fig. 18. 
Closely connedted with fluid mounting is the pro- 
cess of staining tissues. This is used for two widely 
different purposes. The first for rendering very 
transparent bodies more easily visible ; this is easily 
done by immersion in magenta, diluted as the parti- 
cular case may require. The other for more clearly 
defining portions of the tissue in a particular physio- 
logical condition; this is done by using staining fluids 
which adt unequally. For instance, if it be desired to 
stain the nuclei of cells, the solution of carmine, 
described by Dr. Beale in “ How to Work with 
the Microscope,” and reprinted here by his kind 
permission, will answer admirably: — “Carmine, 
io grains ; stiong liquor ammonise, £ drachm ; Price’s 
glycerine, 2 ozs.; distilled water, 2 ozs.; alcohol, £ oz. 
The carmine, in small fragments, is to be placed in 92 
MICROSCOPICAL MANIPULATION. 
a test-tube, and the ammonia added to it. By agi- 
tation, and with the aid of the heat of a spirit lamp, 
the carmine is soon dissolved. The ammoniacal 
solution is to be boiled for a few seconds, and then 
allowed to cool. After the lapse of an hour, much of 
the excess of ammonia will have escaped. The 
glycerine and water may then be added, and the 
whole passed through a filter, or allowed to stand for 
some time, and the perfectly clear supernatant fluid 
poured off and kept for use. This solution will keep 
for months, but sometimes a little carmine is deposited, 
owing to the escape of ammonia, in which case one 
or two drops of liquor ammonias to four ounces of 
solution may be added.” For further information 
relative to the application of the staining process, 
and the observations to be carried out by its means, 
the student is referred to Dr. Beale’s work. 
Solutions of chloride of gold and nitrate of silver 
may also be employed to advantage (see paper by 
Dr. Bastian before quoted; T. Dwight, Monthly 
Microscopical Journal, vol. ii., p. 45). CHAPTER V. 
NEXT in importance to the possession of a good 
the having a good supply of light 
and knowing how to make proper use of it. The 
sources of light available for the microscopist’s use 
bave already been described ; the ways of utilising 
the light so obtained, and the instrumental appliances 
for directing it, form the subjedt of this chapter. 
The natural division of illuminators is into 
two classes — those which adt above the stage 
of the microscope, and send light down upon an 
objedt ; and those which are placed below the stage, 
and send light through it. 
Of instruments of the first class, one—the con- 
densing lens—is usually supplied with every micro- 
scope, however plainly equipped. This lens enables 
light to be concentrated upon the objedt on the stage ; 
either a double-convex or a plano-convex lens may be 
used for this purpose. If the first is employed, no 
particular attention is required beyond placing it at 
such a distance above, and on one side of the stage, 94 
MICROSCOPICAL MANIPULATION. 
that the light falls at a suitable angle, and that the 
objeCt is in or near the focus ; should a plano-convex 
lens be used, its position is of some importance, as, 
if it is turned the wrong way, its spherical aberration 
is greatly increased, and, of course, a corresponding 
amount of light lost. The plano-convex lens, or 
bull’s-eye, when used to concentrate parallel rays— 
daylight, for instance—or divergent rays, such as 
those proceeding from a lamp, should always be 
placed with its convex side turned towards the 
source of light, as the spherical aberration is then 
much less than it would be when placed in the con- 
trary direction ; if the lens is to be used for rendering 
parallel the divergent rays of a lamp, then the bull’s- 
eye is to be placed in the opposite position, with its 
flat side turned to the lamp, and at a distance from 
the flame equal to its focal length. Parallel rays are 
required when using some of the illuminating 
apparatus presently to be described. 
Very much may be done with the condensing lens, 
if skilfully used ; especial care is required that it 
causes the light to fall on the object in the right 
direction, as the appearance of the surface of many 
substances is very different when illuminated from 
opposite sides; the student should, therefore, never 
be contented with a single observation of a strange 
substance, but should change its position, so that it 
may be viewed with the light falling upon it in as 
many directions as possible. This is most easily 
effected by causing the objeCt to rotate while the light 
is directed upon it, so that the alteration caused by ILLUMINATING APPARATUS. 
95 
every change of position can be easily noted. The 
necessary movement is now very generally fitted 
even to the stages of small instruments, and persons 
about to procure a microscope would do well to incur 
the small extra cost of this useful addition. 
The light obtained by the condensing lens may be 
greatly augmented by using two, one of larger dimen- 
sions than the other, the light being brought to a 
certain degree of convergence by the first and larger 
lens, and afterwards concentrated by passing through 
the smaller one, which should be so placed as to 
intercept the cone of light from the large lens at the 
place where it is of its own diameter. 
Most of the other illuminators of this class aCt by 
reflection, mirrors of various forms being employed. 
The optical properties of concave mirrors resemble, 
in many points, those of convex lenses; they cause 
parallel rays to converge (Fig. 19), render divergent 
Fig. 19. 
rays parallel, or convergent, and also form images 
(Fig. 20). Microscopes and telescopes can be con- 
structed with mirrors or specula, instead of objeCt - 
glasses; this principle is still in use as regards tele- 
scopes of large dimensions, as the difficulties of 96 
MICROSCOPICAL MANIPULATION. 
making objedt-glasses of large diameter are very 
great; the largest yet accomplished is only 25 inches, 
Fig. 20. 
while the largest speculum (that of the late Lord 
Rosse) is 6 feet in diameter. 
Professor Amici constructed a very efficient com- 
pound microscope, having an elliptical speculum in 
place of an objeCt-glass; the plan, however, was 
abandoned on the introduction of the achromatic 
principle, although its performances were very 
superior to those of the non-achromatic instrument.* 
Concave mirrors, when formed of segments of spheres, 
are liable to spherical aberration, just as lenses are 
(Fig. 21); therefore, when it is required to render 
divergent rays parallel, or bring parallel rays to a 
focus, it is necessary that the figure of the mirror 
should be that of a parabola. Specula of this 
form are used in astronomical telescopes, the 
refleCtors of lighthouses on the catoptric principle, 
and in some instruments presently to be described. 
The parabolic curve differs from the circle princi- 
pally in being flatter at the edges and deeper at the 
centre. Reflecting instruments are entirely free 
* One of these instruments has recently been presented to the Royal 
Microscopical Society; there are also several old and curious micro- 
scopes in the Society’s colleftion. THE LIEBERKUHN. 
97 
from chromatic aberration. The oldest of the re- 
fledting illuminators is that known, from the name of 
Fig 2i. 
its inventor, as the Lieberkuhn (Fig. 22); it consists 
of a spherical silver mirror, perforated, to allow it to 
Fig. 22. 98 
MICROSCOPICAL MANIPULATION. 
slide over the setting of the objedt-glass, and is so 
adjusted that the focus of the speculum is coincident 
with the working distance of the objedt-glass. The 
objedt is illuminated by light refledted through the 
hole in the stage by means of the mirror; this is again 
refledted, but in a very convergent state, upon the 
objedt, which will be intensely illuminated if the specu- 
lum is well adjusted to focus and properly supplied 
with light. 
It is necessary to place beneath the objedt a black 
stop of sufficient size to fill the field of the objedt 
glass, otherwise the light from beneath entering the 
microscope will cause a disagreeable amount of fog 
and indistindtness. The best kind of background 
consists of a dark well or little cup of proper size 
painted black inside, and placed below the objedt; a 
patch of black paper or paint will, however, answer 
the purpose. Beck’s disc holder (Fig. 23) is 
Fig. 23. 
particularly useful for objedts to be examined by 
the aid of the lieberkuhn, as it forms its own 
black stop. Its late talented inventor was very expert 
in the employment of this kind of illumination. The 
defedts of the lieberkuhn are that its light is nearly THE PARABOLIC LIEBERKUHN. 
99 
vertical, and therefore, like the tropical mid-day 
sun, casts little or no shadow; this, however, may be 
remedied, to some extent, by turning the mirror 
aside and using the light from only one-half 
of the speculum (Fig. 22, B); it also requires the object 
and its mounting to be small enough to allow the 
free passage of the light around it from the mirror. 
These defedts caused the lieberkuhn to fall somewhat 
into disuse; the introduction of the binocular micros- 
cope, however, caused it again to be employed, as it 
Fig. 24. 
was found very suitable for the peculiar class of 
opaque objects which are so well displayed in relief 
by its stereoscopic power. It has, however, again 
been nearly superseded by an improved form, which 
has all its advantages, besides some peculiar to itself. 
This improved instrument, which is known as the 
parabolic lieberkuhn (Fig. 24), is another of the 
numerous contrivances of the late Richard Beck, 
and was described by him in the Microscopical 100 
MICROSCOPICAL MANIPULATION. 
Quarterly Journal for 1865 (vol. xiii., p. 116). It con- 
sists of a portion of a silvered paraboloid, which is 
attached by a ring to the setting of the objeCt-glass, 
so that it has some range of adjustment like the 
ordinary lieberkuhn ; but instead of the light being 
directed upon it from below through the hole in the 
stage, it is supplied from one side, which allows this 
form of lieberkuhn to be used with objects mounted 
in the ordinary way. It is necessary when lamp 
light is used that the rays should be rendered parallel 
by placing a condensing lens between the lamp and 
the reflector, as before-mentioned. As there is a 
very large reflecting surface, and from the parabolic 
figure of the mirror no spherical aberration, the 
amount of light concentrated upon the objeCt is 
much greater than could be obtained from the 
ordinary spherical lieberkuhn. It has also the 
advantage of reflecting rays from one side only, and 
of considerable obliquity. These properties make it 
the most perfeCt illuminator yet produced for view- 
ing opaque objeCts by reflected light. Its effeCt is 
almost like that of brilliant sunshine, lighting up the 
interior of every cavity, and yet, at the same time, 
casting strong shadows and defining minute portions 
of structure in a manner hitherto unapproached. 
The paraboloid as usually constructed is adapted for 
use with objectives of from 2 inches to § focus. An 
ingenious mounting, allowing a very large range 
of adjustment to be given to the paraboloid, has been 
contrived by Mr. Crouch, who uses a short adapter 
screwed into the body of the microscope as a support THE PARABOLIC LIEBERKUHN. 
to the reflector and its fittings ; these consist of 
sliding tubes and ball-and-socket joints, by means of 
which it can be placed in extremely varied positions, 
and is adapted for use with any microscope or objeCt- 
glass fitted with the universal screw. It must be 
borne in mind that these advantages are gained 
at the expense of removing the objeCt-glass a small 
distance, viz., the length of the adapter, from the 
Wenham prism, while, to obtain the best possible 
definition, the back lens of the objective cannot ap- 
proach the prism too closely ; therefore in making 
choice between the two forms of mounting the 
paraboloid, the student must consider whether con- 
venience with a trifling loss of definition will suit 
him, or whether the most perfeCt definition is re- 
quired with the inconvenience attending the ordinary 
form. 
An addition to the parabolic lieberkuhn, consisting 
of a small plane mirror (Fig. 24, m) inclined at 
an angle of 450, and so fitted that it can be 
brought into the proper position for reflecting light 
vertically upon the objeCt by means of the milled 
head, w, has been made by Messrs. Beck, at the 
suggestion of Mr. Sorby, who required this contrivance 
for viewirfg the polished surfaces of specimens 
of iron and steel. When light is directed obliquely 
upon a highly polished surface, it is reflected at an 
angle equal to the angle of incidence, none of it enters 
the microscope, and the surface appears intensely 
black; but when illuminated vertically, all its 
structural peculiarities are at once brought into view. 102 
MICROSCOPICAL MANIPULATION. 
For such researches the plane speculum is in- 
dispensable, and its adaptation in no way interferes 
with the ordinary use of the paraboloid. 
The late Richard Beck made a small paraboloid, 
adapted for use with the 4-ioth objective. This the 
author had an opportunity of working with, and, 
although only in experimental condition, was much 
pleased with its performance. It was returned after 
trial, but has not at present been produced for sale 
by Messrs. Beck, probably on account of its value 
not being generally known. From its very short 
focus, it requires much more careful fitting to the 
objective it is intended to be used with than the 
larger paraboloid ; but when carefully executed, it 
works quite as well with its own objeCt-glass as the 
one above mentioned with the lower powers. The 
author, however, possesses one which was made for 
him by Mr. Bailey, of 162, Fenchurch Street, which 
performs admirably, and is executed in this optician’s 
usual careful manner. The parabolic lieberkuhn is 
of great value with | inch and 4-ioth objectives, as 
these glasses allow but little space between the front 
glass and the objeCt for illumination with the con- 
densing lens. 
A very efficient illuminator was, until recently, 
much in use; it is known as the side reflector, and 
consists of an oblong silvered mirror of spherical 
figure. It has ball-and-socket and sliding adjust- 
ments, and is attached either to the stand of the 
microscope or else is mounted upon an independent 
support; it is placed on one side of the instrument, ILLUMINATION WITH HIGH POWERS. 
103 
and the light directed upon it from the opposite side. 
The speculum is then adjusted until the objeCt is 
properly illuminated. It has, however, been super- 
seded by the parabolic lieberkuhn before described. 
A means of illumination adapted for use with 
objectives of high power, in which the space above 
the objeCt is too small to admit of light being thrown 
upon it by any of the apparatus just described, has 
been contrived by Professor H. L. Smith, of Kenyon 
College, Ohio. He uses the objeCt-glass itself as a 
condenser. A pencil of light is admitted through an 
aperture in the side of an adapter screwed on to the 
body of the microscope, which contains a small 
silvered mirror with suitable adjustments for re- 
flecting the pencil downwards through the objeCt- 
glass which is attached below the adapter. This 
apparatus was sent to Mr. E. G. Lobb, of the Royal 
Microscopical Society, and exhibited at the meeting 
in January, 1866. The instrument was placed in the 
hands of Messrs. R. and J. Beck and Messrs. Powell and 
Lealand, who each produced an improved modifica- 
tion. For the silvered mirror of Professor Smith they 
both substituted an unsilvered glass surface ; that of 
Messrs. Powell and Lealand was a piece of parallel 
surfaced glass, fixed at an angle of 450; Messrs. Beck 
used a disc of thin cover glass (Fig. 25, b), and allowed 
the angle to be altered at pleasure by means of a 
milled head, /, passing through the aperture, e. The 
light of a lamp is directed through the hole, a, in the 
adapter, and forms an image of the flame on the 
objeCt when the objeCt-glass is in focus. The lamp 104 
MICROSCOPICAL MANIPULATION. 
should be placed at a distance of about eight inches 
from the instrument; sometimes a condensing lens 
may be placed between the lamp and microscope with 
advantage. The manipulation with the instruments of 
Fig. 25. 
both makers is precisely similar. The objects to be 
viewed with this illuminator should be uncovered, 
otherwise the cover reflects nearly the whole of the 
light, and scarcely any falls upon the object; some 
light is also lost by reflection on its passage upwards 
through the oblique unsilvered mirror. The impossi- 
bility of obtaining a satisfactory' view of a covered 
object will most probably prevent this instrument from 
coming into very general use, although it affords 
valuable information to those who will take the 
trouble to master the difficulties attending its use. S UB-STAGE ILL UMINA TORS. 
The second class of illuminators, those which are 
placed beneath the stage, are also very numerous. 
The most familiar is the mirror, which forms a part 
of every microscope. A great variety of illumination 
may be obtained from the mirror alone, if properly 
mounted so that it may be turned considerably aside. 
The mirror of many microscopes is now placed on a 
double-jointed arm, which permits very oblique illu- 
mination to be obtained. In order to understand 
practically the difference caused by the position of 
the mirror, the student is recommended to examine 
a diatom of moderate difficulty, such as Pleurosigma 
angulatum, with a good J or £ objective, which should 
be accurately adjusted for the thickness of the cover 
glass, and used with a deep eye-piece. It will 
be found, when the light is central, that none of the 
usual markings will be visible ; but when the illu- 
minating pencil falls very obliquely, the apparent 
cross lines (?) will come into view. With the better 
class of microscopes, the mirror is usually made 
double, one side concave and the other plane ; the 
plane mirror is used for reflecting daylight when 
the greatest intensity is not required, and for use 
with the achromatic condenser and parabolic 
reflector (Wenham’s), and in all other cases when 
parallel rays are needed. The concave mirror acts 
in some degree as a condenser, and is to be used 
with lamp light or when it is required to make 
daylight more intense. The diaphragm plate is used 
in combination with the mirror to regulate the angle 
of the pencil; this can, however, be done with 106 
MICROSCOPICAL MANIPULATION. 
much greater nicety by employing the graduating 
diaphragm of Mr. Collins (Fig. 26) or the very beau- 
Fig. 26. 
tiful iris diaphragm of Messrs. Beck (Fig. 27), both 
of which allow the aperture under the stage to be 
gradually diminished or enlarged without the interval 
Fig. 27. 
of darkness which occurs during the shifting of the 
ordinary wheel of diaphragms. 
A very useful illumination, resembling the light of 
a white cloud, may be obtained by placing a piece 
of white paper over the mirror, and concentrating 
the light of a lamp upon it by means of the con- 
densing lens. The soft white light so produced 
is extremely pleasant to use, and suits delicate and DARK FIELD ILLUMINATION. 
107 
transparent objects viewed with the binocular, and 
will be found of more general service than the full 
light of the mirror, which, with the double body, 
often produces a most disagreeable glare, which only 
obscures and confuses instead of defining. 
The mirror affords the simplest means of obtaining 
what is known as dark field illumination, for which 
we are indebted to the Rev. J. B. Reade, F.R.S., 
President of the Royal Microscopical Society. His 
original contrivance consisted of an ordinary con- 
densing lens, so placed with respect to the lamp and 
the stage, that it transmitted a pencil of such obliquity 
that none of it entered the object-glass, so that the 
object alone was lighted, while the field remained 
dark. The same effedt can be produced with the 
mirror when turned very much aside, and only a low 
power, such as an inch or § objedtive, employed. 
It is a most valuable mode of illumination, and one 
which the author employs very extensively, as inde- 
pendently of the beautiful effedts produced by it when 
skilfully managed, it enables structural peculiarities 
to be observed which are not readily demonstrated 
by other means. 
The black field is still more perfectly obtained by 
the use of the spotted lens (Fig. 28). This consists 
of a small bull’s-eye, mounted so that it will slide up 
and down in a fitting beneath the stage to allow of 
focussing; on the centre of the plane side of the lens 
is placed an opaque black stop, allowing only the 
marginal rays to pass. If an object is placed in the 
focus of the hollow cone of light so transmitted, it 108 
MICROSCOPICAL MANIPULATION. 
will be found, if possessing sufficient opacity, to dis- 
perse a portion of the light, to shine brilliantly, 
and become apparently self-luminous; while, as 
will be seen by the diagram, the rays, after 
Fig. 28. 
crossing at the focus, diverge, and do not enter the 
obje<5t-glass, and so leave the field more or less black. 
The effedt is very much that of causing a semitrans- 
parent objedt to appear like an opaque one illumi- 
nated by refledted light. Diatomacece, living aquatic 
animals and plants, the skeletons of the Polyzoa, 
insedt preparations when not too thin and trans- 
parent, and many other objedts, are displayed to the 
greatest advantage by means of black field illumi- 
nation. BLACK FIELD ILLUMINATION. 
Black field illumination is obtained most perfectly 
by means of a paraboloid placed beneath the stage. 
Mr. Wenham’s first contrivance consisted of a silvered 
parabolic cup, open at the apex, which reflected 
parallel rays very obliquely, the access of direCt light 
being prevented by a stop placed in a proper position. 
The performance of this illuminator was perfect, the 
Fig. 29. 
only objection to it being that it was rather difficult 
to keep the reflecting surface bright. This has been 
remedied by constructing the paraboloid of glass, the 
illuminator now in use being a solid cast in glass of 
the original silvered speculum (Fig. 29). It reflects 
light quite as well as if it were silvered, owing to the MICROSCOPICAL MANIPULATION. 
law of internal reflection. When a ray of light 
passing through glass falls upon a surface the angle 
of which is not less than 38° 41', it cannot pass out 
of the glass into air, but is totally reflected (Fig. 30). 
Fig. 30. 
The ray, a, entering the triangular prism at b, 
passes through to c, where not being able to pass 
out into air, it is reflected as if the surface at c were 
silvered, only far more perfectly, the reflection being 
total. This principle is made extensive use of in the 
construction of optical apparatus, a reflecting prism 
being always preferable when it can be used, on 
account of its wasting less light than a metallic 
speculum or silvered glass mirror. If a tumbler is 
filled with water, and the surface of the water looked 
at upwards through the side of the glass, it will be 
found that the surface of the water will reflect light 
more brilliantly than the best mirror. The glass para- 
boloid, although unsilvered, and appearing at first 
sight to be a lens rather than a mirror, is nevertheless 
a far more perfect refleCtor than its metallic 
predecessor. Parallel rays (Fig. 29, r, r', r"), falling 
upon the plane surface, c, at right angles, enter the 
glass paraboloid without refraction, and, not being BLACK FIELD ILLUMINATION. 
able to pass out through its curved sides, A, B, are 
reflected to the focus, f, and diverge from thence 
at an angle so great that none of them enter the 
objeCt-glass. The apex is ground out to a 
spherical figure, so that the pencil also emerges 
without refraction. The centre stop, s, is attached 
to a wire passing through a hole drilled in the 
block of glass, and furnishes a means of adjustment, 
so that the least oblique rays can be cut off if required, 
which is necessary when the paraboloid is used with 
the higher powers, the stop in that case being pushed 
up as far as it will go. A well constructed paraboloid 
is capable of giving a black field with a 5th of ioo° of 
aperture. The paraboloid is superior to the spotted 
lens on account of its freedom from chromatic and 
spherical aberration, and also from its larger angle, 
which is about 127°, while the angle of the spotted 
lens is a little under go0. The spotted lens, however, 
can be used with advantage in examining objects 
which have a degree of transparency which would 
prevent their perfect observation with the paraboloid, 
this latter illuminator being better suited for the 
examination of semi-opaque or translucent tissues. 
Black field illumination, like that by reflected light, 
is perhaps more free from the deceptive appearances 
which so frequently lead to errors of interpretation, 
and one or both of these modes of lighting should 
always be employed when practicable. As the 
amount of light stopped by the object depends in 
some degree upon its opacity, the relative density of 
the various parts may be fairly judged of by their 112 
MICROSCOPICAL MANIPULA TION. 
respective brilliancy. Dark field illuminators aid 
very much in the production of stereoscopic effeCt, 
no methods of illumination, save those by reflected 
light, giving such correCt views of the relative 
position in depth of the various parts of an objeCt, 
with an advantage peculiar to themselves of 
revealing internal structure to a great extent. 
In the old microscopes, constructed before the in- 
troduction of the achromatic principle, the want of 
light was very evident when any but the lowest 
powers were used ; this soon led to the employment 
of some means of increasing the intensity of the 
illumination. The usual plan was to place a lens 
beneath the stage, which aCted like a burning-glass, 
and allowed the light to be increased to almost any 
extent. When the microscopic objeCt-glass was 
freed from the chromatic and spherical aberrations, 
the increase of illumination following the enlarge- 
ment of its angle of aperture for a time satisfied 
observers ; soon, however, a larger amount of light 
was, in some cases, found desirable, and it was usual 
to employ one of the objeCt-glasses (generally the 
next lowest to the one in use) to concentrate the 
light upon the objeCt. This simple contrivance is 
very effective when nothing else but greater intensity 
is needed, and a foreign i objeCt-glass will make a 
very good combination for this purpose when suitably 
mounted. For the next improvement, we are in- 
debted to Mr. Gillett, who added a series of 
diaphragms ; these, in the most improved form, 
comprised some having marginal as well as central THE CONDENSER. 
apertures, as it was soon found that the direction of 
the light had a very important influence. The con- 
denser has since undergone many improvements, 
each of the three leading opticians modifying it to 
suit the requirements of their respective instruments. 
It consists, as now made, essentially of a combina- 
tion of achromatic lenses closely resembling an 
objeCt-glass, and fitted with one or more diaphragm 
plates, which, either separately or in combination, 
give perfect control over the amount of light admitted 
and its direction; the details of construction vary 
somewhat in different condensers. This is mounted 
beneath the stage of the microscope with suitable 
adjustments for focussing, and also for placing it 
truly in the axis of the instrument, or centering. As 
the instrument is difficult for the beginner to use, it 
is well to give a few directions. 
The first care will be to centre the condenser, as 
the spot of concentrated light is extremely small, and, 
should the adjustment not be accurately made, the 
field of the microscope will be only partially, or not at 
all, illuminated. The simplest way of centering is to 
screw on a very low power, and view the setting of 
the top lens of the condenser; it will then be readily 
seen whether it occupies the centre of the field, and, 
should it not do so, the requisite traversing screws 
are moved until it is found to be accurately in the 
centre. Or the image of a lamp-flame may be formed 
with the condenser, and viewed with a moderately- 
low power, and the screws moved until the image 
occupies the centre of the field. The focus is then 114 
MICROSCOPICAL MANIPULATION. 
to be adjusted by moving the milled head connected 
with the proper rack, and a suitable diaphragm 
turned into place. When the achromatic condenser 
is used, the flat mirror is to be employed, and if a 
lamp is the source of light, the rays must be rendered 
parallel, as before mentioned. Some observers use a 
prism in the place of a mirror, as it reflects more light, 
and of a purer quality, than silvered glass ; this gives 
a reflection from its upper as well as its silvered lower 
surface, which somewhat interferes with the perfect 
illumination of delicate objects. Although the most 
intense light is obtained when the condenser is accu- 
rately in focus, it is sometimes preferable to use 
the condenser either a little within or beyond 
the focus ; for this, as well as the choice of dia- 
phragms, no particular directions can be given, as 
much depends upon the nature of the objeCt to be 
viewed, construction of the instrument, and many 
other circumstances. A little practice, with the help, 
if attainable, of an experienced microscopist, will be 
found the best means of mastering the use of this 
rather difficult instrument. It is an instructive 
exercise to place a suitable objeCt upon the stage— 
a Diatom, for instance—and notice the changes in 
appearance produced by altering the focus of the 
condenser and using different diaphragms ; so varied 
are the kinds of marking produced on some of the 
Diatomacece by changes of illumination, that it would 
hardly be believed that the objeCt was the same. It is 
now tolerably certain that the striae, or lines, whether 
single or crossed, and the dots, seen on some of these THE WEBSTER CONDENSER. 
115 
objeCts, are non-existent, being merely the optical 
rendering of closely-packed transparent hemispheres. 
These were observed some years ago by Mr. 
Wenham, with a i-5oth objective of his own con- 
struction, and quite recently by a new and compara- 
tively simple means of illumination discovered by 
the Rev. J. B. Reade, and described by him in the 
Monthly Microscopical Journal (1869, vol. ii., p. 5). 
The instrument used is an equilateral triangular 
prism, which is so adjusted as to refleCt an oblique 
beam of parallel rays. With this illumination, the 
hemispheres on Pleurosigma formosum may be seen 
with a power as low as a f, provided the angle of 
aperture be sufficient. This simple illuminator may 
probably be of great value for other purposes, besides 
viewing the surfaces of Diatomacecz ; at present, how- 
ever, it has been so short a time in use, that its full 
capabilities have not been tested. 
More recently, a condenser, constructed on a 
different principle, has been introduced, the optical 
portion closely resembling the Kellner eye-piece, in- 
stead of following the usual pattern, which is derived 
from the objeCt-glass. This condenser (Fig. 31), now 
well-known as the “Webster,” is a most efficient 
instrument, and, from the simplicity of its construc- 
tion, is capable of being adapted with advantage to 
small microscopes. The amount of light given by it 
is considerable, so great that with the full aperture it 
is almost more than the eye can bear; this excess of 
light, if it can be considered as a fault, is certainly a 
good one, as it permits a very extensive use to be made 116 
MICROSCOPICAL MANIPULATION. 
of diaphragms. The graduating diaphragm (Fig. 32) 
can be applied to the Webster condenser with the 
greatest advantage, and its effedt is much more 
Fig. 31. 
marked than when merely used below the stage to 
control the illuminating pencil from the mirror. 
Fig. 32. 
The wheel above the graduating diaphragm consists 
of a series of central and lateral stops, by the use of THE WEBSTER CONDENSER. 
117 
which a great variety of oblique dark and field illu- 
mination can be obtained; the latter far more 
efficiently than by the use of the ordinary spotted 
lens. Recently, a revolving carrier for additional 
diaphragms has been added to this condenser. It 
consists of a tube sliding into the lower part, 
provided at its upper extremity with a con- 
trivance for holding a disc of card or thin brass, 
in which one or more apertures may be cut. By 
turning the diaphragm-holder round, the oblique pencil 
may be directed from any azimuth, and the effeft on 
such objects as the Diatomacea is very marked indeed, 
the strias appearing and disappearing as the aperture is 
moved to, or away from, the proper angle for bring- 
ing them out. This contrivance also allows the 
observer to try any forms of stop he may consider 
advantageous, as they may be quickly cut out of a 
piece of blackened card (B. W. Richardson, Quarterly 
Microscopical Journal, vol. vi., pp. io, 86). The long 
focus and large field of the “Webster” render it par- 
ticularly useful for the general purposes of the 
student, as it will work into some depth of water, 
and can be used for illuminating the interior of the 
troughs so frequently employed in observing living 
aquatic animals and plants. Although surpassed by 
the more costly instruments for the most refined 
description of illumination, it possesses merits pecu- 
liarly its own, and no single piece of apparatus can 
be made to perform so great a variety of offices as 
this very useful condenser. 
The most useful forms of illuminating apparatus MICROSCOPICAL MANIPULATION. 
have now been described ; there are many others, 
chiefly meant for special purposes—they wrill be 
found in the works of Quekett and Carpenter, and 
the pages of the Microscopical Quarterly and Monthly 
Journals, to which the student is referred for descrip- 
tions and figures. 119 
CHAPTER VI. 
IN the modes of illumination hitherto described, 
the light has been made use of in exaCtly the same 
condition in which it was received from its source, 
whether from the sun or a lamp. All that instru- 
ments have been required to do has been either to 
alter its direction or, by concentration, to increase 
its intensity. It is now proposed to explain a method 
of conducting microscopical investigations in which 
the properties of the light have undergone such 
changes as to produce effeCts totally different from 
those of ordinary illumination, and with the result 
of giving greater insight into the nature of certain 
structures than could be obtained by other means. 
The light, in the condition now to be described, is 
commonly known as Polarised light. 
With a view to simplify the matter contained in 
the foregoing chapters, no more has been said about 
the nature and properties of light than was abso- 
lutely necessary to enable the aCtion of the apparatus 120 
MICROSCOPICAL MANIPULATION. 
described from time to time to be tolerably well 
understood. And, although, in the present chapter, 
far more notice must be taken of the subjedt, it is 
by no means intended to give an exhaustive account 
of the phenomena of polarised light. Space can 
only be afforded for such an outline as will enable 
the student to use his apparatus, and observe intelli- 
gently. For details, reference must be made to 
works treating more fully on the subject—such as 
the chapters on Optics in Mr. Brooke’s “Manual of 
Natural Philosophy,” and the various authorities 
there referred to. 
Light, in common with the other forces of nature— 
heat, electricity in its various forms, dynamic 
force, &c.,—proceeds from its source in a series of 
undulations or waves, which may be illustrated in 
a rough manner by throwing a stone into a pond, 
when the waves will be seen to spread themselves 
concentrically from the source of motion. 
For convenience of explanation, a ray of light in 
its ordinary condition may be represented in ideal sec- 
tion b)' a circle (Fig. 33,1), and undulations supposed 
to take place in two planes at right angles to each 
other (c, d and N, s). By means presently to be 
described, these two sets of waves can be separated, 
as at 2, c, d and 3, N, s. The ray of light, instead of 
having the same properties on every side, will be found 
to have acquired some qualities peculiar to the state in 
which it now is, and which may be named the pro- 
perties of sides. For instance, 2 will exhibit cer- 
tain phenomena in the direction c, d which do not INTERFERENCE OF WAVES. 
121 
exist when it is examined in other directions. The 
same is the case with the other half of the ray (3), 
which exhibits similar phenomena in the direction n,s. 
As these properties somewhat resembled those of 
the poles of a magnet, the term polarised light was 
used to distinguish light so modified, and, although 
perhaps not the best name that could have been 
given, has still been retained. 
As the phenomena of interference will be frequently 
mentioned, it will be desirable to state what they are. 
The sensation affeCting the optic nerve which is 
Fig. 33. 
known as light is caused by the undulations before 
spoken of—light being represented by motion, dark- 
ness by rest. 
Should two waves start together from the same 
place, they would increase each other’s intensity; 
the result would be a wave of double height—a 
matter easy of comprehension, if water be con- 
sidered as the medium ; with the waves of air pro- 
ducing sound, the result would be a louder sound; 
and, with light, an illumination of double intensity. 122 
MICROSCOPICAL MANIPULATION. 
Should, however, one wave start before the other by 
the length of half a wave, the effedt would be that 
the crest of one wave would occupy the position of 
the hollow of the other, and so fill it up, producing 
a dead level. The result would be, with water, 
calm; with air, silence; with light, darkness. 
This is known to be the case, in some instances, 
where the streams from two channels meet in the 
manner just mentioned: perfectly smooth water is 
produced, although, before meeting, the surface of 
both may be violently agitated. 
Should the waves of light start at an interval of 
less than half a wave, they will, by interference, be 
broken up into smaller waves, the magnitude of 
which depends upon the distance one wave has had 
the start of the other. These small waves produce 
coloured light, the red wave being the longest, and 
the violet the shortest. Mr. Woodward gives the 
following as the lengths of the waves of the various 
coloured rays of the spedtrum :—Red, 266 ; orange, 
240; yellow, 227 ; green, 211; blue, 196; indigo, 185 ; 
violet, 167. The figures represent the numerators 
of fractions, having as a common denominator the 
ten-millionth of an inch. 
These coloured waves may be produced in various 
ways ; for instance, by very thin plates of transparent 
substances, such as mica, films of oil or varnish 
floating on water, and films of air enclosed between 
transparent solid surfaces; which, by causing a 
slight difference in the distance of the starting points 
of the two series of waves of white light reflected NEWTON'S RINGS. 
123 
from the upper and lower surfaces of the film, set 
up interference, and break up the waves of white 
light into smaller coloured ones. The films of varnish 
were very ingeniously taken up from the surface 
of water on enamelled cards, by Mr. De la Rue, 
giving them a beautiful iridescent appearance. 
Other examples may be found in the feathers of 
certain birds, as humming birds, peacocks, &c., 
which possess a metallic lustre produced in the same 
manner. A minutely grooved surface will also 
produce similar efjedts ; for example, mother-of-pearl, 
which consists of a series of thin plates of shell, 
separated by folds of membrane, producing a grooved 
structure ; also in the finely-ruled gold ornaments 
known as “ Barton’s buttons,” and the minute 
specimens of ruling on glass by Nobert, all of which 
produce brilliant metallic tints by the interference 
of the two waves reflected, one from the surface, and 
the other from the bottom of the groove. 
If a convex lens of extremely shallow curvature be 
placed upon a plane glass surface, and an arrange- 
ment be provided for exercising delicate and uniform 
compression, a series of circular concentric coloured 
bands will be seen; these are known as “Newton’s 
rings,” and are caused, as before, by the interference 
of the reflections from the film of air contained 
between the lenses; and as, from the curvature of 
the lens, the film is of a thickness increasing from 
the centre to the circumference, a variety of tints 
are formed at every change of thickness, the rings 
consisting alternately of groups of colour and dark 124 
MICROSCOPICAL MANIPULATION. 
bands, the latter being the places where total inter- 
ference takes place, and darkness or rest is the con- 
sequence. These dark spaces are much better seen 
when the apparatus is viewed by a monochromatic 
light, such as that produced by the flame of a large 
spirit-lamp the wick of which has been sprinkled 
with common table-salt. Not only will the dark 
bands be sharper and more intense, but they will 
also be considerably increased in number. These 
rings may often be seen when plane glass surfaces 
are unequally compressed ; for example, a piece of 
thin cover-glass pressed on a slide with a stick, and 
sometimes between the thick plate and glass negative 
in a photographic printing frame. 
The undulatory motion of light would seem to be 
expressed with considerable clearness in the first 
chapter of Genesis when read in the original Hebrew, 
which, in common with the other languages of the 
same family, is remarkable for the numerous inflexions 
of its verb, which gives it a delicacy and precision of 
expression unattainable in Western languages. The 
first verse concludes:—“ And the Spirit of God moved 
upon the face of the waters.” This sentence im- 
mediately precedes the command that light, which 
may here be taken in its largest sense, including 
electricity and the other forces, should exist. The 
Hebrew word translated “ moved ” is more accurately 
expressed by fluttered; the same inflexion of the verb 
is used in this sense in the only other place in which 
it occurs, viz., Deuteronomy xxxii., n., where it refers 
to the fluttering of an eagle over its nest. It is POLARISATION OF LIGHT. 
125 
certainly a very remarkable expression, and the 
author believes that its bearing on the subjedt of 
light has hitherto escaped notice. The view that the 
word “ light ” includes the other forces, and which 
we have every reason to believe are but different 
manifestations of them, is supported by the fadt, 
that sources of light proper, or luminaries, are not 
mentioned until the fourteenth verse, while the at- 
mosphere or “ firmament ” of the English version, 
land, and water, and vegetable life, were all in 
existence, and under the influence of these mysterious 
powers of nature, respedtingwhich the undiscovered 
and unknown probably far exceeds the little that 
science has at present made us acquainted with. 
Light may be polarised in several ways. If a ray of 
light falls upon glass at an angle of 56° 45', one-half 
(Fig. 34) will be transmitted, the other half refledted; 
and, if, instead of a single plate, about ten sheets 
of thin window-glass be employed, the result will 
be much more perfedt. The refledtion, whether 
one or more plates be used, will be much improved 
by either coating the back with black-varnish, or 
placing in contadt with it a piece of black cloth or 
velvet, which will absorb the transmitted portion of 
the ray. If the light so refledted be examined by 
another glass mirror, placed at the same angle, and 
so mounted that it can be moved horizontally in a 
circular diredtion, it will be found that, in some 
positions, the light will be refledted, while, at others, 
it will pass through, or be absorbed if the back is 
blackened. These intervals of refledtion and transmis- 126 
MICROSCOPICAL MANIPULATION. 
sion occur alternately at every quarter revolution of 
the upper mirror or analyser, corresponding with the 
points in Fig. 33, 1, marked c, d and n, s. 
If a ray of light be passed through a crystal of Ice- 
land spar, one portion will be refradted according to 
Fig. 34. 
the usual law (ante, p. 5); the other half will be refradted 
in a different direction. And if these two rays of light 
be examined with an analyser, they will be found, as 
in the case of the reflected light, to have acquired 
the property of sides, or to be polarised. The ray 
refradted in the common way is known as the or- 
dinary ray; the other, which is polarised in a plane 
at right angles to it, is termed the extraordinary ray. 
If a crystal of Iceland spar be placed on a sheet of 
paper having a black spot on it, the double refradtion NICOL'S PRISM AND TOURMALINE. 
127 
will cause the formation of two images of the spot 
or other device drawn on the paper. 
By an ingenious process, invented by Mr. Nicol, a 
crystal of Iceland spar is divided in the direction 
indicated in Fig. 35, and joined together again with 
Fig. 35. 
Canada balsam. This causes one of the rays to be 
so much refradted that it is thrown altogether out of 
view, and only one polarised ray is transmitted. This 
contrivance is known as the single image or Nicol 
prism, and is the means of polarisation most generally 
adopted for microscopical purposes. 
Polarisation may also be effected by the use of 
thin slices of a mineral known as tourmaline. This 
mineral, when cut into thin plates parallel to the axis 
of the crystal, allows only the undulations in one 
plane to pass, the other being stopped. The cause of 
this adtion is, as yet, not understood. If two plates of 
tourmaline are superposed, and held before a strong 
light, it will be found that the light is alternately 
transmitted and stopped at every go0, when one of 
the plates is rotated. 
The same effeft is produced, in a much greater 
degree, by using a pair of crystals of sulphate of iodo- 
quinine, more commonly known as Herapathite, 
from its discoverer, the late Dr. William Bird Hera- 
path. This salt is prepared by a tedious and com- 128 
MICROSCOPICAL MANIPULATION. 
plicated process, and described in a communication 
by Dr. Herapath to the Royal Society, and quoted 
in many microscopical works (“Micrographic Dic- 
tionary,” second edition, p. 590). The obtaining 
of large regular crystals fit for polariscopes is a 
matter of great difficulty; and, unless the student 
is very expert in chemical manipulation, he is recom- 
mended not to attempt it. Small specimens fit for 
Fig. 36. 
microscopical examination may, however, easily be 
made. This salt is the most powerful polarising 
agent known. If two crystals are superposed with 
their axes parallel (Fig. 36, a), light is readily trans- 
mitted; but, if the axes are crossed, as in b, the 
parts covering each other become perfectly opaque 
to transmitted light. This can easily be seen in a 
slide of the crystals mounted as a microscopical 
objeCt, as some of the crystals are sure to be in this 
position. 
The sky possesses the power of reflecting polarised THE SELENITE FILM. 
light. If the observer stands with one shoulder 
directed to the sun, so that he faces a point 90° from 
it, and looks at a white cloud through a Nicol prism, 
he will find that the light reflected from the cloud 
is polarised, and that, as the prism is rotated, the 
cloud will alternately appear as a white cloud on a 
dark ground and a dark cloud on a light ground. 
129 
The effects here described may readily be seen 
without the special apparatus of mirrors, &c., by 
any one who has a microscope fitted with the usual 
polarising apparatus of two Nicol prisms. If the 
larger one, the polariser, be put in its place below 
the stage, and the mirror so arranged that the light 
of a lamp or daylight be directed through it, it will 
be found, upon rotating the prism in its fitting, that 
no change is apparent, as the light, although polar- 
ised, is transmitted in every position of the prism. 
If the small prism, or analyser, be now put in its 
place, either over the objedt-glass or, better still, 
over the eye-piece, it will be found that the alternate 
transmissions and stoppages of light take place. 
If a film of selenite be now placed on the stage of 
the instrument, it will be found that the light will be 
coloured ; and, when one of the prisms is rotated 90°, 
the colour will change to the complementary tint. 
For instance, a film that transmits red light in one 
position of the prisms will transmit a green of such 
quality as to produce white light, were the two 
mixed. Blue would produce orange every quarter 
revolution; and so on through the other tints of the 
spedtrum. Similar effedts are produced by using 130 
MICROSCOPICAL MANIPULATION. 
films of mica, and all crystals possessing the property 
of double refraction. 
To understand these changes of colour, it will be 
necessary to describe the direction of the axes of a 
crystal of selenite, which is represented in Fig. 37, 
Fig. 37. 
a, d and c, b being the position of the depolarising 
axes, and e, f and c, h that of the optic axes. To 
understand the powers of these regions of the crystal, 
it will be necessary to try another experiment, which, 
although more advantageously shown with a large 
polariscope, can be done sufficiently well under the 
microscope. Let the film of selenite be so mounted 
as to be capable of rotation. If the stage of the 
microscope is capable of concentric rotation, no 
further contrivance is necessary. If the prisms now 
be arranged for the production of colour, and the 
selenite slowly rotated, it will be observed that 
the colour gradually disappears. On continuing the 
rotation, it increases, and regains its intensity. If 
the amount of rotation is noticed, it will be found 
that the disappearances coincide with the position 
of the optic axes, e, f and g, h, while the greatest THE SELENITE FILM. 
131 
intensity of colour is produced when th'e plane of 
polarisation passes through the depolarising axes, 
a, d and b, c. If the analyser be removed, no colours 
are to be seen ; it is therefore evident that the analyser 
plays some important part in the production of these 
colours. 
The selenite, being a doubly-refraCting crystal, 
causes the ray of polarised light to be divided into 
two, which are, as usual, polarised in perpendicular 
planes, and, reaching the eye together, no colour is 
produced; but, if the analyser is added to the com- 
bination, the colourless image is broken up into two 
coloured ones, one only of which reaches the eye. 
If, instead of the Nicol prism, a contrivance known 
as the “ double-image prism ” be used, which will 
transmit both rays, but in a separate condition, the 
two images of complementary colours will be seen 
at once, and, if, by a suitable contrivance, they be 
made partially to overlap, the part where they join 
will be white, produced by the union of the two com- 
plementary tints. 
The position of the optic axes may be easily ob- 
served in the corpuscles of starch and other polari- 
scope objects which produce the well-known black 
cross, which indicates in a very marked manner the 
situation of these axes of no polarisation. 
The apparatus employed for the examination of 
microscopical objects by means of polarised light 
consists of a polariser, analyser, and retarding plate. 
The polariser is generally a Nicol prism, mounted 
so that it may be conveniently rotated ; this is 132 
attached, by a suitable fitting, either beneath the 
stage, or, in large microscopes, to the sub-stage 
movement. 
MICROSCOPICAL MANIPULA TION. 
The analyser varies, being, according to circum- 
stances, a Nicol prism, tourmaline, or Herapathite. 
The Nicol prism is the form of analyser generally 
used, and can be placed either over the eye-piece or 
within the body of the microscope above the objedt- 
glass; in the first position it has the advantages of 
being easily rotated, and of not interfering seriously 
with the definition of the magnified image ; 
but, on the other hand, when used with any eye- 
pieces but those of the lowest power, it cuts off the 
margin of the field and reduces it to an injurious 
extent ; this is owing to the prism, by its thickness, 
causing the removal of the eye to some distance 
from the eye-glass, although the Nicol prism, when 
intended for use as an analyser, is generally made as 
short as is consistent with efficient adtion. When 
the prism is placed within the body, it does not cut 
off any portion of the field, but the interposition of a 
dense substance, like Iceland spar, impairs the 
corredtions and consequently the definition of the 
objedt-glass, and also causes some loss of light. It 
is much to be regretted that in many of the smaller 
microscopes no other provision is made for the 
placing of the analysing prism. When the binocular 
is used with polarised light, the analyser can be 
placed in no other position, and it is usually mounted 
in a short adapter so contrived that the prism can be 
easily rotated. It is well to have the means of using POLARISING CRYSTALS. 
the analyser in both positions, that choice can be 
made of that best adapted to the kind of observation 
in progress; if very perfedt definition is of less 
consequence than a field of full dimensions, as in 
viewing such objedts as crystals, in which very little 
detail is to be seen, then the prism in the body may 
be employed with advantage ; but should the forma- 
tion of an image very perfedt in its details be re- 
quired, then the prism must be placed over the 
eye-piece. 
Tourmaline, when it can be obtained of sufficiently 
pale colour, makes a good analyser, from its thin- 
ness it can be used over deep eye-pieces without 
cutting off the field; good stones are, however, 
scarce, and consequently expensive, as many light 
coloured specimens do not polarise well. The 
tourmaline is mounted in a brass cap similar to the 
one placed on the eye-piece, which is to be removed 
and the analyser substituted. Crystals of Herapath- 
ite polarise more powerfully, and are much lighter 
in colour than the palest specimens of tourmaline, 
and when they can be procured make very perfedt 
analysers; they are extremely thin, and do not inter- 
fere at all with definition, and are to be preferred in 
all delicate investigations. Where, however, total 
freedom from colour is a necessity, the Nicol prism, 
notwithstanding its other disadvantages, must be 
used. 
The retarding plate or selenite film is commonly 
mounted, either on card, like an ordinary slide, or else 
in a brass plate, with a ledge to keep the objedt from 134 
MICROSCOPICAL MANIPULATION. 
slipping off; this is a very disadvantageous form, as 
the selenite cannot be rotated, while in a perfedt 
polarising arrangement, every part, objedt included, 
should be capable of rotation. The most convenient 
and useful arrangement of selenites is that devised 
by the late Mr. Darker, in which a series of three 
discs are by combination made to give as many as 
thirteen different tints. In large microscopeshaving 
a substage, these selenites can be mounted so as to 
be capable of rotation either together or separately, 
and also allowing the selenites to be used or not, 
without disturbing the arrangement of the objedt on 
the stage.* These advantages have hitherto been 
confined to large microscopes ; but Mr. Baily has so 
mounted a set of Darker’s selenites for the author 
that they can be placed upon the stage in the 
ordinary manner, and at the same time allow of discs 
being added or withdrawn and rotated, without 
interfering with the objedt ; the thickness of this 
stage plate is no more than is necessary to contain 
the three discs and allow them space to move, and 
all complicated machinery is dispensed with. The 
arrangement of Darker’s system of selenites appears, 
at first sight, somewhat complicated, but is not so 
in reality, and the power of obtaining such a variety 
of coloured backgrounds is a very great advantage. 
The series consists of three discs, marked J, f, and |, 
which figures represent a certain amount of retarding 
* A very perfedt polarising apparatus is described by Mr. J. J. Field, 
Journal of the Quekett Microscopical Club, vol., p. 215 ; also in Monthly 
Microscopical Journal, vol. ii., p. 276. DARKER’S SELENITES. 
influence upon the wave of polarised light and conse- 
quent colour production. Besides the figures just 
mentioned, each disc has engraved upon its mount- 
ing the mark p.a., meaning positive axis ; when the 
selenites are superposed with these marks coincident, 
the effedt is, that the power of one selenite is added 
to that of the other; for example, if the {, and | 
discs are so placed, the power will correspond to the 
sum of the numbers, viz, |, but if the J be turned 
round go° then the i will have only a power of 
I, the crossed position of the I subtracting instead 
of adding its power to the £. The experiments with 
selenite films already described will have prepared 
the student to understand the cause of this; 
it will be recollected that the colour disappeared 
when the selenite passed through one of the optic axes 
of the selenite, provided the position of the prisms 
remained the same. If, instead of moving the disc 
90° it be only moved 450, the effeCt will be to 
neutralise ; instead of giving a negative power the 
result will be the same as if the selenite were with- 
drawn. The following table of the arrangement of 
Darker’s selenites may be useful to those who 
possess the series. The colours vary somewhat in 
different sets, so the table must be made out by each 
observer for his own use.* The colours in the follow- 
ing table are those given by Richard Beck in his 
work on “The Microscope:”— 
* It will be better in making out this table to imitate, as closely as 
possible, the tint produced by the selenites, instead of attempting to 
express it in writing, as the English and, indeed, all other languages 
are very defedtive in words indicating colour. 136 
MICROSCOPICAL MANIPULATION. 
I. i by itself 
Prisms at 
right angles. 
Very light lavender. 
Complementary 
tint. 
Straw colour. 
2. J - i .. 
Darker do. 
Light yellow. 
3. ,f by itself 
Deep blue. 
Light maize. 
4- i + i .. •• 
Very light blue. 
Orange. 
5- * — 1 - i •• 
Lake. 
Emerald green 
6. i - £ .. .. 
Deep blue. 
Bright yellow. 
7- i ~ I + i •• 
Light green. 
Light purple. 
8. | - J • • 
Light plum colour. 
Pea green. 
g. % by itself 
Blue green. 
Salmon. 
10. | + 4 .. .. 
Green yellow. 
Mauve. 
11. 1 + i - i •• 
Pink light. 
Green. 
12. 4 + f .. .. 
Light pink. 
Deep green. 
13. 5 + i + i •• 
Very light red. 
Stone green. 
From the explanation already given of the various 
modes in which light may be polarised, it is evident 
that one-half of the illuminating power is thrown 
away by the use of the polarising prism ; this loss 
becomes a very serious matter when high magnify- 
ing powers are used, and as much valuable work is 
to be done by employing polarised light in combin- 
ation with objectives of 4 inch and shorter focus, it 
becomes necessary to find some means of increasing 
the intensity of the illuminating pencil under such 
circumstances. Polarised light can be concen- 
trated by lenses in the same manner as common 
light, and, after condensation, still retains its pecu- 
liar properties. In large microscopes, provision is 
made for fitting the Nicol prism below the achromatic 
condenser, and a set of Darker's selenites between 
them ; this, with a good tourmaline or Herepathite 
for an analyser, will enable observations to be carried 
on with very high powers, and with nearly the same 
ease as by ordinal illumination. With small ADVANTAGES OF POLARISED LIGHT. 
137 
microscopes, Collins’s Webster condenser, which is 
constructed to carry a Nicol prism, will be found 
a very efficient illuminator, as its lenses are large; 
and as it supplies an excess of light when used with- 
out diaphragms, it will be found very suitable for 
polarising purposes. Its capability of being adapted 
to any instrument is another recommendation. The 
author can speak favourably of its performance with 
his own microscope, in which the unusually short 
distance between the stage and mirror prevents the 
use of any other condenser. The selenites can be 
placed between the Nicol prism and the condenser, 
as usual in microscopes with substage fittings, but 
with small instruments the stage arrangement must 
be used; the focus of the Webster is sufficiently 
long to work through the three selenites without 
material injury to the illumination, when Mr. Bailey’s 
or other thin mounting is employed. 
In carrying on observations by the aid of polarised 
light, it is necessary that the substance to be ex- 
amined should be rendered as transparent as pos- 
sible, by immersion in a suitable medium. Those 
which render objects so transparent that the details 
are almost invisible under ordinary illumination, are 
in general very suitable for polariscope purposes. 
The fafts which polarised light reveals are prin- 
cipally differences of density in tissues, the existence 
of which we should not be aware of without such 
aid. With regard to crystals, the polarifecope at 
once distinguishes those which belong to the cubic 
system, such as common salt, which has no doubly 138 
MICROSCOPICAL MANIPULATION. 
refractive power, and, in common language, does not 
polarise, from those of the other systems, which, 
owing to their double refraction, are among the most 
brilliant of polariscope objects. Not only differences 
of density are made evident by the use of polarised 
light, but also minute variations of thickness when 
the substance examined is possessed of doubly re- 
fractive properties, which are at once shown by a 
difference of colour, which defines the boundaries of 
the thickened portion, although this from the hyaline 
nature of the substance might be perfectly invisible 
when illuminated in the ordinary manner. This is 
very often the case with the secondary deposits in 
vegetable tissues, which are to be seen most -clearly 
when viewed with polarised light and sufficiently 
high powers. Sections of such substances as horn, 
and tissues resembling it, as whalebone, &c., which 
exhibit little or no structure with common light, at 
once display differences of density indicated by 
colour when examined with the polarising micro- 
scope. A very interesting microscopic objeCt is 
made by Mr. Bailey, consisting of a bar of glass, 
which is capable of being pressed by a screw. This, 
when examined by polarised light, exhibits no doubly 
refraCtive appearances so long as the screw does not 
touch it; but when pressure is applied, dark or 
coloured bands make their appearance around the 
point of the screw, extending to a greater or less 
distance, according to the amount of pressure em- 
ployed, showing at once that some change has taken 
place in the molecular arrangement of the glass. DOUBLE REFRACTION OF GLASS. 
Nearly similar bands are to be seen along the sides 
of a recent diamond cut, and around the dot made by 
a slight blow of a steel centre punch, in both cases 
showing that the glass has been subjedted to some 
strain. Opticians, in fitting lenses into cells, are 
careful to avoid pinching the glass, lest double re- 
fradtion should be produced. Coloured bands are 
easily seen in pieces of thick plate-glass which have 
been rapidly cooled. These are best shown in Le- 
count’s polariscope (Fig. 38), in which the polarised 
Fig. 38. 
ray, g, is made to pass twice through the piece of un- 
annealed glass, f, which very much increases the 
intensity of the coloured bands. In this simple in- 
strument the bundle of glass plates, b, adts as a pola- 
riser by refledtion, and at the same time as an 
analyser by refradtion, the light being refledted from 
the bundle through the objedt, and returned through 
it by the mirror, c, the bundle analysing the polarised 
ray, f, on its passage through it to the eye at e. The 
colours produced by varying thicknesses of selenite 
may be seen with the microscope in a small piece, 
roughly split, and mounted in balsam. It will be 
found that there will be a change of colour at every 
difference of thickness. 140 
MICROSCOPICAL MANIPULATION. 
The objeCt should be viewed, in the first instance, 
with the selenite plate, and the appearances noted 
which present themselves when both analyser and 
polariser are rotated. If the construction of the 
microscope permit, the objeCt itself should also be 
rotated. Should no effeCt be produced by the prisms 
alone, a selenite may be used, commencing with one 
of little retarding power, as i of Darker’s series. 
This should be rotated, and also the prisms, before 
going through the various degrees of retardation. 
Substances having a very feeble doubly refractive 
power are much assisted by using a selenite of suitable 
thickness, and details are often better seen with 
selenites of one colour than another. Darker’s 
series offers great facilities for readily obtaining the 
most suitable tint. When a less power than that 
given by the J is required, it can be obtained by 
turning the plate more or less towards one of the 
optic axes, which are situated at 450 from the P. A. 
mark, and the other depolarising axes. Also by 
using plates of mica, thin enough to just let a little 
light into the darkened field. Care should be taken 
to use sufficient light, and employ the condenser 
whenever necessary. As a general rule, with high 
powers, the light cannot be too strong; sometimes 
direCt sunlight may be used with advantage. The 
effeCt of increase of illuminating power with the 
polariscope is not that of dilution, like excess of 
light pouring through a transparent coloured objeCt, 
but as the coloured wave is augmented, intensity of 
colour and stronger definition is the result. THE POLARISCOPE. 
141 
The polarising microscope is a great aid to the 
knowledge of structure, and an examination cannot 
in any way be considered as complete in which this 
most searching mode of investigation has been neg- 
lected. Hitherto, the polariscope has been con- 
sidered rather in the light of a toy than as a valuable 
instrument of research, and it has therefore become 
necessary to devote so much of this elementary 
course of instruction to the application of polarised 
light to microscopical purposes. 142 
CHAPTER VII. 
THE processes of recording microscopical obser- 
vations are scarcely less important than those 
employed in making them. The fadts accumulated by 
the most painstaking observers are of comparatively 
little use unless means are found of preserving 
and communicating them to others. This is parti- 
cularly the case with regard to microscopical studies, 
and, like most natural-history observations, written 
descriptions, however graphic, are scarcely intelligible 
unless accompanied by truthful drawings. The con- 
cluding portion of these papers could, therefore, 
hardly be considered as complete without some 
mention of the way of writing this language of all 
nations, a subjedt which has, with a few exceptions, 
met with but little attention from writers on the 
microscope : probably being very expert themselves, 
the idea prevailed that drawing was as natural an 
acquirement as writing, and that no special diredtions 
were needed. The ledtures which supplied the 
matter for these pages being intended for persons PHOTOGRAPHY. 
wholly unacquainted with the use of the microscope, 
it was then deemed advisable to treat upon the subjedt 
of microscopical drawing and micrometry at greater 
length than usual, dwelling especially on those points 
upon which little information is to be found in books; 
and the author has seen no reason to alter his opinion 
since the delivery of the ledtures, but has rather added 
than withdrawn matter. 
Photography, from its extreme accuracy and 
delicate rendering of details, claims a very high 
place among the resources of microscopical art. 
When the objedt is suitable for its employment, 
the result is not to be equalled by any other means 
of delineation. The conditions, however, which it 
is requisite to comply with in order to obtain a suc- 
cessful micro-photograph somewhat limit the cases 
in which it is available. The objedt to be photo- 
graphed should be very thin and flat, so that the 
whole, or the greater part of it, lies in the same plane, 
that it may all be in focus at once ; the redudtion of 
aperture commonly used by landscape photographers 
to secure focal depth not being pradticable, on 
account of the great loss of light occasioned by the 
use of small diaphragms, which is so great when the 
objedt is much magnified as to render the produdtion 
of an impression on the prepared plate impossible 
with any reasonable amount of exposure. This is a 
very great drawback, as many of the most interesting 
microscopical objedts can scarcely be seen without 
continual alteration of the focal adjustments. The 
colour of the objedt should also be such as is favour- MICROSCOPICAL MANIPULATION. 
able for photographic purposes; the yellow, brown, 
and red tints of many tissues render it impossible to 
obtain any satisfadtory result. The best photo- 
graphs are always those obtained from colourless 
objedts, such as the Diatomacecz, the delicate sculpture 
on the frustules of which are marvellously rendered ; 
as may be seen by examining the photographs by 
Dr. Maddox, to be procured of Mr. How, of Foster 
Lane, at a merely nominal price.* So minutely are 
the details produced that they will, when photo- 
graphed upon glass, bear a considerable amount of 
enlargement by means of the magic-lantern. 
At present only objedts illuminated by transmitted 
light have yielded impressions on the prepared 
plate, the more feeble images obtained from reflected 
light and dark field illumination have failed in pro- 
ducing photographs, and so a large and interesting 
class of objedts is excluded. Possibly future 
improvements may remove this, and some other 
difficulties which at present limit the use of this 
valuable art. The necessity of employing special 
apparatus and of mastering a delicate set of chemical 
processes will, it is to be feared, prevent many micro- 
scopists from availing themselves of photography as a 
means of delineating the objedts .presented to them in 
the course of their studies. 
The practical details of manipulation and the 
bibliography of the subject are treated at considerable 
♦ A fine series of microphotographs by Colonel Woodward, of the 
United States Army Medical Department, is in the possession of the 
Royal Microscopical Society. Also several by Dr. Maddox and 
others. COPYING OBJECTS. 
length in Dr. Beale’s “ How to Work with the Micro- 
scope,” 4th edition, pp. 229 to 279. 
Fortunately, the other processes used in making 
representations of objedts are within reach of the 
majority of microscopists. The apparatus being 
simple and inexpensive, compared with that needed 
for obtaining photographs, and the use of it so 
easily mastered, that, with a little perseverance, 
most persons will be found able to obtain drawings 
really useful, although, perhaps, somewhat wanting 
in finish and delicacy. Even these may be attained 
in some degree by painstaking application; and, 
although the student’s produdtions may not equal 
the work of professional artists, they will be found to 
possess an amount of truth which would most likely 
be wanting in the work of a more accomplished but 
less scientific draughtsman. 
The simplest, but not the easiest, method 
is to make the drawing without instrumental 
aid. Few but those who are expert draughtsmen 
can accomplish this. The difficulty of obtaining 
anything approaching an accurate representation 
can only be understood by those who are familiar 
with the process. The chief obstacle is the impossi- 
bility of seeing objedt and drawing nearly together, 
as in landscape or other sketching, and the conse- 
quent trouble occasioned by frequently losing the 
place, especially during the earlier stages of the out- 
line ; the peculiar view afforded of the objedt depriving 
the observer of those guides used in ordinary 
drawing from nature. The impossibility of making 146 
MICROSCOPICAL MANIPULATION. 
the drawing to scale is another disadvantage, and 
renders it of but little value as a microscopical 
record. For objedts in adtive motion no other mode 
is available, and in such cases it is of value, also, 
for making slight sketches and memoranda during 
observations, and preserving fadts which would 
otherwise be lost; but where considerable accuracy, 
is needed some one or other of the instrumental 
appliances now to be described must be employed. 
Nearly all the instruments attached to the micro- 
scope with a view to aid delineation adt upon the 
principle of rendering the image of the objedt and 
the paper and pencil-point visible together and ap- 
parently blended. This may be accomplished in 
several ways, although the principle of refledtion is 
used in all cases. 
The oldest of these instruments is the camera 
lucida of Dr. Wollaston ; it consists of a four-sided 
glass prism (Fig. 39), of which the angle a, b, d 
Fig. 39. 
equals go°, the angles b, a, c, and b, d, c, 67° 30’, 
and the angle a, c, d, 1350; it adts by twice CAMERA LUCIDA. 
147 
reflecting the rays r and r', proceeding from 
the eye-glass of the microscope, which enter through 
the side b, d, first at c, d, and afterwards at a, c, 
to the eye, so placed at a that one-half of the 
pupil is over the edge of the prism, and views the 
image of the objeCt in the microscope, the pencil and 
paper being seen by the other half, which is 
placed beyond the edge a. As the reflections are 
internal,* there is scarcely any loss of light; the 
image is consequently very bright, and owing to its 
being twice reflected, it is not inverted when it 
reaches the eye. The prism is mounted in a convenient 
setting, so that it may be fitted over the eye-piece in 
the place of the cap, which is of course removed. A 
lens is sometimes attached to the lower part of the 
camera lucida, between the eye and the paper ; this 
is of use to persons who cannot see the drawing 
distinctly at the usual distance, about ten inches, 
and may be either convex or concave, according to 
the special requirement of those using it. 
A small steel disc, known as Soemmering's mirror, 
placed at an angle of 45°, is used by some 
microscopists. The polished disc is smaller than 
the pupil of the eye; so that, while the image from 
the microscope is viewed by the centre of the pupil, 
its circumference is employed in viewing the pencil- 
point and paper, upon which the image appears to 
be projected, as in the camera lucida. 
Another contrivance, and one which has the 
* Ante, p. no. 148 
MICROSCOPICAL MANIPULATION. 
recommendation of being procured at a very small 
cost, is the neutral tint reflector (Fig. 40). It con- 
Fig. 40. 
sists of a small plate of glass, with surfaces accu- 
rately parallel, and slightly coloured, so as to improve 
its reflecting qualities, but not sufficiently dark to 
prevent the paper from being easily seen through it. 
This is placed, as before, at an angle of 450. As the 
instrument is commonly constructed, the tinted glass 
is a fixture, and the setting too long; so that the 
mirror is removed to a greater distance than is advan- 
tageous from the front glass of the eye-piece ; this 
contracts the field so much, when any but an eye- 
piece of low power is employed, that it is almost 
useless. This defeCt is remedied in the form here 
represented, in which the mirror is brought as close 
as possible to the eye-glass. The tinted glasses are 
also removable, so that a change of tint may be made, 
as it will be found sometimes that one tint suits the 
eye better than another. Some microscopists, instead 
of tinted glass, use. a piece of thin cover-glass, NEUTRAL TINT REFLECTOR. 
which gives a very good reflection, and can 
easily be used with this form of setting, which 
also allows a small right-angled prism to be placed 
in it, and which, although not usually supplied with 
the instrument, will be found a serviceable addition. 
Its use will be described with that of the preceding 
instruments. This refleCtor gives a reversed view 
of the objeCt by a single reflection, as in the steel 
mirror of Soemmering, but, unlike it, the paper, 
instead of being viewed round its edge, is seen 
through the glass. 
As these instruments have much in common, the 
use of them may very conveniently be described 
together, noticing, in passing, such peculiarities as 
render them more or less serviceable, each having 
its own special advantages and defeats. 
The microscope should be placed with the body in 
a horizontal position (Fig. 41), and, if the stand is 
not of suitable height, it should be placed on a box 
or other convenient support. The best distance 
between the eye and the paper, for general purposes, 
is 10 inches, this being the standard distance em- 
ployed in estimating magnifying power; but any 
other that is convenient may be made use of, bearing 
in mind that the greater the distance from the eye- 
piece the larger will be the image ; so that the size 
of the picture is capable of being regulated at will, 
the only limit being the difficulty of seeing the pencil 
when too near, and the trouble of drawing with a 
pencil attached to a long stick if the paper is greatly 
removed from the usual position. 150 
MICROSCOPICAL MANIPULATION. 
With respedt to the images formed by the several 
instruments, the camera lucida, as it reflects doubly, 
has the advantage of giving the .image in the 
same position as when viewed through the micro- 
Fig. 41. COPYING OBJECTS. 
151 
scope directly, which, owing to its perfect internal re- 
flection, is brilliant and well defined. Soemmering’s 
mirror and the tinted-glass reflector reverse the 
image, just as an ordinary looking-glass. This is of 
little consequence if only slight outline sketches 
are required ; but, when the drawing is to be highly 
finished, which is always done by viewing the object 
directly through the microscope, this reversal 
becomes excessively troublesome to those who are 
not, like engravers and lithographers, accustomed to 
reverse their drawings. 
With a view to obviating this inconvenience, the 
author uses the small right-angled prism before men- 
tioned, when drawing with the neutral tint reflector, 
which enables the drawing to be completed, as it 
reverses the image just as the tinted glass; and, as 
the reflection from the internal surface of the prism 
is total, the view is nearly as brilliant as that re- 
ceived directly from the microscope. 
Only one eye is to be used while drawing, and 
great care should be taken to tnaintain its position 
steadily until the sketch is finished (Fig. 41). With 
the camera lucida and Soemmering’s mirror, the 
maintenance of this position is somewhat painful, 
when much prolonged, owing to the divided manner 
in which the eye receives the light from the object 
and the paper; and frequently the power of seeing 
the pencil and drawing is lost after a few minutes’ 
use. With the neutral tint reflector, the view of 
both objedt and paper is much easier ; and, when 152 
MICROSCOPICAL MANIPULATION. 
the reversal of the pidture is immaterial, it is, as 
far as comfort is concerned, much to be preferred. 
The illumination is a matter of great importance 
in making use of drawing instruments. Care should 
be taken not to light the objedt more than is 
necessary, while it will generally be found ad- 
visable to illuminate the paper rather strongly. If 
the image of the objedt is too bright, it will be found 
impossible to see either the pencil-point or the line 
it is tracing. The camera lucida requires far more 
care, in this respedt, than the tinted mirror. 
The author’s practice is always, when drawing, 
to use two lamps ; one the little camphine lamp 
before mentioned,* which is used exclusively for the 
microscope ; the other a large paraffin lamp, with 
shade, which lights the paper. By this means, the 
relative illumination of the objedt and paper can be 
very nicely adjusted—a matter of some difficulty 
when only one lamp is employed. 
These instruments are only used to secure an 
outline, and mark out other main points, the details 
being filled in by free-hand drawing, which will be 
found comparatively easy when an accurate outline 
is obtained to work upon. 
If, when the sketch is finished, before re- 
moving the refledtor, a ruled micrometer-scale is 
placed upon the stage of the microscope, the 
lines can be seen projected upon the paper, just 
as any other objedt, and, by tracing some of them, a 
* Ante, p. 26. MAGNIFYING POWER. 
scale can be formed by which the drawing can 
readily be measured with a pair of compasses, like 
a map. This is one of the simplest methods of 
micrometry. 
The magnifying power of the microscope can also 
easily be ascertained by means of the camera lucida 
or neutral tint refledtor and the stage micrometer. 
By placing the microscope in the position for drawing, 
taking care that the eye-piece is io inches from the 
paper, the image of the micrometer-lines, instead of 
being projected on a sheet of paper, is caused to fall 
upon a divided scale; and, from the amount covered 
by it, the magnifying power can be estimated; for 
instance, the i-inch objective, with No. i eye-piece, 
causes o’oi of the micrometer to cover o'5 inch of the 
measure on the table; the magnifying power will be 
50 diameters. The t-inch makes o'oi cover 2‘5 inches; 
the power will be 250 diameters. And so on, for other 
objectives and eye-pieces. 
Finding the placing of the microscope in a hori- 
zontal position troublesome, and not liking the con- 
straint of the camera lucida, the author thought that 
the method of enlarging and reducing drawings 
commonly employed by artists might be adapted to 
the microscope. This process consists of ruling a 
series of squares of convenient size on the drawing 
to be copied, or placing over it a lattice of threads 
crossed in squares. The copy is then made upon a 
sheet of paper or other material, ruled, either 
in augmented or diminished proportion, as may be 
required. Messrs. R. and J. Beck ruled a disc of 154 
MICROSCOPICAL MANIPULATION. 
glass in squares (Fig. 42), the side of each of which, 
A 
Fig. 42. 
B 
for convenience sake, was made to correspond with 
io° of Jackson’s eye-piece micrometer. This disc was 
dropped into the eye-piece, and rested on the stop, so 
that, when in use, the field appeared similarly divided 
(Fig. 42, A). A sheet of paper (Fig. 42, B), ruled in 
squares of convenient size was employed to make 
the drawing upon; and, by noticing how many 
squares the objedt covered, the direction of the 
various lines—whether, for instance, they ran through 
the sides or the corners of the squares—and setting 
them down in similar positions on the ruled sheet, 
the author found that an accurate drawing might be 
made with great ease and expedition, and without 
the trouble of moving the microscope out of the 
usual inclined position, which is generally the most 
comfortable for observation. The use of the binocu- 
lar did not cause any impediment, and the ruled disc 
only slightly interfered with the definition of the 
objedt, and could easily be removed, when its services COPYING OBJECTS. 
were no longer required, without disturbing the 
arrangement of illumination, objedt, or instrument. 
When large diagrams are wanted, nothing more is 
necessary than to use a large sheet of paper, ruled 
in squares of suitable dimensions, and the objedt 
can be rapidly delineated in this augmented pro- 
portion. 
The measurements can be made either by obtaining 
the value of the side of a square of the disc with each 
objedtive and eye-piece, by means of the stage- 
micrometer, or by seledting two well-marked dots or 
lines in the objedt, and measuring their distance 
with the eye-piece micrometer, and using the distance 
obtained from the corresponding part of the drawing 
as a standard for the formation of a scale. These 
processes will be explained in the account shortly to 
be given of micrometers. 
When many sheets of paper are required to be 
ruled in squares (and it will be found in practice that 
two or three sizes will be in general request), they can 
easily be made by placing a perforated sheet over 
the sheet to be ruled, and rubbing over it a piece of 
wash-leather dipped in black-lead powder, which will 
pass through the holes and leave a series of dotted 
lines on the sheet below, which will be sufficiently 
distindt, and have the advantage of being rubbed out 
with a very light touch of the india-rubber, without 
affedting the pencil-lines of the drawing. The per- 
forated sheets are easily made by means of a comb- 
like steel punch used by harness-makers, which cuts 
a row of small pin-holes, equal in length to its own 156 
MICROSCOPICAL MANIPULATION. 
width, which may be an inch or more. This instru- 
ment can be obtained at the better class of tool- 
shops. 
Some microscopists have endeavoured, with more 
or less success, to make drawings from the image of 
the objedt projedted upon a sheet of paper or ground 
glass, after the manner of the solar microscope or 
camera obscura. All the contrivances for this pur- 
pose seem to have the defedt of giving a very faint 
image, unless a light of greater intensity than that 
of ordinary lamps is employed. The image must be 
received in the dark, which is troublesome, as the 
outline cannot easily be seen. The process is only 
applicable to those objedts which can be viewed by 
transmitted light, besides putting the microscope 
more out of its usual position than the camera 
lucida and other refledting instruments. 
Intimately conne(5ted with microscopical drawing 
is the subjedt of micrometry, the practice of the 
two together forming the records and statistics of 
histological science. The contrivances used by the 
earlier observers were rude in the extreme. Leeuwen- 
hoek compares the dimensions of magnified objedts 
with grains of sand. Dr. Hooke, with a little more 
approach to exadtness, used fine silver-wire. By 
winding a quantity of this closely round a thicker 
wire, he noticed how many coils there were in an 
inch, and used the unit so obtained as a means of 
measurement. The most perfedt of the old micro- 
meters is a somewhat complicated contrivance 
attached to a microscope by the famous Benjamin MICROMETRY. 
Martin, now in the possession of the Royal Micro- 
scopical Society. It consists of a separate stage, 
which is placed on the instrument when measure- 
ments are required to be taken. The objedt is capable 
of being moved through a definite space, by means 
of delicate screws, having large graduated heads, 
upon which the distance traversed by the objedt can 
be read off. This micrometer has, in common with 
all measuring instruments applied to the stage, the 
defedt that any error in the graduation is multiplied 
by the whole magnifying power of the instrument. 
The standards employed in microscopic measure- 
ments are the ruled slips of glass before mentioned. 
They are graduated by a machine invented by the 
late George Jackson, and are now to be obtained of 
most opticians. They are ruled in hundredths and 
thousandths of an inch, and are marvellously accu- 
rate in their divisions, and extremely fine in the 
engraving of the lines, bearing a very high magni- 
fying power without appearing coarse. Scales are 
also ruled in millimetres. The millimetre equals 
°'°3937 English inch, or about i-25th of an inch. 
As the metric system will probably in a few years be 
universally adopted, it is well to place both scales 
on microscopical drawings, especially as this system 
of measurement is common on the Continent. 
One method of measurement has already been 
mentioned in describing the use of the camera 
lucida. 
To obtain the greatest degree of accuracy in micro- 
scopical measurements, it is desirable that, while 158 
MICROSCOPICAL MANIPULATION. 
the objedt to be measured is magnified as much as 
possible, the measuring scale should be but slightly 
enlarged. This is effedted by the use of eye-piece 
micrometers. The most delicate of these is the 
well-known cobweb micrometer of Ramsden. It is 
nearly similar to that employed in astronomical in- 
struments, and consists of a positive or Ramsden’s 
eye-piece, in the focus of which is placed a pair of 
stretched cobweb-lines, one of which is fixed, and 
the other movable by means of a fine screw which 
has a large graduated head. The value of the 
graduations has to be determined for each objedt- 
glass, as is the case with all similar contrivances. 
The cobweb micrometer, when used with a suffi- 
ciently high power, is capable of measuring extremely 
small portions of space with great exadtness ; the 
instrument, however, is rather expensive. 
With a view to avoid the multiplication of ap- 
paratus, the late George Jackson, by a simple con- 
trivance, rendered the ordinary Huyghenian eye- 
piece available for micrometric purposes. A slit was 
cut on each side just above the diaphragm (Fig. 43, A), 
which served to admit a brass slide, B, containing a 
scale ruled on glass, which, when in position, was in 
the focus of the eye-glass, and could be seen in the 
field at the same time with the objedt in the micro- 
scope. The scale is ruled with a long line at every 
fifth division, and a still longer one at every tenth, 
for facility of reading. The scale is allowed a small 
amount of lateral motion, which is controlled by a 
fine screw adting against a spring on the opposite EYE-PIECE MICROMETER. 
side. This movement enables the line from which 
the measurement commences to be brought to the 
edge of the objedt more accurately than it could be 
Fig. 43. 
by means of the stage movements, as the scale of 
the eye-piece micrometer is only magnified by the 
trifling power of the eye-glass, while the motion of 
the stage-racks is enlarged by the whole power of the 
instrument. The operation of measuring is nearly 
as easy as applying an ordinary rule : the scale is 
brought over the objedt, adjusted by the screw, and 
the number of degrees read off in the direction 
required. 
B 
To determine the value of the degrees, which 
differs with each objective, the following process 
must be adopted :— 
Place the micrometer in its eye-piece, and focus, 160 
MICROSCOPICAL MANIPULATION. 
if necessary, for distinct vision of the scale by un- 
screwing the eye-glass, which is usually provided with 
a rather long screw for this purpose. Screw on the 
objective, and place the ruled scale on the stage; and, 
looking through the microscope, focus until the lines 
are sharp and distindt. Suppose the value of the 
micrometer is to be ascertained for the § objedt-glass, 
and it is found that i-ioooth of an inch of the ruled 
scale on the stage occupies a little less than 
two divisions of the micrometer, this will give an 
awkward number for calculation ; so it will be neces- 
sary to increase the power of the microscope to such 
an extent that the i-ioooth should occupy 20 exadtly. 
This can be done by lengthening the body by means 
of the draw-tube, which, for this purpose, should be 
divided into inches and tenths, that the amount of 
extension may be noted. The tube is to be drawn out 
until the divisions of the stage micrometer coincide 
with those of the eye-piece micrometer. Say, 
for example, it is found that, to effeft this, the tube 
has to be lengthened 3-ioths of an inch; then, as 
i-ioooth of an inch equals 20 of the eye-piece micro- 
meter, i° is equal to i-20ooth of an inch. This pro- 
cess should be repeated with each objedt-glass, and 
tried several times, to ensure accuracy. The result 
should be preserved in the following tabular form :— 
Value of Divisions of Eye-Piece Micrometer. 
Objective. 
Draw-tube. Vulgar Fra&ion. 
Decimal. 
n 
13 ri~ 
•OOI 
§ 
3 -'|IJ0 
2 0 0 0 
•0005 
4 
1 0 
22 _J 
4 0 0 0 
•OOO25 EYE-PIECE MICROMETER. 
161 
And so on through the whole series of objectives. 
The slight alteration of distance between the anterior 
combination and the back lenses caused by turning 
the graduated collar which regulates the adjustment 
for covering glass with the higher powers, slightly 
alters the magnifying power; and, when very accu- 
rate measurements are required, the draw-tube cor- 
rection must be ascertained for each degree of the 
adjustment-collar. The value of the divisions of 
Ramsden’s or the cobweb micrometer is calculated 
in the same manner. When this table is once made, 
measurement with the eye-piece micrometer becomes 
very easy indeed. After selecting the objeCt-glass 
and placing the micrometer in the eye-piece, draw 
out the tube to the number of tenths indicated in 
the table, and then the degrees can be read off just 
like an ordinary measure. To secure accuracy in 
measuring, always use the highest convenient magni- 
fying power, as the readings can be made with 
greater minuteness; for instance, a degree with the 
4-ioth or £ equals i-qoooth of an inch ; while, with 
the i, it would be i-i6oooth, and half a degree can 
easily be estimated by the eye; so, by using the 
higher power, the i-320ooth of an inch can easily be 
measured, and greater minuteness still can be ob- 
tained by using higher powers, where practicable. 
A convenient mode of measurement has been 
devised by Dr. J. Matthews. It is an adaptation of 
the indicator, sometimes placed in the eye-piece to 
mark a spot in the field. Two of these pointing 
needles, suitably curved so that they aCt, by means 162 
MICROSCOPICAL MANIPULATION. 
of milled-heads, like a small pair of callipers, are 
placed as just mentioned. The distance on the 
objedt is measured between these points, and, upon 
the removal of the slide, the value of the space can 
be estimated by putting the stage micrometer in its 
place. For counting striae and other marks in a 
given space, and for many purposes, this simple 
contrivance is very effective, as, also, where the 
glass of the stage micrometer might interfere with 
the definition of a very delicate objedt. 
In making the scales on microscopical drawings, 
it is often necessary to divide a given space into a 
certain number of equal parts. When the number 
is a multiple of two, it is readily performed by a 
continued process of bisection; but, as ten is a 
number frequently required, this process will not 
serve beyond the first bisection, which leaves five— 
a rather troublesome number to guess at with the 
compasses. Suppose the line A, b (Fig. 44) is to be 
Fig. 44. 
divided into five parts. From a, rule the line a c 
at any convenient angle, of any suitable length ; 
from b, rule b d, parallel to a c ; from a, set off, with 
the compasses, five equal spaces (i, 2, &c.) towards 
c; and, from b, set off the same towards d; join DRAWING MATERIALS. 
163 
i, i'; 2, 2'; 3, 3'; &c.; and the lines i, T, &c., will 
divide a b into five equal parts. Any number of 
divisions may be made by setting off the number 
required on a c and b d. 
If scales are employed for setting off distances, 
those known as “ feather-edged scales ” are to be 
preferred, as they do not require the use of com- 
passes, the divisions being marked diredtly on the 
paper from the thin edges. For general purposes, 
that known as a builder’s scale is convenient, as it 
contains a large number of different scales, all of 
which are ingeniously contrived to read at the edges. 
It should, however, have the sub-divisions in tenths, 
and not, as usually made, in twelfths. A millimetre 
scale will also be found useful. 
The subjedt of drawing materials is of some little 
importance, and, as it is not treated upon in any 
microscopical work, a few remarks may not be out of 
place. 
Probably no material is capable of representing 
elaborate microscopical subjects with so much truth 
as water-colour. When used with all the appliances 
of the modern school of painting, both colour and 
texture can be very closely imitated by skilful artists ; 
but few have turned their attention to this subjedt; 
and, as the process is costly and not easy to acquire 
without a considerable amount of study, the use of 
this mode of representation will, in all probability, 
be very limited. Those who possess the requisite 
skill are strongly recommended to make use of it. 
Even as pictures, groups of aquatic animals and 164 
MICROSCOPICAL MANIPULATION. 
plants are quite as beautiful, both in form and 
colour, as flower compositions ; and no other means 
of delineation, excepting the still more difficult art 
of oil-painting, can approach the truth of a highly- 
finished water-colour drawing. Unfortunately, at 
present, no means exist of re-producing these beauti- 
ful pictures, as their extreme delicacy places them 
beyond the powers of chromo-lithography. 
The effedt of outline sketches is much improved 
by the judicious employment of tints of water-colour; 
and this is by no means a difficult process, as it is a 
mere matter of laying on colour ; while, in painting 
proper, quite as much is done by taking off paint as 
by putting it on, and also every advantage is taken 
of the texture of both paper and pigment. 
Pencil drawing is particularly useful for micro- 
scopical purposes. Fine lines can readily be made, 
and the shading is capable of much refinement, so 
that very delicate tissues can be faithfully delineated. 
Unless the drawing consists entirely of fine lines 
without shaded tints, the use of hot-pressed or per- 
fectly smooth paper is not to be recommended, but 
one having a small, fine grain is to be preferred. 
The paper should always be supported behind on 
some hard substance, otherwise the pencil-point will 
cut in, the line be difficult to rub out, and also much 
of the power of guiding the pencil lost. For delicate 
drawings, a piece of thick plate-glass makes an admi- 
rable drawing-board. The blocks or solid sketch-books 
so much used in out-door sketching, when made of a 
suitable paper, are particularly pleasant and con- FIXING PENCIL DRAWINGS. 
165 
venient to draw upon. For shading, the pencil should 
not be cut to a sharp point, but rather kept square. 
Those with extra thick leads (such as bbbb and ehb) 
may sometimes be used to advantage, and even the 
broad, flat crayons known as Harding’s tablets. 
For general outlining with camera or ruled disc, 
hb, from its freedom, will be found useful. For a 
fine outline, h should be used. Delicate tints may 
be obtained by rubbing on black-lead powder with a 
leather stump; the most convenient is that known 
as “ Harding’s.” The author has found no black- 
lead pencils equal to those made by Mr. B. S. Cohen; 
they are very even in texture, rub out easily, do not 
readily break, and correspond exactly with their re- 
spective marks. The 6 h, made for drawing on 
wood for engraving, is well adapted for the purpose 
for which it is intended. 
Pencil drawings, and also those in chalk and char- 
coal, may be permanently fixed by applying freely at 
the back, until the paper is saturated, a varnish com- 
posed of white (bleached) shellac, made by mixing 
equal parts of white lac-varnish and methylated 
spirit. The white lac-varnish is always supplied by 
Messrs. Winsor and Newton of uniform strength, 
and will save the trouble and difficulty of dissolving 
bleached lac. The drawing is to be carefully dried 
before a fire, and, when completed, may be rubbed 
with india-rubber with perfect impunity. Water- 
colour may be freely used in combination with pencil, 
as it is not affeCted by this varnish, which does 
not stain the paper when dry, although it soaks in 166 
MICROSCOPICAL MANIPULATION. 
when first applied, and renders it transparent like 
oil. 
The multiplication of microscopical drawings is a 
subjedt worthy of the attention of every observer. 
With the exception of Dr. Beale,* no writer on the 
microscope has given any account of the various 
processes of engraving; and yet, unless the micro- 
scopist can command the services of the very few 
engravers and lithographic artists who have devoted 
themselves to the re-produdtion of microscopical 
subjedts, there is, as the author has found by experi- 
ence, great risk of misinterpretation. 
Photography is capable of copying drawings with 
great exactness, and has no fault saving its cost. 
When only a small number are required, it would 
probably, however, be cheaper than any of the 
printing processes. 
The printing processes proper consist of plate and 
surface printing and lithography. 
Copper and steel plate engraving consist of cutting 
lines in a metal plate with a pointed steel tool of 
square or rhomboidal sedtion, known as a graver. 
The plate, when finished, is rubbed over with a thick 
printing-ink, which is afterwards cleaned off, leaving 
the lines full (Fig. 45, B, 1). The plate is then passed 
through a powerful rolling-press with a sheet of thick, 
porous paper over it, which is forced into the lines, and 
takes the ink out of them, forming the impression 
(Fig. 45, B, 2). Instead of excavating the lines with a 
cutting tool, the plate may be covered with a pre- 
* “ How to Work with the Microscope,” pp. 28—35. ENGRAVED SURFACES. 
Fig. 45. 
A 168 
MICROSCOPICAL MANIPULATION. 
paration capable of resisting acids, known as etching- 
ground. The copper is then laid bare by scratching 
through the ground with a suitably-mounted needle. 
Diluted nitric acid is poured on the plate, and 
allowed to corrode the metal. When sufficient depth 
is obtained, the acid is poured off. Those lines 
which are “ bitten ” sufficiently are filled up with 
varnish. The process of biting is then repeated 
until the deepest lines are sufficiently corroded. 
This process of etching is a great favourite with 
artists, and might, no doubt, be turned to account for 
microscopical purposes, as it is much easier than using 
the graver, which is a very troublesome tool. The 
disadvantage of plate printing is that the obtaining 
of impressions is expensive, and the number limited, 
owing to the rapid wear of the plate ; this latter 
objection, however, may be overcome by copying the 
plate by electrotype. The variety of engraving 
known as mezzo-tint is well adapted for the repre- 
sentation of tissues ; but it requires a skilled engraver, 
and the learning of it would take up too much of the 
observer’s time. 
Surface printing is the reverse of plate printing. 
In this, as will be seen (Fig. 45, A, 1), the light parts 
are excavated and the dark parts left standing; these 
receive the ink from the roller, and yield a copy to 
a sheet of paper upon pressure being applied (Fig. 
45, A, 2). Common type is an example of this kind of 
printing. For art purposes, wood engraving is em- 
ployed. The drawing is made on a block of box-wood, 
which is then placed in the hands of the engraver, who GRAPHOTYPE PROCESS. 
169 
cuts away the light portions, leaving the solid black (if 
any) standing, and variously modifying, by lines and 
dots, the portions which have a tone between black 
and white,—“ half-tints.” The process is a difficult 
one, requiring great skill, which is only to be acquired 
by very long practice. It is capable of rendering 
microscopical subjects with great perfection: the 
re-produCtions of Dr. Beale’s drawings in his various 
works, by Miss Powell, are marvels of delicacy. 
Some beautiful specimens of wood-engraving will 
also be found in the work on the microscope by the 
late Richard Beck.* Wood-engraving has the ad- 
vantage of being cheaply printed, and also of being 
set up along with type, although, in the latter case, 
its beauty is somewhat sacrificed : it never has 
justice done to it unless it is printed by itself, and 
with very great care. A valuable little book on the 
“Art of Wood-Engraving,” by T. Gilks, is published 
by Messrs. Winsor and Newton. 
A very ingenious printing process, known asgrapho- 
type, has been lately brought forward. In this, a 
quantity of finely-powdered chalk is compressed into 
a solid tablet; this is drawn upon with a fine brush 
charged with an ink which hardens the chalk where- 
ever it touches. The drawing is then sent to the 
patentees, who brush away the chalk, leaving the 
lines standing. A mould is made in plaster of Paris, 
from which a cast in type-metal, capable of yielding 
impressions in the common printing-press, is taken. 
* One of these, through the kindness of Messrs. R. and J. Beck 
forms the frontispiece of this work. 170 
MICROSCOPICAL MANIPULATION. 
Every facility is afforded by the Graphotyping Com- 
pany, No. 7, Garrick Street, W.C., to persons wishing 
to test the merits of the process. 
Lithographic printing differs remarkably from all the 
processes of multiplying impressions just described. 
While, in plate and surface printing, it was essential 
that there should be a difference of level between the 
parts intended to print lights and shadows, in the 
various lithographic processes, light and dark are all 
printed from the same surface. The operation is purely 
a chemical one, and depends upon the mutual repulsion 
of oil and water. The stone used is a fine-grained and 
very compact limestone, capable of bearing a high 
polish, principally supplied from quarries at Solen- 
hofen ; and it would seem that it was destined to trans- 
mit natural history information to posterity, as many 
of the slabs enclose fossil-inseCts, as perfectly pre- 
served as if they had been shut up between the leaves 
of a book for a few weeks, instead of ages. The British 
Museum has a very large collection of these speci- 
mens of Nature’s lithographs. If a grease-mark be 
made upon the smooth surface of this or similar 
stone, and it then be wetted, it will be found, 
upon passing a roller charged with printing-ink over 
the stone, that the ink will adhere to the greasy por- 
tions, while it will be repelled by the parts 
that are wet. If the stone, with a sheet of paper on 
it, be passed under the press, an impression will be 
obtained ; and, by a series of wettings and inkings, 
the operation may be repeated any number of times. 
This is the foundation of all the lithographic pro- LITHOGRAPHY. 
cesses, which are numerous, and suited to the pro- 
duction of a great variety of effeCts, mostly by the 
use of means differing less from the ordinary manipu- 
lations of the artist than any of the other means of 
multiplying drawings. The use of grease or oil as a 
material for drawing upon stone is open to many 
practical objections; therefore, a greasy material is 
manufactured, more closely resembling, in form, that 
used in the ordinary process of drawing. It is com- 
posed of a mixture of tallow, soap, wax, and shellac, 
with a portion of lamp-black, to give it sufficient 
colour to guide the artist in making his drawing. 
The proportions vary according to the purpose for 
which it is required, and the combination of the 
materials is a matter of very nice manipulation. It 
can be procured, properly prepared, of the dealers 
in lithographic materials, and will be found in the 
form of crayons of three degrees of hardness, which 
are used like ordinary artists’ chalks, and cakes, 
which are soluble in water, and can be rubbed down 
like Indian-ink, care being taken to use distilled or 
very pure water, otherwise, from the soapy nature 
of the ink, it will not mix freely. 
In making drawings with the ink, a fine brush or 
suitable steel pen may be used ; and, if the drawing is 
to consist entirely of ink-work, a polished stone should 
be employed. Care should be taken not to touch 
the stone with the fingers, as every greasy mark, 
although invisible when made, will print when the 
stone is rolled in. If the crayons, or chalk, are 
used, the stone should be what is called “grained,” 172 
MICROSCOPICAL MANIPULATION. 
that is, its surface should be prepared with a texture 
somewhat like that of drawing-paper, to enable the 
chalk to be rubbed off the crayon and held by the 
stone. The fineness or coarseness of the grain must 
be suited to the nature of the drawing: micro- 
scopical drawings usually require a very fine grain. 
The manipulation is somewhat like that of pencil and 
chalk drawing on paper, only taking certain pre- 
cautions rendered necessary by the nature of the 
material. All light tints should appear darker on 
the stone than they are intended to print, as they 
lose some of their strength in the preparation 
which the stone undergoes before it is printed from. 
Dark tints should be worked up gradually, by re- 
peating the touch of the chalk in as many directions 
as possible, so that the minute papillas, or rough- 
nesses, which form the grain of the stone may be 
loaded with the chalk on all sides, and consequently 
suffer less in the etching process. Any attempt to 
produce a dark tint or spot by a vigorous and sudden 
touch, as in pencil drawing, will generally fail when 
the stone is printed. Ink outline may often be used 
with great advantage in combination with chalk 
shading. In this case, the outline should be put on 
the stone with the ink first, and the shading done 
afterwards, as it is difficult to see the ink outline 
when the stone is covered with shading, and the 
chalk is also likely to hinder the adhesion of the ink 
to the stone. Care should be taken that the work is 
perfect before it is sent to the printer, as but little 
or no alteration can be made after the proof is taken. ENGRAVING ON STONE. 
173 
This is one of the greatest defects of lithography, 
and is unlike copper-plate, where the artist goes on 
improving and re-touching, after a series of proofs, 
until perfection is attained. When the printer re- 
ceives the stone, he washes it with very dilute nitric 
acid, which converts the soapy ink into grease, and 
prevents its being washed off in subsequent pro- 
cesses. The stone is then covered with gum-water, 
which adheres to the parts not touched with ink, 
and prepares the stone to receive the wet. Then, 
by a series of spongings with water and rollings with 
printing-ink, the stone is made ready to yield a very 
large number of impressions. With a little perse- 
verance and the assistance so kindly afforded by 
most lithographic printers,* any person who can draw 
may hope, after a time, to re-produce his works upon 
stone with tolerable success. 
Another process, capable of producing very delicate 
results, and well suited for microscopical purposes, is 
that known as engraving on stone (Plate 3). It is by this 
mode that most of the beautiful works of Mr. Tuffen 
West are executed. It consists in scratching the 
lines and dots forming the picture with a diamond- 
point on a highly polished stone, of which the sur- 
face has been slightly coloured, to render the marks 
visible. Care should be taken not to cut deeply, but 
only slightly to scratch the stone. The printer rubs the 
engraved stone with grease, which adheres to the 
scratches, which, when the stone is rolled in, 
* The author has been indebted to the artists in the office of 
Mr. West, Hatton Garden, for much valuable information. MICROSCOPICAL MANIPULATION. 
print as black lines. This process requires much 
more practice than either chalk or ink drawing ; but 
its results, when well executed, almost rival fine 
steel-engraving. 
White-line lithography, (Plates 4,5, and 6) on a black 
ground, is useful for representing many tissues. It is 
executed on a polished stone, which is prepared by the 
surface being covered either with a coat of lithographic 
ink or grease and lamp-black. The artist, with a 
diamond-point, cuts through the black ground, taking 
care to lay bare and slightly incise the stone. The 
diamond is a very free-working tool, and obeys the 
hand beautifully after a little practice. This process 
is remarkably easy and expeditious, and is worthy of 
having its powers developed. Very little use has 
been made of it at present. It seems capable of 
great delicacy; and, as so many microscopical ob- 
servations are made on a black ground, either with 
the parabola or by refledted light, this process seems 
to be one very well suited to the wants of the 
microscopist. As a compensation for the ease of 
execution, it would seem that black-ground litho- 
graphs entail some trouble on the printer, as the 
fine lines are apt to fill up ; but as this kind of 
printing becomes more frequent in use, doubtless the 
difficulty will be thought much less of. The author 
strongly recommends microscopists who have draw- 
ings to publish, and who cannot afford the cost of 
professional assistance, to master some one or other 
of the lithographic processes. Their work will 
doubtless, even after some practice, be rough, and HOW BEST TO WORK. 
not equal to the productions of experienced litho- 
graphic artists ; but it will have an advantage which 
is possessed by no copy of a drawing, however good : 
it will be an autograph, re-producing all the author’s 
peculiarities of style, and preserving those points 
which are very often lost in the copying of drawings 
by those who are not familiar with the subjects 
represented. 
The student who wishes to render the microscope 
really valuable to him must determine, after master- 
ing the technical difficulties of his instrument, to 
apply himself diligently to the study of some par- 
ticular subject. One of our greatest authorities 
(Dr. Carpenter) speaks of “ microscope power run- 
ning to waste ” in this country. Another author 
says :—“ We have the best microscopes in the world, 
and the fewest observations.” And it is to be feared 
that there is much truth in these statements. The 
microscope is, in the hands of many persons, only a 
costly toy. It should be regarded rather as a tool, 
and the naturalist’s most efficient one. The work of 
the microscope does not consist in resolving the 
striae of difficult diatoms ; this has been done over 
and over again, and yet we seem to be not much 
nearer the truth than before. However, if we cannot 
understand the markings of the diatoms, they have 
done us service : they have caused our instruments 
to be continually improved, till now it is doubtful 
whether much more advance can be made. 
The beginner is strongly recommended to go care- 
fully through the tables at the end of Dr. Beale’s 176 
MICROSCOPICAL MANIPULATION. 
“ How to Work with the Microscope,” carrying out 
the principles there laid down; for, though the work 
is principally written for students of anatomy and 
physiology, it may be consulted by all enquirers with 
great benefit. Great progress may always be made 
if the student has the good fortune to be acquainted 
with some working microscopist. Many such are 
glad of the assistance of others; and, although the 
beginner may not be able to originate an enquiry, 
he may confirm and verify the observations of others, 
and, in so doing, add largely to his own stock of 
knowledge. 
The numerous microscopical societies in London 
and elsewhere offer great facilities to the young 
student, by giving him opportunities of becoming 
acquainted with the best practical microscopists. 
The recent application of the spectroscope to 
microscopical research will no doubt be a very pro- 
mising field of enquiry. Already, besides other dis- 
coveries, the distinction between two vegetable reds 
(those of the grape and elder-berry) has been pointed 
out by its means, and will probably lead to the 
detection of methods of adulteration which have 
hitherto baffled both chemists and microscopists; 
and many more very important results may be ex- 
pected to be elicited by steady application and careful 
use of this most delicate means of distinguishing 
colour. The use of the microscope is far from being 
confined to those sciences which are connected with 
natural history. The instrument has been applied, 
with the greatest advantage, to researches on in- MICROSCOPICAL MANIPULATION. 
organic matter; and much valuable information has 
been obtained by the observations of Mr. Sorby and 
others who have devoted themselves to such en- 
quiries. APPENDIX. 
IN the following lessons, the possession of an 
instrument fitted with Mr. Wenham’s stereo- 
scopic binocular arrangement has been supposed. 
As microscopes of moderate price are now so con- 
structed, the author has no hesitation in arranging 
the following simple course of exercises more 
especially for its use ; nearly all the observations 
can, however, be made with the monocular instru- 
ment. 
The following tables, containing lists of the objec- 
tives made by the three principal London opticians, 
with their approximate magnifying powers and 
angles of aperture, may assist the student in selecting 
a glass suitable for the objeCt to be examined. It 
must be borne in mind that the powers given are 
those of the lenses when used upon the stands of 
their respective makers ; the length of the body 
materially influences the power of the combination, 
as will be seen by the table for the use of the draw- 
tube given in Messrs. Beck’s list :— MAGNIFYING POWERS 
*79 
Linear Magnifying Power (nearly) with 
Angle 
rocal 
Eye-Pieces. 
of 
Aperture 
I 
2 
3 
4 
5 
about 
3 
nches - 
Draw-tube closed 
Do. if drawn out, add for each inch .. 
12 
2 
20'* 
4 
40 
6 
48 
7 
74} 
10 J 
12 degs. 
. 
Draw-tube closed 
20 
38' 
70 
85 
130) 
18 „ 
” 
Do. if drawn out, add for each inch.. 
4 
6 
8 
I2» 
15 J 
ii 
. 
Draw-tube closed 
30 
56 
100 
120* 
190) 
23 
” 
Do. if drawn out, add for each inch ... 
5 
7 
12 
15 
22 j 
. 
Draw-tube closed 
70 
120 
220 
270' 
4io1 
32: ». 
” 
Do. if drawn out, add for each inch .. 
8 
14 
25 
27 
48 [ 
4 
. 
Draw-tube closed 
120 
210 
37° 
460 
710) 
55 
” 
Do. if drawn out, add for each inch .. 
14 
24 
34 
46 
7° I 
4 
. 
Draw-tube closed 
146 
255 
480 
560 
8gol 
go „ 
” 
Do. if drawn out, add for each inch .. 
18 
32 
48 
60 
80} 
i 
. 
Draw-tube closed 
200 
340 
590 
720 
1x20) 
75 » 
” 
Do. if drawn out, add for each inch.. 
24 
42 
63 
85 
120 ) 
1 
Draw-tube closed 
225 
400 
700 
860 
14501 
85 
” 
Do. if drawn out, add for each inch .. 
18 
35 
60 
80 
I3°) 
1 
. 
Draw-tube closed 
225 
400 
700 
860 
I45° 1 
100 „ 
5 
” 
Do. if drawn out, add for each inch .. 
18 
35 
60 
80 
130 f 
. 
Draw-tube closed 
500 
870 
1500 
1850 
2800) 
120 ,, 
” 
Do. if drawn out, add for each inch .. 
60 
100 
180 
i go 
37° I 
1 
5U 
Draw-tube closed 
900 
1570 
2750 
3450 
4950 | 
140 ,, 
” 
Do. if drawn out, add for each inch .. 
80 
150 
300 
350 
goof 
R. and J. Beck. 180 
MICROSCOPICAL MANIPULATION. 
Thomas Ross. 
Objeft 
Glasses. 
Angular 
Aperture. 
Magnifying Powers with the various 
Eye-Pieces. 
A 
B 
c 
D 
E 
F 
5 
inches 
7 degs- 
8 
13 
24 
36 
52 
72 
4 
n 
9 
11 
10 
16 
30 
45 
65 
90 
3 
n 
12 
11 
13 
20 
35 
56 
84 
112 
2 
»» 
15 
11 
20 
32 
55 
90 
135 
l8o 
i£ 
n 
20 
11 
25 
40 
70 
112 
168 
224 
i 
n 
15 
11 
37 
60 
105 
170 
255 
340 
i 
)♦ 
25 
11 
37 
60 
105 
170 
255 
340 
§ 
35 
11 
60 
IOO 
145 
270 
405 
540 
4 
n 
90 
11 
95 
153 
265 
420 
630 
84O 
I40 
n 
no 
11 
140 
220 
37° 
650 
975 
1300 
4 
ii 
100 
11 
195 
310 
54° 
850 
1275 
I7OO 
4 
ii 
140 
11 
195 
3X0 
540 
850 
1275 
I7OO 
1 
ii 
140 
11 
320 
510 
700 
gio 
1360 
1820 
4 
ii 
140 
11 
420 
670 
900 
1200 
1800 
24OO 
1 
T5 
ii 
170 
11 
600 
870 
1200 
2000 
3000 
4000 
Powell and Lealand. 
Objedt 
Glasses. 
Angular 
Aperture. 
Magnifying Power with the various 
Eye-Pieces. 
I 
2 
3 
4 
5 
2 
inches 
14 degrees 
25 
37 
50 
100 
r5° 
Ii 
11 
20 ,, 
37 
56 
74 
150 
220 
I 
?» 
30 „ 
50 
74 
100 
200 
300 
§ 
» J 
32 „ 
75 
III 
150 
300 
450 
* 
11 
7° „ 
100 
148 
200 
400 
600 
1*T5 
M 
80 ,, 
125 
r87 
250 
500 
750 
i 
M 
95 .. 
200 
296 
400 
800 
1200 
4 
11 
130 „ 
— 
— 
— 
— 
— 
\ 
11 
145 >. 
— 
— 
— 
— 
— 
s 
»> 
100 „ 
250 
37° 
500 
1000 
1500 
4 
11 
140 „ 
400 
592 
800 
1600 
2400 
1 
T5 
11 
145 „ 
600 
888 
1200 
2400 
3600 
tV 
11 
175 
800 
1184 
1600 
3200 
4800 
IS 
11 
160 ,, 
1250 
1850 
2500 
5000 
7500 
3*0 
11 
150 „ 
2500 
3700 
5000 
xoooo 
15000 OBJECT-GLASSES AND EYE-PIECES. 
181 
The screws cut upon the nozzles of microscopes, 
and upon objeCt-glasses, are now common amoijg 
English opticians, so that the objectives may be 
attached to any stand at pleasure. 
The following symbols will be employed to indi- 
cate the apparatus to be used. 
Object-Glasses— 
4 in. or 3 in O3 
2 „ if O2 
1 „ § Oi 
i >» t4o Of 
i » i » Oi 
Higher powers, O, with the fraction indicating the 
nominal focal length. 
Eye-Pieces.—When no symbol is used, the lowest 
power, viz., No. 1, or A, is supposed ; medium power, 
E 2 ; deeper, E3 ; return from deep eye-piece to one 
of lower power, E. 
The binocular prism is supposed to be employed 
in general ; when it is to be withdrawn, and the 
instrument rendered monocular, M is used ; the 
return to the binocular is indicated by B. 
The illuminating apparatus first mentioned is that 
to be used if possible ; that following, between 
brackets, may be used as a substitute. 
The apparatus and materials constantly required, 
besides the microscope, are— 
Lamp (pp. 23—27).—A glass stage-plate ; easily 
made by attaching a narrow slip of glass, with marine 
glue (pp. 42—44), to a glass plate of convenient 
dimensions, so as to form a ledge, and prevent 
objedts slipping off when the stage is inclined. 182 
MICROSCOPICAL MANIPULATION. 
Some 3x1 slides ; a small stock of thin cover 
glass, in squares and circles ; forceps ; needles 
mounted in handles (p. 49) ; a few pipettes (p. 38), 
and some blotting-paper ; a small quantity of alcohol 
and turpentine ; and also a supply of water should be 
at hand. 
The following books, being often referred to, will 
be quoted with abbreviated titles :— 
Carpenter.—“ The Microscope and its Revelations,” 
by W. B. Carpenter, M.D. (4th edition, 1868.) 
Beale.—“ How to Work with the Microscope,” by 
Dr. L. S. Bealej F.R.S; (1868.) 
Hassall —11 Adulterations Detedted,” by A. H. 
Hassall, M;D. 
Lesson I. On the Use of the Condensing Lens 
and Mirror. 
Material for Examination—White Blotting-Paper. 
Arrange the microscope at a comfortable inclina- 
tion, and adjust the draw-tubes of the eye-pieces to 
suit the distance betweeil the eyes. Screw on the 
objective, Ot; in doing this, hold the glass within 
the nozzle of the microscope with the first and second 
fingers of the left hand, while it is screwed in with 
the finger and thumb of the right. Do not leave go 
with the left hand until the screws have good hold ; 
observe the same precaution in unscrewing; never 
risk the fall of an objedt-glass. 
Tear with the forceps (not cut) a minute frag- 
ment from the edge of a piece of blotting-paper; USE OF CONDENSING LENS. 
183 
place it upon the glass stage-plate, and bring it, 
as nearly as can be judged, under the centre of 
the objedt-glass, which should be well raised above 
the stage. Place the lamp on the left of the micro- 
scope, at a height about half way between the stage 
and eye-piece, and diredt the light upon the paper 
with the condensing lens (p. 27). Bring the objedt- 
glass down, by means of the coarse adjustment, 
nearly to the working distance of the objedtive; 
this is always considerably shorter than the nominal 
focal length; with Oi it may be a little more than 
half an inch. Miter a little pradtice, the student will 
learn the proper distance for each glass ; until this 
is acquired, it is best to proceed cautiously, to avoid 
injury to the objedt, especially when high powers are 
used. 
Now look through the instrument ; adjust the 
position of the objedt, with the fingers or stage move- 
ments, until it occupies the centre of the field ; bring 
it accurately into focus with the coarse adjustment; 
and alter the position of the condensing lens and of the 
lamp, if necessary, so as to obtain the most perfedt 
illumination. 
The paper will be found to consist of interlaced 
fibres, which are seen to the best advantage at 
the edges, where they are frayed out: hence the 
direction to tear. This applies in numerous cases, 
a laceration or fradture sometimes revealing points 
of structure in a manner not easily demonstrated by 
other means. 
When the object has been fully examined, remove MICROSCOPICAL MANIPULATION. 
the condenser, open the large aperture in the wheel 
of diaphragms beneath the stage, lower the lamp 
Upon its stem into a convenient position for lighting 
the concave mirror, and diredt the convergent pencil 
upon the objedt. It will be found that the view now 
obtained is in every respedt inferior to that by re- 
fledted light; this is owing, partly to the opacity of 
the paper, and partly to the different densities of the 
objedt and of the medium in which it is viewed. If 
a higher power, Oi,M, is used, the result will be 
much worse ; this kind of view is that obtained by 
beginners, Who usually try to examine every objedt 
by transmitted light, and but rarely use other and 
better means of illumination. Change the power to 
Oi, B ; place a drop of water on the objedt with 
A Pipette [or the tip of the finger] ; cover with a 
thin glass; absorb any surplus moisture with blotting, 
paper; replace the slide on the stage; and adjust 
the focus. The confused appearance of the edges 
has now disappeared, and the light to some extent 
penetrates the central portions of the objedt. With 
the binocular, the full light from the mirror will 
be found to produce an unpleasant glare, and the 
white cloud illumination (p. 106) may be substituted 
with advantage. Still, little beyond the fibres at and 
near the edges can be well made out. Remove the 
slide from the stage ; take off the cover, and with a 
pair of mounted needles tear up and spread out the 
moistened paper ; replace the cover, and examine as 
before. All the strudture will now, probably, be 
seen ; if not, tear the objedt up still more, until the 
184 USE OF CONDENSING LENS. 
185 
result is satisfactory. Higher powers may now be 
used with advantage, taking care to make the 
requisite correction for the aberration caused by 
the cover-glass (p. 17), should the objective be pro- 
vided with the proper adjustment. With the glasses 
Oi, *Oj, and higher powers, it will be desirable to 
employ the fine adjustment in completing the 
focussing, and during the observation. Until the 
beginnerhas had some experience, itwill be best to use 
Oi, in preference to a higher power, as the risk of 
damaging the objeCt, or objeCt-glass, is lessened; 
after a time, the use of glasses of short working 
distance will become easy. In removing a slide from 
the stage when a high power is employed, raise 
the body to some distance, to prevent accidental con- 
tact with the front lens, as it might be scratched or 
otherwise injured. 
Try the effeCt of viewing some more torn up frag- 
ments in other media, such as oil, turpentine, or gly- 
cerine. Mount a specimen in balsam (p. 61), taking 
care that the paper has been well saturated with 
turpentine, to remove air bubbles. 
These experiments may be repeated with other 
kinds of paper, and their different degrees of com- 
pactness noticed. The determination of the material 
of which the paper is composed had better be deferred 
until Lesson VI. has been studied. 
Arrange the microscope and lamp for the use of 
the condensing lens ; as before, use Oi, B ; make a 
few marks, with a soft black-lead pencil, on a piece 
of blotting-paper, and notice the disposition of the 186 
MICROSCOPICAL. MANIPULATION. 
particles of plumbago among the fibres. Examine 
ink marks ; printing from plate (a visiting card will 
do); likewise specimens of surface-printing, as wood 
engraving or type, and also lithographs. Notice the 
varying manner in which the ink is distributed. 
Repeat the experiments with the light on the right 
hand, and also in front. Although it is most con- 
venient to place the lamp on the left,"because it is 
out of the way of the right hand moving and adjust- 
ing the objedt in the stage, yet it may sometimes be 
required to place the light elsewhere ; and the student 
should be able to work with it in any situation. 
Pradtice by daylight should not be negledted when- 
ever opportunities offer. 
Try, also, 'the effedt of using different eye-pieces. 
When a complete series of objectives is not at hand, 
an awkward interval of magnifying power may often 
be thus filled up (see Tables, pp. 179,180). In drawing, 
it is often useful to make the objedt fill the field; this 
can generally be done by a suitable change of eye- 
piece. 
Lesson II. 
Material for Examination—Dirt from Sponges. 
This can be obtained in any quantity from dealers. 
It accumulates at the bottom of the boxes in which 
sponge is imported. 
Arrange the microscope as in the former lesson, 
O2, Illuminator. Parabolic Lieberkuhn or [Con- 
densing-Lens].—If artificial light is used, render the DIRT FROM SPONGES. 
187 
rays parallel (p. 94) before they are refledted from the 
lieberkuhn. 
Spread a small portion of the substance over the 
stage-plate. 
The specimen will most likely be found to consist 
chiefly of sand, which prevents a good view of the 
other substances in it being obtained, although, here 
and there, some objedts may be seen. The sand 
may be removed by sifting through a piece of wire- 
gauze, of about 40—50 threads to the inch ; or a 
series of sieves may be used, if it is wished to carry 
out the sorting to a greater extent. Examine some 
of the coarse residue as before. The principal con- 
tents will be coarse sand and fragments of rock, 
fibre, abraded splinters of wood, seaweed, fragments 
of Echinus spines, skeletons of various Hydrozoa 
and Polyzoa (vulg., Zoophytes), sponge, spicules (PI. 2, 
figs. 7—11), and shells (PI. 2, figs. 1—6). 
Separate the shells and other objedts that may be 
required for further study; this may be done by 
picking them up with a small camel-hair pencil, 
moistened and drawn to a point. Small pill-boxes 
or homceopathic-bottles make convenient receptacles 
for keeping these objedts in, when sorted. A pocket- 
lens mounted on a stand, or a watchmaker’s glass 
will afford sufficient magnifying power. If the light 
is concentrated upon the substance to be examined 
with the condensing-lens, and black paper used to 
spread the sand on, a great deal may be done without 
using the glass at all. For dissedting and more 
delicate operations of this kind, Beck’s 3-inch 188 
MICROSCOPICAL MANIPULATION. 
binocular magnifier will be found useful: it is, in 
efifedt, a pair of achromatic spectacles of consider- 
able power, and fatigues the eyes less in prolonged 
operations than the use of a single lens. A more 
complete binocular dissedting microscope is described 
in “ Carpenter,” p. 54. 
Seledt some of the shells (PI. 2, fig. 1—6) re- 
sembling small nautili {Foraminiferce), and make 
arrangements for examining them in varied positions 
with Disc-holder (p. 53) or [stage-forceps]. Observe 
the peculiar structure of the part where the mouth of 
an ordinary univalve-shell (Gasteropoda) usually is 
(PI. 2, fig. x a), closed with a perforated plate, 
instead of being open. Also, in some species, 
perforations will be observed on the sides of the 
shells : hence the name of the group Foraminiferce. 
Mount some of the shells dry in various positions 
(taking especial care that the mouth is well dis- 
played), label, and preserve for reference. 
Bed some of the shells in balsam (p. 64), and 
grind away the surface so as to expose the in- 
terior; carefully polish, and remove the balsam. 
This process will reveal the chambered internal 
structure, which varies extremely in different species. 
An increase of power may now be used with ad- 
vantage (Oi, or Oj if the illuminator for this higher 
objective is accessible). With such augmented 
power, the minute shell-strudture may be observed; 
but this can be accomplished more readily by 
grinding a thin section, which will admit of examina- 
tion with higher powers and the paraboloid or MOUNTING SECTIONS OF SHELLS. 
189 
achromatic condenser. These thin sections can be 
ground by a process devised by Dr. Wallich (Ann. 
Nat. Hist., July, 1861; also “Carpenter,” p. 192, 
note). The shell is to be fastened to a thin plate of 
mica, in the first instance, and this, with the shell 
upwards, is to be cemented to the plate of glass .on 
which it is held during the process. One side is 
ground and polished in the usual manner. The 
slide is then warmed, which permits the removal of 
the mica plate with the half-finished section attached. 
The shell is then cemented by its polished side to 
another grinding-plate, and completed in the usual 
manner. The plate of mica is easily ground away, 
and offers no impediment to the cutting of the shell. 
The resulting section is to be mounted, either dry or 
in balsam, as circumstances may require. 
Foraminiferce and other shells abound in deep-sea 
soundings. As usually obtained from this source, 
they are mixed with the tallow placed at the bottom 
of the lead to bring up the sample : this grease must 
be removed by solution in benzol. Foraminiferce and 
other fossils may be separated from chalk by pro- 
cesses described in Lesson III. 
For further information respecting the Foraminiferce, 
see art. Foraminiferce, “ Micrographic Dictionary,” 
p. 292; “ Carpenter.” pp. 482—523 ; Greene’s “ Manual 
of the Protozoa;” Williamson and Carpenter’s 
Monographs (Ray Society). 190 
MICROSCOPICAL MANIPULATION. 
Lesson III. 
Specimens Required—Flour, Starch (Arrow-root, Potato- 
starch, or Brown and Poison's Corn Flour*), Chalk 
(in Lump, not Whiting or Washed Chalk), 
Powdered Lump-Sugar, and Common Table-Salt. 
Examine by placing a minute quantity of each of 
these white powders on the stage-plate, and examine 
with Oi, by reflected light, as in preceding lessons. 
Notice the different appearances of each. The flour 
will be found to contain numerous rounded, glittering 
bodies (starch granules), mixed up with a quantity of 
matter not easily defined with the power employed. 
The starch consists entirely of these shining sub- 
stances, which, in the larger kinds, as “ Tous-les-mois” 
(PI. 3, fig. 1), cause a distindt glittering appearance 
without any optical aid, if examined in a good light. 
The chalk is apparently structureless. The sugar 
and salt exhibit numerous crystals, more or less 
broken. 
The student will do well to examine the solubility 
of these substances, by shaking a little of each in a 
test-tube, with water. Small portions should also 
be heated to redness, on a slip of platinum foil, in 
the flame of a spirit-lamp. The flour and starch 
will be carbonised and burnt to an ash, if the heat 
is long continued. The chalk will still remain white. 
The sugar will melt, and then carbonise. The salt 
* This is a very cleanly prepared maize-starch (PI. 3, fig. 5), which 
may be used for nearly every purpose where arrow-root is required. 
It would be well if manufacturers would call things by their right 
names. The term “flour” is likely to mislead ; it means something 
quite different. Corn-starch or maize-starch would be more suitable. FLOUR AND STARCH. 
will decrepitate or crackle, and bound off the 
platinum. 
These simple chemical examinations should not 
be negleCted by the microscopist, especially when 
examining unknown substances. Some skill in the 
use of the blowpipe may occasionally be of service. 
Solubility of a substance in water or other fluids 
may be tested under the microscope, and with the 
advantage that very small quantities are sufficient for 
experiment. Other reagents may also be employed. 
“ Beale,” p. 201. 
Flour and Starch.—Place a little of the starch and 
flour on separate slides, with a drop of water; stir 
up with the point of a knife or needle, to diffuse the 
particles; cover with thin glass, and view with same 
power, first with dark-field illumination, and after- 
wards by transmitted light. Then use Of M by trans- 
mitted light. The flour will be seen to consist of the 
before-mentioned rounded bodies, with a small admix- 
ture of fragments of membrane, cell wall, &c. These 
are best seen in meal made by crushing or grating a 
grain of corn, as flour in general is too finely sifted to 
contain much of these textures. The slide of starch 
will exhibit the same rounded bodies, starch granules. 
They are best studied in a large-grained kind, such 
as Tous-les-mois* (PI. 3, fig. 1), the product of Canna 
edulis. With OfM and transmitted light, a number 
of concentric rings will be seen, surrounding a spot 
known as the hilum. Microscopists differ respecting 
* Tous-les-mois can be obtained of Messrs. Fortnum and Mason ; 
also genuine arrow-root and other materials, which can be depended 
upon for use as standard samples. 192 
MICROSCOPICAL MANIPULATION. 
the nature of these markings (see article, Starch, 
“ Micrographic Dictionary,” p. 657 ; “ Carpenter,” 
p. 399). Examine with polariscope Ox, and, if 
possible, with higher powers. Notice the charac- 
teristic black cross, having its centre at the 
hilum. In oat-starch (PI. 3, fig. 4) the black 
cross is wanting, the grains are polygonal, and 
clustered in rounded masses. Test the contents 
of the slides with a solution of iodine in water, 
made by placing a small crystal in distilled water. 
When it has acquired a straw colour, it will be of 
sufficient strength; only a minute quantity will 
be dissolved. A small drop of this reagent is to 
be placed at the edge of the cover with a pointed 
pipette, or, better, with one of the test-bottles with 
perforated conical stoppers. When the iodine 
reaches the starch granules, they will be stained of 
a violet colour. This and the polarisation test will 
readily distinguish starch granules from other round 
bodies. A series of starches from various plants 
should be mounted, and kept for comparison. Two 
slides of each should be prepared, one dry, the other 
in balsam for examination with the polariscope. 
When starch is mounted in balsam, care should be 
taken to employ as little heat as possible. Starch 
granules are not well preserved in fluids. Starch 
may be separated from flour by making it into a 
stiff paste, tying it in a muslin bag, and kneading in 
water. The gluten will be left in the bag, and the 
starch will fall to the bottom of the vessel, and can 
be cleaned by washing and decantation of the super- STARCHES OF DIFFERENT KINDS. 
natant fluid. Roots, &c. (as potatoes and carrots), 
can be crushed or grated, and the starch washed 
out, cleaned, and colledted. Starch may be viewed 
in situ by cutting thin sedtions of potato. These 
may be dried by the ether process (p. 58), and some 
mounted dry, and others transferred to benzol, 
and then mounted in balsam. 
Starches from various sources, and the strudture 
of wheat, barley, and other kinds of grain, are 
accurately figured in “ Hassall,” pp. 242—256 and 
314—321 ; see also Plate 3, figs. 1—6. 
Dr. Letheby, in his “ Ledtures on Food,” remarks 
“that although all starches and arrowroots have the 
same chemical composition and nutritive value, yet 
they are very different in their digestibility, the true 
arrowroots of the West Indies often remaining on 
the stomach of an invalid when the others would be 
rejedted.” Hence the importance of distinguishing 
the starches from various plants by means of the 
microscope. True West India arrowroot is repre- 
sented (PI. 3, fig. 2). 
The student should make accurate outline-sketches 
of all the starches examined, with the camera-lucida 
or tinted refledtor, selecting, in each specimen, the 
largest and smallest granules, and also some of 
intermediate size. A scale should be drawn on the 
paper from the micrometer. The shape and dimen- 
sions of starch granules and other similar objedts 
are readily compared from such drawings, and with 
far greater facility than from lists of micrometrig 
figures. 194 
MICROSCOPICAL MANIPULATION. 
Chalk.—Scrape a small portion of the chalk upon 
a slide. Place upon it a drop of water, stir it up, 
allow the larger particles to subside, and then gently 
tilt the slide, so that the water may run down, and 
carry with it the lighter particles. Absorb the 
surplus wet with blotting-paper, dry cautiously over 
the lamp-chimney, and mount in balsam. 
Examine with Oj, or [Ox, E2 or 3] black-field 
illumination, Parabola or [spotted-lens]. If the pre- 
paration has been successful, ForaminifercB may be 
distinguished among some of the particles. It is 
well to make two or three preparations, in case of 
failure. 
To obtain the shells, sponge-spicules, &c., sepa- 
rately, it will be necessary to break up the chalk. 
This is best efledted by boiling in a solution of 
sulphate of soda, made strong enough to crystallise 
on cooling: on this taking place, the chalk will be 
found to be disintegrated (Quekett’s “ Ledtures on 
Histology,” vol. ii., p. 80). Sufficient water should 
then be added to dissolve the crystals, the mixture 
agitated, and the chalk allowed to settle. The fluid 
should be decanted, the vessel again filled up with 
water, and decantation repeated before the finer 
particles have subsided. By continuing this process, 
if carefully managed, the shells will be obtained, 
eventually, nearly or quite clean. The washings 
should be allowed to settle, and be examined with 
the microscope, to ascertain whether they contain 
any of the smaller fossils. The shells may be 
mounted dry or in balsam. The result will vary SUGAR AND SALT. 
195 
according to the locality from which the chalk was 
obtained. 
Another very efficient process, by Mr. E. H. 
Robertson, will be found in Science Gossip, vol. iii., p. 36. 
If the sponge-spicules and siliceous fossils only 
are required, they can be obtained by dissolving the 
chalk in dilute hydrochloric acid. 
The coarse matter left after chalk has been washed 
for the purpose of making whiting is, when it can 
be procured, a good material to operate upon, as it 
is much richer in minute fossils, which are left in 
the heavier portions of the chalk. 
The Polycystince (PI. 2, figs. 12—14) may be obtained 
from the “ Barbadoes-earth,” by a process fully 
described by S. Furlong, Quarterly Microscopical 
Journal, Jan., 1861; also quoted by Davies, in 
“ Mounting Microscopic Objedts,” p. 64. 
Sugar and Salt.—The preliminary examination has 
already shown that these two substances differ 
materially in appearance from the others with which 
they were compared. While they exhibited none of 
the organised structure of the flour and starch, yet 
the difference between them and the chalk was very 
marked. They presented, when not too much 
crushed, traces of a certain regularity of form, 
which was entirely absent in the latter mineral. 
The condition of both the sugar and salt was very 
unfavourable for the study of these regular forms, 
which are known as crystalline. For further exami- 
nation, it will be necessary to procure uninjured 
specimens. MICROSCOPICAL MANIPULATION. 
196 
Well-formed crystals may generally be found in 
most samples of good moist-sugar: a few of these 
are to be mounted in balsam, for examination. 
Sugar is rather difficult to crystallise in the small 
way, the general result being an amorphous film on 
the slide. For a very full account of sugar, see 
“ Hassall,” pp. 181—198. 
Crystals of salt are easily obtained. Make a 
strong solution in distilled water, by boiling in a 
test-tube, and filter while hot. A drop of this fluid, 
placed upon a slide, will soon deposit a number of 
cubic crystals. These and the sugar-crystals may 
be viewed with a low power, O2, and dark-field 
illumination, by means of the Parabolic Reflector 
or [spotted lens']. This mode of lighting is very 
useful in such examinations, as it aids considerably 
in estimating solidity. Beyond regular mathematical 
form, no structure is to be observed in these bodies. 
Polarised light, however, renders certain optical 
peculiarities apparent. 
Arrange the microscope for the use of the polari- 
scope : it will then be seen that the crystals of salt 
are not at all affedted by the altered illumination, 
and this is the case with all crystals belonging to the 
cubic system: crystals of potash-alum will supply 
another example. Let the sugar now be examined 
in the same way: it will be found, upon rotating 
the analyser or polariser, that they either become 
coloured or, when the field is darkened, remain 
luminous. If the thickness of the crystals is not 
adapted to produce colour, the use of a suitable PREPARATION OF CRYSTALS. 
197 
selenite film will assist in obtaining it. It is here 
evident that polarised light reveals something which 
we should not be aware of without its aid : it 
supplies the means of determining whether a crystal 
possesses the property of double refradtion or not. 
The forms and colours of many crystals are 
extremely beautiful, and a collection is very easily 
made. As a long list will be found in “ Carpenter,” 
p. 773, only a few salts will be mentioned here. 
Make a hot saturated solution of sulphate of 
copper. If a drop of this warm solution is placed 
upon a slip of glass, and examined at once,* long 
crystals, with sloping ends like a turner’s chisel, 
will be seen shooting out from the edge, which will 
eventually cover the centre. If 4 small quantity 
of nitrous ether be added to the solution, a 
number of the crystals will be obtained in the form 
of separate rhomboids, which will shine like richly- 
coloured gems on the black field of the polarising 
microscope. Both slides, when dry, should be 
mounted in balsam, and labelled. 
Some curious phenomena attending the crystal- 
lisation of sulphate of copper are described by Mr. 
R. Thomas in the Quarterly Microscopical Journal 
(1866, p. 177). An abstract of the paper, with figures, 
will be found in “ Beale,” p. 214. 
The crystals of salicine are very easily made, and 
are very good examples of radiating crystals. A 
* For this purpose, the microscope must be placed vertically, to 
prevent the fluid running off the slide, as the observation is best made 
without a cover. The instrument should only be used in this position 
when absolutely necessary, as it is uncomfortable and inconvenient. 198 
MICROSCOPICAL MANIPULATION. 
saturated solution in distilled water is to be made, 
and a drop, placed on a carefully-cleaned slide, is to 
be evaporated over the lamp until it dries into an 
amorphous mass. Upon cooling, a number of 
circular groups of crystals will generally be formed ; 
this may be aided by breathing on the slide, the 
moisture often inducing the formation of the crystals. 
When sufficiently developed, the process should be 
stopped, by gently heating over the lamp-chimney, 
and mounting at once in balsam. 
An account of the mode of making the beautiful 
flower-like crystals of sulphate of copper and mag- 
nesia is given in “ Mounting Microscopic Objedts,” 
by T. Davies, p. 76. 
Lesson IV. 
With the point of a sharp knife, split, not cut, thin 
splinters from a lucifer match or piece of deal. 
Suitable fragments may often be found at the bottom 
of a box of matches. Examine with Oi; illuminate 
with Parabolic Lieberkuhn or [condensing lens], 
using Disc-Holder or [stage forceps] as a support. 
The splinter will exhibit a fibrous strudture, varying 
in charadter according to the direction of the split. 
The appearance presented in Plate i is obtained 
when the cleavage follows one of the lines radiating 
from the centre of the stem, and gives a better view 
of the elementary tissues of which wood is composed 
Structure of Wood. SECTIONS OF WOOD. 
than any other single sedtion. The simplest struc- 
ture in this specimen is the cellular tissue seen in 
the figure crossing the woody fibres ; these lines 
of cells run from the centre of the stem to its circum- 
ference, among the fibres and dudts, keeping up a 
communication between the centre and the growing 
portion between the wood and the bark, known as the 
cambium layer. The sides of the woody fibres are, in 
deal, covered with rows of dots, which are character- 
istic of the Coniferce, although they are found in the 
woody tissues of some few other trees. To see these 
well, a higher power will be required, 0£, and Para- 
bolic, or [spherical lieberkuhn], and to secure the 
most favourable position for observation the disc- 
holder will be found convenient. 
199 
To thoroughly investigate the structure of wood, 
three sections are necessary, one across the stem 
(PL 4, figs. 1, 2, 5) and two in a longitudinal 
direction (PL 4, figs. 3, 4, 6). For the purpose of 
study, where large and fine specimens are not re- 
quired, the use of a section machine may be dispensed 
with, as small seditions in any direction may easily be 
cut with a sharp knife or razor. 
The transverse section (PL 4, fig. 2) shows the 
general arrangement of the tissues, composing the 
stem, consisting of a concentric arrangement of 
fibres and vessels, of which the cut ends only are 
seen in this section ; the concentric rings represent 
periods of growth, and usually, but not always, 
correspond with the number of years the stem has 
been forming; the medullary rays are seen running 200 
MICROSCOPICAL MANIPULA TION. 
from the pith in the centre to the circumference ; 
their cut ends are seen in fig. 4 and their sides in Plate 1 
and Plate 4, fig. 3 c—they are developed to an enor- 
mous extent in the Clematis (PI. 4, fig. 1 r), where their 
grouping in masses gives a marked character to the 
transverse seCtion. 
The other two sections are cuts one parallel to the 
medullary ray (PI. 4, fig. 3) and the other across 
it (PI. 4, fig. 4). The former corresponds with 
the splinter figured in Plate 1. The first, or radial 
section, exhibits the sides of the medullary rays; 
the second, tangential section, their cut ends; these 
are very conspicuous in mahogany. 
The structure of the stem of endogenous plants 
differs considerably from that of exogens, just de- 
scribed ; in these, there is no marked distinction 
between wood and bark (PI. 4, fig. 5)—the rings of 
annual growth and the medullary rays are wanting, 
so that a single longitudinal section (PI. 4, fig. 6) 
only is required, instead of the two needed to 
demonstrate the structure of an exogen (a seCtion 
of cane will supply a good example). For the 
histology of plants, see Bentley’s “ Manual of 
Botany,” Book I. There are many very accurate 
figures of vegetable tissues throughout Hassall. The 
knowledge of the minute structure of plants is of the 
greatest use to the analytical microscopist, as it is by 
this means alone that mixtures of vegetable powders 
can be detected. Full details are given in Hassall. 
Sections of woods, such as ebony, box, and some 
others, which are too hard to be cut in the usual COLLECTING AQUATIC OByECTS. 
manner, may be obtained by grinding, as in the case 
of bone; this process must also be adopted with 
cellular tissue, when hardened by deposits of sclero- 
gen, as cherry and plum stones, ivory nuts, cocoa- 
nut shell, and many other hard substances. Soft 
substances, as leaves, may be cut by being pressed 
between two pieces of cork, which are sliced with it. 
Cellular tissue like that of the common rush, which 
yields so much to the knife that it is pressed aside 
instead of being cut, should be saturated with melted 
wax before attempting to make a seCtion ; this can 
be removed from the thin slices with benzol. 
201 
A quatic Examinations. 
Lesson V. 
The results of aquatic collecting will require a 
somewhat different treatment from that recom- 
mended in the preceding lessons. Owing to the 
density of the medium in which the objects are 
viewed, and the generally diaphanous nature of the 
organisms themselves, comparatively little use can 
be made of reflected light as a means of illumination ; 
its employment is, therefore, rather the exception 
than the rule. 
An account of the varied modes of collecting 
objects of this kind, and their habitats, would almost 
occupy a volume. For obtaining fresh-water speci- 
mens, advantage may be taken of the excursions of 
the various London and provincial societies. The 202 
MICROSCOPICAL MANIPULATION. 
Quekett Microscopical Club arranges a series of 
excursions, which take place every fortnight during 
the summer months; and, as experienced naturalists 
always accompany these expeditions, the student 
may derive much practical instruction in the way of 
collecting and identifying specimens. The micro- 
scope should always accompany the student to the 
sea-side during a temporary residence, and it is well, 
if possible, to take the usual working instrument, 
well equipped with objectives and apparatus, and not 
some small contrivance which has nothing to recom- 
mend it but portability. The following works 
also contain useful information on the subject 
of marine and fresh-water collecting :—“ Handy- 
Book of Algae, &c.,” Rev. W. W. Spicer; “ Beale,” 
p. 146; “The Aquarium, Devonshire Coast, Tenby, 
&c.,” P. H.Gosse; “Seaside Studies,” G. H. Lewes; 
“ Marvels of Pond Life,” H. J. Slack; “ History of 
Infusoria,” A. Pritchard. See also list of micro- 
scopical works in “ Beale,” p. 364. 
The preliminary examination of a quantity of 
aquatic material is generally most conveniently 
done in a large trough (Fig. 15, p. 45), with 
a low power, O3,* and dark-field illumination, mirror 
turned aside, or long-focus spotted-lens; the paraboloid 
has too short a focus for this purpose. 
A good diagnosis can often be made by examina- 
tion in the bottle or tube in which the collection is 
* Ross’s 4-inch objective is very suitable for this kind of work; it 
defines well, bears a considerable amount of eye-piece power, will 
take in an objedt of about o'\ inch diameter, and is low in price. EXAMINING AQUATIC OBJECTS. 
brought home, with the pocket-lens. Many of the 
larger animals and plants can be distinguished with 
this low power, and those too small to be distinctly 
made out can often be identified by a trained eye. 
Objedts in water may be very conveniently examined 
out of doors with the pocket-lens, if placed between 
two small pieces of glass (a 3x1 slide cut in half, 
and the sharp edges smoothed with a corundum 
rubber, answers well): these can be kept in the 
waistcoat pocket, ready for use. 
203 
Portions required for more minute examination, 
if on plants, may be detached with the scissors or 
forceps. Free-swimming animals, and plants, or 
deposits, may be taken up with a suitable pipette, by 
closing the upper end with the finger, and bringing 
the other extremity over the object to be secured. 
The finger is then to be removed; and the water 
rushes in, carrying the objeCt with it. The finger is 
again applied, to close the top of the tube, which is 
then lifted out of the water, and the objeCt trans- 
ferred to a slide, cell, or other convenient vessel. 
If the object is very thin, a common slide, covered 
with a piece of thin glass, will serve for the exami- 
nation with a tolerably high power. Should the 
objeCt be liable to injury from the pressure of the 
cover, a cell may be used, or a hair placed between 
the thin glass and the slide. In all cases in 
which the objeCt is required to be kept for some 
days, the growing-slide (Fig. 16, p. 46) should 
be used : some of these may conveniently be made 
with cells attached. The thin trough (Fig. 14, 204 
MICROSCOPICAL MANIPULATION. 
p. 44) may sometimes be useful. All these con- 
trivances permit the employment of the parabaloid 
for dark-field illumination, and also the achromatic 
condenser. The live-box supplied with most micro- 
scopes is sometimes useful, but has the disadvantage, 
from the height it raises the objeCt above the stage, 
of preventing the employment of any sub-stage 
illuminator but the mirror. 
It is frequently necessary to subjeCt the substance 
under examination to pressure. For this purpose, 
an instrument known as a compressorium is neces- 
sary, two of which, more completely fulfilling the 
requirements of the microscopist than older con- 
trivances, are the invention of the late Richard 
Beck (Quarterly Microscopical Journal, vol. xii., p. 4); 
we are also indebted to him for a live-trap for con- 
fining small aCtive animals within the field of the 
microscope, without compressing them or otherwise 
restraining their movements (Quarterly Microscopical 
Journal, vol. xiii., p. 113). 
The habits of marine or fresh-water animals may 
be watched in aquaria, which need not of necessity 
be expensive : basins and glass jars answer the pur- 
pose extremely well. The marine aquarium should 
always be carefully examined after the introduction 
of fresh specimens of seaweed, as they usually bring 
in with them large numbers of minute organisms. 
The author, instead of throwing away the results 
of fresh-water collection when done with, places 
them in a tank in the garden, used for growing 
aquatic plants, which, although only containing EXAMINATION OF FIBRES. 
205 
about 200 gallons of water, always yields a rich 
supply of microscopic objects, most of which regu- 
larly breed and appear from year to year. 
Some of the commoner microscopic inhabitants of 
fresh and salt water are represented in Plates 5 and 6. 
Fibres used in the Manufacture of Clothing, and Analysis 
of Textile Fabrics. 
Lesson VI. 
The materials of textile manufactures may be 
divided into four classes, two of which are derived 
from the vegetable and two from the animal king- 
dom. 
The vegetable fibres consist either of hairs or liber 
cells, a tissue resembling woody fibre. 
Of hairs, only those covering the seeds of several 
species of Gossypium (a genus of malvaceous plants) 
are used in commerce, and are known as cotton (PI. 7, 
fig- 4)- 
The liber cells are supplied from many sources, 
and are used for a great variety of purposes, every 
kind of fabric, from fine linen to cordage, being made 
from them. 
Familiar examples are flax (Linum usatissimum, 
PI. 7, fig. 5), jute (Corchorus capsularis, PI. 7, fig. 2), 
hemp (Cannabis sativaj ,China-grass or rhea fBceh- 
meria nivea). 
The animal materials consist of silk (PL 3, fig. 9, 
and PI. 7, fig. 3), an albuminous fibre produced by 
various caterpillars. 206 
MICROSCOPICAL MANIPULATION. 
The remaining class comprises the hairs of those 
animals which are capable of being either spun or 
felted—such as wool (PI. 7, fig. 1, and PI. 3, fig. 7) 
and its varieties, as alpaca, &c., hairs of rabbit, 
beaver, &c. 
Specimens Required.—Fibres of cotton, flax, hemp, 
silk, and wool; pieces of calico, muslin, linen, silk, 
flannel or blanket, and any other woven fabrics and 
threads procurable; also hairs of various animals. 
Examine fibres of cotton, flax, hemp, silk, and 
wool, as described in Lessons I. and II.,with Oi or Of, 
on stage-plate, by reflected light. 
Notice the differences of structure. Cotton consists 
of flattened, twisted fibres (PI. 7, fig. 4). Flax and 
hemp are rounded (PI. 7, fig. 5), with more or less 
apparent .transverse markings. Silk is conspicuous 
for the absence of all structural peculiarities (PI. 7, 
fig. 3). Wool exhibits a circular fibre, with delicate 
markings (PI. 7, fig. 1). 
It will be seen that the four classes of fibres have 
all well-marked characters, and can be readily dis- 
tinguished from each other under the microscope. 
Mount specimens of all the fibres collected, by 
dry process (p. 55), taking care, as fibrous 
tissues are very hygroscopic, that they are properly 
dried. As they will bear a heat not exceeding that 
of boiling water without injury, the ether process 
will not be required. Label, and preserve for future 
reference. Place, also, a small portion of the fibres 
of cotton, flax, and hemp in separate bottles, with 
saturated solution of chloride of calcium ; leave EXAMINATION OF FIBRES. 
207 
them to soak for a few days, and then mount in 
same fluid, taking the precaution to separate the 
fibres by tearing them apart with needles, so that 
the single fibres may be well displayed before closing 
the cell. The silk and wool should be mounted dry, 
and also in balsam, with as little heat as possible, if 
transparent specimens are required. 
As the mountings in chloride of calcium will be 
some days in hand, unless the air-pump is used, 
prepare portions of cotton and flax, on slides, with 
turpentine, which will render the fibres transparent; 
and examine with a power of not less than Oi 
(Of will be better), with polarised light, using achro- 
matic condenser and eye-piece analyser (p. 136). If 
the condenser is not accessible, the intensity of the 
illumination may be greatly increased by concen- 
trating the light of the lamp on the concave mirror 
with the condensing-lens. 
The cotton will display more or less colour, indicating 
doubly-refradtive properties, but no very marked 
structural peculiarities (pi. 7, fig. 4). The flax will 
show a vast amount of structure (pi. 7, fig. 5). The 
transverse markings seen by reflected light will 
become more conspicuous, and other markings 
of a more or less spiral nature will, with proper 
adjustment of the selenites (p. 140), be rendered 
visible. These consist of thickenings of the cell 
wall, known as secondary deposits, and are easily 
seen by polarised light, owing to their doubly- 
refraftive power differing from that of the thinner 
portions of the tissue ; while by ordinary transmitted 208 
MICROSCOPICAL MANIPULATION. 
light, they would have been nearly invisible, owing 
to their transparency. It is much easier to dis- 
tinguish the fibres of cotton and flax in a mixed 
fabric by observations with polarised light than by 
any other means. A.power of Oi is quite sufficient 
when merely the presence of cotton in a flax fabric 
has to be determined. 
A careful series of observations on liber cells is 
much wanted. At present, it is difficult to dis- 
tinguish between flax and hemp, and other fibres of 
the same class, so that they might be dotetfted with 
certainty in mixed fabrics. The chief impediment 
consists in the very close resemblance of all these 
fibres to each other. It is, in general, much easier 
to distinguish them in mass, by various peculiarities 
of colour, texture, &c., than by the most careful 
microscopical examination of single fibres. 
The aCtion of dyes might reveal some peculiarities 
connected with these tissues. Experiments on 
cotton have been tried by the late Mr. W'. Crum, 
F.R.S. Transverse sections* have been examined 
by a Continental observer, and, although somewhat 
difficult to obtain, might be studied with advantage. 
The whole subject is much in need of investigation. 
Woody fibres are used occasionally for purposes 
of adulteration; an instance is mentioned under 
silk. A curious case came under the author’s notice, 
in which cotton wick, intended for the manufacture 
* Fibres, hairs, and other long thin substances of which sections 
are required should be made up into bundles with weak glue, and cut 
into thin slices with a sharp razor; the sections can be liberated by 
dissolving the gelatine in hot water. of composite candles, was adulterated with a small 
quantity (about 5 per cent) of some undetermined 
woody fibre. Trivial as was the amount of this ad- 
mixture, it entirely unfitted the wick for the purpose 
for which it was intended, causing it to remain 
unconsumed, and accumulate, instead of bending 
over to the outer part of the flame, and burning away. 
EXAMINATION OF FIBRES. 
209 
For account of liber cells, see—Bentley’s “ Manual 
of Botany,” p. 30; article, Liber, “Micrographic 
Dictionary,” p. 417; Science Gossip, vol. ii., p. 10. 
The length of cotton-fibre (staple) is determined by 
drawing out a tuft of the cotton repeatedly between 
the fingers, until the hairs are laid parallel, and then 
measuring the length of the tuft. This is the mode 
of measurement in use among cotton-brokers. An 
easy and accurate method of measuring single fibres 
of cotton had long been a desideratum in analytical 
operations. In 1862, Captain C. J. Mitchell, of the 
Government Central Museum, Madras, writes, re* 
spedting a process he had used for this purpose:— 
“ It is exceedingly tedious, and very trying to both 
eyes and head.” Shortly afterwards, the author 
endeavoured to measure single fibres by fixing them 
with gum upon a glass slide, making a drawing with 
the camera-lucida, and measuring the curved line so 
obtained with a map-measurer. The enlarged 
drawing was from 18 inches to 2 feet in length. The 
chief objection to this process was the amount of 
time occupied in the investigation, ordinary micro- 
metrical operations not being applicable, on account 
of the great length of the fibres and the impossibility 210 
MICROSCOPICAL MANIPULATION. 
of measuring them as straight lines; hence the 
necessity of making drawings, and following all the 
curves with the little measuring-wheel. A simple 
and accurate process has been invented by Mr. C. 
O’Neill, and is described by him in a communication 
to the Literary and Philosophical Society of Man- 
chester “ Memoirs,” (1863—4, p. 389). The apparatus 
consists of a plate of glass, on which is 
ruled a scale 2 inches long, divided into tenths, a 
pair of fine forceps, and tw'o camel-hair pencils. 
The scale is laid upon a piece of black cloth, and 
well lighted, by daylight or a lamp with condensing- 
lens. The fibres are selected, and held by the 
forceps, and, with one of the pencils, moistened in 
the mouth, pressed and drawn out on the glass 
plate ; the forceps are then dropped, and the other 
pencil brought into use to lay out the fibre, the 
length of which is then read off. The operation 
requires considerable 'practice, but, when acquired, 
single fibres can be measured to inch with suffi- 
cient rapidity for analytical purposes. As some 
cotton-fibres—such as Sea Island—reach the length 
of 2 inches, it is well to have the scale extended to 
3 inches ; this will also prevent the necessity of being 
careful about placing the fibre on the beginning of 
the scale, as there will be plenty of space. And it is 
convenient to have a scale of about the same length 
divided into millimetres for comparison with Con- 
tinental observations. Mr. O’Neill gives the following 
results of some observations on the length of cotton- 
fibres :— EXAMINATION OF FIBRES 
211 
Maximum. 
Mean. 
Minimum. 
in. 
in. 
in. 
Sea Island .. 
2'00 .. 
i-68oo 
•• I"35 
Another sample 
2-05 .. 
1-4440 
I'lO 
Queensland .. 
r95 
1-5010 
.. I'lO 
Egyptian 
r55 •• 
1-2520 
.. 0-95 
Pernambuco 
1-50 .. 
1-6750 
•• o*75 
Surat 
I-I5 •• 
0-9425 
• • 075 
Another sample 
I'lO 
0-9250 
•• 0-55 
Another sample 
r°5 .. 
0-9050 
.. 0-70 
In another communication (1862-3, P* 38g), Mr. 
O’Neill describes an ingenious instrument for mea- 
suring the tensile-strength of fibres. The following 
are some of the mean breaking-weights of single 
cotton-fibres:— 
grs. 
Sea Island 83^ 
Another sample .. .. go’o 
Surat io5'8 
Another sample .. .. i4rg 
Egyptian io8’o 
Another sample .. .. 127x3 
Pernambuco I40’0 
These determinations are of great value to the 
manufacturer. And those intending to make textile 
fabrics their study would do well to consult Mr. 
O’Neill’s papers. 
The amount of twisting in a thread is a very im- 
portant element in the estimation of its strength. 
The famed Dacca muslins owe much of their 
superiority in lightness* and strength to the tight- 
ness of the twist in the delicate filaments of which 
they are composed. This has been determined by 
A piece of fine Dacca muslin, x yard wide and xo yards 12 inches 
long, weighed only 1565 grains (Dr. Watson ; work cited, p. 75). 212 
Dr. J. F. Watson, who gives the following as the 
average number of twists per inch in four samples of 
muslin:—French, 68*8; English, 56*6; Dacca, iio*i; 
Dacca (another sample), 807. The whole subjeCt 
is carefully worked out by Dr. Watson in “The 
Textile Manufactures and Costumes of the People 
of India,” pp. 59—74. 
MICROSCOPICAL MANIPULATION. 
Cotton is mixed with other fibres legitimately 
in the well-known “ union cloth,” a compound of flax 
and cotton, and as an adulteration, with woollen 
fabrics, and in some specimens of lint. 
Silk will be found to burn differently from the 
fibres of the two classes hitherto considered. It 
curls up, and ultimately fuses and burns, giving off 
the disagreeable odour common to animal tissues, 
as hair, wool, feathers, &c. The fibres depolarise 
light, giving more or less colour, but do not exhibit 
any structural peculiarities (PI. 7, fig. 3). Silk 
is entirely dissolved when boiled in strong solu- 
tions of caustic potash or soda. If cautiously 
heated on a slide in a strong solution of soda, the 
fibres will be found to swell, and bulge out in parts 
(PI. 3, figs. 9, 10). 
Admixtures of other fibres with silk are easily de- 
tected, by the appearance of the unravelled threads, 
under the microscope. The material most commonly 
used to adulterate silk is jute (PL 7, fig. 2). The 
microscopical characters of this fibre are not of a 
very marked description. It is best distinguished 
by examining the residue under the microscope after 
the sample has been boiled in a strong caustic EXAMINATION OF FIBRES. 
213 
alkaline solution. Specimens of silk, breaking and 
fraying when pressed into tight folds, may always be 
suspected of containing jute : the beautiful gloss of 
this fibre, when carefully prepared, is the reason of 
its selection as an adulterating material. 
Wool.—As already observed, this fibre presents 
very marked structural peculiarities. In burning, 
the same phenomena are apparent as in the case of 
silk; it is also soluble in hot alkaline solutions. The 
histological nature of the surface-markings may be 
considered undetermined at present, the apparent im- 
brications being interpreted by some as scales ; and 
in many hairs (those of some of the bats especially) 
this character is very marked (M. C. Cooke, Trans- 
actions of the Quekett Microscopical Club, vol. i., pp. 33 
and 55, Plates 1, 2, and 3; article, Hairs of A nimals, 
“Micrographic Dictionary,” p. 330; “Carpenter,” 
p. 704). 
Two valuable communications on “ Wool, Com- 
mercially and Microscopically Considered” were 
made by Mr. N. Burgess to the Quekett Microscopical 
Club. Unfortunately, only abstracts appear in the 
Transactions (vol. i., p. 23). In this paper some im- 
portant points of microscopical structure, bearing 
upon the felting process, are noticed. It is .shown 
that the felting qualities of wool depend upon the 
number of waves or curvatures in the length of a 
fibre, and not upon the apparent serrations or 
imbrications. 
When heated on a slide with strong solution of 
soda, wool swells, the medulla or interior cellular MICROSCOPICAL MANIPULATION. 
214 
portion becomes more distindt, and the imbrications 
disappear, seeming to have unfolded (PI. 3, figs. 7, 8). 
Wool is mixed with other substances in the 
manufacture of fabrics generally with the view of 
improving the texture or appearance, and not usually 
as an adulteration. The most remarkable instance 
is that of a silken thread with fine woollen fibre wound 
round it, the objeCt of this planting being to make a 
very slender, but yet strong, filament, apparently of 
wool. NOTES. 
Page 2.—In the Monthly Microscopical Journal,vol. iii., 
p. 183, Dr. Carpenter gives an account of the “ Comparative 
Steadiness of the ‘ Ross’ and ‘Jackson ’ Microscope Stands.” 
The result of his experience under very trying circum- 
stances is decidedly in favour of the latter mode of con- 
struction. 
Microscope Stands. 
Immersion Objectives. 
Page 18.—Objeft-glasses are now made in which the 
corrections are adapted for viewing an object through water, 
instead of air as in the usual construction ; the advantages 
are increase of light and improved definition. The drop of 
water is held by capillary attraction between the front lens 
and the cover-glass. This system of construction is, of 
course, only applicable to glasses of short focal length, as 
the |th and above. Foreign makers adapt these objectives 
for use only as immersion lenses. The English opticians 
have constructed theirs so as to be capable of use either 
through air or water, by means of an additional front 
combination, which can be substituted at pleasure for the 
ordinary one; this plan is a decided advantage, as it gives 
the power of using the objective in the usual way as well 
as by immersion. 
Molecular Motion and Organic Matter in the 
Air. 
Page 30.—Papers on “ Molecular Motion,” by E. P. Joule, 
LL.D., F.R.S., will be found in the Chemical News, 
vol. xxi., p. 66, and on “ Organic Matter in the Air,” by 
Dr. R. A. Smith, F.R.S., in the same volume, pp. 64, 78. MICROSCOPICAL MANIPULATION. 
Cutting Glass. 
Page 35.—The crystal represented in Fig. 13 exhibits 
several cutting edges besides the one marked a, b. Where 
large quantities of glass are cut, as in wholesale warehouses, 
the edge is frequently worn out; the diamond is then re-set, 
by which one of the other edges is placed in the proper 
position for cutting. 
Fig. 46. NOTES. 
217 
Solution of Canada Balsam in Benzol. 
Page 64.—The solution of Canada balsam in benzol does 
not absorb air like pure balsam ; care should therefore be 
taken to prevent any being included in the object; and, as 
this medium contracts in drying, a sufficient quantity should 
be used to prevent spaces being left under the cover, as the 
fluid shrinks. 
Page 67.—The third volume of Holtzapffel’s “ Turning 
and Mechanical Manipulation ” is entirely devoted to an 
account of various abrasive processes, many of which will 
be found useful to the microscopist who makes petrology 
his study. The machine for cutting rock sections used by 
Mr. Jordan is now manufactured by Messrs. Cotton and 
Johnson, Grafton Street, W.C. It is an extremely compact 
piece of apparatus (Fig. 46), and much more convenient 
than the ordinary lapidary mill for microscopical work, as 
it is provided with means of regulating the thickness of 
the section, and also of keeping it up close to the slicing- 
Cutting Rock Sections. 
Fig. 47. 
disc by means of a self-aCting arrangement; special care 
is taken to make it more cleanly in work than most grinding 
and slitting apparatus. The same firm also manufacture 
a very portable and convenient pair of bellows (Fig. 47), 
requiring no fixing, and which, used in combination with 
Herapath’s gas blow-pipe, will be found convenient for 
such processes of glass-working (p. 38) as require a greater 
heat than can be obtained from the Bunsen burner. 218 
MICROSCOPICAL MANIPULATION. 
Parabolic Lieberkuhn. 
jPage 101.—Mr. Collins attaches the parabolic lieberkuhn 
to a steel rod, provided with suitable adjustments 
Fig. 48. 
somewhat like those of the stage forceps; this is made 
to fit into a hole in the stage, or some other convenient 
part of the stand, and allows the refledtor to be used with 
any objedt-glass, dispensing with the use of the adapter. 
Illuminating Objects by Reflected Light. 
Page 104.—There are two other modes of illuminating 
objects by refledted light with high powers, which are 
made but little use of, notwithstanding the known ad- 
vantages of lighting from above. In one, the invention of 
Mr. Charles Brooke, a small plane speculum or flat 
lieberkuhn is placed on the setting of the objedt-glass in 
the usual manner, its surface being coincident with that 
of the front lens. This receives the oblique rays from 
Wenham’s parabola, and l’efledts them downwards on the 
objedt, which, for being thus viewed, should be uncovered. 
—Brit. Ass. Rep., 1851, pt. 2, p. 7. Mr. Wenham uses a 
small truncated hemispherical lens ; this is temporarily 
attached to the under side of the slide by means of a 
minute quantity of oil of cassia or other highly refradtive 
fluid. The light of the paraboloid is thus caused to pass 
through the slide and fall upon the under side of the thin 
cover-glass, at an angle suitable for total refledfion ; the 
objedt will be found to be brilliantly illuminated if the 
apparatus is properly managed.—Monthly Microscopical 
Journal, vol. ii., p. 2g. This simple contrivance can be 
used with objedtives of the highest power. NOTES. 
219 
Phenomena of Interference. 
Page 122.—The phenomena of interference are most 
readily understood by the aid of a simple and ingenious 
model designed by Charles Woodward, Esq., F.R.S. It 
consists of a wooden frame (PI. 8, fig. i, f, fi), in which 
are arranged a number of square wooden rods, the tops of 
which are cut to the form of a series of waves. They are 
prevented from falling out by pins, suitably placed, and for 
convenience of reference the situation of the summits of 
the waves is marked by stars on the frame, f, fi. A solid 
block of wood (fig. 2, b, bi), having its upper surface cut to 
correspond with fig. i, completes the apparatus. If the 
frame, f, fi, is placed upon the block, b, bi, so that the 
stars are coincident, as in fig. 3, it represents two waves 
starting together, and, by coalescence, augmenting each 
others intensity indicated in the model by a wave of double 
height. But if placed, as in fig. 4, so that the dots on 
b, bi correspond with the stars on F, fi, the tops of the 
rods will sink into a straight line, illustrating the destruc- 
tion of wave motion by interference when a wave starts 
half a wave’s length before another. Plate U. 
oc.alf. Fig. 12 to 14 
ooi 
ScaLe Fig 1 to 11. 
oohn.. 01 Plate nr 
W- Westjmp' Plate W 
1 in 
'01 vn 
W. West irrvp. 
ScaLe for -Fig- 1 PlateV. 
"r.'.Vest im-p Plate VI Plate YII 
y/est imp Plate m INDEX. 
Aberration, chro- 
matic, 15 
— spherical, 14 
Achromatic condenser, 112 
use of with micro- 
polariscope, 136 
Adulteration of textile fa- 
brics, 208 
Air bubbles, absorption of 
by Canada balsam, 61 
microscopical ap- 
pearance of, 29 
— organic matter in, 215 
— pump, use of for drying 
tissues, 57 
in preparing 
objedts, 70 
Alcohol as a preservative 
fluid, 81 
— methylated, 40 
Alkaline solutions, adtion 
of on silk and wool, 213 
Analyser for micro-polari- 
scope, 132 
Aquaria, 204 
Aquatic objedts, 201 
Arsenious acid, 84 
BAILEY’S selenite 
stage, 134 
Balsam, Canada, 59 
Barton’s buttons, 123 
Beale, Dr. L. S., fluid for 
staining tissues, 91 
Beale, Dr. L. S., modifi- 
cation of Thwaites’s 
fluid, 82 
— on use of glycerine, 86 
Beck, R., disc-holder, 53 
— researches with binocu- 
lar microscope, 22 
— parabolic lieberkuhn, 99 
Binocular microscope, 19 
advantages of em- 
ploying, 22 
for high powers, 21 
pseudoscopic, 22 
Black cross in polarisation 
objedts, 131, 192 
Bone, cutting sedtions of, 
65 
Bottle for keeping mounting 
fluids, 91 
CABINETS for pre- 
serving objedts, 76 
Camera lucida, 146 
Camphine lamp, 26 
Camphor water, 81 
Canada balsam, 5g 
solution in benzol, 
64, 217 
vessels for keeping, 
63 
Carbolic acid, 81 
Carmine fluid for staining 
tissues, 91 
Castor oil, 90 222 
Cell, closing of in fluid 
mounting, 72 
Cells, cementing to glass 
plates, 42 
— glass tube, 47 
— metal, 48 
— Mr. McIntire’s cork, 4g 
— wood, for mounting ob- 
jects, 53 
Cement, Canada balsam, 64 
— damar and benzol, 75 
— electrical, 45, 55 
— gold size, 55, 56, 73 
— liquid glue, 56 
— marine glue, 42 
Chalk drawing (litho- 
graphic), 171 
— examination of, 194 
China grass, 205 
Chloride of calcium, 83 
sodium, 84 
Chromatic aberration, 15 
Cleaning glass, 40 
— lenses, 23 
— surplus balsam from 
slides, 62 
Clematis, structure of stem 
of, 200 
Cobweb micrometer, 158 
Colour produced by inter- 
ference, 122 
polarised light 
with selenite, 129 
Coloured light, wave lengths 
of, 122 
Colours, table of Darker’s 
selenites, 136 
Compound microscope, its 
construCtiori, 13 
Compressorium, use of, 204 
Condenser, achromatic, 112 
— Webster, 115 
Condensing lens, 27, 93,182 
Coniferous wood, structure 
of, 199 
INDEX, 
Copper plate engraving, 166 
Correction of objeCt-glass 
for aberration caused 
by covering-glass, 17 
Corundum, tools made from 
for cutting hard sub- 
stances, 37 
Cotton, 206 
— determination of length 
of staple, 209 
— fibres, strength of, 210 
Covering-glass, correction 
of objeCt-glass for aber- 
ration caused by, 17 
Creosote water, 81 
Crystals, examination of, 
x95 
— polarisation of, 196 
DAMAR varnish used in 
fluid mounting, 75 
Dark field illumination, 107 
Darker’s series of sele- 
nites, 134 
Deane’s gelatine, 88 
De La Rue’s iridescent 
cards, 123 
Diamond used for cutting 
glass, 33 
Diaphragm, graduating, 106 
— Iris, 106 
— plate, 105 
Disc-holder, Beck’s re- 
volving, 53 
Disc, ruled, in eye-piece 
for drawing, 154 
Distilled water, 80 
Division of lines, 162 
Double refraction shown by 
polarised light, 137 
Draw-tube, 19 
— use of in micrometry, 
160 
Drawing, instruments for, 
*46 INDEX. 
223 
Drawing materials, 163 
— microscopical, 142 
arrangement of illu- 
mination, 152 
— pencil, 164 
— with ruled disc in eye- 
piece, 154 
Drilling holes in glass, 36 
Dry-mounting objects, 52 
Drying microscopical ob- 
jects, 57 
Dust of cities, 30 
Electrical cement, 
' 45 
Endosmosis, 78 
Engraving, 166 
— on stone, 173 
— wood, 169 
Etching, 168 
Ether used for drying 
tissues, 57 
Excursions, natural history, 
202 
Eye-piece, 18 
— micrometers, 158 
FARRANT’S gum me- 
dium, 89 
Fibres, 205 
Filtering fluids, 83 
Fixing pencil drawings, 165 
Flax, 205, 207 
Flour, examination of, 190 
Fluid, mounting objeCts in, 
69 
Fluids used for mounting 
objects, 77 
Foraminiferxe, 188 
— mode of separating from 
chalk, 194 
Fossil inseCts in litho- 
graphic stone, 170 
Fungi to be avoided in 
mounting objects, 54 
Gaslight, 24 
Genesis and the un- 
dulatory theory, 124 
Glycerine, 84 
— jelly, 88 
Glass, 33 
— cementing with marine 
glue, 42 
— cleaning, 40 
— cutting with the dia- 
mond, 33, 216 
corundum tools, 
37 . 
— drilling holes in, 36 
— smoothing sharp edges 
of. 37 
— thin, for covering ob- 
jects, 35 
— tube cells, 47 
— tubes, working of, 39, 
2x7 
— unannealed, doubly re- 
fractive properties of, 
139 
Gold size as a cement, 55, 
73 
Graduating diaphragm, 106 
Graphotype, 169 
Grinding sections of hard 
substances, 65 
Growing slide, 46 
Gum medium, 89 
HAIRS, vegetable, 
205 
Hand magnifier, mode of 
using, xi 
Hantzsch’s mounting 
fluid, 80 
Hard substances, cutting 
sections of, 65 
— woods, cutting sections 
of, 200 
Hemp, 205 
Herapathite, 127, 133 224 
INDEX. 
Hooke, Dr., mode of 
measuring objects, 156 
Huyghenian eye-piece, 18 
T CELAND spar, double 
refraction by means of, 
126 
Illuminating apparatus, 93, 
218 
achromatic conden- 
ser, 112 
condensing lens, 93 
dark-field, 107 
for polarised light, 
136, 207 
lieberkuhn, 97 
mirror, 105 
parabolic lieberkuhn, 
99, 218 
— — Reade’s prism, 115 
side reflector, 102 
Sorby’s plane mirror, 
for viewing polished 
surfaces, 101 
spotted lens, 107 
vertical illuminator, 
103 
Webster condenser, 
”5 
Wenham’s para- 
boloid, 109 
white cloud, 106 
Illumination, hints on, 27 
— lesson on, 182 
Images, formation of, 7 
Immersion objectives, 215 
Indicator micrometer, Dr. 
Matthews’s, 161 
Ink, lithographic, 171 
Interference of waves of 
light, 121, 219 
Intrusive substances in pre- 
parations, 30 
Iodine test for starch, 
192 
Iridescence, 122 
Iris diaphragm, 106 
TACKSON, GEORGE, 
J ruled micrometer- 
plates, 157 
Lamp-black, use of 
in finishing prepara- 
tions, 56 
Lamps, 24 
Leeuwenhoek, his method 
of measuring objects, 
156 
Lenses, cleaning of, 23 
— formation of images by, 
7 
— properties of, 6 
— use of as single magni- 
fiers, 9 
Lieberkuhn, 97 
Light for observation, 23 
— interference of undula- 
tions, 122, 219 
— length of coloured 
waves, 122 
— reflection of, 3 
— refraction of, 4 
— polarised, 119 
— undulations of, 120, 219 
Liquid glue, 56 
Lithography, 170 
Lucifer match, splinters of, 
198 
Machine for cutting 
rock sections, 217 
Maddox, Dr., his micro- 
photographs, 144 
Magnifying glass, mode of 
using, 11 
— power, mode of ascer- 
taining, 153 
tables of, 179 
Marine glue, 42 index. 
225 
Matthews, Dr. J., his 
micrometer, 161 
Martin, Benjamin, micro- 
meter, 156 
Measuring length of cotton- 
fibres, 209 
Methylated spirit, 40 
Micrometer, adjustment of, 
159 
— Jackson’s eye-piece, 158 
— Dr. Matthews’s cal- 
liper, 161 
— Martin’s, 156, 209 
— Ramsden’s, 158 
— scale attached to draw- 
ings, 152 
Micrometry, 156, 209 
Micro-photography, 143 
Micro-polariscope, applica- 
tion of, 140, 192 
Millimetre, 157 
Microscope, binocular, 19 
— care of, 23 
— construction of, 2 
— compound, its construc- 
tion, 13 
— polarising, 131 
— position of when making 
drawings, 149 
— reflecting, 96 
— stand, 2, 215 
Microscopes, single or 
simple, ix 
Microtome, 50 
Mirror for illumination, 27, 
105 
— Soemmering’s, 147 
Molecular motion, 30, 215 
Mounting-fluids, bottle for 
keeping, 90 
— objects in Canada bal- 
sam, 59 
—;dry> 52 
in fluid, 69 
Muslin, India, 211 
Needles, mounting 
and bending of, 49 
Neutral tint refleCtor, 148 
Newton’s rings, 123 
Nicol’s prism, 127, 132 
OBLIQUE illumination, 
105 
ObjeCt-glass, correction of 
for aberration caused 
by covering glass, 17 
— immersion, 215 
Oil-globules, 29 
— lamps, 24 
O’Neill, C., on cotton 
measurement, 210 
PAPER, microscopical 
examination of, 182 
Parabolic lieberkuhn,g9,218 
Paraboloid, Wenham’s, 109 
Paraffin-lamps, 24 
Pencil drawing, 164 
Photography, 143 
Pipettes, how to make, 39 
Polarisation by reflection, 
125 
Polariscope,LECOUNT’s,i39 
— use of, 192 
with high powers, 
136, 207 
Polarised light, 119 
in examination of 
crystals, 196 
test of double refrac- 
tion, 137 
Polariser for micro-polari- 
scope, 131 
Polarising apparatus, 131 
Polished surfaces, Mr. 
Sorby’s illuminator for 
viewing, 101 
Powell and Lealand, 
binocular microscope 
for high powers, 21 226 
INDEX. 
Preservative fluids, 77 
— media, alcohol, 81 
arsenious acid, 84 
camphor-water, 81 
Canada balsam, 59 
carbolic acid, 81 
castor-oil, 90 
chloride of calcium, 
83 
sodium, 83 
creosote-water, 81 
Deane’s gelatine, 88 
distilled water, 80 
glycerine, 84 
jelly, 88 
gum medium, 89 
Hantzsch’s, 80 
syrup, 89 
Thwaites’s fluid, 82 
Prism, Nicol’s, 127, 132 
— Rev. J. B. Reade’s, for 
oblique illumination, 
115 
Putty powder used for 
polishing, 65 
READE, Rev. J. B., 
prism for oblique 
illumination, 115 
Ramsden’s cobweb micro- 
meter, 158 
Refledting microscope, 96 
Refledtion, internal, no 
— of light, 3 
— polarisation by, 125 
Refledtor, neutral tint, 148 
Refradtion of light, 5 
Retarding plate, 133 
Rhea, 205 
Ross, corredtion for aber- 
ration caused by cover- 
glass, 17 
SALICINE, crystals of, 
197 
Scales, feather-edged, 163 
Scissors, 50 
Sections of Foraminiferse, 
mode of cutting, 188 
hard substances, 
mode of cutting, 65 
wood, 199 
Selenite, effedt of on polar- 
ised light, 129 
— stage, 134 
Side refledtor, 102 
Silk, 212 
Single image prism, 127,132 
Sky refledts polarised light, 
128 
Slides, glass, for mounting 
objedts, 33 
Soemmering’s mirror, 147 
Solenhofen fossil insedts, 
170 
Sorby, arrangement of 
lieberkuhn for viewing 
polished surfaces, 101 
Spherical aberration, 14 
Sponge dirt, examination 
of, 186 
Spotted lens, 107 
Stage micrometer, 157 
Staining tissues, 91 
Starch, examination of, 191 
Stone, engraving on, 173 
— lithographic, 170 
Stones for grindingsedtions, 
65, 67 
Strudture of wood, 198 
Sugar, crystals of, 196 
Surface printing, 168 
Sulphate of copper, crystals 
of1, 197 
soda, use of in dis- 
integrating chalk, 194 
Syrup, 89 
* 
TABLES of magnifying 
power, 179 INDEX. 
227 
Textile fabrics, 205 
adulteration of, 208 
Thin glass for covering ob- 
jects, 35 
Thwaites’s fluid, 82 
Dr. Beale’s modi- 
fication of, 82 
Tin cells for mounting ob- 
jects, 48 
Tourmaline, 127, 133 
Tous-les-mois, 191 
Troughs for viewing aquatic 
objects, 44 
Tubes, metal, for keeping 
balsam and varnishes, 
63 
UNANNEALED glass, 
double refraction of, 
139 
Undulations of light, 120 
VARNISH for fixing 
pencil drawings, 165 
Varnishes used in mounting 
objects, 55, 56, 73, 75 
Vertical illuminator, 103 
painting, 
Watson, Dr. J. F., on textile 
fabrics, 212 
Webster condenser, 115 
Wenham, F. H., binocular 
microscope for high 
powers, 22 
— his binocular micro- 
scope, 20 
— on the construction of 
objeCt-glasses, 17 
— paraboloid for dark-field 
illumination, log 
White cloud illumination, 
106 
— line lithography, 174 
— powders, examination 
of, 190 
Wollaston, Dr., camera 
lucida, 146 
Wood engraving, 169 
— structure of, 198 
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