PC-NRLF. 
 
 a ooo 
 
 APIl 
 
JBRARY 
 
 OF T1IK 
 
 UNIVERSITY OF CALIFORNIA 
 
 Accessions No. 
 
 1 I 
 
 * 
 I 
 
PHOTOMICROGRAPHY. 
 
PLATE I. 
 
PHOTO-MICROGRAPHY 
 
 INCLUDING 
 
 A DESCRIPTION OF THE WET COLLODION 
 
 AND 
 
 GELATINO-BROMIDE PEOCESSES 
 
 WITH 
 
 THE BEST METHODS OF MOUNTING AND PREPARING MICROSCOPIC 
 OBJECTS FOR PHOTO-MICROGRAPHY 
 
 BY 
 
 A. C O WJTf R V_]V[ ALLEY, 
 
 Ifca&F 
 
 THE 
 
 [UNIVERSITY, 
 isj^ 
 
 SECOND EDITION, REVISED AND ENLARGED, WITH ILLUSTRATIONS. 
 
 LONDON 
 
 H. K. LEWIS, 136 GOWER STREET, W.C. 
 1885 
 
CONTENTS. 
 
 CHAPTER I. 
 
 PAGE 
 
 Introduction - - - - - - l 
 
 CHAPTER II. 
 
 Reflection and Refraction . 4 
 
 Aberrations - - - - 10 
 
 Microscopic Objectives ------ 13 
 
 CHAPTER III. 
 
 The Microscope - - - - - - -16 
 
 j^ 
 
 Achromatic Condenser ------ 29 
 
 Illumination . ' 1 < s . . . . -33 
 
 The Dark Room ..,' '.' .... 49 
 
 CHAPTER IV. 
 
 Mounting Microscopic Objects .... 54 
 
 Section Cutting ------- 65 
 
 Staining -.-..... 68 
 
 CHAPTER V. 
 
 Wet Collodion Process ------ 75 
 
 Hartley's Formulae --.... 81 
 
 To wash the Emulsion - - - - -83 
 
 To flow the plates - - 84 
 
CONTENTS. 
 
 PAGE 
 
 To keep the Emulsion ..... 86 
 
 To prepare the Silver - - - - -87 
 
 Description of Washing Box - 87 
 Description of Apparatus for Melting and Filtering the 
 
 Emulsion ...... 88 
 
 Description of Levelling Slab ... 89 
 
 To Develop . . . 90 
 
 Formula for Developing 91 
 
 List of Articles Needed ..... 92 
 
 Cleaning and Preparing the Glass - 92 
 
 CHAPTER VI. 
 
 Former Methods adopted in the Arrangement of the Apparatus 101 
 
 Later Methods 103 
 
 The Method adopted in this Work - - - - 105 
 
 Dr. Dallinger's Illumination .... - 124 
 
 CHAPTEE VII. 
 
 Defects in Negatives - - - 140 
 
 Their Kemedy - - . - < - 141 
 
 CHAPTER VIII. 
 
 Production of Positives ------ 149 
 
 Enlarging - - ----- 159 
 
 Appendix - - 163 
 
 Preservative Media - .... 163 
 
 Bacillus Tuberculosis - - 163 
 
 Binocular Photography - . 164 
 
 Focussing at a Distance ..... 164 
 
PREFACE TO THE SECOND EDITION. 
 
 SINCE the publication of the first edition, Photo- 
 micrography has become so general and the process 
 has so much improved, that it has been found 
 necessary to bring out a second edition, in which an 
 endeavour has been made to keep pace with the 
 advances of microscopy and to incorporate the more 
 recent improvements in photography. 
 
 The title of the first edition was chosen after much 
 deliberation, although I was fully aware of its liability 
 to criticism on account of its ambiguity. The term 
 now employed though less euphonious certainly pre- 
 vents confusion. 
 
 It was my original intention to answer some criti- 
 cisms in this preface, but on further consideration 
 they appeared so trivial and the writers showed such 
 complete ignorance of both the work and the subject, 
 that I thought it better to abandon it, and simply 
 thank those from whom I received many valuable hints, 
 and whose friendly criticism gave me so much en- 
 couragement. I only hope the result will be found 
 worthy of acceptance and of some little use in the 
 advancement of those scientific subjects to which 
 photo-micrography has been lately applied. 
 
 A. COWLEY MALLET. 
 
 December 8th, 1884. 
 
PREFACE TO FIRST EDITION. 
 
 THE publication of this little work has been under- 
 taken with a view to encourage the practice of 
 Micro-photography, and afford a ready means of 
 obtaining information without the trouble of refer- 
 ing to the innumerable papers on the subject, scat- 
 tered up and down several scientific periodicals and 
 publications. 
 
 As far as possible we have mentioned the sources 
 from which our information has been derived ; many 
 have no doubt been overlooked, but the absence of a 
 library for reference, and our isolated position, must 
 serve as an excuse. 
 
 Our thanks are due to several friends for their 
 kindness in supplying any information required, but 
 .especially to the Rev. Gr. B. Powell who revised all 
 the proofs, and whose valuable services have contri- 
 buted in no small measure to hasten the completion 
 and publication of the work. 
 
 A. COWLEY MALLEY. 
 
 Munslow, Shropshire. 
 
PHOTO-MICROGRAPHY. 
 
 CHAPTER I. 
 
 INTRODUCTION. 
 
 BEFORE beginning a detailed description of the 
 apparatus employed in Photo- micrography, a few 
 remarks are necessary on its utility in research, and 
 its"application to the various branches of science. 
 
 All microscopists are aware of the fickleness with 
 which objects display their structure, markings 
 easily perceived at one time may baffle all attempts 
 to resolve them at another, and perhaps when seen 
 are beyond our power to delineate, I have before me 
 at present, some drawings which must have taken 
 the artist a week to finish, and even then, shew the 
 existence in his mind of preconceived notions of 
 their structure. 
 
 Photography not only obviates the necessity of 
 future trouble and perhaps failure in the display of 
 these markings, but in a period varying from a few 
 seconds to as many minutes, imprints the latent 
 image on a sensitive surface, which after develop- 
 ment, can be multiplied a thousand fold, and give to 
 the world results, indisputably proving the truth of 
 
Z INTRODUCTION. 
 
 some favourite theory, or showing the existence of 
 some doubtful structure. 
 
 In the domain of pathology we find many 
 observers differing in their descriptions of well- 
 known lesions. What scientific man engaged in the 
 investigation of the markings of the diatomaceae 
 agrees with others as to their true interpretation, at 
 the present day Agnosticism is the only name 
 expressing the condition of men's minds on some of 
 these subjects. Thousands of questions hitherto un- 
 settled on account of errors of description, or want 
 of agreement between observers, are sure to find an 
 easy solution if the practice of photography becomes 
 more universal among naturalists and our profes- 
 sional brethren. 
 
 I do not wish to lead others to infer from this, 
 that the photographic image may not be false if im- 
 properly obtained, but it can neither add anything 
 to, nor take anything from, the structure, and rnay 
 be relied on to shew what was actually seen by the 
 observer. 
 
 In teaching Histology, Pathology, or any subject 
 in which the microscope plays an important part, a 
 photograph of the object may be thrown on the 
 screen in the usual manner, and the lecture proceed 
 uninterrupted by the use of separate apparatus, or 
 the time taken up by those manipulations which 
 must be made for every different observer. 
 
 It is unnecessary to dwell on the fascination 
 of the pursuit, or the recreation afforded to those 
 who after the arduous duties of the day, relieve the 
 
INTRODUCTION. O 
 
 strain by the study of microscopy, for, from what 
 has been said, the advantages of photography to the 
 Histologist, Pathologist, and student of Natural 
 History, are so obvious, that any tendency to extend 
 its domain to amusement might injure its prestige 
 with students of science. 
 
 In the following chapters besides the methods we 
 have ourselves adopted, it has been our aim to 
 gather together those used by others, and after ana- 
 lysing them to choose the parts most applicable, 
 when considered in conjunction with the recent ad- 
 vances of photography; at the same time by 
 showing the facility of their application, we hope to 
 make photo -micrography more popular, and place it 
 within the reach of all. 
 
 B 2 
 
PROPERTIES OF LENSES. 
 
 CHAPTER II. 
 
 PROPERTIES OF LENSES, IMPERFECTIONS OF RESULTING 
 IMAGES, ABERRATIONS, ETC. 
 
 ACCORDING to the undulatory theory of light an ob- 
 ject becomes visible, when it communicates the rapid 
 vibratory motion of its molecules to the luminiferous 
 ether, which being propagated through it in the form 
 of spherical waves, is transmitted to the retina. 
 
 The vibration of the molecules takes place at right 
 angles to the direction of the wave, for example, if a 
 long string of beads is shaken at one end, the vibra- 
 tions of the beads are at right angles to the length of 
 the string, while the waves propagated through it 
 by the shake, move in the same direction as the 
 length. 
 
 Reflection. When a luminous ray falls, or is inci- 
 dent, on a polished surface, it is reflected at an angle 
 which equals its angle of incidence. (BAG and 
 B"AC Fig. 1.) 
 
 Refraction. "When a luminous ray passes from a 
 rarer to a denser medium it is bent out of its course. 
 
 The Sines of the angles of incidence BAC, and re- 
 fraction B'AC', (Fig. 1.), bear a constant ratio to each 
 other. 
 
PEOPERTIES OF LENSES. 
 
 This ratio is called the refractive index. 
 
 Refractive Index. 
 
 Of Air 
 Diamond 
 Flint Glass 
 ,, Crown Glass 
 
 1-000294 
 2-44 
 1-642 
 1-550 
 
 A' 
 
 If the medium through which the light passes has 
 parallel faces, the emergent B'A' and incident BA 
 rays are parallel, (Fig. 1), if it has not, the tendency 
 of the ray is to bend away from the angle at which 
 the faces meet. 
 
 Lenses are of six forms; double convex 1, plano- 
 convex 2, converging meniscus 3, double concave 4, 
 plano-concave 5, diverging meniscus 6. 
 
6 PROPERTIES OF LENSES. 
 
 All rays falling on Convex lenses are refracted 
 towards the centres of curvature of the faces, those 
 incident on Concave away from the centres, (Figs. 3 
 and 7). 
 
 In convex lenses the PRINCIPAL FOCUS (F. Fig. 3) is 
 that point where all rays parallel before entrance 
 converge after refraction, it almost coincides with 
 the centres of curvature of the faces. 
 
 If the rays diverge from a point A outside the 
 principal focus, they meet after refraction on the 
 other side beyond it B, these points A and B are 
 real foci (Fig. 3). 
 
 If they converge they meet at C within it, B and 
 C are called conjugate foci. 
 
 Eays diverging from a point C Fig. 3, within the 
 principal focus of a convex lens, can never meet at 
 the opposite side, but only become less divergent, 
 they therefore cannot form a real focus. But if the 
 emergent rays are prolonged backwards they will 
 
 FIG. 3. 
 
 meet at V Fig. 3. The point V is called the virtual 
 focus. 
 
PROPERTIES OF LENSES. 
 
 If an image of an object be received on a screen 
 placed opposite a small hole in the shutter of a dark- 
 ened room it will appear inverted, because the rays 
 from different points of the object cross at the aper- 
 ture. 
 
 The size of the image varies inversely as the dis- 
 tance of the object, and directly as the distance of 
 the screen. 
 
 If a convex lens be placed in the aperture, inverted 
 and diminished images of distant objects will be 
 formed on a screen placed at the principal focus. 
 
 If an object (Fig. 4), be placed at twice the focal 
 
 FIG. 4. 
 
 distance of a convex lens, a real inverted image, the 
 same size as the object, will be formed on a screen 
 placed at a similar distance on the opposite side. 
 
 If nearer, a real inverted magnified image (Fig. 5), 
 is formed at increasing distance until the principal 
 focus is reached, when no image is formed on the 
 screen, because the rays can never come to a focus 
 being parallel. 
 
 FIG. 5. 
 
8 
 
 PROPERTIES OF LENSES. 
 
 The human eje consists of a convex lens, the 
 crystaline lens placed behind the aperture of the iris, 
 and a screen, the retina, behind the crystaline lens, 
 C and E (Fig. 6). 
 
 FIG. 6. 
 
 A real inverted image of objects is formed on the 
 retina, (how they appear erect to us has not yet been 
 shown), and as the crystaline lens can alter its form, 
 so as to bring convergent or divergent rays to a 
 focus on the retina, the eye can percei7e clearly the 
 same object when placed at different distances. 
 
 There is a limit to the accommodation of the eye, 
 in normal eyes eight or ten inches is the shortest 
 distance an object can be clearly perceived, without 
 giving rise to an unpleasant feeling owing to our 
 efforts to increase the curvature of the lens, and to 
 enable it to bring the divergent rays to a focus on 
 the retina, but if a convex lens L Fig. 6 be placed 
 between the object and the eye it assists in bringing 
 the rays to a focus on the retina. 
 
 The size of the retinal image varies with that of 
 the angle AOB Fig. 6. This angle is called the 
 visual angle. 
 
PROPERTIES OF LENSES. 8 
 
 As the image of an object is only a collection of 
 the foci of the different points of an object, these 
 images will be real or virtual as the image is situated 
 without or within the principal focus. 
 
 A real magnified and inverted image of an object 
 is seen by the eye if the object is situated outside the 
 principal focus of a lens, and at less than twice the 
 focal distance, because the angle of intersection of 
 the rays from opposite sides of the object, i.e. the 
 visual angle, is increased. 
 
 A virtual erect and magnified image is seen by the 
 eye if the object is situated within the principal focus 
 of the lens, because the crystaline lens of the ob- 
 server C Fig. 6 has the power of bringing the rays 
 to a focus and forming a real image on the retina R, 
 on this principal the magnified image in the simple 
 microscope depends. 
 
 Concave lenses can only form virtual images no 
 matter what the distance of the object. (Fig. 7). 
 
 FIG. 7. 
 
 Up to the present the passage of light through 
 lenses has been considered in its simplest form, it 
 remains now to investigate the imperfections in the 
 
10 
 
 PROPERTIES OP LENSES. 
 
 resulting images, their causes, and the various 
 methods of correcting them. 
 
 When a ray of light passes from one substance 
 through another a part is reflected at the incident 
 surface, a second absorbed in its passage, and a third 
 transmitted. The greater the thickness and number 
 of the transparent media through which the light is 
 transmitted, the greater is the quantity reflected and 
 absorbed. Since Microscopic Objectives are com- 
 posed of several lenses the loss of light is conse- 
 quently very great. 
 
 Spherical Aberration (Fig. 8), shows itself in want 
 FIG. 8. 
 
 of distinctness in an image at the margins when 
 sharp at the centre, and vice versa ; it is caused by the 
 unequal refraction of the rays owing to the spherical 
 shape of the lens, those at the margins coming to a 
 focus before those at the centre. 
 
 Chromatic Aberration (Fig. 9), a ray of white light 
 
 FIG. 9. 
 
PROPERTIES OF LENSES. 1 L 
 
 is composed of rays of different colours, if it pass 
 through, a medium (such as a lens or prism), Fig. 9, 
 whose sides are not parallel, it is divided into its 
 component colours, OP dispersed. 
 
 Now since all the different rays into which a pen- 
 cil of white light can be divided, have different foci, 
 that is, the point where the red rays come to a focus is 
 more distant than that of the violet, the intermediate 
 colours forming other foci between them, V 1 2 3 4 R 
 Fig. 9, the rays are unequally dispersed and the result- 
 ing image will be coloured at its edges. 
 
 There are several methods of remedying these 
 aberrations, some of them diminish Spherical and 
 Chromatic aberration at the same time. 
 
 Spherical Aberration may be destroyed by giving 
 the lens a decreasing curvature towards the edges, 
 in fact an ellipsoidal form, the difficulty of this in 
 practice was found so great that it was abandoned, 
 and if the form was such that its performance was 
 perfect for parallel rays, it would be inaccurate for 
 all others. It is much more easily corrected by altering 
 the curves of the two sides. For instance if the 
 plane side of a plano-convex lens be turned towards a 
 very near object, or the convex side towards a very dis- 
 tant one, the resulting aberration would be about one- 
 fourth of that which would occur if the respective 
 positions of the sides of the lens were reversed 
 
 A method which has been frequently adopted for 
 photographic objectives deserves mention, namely 
 lessening the aperture, by placing a diaphragm in 
 front of or behind the lens which admits the rays at 
 
12 PROPERTIES OF LENSES. 
 
 the centre, but cuts off those at the edges, it will be 
 evident that this lessens the chromatic aberration at 
 the same time. 
 
 The diaphragm has other advantages, it enables 
 objects lying at different distances from the lens to 
 appear distinct, in other words, the penetrating 
 power is increased. Its disadvantages are that it 
 produces distortion, if placed in front of a lens the 
 image of a square becomes barrel-shaped, if behind 
 the reverse. It lessens the light, and diminishes the 
 Angular Aperture, upon the extent of which the 
 most important qualities of an objective depend. 
 
 The aberration of a concave lens being exactly 
 opposite to that of a convex lens, one may be made 
 
 to correct the other without decreasing the magnify- 
 ing power to any great extent. The lens A Fig. 10 
 completely destroys the spherical aberration of the 
 lens B, for it does not change the position of the 
 rays situated near its centre as much as it does those 
 at the edges, owing to its increasing prismatic form. 
 If advantage be taken at the same time of the 
 different relations between the refractive and disper- 
 sive powers of different kinds of glass, and if the 
 lenses which correct the spherical aberration by their 
 
PROPERTIES OF LENSES. 13 
 
 shape are formed from different kinds, chromatic 
 aberration will be destroyed. If the lens A (Fig. 10) 
 of high dispersive power, concave form, and low cur- 
 vature, be joined to B of lower dispersive power and 
 greater curvature, it is evident that the dispersion 
 caused by the latter is neutralysed, whilst its refrac- 
 tive power is only decreased by the opposite refrac- 
 tion of the concave. 
 
 The convex lens of crown is generally corrected by 
 a concave of flint, it has been found that no two 
 lenses can be made to correct each other perfectly, 
 so opticians overcome the difficulty by combining 
 several. 
 
 Before leaving this subject we should mention that 
 in photography errors frequently arise, especially 
 when using low powers, owing to the difference be- 
 tween the visual and chemical foci. A point of 
 white light may appear perfectly distinct at E 
 Fig. 9, when surrounded with a violet areola, and if 
 a photograph be taken it will be quite indistinct; 
 while at V nearer the lens, the image may not ap- 
 pear so distinct, but will be surrounded by a red 
 areola, and if a photograph be taken at this point, it 
 will be found perfect, as the violet rays are the most 
 chemically active. This is owing to the different 
 refrangibility of the red and violet rays, the latter 
 coming to a focus sooner than the former. When 
 photographing, the point V should be chosen where 
 the object is surrounded by a red areola, this being 
 the most accurate for the violet rays. 
 
 Microscopic objectives have of late years arrived at 
 
14 PROPERTIES OF LENSES. 
 
 such perfection that it seems impossible to improve 
 them. They are designated from four inches up to one 
 fiftieth of an inch, according to their magnifying 
 power : for example, a one inch objective is supposed 
 to magnify as much as a single lens of one inch focus, 
 although its own focal length may be different. 
 
 This rule is only approximately correct, as glasses 
 of the same designation by different makers vary in 
 magnifying power. 
 
 Low powers up to two inches generally consist of 
 a single combination, but as it has been found im- 
 practicable to construct objectives of high power free 
 from chromatic and spherical aberrations in this way, 
 all good makers have adopted the plan of correcting 
 one combination by another, so that objectives from 
 two inch to one inch generally consist of two, while 
 those of quarter inch and upwards generally consist 
 of three combinations, formed perhaps of as many as 
 eight different lenses. 
 
 Various devices have been adopted to lessen the 
 aberrations, increase the angular aperture, and at the 
 same time reduce the number of lenses. For an ex- 
 ample of the ingenuity displayed in overcoming these 
 difficulties, we refer the reader to the description of 
 Mr. Wenham's new objective published in the Pro- 
 ceedings of the Royal Society, vol. xxi. p. Ill, and 
 content ourselves with mentioning that it consists of 
 a single front of the usual form, a single plano-convex 
 back whose focus is four and one half times that of 
 the front, and a middle triple in which a single con- 
 cave lens of flint, three times the focal length of the 
 
PROPERTIES OF LENSES. 15 
 
 front, corrects all the others. In this combination 
 only five lenses are used, and the errors arising from 
 the sixteen surfaces of glass in the older forms re- 
 duced to ten. 
 
 A good objective should possess the Standard 
 screw, adopted by the various societies, and now 
 fixed by the best makers to their lenses. 
 
 Its definition should be clear, the field flat, objects 
 at the edge of the field should be as free from colour, 
 and their definition as perfect as those at the centre. 
 
 The illumination should be white, not yellow, as is 
 the case with inferior glasses, especially those of 
 foreign manufacture. 
 
 If of low power, that is of one inch or more 
 nominal focal length, opaque objects should be 
 clearly shown without the use of any apparatus for 
 condensing the light upon them. 
 
 The rotundity of certain objects should come out 
 well, the more distant parts being in as good focus 
 as those nearer the objective. 
 
 Transparent objects possessing a certain thickness, 
 should be clearly defined to a certain depth. This 
 power of penetration is difficult to form a correct 
 opinion of, as we shall find that a glass of given 
 focus magnifies the depth of an object in the pro- 
 portion of the square of the magnification of the 
 diameter laterally. It is in inverse ratio to the 
 magnifying power of the objective. Therefore low 
 powers are most suitable for the display of those 
 objects in which different points, lying on different 
 planes require to be in focus at the same time. 
 
16 PROPERTIES OF LENSES. 
 
 It has been found that the thin glass used for 
 covering microscopic specimens, produces by refrac- 
 tion of the rays passing through it a sufficient nega- 
 tive aberration (Fig. 11) to destroy the adjustment 
 of an objective perfect in its performance on uncovered 
 objects. This may be remedied, as has been shown 
 by Mr. A. Ross, by under-correcting the front andover- 
 
 Fro. 11. 
 
 correcting the two back combinations, at the same 
 time making the distance between them susceptible 
 of alteration by means of a screw collar, this arrange- 
 ment by bringing the front and back combinations 
 nearer together, enables us to give the objective an 
 excess of positive aberration sufficient to counteract 
 the negative produced by the thin glass. 
 
 The screw collar adjustment at the same time cor- 
 rects the errors caused by the difference in the 
 refractive indices of the various media employed for 
 the preservation and mounting of specimens. We 
 therefore consider it an indispensible adjunct to all 
 objectives of higher power than one half inch. It 
 must not be forgotten that these adjustments affect 
 the magnifying power considerably, and allowance 
 
PROPERTIES OF LENSES. 17 
 
 must be made for this when accurate measurements 
 of a covered object are required. 
 
 Many methods of practically making these cor- 
 rections are mentioned in the various manuals,, but I 
 think the following will be found the easiest, and 
 sufficiently correct for all purposes. Turn the index 
 (A Fig. 12) to Zero, in other words adjust for un- 
 
 PIQ. 12. 
 
 covered, the object is now brought into focus. We 
 next turn the screw collar till some dust or scratches 
 on the cover-glass come into focus. The object is again 
 brought into focus by means of the fine adjustment. 
 
 If now on turning the fine adjustment an equal 
 expansion of the outlines of the object takes place 
 when within and without the focus, the correction is 
 perfect. If the greatest expansion occurs when the 
 object is outside the focus we have gone too far, the 
 screw collar must be turned and the index moved 
 back towards or uncovered, and vice versa. When 
 the expansion is the same on both sides it will be 
 perceived that the minutest details become visible, 
 at the same time, and with the same distinctness, as 
 the outlines of the object. 
 
 The number to which the index on the screw 
 collar points is now written on the slide for refer- 
 ence in cases of future examination. 
 
 c 
 
18 PROPERTIES OF LENSES. 
 
 The angular aperture is the capacity, which a lens 
 has for receiving rays from the object and transmitting 
 them to the image, and is determined by the ratio 
 between the diameter of the opening and the focal 
 length. 
 
 The apparent depth of focus of an objective, is 
 in inverse ratio to its magnifying power, and as the 
 utility of the higher powers depends upon their capa- 
 bility for showing the minute surface-structure of 
 markings, and as this increases with the power 
 the objective has of collecting a large number of 
 rays from an object, in other words on its angular 
 aperture, we are obliged to sacrifice depth of 
 focus, in the attainment of magnifying power and 
 angular aperture. 
 
 The immersion principle where fluid is placed be- 
 tween the object and objective increases the angular 
 aperture, as these objectives can be made with larger 
 fronts than dry ones of the same focal length. The 
 homogeneous immersion principle is to be preferred, 
 as it increases the angular aperture as much again as 
 water, and the oil has the great advantage of not 
 evaporating when prolonged investigations are ne- 
 cessary ; care should be taken that the smallest 
 quantity sufficient to cover the aperture of the ob- 
 jective, when focussed on the object, is used, as any 
 excess would cause blurs of irradiation, not to men- 
 tion other objections. 
 
 The old method of designating the angular aper- 
 ture of an objective, by the number of degrees in 
 the angle formed by the most lateral rays meeting 
 
PROPERTIES OP LENSES. 19 
 
 at the focal point of the objective, has been super- 
 seded by the more correct and convenient method 
 of calling the capacity which an objective possesses 
 for collecting the whole pencil of rays from an object 
 in air, Unity, then commencing with the lowest 
 numbers this reaches as far as 1'52 for oil immer- 
 sions. This is called the Numerical aperture and 
 NA is written after the numbers to distinguish it. 
 It may easily be found by multiplying the sign of 
 the semi-angular aperture by the refractive index of 
 the fluid used. 
 
 The angular aperture may be increased by using 
 oblique light, which enables the rays illuminating 
 the object to pass through at a greater angle, or an 
 achromatic condenser, which increases both their 
 number and obliquity. 
 
 This part of the subject would be incomplete with- 
 out reverting to the views enunciated by Professor 
 Abbe of Jena, which have placed the old theories of 
 Microscopic vision on an entirely new footing. Ac- 
 cording to his demonstrations the images produced 
 by minute objects, small multiples of wave lengths, 
 are imaged in an entirely different way from those 
 produced by coarse objects. Objects less than ^rgW 
 of an inch are imaged by the diffracted rays pro- 
 duced by the action of the minute structure. The 
 more diffracted rays reach the eye the truer the 
 structure. The more minute the object the more 
 the diffracted rays are spread, therefore the larger 
 the angular aperture the greater the quantity of 
 diffracted rays transmitted and the truer the result- 
 
 c2 
 
20 PROPERTIES OF LENSES. 
 
 ing image as regards the actual structure of the object.* 
 These diffraction phenomena must not be con- 
 founded with those appearances surrounding the 
 outlines of. an object, mentioned in a previous para- 
 graph when speaking of correction for cover glass. 
 
 It has been recently remarked that microscopic 
 vision was totally distinct from macroscopic. First, 
 because by placing a stop behind the objective that 
 is decreasing the aperture, objects could be made to 
 assume different forms. Second, because under dif- 
 ferent conditions of aperture different objects as- 
 sumed the same form. 
 
 Now Professor Abbe himself says " minute struc- 
 tural details are not as a rule imaged by the micro- 
 scope dioptrically , in accordance with the real nature 
 of the object/' 
 
 Some, less enamoured of the metaphysical aspect 
 of the question, may find it difficult to perceive that 
 images formed optically and dioptrically give us just 
 as little information as to the real nature of the 
 object. If two scarlet cloths the same size, one marked 
 with black squares the other with circles, and one 
 coarser than the other, be placed at such a distance 
 that their images subtend small angles, they will 
 appear identical. If brought nearer, or what is the 
 same thing, made to include a larger angle, a greater 
 number of rays are collected and certain differences 
 appear, and as the angle of vision increases, the 
 structural peculiarities still continue to cause fresh 
 visual phenomena. 
 
 * The Italics are my own. 
 
PROPERTIES OF LENSES. 21 
 
 Professor Abbe goes on to say " and cannot be in- 
 terpreted as Morphological but only as Physical 
 characters, not as images of material forms but as 
 signs of material differences in the nature of the 
 particles composing the object, so that nothing more 
 can safely be inferred from the image as presented 
 to the eye, than the presence in the object of such 
 structural peculiarities as will produce the particular 
 diffraction phenomena, on which the images de- 
 pend." 
 
 Unfortunately Professor Abbe has tacitly granted 
 the accuracy of the general idea of dioptric vision, 
 in order to throw his own discovery into greater pro- 
 minence; consequently in a recent address the whole 
 stress has been laid upon the fact that these images 
 are not exact representations of material forms. The 
 author must either have been blinded by association 
 and inherited materialism, or have been ignorant of 
 the fact that the same thing was proved with regard 
 to all images many years ago ; namely that nothing 
 more can safely be inferred from the image presented 
 to the eye, than the presence in the object of such 
 structural peculiarities, as will produce the particular 
 refraction phenomena on which the image depends. 
 
 Almost all scientists are misled by the error of 
 conceiving material things to exist apart from the 
 mind that perceives them, (we by no means wish to in- 
 fer that their esse is a mere percipi). This confusion of 
 ideas has justly caused Hegel to remark "the English 
 are that nation in Europe which like the Huckster 
 and W orkman Class of the state are destined to pass 
 
22 PROPERTIES OF LENSES. 
 
 their lives immersed in matter." A shout of astonish- 
 ment is raised at an old idea, no doubt in a new 
 dress, and the great discovery itself is missed in the 
 delight of at last conceiving what has been more 
 or less dimly perceived for centuries. 
 
 The great discovery is, that the microscope does 
 not act dioptrically under certain circumstances, and 
 that, we have obtained a new aid to research in these 
 diffraction phenomena, which hold almost as high a 
 position in microscopical investigation, as spectro- 
 scopy in astronomy. 
 
 We hope that these explanations will enable the 
 reader to choose an objective suitable for the parti- 
 cular branch of study he may be engaged in, it must 
 however be remembered that for low powers and the 
 majority of pathological investigations very large 
 angular aperture is not considered advantageous, as 
 with every increase of it the penetration and working 
 distance decreases, also that the extra amount ex- 
 pended in the purchase of first-class objectives, will 
 produce a considerable saving in subsequent expenses, 
 on account of the increase of successful results due to 
 their employment. The amateur is therefore strongly 
 recommended to patronise only the best makers, and 
 pay the highest price for his objectives. 
 
 Very little time will be devoted to the consideration 
 of the principles involved in the formation of the 
 image in the compound microscope, as we are not 
 directly concerned with it in photo-micrography. 
 
PROPERTIES OF LENSES. 
 
 23 
 
 The compound microscope in its simplest form is 
 composed of two lenses the objective and eye lens ; 
 fig. 13, 1 and 2. It will be perceived that the real 
 image a b of the object A B formed by the objective 
 
 FIG. 13. 
 
 at a point just within the focus of the eye-glass is 
 changed into a virtual image at a b' by the latter, 
 both images being inverted as regards the object. 
 The principal of the more complex forms of the com- 
 pound microscope is similar, the number and arrange- 
 ment of the lenses being different both for objective 
 and eye-piece, the former has been already explained. 
 The eye-piece generally used is the Huygeian 
 named after its inventor Huygens, it consists of two 
 plano-convex lenses, 1 and 2 fig. 14, called respec- 
 
 FIG. 14. 
 
 tivcly eye and field lens, the former being one-third 
 
24 PROPERTIES OF LENSES. 
 
 the focus of the latter and the distance of their 
 separation half the sum of their focal lengths. 
 
 Huygens was ignorant of one advantage this com- 
 bination possesses, he adopted it simply to remedy 
 spherical aberration, but it has been since shown 
 that it corrects chromatic aberration also. A refer- 
 ence to the figure will explain the principle on which 
 the formation of the image depends. 
 
 It should never be used in photography except 
 to view the image before focussing, as with all 
 its supposed advantages its employment never gives 
 good results. 
 
THE MICROSCOPE, ETC. 25 
 
 CHAPTER III. 
 
 THE MICKOSCOPE, ILLUMINATION, ETC. 
 
 Before beginning a detailed description of the 
 microscope, a few hints to the uninitiated are neces- 
 sary. 
 
 Avoid purchasing instruments adorned with in- 
 numerable screws and mechanical arrangements for 
 performing the various movements. All superfluous 
 apparatus, is not only useless, but a decided hindrance 
 to accurate investigation, in fact the various additions 
 generally made to the first class instruments of the 
 present day, are both an insult to the skilled micro - 
 scopist and a means of perpetuating clumsy manipu- 
 lations. On the other hand many excellent instru- 
 ments are made, which owing to some peculiarity of 
 shape, are useless for photography. 
 
 The first essential of a microscope is a firm heavy 
 stand, so arranged that the body may be inclined at 
 any angle between horizontal and perpendicular and 
 clamped in that position. The stand should be high 
 enough to allow space beneath the stage for sub-stage 
 apparatus, and the points on which it rests should be 
 sufficiently distant from each other to prevent the 
 instrument being easily overturned. 
 
 The coarse adjustment is best accomplished by 
 rack and pinion movement, (not by one tube sliding 
 
26 THE MICROSCOPE, ETC. 
 
 within another) the rack being attached to a bar 
 placed some distance from the tube carrying the eye- 
 piece and objectives. When attached to the tube 
 itself it is impossible to adopt any arrangement for 
 shortening the tube, the consequence of this is that 
 the surface of the ground glass in the camera, 
 covered by the image, is greatly contracted owing to 
 the length of tube between the objective and mouth 
 of the bellows. 
 
 Nothing belonging to the microscope is susceptible 
 of more improvement than the fine adjustment, and 
 anything which would supersede the present very 
 inferior methods by which this is affected, would be 
 welcomed by microscopists. This adjustment should 
 be separated from the eye-piece tube far enough to 
 allow of the attachments necessary for working it 
 from a distance. It should respond immediately to 
 the slightest rotation in either direction, and the 
 object should suffer no apparent shake or displace- 
 ment, when moving in or out of focus. 
 
 The eye-piece tube must be removable from the 
 body, or better from another tube about an inch long 
 attached to the arm carrying the objectives. The 
 way this is accomplished is of no importance as long 
 as it is possible. 
 
 The stage should be firm, and as thin as is 
 compatible with the use of the sub-stage apparatus, 
 to be described. Circular in form and possessing 
 some arrangement by which movements in a rec- 
 tangular, circular or horizontal direction may be 
 smoothly and easily communicated to the object, by 
 
THE MICROSCOPE, ETC. 
 
 27 
 
 aid of the finger alone without the use of milled 
 heads or other mechanical arrangements. 
 
 This is best accomplished by ivory points moving 
 on a blackened glass surface, a method extensively 
 employed by some of our leading opticians and likely 
 to supersede all others where real work is the object 
 iu view, not a desire to catch the eye of the public. 
 
 FIG. 15. 
 
 A B 
 
 r~ 
 
 11 \ 
 
 X 
 
 I~A 
 
 "F 
 
 ' R 
 
 11 
 
 H o 
 
 U=! 
 
 i 
 
 1 I 
 
 * 
 
 1 
 
 c 
 
 Id if 
 
 =vJ 
 
 1 
 
 The accompanying figure represents a slightly 
 modified form of Smith and Beck's popular monocu- 
 lar microscope. The method adopted for the inclin- 
 ation of the body is susceptible of improvement, but 
 up to the present we have seen few stands to which 
 the same observation is inapplicable. 
 
 The tube A carrying the eye-piece, screws into 
 B, which is permanently attached to the arm X 
 carrying the objectives. The coarse and fine adjust- 
 ments are conveniently placed, especially for photo- 
 graphy, and their performance sufficiently perfect for 
 most purposes. 
 
 The stage has been considerably modified, as the 
 
28 THE MICROSCOPE, ETC. 
 
 original was found to be too thick for investigations 
 requiring very oblique light. 
 
 A thin circular brass plate E covered with black- 
 ened glass, revolves on F in the optic axis of the 
 instrument, on its upper surface two thin brass clips 
 G are fastened, these hold the slide in position and 
 allow of its movement in every direction in the plane 
 of the stage. 
 
 A brass tube H, lined with cloth, screws into the 
 centre of the stage, and holds the sub-stage appara- 
 tus, this can be removed when very oblique light is 
 required. 
 
 A diaphragm I, attached to a short wide tube with 
 a thick rim R, slides up and down in H, the motion 
 being easily imparted to it on account of the cloth 
 lining. A line divided into sixteenths of an inch, is 
 cut on the side of the tube at right angles to the rim 
 E., this enables us to tell the distance between the 
 top of the condenser and the object by calculating 
 the number of divisions between the rim and edge 
 of the other tube H. 
 
 This piece of apparatus, when made in the manner 
 
THE MICROSCOPE, ETC. 
 
 about to be described, and which we 
 
 mend, fulfils all the requirements of the most expen"-"" 
 
 sive sub -stage arrangements. 
 
 Fig. 16 is a diagramatic representation of it in 
 section. 
 
 In the rim R two screws are fitted, (only one is 
 represented in the figure for the sake of clearness) at 
 right angles to each other, opposite to them in the 
 interior of the tube a pretty strong spring S is 
 attached. 
 
 By this means the ring A which fits on the pro- 
 jecting internal flanges of the rim R, can be moved 
 in any direction in the plane of the stage by the 
 screws, as the spring pressing against it on the 
 opposite side compels it to follow their motions. 
 
 The diaphragm plate G is perforated with eight 
 holes varying from one half to one sixteenth of an 
 inch in diameter. In its centre is another aperture 
 quarter of an inch in diameter. Two thin plates half 
 an inch wide, through which the screw 7 fig. 16 
 passes, are placed above and below the diaphragm 
 before it is fastened in position, thus allowing it to be 
 displaced nearly quarter of an inch in its own plane, 
 and parallel to that of the stage, quite independently 
 of the remainder of the sub-stage apparatus. 
 
 Any one possessed of ordinary skill and a few tools 
 for cutting sheet brass, will find little difficulty in ap- 
 plying this principle to existing instruments. 
 
 From what has been previously mentioned with 
 regard to the resolution of certain structural pecu- 
 
30 THE MICROSCOPE, ETC. 
 
 Rarities of microscopic objects, it follows, that their 
 accurate delineation depends as much on the cor- 
 rections of the condenser through which the light 
 passes to the object, for achromatism, and on the size 
 of its angular aperture, as it does on the perfection 
 of the objective in these particulars. 
 
 It must be remembered however that a condenser 
 is not necessary when using the one inch or lower 
 powers, but is indispensable with those above it. 
 
 A good achromatic object glass of the French form, 
 consisting of three powers, screwing on top of each 
 other will answer the purpose, if the microscope is 
 not already fitted with Abbe's illuminator or one of 
 Powell and Leland's condensers. When in use it 
 should be fitted in the centre of the ring A so as to 
 be removable at pleasure, and with the face of the 
 uppermost combination flush with the top of the 
 substage tube, to allow of its close approximation with 
 the under surface of the glass slip on which the 
 object is mounted. 
 
 Besides the condenser itself being freely remov- 
 able from the ring in the sub-stage, the three com- 
 binations which compose it should be easily un- 
 screwed from one another, as on no account must the 
 power of the condenser exceed that of the objective ; 
 we therefore require no condenser with the one inch, 
 while with the quarter two and with the eighth all 
 three combinations are necessary. 
 
 If the condenser is not an immersion, a pin hole 
 cap similar to that figured in section 4, fig. 16, will 
 be found an extremely useful addition placed on the 
 
THE MICROSCOPE, ETC. 31 
 
 top combination when using the eighth and higher 
 powers ; it not only prevents the passage of any rays 
 except those actually concerned in the direct illu- 
 mination of the object and the subsequent formation 
 of the image on the focusing screen, but also if 
 brought into view with a low power objective enables 
 us to make the optic axis of the condenser coincident 
 with that of the objective, and therefore with any 
 other substituted for it. This will be more fully ex- 
 plained when treating of the arrangement of the 
 microscope prior to taking a photograph. 
 This pin hole cap is easily made as follows. 
 Procure a piece of tubing, that shall fit the top of 
 the condenser accurately, lead will do, but brass is 
 to be preferred. Cut it so that it projects slightly 
 above the surfaces of combination, and while in this 
 position press a piece of sheet zinc, previously cut to 
 fit it, down into the tube till it just touches the glass. 
 Having filed down the part of the tube projecting 
 above the zinc, we find the centre of the latter and 
 pierce it with a hole about the diameter of an ordin- 
 ary small pin. The cap is now blackened both ex- 
 ternally and internally, with oxide of copper or any 
 other material giving a dull black. 
 
 It has been found that the nearer the diaphragm 
 approaches the back combination of the condenser, 
 the more brilliant the illumination. The following 
 arrangement which enables us to place it in immedi- 
 ate contact, besides possessing several advantages in 
 practice, lessens the spherical aberration and improves 
 the illumination, though it decreases the angle of 
 aperture. 
 
32 THE MICROSCOPE, ETC. 
 
 To the largest hole of the diaphragm a short tube, 
 1, fig. 16, lined with cloth is attached, another tube 
 2 of sufficient length to reach the under surface of 
 the condenser, slides within it, at the upper extremity 
 of the inner tube and a short distance from its ori- 
 fice a slight rim projects into the interior, on which 
 brass discs having different sized central apertures 
 may be fitted. 
 
 Another tube E carrying a disc of blue glass may 
 be made to slide within the tube 2. If the tint of 
 this glass is properly chosen it obviates the neces- 
 sity of using a part of the spectrum to produce 
 monochromatic light. The intensity of the colour is 
 increased or diminished by increasing or diminishing 
 the distance between the blue glass and the aperture 
 of the slot or back of the condenser. 
 
 The description of this substage arrangement was 
 originally given to enable anyone possessing a cheap 
 instrument, or unable to afford an expensive one 
 already "fitted with an achromatic condenser, to con- 
 struct an apparatus which would answer that pur- 
 pose, and whose chief advantages were that no 
 light could reach the object or enter the objective 
 except through the diaphragm and condenser them- 
 selves, the ease and simplicity with which the several 
 adjustments are made, and the possibility of adapt- 
 ing it to any existing microscope stand. 
 
ILLUMINATION. 33 
 
 ILLUMINATION. 
 
 The best light for Photo- micrography is sunlight, 
 but the difficulties of its employment in our climate, 
 more than counterbalance the excellence of its re- 
 sults, and a description of the apparatus necessary 
 is only given for the benefit of those who can afford 
 sufficient time during daylight for Photo- micro- 
 graphy, or who may be more favourably situated 
 atmospherically. 
 
 It should be borne in mind that the actinic power 
 of the sun is subject to considerable variations, due 
 to its elevation above the horizon; this depends 
 on the hour of the day and time of the year, the 
 greatest intensity being about noon in midsummer, 
 while at the same hour in midwinter it is about one 
 third less. No fixed rule can be given for exposure, 
 its duration therefore must be left to the judgment 
 and experience of the operator. 
 
 The rays of the sun may be thrown on the con- 
 denser of the microscope from a mirror moved by 
 hand. This is inconvenient and requires an assis- 
 tant. Some means of keeping the light in position 
 is almost a necessity, and for this purpose several 
 instruments have been invented, the cheapest being 
 designed by Stoney, and lately modified by Spencer 
 of Dublin. As all these instruments are expensive, 
 we shall describe a form of Heliostat very easily 
 made and sufficiently accurate for the purpose. 
 
 A thick well- seasoned oak or mahogany board 
 
34 ILLUMINATION. 
 
 about six inches wide and twelve long, A, fig. 17, is 
 fitted with levelling screws,, + + + +, at its four 
 corners. On it a small French clock, M, is placed, a 
 boxwood wheel one inch in circumference having 
 been previously attached to the hour hand axle. 
 
 A sheet of white paper, with a line NS drawn 
 across it, is gummed to the back of a square of thick 
 plate glass, D, the whole being fastened to A, as in 
 the figure. 
 
 A ball and socket joint is fixed at E, the ball 
 having a hole half way through it, the orifice being 
 on a level with the top of the glass plate, and in a 
 direct line with NS. 
 
 A wooden pillar F, the top being cut obliquely is 
 placed as shown; on it is fastened a thick brass 
 plate, by a binding screw, B, passing through the 
 slot at one extremity, the other extremity being 
 perforated to receive a knitting needle, H. 
 
 This knitting needle must be perfectly straight, 
 and work very smoothly in E and G. On it between 
 E and G a boxwood wheel, I, four inches in circum- 
 ference is fixed, and above G a small mirror K. 
 
 A motion four times as slow as that of the hour 
 hand of the clock is imparted to the needle and thus 
 to the mirror, by a silk cord passing round the box- 
 wood wheels M and I. 
 
 An elastic band and a small hook is the best 
 means of keeping the cord tight, it should always be 
 detached when the instrument is not in use. 
 
 Another and large mirror, L, mounted to allow of 
 its rotation in all directions, and elevation to any 
 
ILLUMINATION. 
 FIG. 17. 
 
 35 
 
36 
 
 ILLUMINATION. 
 
 required height, is placed in front of the mirror K and 
 generally on its left hand -side. 
 
 A stout card E- whose sides are the same length 
 as the needle, is divided into degrees, minutes, and 
 seconds. 
 
 A small plumb line, P, a spirit level and a compass 
 complete the apparatus. 
 
 Before describing the adjustment of the heliostat, 
 it is necessary to call to mind the following facts. 
 
 The sun moves apparently in a circle of which the 
 earth is the centre and the line joining the poles PP' 
 the axis, fig. 18. 
 
 FIQ. 18. 
 
 At any place on the earth's surface a line AO 
 
ILLUMINATION. 37 
 
 drawn pointing to the pole will be parallel to PF, as 
 the pole is infinitely distant. 
 
 If OC be now drawn and TT' at right angles to it 
 and tangent to the place, the angle AOT, i.e. the 
 altitude of the pole = the angle OCF, i.e. the latitude 
 of the place. 
 
 Now since the sun completes a revolution in 24 
 hours it is evident that a mirror fixed at an angle 
 with the horizon equal to the latitude of the place, 
 will point to the pole, and if .nade to revolve by 
 clockwork once in 24 hours will always face the sun. 
 If instead of facing the sun it is required to throw its 
 reflection on a given point, we must then employ 
 another mirror to receive the reflection from the one 
 looking towards the sun, and give the latter a mo- 
 tion twice as slow to enable it to keep the reflected 
 ray in position on the second mirror. It is on this 
 account the boxwood wheel on the needle is four 
 times the circumference of that on the hour axle of 
 the clock. 
 
 When adjusting the heliostat it is best to fix it 
 permanently in position. The window of some room 
 looking towards the south and devoted entirely to 
 this purpose, should be chosen. 
 
 The stand is placed on a firm support at the win- 
 dow, (which should be open), so that the line NS 
 points north and south, this can easily be done by 
 means of a compass laid on the glass plate D over 
 NS. The levelling of D being carried on at, the 
 same time, by means of the screws + + + and a 
 small spirit level. 
 
38 ILLUMINATION. 
 
 The plumb-line is attached to the top of the needle 
 H, and the brass plate G moved till the lead of the 
 plumb-line hangs directly over NS. At the same 
 time the card E, (which should be very accurately 
 made), is placed with its upper extremity at E, the 
 lower side being parallel with NS, and the needle H 
 made parallel with the line corresponding to the 
 latitude of the place on the card. H now points to 
 the pole. 
 
 During these adjustments, the level of the appar- 
 atus, and the north and south positions of the line 
 NS should not be disturbed. The position of the 
 needle should finally be tested by seeing that the 
 plumb line hangs directly over the N extremity of 
 NS. The silk cord is placed round the wheels on 
 the clock and needle, so that the mirror revolves in 
 the direction of the sun's motion when the clock is 
 set going. The sun's rays are directed on the mirror 
 L by the mirror K, and as L can be moved in all 
 directions, the reflected rays may be made to occupy 
 any position. 
 
 This instrument has been described for the benefit 
 of those who have the time and ability for the manu- 
 facture of their own instruments, and because it 
 cannot be purchased ready made. It was found 
 sufficiently accurate for exposures of moderate 
 length, but like all instruments of the kind it re- 
 quires considerable care and practise to adjust. 
 When once fixed, its position should be left un- 
 changed as a separate adjustment every time it is 
 required will be found very troublesome. 
 
ILLUMINATION. 
 
 39 
 
 Stoney's heliostat can be purchased for five 
 pounds. It is a very reliable instrument and pos- 
 sesses the great advantage of only once reflecting 
 the incident ray. 
 
 Artificial light has so many advantages over sun- 
 light that its employment is almost universal in 
 photo-micrography, Swan's electric lamp is the best 
 form, but as an ordinary paraffin lamp gives excellent 
 results, and the arrangements are similar for both, 
 we will confine ourselves to a description of the latter. 
 
 Fig. 19 shows a simplified form of that used by 
 
 FIG. 19. 
 
 Dr. Dallinger and described in the Journal of the 
 Microscopical Society. 
 
 To the back of an ordinary tin paraffin lamp A, a 
 
40 ILLUMINATION. 
 
 board is attached to give rigidity; this board 
 is fastened by screws to a block which can be 
 raised or lowered on the pillar D by rack and 
 pinion movement. A lateral motion is communi- 
 cated to the pillar D by means of the screw F. 
 
 The lid of an oblong tin box abcut one inch wider 
 than the chimney of the lamp, has a hole cut in it 
 of sufficient size to allow of its fitting tightly on the 
 small flange below the tongues of the burner, and as 
 near as possible to the side of the lid intended for 
 the front, that for the back being turned down hori- 
 zontally. 
 
 Another round hole two inches in diameter, is cut 
 in the front of the box, at such a level that the Same 
 may occupy its centre. 
 
 In the middle of the opposite side a slit three 
 inches long is made, the upper extremity of which is 
 cut again at right angles ; the flaps thus formed are 
 turned outward and a plane silvered mirror fastened 
 between them. 
 
 The spaces left at the top and bottom of the flaps, 
 allow a current of air to circulate between the 
 mirror and the chimney of the lamp, and prevents 
 their cracking. 
 
 When using Swan's incandescent lamp, the same 
 method of preventing extraneous light from reaching 
 the microscope, and condensing the available portion 
 on the object is employed. All batteries and appar- 
 atus for working it are best purchased ; with regard 
 ^o this, full information will be supplied by any 
 leading electrical firm. 
 
THE CAMERA, ETC. 41 
 
 THE CAMERA AND OTHER APPARATUS. 
 
 As the camera plays a very important part in 
 photo- micrography, we recommend the reader, un- 
 less he is a first rate mechanic, to purchase one; 
 great care being required in its manufacture. It 
 should be quarter plate size, with bellows body, 
 the interior lined with black velvet. The focussing 
 screen which should consist of the finest patent plate 
 (oiled), must be carefully adjusted to occupy exactly 
 the same position as the sensitized plate. 
 
 It will be found convenient when working with 
 dry plates, to have one or two double dark slides. 
 Several plates can then be exposed consecutively, and 
 if developed together a great waste of time and solu- 
 tion is avoided. 
 
 The front, to which the lens is attached in ordi- 
 nary photography, should slide in groves fixed to the 
 body of the camera, we can then substitute for it 
 a conical bellows, similar to that in fig. 24, also 
 lined with black velvet. 
 
 To the end of the conical bellows a tube an inch 
 long is attached, this fits into the short tube of the 
 microscope smoothly and accurately, its interior 
 must be blackened, or better, covered with velvet, 
 to prevent reflection from the sides. 
 
 The distance of the focussing screen from the 
 front of the camera should be regulated by a rack 
 and pinion or screw motion, and when the desired 
 
42 THE CAMERA, ETC. 
 
 position is obtained, some means of fastening it is 
 necessary. 
 
 The plate carrier or dry back should be easily 
 substituted for the focussing screen, as the slightest 
 shake might destroy an arrangement of the micro- 
 scope and its accessories, that consumed a consider- 
 able time in preparation. 
 
 The camera, when these additions are completed, 
 is fastened to an oblong board, the same width as 
 itself, but projecting about two inches beyond it, 
 both back and front. To the corners of this board 
 levelling screws are attached which enable the 
 focussing screen to be made coincident with the 
 optic axis of the microscope, and the tube on the 
 bellows to be placed in the most favourable position 
 for adjustment to that instrument. (See fig. 24). 
 
 The greatest difficulty that besets us, especially 
 when using artificial light, is the impossibility of 
 focussing minute markings on the screen.* This is 
 due to three causes, first the coarseness of the sur- 
 face on which the image is formed, second the 
 minuteness of the image itself, and thirdly want of 
 light. The first is irremediable as nothing has yet 
 
 * A white card has been suggested as a substitute for patent 
 plate, it is not recommended for the following reason : our 
 aim being to photograph with high powers (anyone can photo- 
 graph with the |) and lamp light, the adoption of a white card 
 prevents the use of a focussing glass which is indispensable to 
 the resolution of minute markings, and also very sensibly in- 
 creases the illumination and renders faint shadows visible which 
 are invisible to the naked eye owing to the weak illumination. 
 
THE CAMERA, ETC. 43 
 
 been found, of sufficient surface opacity and fine- 
 ness of texture, to take the place of patent plate. 
 
 The second may be remedied by magnifying the 
 image. A focussing glass answers this purpose, an 
 excellent one being made as follows : 
 
 With a piece of stout cardboard make a tube four 
 or five inches long to fit one of the eye-pieces of the 
 microscope, and blacken it inside. In the opposite 
 end fix a plano-convex lens about three inches focus, 
 its convex side being turned towards the eye-piece, 
 or preferably a universal screw to receive an ob- 
 jective of about the same power. Make another 
 tube six or seven inches long to fit over the first, and 
 the focussing glass is completed. 
 
 The end of the outer tube being placed against 
 the screen, its roughened side is brought into focus 
 by sliding the inner tube within the outer. When 
 the best focus has been obtained, which may be done 
 by fastening a very small fly or other minute object 
 on the focussing screen, the inner tube is marked 
 with a circle where it joins the outer, thus enabling 
 it to be placed in the same position when again 
 required. 
 
 The third difficulty, namely, want of light, cannot 
 be overcome, as any increase in quantity of the light, 
 decreases the visibility of the structure. 
 
 The stand intended to support the microscope and 
 its accessories requires to be made as firmly as possi- 
 ble. The following is a description of the form 
 finally adopted by the writer after more than ten 
 
44 THE CAMERA, ETC. 
 
 years' experience, during which time scarcely a 
 month elapsed without the trial of some fresh device. 
 It is still far from perfect, but we hope, its simplicity 
 will in some degree atone for its numerous defects. 
 
 A beam ten inches wide, two inches thick and six 
 feet long, is sawn into three separate portions, three, 
 one, and two feet long respectively (see figs. 2 1 and 
 26). On the upper surface at each side flush with 
 the edges, two laths one inch wide, half an inch 
 thick, and the same length as the beam, are 
 fastened, and divided into three parts, the same 
 way as the beam. These not only prevent any- 
 thing placed on the stand from rolling or being 
 knocked off, but if divided into inches and half 
 inches, enable the apparatus to be placed in any 
 position they may have formerly occupied on the 
 stand. 
 
 Parts 1 and 2 are joined together on their under 
 surface by two strong hinges, let in flush with the 
 wood. 2 and 8 are joined on their upper surface, in 
 the same way where the laths meet as in fig. 24. 
 
 Along the sides of the beams ten bolts are iiife jrted, 
 projecting one inch and a quarter from the surface, 
 and six inches distant from each other. Their proper 
 position is best determined by first fixing two, three 
 inches on each side of the centre of plank no. 2, or 
 three inches from where it joins 1 and 3 ; then in- 
 serting the remaining eight, ten inches from these 
 and from each other at four equal distances on planks 
 1 and 3. This description will be easily understood 
 by a reference to the figure. 
 
THE CAMERA, ETC. 45 
 
 A board three feet long, two and a half inches 
 wide, and one inch thick, B fig. 24, has six holes 
 drilled in it, six inches apart, the last holes on either 
 side being three inches from its extremities. This 
 enables it to be screwed on to any six bolts at the 
 same time, thus keeping the several parts of the 
 beam steady, in the various positions we are com- 
 pelled to place it, owing to the different methods 
 adopted to meet the requirements of every case. 
 
 The first division of the beam I, fig. 24, is intended 
 to support the oblong board to which the camera 
 is fastened; a binding screw and a brass slip 
 working in a slot cut down the centre of the 
 beam attaches them to each other. 
 
 On the second division, 2, a platform of sufficient 
 height to enable the microscope to be adjusted to 
 the camera is erected, the microscope being pre- 
 viously firmly attached to a separate board, sliding 
 to and from the lamp, between two grooved slips on 
 the top of the platform. This should also be 
 clamped in position by a binding screw. 
 
 Owing to the different forms of microscope stands 
 it is ^mpossible to adhere to any fixed rule with 
 regard to the method of attaching the microscope to 
 the platform. It must, however, be as accurately 
 and firmly fastened as possible, while its motion to 
 and from the lamp must take place without disturb- 
 ing the centring of the different instruments. 
 
 A thick board the same width as the stand and 
 about twelve or fourteen inches long, is fastened at 
 right angles to plank No. 3 on the extremity behind 
 
46 THE CAMERA, ETC. 
 
 the lamp ; an aperture six inches square being pre- 
 viously cut in it, on a level with the top of the plat- 
 form to which the camera is attached. This aperture 
 enables direct sunlight to be used, with the appara- 
 tus in the horizontal position. 
 
 A division about a quarter of an inch wide, runs 
 along the centre of the plank to within two or three 
 inches of its extremities, this enables the lamp, bull's 
 eye condenser, and sulphate of copper cell to be 
 firmly clamped in position by binding screws. 
 
 The stand can be placed at any angle, by shorten- 
 ing or lengthening the camera legs attached to the 
 bolts on the extremity of plank No. 1. They may 
 be detached when not required. 
 
 A reference to figures 24, 26, 28, will enable us 
 to understand why the arrangement is so compli- 
 cated. It will be seen that five different methods of 
 placing the apparatus are adopted, and the stand 
 made to suit them all. A full description is reserved 
 for another portion of the work, devoted to the 
 particular arrangement of the stand, with certain 
 objects and objectives. 
 
 Those positions in which the apparatus is hori- 
 zontal should always be chosen if possible, not only 
 because it is the most convenient for manipulation, 
 but on account of the superiority of the illumination. 
 
 The perpendicular position is only necessary when 
 the object is fluid, and the positions between these 
 when oblique light is required. 
 
 An iron rod three feet long, sliding in a tube be- 
 neath the oblong board supporting the camera, is 
 
THE CAMERA, ETC. 47 
 
 fixed so that a wheel, attached to the extremity next 
 the microscope, may always occupy the same position 
 beneath the fine adjustment, independently of the 
 distance of the camera from the platform. A silk 
 cord fastened round this wheel and the fine adjust- 
 ment, enables an observer, by turning the milled 
 head at the opposite end of the rod, to focus the 
 image on the screen of the camera when the adjust- 
 ment is beyond reach. An assistant is then un- 
 necessary, as no matter how intelligent he may be, 
 it will be found more satisfactory to have the focus- 
 sing under our own control. 
 
 This method is a modification of that adopted by 
 Mr. Woodward when photographing without a 
 camera, under which circumstances we never use it, 
 having found the following arrangement much more 
 satisfactory. 
 
 A cork with a slight rod attached to it by two wire 
 holdfasts, is slipped into a tube fastened to the fine 
 adjustment of the microscope; this enables us to act 
 directly on the fine adjustment without the inter- 
 vention of any cord or wheels ; unfortunately its use 
 is limited to those methods in which the microscope 
 is not attached to the camera. 
 
 There is always great danger of the object and 
 objective being destroyed by the heat rays focussed 
 on them by the condenser. This may be partially 
 avoided by putting the condenser a little out of focus, 
 or we may entirely eliminate them by the interposi- 
 tion of a plate of alum between the bulFs eye conden- 
 
48 
 
 THE CAMERA,, ETC. 
 
 ser and microscope. The best method, however, is 
 to remove the blue glass, and place a cell having 
 parallel sides, filled with a solution of ammonio- 
 sulphate of copper in a similar position to that 
 recommended for the alum plate. The cell is made as 
 follows : 
 
 A piece of round india-rubber placed between two 
 quarter plates, is made to occupy the same position 
 as the dotted lines in figure 20. A board slightly 
 narrower than the plates and india-rubber, has a 
 
 FIG. 20. 
 
 piece cut out of it 4^ inches wide and about the same 
 length ; four thin stripes are fastened along its edges 
 and the plates with the india-rubber forced down be- 
 tween thfim ; when this has been done the cell is 
 filled with the solution, and the india-rubber pressed 
 down so as to complete the ring and prevent evapor- 
 ation. This cell may with advantage be used on all 
 occasions instead of the blue glass. 
 
 Two plano-convex lenses each about 4J inch focus, 
 when fixed in a shallow tube with their convex sur- 
 faces almost touching, make the best condenser (when 
 high powers are employed) if placed a quarter of an 
 inch in front of the lamp and six inches from the 
 achromatic condenser. 
 
THE CAMERA, ETC. 49 
 
 Having finished our description of the apparatus 
 required in photo -micrography, we wish finally to 
 impress on the reader the necessity of making them 
 as well and accurately as possible, and not to attempt 
 their manufacture himself unless he is a good 
 mechanic. 
 
 We now pass to the arrangement of the dark 
 room. The outlay is very small and will amply re- 
 pay the photographer. Any spare room may be 
 selected for its erection, preferably on the ground 
 floor, near, or if possible in, the apartment set apart 
 for photo-micrography and the instruments used for 
 that purpose. 
 
 About six feet from one wall and twelve from the 
 other, a post A, fig. 21, reaching from floor to ceil- 
 ing is erected, two more posts B and C are placed 
 opposite to it against the walls, and two or three 
 long laths are fastened at equal intervals horizontally 
 between A and B. 
 
 FIG. 21. 
 
 Half way between A and C another post D is 
 fixed, and about seven feet from the floor a cross 
 
50 THE CAMEKA, ETC. 
 
 beam between A and D ; a wooden frame fitting 
 accurately in this interval is hinged to A, and forms 
 the basis of the future door. 
 
 The whole is covered with two thicknesses of old 
 newspaper on the outside, care being taken that they 
 are firmly pasted to both floor and ceiling; when dry 
 the part covering the frame-work of the door is cut 
 along the edges and the door opened. 
 
 The inside is now covered in the same way, and 
 when dry the process repeated inside and outside 
 with the thickest tarred paper. A black curtain is 
 hung over the door. The apartment will now be 
 found to be completely light tight. 
 
 The advantage of the paper walls is that a window 
 can be cut in any convenient part, and a couple of 
 sheets of ruby glass a little larger than the orifice 
 fastened over it, by a few strips of orange paper 
 pasted round their edges. 
 
 The best position for the window is four feet from 
 the floor in the longest side, and the same distance 
 from the wall opposite the door. 
 
 Underneath the window a wooden trough lined 
 with lead, about three feet long, eighteen inches 
 wide, and three inches deep, is fixed ; it should have 
 a gradual incline towards a hole in its centre, where 
 the waste pipe is attached, which should pass out- 
 side both apartments if possible. The top should be 
 levelled and a sliding framework, or a board with 
 holes placed upon it, as in (fig. 22). 
 
 If no better water supply can be obtained a barrel 
 capable of holding a sufficient quantity and having a 
 
THE CAMERA, ETC. 
 FIG. 22. 
 
 51 
 
 brass rose cock near the bottom, may be fixed on a 
 stand, about three or four inches higher than the 
 trough and on its left hand side. 
 
 Some shelves to hold stock solution, etc., are 
 placed against the wall opposite to the window, a 
 small shelf being fastened above and below the 
 window itself to hold the bottles and dishes in 
 actual use. 
 
 On the right hand side of the trough a square box 
 is fixed just deep enough, to allow the flame of a 
 lamp, with a chimney of ruby glass, to appear above 
 it. 
 
 The best method of preventing any actinic light 
 from the lamp reaching the sensitive plates, is to cut 
 
 E2 
 
52 THE CAMEKA, ETC. 
 
 two holes in a large American meat tin, one on a 
 level with the flame, the other in the top. In the 
 former a piece of ruby glass and in the latter a 
 crooked chimney, the same as is used for a magic 
 lantern, is inserted. The whole is placed over the 
 lamp in the box, (the sides of the tin near the bottom 
 having a few holes previously made in them, to allow 
 of the free entrance of air). 
 
 One or two cupboards are useful, they should be 
 large enough to hold tin boxes for plates, sensitive 
 tissue, etc. 
 
 It will be seen by the figure that, in the unoccu- 
 pied portion of the paper wall next the door, about 
 three feet from the ground, a window twelve inches 
 wide and about four or five feet long, has been cut, 
 a board two feet long the same width as the window 
 projects from its lower end into the room, where it 
 rests on a support which keeps it perfectly level. 
 Two laths or posts are erected at the dark room ex- 
 tremity of this platform, and the whole covered over 
 with newspapers and tarred paper, the same way as 
 the dark room itself; a reference to fig. 22 will ex- 
 plain this better than any words can do. 
 
 A recess is thus formed in the wall outside of the 
 dark room. Inside the dark room in the side walls 
 of this recess, two windows about a foot square are 
 cut, and covered with sleeves of black cloth, fastened 
 at their open ends with indiarubber. 
 
 In the partition between the dark room and in- 
 terior of the recess, between these two walls an ori- 
 fice is made, about six inches in diameter also 
 covered with a sleeve of black cloth. 
 
THE CAMERA, ETC. 53 
 
 The legs of the stand described in the previous 
 chapter are taken off, plank no. 1 from which the 
 camera is detached folded beneath 2 and 3, and 
 placed in this recess with the microscope towards 
 the dark room, all the necessary manipulations to be 
 described in future pages, are carried on by the arms 
 passed through the two sleeves situated at the side 
 of the recess. The third sleeve is fastened round 
 tube of the microscope, and the fine adjustment 
 screw, the milled head being removed, passed 
 through a small orifice in it; the rod and cork 
 before described are now put on, and all arrange- 
 ments for working, without leaving the dark room, 
 completed. 
 
 When possible we strongly recommend this latter 
 arrangement. 
 
54 MOUNTING AND PREPARATION OF OBJECTS. 
 
 CHAPTER IY. 
 
 MOUNTING AND PREPARATION OF OBJECTS. 
 
 THE present chapter might be considered superfluous 
 but for the fact that objects designed for Photo- 
 micrography require different treatment from those 
 intended for ordinary microscopic examination. In 
 addition to this we wish to impart to others the little 
 knowledge we have obtained, and thus prevent the 
 disappointment and loss of time, consequent on a 
 dearly bought experience. 
 
 The usual method of mounting microscopic speci- 
 mens is, having previously prepared them by some of 
 the ways mentioned farther on, to place them on 
 plate-glass slips three inches long and one wide, then 
 after the addition of a small quantity of a suitable 
 preservative medium, to cover them with a square or 
 circle of very thin glass, which is fastened in posi- 
 tion either by the medium itself, or by a ring of 
 cement painted round its edge. 
 
 The disadvantages of this method will be apparent, 
 when the advantages of the one now advocated are 
 stated. Its universal adoption is not expected, be- 
 cause the old plan gives greater scope for artistic 
 display, and the manufacture of a kind of article 
 whose external appearance makes it more saleable. 
 
 The method is as follows. After the usual pre- 
 
MOUNTING AND PREPARATION OF OBJECTS. 55 
 
 paration, the specimen is placed on a square of thin 
 glass, (which may be fastened to an ordinary wooden 
 slip or not, preferably not), and covered after the 
 application of a suitable medium with another 
 square of the same size, both if not fastened by the 
 medium itself are cemented by passing a brush 
 charged with any of the usual varnishes round their 
 edges. When dry they are either permanently in- 
 serted in a boxwood slip A, fig. 23, or what is much 
 more convenient, placed when required for examina- 
 tion within or on one, by any of the methods shown 
 in the figure. 
 
 The advantages claimed for this plan are, con- 
 venience of storage, postal transmission, etc. ; possi- 
 bility of examining both sides of the specimen ; a 
 high power objective sustains no injury if it happens 
 to be driven through the preparation ; the aberra- 
 tions caused by the thickness of the glass slides 
 usually employed, are removed ; and when using high 
 powers the condenser can be brought close to the 
 object. The examination of objects with oblique 
 light is facilitated, their definition wonderfully im- 
 proved ; and even with direct light markings can be 
 seen, which defy resolution if the object be mounted 
 in the usual way ; finally one slip alone is necessary 
 for the reception of any preparation requiring ex- 
 amination. 
 
 Many objects, among which may be mentioned, 
 scales of moths and butterflies, etc., require no 
 previous preparation, all that is necessary after 
 placing them between thin glass, is to pass a 
 
56 MOUNTING AND PREPARATION OF OBJECTS. 
 FIG. 23. 
 
MOUNTING AND PREPARATION OF OBJECTS. 57 
 
 brush charged with asphaltum round their edges, 
 This operation is facilitated if the thin glass is held 
 in the clip 4, fig. 23. The cement should be as 
 thick as possible to prevent its running in between 
 the glasses. Preparations liable to injury from pres- 
 sure, will if thin, require a ring of cement painted 
 round one or both glasses and allowed to dry before 
 the preparation is placed between them, and if thick 
 a ring of paper or zinc answers the same purpose. 
 
 Whole insects or opaque parts of the same are 
 rendered transparent by soaking in turpentine for 
 two or three days, and afterwards mounted in balsam. 
 The more opaque parts may be rendered transparent 
 by previous maceration in solution of potash. 
 
 The balsam must be first evaporated by gentle 
 heat, and when it has attained the consistency of 
 resin, it is dissolved in an equal quantity of bensol 
 and kept in a bottle with an air-t : ght glass cap for use. 
 
 Balsam should only be used when nothing else 
 will answer, as its high refractive index renders the 
 finer details of certain structures invisible, beside s 
 the yellow colour of this medium causes as much 
 diminution of the actinic power of the light in the 
 illuminated parts of the field, as the shaded portions 
 of the object itself ; thus markings, plainly visible 
 in the microscope, fail to make any impression on 
 the sensitised surface of the plate. 
 
 Damar, being whiter in colour and its refractive 
 index less, gives better results. As a cement it is 
 much superior, not becoming brittle like balsam 
 after some time. 
 
58 MOUNTING AND PREPARATION OF OBJECTS. 
 
 Minute algse, infusoria, etc., require no previous 
 preparation, but may be at once placed in glycerine 
 and camphor water, by this means their original 
 colour is preserved and the growth of mycelium pre- 
 vented. It should be remembered that glycerine 
 cannot be employed as a preservative for objects 
 containing carbonate of lime, as it is a solvent of 
 that substance. Dr. Carpenter recommends its 
 saturation by pieces of marble as a preventative. 
 It is much safer to mount such specimens in dis- 
 tilled water to which a minute quantity of creosote 
 has been added. 
 
 For further information as to the relative merits 
 of different media, we refer the reader to the works 
 of Klein, Carpenter, Beale, etc., mentioning at the 
 same time, that those recommended in these pages 
 will be found generally useful. 
 
 Few more interesting objects present themselves 
 for examination than the Polycystina3, their variety 
 of form and beauty of outline, rendering them equally 
 a source of delight to the observer and of admiration 
 to the artist. 
 
 Their distribution is very general, beautiful forms 
 being found in chalk, limestone, and many other 
 deposits. Large quantities are contained in the sand 
 removed from sponges, this may be obtained from 
 any chemist or sponge merchant without payment. 
 
 The best method of separating them from the dirt 
 and debris, with which they are mixed, is to wash 
 the deposit in a large quantity of water with frequent 
 
MOUNTING AND PREPARATION OF OBJECTS. 59 
 
 shakings for an hour. After standing the same 
 length of time, the fluid is removed without dis- 
 turbing the sediment at the bottom of the vessel. 
 This is repeated till the washings become colourless. 
 
 A small quantity of the sediment is transferred 
 by a pipette to a piece of thin glass, and the fluid 
 allowed to evaporate ; the evaporation may be ac- 
 celerated by heat. 
 
 The thin glass is next fixed in the slip and placed 
 on the stage of the microscope. A low power objec- 
 tive is adjusted and the coarser uninteresting parti- 
 cles removed in the following manner : A bristle 
 from an old shaving brush is fastened in a wooden 
 handle ; these bristles are nearly always split, and 
 when pressed on the glass, their ends separate ; the 
 object is allowed to occupy a position between them ; 
 on removal of the pressure the bristle closes and the 
 object if valuable maybe transferred to another slide, 
 or if not, discarded. 
 
 It may be perceived that two methods are adopted, 
 either the removal of the debris from the original 
 slide, or the transference of the objects to a fresh 
 one, the former being employed when the objects 
 are in excess of the debris, the latter when the op- 
 posite is the case. 
 
 Whichever plan is adopted, a perfectly clean cover- 
 glass being seized by a small pointed forceps, a 
 ring of stiff cement is painted round the edge and 
 the preparation mounted dry, or a drop of damar is 
 placed near the edge of the side farthest from the 
 forceps, this side is brought into contact with the 
 
60 MOUNTING AND PREPARATION OF OBJECTS. 
 
 corresponding side of the slip on which the objects 
 lie, the other is allowed to sink gradually to its 
 position, in such a manner, that the fluid goes in a 
 wave from one side to the other, carrying all air 
 bubbles before it. 
 
 Should air bubbles make their appearance, one 
 edge of the cover glass may be raised with a fine 
 needle and an effort made to bring them to the side, 
 as they are inclined to adhere to the edge of the 
 fluid in its passage outwards. They may also be 
 removed by placing the preparation under a small 
 air pump. This latter piece of apparatus will be 
 found very useful for removing air bubbles from 
 structures liable to injury by displacement of the 
 cover glass. 
 
 When Foraminifera are contained in limestone or 
 other hard substances, sections of the substance suffi- 
 ciently thin to be transparent are required, instruc- 
 tions for cutting them will be given farther on. 
 
 We now pass to the preparation of the Diato- 
 maceee, they are closely allied to the Polycystinse 
 and are found in the same deposits. Beautiful forms 
 have been obtained from guano, infusorial earths, 
 sea dredgings, and stomachs of mollusca. They are 
 almost ubiquitous, every road and ditch being filled 
 with them, especially those containing brackish 
 water. They may be obtained from the latter toler- 
 ably free from admixture, if proper care be taken, 
 during then' collection, to leave the bottom mud un- 
 
PLA.TE II. 
 
 1. SECTION O-F LTJNO, CONTAINING* BACILLUS 
 ANTHRACIS FROM A CASE or SPLENIC FEVEB. 
 
 420 DIAMETERS. 
 
 3, S. GEMMA AND P. SPENCERII. 1000 DIAMETERS. 
 
 2. CENTRAL PORTION OF A. KITTONTI. 1500 DIA- 
 METERS. 
 
 4. SCALES OF P. ARG~ TERS, 
 
MOUNTING AND PEEPAEATION OP OBJECTS. 61 
 
 disturbed. They are next placed in a shallow saucer 
 and covered with a piece of muslin which lies in 
 immediate contact with the mud, while a film of 
 water lies above it. The saucer is now exposed to 
 daylight and the diatoms creep through the muslin, 
 collecting in a consistent film on its upper surface. 
 
 If desirable, they may be mounted in this con- 
 dition in distilled water and camphor, but if the 
 silicious skeletons alone are required, the gelatinous 
 envelope must be removed by boiling in nitric acid, 
 the sediment well washed till all trace of acid has 
 disappeared, and the residue mounted dry. 
 
 Sections may be cut by freezing, to be hereafter 
 described, using gelatin jelly instead of gum, and 
 mounting direct in glycerine on a slide. 
 
 When contained in other deposits two ounces of 
 the mixture are placed in two gallons of water, after 
 violent shaking allowed to stand two hours, and the 
 supernatant fluid removed. This process is repeated 
 till the water is no longer coloured. As much fluid 
 as possible being removed, the deposit is treated 
 with strong hydrochloric acid, and allowed to stand 
 for an hour. The acid is then poured off and a fresh 
 supply added, the whole being boiled for one hour 
 and washed in the manner first described, until all 
 traces of acid are removed. The process is repeated 
 with strong nitric acid, and after subsequent washing 
 to free it from acid, the deposit is placed in a tum- 
 bler full of water. Now comes the most trying part 
 of the preparation. 
 
 The tumbler is allowed to stand five minutes, at 
 
62 MOUNTING AND PREPARATION OP OBJECTS. 
 
 the end of that time its liquid contents are trans- 
 ferred to another tumbler which we shall call number 
 2, number 1 being* filled and shaken or stirred with 
 a wooden rod, after standing five minutes its fluid 
 contents are transferred to a number 3, number 1 is 
 again filled and stirred, left to stand for five minutes, 
 at the end of which time the liquid in number 2 is 
 transferred to a number 4, and the contents of num- 
 ber 1 put in its place ; number 1 being again filled 
 and left standing five minutes, the contents of num- 
 ber 3, are transferred to a number 5 and the fluid of 
 number 1 put in its place; numbers 4 and 5 are 
 allowed to stand a quarter of an hour, the changes 
 being regulated in the other tumblers to suit this, by 
 adding 6 and 7 to them and so on till we manage to 
 collect 12 single tumblers, whose contents represent 
 washings lasting from 5 to 60 minutes respectively, 
 this process will take a long time as the washings 
 multiply indefinitely ; towards the end some of the 
 tumblers will be found to contain all the diatomacese 
 tolerably free from impurities. The labour is not so 
 great as might appear at first sight, for every tum- 
 bler that has undergone twelve washings is put 
 aside. 
 
 Any flocculent matter remaining in the washed 
 deposits may be removed by pouring the water con- 
 taining the deposit gently upon an equal quantity of 
 glycerine in a test tube, so as to cause as little admix- 
 ture of the two liquids as possible. The diatoms on 
 account of their greater specific gravity sink to the 
 bottom, leaving the flocculent matter on top. 
 
MOUNTING AND PEEPAEATION OF OBJECTS. 63 
 
 It has been recommended to mount diatomacese 
 in bisulphide of carbon, as its high refractive index 
 makes their markings more distinct. We have as 
 yet had no experience of its efficacy in rendering 
 their details developable on a sensitised surface. 
 
 Since the first discovery of the markings on the 
 diatom aceae their true nature has been the source of 
 endless strife, and is at the present moment in as 
 unsettled a condition as ever. I remember having 
 experienced immense delight many years ago, when 
 for the first time I perceived that the dots on some 
 of the coscinodisceae consisted of a coarse and fine 
 variety, and that I could reproduce exactly the same 
 appearance by placing two pieces of glass covered 
 with hemispherical elevations within two or three 
 inches of each other. Since then my ardour with 
 regard to the investigation of the structure of the 
 diatomaceae has cooled, and I have made no further 
 attempt to prove how far the foregoing experiment 
 is an explanation of their appearance. My belief is 
 that they are hemispherical tuberosities, in the 
 diatomaceae proper. Their markings possess little 
 interest now, since they are allowed to have no value 
 even as tests, for resolving power of objectives; in 
 fact the investigation of their structure has led to 
 such a mis-application of talent and waste of time, 
 that the majority of workers in science have handed 
 this department over to the amateur. 
 
 Botanical preparations require considerable care 
 in their preparation, and as a rule are best examined 
 in the fresh state. A few, such as sections of stems, 
 
64 MOUNTING AND PREPARATION OF OBJECTS. 
 
 etc., may be mounted in glycerine and a thick solu- 
 tion of gum in camphor water. Opaque objects as 
 sori of ferns, may after soaking in turpentine be 
 mounted in balsam ; but others require a process of 
 maceration, staining and dissection, which will be 
 best understood by a reference to some text-book on 
 botany. 
 
 Pathological and histological objects are prepared 
 and mounted by the following methods. 
 
 When the intimate structure of tissue requires in- 
 vestigation, it should be obtained as fresh as possible 
 and a small portion immediately teased out with 
 needles, in a little serum or glycerine on a glass 
 slide. It will be found advantageous to insert the 
 needles into light wooden handles with a pliers, and 
 to place a piece of black cloth or white paper under- 
 neath the slide during dissection. When the dissec- 
 tion is finished, the tissue is steeped for three 
 minutes in a half per cent, solution of chloride of 
 gold, or a small quantity of the toning solution used 
 for prints diluted with three or four times its weight 
 of distilled water. After an immersion of three 
 minutes it is removed from the gold solution and 
 exposed to the light in a little glycerine, until it 
 assumes a violet gray shade. This will take about 
 twelve hours. A half per cent, solution of nitrate of 
 silver may be used in the same way, and is extreme- 
 ly useful for histological work especially the demon- 
 stration of the endothelial linings of serous mem- 
 branes. 
 
 These preparations are finally mounted in gly- 
 
MOUNTING AND PREPARATION OF OBJECTS. 65 
 
 cerine, and kept in the dark when not under ex- 
 amination. 
 
 The majority of pathological products require to 
 be cut into thin sections, before their examination is 
 possible. For this purpose they are placed while 
 fresh in Muller's fluid, which consists of: 
 
 Bichromate of Potash, 2 parts. 
 Sodium Sulphate, 1 part. 
 Water, 100 parts. 
 
 This should be omitted if the sections require 
 staining with chloride of gold, or nitrate of silver. 
 
 The organ or tissue is cut into sufficiently small 
 pieces, and placed for three hours in a very thick 
 solution of gum. A little alcohol added to the gum 
 prevents putrefaction and allows it to be used for a 
 considerable time. 
 
 The instruments required for section cutting, are a 
 razor and a microtome. The razor is set in a strong 
 wooden handle, it should have a good thick back, 
 loth sides being hollow ground. 
 
 Rutherford's microtome consists of a brass table, 
 in which a cylinder containing a piston is inserted. 
 The piston can be raised or lowered by a fine 
 threaded screw. A box covered with gutta percha 
 and projecting beyond the table, surrounds the cy- 
 linder ; in its bottom is a drainage tube to carry off 
 the melted ice and salt. 
 
 Several modifications of Rutherford's microtome 
 have been lately introduced, every one of which is 
 greatly inferior to the original, the worst form being 
 
66 MOUNTING AND PREPARATION OF OBJECTS. 
 
 that in which an attempt has been made to use ether 
 as the freezing agent. 
 
 The microtome is attached to a firm table, the 
 piston well oiled and the brass table polished ; near 
 at hand, we place the razor and a strop, as it requires 
 sharpening after two or three sections have been cut. 
 
 A block of ice splintered by a sharp awl, is pounded 
 as fine as possible and placed in an earthen-ware 
 crock or other suitable receptacle. An equal quan- 
 tity of coarse salt being put in a similar vessel. 
 
 The razor and a clean camel's hair brush are placed 
 in a dish containing water to which a small quantity 
 of alcohol has been added. 
 
 The cylinder is nearly filled with thick gum. One 
 of the pieces of tissue or organ being submerged in 
 it, the orifice is covered by an inverted watch glass, 
 and the box filled with alternate spoonfuls of ice and 
 salt. The mixture must be tightly rammed round 
 the cylinder, care being taken not to stop up the 
 drainage tube. 
 
 The freezing should proceed slowly, and only be 
 carried far enough to cause the gum and tissue to 
 assume a grizzly consistency. If they become white 
 and icy looking it has been carried too far, and time 
 must be allowed for their return to a proper condi- 
 tion before using the razor. 
 
 The rough top being sliced off and the razor well 
 wetted with spirit and water, the handle is grasped 
 by the right hand the edge being turned from us. 
 
 A slight turn is now given to the screw to elevate 
 the cylinder of gum above the level of the table, 
 
MOUNTING AND PREPARATION OF OBJECTS. 67 
 
 the ends of the fingers of the left hand are placed on 
 the opposite extremity of the razor from the handle, 
 the edge of the razor near the left hand fingers is 
 applied to the near side of the gum cylinder, and 
 passed through it from point to heel. The edge 
 during this manoeuvre being lightly applied to the 
 brass table, while the back is slightly elevated above 
 it. 
 
 The thickness of the section depends on the dis- 
 tance through which the screw is turned, if the latter 
 be graduated, which is very easily done, the exact 
 thickness may be regulated. To graduate the screw 
 a measure is placed in the cylinder, and the number 
 of turns required to elevate the piston a quarter of 
 an inch, counted. If it takes twenty-five, every 
 revolution of the screw, elevates the cylinder one- 
 hundreth of an inch. A mark is now made on the 
 milled head of the screw, and the end of the cylinder 
 round which it works is divided (round its circumfer- 
 ence) into five equal parts. The mark on the screw 
 when it moves through one of these divisions raises 
 the section one five-hundreth of an inch, a thinness 
 rarely attained in section cutting. 
 
 Several sections being cut by this method without 
 stopping to remove them singly from the razor, the 
 razor with the sections on it, are placed in the dish 
 containing the spirit and water; after a minute or 
 two and a little gentle agitation they will float off, 
 any that adhere being cautiously displaced with the 
 camel's hair brush. 
 
 When a sufficient number of sections are cut, they 
 
 F2 
 
68 MOUNTING AND PREPARATION OP OBJECTS. 
 
 are taken from the spirit and water, and placed in 
 the staining solution ; a flat tin spoon having a. hole 
 in the centre of its rounded extremity and its handle 
 bent at right angles, will be found useful for this 
 purpose. 
 
 The best staining fluid for all preparations in- 
 tended for microscopical photography is Beale's 
 carmine solution. Klein recommends the following 
 modification : 
 
 Powdered Carmine, 2 grammes, 
 rub up with a few drops of distilled water and add 
 
 Liquor. Ammon. Fort., 4 c.c. 
 Distilled Water, 48 c.c. 
 
 Shake up well and place in a bottle secured with 
 an india rubber or greased cork to prevent evapora- 
 tion. Glass stoppers are useless for this purpose and 
 should only be used for acids. 
 
 When required one drop is added to 10 or 20 of 
 water. If the tissue is very hard or has been kept a 
 long time in Muller's fluid, a stronger solution will 
 be required, and the vessel containing the staining 
 fluid with the sections must be accurately closed, as 
 its penetration depends to a considerable degree on 
 the quantity of ammonia. If however the sections 
 are fresh one drop is sufficient and the greater part 
 of the ammonia should be allowed to evaporate 
 before the addition of water. The proper amount of 
 staining requires considerable judgment to deter- 
 mine, but the more dilute the solution, the easier it 
 becomes and the greater the differentiation of tissue 
 
MOUNTING AND PEEPAEATION OF OBJECTS. 69 
 
 When forming an opinion, the condition of the 
 tissue, as regards its age, (embryonic tissues stain- 
 ing very readily), its hardness, the alkalinity of the 
 solution, and the magnifying power required to show 
 it properly should all be taken into consideration. 
 For further particulars we refer to Beale's " How to 
 Work with the Microscope," etc. ; with this caution 
 that all blue and violet staining solutions are useless, 
 unless the operator has unlimited time at his dis- 
 posal for the modification of the photographs by 
 various methods of intensification, after their direct 
 production. 
 
 If the sections are thin and intended for minute 
 investigation, they are removed from the carmine 
 solution by the flat spoon and placed for a short 
 time in equal parts of distilled water and alcohol, 
 this removes excess of colouring matter; they are 
 next transferred to glycerine and camphor water, 
 where they may be allowed to remain for a day or 
 two, (covered with a bell jar), before mounting, iu 
 gum and glycerine. If thick and only required for 
 very low powers, after removal from the carmine, 
 they are placed in absolute alcohol, for twenty-four 
 hours. When this period has elapsed each section 
 is taken up separately by the spoon, both are firmly 
 pressed between two folds of blotting paper held 
 between the finger and thumb, (no danger of injur- 
 ing the specimens need be apprehended, as they 
 have been considerably hardened by the alcohol), 
 and transferred to a saucer containing clove oil, in 
 which they are left for two or three hours, covered 
 by a bell jar as before. 
 
70 MOUNTING AND PREPARATION OF OBJECTS. 
 
 The clove oil is removed from the section in the 
 same manner as the alcohol, and a drop or two of 
 damar placed upon it before its removal from the 
 spoon. When it becomes transparent, which gener- 
 ally takes place after the lapse of a few seconds, it is 
 floated on to the slide by the aid of a needle, and 
 finally mounted in the manner already described. 
 
 The following method of staining with chloride of 
 gold has given more uniform and successful results, 
 when sections are required, than the original plan of 
 freezing the fresh tissue before staining. Place the 
 fresh tissue in one an a half per cent, solution of 
 bichromate of ammonia for fifteen to twenty days, 
 make sections in the ordinary way and dip them in 
 a solution of one part of double chloride of gold and 
 potassium in 10,000 of distilled water, wash in hy- 
 drochloric acid, 1 part in 2,000 of water, then place 
 them for ten minutes in hydrochloric acid one part, 
 and sixty per cent, solution of alcohol 1,000 parts, 
 clear with oil of cloves and put up in damar or bal- 
 sam in the usual way. 
 
 The discovery of bacteria in diseased tissue, and 
 the probability that a special form accompanies each 
 disease, has excited considerable interest in the 
 labours of Elrich, Koch, and others, who have in- 
 vestigated the subject, and to whom we are in- 
 debted for the methods of rendering the organisms 
 visible. 
 
 The following is a modification of the method 
 adopted for demonstrating the presence of the 
 
MOUNTING AND PREPARATION OF OBJECTS. 71 
 
 tubercle bacillus in sputa or diseased tissue, and is 
 an abstract from a paper read in the pathological 
 section of the British Medical Association at Wor- 
 cester, in August, 1882, by Dr. Heneage Gibbes. 
 
 The following stock solutions are prepared : 
 
 I. Magenta Crystals, 2 grammes 
 Pure Aniline, 3 c.c. 
 Alcohol, sp. gr. -830, 20 c.c. 
 Distilled Water, 20 c.c. 
 
 Dissolve the aniline in the spirit; rub up the 
 magenta in a glass mortar ; add the spirit gradually 
 while stirring, till all the colour is dissolved, then 
 add the water slowly, still stirring, and put in a 
 stoppered bottle. 
 
 II. Saturated solution of chrysoidin in dis- 
 tilled water, to which is added a crystal of 
 thymol dissolved in a little absolute alcohol. 
 
 This solution must be kept in a dark place. 
 
 III. Commercial Nitric Acid, 1 part. 
 Distilled Water, 2 parts. 
 
 The first two solutions must not be filtered. 
 
 The solutions are used as follows : 
 
 The sputum is spread on a cover glass and al- 
 lowed to dry, it is then passed three or four times 
 through the flame of a spirit lamp, and left to cool. 
 A few drops of solution number 1, are filtered into 
 a watch glass, and the cover glass, sputum down- 
 wards, placed on it, care being taken that no air 
 
72 MOUNTING AND PREPARATION OF OBJECTS. 
 
 bubbles are under the cover glass ; it is allowed to 
 remain twenty minutes. It is then placed in the 
 acid solution, number 3, until the colour is removed, 
 for about ten minutes. It is then washed in distilled 
 water until the nitric acid is removed, and then 
 placed in a little chrysoidin solution which has been 
 filtered into a watch glass, for a few minutes. It 
 must again be washed in distilled water, and the 
 superfluous water drained off on filtering paper ; it 
 is then placed in absolute alcohol and dried tho- 
 roughly in air. When dry it is mounted in balsam 
 in the usual manner. 
 
 Sections of hardened tissue are treated in the same 
 manner, and the bacillus is shown by this method 
 equally well in sections hardened in spirit and chromic 
 acid 
 
 We consider this an excellent modification of the 
 older methods, and although the photograph of the 
 bacillus anthracis in the frontispiece, was prepared 
 by Elrich's original method, the results obtained with 
 the tubercle bacillus, by the modified plan, were 
 superior. 
 
 Bone and all substances containing an organic 
 basis impregnated with earthy salts may be softened 
 by dissolving out the latter by prolonged maceration 
 in dilute acid, their consistency after this treatment 
 will allow of their being cut in the microtome with- 
 out freezing, if embedded in paraffin and wax. 
 
 Eocks, fossils, and bone when not softened, require 
 entirely different treatment and considerable skill 
 
MOUNTING AND PREPARATION OF OBJECTS. 73 
 
 before they arrive at a condition suitable for micro- 
 scopic investigation. A very slight sketch of the 
 plan adopted is here given to enable those who do 
 not possess a lapidary's workshop to investigate 
 these substances under low powers. 
 
 A rough slice is cut from the substance with a 
 small saw or by chipping ; one side is fastened with 
 balsam about an inch from the extremity of a board ; 
 twelve inches long, two inches wide, and half an 
 inch thick. When the balsam has hardened, the 
 upper surface of the specimen is flattened with a file, 
 next rubbed down on a perfectly flat Arkansas stone; 
 and finally polished with putty powder spread on a 
 leather pad ; a simple microscope is useful for watch- 
 ing the progress of the latter operation. When 
 finished this side is fastened on the wood ; the 
 specimen filed down as thin as possible, and the 
 foregoing process repeated. 
 
 If the specimen is very brittle it is best attached 
 to a glass slip, and saturated with balsam, before 
 commencing operations on the second surface. 
 
 The finished section may be now removed from 
 the wooden support by soaking in turpentine, after 
 which it is transferred to clove oil, and then to ab- 
 solute alcohol. On removal from this the alcohol is 
 allowed to evaporate spontaneously, and the section 
 mounted dry or in balsam. 
 
 For the preparation of injected specimens and 
 other processes, we refer the reader to the authorities 
 already mentioned, reminding them of the fact,, that 
 violet and blue solutions are unsatisfactory for stain- 
 
74 MOUNTING AND PREPARATION OF OBJECTS. 
 
 ing or injecting sections intended for photography, 
 and also that only two methods of mounting, namely, 
 in gum and glycerine, and dry, are required for 
 any preparation within the domain of microscopy. 
 
 The secret of successful mounting is cleanliness ; 
 all solutions must be filtered before and after using; 
 specimens, while in them, should be covered with a 
 bell jar ; and all media should be kept in wide mouth- 
 ed bottles, closed by glass caps, not corks or stoppers. 
 
 The most convenient articles for keeping sections 
 in during the staining and cleaning processes, are 
 large ointment pots ; in lieu of these saucers may be 
 used. 
 
 Glass rods should be kept in the bottles, for re- 
 moving small quantities of the media to the slides. 
 
 The thin glass when purchased should be cleaned 
 in dilute nitric acid, and kept for use in small jars 
 containing alcohol. When required one is taken 
 out, dried in an old linen or calico rag, and finally 
 polished with a piece of soft wash-leather ; this may 
 be easily accomplished by folding the leather over it, 
 and placing it when thus covered between the finger 
 and thumb ; a good deal of pressure and polishing 
 can be done in this way without much risk of frac- 
 ture. 
 
 All specimens when mounted must be kept in flat 
 trays in a horizontal position, the trays themselves 
 being placed in a box opening at the side and top 
 to allow of their easy removal. 
 
PHOTOGRAPHIC PROCESSES. 75 
 
 CHAPTER Y. 
 
 PHOTOGRAPHIC PROCESSES. 
 
 FROM among the many processes used in photogra- 
 phy we select the two best known, and most gener- 
 ally practised, referring the reader for further details 
 to works devoted to that subject. 
 
 The wet collodion process will first claim our 
 attention, not only on account of the priority of its 
 invention, but because the gradations of the resulting 
 image and the fineness of the deposit give a beauty 
 to the results, hitherto unapproached by any other 
 method. Unfortunately on account of the lengthen- 
 ed exposure required, its employment in Photo- 
 micrography with high powers, is only possible when 
 sunlight is the source of illumination ; but with low 
 powers, and when an exposure of not more than ten 
 minutes is necessary, it is generally applicable. 
 
 The size of plate required for Photo-micrography 
 is the carte-de-visite or quarter plate; the best ob- 
 tainable are made of imprimatur glass. 
 
 If used before for the production of a negative, 
 the old picture can be removed from the glass by 
 warm water and a soft rag, then washed in a strong 
 solution of caustic potash to remove grease ; dipped 
 in water again several times, next in nitric acid, and 
 finally left soaking in a dish of water acidulated with 
 nitric acid. 
 
76 PHOTOGRAPHIC PROCESSES. 
 
 When required, a plate is taken out rinsed in pure 
 water and polished with a soft rag or piece of wash- 
 leather, kept specially for that purpose. 
 
 The easiest method of testing the cleanliness of 
 the surface is by breathing on it ; if the moisture of 
 the breath is evenly distributed, the plate is clean. 
 
 Collodion is difficult to prepare, but bromo-iodised 
 collodion, of first-rate quality, can be purchased from 
 any leading firm ; and will give better results than 
 that prepared at home. 
 
 A vertical glass bath, with a cover to keep out the 
 dust, etc., will be found the most useful ; a pure 
 silver wire dipper, for immersing the plate in the 
 solution, being purchased along with it. 
 
 The sensitizing solution placed in the bath is made 
 as follows : 
 
 Eecrystallized Nitrate of Silver, 80 grammes. 
 Pure Distilled Water, 1 litre. 
 Iodide of Potassium, 25 grammes. 
 
 with the subsequent addition of a two per cent. 
 barium nitrate solution ; this and the following 
 formulas are taken from Abney's excellent treatise, 
 to which the reader is referred for fuller information 
 on the subject. 
 
 The nitrate of silver bath should be exposed to the 
 light, strong sunlight if possible, when not in use. 
 When required, it is filtered, and a few crystals 
 added until it regains its proper strength. An 
 argentometer is very useful for ascertaining the 
 amount of silver in solution. 
 
PHOTOGRAPHIC PROCESSES. 77 
 
 The developing solutions are made as follows : 
 
 Ferrous Sulphate, 40 grammes. 
 Glacial Acetic Acid, 30 to 40 c.c. 
 Alcohol, q.s. 
 Water, 1 litre. 
 
 The addition to this developer, of a very minute 
 quantity of gelatine (dissolved in water), adds to the 
 density and fineness of the deposit, a very desirable 
 result in Photo-micrography. 
 
 The amount of alcohol in the solution depends on 
 the age and condition of the bath ; with a new bath 
 none is required. 
 
 The iron should be dissolved before the other in- 
 gredients are added. 
 
 When the picture lacks density, the following in- 
 tensifying solution will answer. 
 
 Pyrogallic Acid, 4 grammes. 
 Citric Acid, 4 to 8 grammes. 
 Distilled Water, 1 litre, 
 to this a few drops of 
 
 Silver Nitrate, 2 grammes. 
 
 Distilled Water, 50 c.c. 
 
 must be added immediately before its application to 
 the negative. 
 
 After the plate has undergone treatment with 
 these solutions, the bromides and iodides unaffected 
 by light are dissolved away, by immersing in 
 
 Hyposulphite of Soda, 1 oz. 
 Water, 6 oz. 
 
78 PHOTOGRAPHIC PROCESSES. 
 
 After washing and drying, the plate may be var- 
 nished with any of the usual negative varnishes sold 
 by photographers. 
 
 We now proceed to the manipulations necessary 
 for the preparation of the sensitive surface, before 
 exposure in the camera. 
 
 A plate being removed from the dish, it is cleaned 
 as described, (care being taken to avoid touching the 
 surface with the fingers,) then either grasping the 
 right hand upper corner with the thumb and finger 
 of the right hand, or supporting the plate with a 
 plate holder, the collodion is poured on it, form- 
 ing a pool at the same corner, then flowing it to 
 the opposite, then to the left hand bottom corner, 
 and finally after completely covering the plate, off at 
 the right hand bottom corner. The plate being now 
 held in a nearly vertical position over the mouth of 
 the collodion bottle, a gentle rocking motion is im- 
 parted to it to prevent the collodion setting in 
 ridges. When no longer tacky, which is known by 
 barely touching one of the bottom corners with the 
 finger, the plate is placed in the nitrate of silver 
 bath, by a steady downward motion of the dipper, 
 moved about for a few seconds, and finally left for a 
 period varying from one to five seconds, according 
 to the temperature and condition of the solutions. 
 It is then removed, and (after all superfluous fluid 
 has been drained off) placed in the dark slide, ready 
 for exposure in the camera. This should take place 
 as soon as possible, as delay tends to injure the 
 plate. 
 
PHOTOGRAPHIC PROCESSES. 79 
 
 The dark slide enveloped in a dark cloth is now 
 placed in the camera, care being taken to keep the 
 side of the plate which was uppermost in the bath, 
 in the same position in both dark slide and camera. 
 
 The requisite exposure being given, the slide is 
 carried back to the dark room, its original position 
 being still maintained. The developer is poured 
 into a glass measure, and the plate covered with the 
 solution in the same manner as it was with collodion, 
 care being taken that none flows over the edges. 
 
 If the picture flashes out at once, over-exposure is 
 indicated; the developer should immediately be 
 dashed off, and the plate washed under the rose tap. 
 
 Should it develope gradually the developer should 
 be swept slowly backward and forward over the 
 plate, as long as the action is apparent, and removed 
 before any symptoms of fogging make their appear- 
 ance. 
 
 The plate is now thoroughly washed, and if not 
 sufficiently dense, the intensifier is poured over it, 
 while upon it a few drops of nitrate of silver is 
 placed in the measure ; the intensifier is then poured 
 back into the measure and the mixed solutions again 
 swept over the plate. 
 
 Intensification requires great judgment and should 
 only be continued as long as all detail is perfectly 
 clear; the instant, or better before, the slightest 
 fogging appears, the intensifier should be removed 
 and the plate again well washed. 
 
 We now immerse it in the hypo-solution, where it 
 
80 PHOTOQEAPHIC PROCESSES. 
 
 should remain till all the unaltered salts are dissolved 
 away, this is known by the creaminess having dis- 
 appeared from the back of the plate; it is then 
 washed in frequent changes of water for several 
 hours, and finally put aside to drain. 
 
 When dry, the plate is warmed before a clear fire, 
 the temperature not being raised higher than the 
 hand can very comfortably bear, the varnish is then 
 applied in exactly the same manner as collodion, and 
 when all superfluous fluid has drained away, heat is 
 again applied ; the temperature being carried much 
 higher than at first, to prevent the formation of a 
 mat surface. Should the intensifier not be used, and 
 the plate found to lack density after fixing, the 
 mercurial solution mentioned in the following process 
 may be applied, (as little exposure to actinic light as 
 possible being given before its application). 
 
 When the reproduction of very minute markings 
 is necessary, dry plates never give as good results as 
 the wet, at least in our hand; they are, however, 
 sufficiently perfect for all practical purposes, while 
 the shortness of the exposure, cleanliness of manipu- 
 lation, and when purchased, the time saved by the 
 absence of any previous preparation, almost counter- 
 balance this disadvantage. 
 
 Great care is required in using these plates, as the 
 slightest glimpse of actinic, light will utterly spoil 
 them. A double thickness of ruby glass must be 
 substituted for the ordinary yellow glass of the dark 
 room, and even of this light, as little as possible 
 
PHOTOGRAPHIC PROCESSES. 81 
 
 should be allowed to reach them. The dark slide 
 should be carefully examined, and if of the double 
 dry form, two sheets of zinc the same size as the 
 plate, each covered with black velvet on one side and 
 having a spring between them, should be placed 
 with the velvet side next the back of the plates, in 
 the dark slide. 
 
 The following formula for the preparation of dry 
 plates, having given almost perfect results; our 
 opinion as to their purchase, has been considerably 
 modified since the publication of the last edition. 
 Its production is due to Mr. Hartley of Chicago, and 
 is here inserted in almost his own words. 
 
 FORMULA. 
 
 Take any hard gelatine Swiss or Heinrich's 
 soak it for twelve hours in water, changing the 
 water three times during the twelve hours. Do not 
 cut it up. Take it out of the water and lay it on 
 clean paper to dry. No matter how much of this 
 you fix in this way, as when dry it will keep as 
 before. 
 
 Take 75 grains of carbonate of soda (not bicar- 
 bonate) and 60 grains of citric acid, and put into 
 three ounces of warm water in a quart pitcher; 
 when the citric acid and carbonate of soda are dis- 
 solved and all effervescence ceases and carbonic acid 
 gas has passed off, add 16 ounces cold water and 720 
 grains of the soaked and dried gelatine and let it 
 stand thirty minutes ; now dissolve 720 grains of 
 
 G 
 
82 PHOTOGRAPHIC PROCESSES. 
 
 silver (prepared according to formula given) in six 
 ounces in water. Place the pitcher containing the 
 gelatine in hot water do not let the temperature 
 exceed 110 degrees. When the gelatine is all dis- 
 solved, which will take about fifteen minutes, add 
 the silver solution to the warm gelatine ; rinse out 
 the vessel you dissolve the silver in with two ounces 
 of water, and add it to the gelatine solution ; when 
 the silver is added it will immediately turn white (if 
 it turns brown the gelatine is not good, and must be 
 discarded). Stir well. Now take a bowl large 
 enough to hold the emulsion, wax it inside with 
 beeswax, being careful not to leave an excess of 
 wax ; this is to keep the emulsion from sticking to 
 the bowl. Pour the silvered gelatine into the bowl 
 and set away in a temperature of 40 to 60 degrees 
 to set. When this becomes a jelly, which will take 
 about four hours, cut it into strips about one- fourth 
 inch square, using a silver knife or horn spatula. 
 Put strips of silver gelatine into a half-gallon 
 pitcher, put pitcher into the washing box (described 
 hereafter), put on covering and pour the following 
 solution through the pipe into the pitcher on to the 
 gelatine. 
 
 Soda carbonate, 150 grains. 
 Ammonium bromide, 720 grains. 
 Alcohol, 4 ounces. 
 Water (about 60 to 70 degrees) 12 ounces. 
 
 Stir this every half-hour for two hours. When 
 you stir it, take washing box into dark room, shut 
 
PHOTOGRAPHIC PROCESSES. 83 
 
 the door, and by red light only take off the cover ; 
 give it a good stirring with a glass rod and replace 
 the cover. To tell when the silver is all formed into 
 bromide of silver, take a small piece of the jelly to 
 the light and cut it in two; if it is all alike, the 
 action has taken place, if it is not the same colour all 
 the way through, there is still free silver present. 
 Do not put the piece back into the pitcher, as it 
 would fog the balance. When the silver has all been 
 formed into bromide of silver, the emulsion could be 
 washed, melted, and plates prepared, but they would 
 be slow. Now leave the emulsion standing in this 
 brine of bromide of ammonium, &c., from one to five 
 days or more, according to rapidity you want. Three 
 days makes a rapid plate, five to six days makes a 
 very rapid plate. The reason of this is the excess of 
 bromide of ammonium partially dissolves the bromide 
 of silver. The longer it remains in the brine, the 
 finer it becomes ; also, the weaker the brine, the finer 
 the bromide of silver. But by making it weaker 
 than is recommended here takes too long for the 
 bromide of silver to form. 
 
 To WASH THE EMULSION. 
 
 Let the water run through the tube to bottom of 
 pitcher and off at faucet below. To tell when the 
 emulsion is sufficiently washed, take some of the 
 waste water running from the faucet into a two- 
 ounce bottle and add a few drops of silver solution ; 
 there will be a precipitate of bromide of silver. In 
 
 a2 
 
84 PHOTOGRAPHIC PROCESSES. 
 
 an hour take some more of the waste water, and add 
 a few drops of silver solution, and if there is no pre- 
 cipitate of bromide of silver, the emulsion is washed 
 enough. If there is still a precipitate of bromide of 
 silver, continue to wash until, upon trial, there is no 
 precipitate formed. Stirring the emulsion several 
 times will hasten the washing. Never take off the 
 cover to the washing box, except in red light after 
 you add the brine. 
 
 The emulsion is now ready to be preserved for 
 future use, or to be used at once. 
 
 To use at once, tie a piece of coarse canvas over a 
 large bowl, pour the emulsion on to canvas and let 
 it drain free of excess of water ; put back into pitcher 
 and place into hot water in apparatus described 
 hereafter. Melt at a temperature of 140 to 150. 
 Add two ounces alcohol and two ounces pure albu- 
 men. (To prepare the albumen, beat the white of 
 eggs to a stiff froth and set aside to go back to liquid). 
 Add two drops of a saturated solution of chrome alum 
 in water to each ounce of emulsion; this is to keep the 
 gelatine from frilling. There should be 35oz. of 
 emulsion when finished ; if not, make up with water. 
 Make smaller quantities in proportion. 
 
 To FLOW THE PLATES. 
 
 Filter the emulsion through a piece of moist 
 flannel in the glass funnel, placed in the tin funnel 
 as described hereafter ; filter into a small pitcher 
 that will hold about six ounces. You can have 
 
PHOTOGRAPHIC PROCESSES. 
 
 several of those small pitchers in hot water ; as you 
 empty one you can be filtering more while you use 
 the others. The small pitchers are for flowing out. 
 Have your plates cleaned as described hereafter, and 
 have them about as warm as when you varnish. 
 Hold the plate with your left hand, the long way to- 
 wards you, pour some emulsion on the centre of 
 plate, let run to the farther right-hand corner, then 
 to farther left hand-corner, then to corner you have 
 hold of, and off at the nearest right hand corner ; 
 leave sufficient on the plate to make a rather opaque 
 film. Prac-tice will guide you how thick to have 
 them. If they come out too intense, you have too 
 much on : if too thin, you have not enough on. Move 
 the emulsion on the plate until it is smooth, and then 
 place upon screw-eyes as described hereafter. When 
 you have six flowed, the first one will be ready to put 
 upon a rack to dry. As soon as a plate is coated it 
 must be put in a dark place to dry not even a red 
 light should get to the plates after they are flowed. 
 The place you put them to set should be shaded from 
 all red or white light ; a dry plate on a negative ex- 
 posed for five minutes to a red light will make a 
 transparency ; so, of course, will fog if exposed too 
 long to red light in making and drying. The plates 
 will dry in a few hours and are ready for use. 
 
 The alcohol and albumen are added to hasten the 
 setting and drying, and also to aid in the flowing. 
 Gelatine with albumen flows more readily than gela- 
 tine alone ; the albumen also helps to keep the silver 
 in suspension in the gelatine. 
 
86 PHOTOGRAPHIC PROCESSES. 
 
 To KEEP THE EMULSION. 
 
 Take the emulsion strips and put them into a wide- 
 mouth fruit jar ; pour enough alcohol on to cover the 
 emulsion, screw on the top, and the emulsion will 
 keep. When you wish it, take up what you want to 
 use, wash it to free it of alcohol, drain and melt. 
 Add albumen, alcohol, and chrome alum as before, 
 and flow the plates. 
 
 If you are in a hurry and do not wish to wait the 
 three to five days to gain rapidity, you can take 
 emulsion as soon as all free silver has been formed 
 into bromide of silver. Melt the emulsion, heat to 
 140 to 150, add 480 grains of bromide of potassium, 
 and let stand in the water at 140 to 150 for 30 
 minutes. Set aside in temperature of 40 to 60 to 
 set, and then wash and flow the plates. But if this 
 way is chosen, the emulsion must be washed in a 
 different way than described above, as the soluble 
 ammonium nitrate left in the emulsion will not wash 
 out as in the other process of washing. When the 
 bromide of silver is formed in the gelatine, by placing 
 the silvered gelatine in the brine the emulsion does 
 not take up the soluble nitrate of ammonium, so only 
 needs sufficient washing to free the outside from the 
 nitrate of ammonium. But in the latter case the 
 nitrate of ammonium is all through the emulsion and 
 must be treated as follows : Squeeze the set emulsion 
 through a piece of coarse canvas into a large bowl of 
 water, take another large bowl, tie a piece of coarse 
 
PHOTOGRAPHIC PROCESSES. 87 
 
 canvas around the top, pour emulsion and water on 
 to the canvas, so as the water will filter off, take 
 emulsion with a silver spoon off of the canvas into 
 another bowl of water \ wash this way three times, 
 let drain, melt, add the alcohol and albumen as before 
 stated, and flow the plates. 
 
 To PREPARE THE SILVER. 
 
 Put a quantity of nitrate of silver into an eva- 
 porating dish on a sand bath, with a small amount 
 of water ; add to every pound of silver about the half 
 of the white of an egg ; fuse the silver until it has 
 melted and run back to an oily liquid ; take it off the 
 fire, cool and granulate. 
 
 DESCRIPTION OF WASHING Box. 
 
 Take a wooden pail, make a light-tight cover for 
 it ; put near the bottom a good sized wooden faucet ; 
 make out of galvanised iron a half-inch tube, with 
 three right angles in it, to keep light out, and on top 
 a small funnel of same material ; insert this tube 
 near the top of wooden pail ; let tube extend into 
 pail about two inches, and connect a rubber hose to 
 tube that will reach to bottom of pitcher containing 
 emulsion. The brine can be poured into the funnel, 
 through the tube, on to the emulsion, and when 
 ready to wash let water run into funnel, through 
 pitcher, and off at faucet below. 
 
88 PHOTOGRAPHIC PROCESSES. 
 
 DESCRIPTION OP APPARATUS FOR MELTING AND FIL- 
 TERING THE EMULSION. 
 
 Make a tin box 18in. deep, 12in. high, 12in. wide, 
 all sides inclosed except one. On the side that is not 
 inclosed make flange Gin. wide all round the opening. 
 Cut a hole in the partition where you intend flowing 
 your plates large enough to admit this box, let flange 
 fit up against the partition tight, so as not to admit 
 any light. Put oil stove in this box. It can, by this 
 means, be lighted and turned out without getting 
 light to plates, and the stove gets what air it needs 
 from the room not used for flowing the plates. 
 Also this plan keeps the smoke from the flowing 
 room. 
 
 Make a tin dish 14in. long, Sin. wide, and Sin. 
 deep. In one end fasten a tin funnel in which a 
 glass funnel holding a pint can be put. Rivet this 
 dish upon top of tin box, leaving about 2in. of the 
 end, where the funnel is, extending over the side of 
 tin box, so as to set flowing pitcher under funnel in 
 filtering the emulsion. Put water in this dish and 
 keep it at 140 while flowing the plates. Set pitchers 
 containing emulsions in this water. Use dipping 
 thermometer to tell when the temperature is right. 
 The hot water will be around the tin funnel and keep 
 emulsion hot while it is filtering. Use a good-sized 
 oil stove so as to be sure and keep the temperature 
 at 140 to 150 while filtering and flowing. 
 
PHOTOGRAPHIC PROCESSES. 89 
 
 DESCRIPTION OF LEVELLING SLAB. 
 
 Screw in top of table or shelf three screweyes for 
 each plate ; level plates by means of spirit level. In 
 very hot days or climates it may be necessary to have 
 underneath the shelf a zinc-lined drawer in which ice 
 can be placed ; in this case the shelf above the drawer 
 should be lattice work. 
 
 There is another way of working this formula 
 which some might prefer. I do not. But as good 
 results can be obtained as by the other, I will give it. 
 
 Take the silvered gelatine, heat it to 150, add the 
 alcohol, albumen, and chrome alum, and let set as 
 before described, but not get dry. Make a bath as 
 follows : 
 
 Ammonium bromide, 720 grains. 
 Soda carbonate, 160 grains. 
 Alcohol, 4 ounces. 
 Water, 12 ounces. 
 
 The alcohol in this formula is not absolutely 
 necessary; but when all water is used it takes longer 
 to get the bromide of silver to form. If you do not 
 use the alcohol employ water instead, and leave plates 
 in brine longer. 
 
 Put this bath into a grooved box the size of plates 
 you wish to make, put the silvered plates in the 
 bromide of ammonium bath and let set 24 hours, 
 take them out, put into another grooved box and 
 wash, put them on rack to dry, and they are ready 
 to use ; or they can be used wet but they will be 
 slower. 
 
90 PHOTOGRAPHIC PROCESSES. 
 
 To DEVELOP. 
 
 Any developer that will work on any plate will 
 work on mine the same. But I claim that all 
 published developers given by dry plate factories are 
 right if the exposure is. But unless the exposure is 
 right, or nearly so, a failure is almost sure to occur. 
 My plan of developing, while I use the same chemi- 
 cals, is on a different theory, making the developer 
 suit any exposure, no matter how long. I claim that 
 it is impossible for any one to so accurately judge the 
 time needed as to suit a standard developer, but must 
 make the developer to suit any exposure, and by the 
 following plan you can take any number of plates 
 and nob know the time of exposure or amouut of light 
 on subject at time of exposure, and if there is plenty 
 of time, no matter how much, you can make a nice 
 negative by this plan of developing. In the first 
 place I will give the theory of development, as there 
 will be, no doubt, some of you that do not under- 
 stand it. 
 
 . Pyrogallic acid is used to give strength to the 
 negative, and should be used according to the 
 amount of silver used in the emulsion. The smaller 
 the quantity of silver the smaller the quantity of 
 pyro. The more silver the more pyro. If more pyro. 
 is used than should be for the amount of silver, there 
 will be green fog ; if the proportion is right, the 
 plates will be clear in the shadows and no green 
 fog. 
 
PHOTOGRAPHIC PROCESSES. 91 
 
 The ammonia is used for detail. The bromide is 
 used to correct over-exposure. Citric acid is used to 
 keep the pyro. from oxidising. 
 
 FORMULA. FOR DEVELOPING. 
 
 No. I. Pyrogallic acid, 3 grains. 
 Citric Acid, 1 grain. 
 Water, 1 ounce. 
 
 No. II. Ammonium bromide, 48 grains. 
 Ammonia, 3 ounces. 
 Water, 3 ounces. 
 
 Take enough of the pyro. solution in your deve- 
 loping tray to well cover the plate ; let it remain in 
 this solution for a few seconds ; put two or three 
 drops of the ammonia solution into your developing 
 cup ; pour pyro. solution out of dish into cup con- 
 taining ammonia, then pour contents of cup on to 
 the negative ; in a few seconds the image will begin 
 to appear. Repeat the operation of adding the 
 ammonia, drop by drop, until you get all the detail 
 out. 
 
 Remember that the pyro. gives the strength : the 
 more pyro. the more strength; the less pyro. the less 
 strength. 
 
 Ammonia gives the detail : the more time the less 
 ammonia. Therefore if you take plenty of time and 
 commence with very little ammonia, you will get a 
 fine negative. Always commence with not more 
 than 2 or 3 drops of ammonia solution, then, no 
 matter what the time is, you have the plate under 
 
92 PHOTOGRAPHIC PROCESSES. 
 
 control. I have developed very fine negatives with 
 but two drops of ammonia for a 5 by 8 plate ; of 
 course the plate had plenty of time. It takes about 
 five minutes to 'develope a dry plate properly. If 
 you use the oxalate developer, use it on the same 
 theory as the pyro. Oxalate in the place of pyro. ; 
 iron in the place of ammonia ; only that you must 
 add the iron to the oxalate not the reverse* Oxa- 
 late gives the strength and iron the detail. If you 
 commence slow, you need not use any bromide in 
 either case. As bromide is only used to correct 
 over-exposure, it takes off part of time, the same 
 as when it is not washed out of the emulsion. Fix 
 in hypo, and wash as usual. 
 
 LIST OP ARTICLES NEEDED. 
 
 Washing box ; heating box, for melting and fil- 
 tering emulsion ; dipping thermometer ; oilsfcove ; 
 racks, for drying ; Swiss or Heinrich/s gelatine ; 
 Hartley's silver; ammonium bromide; pure car- 
 bonate of soda ; citric acid ; alcohol ; chrome alum ; 
 one quart pitcher ; one quart bowl ; half-gallon pit- 
 cher ; one gallon bowl ; several small pitchers, for 
 flowing ; silver knife or horn spatula get one at 
 any drug store. 
 
 CLEANING AND PREPARING THE GLASS. 
 
 Soak the glass in lye, well wash, and put into strong 
 nitric acid, and albumenise same as in the wet pro- 
 cess, using the albumen a little thicker. Do not 
 
PHOTOGRAPHIC PROCESSES. 93 
 
 add any ammonia, use a few drops of nitric acid in- 
 stead. 
 
 Another way Eub the glass over with the follow- 
 ing solution : Silicate of soda, loz. ; water, 30oz. ; 
 rub dry with tissue paper. 
 
 Another way is to use the glass without any 
 substratum. This is less trouble and just as good. 
 Do not polish, simply rub off dirt with dry cloth. If 
 the emulsion does not flow readily, on account of 
 plates being too ccld, you can assist the emulsion to 
 the edges with a glass rod or your finger. If air 
 bubbles get on the plate, break them with pieces of 
 filtering paper, The greatest cause of failure is too 
 much light in flowing and drying the plates. Also 
 dust is a great enemy. Fog, if not from light, comes 
 from free silver left in the emulsion. An emulsion 
 of this kind can be made all right by putting it again 
 into the brine, leavirg for a few hours, and washing 
 as before. The temperature of the brine should be 
 CO or 70. I would advise you to make all your 
 plates in spring for summer use, and in the fall for 
 winter use, as it is much more pleasant. Do not have 
 the flowing room over 80, 60 to 70 is better. Plates 
 that have been exposed to light and not developed, 
 can be soaked in a solution of bichromate of potash and 
 washed and dried, and they are as good as before ex- 
 posure. Be sure and keep plates dry. Dampness 
 is a great enemy to the dry plate. Plates that take 
 along time to dry are apt to frill. If you wish to make 
 a more intense negative than this formula gives, use 
 same amount of gelatine and less silver ; if you want 
 
94 PHOTOGRAPHIC PROCESSES. 
 
 a less intense negative, use more silver and same 
 amount of gelatine. 
 
 Always use the same number of grains of bromide 
 of ammonium in the brine as you use silver in the 
 gelatine, and reduce or increase the carbonate of 
 soda and citric acid in same proportion you reduce 
 or increase the silver. Always use the same amount 
 of gelatine. Any water that is fit to drink is fit to 
 make emulsion. Water that is strong of lime is not 
 good. 
 
 The plates being prepared by Hartley's formulas 
 or purchased, the following methods, of development 
 are recommended; a dish, preferably of ebonite, just 
 large enough, to hold a quarter plate, and another 
 of the same material to hold four or a larger number 
 are obtained, (a great saving both of time and solu- 
 tion being affected if several plates, which have each 
 received a similar exposure, are developed at the 
 same time.) Also a dish of earthenware to hold a 
 saturated solution of alum, another for a similar 
 solution of mercuric chloride, and one for hyposul- 
 phite of soda or fixing solution : these should all 
 differ in appearance, to avoid the possibility of 
 putting a solution into one, which had previously 
 contained another. 
 
 The dishes being placed in a convenient position 
 in the dark room, one or two plates according to 
 circumstances are placed in the dark slide; every 
 precaution being taken during this and all subse- 
 quent operations for the exclusion of actinic light. 
 The exposure being made, the slide with its contained 
 
PHOTOGRAPHIC PROCESSES. 95 
 
 plates may be put aside, till another batch has been 
 exposed, or for an indefinite period, and developed 
 at leisure. 
 
 The following formulae are recommended by Mr. 
 Swan for the development of the dry plates prepared 
 by him. 
 
 There are two different developers, alkaline pyro- 
 gallic acid and ferrous oxalate. The former is pre- 
 ferred by many, especially for views and portraits, 
 on account of the control it gives the photographer 
 over the character of the resulting negative. We 
 shall describe it first, although the latter has given 
 more satisfactory results in Photo -micrography. 
 
 No. I. Liquor Ammonia, ('880) 2 drachms. 
 Bromide of Ammonia, H drachms. 
 Distilled Water, 20 ounces. 
 
 This solution will keep for some time if the bottle 
 containing it is securely corked. Care should be 
 taken that the ammonia is the full strength specified, 
 if weaker the whole formula will be ruined. 
 
 No. II. Pyrogallic Acid, 4 grs. 
 Water, 2 oz. 
 
 This solution should be mixed immediately before 
 development. 
 
 The plate or plates being removed from their re- 
 spective slides, are placed in the ebonite dish. 
 
 An equal quantity of No. I. solution is added to 
 No. II., and the whole poured equally over the plates 
 which are left at rest in it. 
 
96 PHOTOGRAPHIC PROCESSES. 
 
 As it would be difficult to weigh a less quantity of 
 pyrogallic acid, and as the resulting solution is far 
 too large a quantity for a single quarter plate, we 
 recommend the development of at least four at the 
 same time. 
 
 Should the picture flash out suddenly after the 
 application of the developer, over exposure is indica- 
 ted; the developer should be immediately poured 
 back into the measure, the plates washed for a 
 second or two under the tap, and left covered with 
 water in the dish while one or two drops of a solu- 
 tion, 
 
 Bromide of Ammonia, 1 oz. 
 Water, 1 oz. 
 
 are added to the developer. 
 
 The water is poured from the plates, the developer 
 again applied, the process carefully watched, and the 
 solution poured off before any symptoms of fogging 
 appear in the whites of the negative. 
 
 In the opposite case, where the image is slow in 
 making its appearance, the solution should be poured 
 back into the measure, and a quantity of no. I. solu- 
 tion, varying from J to double the quantity at first 
 used, added to the developer, and at once applied to 
 the plate, without previous washing. 
 
 It will be seen that owing to the variations ad- 
 missible in the strength and preparations of the 
 solutions employed, the condition and density of 
 the negative is almost completely under control, if 
 the exposure has been kept within anything like 
 reasonable limits. 
 
PHOTOGRAPHIC PROCESSES. . 97 
 
 The developer is now poured off and the plate 
 washed for a few minutes. If not sufficiently dense 
 (especially when owing to under exposure), the 
 washing is continued for some time, and the ordinary 
 pyrogallic acid and silver solution, mentioned under 
 the wet process, employed. 
 
 Whether intensified or not at this stage, the nega- 
 tive is quickly washed under the tap and placed in a 
 solution, consisting of: 
 
 Hyposulphite of Soda, 2 oz. 
 Water, 10 oz. 
 
 (this solution should be fresh), where it is left for 
 about five minutes. 
 
 After all creaminess has disappeared from the back 
 of the film, the plate is washed in frequent changes 
 of water, for not less than six hours. It is then 
 placed in a saturated solution of alum for fifteen 
 minutes, and again thoroughly washed. 
 
 After this washing, if the negative on examination 
 appears to lack density and be deficient in vigour 
 owing to over-exposure, it is immersed in a saturated 
 solution of bichloride of mercury, until perfectly 
 white; again thoroughly washed for several hours, 
 and finally placed in a solution consisting of: 
 
 Liquor Ammonise, 3 drachms. 
 Water, 10 oz. 
 
 which changes the white colour to a dense black. 
 
 By modifying the strength of this solution, any 
 density between that produced by the mercuric 
 
 H 
 
98 PHOTOGRAPHIC PROCESSES. 
 
 chloride alone, and its complete reduction to the 
 metallic state by the ammonia, may be obtained, if 
 the plate is washed immediately on the appearance 
 of the desired colour. 
 
 The plate is put aside to dry spontaneously, as the 
 application of heat is liable to melt the film and 
 destroy the negative. 
 
 Yarnish is unnecessary. 
 
 If only one plate is developed at a time, or the 
 method of development described, considered too 
 complicated, Edwards' Developer may be used. 
 
 Two stock solutions are prepared as follows : 
 
 No. I. Pyrogallic Acid, 1 drachm. 
 Glycerine, 1 drachm. 
 Methylated Alcohol, 6 drachms. 
 
 Mix the glycerine and alcohol, then add the acid. 
 
 No. II. Bromide of Ammonia, gr. 7J. 
 
 Liquor Ammonia?, '880, 1 drachm. 
 Glycerine, 1 drachm. 
 Distilled Water, 6 drachms. 
 
 Add one part of each to fifteen parts of water and 
 use in equal proportions. 
 
 These solutions will keep a long time if well corked. 
 
 Ferrous oxalate or Eder's developer on account of 
 its simplicity and cleanliness, has lately become a 
 favourite with amateurs. It possesses few other ad- 
 vantages except that it can be used side by side with 
 
PHOTOGRAPHIC PROCESSES. 99 
 
 the wet process, an impossibility where ammonia is 
 given off, as it contaminates the atmosphere of the 
 dark room. 
 
 The following solutions are used : 
 
 No. I. Neutral Oxalate of Potash, 6 oz. 
 Boiling water, 20 oz. 
 
 Place the oxalate of potash in an earthenware 
 vessel and add the boiling water, stirring with a glass 
 rod till sufficiently cool to be poured into the bottle 
 intended for its reception. If on testing with red 
 litmus paper the solution is found to be alkaline, 
 sufficient dilute sulphuric acid is added to cause a 
 very faint acid reaction with blue litmus paper. If 
 too acid, carbonate of potash may be added to 
 neutralize the excess. The solution is now securely 
 corked. 
 
 No. II. Sulphate of Iron, 3 oz. 
 Distilled Water, 6 oz. 
 
 This solution is also securely corked. 
 
 Suppose we wish to develope a quarter plate; 
 four parts or two drachms of No. I. solution are 
 placed in a glass measure, and one part or \ drachm 
 of No. II. solution is added : not vice versa, or a 
 precipitate of oxalate of iron is formed which weak- 
 ens the mixture. One or two drops, according to 
 circumstances, of the bromide of ammonia solution, 
 the same as that used as a restrainer in alkaline 
 pyro. developer, is added to the whole. The plate is 
 
 H2 
 
100 PHOTOGRAPHIC PROCESSES. 
 
 placed in the vulcanite dish, the developer caused to 
 wave to and fro over its surface, till the required 
 density is obtained ; the same precautions as those 
 previously mentioned with regard to fogging, etc., 
 being observed. 
 
 After development the mixed solution is trans- 
 ferred to a separate bottle holding about eight or 
 ten ounces ; when full, this is boiled in an iron sauce- 
 pan for ten minutes, returned to the bottle and 
 securely corked; it will answer admirably for the 
 development of several future plates or paper pic- 
 tures, if always boiled after use, and the clear liquor 
 poured off. 
 
 Fixing and subsequent intensification are pro- 
 ceeded with in exactly the same way as for the 
 other processes. 
 
 The blackening of the plate with ammonia, after 
 whitening with mercury, is carried on in the open 
 air, at all events in another apartment, as it would 
 spoil all subsequent manipulation with the wet plate 
 process. 
 
 It has been recommended to add citric acid to 
 the alum solution when pyro. is used and oxalic acid 
 with ferrous oxalate, to remove any stain due to the 
 developer on the resulting negative. There should 
 be no stain after developing, and we cannot too 
 strongly condemn the use of acids in any of the 
 solutions used subsequent to development. Without 
 entering into the theoretical grounds of this advice, 
 we simply state that nothing tends more, except 
 traces of hypo., to impair the permanency of the 
 negative. 
 
ARRANGEMENT OP APPARATUS. 10 L 
 
 CHAPTER VI. 
 
 ARRANGEMENT OF APPARATUS, ETC. 
 
 MOST methods adopted in these pages are taken 
 from the works of others, at least the principle is 
 the same although the arrangements are slightly 
 modified. Our claim is simply to have shown the 
 possibility of obtaining results with an ordinary 
 parafin lamp, equal if not superior to those hitherto 
 obtained with sunlight ; thus placing Photo-micro- 
 graphy within the power of all. 
 
 It would be an impertience as well as an injus- 
 tice to those from whom we have learned much, 
 if mention was not made of their work in these 
 pages. No classification on the ground of superior- 
 ity has been attempted, but the processes mentioned 
 are simply in chronological order. 
 
 All microscopists are acquainted with the beauti- 
 ful photographs of N". Rhomboides, published by 
 Mr. Woodward in the Journal of the Microscopical 
 Society. The arrangement he adopted was very 
 similar to that employed with the eighth immersion 
 when the photograph of S. Gemma was taken. He 
 seems to have always used sunlight and the wet pro- 
 cess, which as a rule give results far superior to those 
 obtained by lamplight and dry plates. 
 
 We can therefore hardly blame those who, perhaps 
 
102 ARRANGEMENT OP APPARATUS. 
 
 more enlightened than ourselves, perceive that most 
 people even if they had the opportunities of Mr. 
 Woodward, lack the ability to use them. 
 
 Mr. Wenham, as early as 1855, gave instructions 
 in the Quarterly Journal of Microscopical Science, for 
 improving Microscopic Photography. The plan tlieti 
 adopted is not to be recommended. Mr. Highley we 
 believe subsequently obtained very good results, but 
 his method rendered necessary the use of a special 
 apparatus, distinct from the ordinary microscope. 
 
 Captain Abney has given a few good hints, and it 
 is to be regretted he has not told us more. The 
 impression left, after ft perusal of his opinions, was 
 that he must have worked with inferior lenses. He 
 considers that higher powers than the quarter- inch 
 do not give as good results, on account of "the 
 
 diffraction images of parts of the object this 
 
 being dependent on the relative sizes of the object 
 and of the aperture of the objective." This is directly 
 contrary to our experience, as no objectives gave such 
 good results as the eighth and one twenty -fifth of 
 Messrs. Powell and Leland. This was no doubt 
 owing to the proper relation between the size of the 
 object and the aperture of the glass being strictly 
 observed ; the adjustment for cover glass being made 
 at the same time with extreme accuracy ; and prin- 
 cipally because the balance between the power and 
 aperture of the condenser, and that of the object, 
 was more easily equalised with these objectives than 
 with any others. 
 
 Good results can never be obtained unless we are 
 
ARRANGEMENT OF APPARATUS. 103 
 
 careful to employ suitable objectives with certain 
 objects. Low powers should not possess excessive 
 angular aperture, as their utility depends more upon 
 their penetration (that is their power of showing 
 with sharp definition different parts at different 
 depths) than it does on their resolution (or capa- 
 bility of differentiating very fine peculiarities of 
 structure lying on the same plane). On the other 
 hand, high powers are not required to show the re- 
 lation existing between the different parts of a struc- 
 ture lying at different depths, but to define the 
 delicate markings on the surface of those, whose 
 relations at different depths have already been in- 
 vestigated by lower powers. What has before been 
 said about the relation existing between NA and 
 penetration, will show the folly of expecting a lens 
 to combine, great penetration, magnifying power, 
 and angular aperture, at the same time. 
 
 Lately M. Tisandier has described three methods 
 adopted in Paris. All have at least one great dis- 
 advantage ; they require the employment of electri- 
 city in its most expensive form, this places them 
 beyond the reach of ordinary individuals. 
 
 In the first the virtual image is transformed into 
 a real one by displacing the eyepiece, so that the 
 image, formed by the objective, falls on the opposite 
 side of the ocular; this may < answer with the one 
 inch and lower powers, but with higher powers the 
 light is so much diminished by the interposition of 
 four surfaces of glass between the objective and 
 image, that focussing becomes impossible. 
 
104 ARRANGEMENT OF APPARATUS. 
 
 The second method due to M. Vogel, consists in 
 placing a short focus photo lens, as well as the 
 ocular, between the objective and image. This 
 method is evidently worse than the first, as we have 
 eight fresh surfaces interposed. It is an endeavour 
 to do two things at the same time, which are better 
 done separately. 
 
 In the third and last a considerable deviation from 
 the others is noticeable. The ocular being removed, 
 a short focus carte lens is substituted and the whole 
 apparatus is placed in the horizontal position. This 
 improves the illumination as the mirror is not re- 
 quired to reflect light on the object. The same ob- 
 jections, however, hold good with regard to this. But 
 if a sufficiently strong light can be obtained, we are 
 confident that results exceeding those obtained by 
 M. Tisandier are possible, as according to him the 
 highest magnification was eight hundred diameters. 
 
 It has been the custom with some microscopists 
 when increased magnification is required to place a 
 concave, and we believe sometimes a convex lens, 
 between the objective and focussing screen. Mr. 
 Woodward was the first to suggest this practice ; it 
 is not to be recommended, as the increased mag- 
 nification is more easily obtained by enlarging the 
 negative; besides, any combination above the objec- 
 tive impairs the image. It is our firm conviction that 
 nothing has been such an obstacle to the practice of 
 Photo-micrography, as the failures consequent on 
 allowing the eyepiece to remain in its usual position. 
 
ARRANGEMENT OF APPARATUS. 105 
 
 We shall now point out a few of the advantages 
 of our own method. 
 
 Any microscope can be fitted with the necessary 
 additions at a trifling cost, the amount depending 
 on what can be done by the possessor himself; in 
 fact, the majority of first-class instruments, already 
 possess these additions. 
 
 The same apparatus answers with every method of 
 illumination, it can be made to assume any position, 
 the use of oblique light is facilitated, and the em- 
 ployment of photography with objects in fluid be- 
 comes possible. 
 
 On account of its portability the several changes 
 are easily made, while the simplicity of its construction 
 prevents the possibility of its getting out of order. 
 
 In the following pages we have adopted the plan 
 of describing a different method of illumination, and 
 arrangement of apparatus with each objective, in 
 order to illustrate the employment of different 
 sources of light; not on account of any advantage 
 gained by using the illumination and arrangement 
 described with that particular objective. For in- 
 stance, sun-light, lamp-light, and electricity, give 
 equally good results with the eighth immersion if 
 the adjustments of the microscope are suitable for 
 this objective, and the conditions of their employment 
 identical. 
 
 With regard to illumination, we most decidedly 
 recommend the use of an ordinary parafin lamp, 
 with one broad single wick, one and a quarter inch 
 
106 ARRANGEMENT OP APPARATUS. 
 
 or more in width, in preference to all other kinds ; it 
 is always obtainable, requires little care, and the ex- 
 pense incurred is very trifling. If properly employed 
 a negative can be taken by this light in five minutes, 
 with the one twenty- fifth, having a magnification 
 from 1000 to 5000 diameters, which will bear sub- 
 sequent enlargement to 50000 before the finest details 
 become visible to the naked eye. 
 
 The Triplexicon lamp may be substituted for the 
 single wick form. It gives a brilliant illumination, 
 but on account of the great heat generated special 
 precautions must be taken to prevent injury to the 
 object and objective. It is also troublesome to 
 manage and difficult to prevent from smoking. 
 
 Swan's incandescent lamp has numerous advan- 
 tages, among which may be mentioned the facility 
 of focussing, on account of the whiteness and bril- 
 liancy of the light, and the possibility of placing the 
 apparatus in any position during its employment. 
 
 Care should be taken that the carbon filament 
 occupies the centre of curvature of the glass globe, 
 otherwise aberrations will be produced by the inclin- 
 ation of the surfaces j this might be avoided by par- 
 tially flattening the globe on two sides, one being 
 behind and another in front of the edge of the carbon 
 filament. 
 
 The only serious objections to the use of Swan's 
 lamp for Photo -micrography, is the care and atten- 
 tion required when the electrical supply is produced 
 by a battery. The enormous expense entailed by 
 the purchase and working of dynamos, placing them 
 
ARRANGEMENT OF APPARATUS. 107 
 
 beyond the reach, of private individuals, in fact, 
 until electricity is supplied by accumulators or from 
 a central station, parafiu will be found far superior. 
 
 The actinic power of the electric light is inferior 
 to the intensity of its illumination, allowance must 
 be made for this when judging of the time necessary 
 for correct exposure. 
 
 The lamp should be covered and mounted in the 
 same way as the parafin lamp before described ; or 
 one may be substituted for the other, if a flat hook 
 capable of slipping into an arrangement on the 
 pinion block of the stand, is fastened to the upright 
 back of both. 
 
 Grove's or Bunsen's elements are the best form of 
 battery ; bichromate cells from their inconstancy be- 
 ing a continual source of trouble. 
 
 Magnesium in the form of Solomon's lamp may be 
 employed with low powers, when it is necessary to 
 shorten the exposure; but with high powers want of 
 light when focussing is the difficulty to be contended 
 with. The costliness of magnesium renders its pro- 
 longed use inapplicable to this purpose. 
 
 Dr. Hayes has recently obtained excellent results 
 with the lime light by using an ordinary lantern with 
 4i inch condensers, the objective being removed and 
 a plano-convex lens substituted for it, about ten or 
 twelve inches in front of the lantern. This gives a i- 
 inch disc and is easily centred The same method 
 will obviously answer with the triplexicon or other 
 lamp. 
 
 A minute intensely brilliant spot of light, requir- 
 
]08 ARRANGEMENT OF APPARATUS. 
 
 ing no care, free from danger,, and capable of being 
 placed in any position, is required by those who can- 
 not afford batteries, dynamos, etc. But up to the 
 present nothing fulfils these requirements as well as 
 a parafin lamp with a bull's eye condenser and from 
 the short strides electrical illumination has made 
 within the last twenty years, no substitute is likely 
 to make its appearance from that quarter. 
 
 Those resident in cities have a great advantage 
 over their country neighbours, (who require photo- 
 graphy more, on account of their isolated position), 
 in possessing gas, from which we may now expect 
 something, owing to the stimulus given to its im- 
 provement by the introduction of electricity. 
 
 In every practical art the rule has been to proceed 
 from simpler methods to those more difficult. We 
 shall not decart from it, but endeavour to select such 
 examples as will lead gradually to a full understand- 
 ing of the theoretical and practical principles involved, 
 the increasing difficulty of manipulation at the same 
 time producing the requisite amount of skill. 
 
 It is almost impossible to plan a method in which 
 the practical manipulation and theoretical knowledge 
 proceed hand in hand. A perusal of the following 
 chapters is therefore recommended before attempting 
 to photograph by any of the methods described in 
 this. 
 
 A note book is a necessity; every proceeding 
 should be entered, to enable any particular plan pre- 
 viously adopted to be repeated, and from a com- 
 
ARRANGEMENT OP APPARATUS. 109 
 
 parison of failures and successes to eliminate the 
 causes producing the former. 
 
 The following is an example of the form of entry- 
 adopted : 
 
 Apparatus Horizontal. 
 
 I. Object, Polyomatus Argus, mounted in balsam 
 
 and bensol equal parts. 
 
 II. Objective, i inch corrected 10 for cover glass. 
 
 III. Condenser, about quarter inch in focal length, 
 and distant ^tli f an inch from the object. 
 
 IV. Apertura of diaphragm one-eighth of an inch in 
 diameter. 
 
 V. Lamp, 13 inches from stage, edge of flame to- 
 
 wards the object. 
 
 VI. Bull's eye condenser, four inches focal length, 
 four inches from flame of lamp with convex side 
 turned towards object. 
 
 VII. Ground glass of camera, twenty-four inches 
 from object. 
 
 VIII. Focus till the dots appear surrounded by a 
 red areola. 
 
 IX. Sulphate of copper cell placed midway between 
 bulPs eye and substage condenser. 
 
 X. Gelatine dry plate 10 times collodion. 
 
 XI. Exposure, one minute. 
 
 XII. Ferrous oxalate developer, with one drop of 
 bromide solution to the ounce. 
 
 XIII. Result, completely successful, or over or un- 
 der-exposed as case may be, in this case very 
 much over-exposed. 
 
110 ARRANGEMENT OF APPARATUS. 
 
 It will be seen from the foregoing notes the neces- 
 sity for having the laths at the side, marked off in 
 inches and half inches. 
 
 We now proceed to photograph with the one inch 
 objective. The object is supposed to be mounted in 
 fluid, as an illustration of the method to be adopted 
 under these circumstances. 
 
 The microscope being placed on the platform, fig 24, 
 the divisions, nos. 1 and 2, of the stand are rigidly 
 fastened together, by tightly screwing down the 
 board fitting on the bolts projecting from their 
 sides. 
 
 They are then raised till at right angles to no. 3. 
 The camera legs are fastened to the end bolt on no. 
 1, their pointed extremities resting on the ground, 
 maintain this end of the stand in the perpendicular 
 position. 
 
 The horizontal position of the stage is ascertained 
 by a spirit level. 
 
 The tube containing the eyepiece, if not previously 
 attached to the microscope, is now put on ; the ob- 
 jective we wish to use, in this case the one inch, is 
 adapted. 
 
 The substage apparatus, with its condenser and pin 
 hole cap, is fixed in position. 
 
 The lamp previously trimmed and lighted, is 
 placed on no. 3 division of the stand, about ten or 
 twelve inches from the mirror below the condenser. 
 The largest hole of the diaphragm is turned till it 
 occupies a position approximately in the optic axis of 
 
ARRANGEMENT OF APPARATUS. 
 FIG. 24. 
 
 Ill 
 
 the microscope. The plane side of the mirror is 
 brought as close as possible to the stage of the 
 microscope, without interfering with the motions of 
 either itself or the condenser. 
 
112 ARRANGEMENT OF APPARATUS. 
 
 The lamp should now be brought near the stand, 
 on which it rests, (i.e., as low as possible), by the 
 rack and pinion movement attached to its back. 
 
 Our reason for keeping the lamp low and the 
 mirror high is the greater the angle made by the 
 incident and reflected rays, the better the illumina- 
 tion. 
 
 The light from the lamp may be thrown on the 
 condenser by altering the inclination of the mirror, 
 the eye at the same time being applied to the eye- 
 piece. 
 
 Still looking through the microscope, the pin hole 
 cap is brought into focus, and centred, by turning 
 the screws in the rim of the substage tube. 
 
 When central, the diaphragm, plate is turned till 
 a medium-sized hole is under the condenser ; this 
 aperture is now brought into focus by increasing the 
 distance of the objective from it, and made coinci- 
 dent with the optic axis of the instrument, by dis- 
 placing the diaphragm wheel sufficiently in its own 
 plane. 
 
 This being accomplished the flame of the lamp is 
 focussed, by altering the distance between the top of 
 the condenser and the objective, (in other words by 
 using the coarse or fine adjustments of the micro- 
 scope), and centred by altering the inclination of 
 the mirror. We now make the image of the flame 
 of the lamp itself, and that of its reflection in the 
 mirror placed behind it, coincident. This may be 
 done by giving a slight twist or tilt, as the case may 
 be, to the tin cover surrounding the lamp. The 
 
AREANGEMENT OF APPARATUS. 113 
 
 bull's eye condenser is placed from J to 2 inches in 
 front of and from the flame of the lamp, the convex 
 side, if the condenser be a single plano-convex 
 lens, should face the microscope, and be centred by 
 observing the position of its image in the microscope ; 
 this will be known by its appearing as a brilliant 
 disc of light without flaw or spot, in fact a regular 
 sun, in the centre of the field of vision. 
 
 We now remove the condenser from its tube ; this 
 is best done by racking back the objective, and un- 
 screwing the lenses from the diaphragm tube at the 
 object side of the stage, without disturbing the 
 diaphragm or any apparatus except those requiring 
 removal. If on account of their position they cannot 
 be removed in this manner; the substage tube H, is 
 unscrewed without altering the position of either the 
 diaphragm or mirror. The condenser can then 
 be easily taken out and the substage tube replaced, 
 the same precautions being observed as for its 
 removal. 
 
 All the apparatus required are now perfectly cen- 
 tral with each other. It might be thought that 
 keeping the condenser in the substage would be 
 superfluous, but by its aid the images of the dia- 
 phragm, lamp, and bull's eye condenser are ob- 
 served through the microscope, and all made coin- 
 cident with its optic axis. Perfect accuracy of 
 adjustment in this respect, is one of the greatest aids 
 to the production of good and truthful negatives. 
 
 The object, chosen by the rules laid down in the 
 following pages, is placed on the stage and brought 
 
114 ARRANGEMENT OF APPARATUS. 
 
 into focus. If the light is too strong, the distance 
 of the diaphragm is increased, or a smaller aperture 
 substituted, taking care that it occupies exactly the 
 same position with regard to the optic axis of the 
 apparatus as the former one, and vice versa. It 
 should be born in mind that the less light incident 
 on the object, consistent with clear definition and 
 subsequent facility in focussing, the better. 
 
 It would be much simpler to centre the tube 
 holding different sized discs, as they might be sub- 
 stituted for each other without nny danger of alter- 
 ing the position of the other parts, but withdrawing 
 the inner tube would very likely displace the mirror; 
 this plan is more suitable when the apparatus is 
 placed in the horizontal position, no mirror being 
 then necessary. Whichever plan is adopted, the 
 differentiation of the structure should be distinct : 
 the markings dark; their interspaces bright and 
 clear. The attainment of the proper mean will be 
 facilitated by remembering that too great a quantity 
 of light impairs definition; too little increases the 
 difficulty of focussing and unnecessarily prolongs the 
 exposure. Intensity is what is required, not quan- 
 tity. 
 
 The best light being obtained, the eyepiece tube of 
 the microscope is removed, and the camera arranged 
 vertically over the microscope, in the following man- 
 ner. 
 
 The camera is fixed over the microscope by the 
 binding screw attached to the stand beneath it, the 
 conical bellows being removed from its front. The 
 
ARRANGEMENT OF APPARATUS. 115 
 
 round disc of light formed on the ground glass is 
 placed exactly central by means of the levelling 
 screws at each corner of the oblong board, to which 
 the camera is attached. When this is accomplished, 
 the binding screw is tightened, and the conical bel- 
 lows slipped into its original position on the front of 
 the camera. Great care is now required in attaching 
 the end of the conical bellows to the short tube of 
 the microscope. It will be much more easily done if 
 the interior of the tube fixed to the end of the coni- 
 cal bellows is covered with black velvet, as well as 
 its interior ; it will then slip easily into that of the 
 microscope, and the entrance of all light rays will be 
 prevented. 
 
 The image of the object is roughly focussed on 
 the ground glass ; the desired magnification ob- 
 tained by racking the" ground glass backwards or 
 forwards to increase or diminish it, bearing in mind 
 that the actinic power of the light is said to decrease 
 in proportion to the square of the distance from its 
 source. 
 
 The part of the object we wish to focus should, if 
 possible, completely fill the plate ; this is sometimes 
 impossible, as its thickness prevents the use of len- 
 ses of sufficient power to magnify the lateral dimen- 
 sions, while their penetration defines those parts ly- 
 ing on different planes. 
 
 The most satisfactory magnification being ob- 
 tained, we pass the silk cord round a bevelled ring 
 attached to the fine adjustment of the microscope, 
 and the wheel on the rod passing under the camera 
 
 i2 
 
116 ARRANGEMENT OF APPARATUS. 
 
 stand. The focussing glass previously adjusted, is 
 applied to that part of the image on the ground 
 glass, requiring the most accurate definition. The 
 best focus is obtained by observing the appearance 
 of the structure through the focussing glass during 
 the revolution of the milled head attached to the rod 
 connected with the fine adjustment. 
 
 The chemical focus is found when the object 
 appears clearly defined, although its markings are 
 surrounded by a red areola, (see previous pages'). A 
 black cloth is now hung over camera and stand, but 
 not reaching lower than the stage of the microscope ; 
 the blue glass, sulphate of copper cell, or plate of 
 Alum placed between the bull's eye condenser and the 
 mirror ; and an opaque card between the two latter, 
 to enable the exposure to be given at the proper time. 
 
 We now proceed to the dark room, and having lit 
 the lamp, observe the condition of the trays and 
 measures, their position, and that of the various 
 bottles containing solutions. 
 
 The barrel should contain a good supply of fresh 
 and pure water; the tin box containing the dry 
 plates is placed on the floor or a shelf, on the oppo- 
 site side of the dark room, to that occupied by the 
 washing trough and lamp. 
 
 We recommend the use of dry plates twice as fast 
 as ordinary collodion in this case, as the intensity 
 of the light is insufficient and the position of the 
 camera unsuitable for wet plates. 
 
 The dark slide is examined ; the side on which the 
 
ARRANGEMENT OF APPARATUS. 117 
 
 plates are inserted opened, and placed with the zinc 
 and velvet partitions, on some dry support. 
 
 The door of the dark room being securely fastened 
 and the curtain drawn across it, the tin cover is 
 placed over the lamp. 
 
 The tin box containing the packages of dry plates 
 is now opened ; the lid should fall back to a hori- 
 zontal position, thus forming a shelf on which the 
 pasteboard box, in which the plates are packed with 
 its cover, can be placed during the removal of the 
 desired number from it. As we are now using a 
 double dry slide, two plates are removed, and held 
 one above the other by their edges between the 
 thumb and finger of the left hand, with the right we 
 replace the cover on the cardboard box, shut the tin 
 box, and if necessary, cover it with a dark cloth kept 
 for the purpose. 
 
 Holding the plates in our left hand, we go to the 
 support on which the dark slide has been placed, 
 and insert one plate with the gelatine surface down- 
 wards or looking towards the unopened side. The 
 gelatinised surface may be distinguished from the 
 other, by its want of lustre, when reflecting the 
 image of the lamp ; care being taken to use only 
 sufficient light to enable us to barely distinguish the 
 difference. One zinc partition is placed with its 
 velvet side next the back of the plate, the other 
 with it in the opposite direction. The second plate 
 is laid with its back on the velvet side of the second 
 zinc partition, its gelatinised surface then looks to- 
 wards us. Whatever plan is now adopted for fas- 
 
118 ARRANGEMENT OF APPARATUS. 
 
 tening the plates in position, great care must be 
 taken to avoid touching them with the fingers, as 
 should this happen and indelible stain will make its 
 appearance at that spot during the subsequent de- 
 velopment. Having fastened the plates in position, 
 we shut up the dark slide or plate carrier, and 
 enveloping it in a dark cloth, or better placing it in 
 the inside breast pocket of our coat, we carry it to 
 the apartment where the microscope and apparatus 
 are arranged. 
 
 The right hand side of the cloth hanging over the 
 apparatus is then slightly raised, the dark slide 
 slipped quietly and carefully underneath it, and 
 substituted for the ground glass of the camera. 
 
 The sliding door covering the plate next the miaro- 
 scope is then drawn out, and a delay of a few seconds 
 made, to allow all vibration to cease. 
 
 The utmost care is required for these manipula- 
 tions, and if the dark slide and camera are not ac- 
 curately made, some sticking or jarring very likely 
 to cause displacement and endanger the centring of 
 the apparatus is certain to occur. 
 
 During this interval a watch is placed on the stand 
 near the lamp where the time can be easily observed. 
 The opaque card is now gently removed, the re- 
 quisite exposure, say ten seconds given, and the card 
 gently replaced ; the dark slide shut, the carrier re- 
 moved from the camera, and placed with the ex- 
 posed plate next the person in the breast pocket of 
 the coat ; every precaution being taken as before, to 
 prevent displacement. 
 
ARRANGEMENT OP APPARATUS. 119 
 
 Now if uncertain as to the proper amount of ex- 
 posure required, or desirous of photographing an- 
 other portion of the object ; we remove the card, 
 re-examine the image, and correct the focus if neces- 
 sary. The card being replaced, the dark slide is 
 again substituted for the ground glass, care being 
 taken that the plate farthest from our person while 
 the slide was in the pocket, is placed facing the 
 microscope ; the sliding door is withdrawn ; a slight 
 rest allowed, and the requisite exposure given, the 
 same precautions being observed. 
 
 Having exposed the required number of plates, 
 we carry them to the dark room, and either put 
 them carefully away till a more convenient time, or 
 proceed at once to develope by one of the processes 
 suitable for dry plates ; preference being given to 
 the ferrous oxalate, on account of its giving perfect 
 results, where the time of exposure, fastness of the 
 plate, and intensity of the light are previously 
 known. 
 
 With the same arrangement, it is quite possible 
 to photograph opaque objects, and those illuminated 
 by dark ground or oblique illumination. Wenham's 
 parabolic illuminator, a spot lens, or what is the same 
 thing, a central stop in the condenser, are all used 
 for the latter purpose. We, however, prefer the 
 following simple arrangement. 
 
 A piece of electro-plated copper, bent in the form 
 of a ring B, fig. 25, is substituted for the tube fitting 
 into the substage of the microscope. About an 
 eighth of an inch from its upper edge, a carboard 
 
120 ARRANGEMENT OF APPARATUS. 
 
 disc is placed with a slit C in it ; all the interior of 
 the tube is blackened except a narrow strip, corres- 
 ponding in size and position to the slit. This part 
 of the ring should be flattened. An opening D is 
 
 made in the front, to enable the angle at which the 
 light falls on the object to be changed. The ring B 
 is covered on its outside with black cloth, so that it 
 may slip easily up and down in the aperture, in the 
 centre of the stage. 
 
 The light is concentrated by the bull's eye on the 
 narrow strip corresponding to the slit, and from 
 thence on the object. 
 
 The next method is the only one possible, when it 
 is desired to photograph objects in fluid, with arti- 
 ficial light, and which require the Jth or jVth for their 
 resolution. We shall confine ourselves to the i inch 
 
ARRANGEMENT OF APPARATUS. 
 FlG. 26. 
 
 121 
 
122 ARRANGEMENT OF APPARATUS. 
 
 objective. The apparatus is considered as still re- 
 maining in the position adopted in our first ex- 
 periment. 
 
 The lamp stand, and bull's eye condenser, are 
 clamped in their original position by binding screws 
 fitting in the division running down the centre of 
 plank no. 3. 
 
 The camera legs are shortened to allow of the 
 upright division no. 1 and no. 2 assuming the hori- 
 zontal position, but need not be removed (they are 
 omitted in the figure). The side board is detached, 
 and replaced two bolts lower down. When firmly 
 screwed on, it keeps all three division of the plank 
 perfectly rigid, and in a straight line with each other. 
 
 The camera and sulphate of copper cell are re- 
 moved; Swan's incandescent lamp substituted for 
 the parafin, the edges of the carbon filament being 
 turned towards the microscope. 
 
 Connection is now made with the source from 
 which the electricity is supplied. We shall here 
 only mention that dynamos are preferable to a 
 battery, but unfortunately the great expenditure 
 necessary for their maintenance, as well as first pur- 
 chase, puts their application to photographic pur- 
 poses beyond the reach of ordinary individuals. In 
 a late number of the Photographic News an electric 
 generator worked by hand is proposed, which may 
 prove practicable if sufficiently low in price. 
 
 If battery power is used, thirty cells of Grove's 
 battery will be found sufficient for a full sized Swan's 
 lamp. We have had no experience of the smaller 
 
ARRANGEMENT OF APPARATUS. 123 
 
 forms recently made, but from a consideration of the 
 character of the light required, we have some hesita- 
 tion in recommending them. 
 
 One or two cautions are necessary with regard to 
 the batteries, and lamp. Bichromate cells are useless 
 for many reasons, but principally for not being suffi- 
 ciently constant. Somes means of regulating the 
 current is useful, as the sudden passage of a strong 
 current is liable to cause the lamp to burst. The 
 ordinary method of attaching the lamp by a spring 
 is most objectionable, as the slightest movement on 
 the same floor or adjoining apartment, will cause 
 sufficient tremor to utterly ruin the resulting nega- 
 tive. 
 
 The whole stand is now raised to the perpen- 
 dicular ; the microscope stage accurately levelled, 
 and supported in that position by lengthening the 
 camera legs. 
 
 The eyepiece tube being fitted to the microscope, 
 a one inch or lower power is screwed on, and the 
 condenser, with its pin hole cap, lamp and bull's 
 eye, centred as before. We remove the inner tube, 
 or central sliding diaphragm as it is called, from the 
 cloth lined tube fastened to the largest hole on the 
 wheel diaphragm. The latter being approximately 
 centred under the condenser, we insert the inner 
 tube fitted with a perforated disc, (the perforation 
 being about one-tenth of an inch in diameter or less) 
 till it touches the surface of the lowest combination 
 of the condenser. It is now made accurately cen- 
 
124 ARRANGEMENT OF APPARATUS. 
 
 tral with the pin hole cap, by bringing it into focus, 
 and displacing the wheel diaphragm sufficiently. 
 The low power objective is now racked back, and the 
 quarter inch substituted. 
 
 The pin hole cap is removed and the perforated 
 disc brought into focus ; if not exactly central it is 
 made so by the centring screws fitted in the rim of 
 the diaphragm tube. 
 
 At this stage in the arrangement of the apparatus 
 it is well to consider a peculiar method of illumina- 
 tion first described by Dr. Dallinger in the Micros- 
 copical Journal, and I believe called by him the sun 
 light. The following description will we hope ena- 
 ble others to obtain it. Unfortunately so much is 
 still left to individual intuitive skill, owing to no fixed 
 rules being found by which we might ascertain the 
 relative proportions of diaphragm aperture, power 
 and NA of condenser, intensity of illumination, and 
 other factors, that its accomplishment will at first be 
 found difficult. 
 
 The lamp and bull's eye being centred, the per- 
 forated disc is brought into focus with the quarter 
 inch objective and also centred. This must be done 
 by the centring screws, to prevent disturbance of 
 the relative positions of the substage apparatus. 
 The aperture in the disc, when the sunlight is ob- 
 tained, should appear as an intensely bright spot in 
 the centre of an illuminated field A, fig. 27. 
 
 The chances are a hundred to one that it appears 
 as represented at either B or C. If as at C it shows 
 that either the lamp or bull's eye condenser is en- 
 
ARRANGEMENT OF APPARATUS. 125 
 
 tirely out of the optic axis of the instrument ; if as 
 at B, one or other is too much to the left of the 
 
 FIG. 27. 
 
 instrument ; the condenser and diaphragm are sup- 
 posed to be already accurately centred, and in fact 
 must be if the foregoing directions have been pro- 
 perly carried out. 
 
 Whichever appearance presents itself the bull's 
 eye condenser is turned to one side, and the image 
 of the lamp brought into focus. If the flame is not 
 central it is made so, by the rack and pinion, or 
 lateral screw motion attached to its stand. The 
 position of its reflected image in the mirror behind it 
 should be observed, and if not coincident with the 
 flame itself, it is made so by tilting the tin shade sur- 
 rounding the lamp. The bull's eye is again brought 
 into view and centred. If the sun-light is not yet 
 perfect or if it appears as at B, the lamp is moved 
 more to the left or right according to the position of 
 the bright ray proceeding from the aperture of the 
 diaphragm. These manipulations are greatly facili- 
 tated by remembering the relation the bright ray 
 bears to the position of the lamp and bull's eye ; for, 
 
120 ARRANGEMENT OF APPARATUS. 
 
 when considered as pointing from the periphery to the 
 central hole, it indicates directly the position of the 
 lamp and bull's eye with regard to the optic axis of 
 the instrument. At the same time the distance of 
 the bull's eye from the lamp may be slightly altered, 
 care being taken to keep it central. When all other 
 means have failed, a very slight alteration of the 
 position of the condenser by the centring screws, 
 will sometimes cause its almost magical appearance. 
 For further details we refer the reader to Dr. 
 Dallinger's communication. 
 
 Having obtained the sunlight by some means or 
 another, we rack back the objective. Now if the 
 object is flat with fine markings on or near its sur- 
 face, we place it on the stage, but should it consist of 
 delicate scarcely differentiated structure, lying on dif- 
 ferent planes, we replace the pin hole cap, on the top 
 of the condenser before placing the object on the 
 stage. The pin-hole cap should itself be accu- 
 rately centred, and if not, rejected and another 
 tried. With the objective corrected for uncovered, 
 (the ultimate correction for thickness of cover 
 glass being made according to the method de- 
 scribed on page 17, chap, ii.) we bring the 
 object into focus. If the light is too great or 
 deficient, the condenser is slightly moved farther 
 from, or nearer to the object, or the inner tube con- 
 taining the perforated disc may be removed and an- 
 other substituted, and the tube returned to exactly 
 the same position, care being taken to avoid disturb- 
 ing the relative positions of any of the other appar- 
 atus. During its slow removal the eye should be 
 
ARRANGEMENT OF APPARATUS. 127 
 
 kept on the object, as frequently a slight alteration 
 of the distance of the perforated disc from the glass 
 slip, especially when the light is too great, produces 
 the desired effect. With regard to the proper dis- 
 tance of the condenser from the object; we have 
 found double its focal length, with the bull's eye one 
 inch from the lamp flame, the most favourable posi- 
 tion as a rule. Much, however, depends on the 
 thickness of the glass slip, on which the object is 
 mounted. Some recommend the image of the lamp 
 focussed on the object, this practice is only men- 
 tioned to be condemned. 
 
 Having once found the proper distance for a con- 
 denser with any particular object, the number of 
 divisions marked on the tube of the substage appar- 
 atus, if entered in our note book, enables us to re- 
 peat it ad infinitum. 
 
 When the proper quantity, and intensity, of illu- 
 mination is obtained, we proceed to place the camera 
 in position, observing the precautions mentioned 
 when describing a similar process with the one inch. 
 
 The actinic focus is found in the same way, and 
 the camera being covered with a dark cloth, the 
 sulphate of copper cell is clamped in position. 
 
 The light is sufficiently intense for the wet plate 
 process. We therefore proceed to the dark room, 
 and sensitise a plate according to the instructions 
 contained in a previous chapter, drain it as quickly 
 and thoroughly as possible, and place it face down- 
 ward in the dark slide used for that purpose. 
 
 If it was necessary to caution the amateur against 
 touching the sensitised surface with his fingers in the 
 
128 ARRANGEMENT OP APPARATUS. 
 
 dry process, ten times the precautions are neces- 
 sary here, as the slightest touch will ruin the plate. 
 
 We shut the slide and convey the plate in as 
 horizontal a position as possible to the camera, care 
 being taken to avoid its knocking against anything 
 or being shaken during the journey. After insertion 
 it is exposed in the manner previously described, 
 three to six minutes being sufficiently long, and when 
 removed from the camera immediately carried to the 
 dark room. 
 
 Any development suitable for the wet plate pro- 
 cess, is at once proceeded with. The resulting nega- 
 tive, after fixing and subsequent washing, being 
 dried and varnished. 
 
 During the description of this method exception 
 might be taken to needless repetition. We have 
 only one excuse to offer. Having seen numerous 
 failures and the destruction of many plates caused 
 by the neglect of some trifling detail only remedied 
 by perseverance, we prefer repetition on our own 
 part, to failure on that of our readers. 
 
 The following arrangement should be selected by 
 those compelled to adopt one plan alone. Its advan- 
 tages are, the ease and quickness with which the 
 different manipulations are performed; the small 
 number of adjustments necessary; and the absence 
 of all danger of disturbing the centring of the 
 different instruments, as the microscope and camera 
 are not placed in direct continuity. In the former 
 arrangement this was very liable to occur, when fix- 
 ing the bellows front to the camera and microscope, 
 
ARRANGEMENT OF APPARATUS. 129 
 
 or when substituting the dark slide for the focussing 
 screen. 
 
 Perhaps its greatest advantages are the possibility 
 of focussing at any distance from the microscope and 
 cf manipulating without leaving the dark room. 
 
 The drawback connected with this method, is the 
 impossibility of photographing objects in fluid on 
 account of the horizontal position of the microscope. 
 For this reason also we should be extremely careful 
 to accurately arrange the distance of the condenser 
 from the slide, because if the heat rays are brought 
 to a focus on the object, (the heat being greatly 
 increased owing to the absence of a reflecting sur- 
 face even when an ordinary parafin lamp is the 
 source of illumination), objects mounted in balsam 
 are liable to change their position, owing to the 
 melting of the medium during exposure. 
 
 The recess jutting into the dark room, full descrip- 
 tion of which has been already given, being con- 
 structed, the entrance of all actinic rays is pre- 
 vented, by pasting several folds of yellow or black 
 paper, (the latter being preferable) over both interior 
 and exterior. The edges of the sleeves where they 
 join the partition are further secured by tacking thin 
 deal laths round them, which are also covered with 
 black paper. A black cloth curtain with an orifice 
 for the tube of the microscope and fine adjustment, 
 should be placed inside the dark room so that it can 
 be let down when the arrangement of the apparatus 
 is complete. 
 
 We suppose the apparatus continuing in the posi- 
 
130 ARRANGEMENT OF APPARATUS. 
 
 tion assumed during the manipulation necessary for 
 the process last described. 
 
 The stand is placed in the horizontal position by 
 the removal of the camera legs ; all the instruments 
 are detached from it and carefully put aside; the 
 side boards are changed from their original position 
 and shifted two bolts lower down, or till flush with 
 the extremity of division No, 3, and firmly screwed 
 on. This keeps the two last divisions perfectly rigid, 
 and enables us to fold division No. 1 under them ; 
 where it also is firmly secured by one or more of the 
 binding screws, running in the slits with which the 
 centres of Nos. 1 and 3 are furnished. 
 
 Thus folded up and tightly secured, the stand is 
 placed, with the platform for the microscope in front, 
 on the stand forming the floor of the recess. 
 
 The ruby lamp is now lit in the dark room, and 
 all necessaries (such as developing solutions, dry 
 plates, dishes, etc.,) examined and put in their pro- 
 per places. 
 
 The microscope lamp or Swan's electric light, the 
 former being preferred witti the power, we are about 
 to use, is got ready and placed on the stand. The 
 microscope with eye- piece attached being fixed in 
 position, the centring is carried out by a low power 
 objective as before described. All these manipula- 
 tions are performed by the hands through the 
 sleeves, or better through the windows in the same 
 position. These windows should of course be cap- 
 able of subsequent closure by sliding doors. The 
 sleeves were only mentioned on account of being 
 
AERANGEMENT OF APPARATUS. 
 
 131 
 
 easily made, and their completely excluding actinic 
 light. 
 
 FIG. 28. 
 
 Whichever method is adopted, before centring 
 with the low power objective, we may substitute the 
 dry front of the J, if it possesses one, for the top 
 combination and pin-hole cap of the French con- 
 denser. It can be easily made to fit it, if too large, 
 by a card-board ring slipping on the screw of the 
 French lens; or if too small by placing it in a card- 
 
 K2 
 
132 ARRANGEMENT OF APPARATUS. 
 
 board tube fitting round the outside of the two 
 French lenses. Should the microscope be fitted with 
 a modern movable substage, and achromatic con- 
 denser with pin-hole cap, the additions mentioned 
 are of course unnecessary. 
 
 This arrangement may appear subversive of the 
 rules already laid down with regard to the achroma- 
 tism of the condenser, as the front is supposed to 
 consist of a single uncorrected plano-convex crown. 
 Practically this objection does not hold good, as the 
 light is monochromatic. Spherical aberration is 
 produced but the errors from it are counter-balanced 
 by the increase of NA. which now bears almost ex- 
 actly the proper proportion to that of the objective 
 itself. It will be seen that the definition is perfect, 
 and the ease with which the sunlight illumination is 
 obtained is remarkable. The low power objective 
 being attached to the microscope, we proceed in the 
 same manner with the centring as in the last 
 method. 
 
 The object is placed on the stage of the micro- 
 scope: it should be remembered that when using high 
 powers such as the one-eighth imm. it is better to 
 select a flat thin object, as the angular aperture ami 
 magnifying power are too great to allow of a large 
 amount of penetration. 
 
 The part we wish to photograph being chosen, the 
 low power is removed. 
 
 The J- objective, if a water immersion, may be 
 wetted with either water or glycerine. The former 
 is better as far as definition is concerned, but the lat- 
 
ARRANGEMENT OP APPARATUS. 133 
 
 ter on account of not evaporating, allows of a greater 
 length of time for arrangement of apparatus, and a 
 more protracted exposure. An equal mixture of 
 both will be found most suitable. 
 
 The proper focus and correction for cover glass 
 obtained, the eye-piece tube is removed, and the 
 sleeve securely fastened round the short tube, by a 
 strong elastic band in addition to that already in- 
 serted in its orifice. 
 
 Before proceeding with this description, it should 
 be mentioned, that the most favourable position for 
 the condenser is about one and half to twice its focal 
 length from the object, and the sliding diaphragm is 
 undoubtedly the best to use with this and all higher 
 powers. The best sized hole is that which, when 
 brought into focus, is slightly smaller than the field. 
 
 The fine adjustment wheel is screwed off, and the 
 screw passed through a small hole in the sleeves. A 
 light rod attached to a cork,* as before described, is 
 fitted to the wheel; this is now returned to its 
 original position on the microscope. 
 
 The camera, from which the oblong board and 
 conical bellows front have been removed, is attached 
 to an ordinary camera stand, and placed so that an 
 image of the object may be properly received on the 
 focussing screen. 
 
 The distance of the screen, owing to its not being 
 continuous with the microscope, is only limited by 
 the length of the dark room. Practically it will be 
 found that perfect results are not obtained when it 
 
 * See Appendix. 
 
Io4 ARRANGEMENT OF APPARATUS. 
 
 exceeds three feet. It should also be remembered 
 that the actinic power of the light is said to decrease 
 as the square of the distance of the plate from the 
 source of illumination, and the duration of the ex- 
 posure varies inversely as the actinic power. 
 
 Seating ourselves behind the camera and taking 
 the focussing rod, (which may be conveniently 
 supported within reach by a string) in our left hand, 
 we apply the focussing glass to the screen with the 
 right. When the proper focus is obtained the rod 
 is let gently down. The sulphate of copper cell 
 or blue glass is placed in position; the windows 
 closed or sleeves fastened; and the curtain which 
 has an orifice for the tube of the microscope only, 
 allowed to envelope the whole of the recess, except 
 the tube. 
 
 Two tightly stretched strings or laths, reaching for 
 about four or five feet beyond the camera and about 
 seven from the floor, will be found very convenient to 
 hang a black cloth over, covering the camera and 
 making it practically continuous with the microscope 
 during exposure. The possibility of any actinic light, 
 except that from the microscope, reaching the sensi- 
 tive plate is thus prevented. 
 
 A cap is placed over the orifice of the microscope 
 and we proceed to place the dry plate in the carrier. 
 Twenty times collodion should be used. Great care 
 must be taken to avoid shake and prevent the en- 
 trance of actinic light. The subsequent manipula- 
 tions are identical with those already described. 
 
 The following notes of the manipulations employed 
 
ARRANGEMENT OF APPARATUS. 135 
 
 for the production of the Negative, from which the 
 print of the Bacillus Anthracis in the frontispiece was 
 produced, may prove of use as an illustration. 
 
 Apparatus, horizontal, placed in recess of dark 
 room, camera not attached to microscope. 
 
 1. Section of lung containing Bacilli Anthracis pre- 
 pared by Ehrlich's method. 
 
 2. Objective one-eighth imm., corrected to thirty- 
 five for cover glass. 
 
 3. Condenser single French front, with dry eight 
 top, one-sixteenth of an inch from object. Aperture of 
 sliding diaphragm as close to the back of condenser 
 as possible, and covering half the diameter of the 
 field when brought into focus with one-fourth 
 objective. 
 
 4. Blue glass near condenser. 
 
 5. Bull's-eye eleven inches from stage of micro- 
 scope. 
 
 6. Lamp one inch from bull's eye, parafin and edge 
 of wick. 
 
 7. Ground glass of camera twenty-four inches 
 from object. 
 
 8. Usual focus. 
 
 9. Glycerine and water the immersion fluid. 
 
 10. Gelatine plate, twenty times collodion. 
 
 11. Exposure three minutes. 
 
 12. Ferrous oxalate developer; two drops of fifty 
 per cent, bromide solution added to one ounce. 
 
 13. Result shown in photo. 
 
136 ARRANGEMENT OF APPARATUS. 
 
 The last method requiring description is that in 
 which sunlight is used. 
 
 Any of the previous arrangements may be em- 
 ployed if the apparatus is situated so as to allow the 
 light from the heliostat to fall on the condenser. 
 
 It will be found advisable when the distance be- 
 tween the microscope and reflecting mirror exceeds 
 six feet, to place a plano-convex lens, (whose focal 
 length is about equal to a quarter or a fifth of the 
 distance, and whose diameter is not less than one- 
 twelfth of its focal length) with its plain side towards 
 the microscope, so that an image of the sun may be 
 formed about two inches from the diaphragm wheel. 
 This is easily done by placing a card at the dia- 
 phragm wheel to receive the image of the sun. 
 
 The stand, from which the lamp and bull's eye con- 
 denser are removed, is fixed in the horizontal posi- 
 tion, on a firm support, so that the second mirror of 
 the heliostat may be easily made to occupy a position 
 coincident with the optic axis of the microscope. 
 
 The heliostat should be arranged and left working 
 for a quarter of an hour previous to the arrangement 
 of the apparatus for photography. This enables us 
 to test the accuracy of its adjustments, and allows 
 the action of the first wheel full time to be com- 
 municated to that on the mirror. 
 
 These arrangements made, the microscope is fixed 
 in position, the sulphate of copper cell placed be- 
 tween it and the heliostat and everything carried 
 out in exactly the same manner as described when 
 photographing with Swan's incandescent lamp. 
 
ARRANGEMENT OF APPARATUS. 137 
 
 The sixteenth immersion being employed, the dry 
 front of the eight will be found to answer admirably 
 when used as in last process. 
 
 All subsequent operations are conducted in exactly 
 the same manner. 
 
 Dry plates or the wet process may be used, the 
 former is ten times as rapid as collodion requiring an 
 exposure of from one to five seconds. No fixed rule 
 can be given for exposure with sun-light for the rea- 
 sons already mentioned. 
 
 Our readers are cautioned against expecting suc- 
 cess at the first trial, unless they have had some 
 previous experience in photography. On this ac- 
 count the production of negatives with an ordinary 
 camera and lens is recommended before attempt- 
 ing photo-micrography. 
 
 When carrying out the methods here described, 
 avoid speaking or walking in the same or adjoining 
 apartment during exposure as this is very likely to 
 cause vibration of the instruments. 
 
 Too great care cannot be taken to prevent the 
 entrance of actinic light. All instruments must be 
 lined with black velvet; or perhaps better, painted 
 inside with a very thick mixture of lamp black in 
 thin glue. When in position the microscope and 
 camera should be covered with a dark cloth be- 
 fore the substitution of the plate carrier for the 
 ground glass and subsequent exposure. Every means 
 must be adopted to prevent the entrance of actinic 
 
138 ARRANGEMENT OF APPARATUS. 
 
 light into the dark room, and while placing the sen- 
 sitised plate in the carrier as well as during develop- 
 ment, no more light should come through the ruby 
 glass, or exposure of the plate to it be allowed, than 
 shall just enable us to work. 
 
 Before concluding our remarks on this part of the 
 subject, we would impress upon the photographer 
 the necessity for determining the magnifying power 
 in every case. This may be done as follows : After 
 removal of the carrier containing the sensitised plate 
 from the camera, an ordinary micrometer slide di- 
 vided into one-hundredths and one- thousandths of an 
 inch is substituted for the object. Its image is 
 focussed on the ground glass, and the division 
 measured with small rule. For example if one of the 
 divisions corresponding to one-hundredth of an inch 
 on the micrometer measures two inches on the ground 
 glass, the magnification equals two hundred diame- 
 ters. It is not necessary to adopt this method in 
 every case, for, if the magnifying power of a certain 
 objective is known when the image formed by it is at 
 two separate distances from any object, the magnify- 
 ing power can be determined when used at any other 
 distance. Suppose the magnifying power with the 
 quarter inch six inches from the object, has been 
 found to be fifty diameters, and at two feet and a 
 half, to be two hundred diameters. If on a sub- 
 sequent occasion we are photographing with the 
 same lens, and the screw is twenty-four inches from 
 the object, the magnifying power would be one hun- 
 dred and fifty diameters. 
 
ARRANGEMENT OF APPARATUS. 139 
 
 It is sometimes difficult to tell if the srm illu- 
 minates the object equally when a heliostat is not 
 used. The most convenient method of ascertaining 
 this, is by observing the image formed on the sensi- 
 tised plate through a piece of ruby glass let into the 
 shutter of the plate carrier, or in the top of the 
 camera itself. The former is the better method with 
 dry plates, the latter with wet. 
 
340 DEFECTS IN NEGATIVES. 
 
 CHAPTER VII. 
 
 DEFECTS IN NEGATIVES, THEIR CAUSES AND CURB. 
 
 Before attempting the production of negatives 
 with the microscope, the beginner is recommended 
 to obtain some skill in ordinary photography, by the 
 perusal of a standard work on the subject, with the 
 subsequent reproduction of views by the camera. 
 This will at least prevent the disappointment occa- 
 sioned by unsatisfactory results, arising from want 
 of skill or errors in development. 
 
 It should, however, be remembered that a wider 
 and more scientific knowledge is required than is 
 generally obtainable by these means. The ordinary 
 photographer has only to place his camera in such a 
 position, that a picture formed by artistic rules is 
 thrown upon the screen. Having given an exposure 
 suitable to the intensity of the illumination, fastness 
 of the plate, and tints in the picture, a latent image 
 is obtained which on the application of a well chosen 
 developer, reproduces every characteristic detail in 
 the original view. The Photo -micrographer in ad- 
 dition to a knowledge of the same kind, must recog- 
 nise and allow for the chemical changes produced in 
 different sensitive compounds by light ; which is it- 
 self modified by agencies beyond the perception of 
 unaided vision. 
 
DEFECTS IN NEGATIVES. 141 
 
 Many of these changes and agencies have only 
 lately been discovered, and a very little experience 
 will convince us that others exist, which owing to a 
 want of continuity between cause and effect, are in- 
 capable of demonstration in the present state of our 
 knowledge. Some are certainly dimly present to 
 our minds, and although not fully recognised, are 
 allowed for by an unconscious cerebration, if we may 
 be allowed the term. At the same time the direction 
 in which further experiment is required, will be in- 
 dicated further on. 
 
 The best method of arriving at a knowledge of 
 how to produce good negatives, is by studying the 
 defects of bad ones, endeavouring at the same 
 time to discover the causes producing these defects 
 and the remedies for them. 
 
 Inaccuracy in the preparation of solutions and 
 want of manipulative skill, are the principal diffi- 
 culties besetting a beginner. It will only be neces- 
 sary to mention where and how these inaccuracies 
 are most liable to occur, to enable the manipulator 
 to guard against them. 
 
 When distilled water is mentioned never use any 
 other ; pure spring water, not rain, being employed 
 for its production. Neutral solutions must be tested, 
 and what are sold as neutral salts can never be taken 
 upon trust, but must be made so. Obtain pure 
 chemicals ; see that all solutions are of the proper 
 strength; keep all bottles requiring it, tightly 
 corked ; and filter solutions when directed. Have 
 the dark room well ventilated, and on no account 
 
142 
 
 DEFECTS IN NEGATIVES. 
 
 allow a trace of ammonia to be present where the 
 wet plate process is employed. 
 
 Among errors of manipulation may be classed 
 those in which the plate is fogged by the entrance 
 of actinic light. This is most liable to occur when 
 working with very sensitive dry plates. An enu- 
 meration of the various means by which it may gain 
 access to them and the precautions to be taken for 
 its prevention, although incidentally mentioned in 
 other places, will be repeated here. 
 
 The dark room may allow light to enter by the 
 door, or the ruby glass window. The former may 
 be remedied by hanging a curtain both outside and 
 inside, the latter by the addition of another sheet of 
 ruby glass or non-actinic paper. The lamp may be 
 defective, and is almost certain to be so unless 
 covered by the tin shade, with a box beneath it, as 
 before described. 
 
 The box in which the plates are stored may not be 
 light tight ; keeping it enveloped in a rug or dark 
 cloth is the best preventative, care being taken that 
 the dark room door is properly fastened before the 
 box is opened. When a plate has been removed the 
 box should be shut and covered up at once, other- 
 wise it might easily be forgotten. 
 
 Prolonged exposure of the plate to the light, even 
 when filtered through two thicknesses of double 
 flashed ruby glass, will produce a fog. The inter- 
 val therefore during its transmission from the box 
 to the plate carrier should be as short as possible. 
 
 Every point of the plate carrier must be examined, 
 
DEFECTS JN NEGATIVES. 143 
 
 and its accurate closure ascertained, before the plate 
 is consigned to it; and afterwards covered with a 
 dark cloth. 
 
 The camera is to be examined in the same way. 
 Entrance of light need not be apprehended, if it and 
 the microscope tube are lined with black velvet, and 
 when in position covered with a dark cloth. The 
 substitution of the carrier for the focussing screen 
 should take place underneath this or another cloth, 
 the rays from the lamp being cut off from the 
 microscope by a blackened card placed between 
 them, before the drawing up of the slide and its re- 
 placement. 
 
 Actinic light must be guarded against after re- 
 moval from the camera, and during the subsequent 
 operations ; the slightest glimpse will produce a fog 
 on the negative. Fortunately this may be removed 
 by immersing the negative in a solution of bichro- 
 mate of potash, care must be taken that the clearing 
 off is not carried too far else weakness may be pro- 
 duced. Another kind of fog may occur when using 
 wet plates, owing to alkalinity of the bath. A similar 
 condition of the oxalate of potash solution, and too 
 much iron in the mixed developer produces a 
 whitish deposit on the film of dry plates, it is there- 
 fore advisable to add a little sulphuric acid to oxalate 
 of potash solution after its complete neutralisation. 
 
 Pin-holes are due to dust on the plate. A soft 
 large camel's hair brush specially kept for the pur- 
 pose should always be passed over dry plates before 
 placing them in the dark slide. Black markings are 
 
144- DEFECTS IN NEGATIVES. 
 
 generally caused by the plate coming in contact with 
 the fingers, or some unclean surface, and in the 
 collodion process insufficient drainage before placing 
 it in the carrier. 
 
 Frilling is very liable to occur in hot weather with 
 gelatino-bromide plates. It commences by a blister- 
 ing of the film at the edges, and its extension may 
 be prevented by immediately immersing the plate in 
 a saturated solution of alum. This also serves to 
 clear the negative. 
 
 Blurring of the image may be due to a variety of 
 causes. The principal are tremor of the apparatus 
 during exposure, and reflection from the back of the 
 plate. A black velvet backing similar to that already 
 described will entirely prevent the occurrence of the 
 latter. 
 
 Reflection from the surfaces of the crystals sus- 
 pended in the film has been mentioned, and dying 
 the film suggested as a remedy. This lessens the 
 rapidity too much to be available in photo-micro- 
 graphy. 
 
 It is well known that the invisible part of the 
 spectrum acts on bromo-iodised plates, and from the 
 results obtained with mono-chromatic light, we are 
 inclined to refer a blurred condition of the image to 
 the unequal refrangibility of the different parts of 
 the spectrum. It is for this reason also that the em- 
 ployment of cobalt blue glass increases the distinct- 
 ness of the image. 
 
 The character of the negative differs considerably 
 from that required in ordinary photography. All 
 
DEFECTS IN NEGATIVES. 145 
 
 beginners as a rule fall into the error of supposing 
 that the field surrounding the object must be opaque. 
 This has evidently arisen from the false impression 
 conveyed by the appearance of microscopic objects in 
 engravings. All photo-micrographs should be trans- 
 parent in the high lights, because there are parts of 
 certain objects, the relative brightness of which may 
 easily escape notice in the microscope owing to their 
 minuteness. For example: the visibility of the 
 structure of the diatomacese depends on the forma- 
 tion of extremely bright spots or lines on a ground, 
 itself possessing considerable brightness, while the 
 surrounding field has an intensity less than the for- 
 mer and greater than the latter. Now if the field be 
 opaque the finer details of the original structure will 
 be lost, not only by a want of variety in the different 
 shades, but also by a blocking up of the minute 
 spaces with a dense deposit. 
 
 Great density is preferable to weakness. The 
 former may be easily remedied by flooding the plate 
 with a solution containing thirty drops of perchloride 
 of iron, twenty grains of bromide of potassium to ten 
 ounces of water, and when the required transparency 
 is obtained, washing the negative rapidly in flowing 
 water. 
 
 A weak image is produced by so many causes, 
 that a complete enumeration would be impossible 
 without entering farther into the subject than is 
 required for our purpose. 
 
 The principal are however : 
 
146 . DEFECTS IN NEGATIVES. 
 
 I. A weak bath solution, or too strong a developer 
 with wet plates. 
 
 II. Over exposure, or unsuitable condition of de- 
 veloper with dry plates. 
 
 III. High refractive index of the medium in which 
 the object is mounted. This prevents proper diffe- 
 rentiation of structure both visually and chemically. 
 Even when it does not do so visually, it seems to 
 disturb the corrections of the object glass, so that a 
 weak negative is the result. 
 
 IY. Non-actinic colour of medium. This and the 
 former fault, are especially noticeable with balsam. 
 Diffusion of the colouring matter of the object, 
 particularly if red, through the medium may also 
 weaken the image. 
 
 V. Delicate structure of the object produces a 
 weak image. This may be obviated by staining the 
 specimen with carmine, which cuts off most of the 
 actinic rays, and if cobalt blue glass is placed be- 
 tween the source of illumination and the object, it 
 stops off the remainder. The resulting negative will 
 be more distinct than the visual one. 
 
 YI. Specimens unless stained very deeply with 
 logwood or blue pigments are unsuitable for photo- 
 micrography. 
 
 Objects of a yellow colour or great delicacy give 
 the best results with wet plates. Those of a red 
 colour or coarse structure the best with dry. 
 
 With different kinds of development a plate will 
 give different results. For instance, where it is 
 necessary to reproduce a great variety of shades,, 
 
DEFECTS IN NEGATIVES. 147 
 
 alkaline pyro development is superior to ferrous oxa- 
 late with dry plates. No intensification should be 
 attempted with wet plates, other than that obtained 
 by ordinary development. This is especially the case, 
 when the negative is required for enlargement. 
 
 For direct printing, a thin negative obtained with 
 a wet plate, sometimes gives better gradations when 
 subsequently intensified with silver. A dry plate, 
 if the ferrous oxalate development is stopped before 
 the slightest fogging appears, generally requires in- 
 tensification with mercury and ammonium hydrate 
 after fixing, especially if intended for the production 
 of lantern transparencies by contact. 
 
 From experiments with different sensitive com- 
 pounds it seems probable, that iodide of silver, as 
 its maximum intensity ends suddenly in the indigo 
 portion of the spectrum, will give the greatest 
 differentiation, and should therefore be used with 
 delicate structures. 
 
 Bromo-iodide emulsions depend for the character 
 of their sensitiveness on the condition to which the 
 emulsion is brought as regards colour during the 
 cooking process, and as this sensitiveness extends 
 considerably into the invisible part of the spectrum, 
 a determination of when and with what structures 
 they should be used, becomes a very difficult matter. 
 
 The amount of intensification required will be 
 found to vary directly as the magnifying power of the 
 objective. 
 
 To sum up. The kind of plate to be employed, 
 depends on the character of the object, nature and 
 
 L2 
 
148 DEFECTS IN NEGATIVES. 
 
 intensity of the illumination, and magnifying power 
 of objective. The development depends on the 
 purpose for which the resulting negative is in- 
 tended, the character of the object, and the kind of 
 plate. 
 
 It is often impossible to obtain a sufficiently dense 
 negative directly. When this is the case, the weak 
 negative should be copied in the enlarging appara- 
 tus (to be described), using a very weak illumination. 
 A positive will be obtained which on development 
 will be at all events as dense as the negative, and 
 when intensified much more so. If then another 
 copy be taken from this positive, a negative is 
 obtained, very much denser than the original nega- 
 tive. 
 
 This simple enumeration will be sufficient to en- 
 able any intelligent person to avoid the defects 
 mentioned, or to apply the proper remedies for them. 
 For fuller information we refer our readers to any of 
 the numerous text books on this subject. 
 
V 
 
 UNIVERSITY 
 
PLATE III. 
 
 *RACHX01DISCUS OBXATUS. 
 
 MAGNIFIED 450 lUAilETERS. 
 
THE PRODUCTION OF POSITIVES. 
 
 UNIVERSITY 
 
 CHAPTER 
 
 THE PRODUCTION OP POSITIVES, 
 
 Silver printing by contact calls for little comment, 
 as the process is much simplified by the sale of 
 sensitised albuminised paper possessing the great ad- 
 vantage of keeping for many months without dete- 
 rioration. 
 
 A few dishes, and a printing frame are the 
 only apparatus necessary. The latter consists of a 
 shallow wooden box, the bottom of which is formed 
 of a sheet of thick plate glass. The negative is 
 placed on the glass, a sheet of sensitised paper over 
 its prepared side, then a thick cloth pad, and over 
 all a hinged back. Two cross bars having springs 
 attached to them, are hinged to one side of the box, 
 and when pressed down on the hinged back, can be 
 fastened in position by clips fixed on the opposite 
 side. The process may be watched by unfastening 
 one of the cross bars and lifting that side of the 
 sensitised paper ; when released it will fall back to 
 its original position on the negative. 
 
 The character of the resulting picture can be 
 modified to a great extent by a proper consideration 
 of the kind of light required, and very artistic effects 
 may be produced by shading under-exposed portions 
 of the negative. An intense diffused light will be 
 required for a dense negative, while one possessing 
 
150 THE PRODUCTION OF POSITIVES. 
 
 the qualities before recommended will require a sub- 
 dued light and two or three hours exposure for the 
 differentiation of the markings and the proper repro- 
 duction of the tones existing in the original. Bright 
 sunlight must never be employed for silver printing 
 by contact. 
 
 The depth of the print requires some practice to 
 determine. As a rule the printing must be carried 
 farther than will be necessary in the finished picture, 
 because it loses intensity in the subsequent toning 
 and fixing processes. These processes should not be 
 commenced until several prints have been taken, as 
 one print wastes as much solution and gives as much 
 trouble as a dozen. 
 
 When a sufficient number have been printed, they 
 are placed in a large quantity of water in a darkened 
 room. The water is changed every hour or so until 
 all milkiness disappears, and they are then immersed 
 in a solution consisting of: 
 
 Gold Trichloride, 4 grains. 
 Sodium Acetate, 108 grains. 
 Distilled water, 10 ounces. 
 
 This solution is best made with boiling distilled 
 water if immediately required for use. It would be 
 better to make it the day before. 
 
 A large flat dish will be found the most convenient 
 for holding the prints and solution, as they require 
 to be kept in continual motion during the process. 
 The tint must be deeper, and as in printing, the 
 process must be carried farther than is necessary 
 in the finished picture. A very deep chocolate 
 
THE PRODUCTION OF POSITIVES. 151 
 
 brown verging on purple gives the most artistic ap- 
 pearance when finished. If an engraving tone 
 be required the process must be continued until a 
 decided purple tint is produced. Overtoning is to 
 be avoided as a cold grey picture is the result. 
 
 After toning the washings are repeated, and the 
 prints finally fixed in a solution containing : 
 Sodium Hyposulphite, 1J ounces. 
 Liq. Ammon. Fort., 3 drops. 
 Water, 9 ounces. 
 
 This solution should not be above 85 or below 75 
 Far. and always freshly made. 
 
 After ten or fifteen minutes immersion, with con- 
 tinual motion, the unaltered silver will be dissolved 
 away. The prints are then immediately removed to 
 a large tub of water, and kept in continual motion 
 for a quarter of an hour. The water is then 
 changed ; at the end of an hour the change re- 
 peated ; at two hours again repeated, and so on for 
 eight hours. At the expiration of this time all 
 traces of hypo will have disappeared ; the prints are 
 then hung up to dry. 
 
 All operations, except the final washings must be 
 conducted in a subdued light, coloured light will not 
 answer, white light alone enabling us to distinguish 
 the proper tint when toning. The prints when dry 
 are cut to the required shape, with a sharp knife, not 
 scissors, and mounted on cardboard with thick starch 
 or glue, to which a few drops of carbolic acid have 
 been added. When perfectly dry their appearance 
 may be much improved, by passing through a rolling 
 
152 THE PRODUCTION OF POSITIVES. 
 
 press, or in its absence pressing them with a heavy 
 hot smoothing iron, a sheet of clean paper being 
 interposed between the surface of the iron and the 
 print. 
 
 We strongly recommend the employment of a 
 professional photographer for the production of these 
 prints from ordinary negatives, as no amateur can 
 finish them off so well, without a useless expenditure 
 of time and money. 
 
 An excellent method of producing glass or paper 
 positives by development, has lately been introduced 
 to the notice of photographers. It is more suitable 
 for amateurs than the process just described, as the 
 tedious washings between the application of the 
 different solutions is avoided, and the development 
 itself reduced to the simplest form by the use of the 
 ferrous oxalate process employed for dry plates. 
 Glass positives may be obtained by l.he employment of 
 Swan's opal plates which leave nothing to be desired 
 as far as artistic display and ornamental work are con- 
 cerned. Many of the most beautiful prints of polycy- 
 stinge, and diatoms especially coscinodisci we have 
 ever seen, were produced by this process. 
 
 The simplicity of the manipulations and the direct 
 production of a positive by one process, is in itself a 
 recommendation to those who do not require a mul- 
 tiplication of proofs. All that is necessary after 
 exposure, development, and fixing in the ordinary 
 manner, is the application of a saturated solution of 
 bichloride of mercury, until the film becomes per- 
 fectly white. After the plate has been well washed 
 
THE PRODUCTION OP POSITIVES. 153 
 
 and allowed to dry spontaneously, a black backing is 
 attached. This produces that exquisite transparency 
 and softness so seldom seen since the Daguerreotype 
 process became extinct. 
 
 For ordinary scientific work, however, gelatino- 
 bromide paper is preferable, not only on account of 
 its superior distinctness, but also because storage is 
 facilitated by its lightness, and its examination, by 
 the absence of any risk of fracture when handling it. 
 
 Should it be desired to produce this paper at home, 
 it is only necessary to coat ordinary albumenised 
 paper with the emulsion described on a previous 
 page, as follows : 
 
 The melted emulsion is poured into a flat ebonite 
 tray, slightly larger than the sheet of paper to be 
 coated. The sheet being held at two opposite cor- 
 ners, so as to form a kind of angular spout, its most 
 central and lowest part is allowed to rest on the 
 emulsion, the ends at the same time being allowed 
 to sink gradually until the whole sheet rests evenly 
 on the surface of the emulsion. This gradual 
 descent prevents the possibility of any air bubbles 
 remaining beneath the sheet. Should this however 
 happen, the end nearest the bubbles is raised and 
 again allowed to sink gradually, when it will be 
 found to push them before it in its descent. The 
 sheet is allowed to rest for a period varying from one 
 to ten minutes, according to the temperature of the 
 emulsion and finally hung up in the dark to dry. If 
 carefully guarded from actinic light and damp, this 
 sensitised paper will keep indefinitely. 
 
154 
 
 THE PRODUCTION OF POSITIVES. 
 
 All the trouble of the foregoing manipulations 
 may be avoided, by purchasing the paper ready 
 coated. An excellent quality is supplied by Morgan 
 and Co. In fact we recommend all to whom time is 
 of value, to purchase everything from those whose 
 business it is to manufacture articles of this descrip- 
 tion, as in the majority of cases home production is 
 false economy. As this firm has every facility for 
 producing enlargements on their own premises, those 
 who have not time for the productions of their own 
 enlargements are strongly recommended to send their 
 negatives to them. 
 
 The extreme sensitiveness of this paper renders 
 printing by contact, especially by daylight, a rather 
 difficult matter, unless the light is subdued by plac- 
 ing tissue paper or muffed glass a couple of inches in 
 front of the printing frame. The exposure can then 
 be prolonged, a great advantage when accurate re- 
 sults are required. It should be remembered that 
 the intensity of the illumination and duration of the 
 exposure have more influence on the condition of the 
 resulting positive than the character of the negative 
 itself. For instance, a very thin negative may be so 
 weakly illuminated that a harsh positive is the re- 
 sult; while a very dense negative, if exposed to 
 bright sun-light, will produce a positive completely 
 wanting in proper contrast. Advantage should be 
 taken of this and the illumination arranged to suit 
 the character of the negative. 
 
 It is therefore evident that no rule can be given 
 for exposure when daylight is employed, and even 
 
THE PRODUCTION OF POSITIVES. 155 
 
 with lamp light, owing to the variations in density 
 of different negatives,, an approximation only is pos- 
 sible. At the same time an over-exposed negative 
 always gives the best results, as a weak light and 
 under-exposure is all that is necessary for the pro- 
 duction of a good positive. We have found fifteen 
 seconds, three feet from an ordinary paraffin lamp, 
 sufficient exposure for a negative possessing the 
 characteristics recommended in a former chapter. 
 When no other means of printing but by contact 
 are available, a denser negative would give better re- 
 sults. 
 
 Copying with the camera is to be preferred to 
 direct printing ; first, because the exposure is length- 
 ened ; and secondly, because the character of the 
 resulting picture depends more on the size of the 
 stop, and intensity of the illumination than on the 
 density of the negative, and as a micro-negative is 
 less dense than an ordinary negative, greater power 
 of modifying the positive is placed in the hands of 
 the operator. 
 
 Any form of doublet may be used. The ordinary 
 Petzval portrait combination is to be preferred. It 
 should be capable of taking a cabinet picture. 
 
 A quarter plate negative is the most convenient 
 to copy from, especially for enlarging, because 
 the pictures, produced by a combination cover- 
 ing that sized plate, are more perfect in detail, and 
 when artificial light is employed, it is possible to 
 obtain good illumination without the use of very 
 large condensers or equally large photographic com- 
 
156 THE PRODUCTION OF POSITIVES. 
 
 binations, which in addition to their costliness 
 possess inherent faults that cannot be corrected. 
 
 If we desire a copy the same size or smaller than 
 the original ; the brass tube containing the lenses is 
 unscrewed from the camera ; the cell containing the 
 back combination removed ; the lenses are taken out 
 of it ; the ring separating them is next removed and 
 put back in the cell, and the lenses replaced in their 
 original order but in contact with each other. By 
 this means the definition is considerably improved, 
 and the consequent decrease of focal depth prevents 
 the images of objects, situated beyond the film of the 
 negative, being impressed on the sensitive surface. 
 
 The modified objective is fitted to the camera and 
 levelled at the negative. The latter should be 
 placed in a window having a northern aspect and an 
 uninterrupted view of the sky. To obtain this it is 
 sometimes necessary to tilt the camera upwards, 
 great care is then required to keep the surface of the 
 ground glass parallel with the negative, and both 
 perpendicular to the optic axis of the objective. 
 When the most accurate focus, with the full aperture 
 of the objective is obtained ; a stop of sufficient size 
 is introduced, and the camera covered with a black 
 cloth. A great improvement will be effected, and 
 the entrance of all extraneous light prevented by 
 pinning the black cloth round the negative, so as to 
 form a sleeve between it and the camera; it must, 
 however, be left unfastened at the bottom to allow of 
 the removal of the cap on exposure. 
 
 Before describing the remaining manipulations it 
 
THE PRODUCTION OF POSITIVES. 157 
 
 is necessary to remind the operator, that the aper- 
 tures of all stops or diaphragms are best named in 
 terms expressing their relation to the focal length 
 of the objective. As T ^ when the aperture is one 
 inch and the focal length of the objective ten 
 inches, and so on, the smallest aperture generally 
 employed being one fiftieth of the focal length or ^. 
 A combination of great focal length will bear a 
 smaller aperture proportionally than a shorter one. 
 For instance, with a negative possessing the char- 
 acteristics before mentioned, a quarter plate photo- 
 graphic objective requires an aperture = ^-, while 
 One = ^g- will be necessary when using a half plate 
 portrait combination. 
 
 We now proceed to the dark room, and having cut 
 our gelatino-bromide paper to the required size, float 
 the unprepared side on the surface of some perfectly 
 clean water (the greatest care must be taken to 
 prevent the water from flowing over the prepared 
 side). When perfectly flat it is laid evenly on a 
 sheet of patent plate and finally placed in the dark 
 slide. Some recommended the complete immersion 
 of the paper in water before laying it on the glass 
 plate, but the length of time necessary for perfect 
 drainage, and the risk of spoiling the picture if 
 sufficient time is not allowed for it, has led us to 
 adopt the former plan, which, if it requires more skill 
 and care, has at least the advantage of celerity. 
 
 After an exposure of say ten seconds, we return 
 to the dark room and on removal of the paper from 
 the dark slide, replace it in the water. A sufficient 
 
158 THE PRODUCTION OF POSITIVES. 
 
 quantity of ferrous oxalate developer, in the propor- 
 tion of four parts of a saturated solution of oxalate of 
 potash to one of ferrous sulphate (care being taken 
 to add tho latter to the former, not vice versa, else 
 a precipitate is formed which weakens the developer), 
 and one or two drops of Bromide of Ammonium are 
 placed in a glass measure. The mixed solutions are 
 then poured over the paper, previously placed in a 
 developing tray after its removal from the water. We 
 may now utilise all the ruby light at our command to 
 watch the process of development, as the colour of 
 the solution covering the paper is sufficiently non- 
 actinic to prevent the image being injured by too 
 strong a light. In about half a minute the picture 
 will begin to appear and in about three minutes the 
 process will be complete. It must not be carried too 
 far, in fact not so far as would be desirable in the 
 finished picture, as the intensity is considerably in- 
 creased by the fixing solution. After a slight rinse in 
 water it is immersed in the alum bath for one minute, 
 and after another rinse placed in the hyposulphite 
 solution for three minutes. It is then washed in fre- 
 quent changes of water and finally dried and mounted 
 in the manner described when treating of ordinary 
 silver prints, with this exception, that the picture 
 when pasted on cardboard must be allowed to dry 
 perfectly before the application of the hot iron, or the 
 gelatinised surface will be certain to adhere to any- 
 thing placed over it during the process. We wish 
 here again to impress on the operator the necessity of 
 using the developing solution perfectly fresh, as the 
 
THE PRODUCTION OP POSITIVES. 159 
 
 formation of the ferric salt from use and exposure 
 tends to slow the process with consequent weakening 
 of the image, to say nothing whatever of its de- 
 structive effect on the silver compounds which form 
 the image. 
 
 These positives may be intensified by mercury and 
 ammonium hydrate in the same way as ordinary 
 dry plates, but we do not recommend this method, 
 as the prints are liable to turn yellow on the applica- 
 tion of a hot iron. 
 
 Enlarging. There are innumerable methods em- 
 ployed for this purpose, we select two as being most 
 suitable for our work, and requiring very little ad- 
 ditional apparatus. 
 
 The first method is identical with that last de- 
 scribed, except that the lenses composing the ob- 
 jective are reversed, i.e., the front lenses are placed in 
 the cell containing the back combination, with the 
 convex surface towards the screen, while the back 
 combination is placed in the cell, from which the 
 front lenses have been removed, so that the lens which 
 formerly faced the screen, now faces the object to be 
 enlarged. If the cells themselves will fit either 
 end of the tube, this reversal is easily accomplished 
 without removing the lenses. It should always be 
 remembered, that the lenses forming what is con- 
 sidered as the back combination in ordinary photo- 
 graphy, must be placed in close apposition, and the 
 ring which separates them placed in the cell before 
 them. 
 
160 THE PRODUCTION OF POSITIVES. 
 
 Every part of the negative not required for re- 
 production should be masked, and all extraneous 
 light cut off. 
 
 After focussing, the smallest stop compatible with 
 a proper differentiation of the several shades in the 
 negative should be inserted, and an exposure accord- 
 ing to the size of the enlargement and density of the 
 negative being given, the usual manipulations are 
 proceeded with. 
 
 The advantage this method possesses over that to 
 be described, is the possibility of enlarging from a 
 negative of any size. This, however, can be accom- 
 plished by other means, and is only mentioned as an 
 additional resource where time is important, or 
 where the markings are so fine that they would be 
 injured by the coarseness of the film on dry plates, 
 when the collodion process is not available for the 
 production of a reduced negative. 
 
 The easiest method when daylight is not available 
 is to place an ordinary magic lantern (the condensers 
 of which are not less than four and a half inches in 
 diameter) in the recess of the dark room. The 
 entrance of actinic light being prevented by fastening 
 the sleeve intended for the microscope over the noz- 
 zle of the lantern. 
 
 The focus is obtained by pinning a sheet of white 
 paper on a moveable stand, and substituting the sen- 
 sitized surface for it after placing a cap over the 
 nozzle. The latter operation is much facilitated, if a 
 piece of ruby glass is let into the cap. 
 
THE PEODUCTION OP POSITIVES. 161 
 
 Many artists prefer the delicate tone of the ordin- 
 ary silver print to that produced on a gelatino- 
 bromide surface. All that is then necessary is the pro- 
 duction of a positive on paper, if a negative by 
 daylight ; or on glass, if one by lamplight is re- 
 quired. This method has the advantage of allowing 
 the production of any degree of density in the several 
 proofs by subsequent intensification. 
 
 By varying the processes, immense power is given 
 the operator, and no matter what the character and 
 condition of a photo-micrographic negative, it is 
 quite possible to change it completely without alter- 
 ing the essentials of the structure depicted on it, 
 thus rendering possible the production of a print 
 from what would otherwise bo considered a useless 
 negative. 
 
 It might be objected that the whole process, from 
 the first production of a negative with the micros- 
 cope to the finished print, was too tedious to be 
 practicable. This is by no means the case, because 
 the production of a negative only takes one hour, and 
 several can be produced together with a very little 
 increased expenditure of time. The subsequent 
 washing is not considered, as it requires no special 
 attention. The printing by camera, contact, or 
 enlarging, takes about half an hour, and the 
 finishing about another half hour, therefore from 
 beginning to end the actual time consumed is about 
 two hours. 
 
APPENDIX. 
 
 PRESERVATIVE MEDIA. The most generally useful 
 medium for mounting microscopic objects is Gum 
 and Glycerine, it is made as follows : 
 
 In a glass measure, place sufficient clean picked 
 gum arabic, to reach the line marking half an ounce, 
 add cold distilled water to make an ounce. This 
 should be left standing two days and stirred at in- 
 tervals till completely dissolved. The solution is 
 filtered by squeezing it two or three times through a 
 fine linen cloth. One sixth part of a saturated solu- 
 tion of Boracic acid in Glycerine is now added, and 
 the whole placed in a capsuled bottle containing a 
 lump of camphor. 
 
 The formation of air bubbles by filtering and stir- 
 ring is of no consequence, as they disappear com- 
 pletely after a few days. 
 
 BACILLUS TUBERCULOSIS. Dr. Gibbes recommends 
 staining the specimen with Methyline Blue instead 
 of Chrysoidine, the acid being previously removed 
 by frequent washings in distilled water. 
 
 This is a great improvement and if the Bacilli are 
 mounted in Gum and Glycerine instead of Balsam, 
 the reproduction of their appearance by means of 
 photography is rendered comparatively easy. 
 
 M2 
 
164 APPENDIX. 
 
 BINOCULAR PHOTOGRAPHY. Stereoscopic photo- 
 graphs may be produced by Stephenson's Binocular 
 arrangement, Polycystinas and Discoid al Diatoms 
 form beautiful objects when seen in the Stereoscope. 
 
 The prisms should be placed as near the back of 
 the objective as possible, and an ordinary stereos- 
 copic camera substituted for that already mentioned. 
 
 Wenham's and most other arrangements are com- 
 paratively useless, as the illumination is unequal on 
 the plates, and they require to be placed at an in- 
 convenient angle. 
 
 FOCUSSING AT A DISTANCE. The ordinary rod and 
 cork already described will be improved by the fol- 
 lowing addition. The cork being made slightly 
 smaller than the fine adjustment, three pieces of split 
 cane almost large enough to surround it, and long 
 enough to project a few inches beyond the end 
 farthest from the rod, are glued and tightly fastened 
 to it. A wire ring made to slip up and down on 
 these canes, forms a large crayon holder which will 
 grasp any sized adjustment firmly. 
 
INDEX, 
 
 Abbe, Prof., 20 
 Absolute Alcohol, 69 
 Absorption, 10 
 Achromatic Condenser, 28 
 Achromatic Object Glass, 15 
 Achromatism, 11 
 Actinic Focus, 14 
 Adjustment, Fine, 25 
 Algae, 58 
 
 Aperture, Angular, 19 
 Aperture, Numerical, 20 
 Artificial Light, 38 
 
 Bacilli, 69 
 
 Balsam and Benzol, 57 
 Bath, Sensitizing, 75 
 Blue Glass, 32, 40 
 Boxwood Slips, 55 
 Bull's Eye, 40, 48 
 
 Camera, 41 
 
 Carbon Bisulphide, 62" 
 
 Carmine, 67 
 
 Cell for Sulphate of Copper, 47 
 
 Centring, 112 
 
 Chloride of Gold, 63 
 
 Chromatic Aberration, 10 
 
 Cleaning Plates, 75, 92 
 
 Coarse Adjustment, 25- 
 
 Collodion, 76 
 
 Compound Microscope, 24 
 
 Concave Lenses, 5 
 
 Condensers, 28 
 
 Conjugate Foci, 6 
 
 Convex Lenses, 5 
 
 Copper Sulphate, 47 
 
 Copying Camera, 156 
 
 Coscinodisci, 62 
 
 Cover Glass Correction, 17 
 
 Damar, 57 
 
 Dark Ground Illumination. 120 
 
 Dark Room, 48 
 
 Density to Increase, 80, 148 
 
 ,, Decrease, 145 
 Developers, 75, 83 
 Diaphragm, 28 
 Diatomacese, 60 
 Diffraction, 20 
 Dry Mounting Objects, 55 
 Dry Plates, 80 
 
 Electricity, 38, 95 
 Endothelium, 64 
 Enlarging, 159 
 Eye, 8 
 Eyepiece, 24 
 
 Ferrous Oxalate, 37 
 
 Fine Adjustments, 25 
 
 Fixing Solution, 78 
 
 Foci, & 
 
 Focussing Rod, 47 and Appendix 
 
 Glass, 42 
 
 ,, Screen, 41 
 Fog, 130 
 Foraminifera, 60 
 Frames, Printing, 137 
 Freezing Microtome, 65 
 French Photo-micrography, 105. 
 
 Gelatine Emulsion, 80 
 Gibbes, Dr., 69 
 Glass Slides, 73 
 
 Thin, 73 
 
 Glycerine and Gum, 68. 72 
 Gold Trichloride, 63 
 
166 
 
 INDEX. 
 
 Hartley's Process, 81 
 Heliostat, 33 
 Huyghenian Eyepiece, 24 
 Hyposulphite of Soda, 97 
 
 Illumination, 124 
 Immersion Principle, 19 
 Incandescent Lamp, 38, 123 
 Insect Mounting, 57 
 Intensifying, 79, 100 
 
 Latitude to Find, 36 
 Lamp for Dark Room, 51 
 Lamp, Parafin, 39 
 Lantern Enlarging, 159 
 Lenses, 5 
 
 Magnifying Power, 14 
 Markings on Diatoms, 62 
 Media Mounting, 57, 58 
 Microscope, 25 
 Microtome, 64 
 Mounting Objects, 55 
 ,, Prints, 151 
 Morgan's Paper, 154 
 Muller's Fluid, 64 
 
 Negative, Properties of, 145 
 Neutral Oxalate, 99 
 
 Oblique Illumination, 120 
 Object Glass, 15 
 
 Opaque Objects Photography, 119 
 Over-exposure, 146 
 
 Paper, Sensitized, 149 
 Patent Plate Glass, 41 
 Penetration, 16 
 Petzval Portrait Lenses, 155 
 Photographing Horizontally, 128 
 Objects in Fluid, 
 
 110, 121 
 
 Photographing with 1 inch, 110 
 i inch, 120 
 I inch, 128 
 T6 inch, 136 
 
 Potash Bichromate, 65 
 
 Principal Focus, 6 
 
 Printing, 149 
 
 Production of Positives, 149 
 
 Pyrogallic Acid, 84 
 
 Real Foci, 6 
 Reflection, 4 
 Refraction, 4 
 Rutherford's Microtome, 64 
 
 Scales of Moths, 55 
 Section Cutting, 64 
 Silver Nitrate, 87 
 Sodium Sulphate, 65 
 
 ,, Hyposulphite, 97 
 Spectrum, 11 
 Stage of Microscope, 26 
 Staining, 67 
 Stand for Apparatus, 43 
 Substnge, 32 
 Sun Light, 32 
 Swan's Lamp, 106 
 
 Testing Solutions, 37 
 Thin Glass, 73 
 Toning, 150 
 
 Undulatory Theory, 4 
 
 Varnishing, 79 
 
 Virtual Foci, 6, 7 
 
 Visual and Chemical Foci, 14 
 
 Wenham Object Glass, 15 
 
 Wet Process, 75 
 
 Window of Dark Room, 50 
 
 Printed by H. K. Lewis, 136 Gower-st., London, W.C. 
 
April, 1885. 
 
 CATALOGUE OF WORKS 
 
 Published fy 
 
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 BODILY DEFORMITIES AND THEIR TREATMENT: A 
 
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 OF THE URINE DEPENDENT ON FUNCTIONAL DERANGE- 
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12 Catalogue of Works 
 
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 Formerly Assistant Professor of Physiology in Harvard College. 
 I. 
 
 EXPERIMENTAL RESEARCHES ON THE RE- 
 
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 flN THE NORMAL TEMPERATURE OF THE 
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 THE SCIENCE AND ART OF MIDWIFERY. Second 
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 JOHN MACPHERSON, M.D. 
 
 Inspector-General of Hospitals H.M. Bengal Army (Retired). 
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 ANNALS OF CHOLERA FROM THE EARLIEST 
 A PERIODS TO THE YEAR 1817. With a map. Demy 
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 DR. V. MAGNAN. 
 
 Physician to St. Anne Asylum, Paris ; Laureate of the Institute. 
 
 f|N ALCOHOLISM, THE VARIOUS FORMS OF 
 u ALCOHOLIC DELIRIUM AND THEIR TREAT- 
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Published by H. K. Lewis. 13 
 
 A. COWLEY MALLEY, B.A., M.B., B.CH. T.C.D. 
 
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 PATRICK MANSON, M.D., C.M. 
 
 Amoy, China. 
 
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 MARTIN'S ATLAS OF OBSTETRICS AND 
 COLOGY. Edited by A. MARTIN, Decent in the University 
 of Berlin. Translated and edited with additions by FANCOURT 
 BARNES, M.D., M.R.C.P., Physician to the Chelsea Hospital ; 
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 J. F. MEIGS, M.D. 
 
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 Lecturer on Clinical Medicine in the University of Pennsylvania, 
 
 A PRACTICAL TREATISE ON THE DISEASES 
 " OF CHILDREN. Seventh Edition, revised and enlarged 
 roy. 8vo, 28s. 
 
14 Catalogue of Works 
 
 WILLIAM MARTINDALE, F.C.S. 
 
 Late Examiner of the Pharmaceutical Society, and late Teacher of Pharmacy 
 and Demonstrator of Materia Medica at University College. 
 
 AND 
 
 W. WYNN WESTCOTT, M.B. LOND. 
 
 Deputy Coroner for Central Middlesex. 
 
 THE EXTRA PHARMACOPOEIA of Unofficial Drugs and 
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 with numerous additions, limp roan, med. 241110, 73. 
 
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 WM. JULIUS MICKLE, M.D., M.R.C.P. 
 
 Member of the Medico-Psychological Association of Great Britain and Ire- 
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 Grove Hall Asylum, London. 
 
 PENERAL PARALYSIS OF THE INSANE. 8vo, IDS. 
 
 KENNETH W. MILLICAN, B.A. CANTAB., M.R.C.S. 
 THE EVOLUTION OF MORBID GERMS : A Contri- 
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 STEPHEN MONCKTON, M.D., F.R.C.P. 
 
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 Assistant to the Professor of Medicine in University College, London. 
 TABLES OF THE PHYSIOLOGICAL ACTION OF 
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 DEFRACTION OF THE EYE: Its Diagnosis, and the 
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Published by H. K. Lewis. 15 
 
 WILLIAM MURRELL, M.D., F.R.C.P. 
 
 Lecturer on Materia Medica and Therapeutics at Westminster Hospital; 
 Examiner in Materia Medica in the University of Edinburgh. 
 
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 HAT TO DO IN CASES OF POISONING. Fourth 
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 ITRO-GLYCERINE AS A REMEDY FOR ANGINA 
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 DR. FELIX VON NIEMEYER. 
 
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 A TEXT-BOOK OF PRACTICAL MEDICINE, WITH 
 PARTICULAR REFERENCE TO PHYSIOLOGY AND 
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 Surgeon H.M, Indian Forces; late in Medical charge of the Dalhousie 
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 WHAT IS MALARIA? AND WHY IS IT MOST 
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16 Catalogue of Works 
 
 G. OLIVER, M.D., M.R.O.P. 
 
 i. 
 
 THE HARROGATE WATERS: Data Chemical and 
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 Addressed to the Medical Profession. Crown 8vo, with Map of 
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 AN BEDSIDE URINE TESTING : a Clinical Guide to 
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 considerably enlarged, fcap. 8vo, 33. [Just published 
 
 JOHN 8. PARRY, M.D. 
 
 Obstetrician to the Philadelphia Hospital, Vice-President of the Obstetrical 
 and Pathological Societies of Philadelphia, &c. 
 
 I7XTRA-UTERINE PREGNANCY; Its Causes, Species, 
 ^ Pathological Anatomy, Clinical History, Diagnosis, Prog- 
 nosis and Treatment. 8vo, 8s. 
 
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 Late Professor of Gynaecology in the Medical Department of Dartmouth Col- 
 lege ; President of the New York Academy of Medicine, &c., &c. 
 
 QVARIAN TUMOURS: Their Pathology, Diagnosis, and 
 ^ Treatment, especially by Ovariotomy. Illustrations, roy. 
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 Professor of Medical Jurisprupence, University College; Assistant Physician 
 
 and Physician m charge of the Throat Department of University 
 
 College Hospital. 
 
 T ECTURES ON THE PHYSICAL EXAMINATION 
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 R. DOUGLAS POWELL, M.D., F.R.C.P., M.R.C.S. 
 
 Physician to the Hospital for Consumption and Diseases of the Chest at 
 Brompton, Physician to the Middlesex Hospital. 
 
 niSEASES pF THE LUNGS AND PLEURA. 
 
 *^ Third Edition, re-written and enlarged, with Illustrations, 
 
 8vo. \In the press. 
 
 C. H. RALFE, M.A., M.D. CANTAB., F.R.C.P. LOND. 
 
 Assistant Physician to the London Hospital; late Senior Physician to the 
 Seamen's Hospital, Greenwich. 
 
 DISEASES OF THE KIDNEY AND MORBID 
 
 CONDITIONS OF THE URINE DEPENDENT ON 
 
 FUNCTIONAL DERANGEMENTS. With Illustrations, 
 
 crown 8vo. [In the press. 
 
Published by H. K. Lewis. 17 
 
 AMBROSE L RANNEY, A.M., M.D. 
 
 Adjunct Professor of Anatomy in the University of New York, &c. 
 
 THE APPLIED ANATOMY OF THE NERVOUS 
 
 1 SYSTEM, being a study of this portion of the Human 
 Body from a stand-point of its general interest and practical 
 utility, designed for use as a Text-book and a work of Reference. 
 With 179 Illustrations, 8vo, 203. 
 
 H. A. REEVES, F.R.C.S. ED. 
 
 Senior Assistant Surgeon and Teacher of Practical Surgery at the London 
 Hospital ; Surgeon to the Royal Orthopaedic Hospital, &c. 
 
 BODILY DEFORMITIES AND THEIR TREAT- 
 MENT : A Handbook of Practical Orthopaedics. With 
 numerous Illustrations, crown 8vo, 8s. 6d. [Now ready. 
 
 Lewis's Practical Series']. 
 
 RALPH RICHARDSON, M.A., M.D. 
 
 Fellow of the College of Physicians, Edinburgh. 
 
 N THE NATURE OF LIFE : An Introductory Chapter 
 to Pathology. Second Edition, revised and enlarged, 
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 W. RICHARDSON, M.A., M.D., M.R.C.P. 
 
 DEMARKS ON DIABETES, ESPECIALLY IN RE- 
 
 ** FERENCE TO TREATMENT. Demy 8vo, 2S. 6d. 
 
 SYDNEY RINGER, M.D., 
 
 Professor of the Principles and Practice of Medicine in University College ; 
 
 Physician to, and Professor of Clinical Medicine in, University 
 
 College Hospital. 
 
 I. 
 
 A HANDBOOK OF THERAPEUTICS. Eleventh Edition, 
 revised, 8vo . [In the press. 
 
 n. 
 
 ON THE TEMPERATURE OF THE BODY AS A 
 MEANS OF DIAGNOSIS AND PROGNOSIS IN 
 PHTHISIS. Second Edition, small 8vo, 2s. 6d. 
 
18 Catalogue of Works 
 
 FREDERICK T. ROBERTS, M.D., B.SC., F.R.C.P. 
 
 Examiner in Medicine at the Royal College of Surgeons ; Professor of Thera- 
 peutics in University College ; Physician to University College Hospital ; 
 Physician to the Brompton Consumption Hospital, &c. 
 
 I. 
 
 A HANDBOOK OF THE THEORY AND PRACTICE 
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 one volume, large 8vo, 2is. [Just published. 
 
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 ii. 
 
 OTES ON MATERIA MEDICA AND PHARMACY. 
 
 Fcap. 8vo, 73. 6d. [Now ready. 
 
 D. B. ST. JOHN ROOSA, M.A., M.D. 
 
 Professor of Diseases of the Eye and Ear in the University of the City of New 
 
 York ; Surgeon to the Manhattan Eye and Ear Hospital ; Consulting 
 
 Surgeon to the Brooklyn Eye and Ear Hospital, &c., &c. 
 
 A PRACTICAL TREATISE ON THE DISEASES OF 
 
 * THE EAR, including the Anatomy of the Organ. Sixth 
 Edition, Illustrated by wood engravings and chromo-lithographs, 
 large 8vo, 255. 
 
 W. H. 0. SANKEY, M.D. LOND., F.R.C.P. 
 
 Late Lecturer on Mental Diseases, University College, and School of Medi- 
 cine, London ; Formerly Medical Superintendent (Female Department) of 
 Hanwell Asylum ; President of Medico-Psychological Society, &c. 
 
 T ECTURES ON MENTAL DISEASE. Second Edi- 
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 ALDER SMITH, M.B. LOND., F.R.C.S. 
 
 Resident Medical Officer, Christ's Hospital, London. 
 
 "DINGWORM: ITS DIAGNOSIS AND TREATMENT. 
 * Third Edition, rewritten and enlarged, fcap. 8vo. 
 
 [In the press. 
 
Published by H. K. Lewis. 19 
 
 J. LEWIS SMITH, M.D. 
 
 Physician to the New York Infants' Hospital ; Clinical Lecturer on Diseases 
 of Children in Bellevue Hospital Medical College. 
 
 A TREATISE ON THE DISEASES OF INFANCY 
 ** AND CHILDHOOD. Fifth Edition, with Illustrations, 
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 FRANCIS W. SMITH, M.B., B.S. 
 
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 on the Climate of Leamington. With Illustrations, crown 8vo, 
 2s. 6d. 
 
 JAMES STARTIN, M.B., M.R.C.S. 
 
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 T ECTURES ON THE PARASITIC DISEASES OF 
 
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 LEWIS A. STIMSON, B.A., M.D. 
 
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 the Medical Faculty of the University of the City of New York. 
 
 A MANUAL OF OPERATIVE SURGERY. With 
 
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 HENRY R. SWANZY, A.M., M.B., F.R.C.S.I. 
 
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 National Eye and Ear Infirmary, Dublin ; Ophthalmic Surgeon 
 
 to the Adelaide Hospital, Dublin. 
 
 HANDBOOK OF DISEASES OF THE EYE AND 
 THEIR TREATMENT. Illustrated with Wood En- 
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20 Catalogue of Works 
 
 HUGH OWEN THOMAS, M.R.C.S. 
 
 DISEASES OF THE HIP, KNEE, AND ANKLE 
 
 *^ JOINTS, with their Deformities, treated by a new and effi- 
 cient method. With an Introduction by RUSHTON PARKER, 
 F.R.C.S., Lecturer on Surgery at the School of Medicine, 
 Liverpool. Second Edition, 8vo, 255. 
 
 CONTRIBUTIONS TO MEDICINE AND SURGERY: 
 
 PART i. Intestinal Obstruction ; with an appendix on the Ac- 
 tion of Remedies. IDS. 
 
 ,, 2. The Principles of the Treatment of Joint Disease, 
 Inflammation, Anchylosis, Reduction of Joint De- 
 formity, Bone Setting. 53. 
 
 5. On Fractures of the Lower Jaw. is. 
 
 . The Inhibition of Nerves by Drugs, 
 hibitory Nerve-Fibres do not exist. 
 
 (Parts 3, 4, 6, 7, 9, 10, are expected shortly). 
 
 8. The Inhibition of Nerves by Drugs. Proof that In- 
 hibitory Nerve-Fibres do not exist, is. 
 
 J. ASHBURTON THOMPSON, M.R.C.S. 
 
 FREE PHOSPHORUS IN MEDICINE WITH SPE- 
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 A contribution to Materia Medica and Therapeutics. An account 
 of the History, Pharmaceutical Preparations, Dose, Internal 
 Administration, and Therapeutic uses of Phosphorus; with a 
 Complete Bibliography of this subject, referring to nearly 200 
 works upon it. Demy 8vo, ys. 6d. 
 
 J. C. THOROWGOOD, M.D. 
 
 Assistant Physician to the City of London Hospital for Diseases of the Chest. 
 
 THE CLIMATIC TREATMENT OF CONSUMPTION 
 AND CHRONIC LUNG DISEASES, Third Edition, 
 post 8vo, 35. 6d. 
 
Published by H. K. Lewis. 21 
 
 EDWARD T. TIBBITS, M.D. LOND. 
 
 Physician to the Bradford Infirmary and to the Bradford Fever Hospital. 
 
 TMEDICAL FASHIONS IN THE NINETEENTH 
 
 IYJ - CENTURY : including a sketch of Bacterio-Mania and 
 the Battle of the Bacilli. Crown 8vo, 2s. 6d. 
 
 LAURENCE TURNBULL, M.D., PH.G. 
 
 Aural Surgeon to Jefferson Medical College Hospital, &c., &c. 
 
 ARTIFICIAL ANAESTHESIA: A Manual of Anesthetic 
 ** Agents, and their Employment in the Treatment of Disease. 
 Second Edition with Illustrations, crown 8vo, 6s. 
 
 |W. H. VAN BUREN, M.D., LLD. 
 
 Professor of Surgery in the Bellevue Hospital Medical College. 
 
 TVISEASES OF THE RECTUM: and the Surgery of the 
 ^ Lower Bowel. Second Edition, with Illustrations, 8vo, 
 
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 RUDOLPH VIRCHOW, M.D. 
 
 Professor in the University, and Member of the Academy of Sciences of 
 Berlin, &c. 
 
 INFECTION-DISEASES IN THE ARMY, chiefly 
 Wound Fever, Typhoid, Dysentery, and Diphtheria. 
 Translated from the German by JOHN JAMES, M.B., F.R.C.S. 
 Fcap. 8vo, is. 6d. 
 
 ALFRED VOGEL, M.D. 
 
 Professor of Clinical Medicine in the University of Dorpat, Russia. 
 
 A PRACTICAL TREATISE ON THE DISEASES 
 A OF CHILDREN. Translated and Edited by H. RAPHAEL, 
 M.D. From the Fourth German Edition, Illustrated by six 
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22 Catalogue of Works 
 
 A. DUNBAR WALKER, M.D., C.M. 
 
 HIRE PARENTS' MEDICAL NOTE BOOK. 
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 JOHN R. WARDELL, M.D., F.R.C.P. 
 
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 u PRACTICE OF MEDICINE. Medium 8vo. [In the press. 
 
 A. DE WATTEVILLE, MA, M.D., B.SC., M.R.C.S. 
 
 Physician in Charge of the Electro-therapeutical Department of St. Mary's 
 Hospital. 
 
 A PRACTICAL INTRODUCTION TO MEDICAL 
 ** ELECTRICITY. Second Edition, re-written and en- 
 larged, copiously Illustrated, 8vo, gs. 
 
 W. SPENCER WATSON, F.R.C.S., M.B. 
 
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 EYEBALL TENSION: its Effects on the Sight and its. 
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 n. 
 
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 Army Data at Home and Abroad. Demy 8vo, 55. 6d. 
 
Published by H. K. Lewis. 23 
 
 DR. F. WINCKEL 
 
 Formerly Professor and Director of the Gynaecological Clinic at the Univer- 
 sity of Rostock. 
 
 rFHE PATHOLOGY AND TREATMENT OF CHILD- 
 * BED; A Treatise for Physicians and Students. Trans- 
 lated from the Second German Edition, with many additional 
 notes by the Author, by J. R. CHADWICK, M.D. 8vo, 143. 
 
 EDWARD WOAKES, M.D. 
 
 Senior Aural Surgeon and Lecturer on Aural Surgery at the London Hospital ; 
 Senior Surgeon to the Hospital for Diseases of the Throat. 
 
 AN DEAFNESS, GIDDINESS, AND NOISES IN 
 THE HEAD. 
 
 PART I. POST-NASAL CATARRH, AND DISEASES 
 OF THE NOSE CAUSING DEAFNESS. With Illus- 
 trations, crown 8vo, 6s. 6d. 
 
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 8vo. [In preparation. 
 
 E. T. WILSON, B.M. OXON., F.R.C.P. LOND. 
 
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