MICRO-PHOTOGEAPHY 
 
 MALLEI 
 
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AGFA ANSCO 
 
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MICEO-PHOTOGEAPHY. 
 
j . Section of I.ung, containing 
 Bacillus Anthracis from a case 
 OF Splenic Fever. 420 diameters. 
 
 3, S. Gemma and P. Spencerii. jooo 
 diameters. 
 
 2. Central portion of A. Kittonh. 
 1500 diameters. 
 
 4. Scales of P. Argus. 320 diameters^ 
 
MICRO-PHOTOGRAPHY 
 
 INCLUDING A 
 
 DESCRIPTION OF THE WET COLLODION 
 
 AND 
 
 GELATINO-BROMIDE PROCESSES 
 
 TOGETHER WITH THE BEST METHODS OF MOUNTING 
 AND PREPARING MICROSCOPIC OBJECTS 
 FOR MICRO PHOTOGRAPHT 
 
 BY 
 
 A. COWLEY MALLEI, B.A.,M.B.,B.Ch,T.C.D. 
 
 LONDON 
 
 H. K. LEWIS, 136 GOWER STREET, W.C. 
 1883 
 
PRINTED BY 
 
 K. LEWIS, 136 GOWER STREET, 
 
 LONDON, WX. 
 
PREFACE. 
 
 The publication of this little work has been under- 
 taken with a view to encourage the practice of 
 Micro-photography, and alford 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. G. B. Powell who revised all 
 the proofs, and whose valuable services have contri- 
 buted in no small measure to hasten the comple- 
 tion and publication of the work. 
 
 A. Cowley M alley. 
 
 MunsloWj Shropshire, 
 
COl^TENTS. 
 
 CHAPTER I. 
 
 Introduction ..... 
 
 CHAPTER II. 
 
 Reflection and Reiraction 
 
 Aberrations ..... 
 
 Microscopic Objectives 
 
 CHAPTER HI. 
 
 The Microscope .... 
 
 Achromatic Condenser 
 Illumination .... 
 
 The Dark Room .... 
 
 CHAPTER IV. 
 
 Mounting Microscopic Objects 
 
 Section Cutting .... 
 
 Staining ..... 
 
 CHAPTER V. 
 
 Wet Collodion Process 
 Gelatino -Bromide Emulsion 
 
Vlll 
 
 CONTENTS. 
 
 . CHAPTER VI. 
 
 PAGE 
 
 Former Methods adopted in the Arrangement of the Apparatus 90 
 
 Later Methods 
 
 . 
 
 . 92 
 
 The Method adopted in this Work 
 
 • 
 
 . 94 
 
 Dr. Ballinger’s Illumination 
 
 . 
 
 .112 
 
 CHAPTEE 
 
 VII. 
 
 
 Defects in Negatives 
 
 . 
 
 . 128 
 
 Their Remedy 
 
 . 
 
 . 129 
 
 CHAPTER 
 
 VIII. 
 
 
 Production of Positives 
 
 • 
 
 . 137 
 
 Enlarging .... 
 
 
 . 147 
 
MICEO-PHOTOGEAPHY. 
 
 CHAPTER I. 
 
 Introduction. 
 
 Before beginning a detailed description of the ap- 
 paratus employed in Micro-photography^ a few re- 
 marks 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 bafSe 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 some favourite theory, or shewing the existence 
 of some doubtful structure. 
 
 B 
 
2 
 
 INTRODUCTION. 
 
 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 diatomacese agrees with others as 
 to their true interpretations^ at the present day Ag- 
 nosticism is the only name expressing the condition of 
 men^s minds on some of these subjects. Thousands of 
 questions hitherto unsettled 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 natural- 
 ists and our professional brethren. 
 
 I do not wish to lead others to infer from this^ 
 that the photographic image may not be false if 
 improperly obtained^ but it can neither add anything 
 to^ nor take anything from^ the structure^ and may 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 strain by 
 the study of microscopy^ for from what has been 
 said the advantages of photography to the Histolo- 
 gist, Pathologist, and student of Natural History, 
 
INTRODUCTION. 
 
 3 
 
 are so obvious that any tendency to extend its 
 domain to amusement might injure its prestige 
 with students of science. 
 
 In the following chapters our aim has been^ not 
 so much to supply new methods as to increase the 
 popularity of those already known^ by shewing the 
 facility of their application. 
 
4 
 
 PROPERTIES OP LENSES. 
 
 CHAPTER II. 
 
 Properties op Lenses^ Imperpections op 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 beiug 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 BAG, and re- 
 fraction B'AC', (Fig. 1), bear a constant ratio to each 
 other. 
 
 This ratio is called the refractive index. 
 
 Refractive Index. 
 
 Of Air 1-000294. 
 
 „ Diamond 2*44 
 „ Flint Glass 1*642 
 ,, Grown Glass 1*550 
 
PROPERTIES OP LENSES. 
 
 5 
 
 Fig. 1. 
 
 If the medium through which the light passes has 
 parallel faces,, the emergent B'A' and incident rays 
 BA are parallel, (Fig. 1), if it has not, the ten- 
 dency of the ray is to bend away from the angle at 
 which the faces meet. 
 
 Lenses are of six forms; double convex 1, piano 
 convex 2, converging meniscus 3, double concave 4, 
 piano concave 5, diverging meniscus 6. 
 
 Fig. 2. 
 
 1^3 4i 
 
 
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 4). 
 
 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. 
 
 Bays 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. 
 
PROPERTIES OF LENSES. 
 
 7 
 
 meet at V Fig. 8. The point V is called the virtual 
 focus. 
 
 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. 
 
 Fig. 4. 
 
 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 be placed at twice the focal 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 the opposite side. 
 
8 
 
 PROPERTIES OF LENSES. 
 
 Pig. 5. 
 
 If nearer^ a real inverted magnified image 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. 6. 
 
 The human eye consists of a convex lens, the 
 
 Fig. 7. 
 
PROPERTIES OF LENSES. 
 
 9 
 
 crystaline lens placed behind the aperture of the iris, 
 and a screen, the retina, behind the crystaline lens, 
 C and R. 
 
 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 perceive 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 
 enable- it to bring the divergent rays to a focus on 
 the retina, but if a convex lens L Fig. 7 be placed 
 between the object and the eye it assists in bring- 
 ing the rays to a focus on the retina. 
 
 The size of the retinal image varies with that of 
 the angle AOB Fig. 7. This angle is called the 
 visual angle. 
 
 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, e»g, the 
 visual angle is increased. 
 
10 
 
 PROPERTIES OF LENSES. 
 
 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 0 Fig. 7 has the power of bringing the rays 
 to a focus and forming a real image on the retina 
 on this principle the magnified image in the simple 
 microscope depends. 
 
 Concave lenses can only formvirtual images no 
 matter what the distance of theobject. (Fig. 4). 
 
 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 
 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 shows itself in want of dis- 
 tinctness in an image at the margins when sharp at 
 centre and vice versa, it is caused by the unequal re- 
 fraction 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 ; a ray of white light is 
 composed of rays of different colours, if it pass 
 
PROPERTIES OF LENSES. 
 
 11 
 
 Fig. 8. 
 
 
 
 througli a medium (such as a lens or prism)^ Fig. 8^ 
 whose sides are not parallel^ it is divided into its 
 component colours,, or dispersed. 
 
 Now since all the diSerent rays into which a pencil 
 of white light can be divided^ have different foci^ 
 {e.g, the point where the red rays come to a focus 
 is more distant than that of the violet)^ the inter- 
 mediate colours forming other foci VI 2 34 it Fig. 9 
 between them^ are all unequally dispersed and the 
 resulting 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 
 
 Fig. 9. 
 
12 
 
 PROPERTIES OP LENSES. 
 
 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 easier 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 distant 
 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 
 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 barrell-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 
 
PROPERTIES OE LENSES. 
 
 13 
 
 Fig. 10. 
 
 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 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 tbe same time of the 
 different relations between the refractive and dis- 
 persive powers of different kinds of glass^ and if the 
 lenses which correct the spherical aberration by tbeir 
 shape are formed from different kinds^ chromatic 
 aberration will be destroyed. If tbe 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 neutralised^ 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. 
 
14 
 
 PROPERTIES OF LENSES. 
 
 SO opticians overcome the diflBculty by combining 
 several. 
 
 Before leaving this subject we should mention 
 that in photography errors frequently arise^ espe- 
 cially when using low powers^ owing to the differ- 
 ence between the visual and chemical foci. 
 
 A point of white light may appear perfectly dis- 
 tinct at R Fig. 9^ when surrounded by a violet areola, 
 and if a photograph be taken it will be quite indis- 
 tinct; while at V nearer the. lens the image may not 
 appear 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 when the object is sur- 
 rounded by a red areola, this being the most ac- 
 curate for the violet rays. 
 
 Microscopic objectives have of late years arrived 
 at such perfection that it seems impossible to im- 
 prove them. 
 
 They are designated from four inch 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. 
 
PROPERTIES OF LENSES. 
 
 15 
 
 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 example of the ingenuity displayed in over- 
 coming these difficulties, we refer the reader to the 
 description of Mr. Wenham^s new objective published 
 in the Proceedings of the Royal Society, Yol. 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 concave lens of flint, three times 
 the focal length of the front, corrects all the others. 
 
 In this combination only flve lenses are used, and 
 the errors arising from the sixteen surfaces of glass 
 in the older forms reduced to ten. 
 
 1. A good objective should possess the Standard 
 screw, adopted by the various societies, and now 
 fixed by the best makers to their lenses. 
 
 2. Its definition should be clear, the field flat, 
 objects at the edge of the field should be as free 
 
16 
 
 PROPERTIES OF LENSES. 
 
 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 diflScult to form a 
 correct opinion of, as we shall find that a glass of 
 given focus magnifies the depth of an object in the 
 proportion 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. 
 
 3. 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 un- 
 covered objects. 
 
 This may be remedied, as has been shown by Mr. 
 A. Koss, by under-correcting the front and over- 
 
FROPERTIES OF LENSES. 
 
 17 
 
 Fig. 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 by 
 bringing the front and back combinations nearer 
 together, enables us to give the objective an excess of 
 positive aberration suflScient to counteract the nega- 
 tive produced by the thin glass. 
 
 The screw collar adjustment at the same time 
 corrects 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 indispensable 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 allow- 
 ance must be made for this when accurate measure- 
 ments 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 
 
 c 
 
18 
 
 PKOPERTIES OF LENSES, 
 
 Fig. 12. 
 
 adjust for uncovered, 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 to- 
 wards 0 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 distinct- 
 ness, 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. 
 
 4. 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 
 
PROPERTIES OF LENSES. 
 
 19 
 
 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 aper- 
 ture, we are obliged to sacrifice depth of focus, in 
 the attainment of magnifying power and angular 
 aperture. 
 
 The angular aperture is the capacity a lens hasj 
 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 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 neces- 
 sary; care should be taken that the smallest quantity 
 sufficient to cover the aperture of the objective, luhen 
 focussed on the object^ is used, as any excess would 
 cause blurs of irradiation, not to mention other ob- 
 jections. 
 
 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 at the 
 focal point of the objective, has been superseded by 
 the more correct and convenient method of calling 
 the capacity which an objective possesses for collect- 
 ing the whole pencil of rays from an object in air, 
 
 c 2 
 
20 
 
 PROPERTIES OE LENSES. 
 
 Unity, tlien commencing with the lowest numbers 
 this reaches as far as 1*52 for oil immersions. 
 
 This is called the Numerical aperture and NA is 
 written after the numbers to distinguish it. 
 
 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. 
 
 We cannot leave this part of the subject without 
 reverting to the views enunciated by Professor Abbe 
 of Jena, which have placed the old theories of Micros- 
 copic vision on an entirely new footing. 
 
 According to his demonstrations the images pro- 
 duced by minute objects, small multiples of wave 
 lengths, are imaged in an entirely different way 
 from those produced by coarse objects. 
 
 Objects less than of an inch are imaged by the 
 diffracted rays produced 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 resulting image as 
 regards the actual structure of the object. 
 
 It has been recently remarked that microscopic 
 vision was totally distinct from macroscopic. 
 
 First, because by placing a stop behind the objec- 
 tive that is decreasing the aperture, objects could 
 be made to assume different forms. 
 
PROPERTIES OF LENSES. 
 
 21 
 
 Second, because under different conditions of aper- 
 ture different objects assumed the same form. 
 
 Now Professor Abbe himself says minute struc- 
 tural details are not as a rule imaged by the Micros- 
 cope Bioptrically , 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. 
 
 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 materia] 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.^^ 
 
 The w'onderful discovery is that the Microscope 
 
22 
 
 PROPERTIES OF LENSES. 
 
 does not act dioptrically under certain circumstances^ 
 and that we have a new aid to research in these dif- 
 fraction phenomena; like polarisation and other pro- 
 perties of light. 
 
 Unfortunately the whole stress has been laid upon 
 the fact that these images are not exact representa- 
 tions of material forms. 
 
 Association and inherited materialism has taken 
 too great a hold upon our minds^ and we have for- 
 gotten 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 do not mean by this 
 that their esse is a mere percipi. 
 
 Some of our foreign brethren have justly said, 
 
 the English are that nation in Europe which like 
 the Huckster and Workman Class of the state are 
 destined to pass their lives immersed in matter.'’^ 
 We raise a shout of astonishment at an old idea, no 
 doubt in a new dress, and we miss the great dis- 
 covery itself in our delight of at last perceiving by 
 it, what has been dimly present to our minds for 
 centuries. 
 
 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. 
 
 I 
 
PROPERTIES OF LENSES. 
 
 23 
 
 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. 
 
 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. 
 
 The extra amount expended 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 employ- 
 ment. We therefore strongly recommend the ama- 
 teur to patronise only the best makers^ and pay the 
 highest price for his objectives. 
 
 We shall devote a little time to the consideration 
 of the principles involved in the formation of the 
 image in the compound microscope^ although we are 
 not directly concerned with it in microphotography. 
 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 
 
 Fig. 13. 
 
 image a b of the object A B formed by the objective 
 at a point just within the focus of the eye-glass is 
 
24 
 
 PROPERTIES OF LENSES. 
 
 changed into a virtual image at a' b' by the latter^ 
 both images being inverted as regards the object. 
 The principle 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 
 piano convex lenses, 1 and 2 fig. 14, called respec- 
 
 Fig. 14. 
 
 tively eye and field lens, the former being one-third 
 the focus of the latter and the distance of their 
 separation half the sum of their focal lengths. 
 
 Huygens was ignorant of one advantasre this com- 
 bination possessed, 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. 
 
 We advise the amateur not to use it in photo- 
 graphy except to view the image before focussing, , 
 as with all its supposed advantages its employment 
 never gives good results. 
 
MICROSCOPE^ ETC. 
 
 25 
 
 CHAPTEE III. 
 
 The Microscope^ Illumination^ Etc. 
 
 Before beginning a detailed description of tbe 
 microscope^ a few hints to the uninitiated are neces- 
 sary. Avoid purchasing instruments adorned with 
 innumerable 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 an insult to 
 the skilled microscopist and a means of perpetuating 
 clumsy manipulations. On the other hand many 
 excellent instruments are made^ which^ owing to some 
 peculiarity of shape^ are useless for photography. 
 
 The first essential of a miiTOscope is a firm heavy 
 stands so arranged that the body may be inclined at 
 any angle between horizontal and perpendicular and 
 clamped in that position. It should be high enough 
 to allow space beneath the stage for sub-stage appar- 
 atus, 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 
 within another) the rack being attached to a bar 
 placed some distance from the tube carrying the 
 
26 
 
 MICROSCOPE^ ETC. 
 
 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. 
 
 The fine adjustment should also be separate from 
 the eye- piece tube to allow of attachments necessary 
 for working it from a distance. It should respond 
 immediately to the slightest rotation in either direc- 
 tion, and the object should suffer no apparent shake 
 or displacement, when moving in or out of focus. 
 
 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 effected, would be 
 welcomed by microscopists. 
 
 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 compa- 
 tible with the use of the sub-stage apparatus, to be 
 described. Circular in form and possessing some 
 arrangement by which movements in a rectangular, 
 circular and horizontal direction may be smoothly 
 and easily communicated to the object, by aid of 
 the finger alone without the use of milled heads or 
 other mechanical arrangements. 
 
MICROSCOPE^ ETC. 
 
 27 
 
 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 
 in view^ not a desire to catch the eye of the public. 
 
 Fig. 15. 
 
 The accompanying figure represents a slightly 
 modified form of Smith and Beckys 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 
 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 
 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 
 
28 
 
 MICROSCOPE^ ETC. 
 
 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 in position, this can be removed when very 
 oblique light is required. 
 
 A diaphragm I, attached to a short wide tube with 
 a thick rim E, 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 
 about to be described, and which we strongly recom- 
 mend, fulfils all the requirements of the most expen- 
 sive sub-stage arrangements. 
 
 Fig. 16 is a diagramatic representation of it in 
 section. 
 
 Fig. 16. 
 
MICROSCOPE, ETC. 
 
 29 
 
 In the rim E 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 fianges of the rim E, 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 8 fig. 1 6 
 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 inde- 
 pendently 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 applying this principle to existing instruments. 
 
 From what has been previously mentioned with 
 regard to the resolution of certain structural pecu- 
 liarities 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. 
 
30 
 
 MICROSCOPE^ ETC. 
 
 It must be remembered however that a condenser 
 is not necessary when using the one inch or lower 
 power^ but is indispensable with those above it. 
 
 A good achromatic condenser of the French form^ 
 consisting of three powers^ screwing on top of each 
 other will answer the purpose. 
 
 A much better form is Powell and Leland^s new 
 homogeneous immersions; whichever is used^ it should 
 be fitted in the centre of the ring A so as to be remov- 
 able at pleasure^ and with the face of the uppermost 
 combination flush with the ^top of the substage tube^ 
 to allow of its close aproximation 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 substage^ the three com- 
 binations which compose it should be easily unscrewed 
 from one another^ as on no account must the power 
 of the condenser exoeed that of the objective^ we 
 therefore require no condenser with the one inch, 
 while with the quarter two and with the eight 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 
 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 
 
MICEOSCOPE, ETC. 
 
 31 
 
 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 follow- 
 ing arrangement which enables us to place it in 
 immediate contact, besides possessing several advan- 
 tages in practice, lessens the spherical aberration 
 and improves the illumination, though it decreases 
 the angle of aperture. 
 
 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- 
 
32 
 
 ILLUMINATION. 
 
 fice a slight rim projects into the interior, on which 
 brass discs having diflFerent 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 dimin- 
 ished by increasing or diminishing the distance be- 
 tween the blue glass and the aperture of the slot or 
 back of the condenser. 
 
 The advantage of this sub-stage arrangement 
 is that no light can reach the object or enter the ob- 
 jective except through the diaphragm and condenser 
 themselves ; the ease and simplicity with which the 
 several adjustments are made, and the possibility 
 of adapting it to any existing microscope stand. 
 
 Illumination. 
 
 The best light for Micro-photography is sunlight, 
 but the difficulties of its employment in our climate, 
 more than counterbalance the excellence of its re- 
 sults. 
 
 We shall give a description of the apparatus neces- 
 sary for the benefit of those who can afford sufficient 
 time during daylight for Micro-photography, or who 
 may be more favourably situated atmospherically. 
 
 It should be borne in mind that the actinic power 
 
ILLUMINATION. 
 
 33 
 
 Fro. 17. 
 
 
34 
 
 ILLUMINATION. 
 
 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 great- 
 est 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 assistant. 
 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 
 about six inches wide and twelve long. A, fig. 1 7, is 
 fitted with levelling screws, xxxx, at its four corners. 
 On it a small French clock M is placed, a boxwood 
 wheel one inch in circumference being 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 
 
ILLUMINATION. 
 
 35 
 
 on a level with the top of the glass plate^ and in 
 a direct line with NS. 
 
 A wooden pillar 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 per- 
 forated 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 larger mirror, L, mounted to allow of 
 its rotation in all directions, and elevation to any 
 required height, is placed in front of the mirror K and 
 generally on its left hand-side. 
 
 A stout card R 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 pole PF the axis, fig. 18. 
 
 D 2 
 
36 
 
 ILLUMINATION. 
 
 Fig. 18. 
 
 A 
 
 At any place 0 on the earth^s surface a line AO 
 drawn pointing to the pole will be parallel to PF^ as 
 the pole is infinitely distant. 
 
 If 00 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^ Le. 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 made to re- 
 
ILLUMINATION. 
 
 37 
 
 volve 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 pointy we must then 
 employ another mirror to receive the reflection from 
 the one looking towards the sun^ and give the latter a 
 motion four times 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 flx 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 Arm support at the win- 
 dow^ (which should be open)^ so that the line NS 
 points north and souths 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 XXX and a small spirit level. 
 
 The plumb-line is attached to the top of the needle 
 and the brass plate G moved till the lead of the 
 plumb-line hangs directly over NS. At the same 
 time the card R (which should be very accurately 
 made)^ is placed with its upper extremity at 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 
 
38 
 
 ILLUMINATION. 
 
 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 refiected 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 practice 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. 
 
 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 
 micro-photography. Swanks 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. 
 
ILLUMINATION. 
 
 39 
 
 Fig. 19 shows a simplified form of that used by 
 Dr. Dallinger and described in the Journal of the 
 Microscopical Society. 
 
 To the back of an ordinary tin paraffin lamp a 
 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 a rack and 
 pinion movement. A lateral motion is communi- 
 cated to the pillar D by means of the screw F. 
 
 Fig. 19. 
 
 The lid of an oblong tin box about one inch wider 
 than the chimney of the lamp, has a hole cut in it 
 
40 
 
 ILLUMINATION. 
 
 of suflScient 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 turnd down hori- 
 zontally. 
 
 Another round hole two inches in diameter, is cut 
 in the front of the box, at such a level that the flame 
 may occupy its centre. 
 
 In the middle of the opposite side a slit three 
 inches long is ndade, 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, 
 allows a current of air to circulate between the 
 mirror and the chimney of the lamp, and prevents 
 their cracking. 
 
 An ordinary plano-convex condenser, its plane 
 surface being turned towards the lamp, is placed 
 about one inch from the latter, (when high powers 
 are employed), and a stand to hold blue glass between 
 this condenser and the microscope. The stand is 
 unnecessary if the arrangement for obtaining a 
 monochromatic light mentioned on a previous page 
 has been carried out. 
 
 When using Swanks 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 
 to this full information will be supplied by any 
 leading electrical Arm. 
 
CAMERA. 
 
 41 
 
 The Camera and other Apparatus. 
 
 As the camera plays a very important part in 
 micro-photography^ 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 whein working with 
 dry plates^ to have one or two double dark slides. 
 Several plates can then be exposed consecutively, and 
 developed together, by this a great waste of time- 
 and solutions 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. 23, 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 
 
42 
 
 HAND AND OTHER APPARATUS. 
 
 and pinion or screw motion^ and when the desired 
 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 considera- 
 ble time in preparation. 
 
 The camera^ when these additions are completed^ 
 is fastened to an oblong boards 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. 
 
 The greatest difficulty that besets us^ especially 
 when using artificial lights is the impossibility of 
 focussing minute markings on the screen. This 
 is due to three causes^ first the coarseness of the 
 surface 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 
 been founds 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 
 
HAND AND OTHER APPARATUS. 
 
 43 
 
 microscope^ and blacken it inside. In the opposite 
 end fix a piano 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 adapted by the writer after more than ten 
 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. On the upper 
 surface at each side flush with the edges, two laths 
 one inch wide, half an inch thick, and the same 
 
44 
 
 HAND AND OTHER APPARATUS. 
 
 length as the beam^ are fastened^ and divided into 
 three parts^ the same way as the beam. These not 
 only prevent anything 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 3 are joined on their upper surface^ in 
 the same way where the laths meet as in fig. 23. 
 
 Along the sides of the beams ten bolts are inserted 
 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. 
 
 A board three feet long^ two an'd a half inches 
 wide, and one inch thick, B fig. 23, 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. 23, is in- 
 
HAND AND OTHER APPARATUS. 
 
 45 
 
 tended 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 boards slid- 
 ing 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 impossible 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 disturbing 
 the centering 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 
 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 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, bulhs 
 eye condenser, and sulphate of copper cell to be 
 firmly clamped in position by binding screws. 
 
46 
 
 HAND AND OTHER APPARATUS. 
 
 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 (23, 24, 25), 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 
 fixed so that a wheel, attached to the extremity 
 next the microscope, may always occupy the same 
 position beneath the fine adjustment, indepen- 
 dently of the distance of the camera from the plat- 
 form. A silk cord fastened round this wheel and 
 the fine adjustment, 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 adjustment is beyond reach. An assistant, is 
 then unnecessary as no matter how intelligent he may 
 
HAND AND OTHEE APPARATUS. 
 
 47 
 
 be^ it will be found more satisfactory to have the 
 focussing 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 in- 
 tervention of any cord or wheels ; unfortunately its 
 use is limited to those methods in which the micro- 
 scope is not attached to the camera. 
 
 When sunlight is the source of illumination, there 
 is great danger of the object and objective being de- 
 stroyed by the heat rays focussed on them by the 
 condenser. This may be partially avoided by put- 
 ting the condenser a little out of focus, or we may 
 entirely eliminate them by the interposition of a plate 
 of alum between the heliostat and condenser. 
 
 The best method, however, is to remove the blue 
 glass, and place a cell having parallel sides, and filled 
 with a solution of ammonia sulphate of copper in a 
 similar position to that recommended for the alum 
 plate. The cell is made as follows : — 
 
 Fig. 20 . 
 
48 
 
 HAND AND OTHER APPARATUS. 
 
 A piece of round india-rubber placed between two 
 quarter plates, is made to occupy tbe same posi- 
 tion as tbe dotted lines in figure (20). A board 
 slightly narrower than the plates and india-rubber, 
 has a piece cut out of it inches wide and about 
 the same length ; four thin strips are fastened along 
 its edges and the plates with the india-rubber forced 
 down between them ; 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 
 evaporation. 
 
 This cell may with advantage be used on all occa- 
 sions instead of the blue glass. 
 
 A bulFs eye condenser of about four inches focus and 
 one and a half inches diameter, is indispensable. 
 It should be mounted as shown in the engraving 
 the base being made of lead to increase its stabi- 
 lity. 
 
 Having finished our description of the apparatus 
 required in Micro-photography, 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 micro-photography and 
 the instruments used for that purpose. 
 
HAND AND OTHER APPARATUS. 
 
 49 
 
 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. 
 
 5b 
 
 □ □ □ 
 
 U D A 
 
 Half way between A and C another post D is 
 fixed, and about seven feet from the floor a cross 
 beam between A and Dj 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 
 
50 
 
 HAND AND OTHER APPARATUS. 
 
 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 
 
 Fia. 22. 
 
HAND AND OTHER APPARATUS. 
 
 51 
 
 the waste pipe is attached^ which should pass out- 
 side both apartments if possible. 
 
 The top should be levelled and a sliding frame- 
 work^ 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 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 
 two holes in a large American meat tin, one on a 
 level with the flame, the other in the top. In the 
 latter a crooked chimney, the same as is used for a 
 magic lantern, is inserted; and in the former a piece 
 of ruby glass. 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. 
 
 E 2 
 
52 
 
 HAND AND OTHER APPARATUS. 
 
 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 OP 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. 26 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 thirty inches in diameter also 
 covered with a sleeve of black cloth. 
 
 The legs of the stand described in the previous 
 chapter are taken ofi*, plank no. 1 from which the 
 camera is detached folded beneath 2 and 8, 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 the 
 tube of the microscope, and the fine adjustment 
 screw, the milled head being removed, passed 
 
HAND AND OTHER APPARATUS. 
 
 53 
 
 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 OP OBJECTS. 
 
 CHAPTER IV. 
 
 Mounting and Preparation of Objects. 
 
 The present chapter might be considered superfluous 
 but for the fact that objects designed for Micro-pho- 
 tography require different treatment from those in- 
 tended for ordinary microscopic examination. In 
 addition to this it is right that those who have ob- 
 tained even a small amount of knowledge in practical 
 science should impart it to others^ and thus prevent 
 the disappointment and loss of time^ consequent on 
 a dearly bought experience. 
 
 The usual method of mounting microscopic speci- 
 mens^ is after preparing 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^ they are covered with a square or circle of 
 very thin glass^ which is fastened in position 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 we advocate, are 
 stated. We never expect its universal adoption, 
 because the old plan gives greater scope for artistic 
 display, and the manufacture of a kind of article 
 whose external appearance is more likely to catch the 
 eye of the public. 
 
 Our method is as follows. After the usual pre- 
 
MOUNTING AND PREPARATION OP OBJECTS. 55 
 
 paration, the specimen is placed on a square of thin 
 glass, (which may be fastened to an ordinary wooden 
 slip or not, we prefer 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 being adopted. 
 
 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 ; when using high 
 powers the condenser can be brought close to the 
 object. The examination of objects with oblique 
 light is facilitated, and their definition wonderfully 
 improved ; and even with direct light, markings can 
 be seen which defy resolution, if the object be 
 mounted in the usual way; and finally one slip alone 
 is necessary for the reception of any preparation re- 
 quiring examination. 
 
 Many objects, among which may be mentioned, 
 scales of moths and butterfiies, 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. 
 
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 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-tight 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, besides 
 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. 
 
68 MOUNTING AND PREPARATION OF OBJECTS. 
 
 Minute algoe 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 preventitive. 
 In 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 polycystinoe, 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 
 shakings for an hour. After standing the same 
 
MOUNTING AND PREPARATION OF OBJECTS. 59 
 
 length of time^ the fluid is removed without disturb- 
 ing 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 flxed in the slip and placed 
 on the stage of the microscope. A low power ob- 
 jective adjusted and the coarser uninteresting par- 
 ticles removed by a bristle from an old shaving 
 brushy fastened in a wooden handle. These bristles 
 are nearly always splits 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 
 may be transferred to another slide^ or if not^ dis- 
 carded. 
 
 It may be perceived that two methods are adopted^ 
 either the removal of the debris from the original 
 slide^ or the transferrence of the objects to a fresh 
 one^ the former being employed when the objects 
 are in excess of the debris^ the latter when the 
 opposite is the case. 
 
 Whichever plan is adopted^ a perfectly clean cover 
 glass being seized by a small pointed forceps^ a 
 drop of damar is placed near the edge of the side 
 farthest from the forceps^ this side is brought into 
 contact with the 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 
 
60 MOUNTING AND PREPARATION OF OBJECTS. 
 
 fluid goes in a wave from one side to tlie other^ carry- 
 ing all air bubbles before it. 
 
 Should air bubbles make their appearance, one 
 edge of the cover glass may be raised with a flne 
 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 faraminefera 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- 
 maceoe, they are closely allied to the polycystinoe 
 and are found in the same deposits. Beautiful forms 
 have been obtained from guano, infusorial earths, 
 sea dredgings, and stomachs of molluscae. They are 
 almost ubiquitous, every road and ditch being fllled 
 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 their collection, to leave the bottom mud un- 
 disturbed. 
 
 If desirable, they may be mounted in their original 
 condition in distilled water and camphor, but if the 
 silicious skeletons alone are required, the gelatinous 
 
MOUNTING AND PKEPARAITON OF OBJECTS. 
 
 G1 
 
 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. 
 
 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 flrst described, till 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 flve minutes, at 
 the end of that time its liquid contents are trans- 
 ferred to another tumbler which we shall call number 
 2, number 1 being fllled and shaken or stirred with 
 a wooden rod, after standing five minutes its fluid 
 contents are tranferred 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 
 
62 MOUNTING AND PREPARATION OF OBJECTS. 
 
 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 diatomaceae 
 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. 
 
 It has been recommended to mount diatomaceae 
 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 
 diatomaceae 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 coscinodesceae 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 ex- 
 periment is an explanation of their appearance. My 
 
MOUNTING AND PREPARATION OF OBJECTS. 63 
 
 belief is that they are hemispherical tuberosities, in 
 the diatomaceaa 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, 
 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 J px, 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 dis- 
 
64 MOUNTING AND PREPARATION OF OBJECTS. 
 
 tilled 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 i _p. c. solution of nitrate of silver may 
 be used in the same way^ and is extremely useful 
 for histological work especially the demonstration of 
 the endothelial linings of serous membranes. 
 
 These preparations are finally mounted in gly- 
 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 MulleFs fiuid, 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, 
 both sides being hollow ground. 
 
 Rutherford^s microtome consists of a brass table, 
 
MOUNTING AND PREPARATION OF OBJECTS. 65 
 
 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. 
 
 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 camekshair 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 wine 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 
 
 F 
 
66 MOUNTING AND PREPARATION OP OBJECTS. 
 
 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, 
 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-hundredth 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 
 
MOUNTING AND PREPARATION OF OBJECTS. 
 
 67 
 
 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 
 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 sec- 
 tions are fresh one drop is sufficient and the greater 
 part of the ammonia should be allowed to evaporate 
 
 F 2 
 
68 MOUNTING AND PREPARATION OF OBJECTS. 
 
 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. 
 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 consider- 
 ation. 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 disposal for the modification of the photo- 
 graphs 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, to 
 remove excess of colouring matter ; then 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, in 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 injuring the specimens need be appre- 
 
MOUNTING AND PREPARATION OP OBJECTS. 69 
 
 hended^ 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. 
 
 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 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 indebted 
 for the methods of rendering the organisms visible. 
 
 The following is a modification of the method 
 adopted for demonstrating the presence of the 
 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, grammes 2. 
 Pure Aniline, C.O. 3. 
 
 Alcohol sp. gr. *830, C.C. 20. 
 Distilled Water, C.C. 20. 
 
70 MOUNTING AND PREPARATION OP OBJECTS. 
 
 Dissolve the aniline in the spirit ; rub up the 
 magenta in a glass mortar; add the spirit gradually 
 while stirrings till all the colour is dissolved^ then 
 add the water slowly^ still stirrings and put in a 
 stoppered bottle. 
 
 II. Saturated solution of chrysoiden in dis- 
 tilled water, to which is added a crj^stal 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 fiame 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 
 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 
 or 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- 
 
MOUNTING AND PREPARATION OF OBJECTS. 71 
 
 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. 
 
 W e consider this an excellent modification of the 
 older methods, and although the photograph of the 
 bacillus anthracis in the frontispiece, was prepared 
 by Elrichs 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 parafin and wax. 
 
 Eocks, fossils, and bone when not softened, re- 
 quire entirely different treatment and considerable 
 skill before they arrive at a condition suitable for 
 microscopic investigation. A very slight sketch of 
 the plan adopted is here given to enable those who 
 do not possess a lapidary^s worksliop 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 
 
72 MOUNTING AND PREPARATION OF OBJECTS. 
 
 upper surface of tlie specimen is flattened with a 
 file^ next rubbed down on a perfectly flat Arkansas 
 stone ; and Anally polished with putty powder 
 spread on a leather pad; a simple microscope is 
 useful for watching the progress of the latter oper- 
 ation. When flnished this side is fastened on the 
 wood; the specimen flled 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 flnished 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 authori- 
 ties already mentioned, reminding them of the fact, 
 that violet and blue solutions are unsatisfactory for 
 staining or injecting sections intended for photo- 
 graphy, and also that only two methods of mounting^ 
 namely, in gum and glycerine, and dry, are re- 
 quired 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 mouthed 
 bottles, closed by glass caps, not corks or stoppers. 
 
MOUNTING AND PREPARATION OF OBJECTS. 
 
 /O 
 
 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 fiat 
 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. 
 
7i 
 
 PHOTOGRAPHIC PROCESSES. 
 
 CHAPTER V. 
 
 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 re- 
 sulting image and the fineness of the deposit give 
 a beauty to the results, hitherto unapproached by 
 any other method. Unfortunately on account of the 
 lengthened exposure required, its employment in 
 Micro-photography with high powers, is only possi- 
 ble 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 ap- 
 plicable. 
 
 The size of plate required for Micro-photography 
 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 
 
PHOTOGRAPHIC PROCESSES. 
 
 finally left soaking in a dish of water acidulated with 
 nitric acid. 
 
 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.j 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 : — 
 
 Eecrystalized 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 
 formulae are taken from Abney^s excellent treatise^ 
 to which the reader is referred for fuller informa- 
 tion on the subject. 
 
 The developing solutions are made as follows : — 
 
 Ferrous Sulphate, 40 grammes. 
 
 Glacial Acetic Acid, 30 to 40 c.c. 
 
 Alcohol, 2 s. 
 
 Water, 1 litre. 
 
76 
 
 PHOTOGRAPHIC PROCESSES. 
 
 The addition of a very minute quantity of gelatine 
 (dissolved in water)^ to this developer^ adds to the 
 density and fineness of the deposit a very desirable 
 result in Micro-photography. 
 
 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. 
 
 PyrogalHc Acid_, 4 grammes. 
 
 Citric Acid^ 4 to 8 grammes. 
 
 Water Distilled^ 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, ^ i. 
 
 Water, ^ vi. 
 
 After washing and drying, the plate may be var- 
 nished with any of the usual negative varnishes sold 
 by photographers. 
 
 The nitrate of silver bath should be exposed to the 
 light, strong sunlight if possible, when not in use. 
 
PHOTOGRAPHIC PROCESSES. 
 
 77 
 
 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. 
 
 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^ we clean it 
 as described^ taking care to avoid touching the sur- 
 face 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^ we pour the collodion on it, forming a pool 
 at the same corner, then fiowing it to the opposite, 
 then tq the left hand bottom corner, and finally after 
 completely covering the plate, off at the right hand 
 bottom corner. It being now held in a nearly ver- 
 tical position over the mouth of the collodion bottle, 
 a gentle rocking motion is imparted to it to prevent 
 its setting in ridges. When no longer tacky, which 
 is known by barely touching one of the bottom cor- 
 ners with the finger, it 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 superfiuous 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 all delay tends to injure the 
 plate. 
 
78 
 
 PHOTOGRAPHIC PROCESSES. 
 
 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 be- 
 ing still maintained The developer is poured into a 
 glass measure, and the plate covered with the solu- 
 tion 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 intensifler is poured over it, 
 while upon it a few drops of nitrate of silver is 
 placed in the measure; the intensifler is then poured 
 back, and the solution again poured 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 intensifler should be removed 
 and the plate again well washed. 
 
 We now immerse it in the hypo- solution, where it 
 should remain till all the unaltered salts are dissolved 
 away, this is known by the creaminess having dis- 
 
FHOTOGRAFHIC PROCESSES. 
 
 79 
 
 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 superfiuous fluid has drained away^ heat 
 is again applied ; the temperature being carried 
 much higher than at firsts 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 m 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 re- 
 sults as the wet, at least in our hands; they are, 
 however, suflBciently perfect for all practical pur- 
 poses, while the shortness of the exposure, cleanli- 
 ness of manipulation, and when purchased, the time 
 saved by the absence of any previous preparation, 
 almost counterbalance 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 possi- 
 ble should be allowed to reach them. The dark 
 slide should be carefully examined, and if of the 
 
80 
 
 PHOTOGRAPHIC PROCESSES. 
 
 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. 
 
 These plates can now be purchased so cheaply, 
 with the degree of sensitiveness as regards collodion 
 marked on each box, that we do not recommend the 
 amateur to attempt their manufacture. As a prac- 
 tical knowledge of their preparation may be an as- 
 sistance, a description is appended of a process 
 which has afforded excellent results. 
 
 The preparation of the following solutions may be 
 carried out in daylight. 
 
 No I. Bromide of Potassium, 43 grs. 
 
 Nelson’s Gelatine, 10 grs. 
 
 Distilled Water, 6 drachms. 
 
 One p. c. solution of hydrochloric acid, 
 10 minims. 
 
 This solution, is put aside, and we place in another 
 earthenware vessel — 
 
 No. II. 60 grains of special hard dry plate 
 gelatine, covering it with three or 
 four ounces of water. 
 
 Both are allowed to soak for twenty-four hours. 
 
 All the following manipulations are done in non- 
 actinic light. 
 
 No. III. Nitrate of Silver pure, 50 grs. 
 
 Distilled Water, 1 ounce. 
 
PHOTOGRAPHIC PROCESSES. 
 
 81 
 
 Nos. I. and III. are placed in hot water till their 
 temperature reaches 120° Fahr. No. I. is now gra- 
 dually added to no. Ill with constant stirring and 
 shakings no. Ill being placed in a bottle for the 
 purpose ; this process should take at least half an 
 hour. 
 
 No. IV. Iodide of Potassium, 4 grs. 
 
 Distilled Water, 2 drachms. 
 
 is now added, well shaken, and the whole boiled 
 for three quarters to one hour or more, according to 
 the sensitiveness required. No. II. from which all 
 the water has been removed being gradually added 
 with constant stirring during the boiling. 
 
 The emulsion while hot is poured into a bowl to 
 set, and when cold placed in three thicknesses of 
 coarse muslin, through the pores of which it is 
 wrung out into a deep earthenware vessel. It is 
 washed with six changes of water with frequent 
 stirring for one hour. The ringing and washing 
 being repeated, the emulsion is thrown upon a hair 
 sieve to drain, a process that will take at least an 
 hour. 
 
 We again dissolve it by heat, and after filtration 
 through cambric, neutralize it by the addition of a 
 few drops of a dilute solution of ammonia, (if great 
 sensitiveness is required). 
 
 Two drachms of alcohol are finally added and the 
 whole put away for a couple of days. 
 
 The most dijfficult parts of the process are now 
 before us, and the amateur will find his skill, in- 
 
 G 
 
82 
 
 PHOTOGRAPHIC PROCESSES. 
 
 genuity and patience severely taxed^ but practice 
 will enable bim soon to overcome tbe difficulties. 
 
 Having cleaned and prepared the plates in the 
 same way as when about to coat them with collo- 
 dion, we hold them in exactly the same manner, 
 that is, between the finger and thumb of the right 
 hand, or by a pneumatic holder. One is now warmed 
 and a little more than one drachm of the melted 
 emulsion poured on, spreading it evenly over the 
 surface with a swaying motion. When covered, 
 keeping it horizontal we place it on some perfectly 
 level surface, (such as a large sheet of plate glass), 
 to set. 
 
 A sufficient number being prepared and allowed 
 to set, they are placed in a drying closet. Of these 
 there are innumerable forms, the arrangement w^e 
 leave to the reader, simply stating that the plates 
 must be kept horizontal and as strong a current of 
 heated air as can be obtained, allowed to pass across 
 their surfaces. Every glimpse of actinic light being 
 excluded during the process. 
 
 For further details we recommend Abney^s Emul- 
 sion Processes. 
 
 The plates being prepared according to the fore- 
 going instructions, or better still procured from 
 some respectable firm, the following articles are ob- 
 tained. 
 
 A dish, preferably of ebonite, just large enough to 
 hold a quarter plate. 
 
 Another of the same material to hold four or a 
 larger number will be found very useful, as a great 
 
PHOTOaRAPHIC PROCESSES. 
 
 83 
 
 saving both of time and solution is effected if several 
 plates^ which have each received a similar exposure, 
 are developed at the same time. 
 
 A dish of earthenware to hold a saturated solution 
 of alum, another for a similar solution of mercuric 
 chloride, and one for hyposulphite 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 
 plates may be put aside, till another batch has been 
 exposed, or for an indefinite period, and developed 
 at leisure. 
 
 The following formulas 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 Micro-photography. 
 
 No. I. Liquor Ammonia, (*880) 3 ii. 
 
 Bromide of Ammonia, 3 H, 
 
 Distilled Water, ^ 20. 
 
 G 2 
 
84 
 
 PHOTOGRAPHIC PROCESSES. 
 
 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. 
 
 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 
 indicated ; 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, ^j. 
 
 Water, 
 
 are added to the developer. 
 
PHOTOGRAPHIC PROCESSES. 
 
 85 
 
 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 
 appears 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 i 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. 
 
 The developer is now poured ofi* 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 ordin- 
 ary 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, ^ ii. 
 
 Water, J x. 
 
 this solution should be fresh. 
 
 The plate is left in it for about five minutes after 
 
86 
 
 PHOTOGRAPHIC PROCESSES. 
 
 all creaminess has disappeared from the back of the 
 film^ and then 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 washings if the plate 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 Ammonia, 3 iii. 
 
 Water, J x. 
 
 which changes the white colour to a dense black. 
 
 By modifying the strength of this solution, any 
 density between that produced by the mercuric 
 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. 
 
 Yarnishing 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 : — 
 
PHOTOGRAPHIC PROCESSES, 
 
 87 
 
 No. I. Pyrogallic Acid, 3 i. 
 
 Glycerine, 3 i. 
 
 Methylated Alcohol, 3 vi. 
 
 Mix the glycerine and alcohol, then add the acid. 
 
 No. II. Bromide of Ammonia, gr. 7i. 
 
 Liquor Ammonia *880, 3 i 
 Glycerine, 3 i. 
 
 Distilled Water, 3 vi. 
 
 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 EdeFs 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 
 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, ^ vi. 
 
 Boiling Water, ^ xx. 
 
 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 
 
88 
 
 PHOTOGEAPHIC PROCESSES. 
 
 too acid, carbonate of potasb may be added to nutral- 
 ize the excess. The solution is now securely corked* 
 
 No. II. Sulphate of Iron, ^iii. 
 
 Distilled Water, ^ vi. 
 
 This solution is also securely corked. 
 
 Suppose we wish to develope a quarter plate; 
 four parts or 3 viii of no. I. solution are placed in a 
 glass measure, and one part or 3 ii of no. II. solu- 
 tion are added; not vice versa, or a precipitate of 
 oxalate of iron is formed which weakens the mix- 
 ture. 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 placed in the 
 vulcanite dish, the developer caused to wave to and 
 fro over its surface, till the required density is ob- 
 tained; the same precautions as those previously 
 mentioned with regard to fogging, etc., being ob- 
 served. 
 
 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. 
 
PHOTOGRAPHIC PROCESSES. 
 
 89 
 
 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 development, 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. 
 
90 
 
 ARRANGEMENT OF APPARATUS^ ETC. 
 
 CHAPTEE 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 Micro-photo- 
 graphy within the power of all. 
 
 It would be an impertinence as well as an injus- 
 tice to those from whom we have learned much, 
 if no mention was made of their work in these 
 pages. We have no intention of attempting a 
 classification on the ground of superiority or priority 
 but will mention what we know, in the order it 
 happens to present itself. 
 
 All microscopists are acquainted with the beauti- 
 ful photographs of N. Ehomboides, published by 
 Mr. Woodward in the Journal of the Microscopical 
 Society. The arrangement he adopted was very 
 similar to that employed with the eight immersion 
 by us, and with which the photograph of S. Gemma 
 was taken. He seems to have always used sunlight 
 and the wet process, which as a rule give results far 
 superior to those obtained by lamplight and dry 
 plates. 
 
ARRANGEMENT OF APPARATUS, ETC. 91 
 
 Few amateurs can ever produce anything equal to 
 his : first, because every assistance was given by a 
 generous government, who placed all instruments 
 likely to aid in the production of perfect results at 
 his disposal : secondly, a peculiar training is re- 
 quired for the attainment of that skill, of which only 
 a few are capable, but which must be acquired before 
 any progress can be made in a special art, when it 
 arrives at that perfection which brings it just within 
 the borderland of science. 
 
 We can therefore hardly blame those who, perhaps 
 more enlightened than ourselves, perceive, that even 
 if we had the opportunities of Mr. Woodward, we 
 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. We do not 
 recommend the plan then adopted. 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 us a few good hints, and 
 we regret he has not told us more. The impression 
 left, after a 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 ex- 
 perience, as no objectives we possess give as good 
 
02 ARRANGEMENT OF APPARATUS^ ETC. 
 
 results as the eighth and one twenty-fifth of Messrs. 
 Powell and Leland. This we think was 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 I think 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 
 the others. 
 
 Good results can never be obtained unless we are 
 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 dijfferent 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- 
 
ARRANGEMENT OF APPARATUS, ETC. 93 
 
 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. 
 
 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 reminds us of a 
 person trying 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 refiect 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 of our Parisian 
 brethren are possible, as according to M. Tisandier 
 the highest magnification was eight hundred dia- 
 metres. 
 
 It has been the custom with some microscopists 
 
94 ARRANGEMENT OF APPARATUS^ ETC. 
 
 to place a concave^ and we believe sometimes a con- 
 vex lens^ between the objective and focussing screen, 
 when increased magnification is required. 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 
 Micro-photography, as the failures consequent on 
 allowing the eyepiece to remain in its usual position. 
 
 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 diiSerent method of illumination, and 
 arrangement of apparatus with each objective, in 
 order to illustrate the employment of different 
 
ARRANGEMENT OF APPARATUS^ ETC. 95 
 
 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 employ- 
 ment 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 
 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 subsequent enlargement to 50000 
 before the finest details become visible to the naked 
 eye. 
 
 Swanks 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 ; 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. 
 
96 
 
 ARRANGEMENT OF APPARATUS^ ETC. 
 
 The only serious objections to the use of Swanks 
 lamp for Micro-photography^ 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 electro- motors, placing 
 them beyond the reach of private individuals, in 
 fact, until electricity is supplied by accumulators or 
 from a central station parafin 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. 
 
 Grovers or Bunsen^s elements are the best form of 
 battery ; bichromate cells from their inconstancy be- 
 ing a continual source of trouble. 
 
 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 fiat hook 
 capable of slipping into an arrangement on the 
 pinion block of the stand, is fastened to the up- 
 right back of both. 
 
 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. 
 
 Lime light gives excellent results, but the danger 
 and trouble connected with its use, along with the 
 impossibility of moving it about and centering, pre- 
 vent its extensive employment. 
 
ARRANGEMENT OF APPARATUS^ ETC. 97 
 
 A minute intensely brilliant spot of lights requir- 
 ing no care, free from danger, and capable of being 
 placed in any position, is required by those who can- 
 not afford steam power and electro-motors. Up to 
 the present nothing fulfils these requirements as well 
 as a parafin lamp with a bulhs 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 neisrhbours, (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 diflBcult. We 
 shall not depart 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; we therefore recommend a 
 perusal of the following chapters, 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 us to repeat any par- 
 ticular plan previously adopted, and from a com- 
 
 H 
 
98 
 
 AEEANGEMENT OF APPAEATUS^ ETC. 
 
 parison of failures and successes to eliminate the 
 causes producing the former. 
 
 The following is an example of the form of entry 
 adopted by us : 
 
 Apparatus Horizontal, 
 
 I. Object^ coscinodiscu from guano^ mounted in 
 
 balsam and bensol equal parts. 
 
 II. Objective^ quarter inch^ corrected 10° for C07er 
 
 glass. 
 
 III. Condenser^ two French combinations, together 
 about half an inch in focal length, and distant yq 
 of an inch from the object. 
 
 IV. Aperture of diaphragm quarter of an inch in 
 diameter. 
 
 V. Lamp 13 inches from stage, edge of flame to- 
 
 wards the object. 
 
 VI. BulFs 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 
 bulFs 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. 
 
ARRANGEMENT OF APPARATUS, ETC. 
 
 99 
 
 Fig. 24 . 
 
 H 2 
 
100 ARRANGEMENT OP APPARATUS^ ETC. 
 
 XIII. Eesult^ completely successful^ or over or un- 
 der-exposed as case may be^ in this case very 
 much over-exposed. 
 
 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 
 fluids as an illustration of the method to be adopted 
 under these circumstances. 
 
 The microscope being placed on the platform^ the 
 divisions^ nos. I and 2^ of the stand are rigidly fas- 
 tened 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. their pointed extremities resting on the 
 ground^ maintain this end of the stand in the per- 
 pendicular 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 wisb to use, in this case the one inch, is 
 adapted. 
 
 The substage apparatus, with its condenser and join 
 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. 
 
ARRANGEMENT OF APPARATUS, ETC. 101 
 
 The largest hole of the diaphragm is turned till it 
 occupies a position approximately in the optic axis of 
 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. 
 
 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 suflS.ciently 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- 
 
102 ARRANGEMENT OF APPARATUS^ ETC. 
 
 scope) ^ and centered 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 
 bulFs eye condenser is placed from i to 2 inches 
 in front of and from the flame of the lamp^ with 
 its convex side facing the microscope^ and cen- 
 tred 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 fleld 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 can- 
 not 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 re- 
 placed, 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 bulfls eye condenser are ob- 
 served through the microscope, and all made 
 
ARRANGEMENT OF APPARATUS^ ETC. 103 
 
 coincident with its optic axis. Perfect accuracy of 
 adjustment in this respect^ is one of the greatest 
 aids to the production of good and truthful nega- 
 tives. 
 
 The object^ chosen by the rules laid down in the 
 following pages, is placed on the stage and brought 
 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 any 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 means 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 
 
104 ARRANGEMENT OP APPARATUS^ ETC. 
 
 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 
 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 at- 
 taching 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 conical bellows is covered with black 
 velvet, as well as its interior; it will then slip 
 easily into that of the microscope, and the en- 
 trance of all light rays will be prevented. 
 
 The image of the object is now roughly focussed on 
 the ground glass ; the desired magnification obtained 
 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 pro- 
 portion 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 some- 
 times impossible, as its thickness prevents the use of 
 lenses of sufiicient power to magnify the lateral 
 dimensions, while their penetration defines those 
 parts lying on different planes. 
 
ARRANGEMENT OF APPARATUS^ ETC. 105 
 
 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 
 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 or sulphate of copper cell placed be- 
 tween the bulFs 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 in- 
 
106 ARRANGEMENT OP APPARATUS, ETC. 
 
 tensity 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 
 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 and cover can be placed during the 
 removal of the desired number from it. As we are 
 now using a double dry slide, two are, removed, 
 and held one above the other by their edges be- 
 tween the thumb and finger of the left hand, with 
 the right we replace the cover on the cardboard box 
 containing the remaining plates, 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 refiecting 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 
 
ARRANGEMENT OF APPARATUS, ETC. 107 
 
 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- 
 tening the plates in position, great care must be 
 taken to avoid touching them with the fingers, dur- 
 ing tbe process; as should this happen an indelible 
 stain will make its appearance at that spot during 
 the subsequent development. Having fastened 
 them 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 ap- 
 paratus are arranged. 
 
 The right hand side of the cloth hanging over the 
 apparatus is 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 micro- 
 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 centering 
 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- 
 
108 ARRANGEMENT OF APPARATUS^ ETC. 
 
 posed plate next the person in the breast pocket of 
 the coat ; every precaution being taken as before^ to 
 prevent displacement. 
 
 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 as be- 
 fore, 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 
 
ARRANGEMENT OF APPARATUS, ETC. 
 
 109 
 
 of a ring B, fig. 25, is substituted for the tube fitting 
 into the substage aperture of the microscope. About 
 
 Fig. 25. 
 
 an eighth of an inch from its upper edge, we place a 
 cardboard disc with a slit 0 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 bulFs 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- 
 
ilO 
 
 AKRANGEMExMT OF APPARATUS^ ETC. 
 
 Fig. 26. 
 
 O 
 
 ficial light, and which re- 
 quire high powers for their 
 resolution. We shall con- 
 fine ourselves to the J inch 
 objective. The apparatus is 
 — considered as still remaining 
 in the position adopted in 
 our first experiment. 
 
 The lamp stands and bulFs 
 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 short- 
 ened to allow of the up- 
 right division no. 1 and no. 
 2 assuming the horizontal 
 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 divisions of the 
 plank perfectly rigid, and 
 in a straight line with each 
 other. 
 
 The camera and sulphate 
 ^ of copper cell are removed ; 
 Swanks incandescent lamp 
 substituted for the parafin. 
 
 
ARRANGEMENT OF APPARATUS, ETC. Ill 
 
 the edges of the carbon filament being turned to- 
 wards the microscope. 
 
 Connection is now made with the source from 
 which the electricity is supplied. We shall here 
 only mention that electro motors 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 Groves^ 
 battery will be found sufficient for a full sized Swanks 
 lamp We have had no experience of the smaller 
 forms recently made, but from a consideration of the 
 character of the light required, we have no hesitation 
 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. Some 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 perpendicular; 
 the microscope stage accurately levelled, and sup- 
 ported in that position by lengthening the camera legs. 
 
112 ARRANGEMENT OP APPARATUS^ ETC. 
 
 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 bulbs 
 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 
 centered 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- 
 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 centering 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. 
 
ARRANGEMENT OF APPARATUS, ETC. 113 
 
 The lamp and bull’s eye being centered, the per- 
 forated disc is brought into focus with the quarter 
 inch objective and also centred. This must be done 
 by the centering 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 0. If as at C it shows 
 that either the lamp or bull’s eye condenser is en- 
 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 centered, 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 
 
 I 
 
114 ARRANGEMENT OF APPARATUS^ ETC. 
 
 position of its reflected image in tlie 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 bulFs eye is again brought 
 into view and centered. If the sun-light is not yet 
 perfect or if it appears as at the lamp is moved 
 more to the left or the right according to the posi- 
 tion of the bright ray proceeding from the aperture 
 of the diaphragm. These manipulations are greatly 
 facilitated by remembering the relation the bright ray 
 bears to the position of the lamp and bulFs eye ; for, 
 when considered as pointing from the periphery to the 
 central hole^ it indicates directly the position of the 
 lamp and bulFs eye with regard to the optic axis of 
 the instrument. At the same time the distance of 
 the bulFs 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 centering 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- 
 erent planes, we replace the pin hole cap, which, by 
 the by, should itself be accurately centred, and if not, 
 rejected, and another tried. With the objective cor- 
 rectedfor uncovered^ (the ultimate correction for thick- 
 
ARRANGEMENT OF APPARATUS^ ETC. 115 
 
 ness of cover glass being made according to the 
 method described 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 
 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 bulFs 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. 
 
 The proper quantity, and intensity, of illumination 
 obtained, we proceed to place the camera in position, 
 observing the precautions mentioned when describ- 
 ing a similar process with the one inch. 
 
 i2 
 
116 ARRANGEMENT OF APPARATUS, ETC. 
 
 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 
 dry process, ten times the precautions are necessary 
 here, as the slightest touch will infallibly 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 sufiiciently 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 
 
ARRANGEMENT OF APPARATUS, ETC. 117 
 
 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 centering 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, 
 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 
 of 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, even when an ordinary parafin 
 lamp is the source of illumination, those 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- 
 
118 ARRANGEMENT OE APPARATUS^ ETC. 
 
 vented^ by pasting several folds of yellow or black 
 paper^ (tbe latter being preferable) over both interior 
 and exterior. Tbe edges of tbe sleeves where they 
 join tbe partition are farther 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 adjust- 
 ment, 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- 
 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 dinsion 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 
 c ntres 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- 
 pc^r places. 
 
PHOTOGRAPHIC PROCESSES. 
 
 119 
 
 Fig. 28 . 
 
 The microscope lamp or Swanks electric lights the 
 former being preferred with 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 centering 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 
 
120 ARRANGEMENT OF APPARATUS^ ETC. 
 
 sleeves were only mentioned on account of being 
 easily made^ and their completely excluding actinic 
 light. 
 
 Whichever method is adopted^ before centering 
 with the low power objective, we may substitute the 
 dry front of the 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 
 cardboard tube fitting round the outside of the two 
 French lenses. 
 
 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 piano 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 centering as in the last 
 method. 
 
 The object is placed on the stage of the micro- 
 scope: it should be remembered that when using high 
 power such as the one-eighth imm. it is better to 
 select a flat thin object, as the angular aperture and 
 
ARRANGEMENT OF APPARATUS^ ETC. 
 
 magnifying power are too great to allow of a large 
 amount of penetration. Tlie part we wish to photo- 
 graph being chosen^ the low power is removed. 
 
 The i objective^ if a water immersion^ may be 
 wetted with either water or glycerine. The former 
 is better as far as definition is concerned^ bub the lat- 
 ter on account of not evaporatings allows of a greater 
 length of time for arrangement of apparatus^ and a 
 more protracted exposure. 
 
 The proper focus and correction for cover glass 
 obtaineds 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 stands and placed so that an 
 image of the object may be properly received on 
 the focussing screen. 
 
122 AERANGEMENT OF APPARATUS^ ETC. 
 
 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 ex- 
 ceeds three feet. It should be also remembered that 
 the actinic power of the light decreases as the square 
 of the distance of the plate from the source of illu- 
 mination, and the duration of the exposure varies in- 
 versely 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 ori- 
 fice 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 con- 
 venient 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 sensitive 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- 
 
ARRANGEMENT OF APPARATUS^ ETC. 123 
 
 trance of actinic light. The subsequent manipula- 
 tions are identical with those already described. 
 
 The following notes of the manipulations employed 
 for the production of the Negative^ from which the 
 print of the Bacillus Authacis 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 Anthacis 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 inch from object. Aperture of slid- 
 ing 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. BulFs-eye eleven inches from stage of micro- 
 scope. 
 
 6. Lamp one inch from bulls eye paraflBn and edge 
 of wick. 
 
 7. Ground glass of camera twenty- four inches 
 from object. 
 
 8. Usual focuss. 
 
 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 
 p. c. bromide solution added to one ounce. 
 
 13. Result shown in photo. 
 
124 ARRANGEMENT OF APPARATUS^ ETC. 
 
 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 plane 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 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 stands from which the lamp and bulbs 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 
 a position coincident with the optic axis of the 
 microscope. 
 
 The heliostat should be arranged and left work- 
 ing for a quarter of an hour previous to the arrange- 
 ment of the apparatus for photography. This en- 
 ables us to test the accuracy of its adjustments^ and 
 allows the action of the first wheel full time to be 
 communicated 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 Swanks incandescent lamp. 
 
ARRANGEMENT OF APPARATUS^ ETC. 125 
 
 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 if 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. 
 
 In conclusion we must caution our readers against 
 expecting success at the first trials unless they have 
 had some previous experience in photography. On 
 this account we recommend the production of nega- 
 tives with an ordinary camera and lens before at- 
 tempting micro-photography. 
 
 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. When in position the mi- 
 croscope and Camera should be covered with a dark 
 cloth before the substitution of the plate carrier for 
 the ground glass and subsequent exposure. Every 
 means must be adopted to prevent the entrance of 
 actinic light into the dark room, and while placing 
 the sensitised plate in the carrier as well as during 
 developement, 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. 
 
126 ARRANGEMENT OF APPARATUS^ ETC. 
 
 Before concluding our remarks on this part of 
 of the subject^ we would impress upon the photo- 
 grapher the necessity for determining the magni- 
 fying power in every case. This may be done as 
 follows : 
 
 After removal of the carrier containing the sen- 
 sitised plate from the camera^ an ordinary micro- 
 meter slide divided into one-hundreths and one-thou- 
 sandths of an inch is substituted for the object. Its 
 image is focussed on the ground glass_, and the divi- 
 sion measured with small rule. For example if one 
 of the divisions corresponding to one-hundreth of an 
 inch on the micrometer measures two inches on the 
 ground glass^ the magnification equals two hundred 
 diameters. 
 
 It is not necessary to adopt this method in every 
 case^ for^ if the magnifying power of a certain objec- 
 tive is known when the image formed by it is at two 
 separate distances from any object^ the magnifying 
 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 subsequent occa- 
 sion we are photographing with the same lens^ and 
 the screw is twenty-four inches from the object^ the 
 magnifying power would be one hundred and fifty 
 diameters. 
 
 It is sometimes difficult to tell if the sun illu- 
 minates the object equally when a heliostat is not 
 
ARRANGEMENT OF APPARATUS, ETC. 127 
 
 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. 
 
128 
 
 DEFECTS IN NEGATIVES. 
 
 CHAPTER VII. 
 
 Defects in Negatives^ Their Causes and Cure. 
 
 Before attempting the production of negatives 
 with the microscope^ we recommend the beginner 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, how- 
 ever, 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 Micro-photographer in addition to a know- 
 ledge of the same kind, must recognise and allow 
 for the chemical changes produced in different sen- 
 sitive compounds by light ; which is itself modified 
 by agencies beyond the perception of unaided vision. 
 
 Many of these changes and agencies have only 
 
DEFECTS IN NEGATIVES. 
 
 129 
 
 lately been discovered. 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. 
 
 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 their cause, and the remedies for them. 
 
 Inaccuracy in the preparation of solutions and want 
 of manipulative skill, are the principal difiSiculties 
 besetting a beginner. It will only be necessary 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 
 allow a trace of ammonia to be present where the 
 wet plate process is employed. 
 
 Among errors of manipulation may be classed 
 
 K 
 
130 
 
 DEFECTS IN NEGATIVES. 
 
 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, 
 and its accurate closure ascertained, before the plate 
 is consigned to it ; and afterwards covered with a 
 dark cloth. 
 
DEFECTS IN NEGATIVES. 
 
 13] 
 
 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 bichromate of 
 potash, care must be taken that the clearing off is 
 not carried too far else weakness may be produced. 
 Another kind of fog may occur when using wet 
 plates, owing to alkalinity of the bath. A similar con- 
 dition of the oxalate of potash solution produces a 
 whitish deposit on the film of dry plates, it is there- 
 fore advisable to add a little sulphuric acid to this 
 solution after its complete neutralisation. 
 
 Pin-holes are due to dust on the plate. A soft large 
 cameFs hair brush specially kept for the purpose 
 should always be passed over dry plates before plac- 
 ing them in the dark slide. Black markings are 
 generally caused by the plate coming in contact with 
 the fingers, or some unclean surface, and insufficient 
 drainage before placing it in the carrier. 
 
 Frilling is very liable to occur in hot weather with 
 
 K 2 
 
132 
 
 DEFECTS IN NEGATIVES. 
 
 gelatino bromide plates. It commences by a blister- 
 ing of tbe 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. 
 
 Eeflection 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 micro- photo- 
 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 
 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 of the appearance of microscopic objects by 
 engravings. All micro -photographs should be trans- 
 
DEFECTS IN NEGATIVES. 
 
 133 
 
 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 diatomaceae 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 fiooding the plate 
 with a weak solution of perchloride of iron, and when 
 the required transparency is obtained, washing the 
 negative rapidly in fiowing 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 : 
 
 I. A weak bath solution, or too strong a deve- 
 loper 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 
 
134 
 
 DEFECTS IN NEGATIVES. 
 
 disturb the corrections of the object glass^ so that a 
 weak negative is the result. 
 
 IV. 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. 
 
 VI. Specimens stained with logwood or blue pig- 
 ments are unsuitable for micro-photography. 
 
 Objects of a yellow colour or great delicacy give 
 the best results with wet plates. Those ot 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, 
 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 
 
DEFECTS IN NEGATIVES. 
 
 135 
 
 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 chaacter 
 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, 
 and beyond the scope of a work of this description. 
 We shall therefore content ourselves with the indi- 
 cations for their employment already given. 
 
 The amount of intensification required will be 
 found to vary directly as the magnifying power of the 
 objective. 
 
 To sam up. The kind of plate to be employed, 
 depends on the character of the object, nature 
 and intensity of the illumination, and magnifying 
 power of objective. The development depends on 
 the purpose for which the resulting negative is 
 intended, the character of the object, and the kind 
 of plate. 
 
 It is often impossible to obtain a sufficiently dense 
 
136 
 
 DEFECTS IN NEGATIVES. 
 
 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 illu- 
 mination. 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 negative. 
 
 This simple enumeration will be suflScient to en- 
 able any intelligent person to avoid the defects 
 mentioned, or to apply the proper remedies for them. 
 For fuller imformation we refer our readers to any 
 of the numerous text books on this subject. 
 
THE TRODUCTION OF POSITIVES^ ETC. 
 
 137 
 
 CHAPTER VIII. 
 
 The Production op Positives etc. 
 
 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. 
 
 In addition to a few dishes^ a printing frame is 
 the only apparatus necessary. It 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 origi- 
 nal 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 re- 
 quired, 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 
 
138 THE PRODUCTION OF POSITIVES, ETC. 
 
 negative, while one possessing the qualities before 
 recommended will require a subdued light and two 
 or three hours exposure for the differentiation of the 
 markings and the proper reproduction 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 uses 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, gr. iv. 
 
 Sodium Acetate, gr. cviii. 
 
 Distilled water, ^ x. 
 
 This solution is best made with boiling distilled 
 water if immediately required for use. We prefer to 
 make it the day before. 
 
 A large flat dish will be found the most con- 
 venient 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, ETC. 139 
 
 brown verging on purple gives the most artistic ap- 
 pearance when finished. Should 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 Hyposluphite, ^ is. 
 
 Liq. Ammon. Fort, ui iii. 
 
 W ater, ^ ix. 
 
 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 these 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 ap- 
 pearance maybe much improved, bypassing through 
 
140 THE PRODUCTION OF POSITIVES, ETC. 
 
 a rolling 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 suit- 
 able for amateurs than the process just described, 
 as the tedious washings between the application 
 of the difierent solutions is avoided, and the develop- 
 ment itself reduced to the simplest form by the use 
 of the ferrous oxalate process, employed for dry 
 plates. The results obtained by the employment of 
 Swanks opal plates, leave nothing to be desired as 
 far as artistic display and ornamental work is con- 
 cerned. Many of the most beautiful prints of poly- 
 cystinas 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 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^ ETC. 141 
 
 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, the paper is 
 preferable, not only on account of its superior dis- 
 tinctness, 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 de- 
 scent prevents the possibility of any air bubbles re- 
 maining 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. 
 
142 THE PRODUCTION OF POSITIVES^ ETC. 
 
 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. 
 
 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 
 results 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 evident from this that no rule can be given 
 for exposure when daylight is employed, and even 
 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 
 
THE PRODUCTION OF POSITIVES^ ETC. 143 
 
 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, 
 sufl&cient 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. 
 
 The ordinary quarter plate negative is the most 
 convenient to copy from, especially for enlarging, 
 because the pictures produced by a combination 
 covering 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- 
 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 
 
144 THE PEODUCTION OP POSITIVES, ETC. 
 
 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 im- 
 proved, 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. 
 
 The most accurate focus, with the full aperture of 
 the objective is obtained; a stop of sufficient size in- 
 troduced, and the camera covered with a black cloth. 
 A great improvement will be effected, and the en- 
 trance 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 re- 
 moval of the cap on exposure. 
 
 Before describing the remaining manipulations it 
 is necessary to remind the operator, that the aper- 
 ture of all stops or diaphragms are best named in 
 terms expressing their relation to the focal length 
 
THE PRODUCTION OF POSITIVES, ETC. 145 
 
 of the objective. As when the aperture is half 
 an 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 = 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 recommend 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 
 sufl&cient 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 suflScient 
 quantity of ferrous oxalate developer, in the propor- 
 tion of five parts of a saturated solution of oxalate of 
 potash to one of ferrous sulphate (care being taken 
 
 L 
 
146 THE PRODUCTION OF POSITIVES^ ETC. 
 
 to add the 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-ac- 
 tinic 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 
 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- 
 
THE PRODUCTION OF POSITIVES^ ETC. 147 
 
 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 metliod 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 conbination, 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 conbination in ordinary photo- 
 grahy, must be placed in close apposition, and the 
 ring which separates them placed in the cell before 
 them. 
 
 Every part of the negative not required for re- 
 production should be masked, and all extraneous 
 light cut off. 
 
148 THE PRODUCTION OF POSITIVES^ ETC. 
 
 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 descHbed, 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. 
 
 An ordinary magic lantern, the condensers of 
 which are not less than four and a half inches in 
 diameter, answers excellently when placed in the 
 recess of the dark room. The entrance of actinic 
 light being prevented by fastening the sleeve in- 
 tended for the microscope over the nozzle 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. 
 
 Many artists prefer the delicate tone of the ordin- 
 ary silver print to that produced on a gelatino-bro- 
 mide surface. All that is then necessary is the 
 production of a positive on paper, if a negative by 
 
THE PRODUCTION OF POSITIVES, ETC. 149 
 
 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 micro- photographic negative, it is 
 quite possible to change it completely without alter- 
 ing the essentials of the structure depicted on ifc, 
 thus rendering possible the production of a print 
 from what would otherwise be 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 produc- 
 tion 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. 
 
 Peeseevative 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 one 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 Tubeeculosis. — 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 comparitively easy. 
 
APPENDIX. 
 
 151 
 
 Binocular Photography. — Stereoscopic photo- 
 graphs may be produced by Stephenson^s Binocular 
 arrangement^ Polycystina3 and Discoidal 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 light is not the same on 
 both plates, and the plates themselves require to be 
 placed at an inconvenient angle. 
 
INDEX. 
 
 Abbe Prof, 20 
 Abney Captain, 75 — 91 
 Absolute Alcohol, 6S 
 Absorption, 10 
 Achromatism, 11 
 Achromatic Condenser, 28 
 Achromatic Object Glass, 15 
 Actinic Focus, 14 
 Actinic Light, (prevention of), 
 51 
 
 Adjustment Fine, 25 
 Algae, 58 
 
 Aperture Angular, 19 
 Aperture Numerical, 20 
 Apparatus, 48 
 Artificial Light, 38, 95 
 Association, Eff’ects of, 22 
 
 Bacilli, 69 
 
 Balsam and Benzol, 57 
 Bath Sensitizing, 75 
 Battery, 96 
 Beale, Dr., 68 
 Black Velvet Backing, 106 
 Blue Glass, 32, 40 
 Boxwood Slips, 55 
 Bull’s Eye, 40, 48 
 
 Camera, 41 
 Carbon Bisulphide, 62 
 Carmine, 67 
 Carpenter, Dr., 58 
 Centering, 101 
 
 Cell for Sulphate of Copper, 47 
 Chloride of Gold, 63 
 Chromatic Aberration, 10 
 Cleaning Plates, 74 
 Coarse Adju.stment, 25 
 Collodion, 75 
 Conjugate Foci, 6 
 Compound Microscope, 24 
 Concave Lenses, 5 
 
 Condensers, 28 
 Convex Lenses, 5 
 Copying Camera, 143 
 Copper Sulphate, 47 
 Coscinodisci, 62 
 Cover Glass Correction, 17 
 
 Dallinger, Dr., 39 
 Damar, 57 
 
 Dark Ground Illumination, 109 
 Dark Boom, 48 
 Density to Increase, 135 
 Developers, 75, 83 
 Diaphragm, 28 
 Diatomaceae, 60 
 Diffraction, 20 
 Drying Plates, 82 
 Dry Mounting Objects, 55 
 Dry Plates, 80 
 
 Electricity, 38, 95 
 Emulsion, 80 
 Endothelium, 64 
 Enlarging, 14 
 Exposure, 107 
 Eye, 8 
 Eyepiece, 24 
 
 Ferrous Oxalate, 37 
 Pine Adjustment, 25 
 Fixing Solution, 78 
 Focal Adjustment, 104 
 Foci, 6 
 
 Focussing Rod, 47 
 Focussing Glass, 42 
 Focussing Screen, 41 
 Fog, 130 
 Foraminifera, 60 
 Frames Printing, 137 
 Freezing Microtome, 65 
 French Micro-photography, 92 
 
Ib4 
 
 INDEX, 
 
 Gelatine Emulsion, 80 
 Gibbes, Dr., 69 
 Glass Slides, 73 
 Glass Thin, 73 
 Glycerine and Gum, 68, 72 
 Gold Trichloride, 63 
 
 Heliostat, 33 
 
 Huyghenian Eyepiece, 24 
 Hyposulphite of Soda, 78 
 
 Immersion Principle, 19 
 Illumination, 82 
 Incandescent Lamp, 38, 95 
 Intensifying, 76, 86 
 Insect Mounting, 57 
 
 Latitude to Find, 36 
 Lamp for Dark Room, 51 
 Lamp, Parafin, 39 
 Lantern Enlarging, 148 
 Lenses, 5 
 
 Magnifying Power, 14 
 Markings on Diatoms, 62 
 Media Mounting, 57, 58 
 Microscope, 25 
 Microtome, 64 
 Mounting Objects, 55 
 Mounting Prints, 139 
 Morgan’s Paper, 142 
 Muller’s Fluid, 64 
 
 Negative, Properties of, 132 
 N eutral Oxalate, 87 
 
 Oblique Illumination, 109 
 Object Glass, 15 
 Oil Immersion Condenser, 30 
 Opaque Objects Photography, 108 
 Overexposure, 133 
 
 Paper Sensitized, 137 
 Patent Plate Glass, 41 
 Penetration, 16 
 Petzval Portrait Lenses, 143 
 
 Photographing with 1 inch, 100 
 Photographing Objects in Fluid, 
 ]00, 110 
 
 Photographing with \ inch, 110 
 Photographing with | inch, 121 
 Photographing with -y’g inch, 125 
 Photographing Horizontally, 118 
 Potash Bichromate, 64 
 Potash Oxalate, 87 
 Principal Focus, 6 
 Printing, 137 
 
 Production of Positives, 137 
 Pure Chemicals, 129 
 
 Radiation, 132 
 Real foci, 6 
 Reflection, 4 
 Refraction, 4 
 
 Rutherford’s Microtome, 64 
 
 Scales of Moths, 55 
 Section Cutting, 64 
 Silver Nitrate, 75 
 Sodium Sulphate, 64 
 Sodium Hyposulphite, 78 
 Spectrum, 11 
 Staining, 67 
 Stage of Microscope, 26 
 Stand for Apparatus, 43 
 Substage, 32 
 Sun Light, 32 
 Swan’s Lamp, 111 
 
 Testing Solutions, 37 
 Thin Glass, 73 
 Toning, 138 
 
 Undulatory Theory, 4 
 
 Varnishing, 79 
 Virtual Foci, 6 and 7* 
 
 Visual and Chemical Foci, 14 
 
 Wet Process, 75 
 Wenham Object Glass, 15 
 Window of Dark Room, 50 
 
 ERRATUM. 
 
 Pages 42—53, folio lines, for Hand &c., read Stand. 
 
ipcWl 
 
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