JLNE, 1912. 



KNOWLEDGE. 



PHOTOGRAPHY WITH A 

 Mir KOSCOPK.— Photography from 

 quite an early period of its existence 

 appears to have been employed to 

 secure images of microscopic objects, 

 for we find it stated that Wedgewood 

 and Davey in 1802 obtained photo- 

 graphic records by means of the 

 solar microscope, employing paper 

 rendered sensitive to light by treat- 

 ment with a solution of silver nitrate. 

 They found that images of small 

 objects could be produced without 

 difficulty in this way. Thus, among 

 the very first experiments in photo- 

 graphy was the aid of the microscope 

 sought as a means for forming images 

 intended to be photograplied. 

 -Although so early in the field, photo- 

 graphy with the microscope (photo- 

 micrography) can scarcely lay claim 

 to have been the most successful 

 of the many branches of 

 photography. This may be traced 

 to several causes. In the first 

 place a inicroscope is primaril\- 

 intended for use as an instrument 

 for visual observations only, there- 

 fore its objectives and eyepieces 

 have naturally been constructed to 

 gi\e the best results when employed 

 in this manner. Such being the 

 case those rays which are of 

 such prime importance in photo- 

 graphy are left outstanding, or in 

 other words, are not united at the 

 same focus as they are in the 

 case of a photographic objective. 

 with the result that a picture. 

 sharp visually, would be wanting in 

 definition when photographed, owing 

 to chromatic difierences of 

 focus. I'urther, the great 

 majority of objects have to 

 be illuminated by transmitted. 

 instead of reflected light, and 

 the shortness of focus of the 

 lenses, together with their 

 smallness, renders the proper 

 illumination of the objects 

 anything but an easy matter, 

 and this, together with the 

 want of sharpness over the 

 entire field " with any e.xcept 

 low powers." has contributed 

 to make photo - micrography 

 less successful than is ordinary 

 photography. So nuich atten- 

 tion, however, has been given 

 to the subject of late years, 

 that, what with the great 

 improvements made in the con- 

 struction of objectives, and the 

 use of orthochromatic plates. 

 and suitable light filters, excellent 

 results can now be obtained 

 with ordinary achromatic objec- 

 tives, while the apochromats and 

 projection oculars place in the 

 hands of those, not specially 

 skilled, a means of obtaining 

 good results with comparative 

 ease. The problem of illumina- 

 tion, too, has received so ijiuch 

 attention from skilled micro- 

 scopists, that many of the 

 former troubles no longer exist. 





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FlGUKE 2h'). A Rose Beetle. X 16 diameters. 



Photographed with a i^eiss Planar series I A 



No. 5. 100 mm. focus stopped down to F16. 



FiGl-KE -'70. The Proboscis of a Blow Fly. X 

 diameters. Photographed with .Messrs. James S\ 

 and Son's 1-inch objective without eyepiece. 



PHOTO - MICROGRAPHS AT 

 A LOW MAGNIFICAIION.— 

 Many large transparent objects, 

 insects, and so on, require to be 

 photographed so as to show the 

 entire specimen. These must be 

 taken at a low n-.agnification. and an 

 objective employed which has a field 

 sufficiently large to include the whole 

 of the object, and in order to ensure 

 successful results attention must be 

 given to obtaining as_ uniform a 

 lighting as possible. The illustration 

 (Figure 269) is from an object photo- 

 graphed under the conditions neces- 

 sary to include the whole of the 

 specimen, and was taken with a 

 2eiss planar of one-hundred milli- 

 metres focus. This objective was 

 screwed into the end of a conical 

 tube and attached to the body of a 

 2eiss photo-niicrographic stand, from 

 which the draw tube had been re- 

 moved. The source of light was a 

 thirty-ampere arc lamp. To collect 

 the light, a plano-convex condenser 

 was placed in such a position that 

 the emergent rays were rendered 

 parallel. A second lens of shorter 

 focus was then placed in the path 

 of this beam, by means of which 

 the light was made to converge, and 

 fall upon a simple spectacle lens con- 

 denser placed in the sub-stage. By 

 this means a uniformly-lit field was 

 obtained, and by careful manipulation 

 of an iris diaphragm placed in the 

 path of the parallel beam, all light 

 not required was excluded. On 

 placing the specimen on the stage 

 and focussing, a brilliant image on 

 a perfectly evenly illuminated 

 field was the result. A green 

 screen was employed to give 

 the necessary contrast, and an 

 exposure of five seconds given, 

 using an Imperial N. F. plate 

 of speed two - hundred H. 

 and D., the developer being 

 Pyro-soda. In photographing 

 the example shown in Figure 

 270, while the same general 

 arrangement for illumination 

 was retained the objective 

 employed was a one - inch 

 made by Messrs. James Swift 

 and Son, of Tottenham Court 

 Road. This was screwed into 

 the lower end of the micro- 

 scope, the light conical adapter 

 still occupying the place of 

 draw tube, which had been 

 removed in order to avoid any 

 internal reflections as well as 

 restriction of field of view. In 

 any case, when photographing 

 without an eyepiece, if the 

 draw-tube remains in position 

 its end must be lined with 

 black velvet to avoid these 

 reflections. After carefully 

 focussing the source of light, 

 a perfectly illuminated field was 

 obtained. The specimen was 

 then placed upon the stage and 

 focussed for those hairs which 

 form the distinctive feature of 



