PLATE III 



EXAMPLES OF MEDIUM-POWER PHOTO-MICROGRAPHY 



{The negatives and reproductions are untouched) 



Fig. I. Tongue of a Cricket. Photographed with a photo-achromatic inch by 

 Wray, Attention is called to the excellent definition at the edges, more 

 especially, of the specimen : compare with Fig. 6, Plate I. x 20 



Fig. 2. Piece of a Diatom. This has been photographed to show the deleterious 

 effect of closing the iris diaphragm too much : in other words, using too 

 small " a cone " of light. Compare this with Fig. 5. 



Fig. 3. White-line effect around the extremely fine hairs on the proboscis of a blow-fly. 



This has been caused by using too small a cone of light. x 400 



Fig. 4. Absence of white-line effect when using a solid cone of the correct size. 



Each hair is seen sharp and crisp, although all are not quite in focus from 

 irregularity on the surface of the proboscis. Note the entire absence of the 

 white-line diffraction effects. Photographed with \ apo — 6 eye-piece. 



X 400 



Fig. 5. Arachnoidiscus Ehrenberghii. Example of a photograph taken with low- 

 power {\ inch) apochromatic and projection eye-piece 6. x 220 



(This specimen was expressly prepared by Mr. Firth of Belfast, and is 

 mounted especially flat.) 



Fig. 6. Hind-leg of " working " Bee. Showing corbicula. Photography of insects. 



Here the cone had better be not too large, but care must be used to avoid 

 diffraction effects by closing the iris too much, i inch apo : projection eye- 

 piece 6.* X 55 



Fig. 7. Hair of Pencil Tail. A good apochromatic shows this without shading between 

 the limiting lines, which is caused in inferior lenses by bad colour correction. 

 Photographed with | Zeiss apo : projection eye-piece 6. x 400 



Fig. 8. Proboscis of Blow-Fly. Tal<en with i inch apo. 6 compensating eye-piece, 

 as it gives a larger field than the projection. The suctorial tubes should 

 appear well defined. A medium cone required. x 60 



Fig. 9. Foot of very small Garden Spider. Medium cone, photographed with 

 \ inch apo. Projection eye-piece 6. _ x 400 



Fig. 10. Navicula Lyra. Fig. 10 was photographed with low N. A. ("65) the magnifi- 

 cation X 600 being the same as that of Fig. 1 1 which was taken with a high 

 N. A. (i'4o)' Note the difference in detail afforded by the lens with the low 

 numerical aperture and compare with 



Fig. II. Navicula Lyra. Taken with high aperture. It is very evident the important 

 part that numerical aperture plays in the rendering of fine details such as 

 dots, &c. &c. 



* It will be seen that this specimen, as well as others occasionally mentioned, appear magnified less 

 than the optical combination of eye-piece and objective must of necessity produce with a lo-inch camera 

 extension. This reduced magnification is obtained by shortening the camera-extension a trifle : the field is 

 reduced in size by the limiting diaphragm, but at times, as in these cases, is a matter of convenience. 



