MICROSCOPIC OBJECTS. 



5 



taining photographs absolutely sharp and 

 well-defined to the very edge of the field. 

 This is also the experience of many other 

 photo-micrographers. In the writer's opin- 

 ion it is a mere question of convenience ; 

 with low powers — say up to \ inch — the 

 eye-piece may be employed, as the loss of 

 light attending its use is very slight; but 

 with higher powers the loss becomes a seri- 

 ous matter, so it is then necessary to dis- 

 card the eye-piece, or focussing v/ill be very 

 difficult, and the exposure of the plate in- 

 conveniently long. 



An achromatic condenser is a very useful 

 piece of apparatus, but may be dispensed 

 with f.)r general work ; however, a good 

 one will save much labor and "dodging," 

 when using high powers with difficult ob- 

 jects. A bull's-eye lens accompanies most 

 microscopes, and is really invaluable when 

 the photo- micrographer has learnt how to 



use it. For a very oblique light .a hemi- 

 spherical lens is as good as anything. It is 

 attached to the under side of the slide with 

 glycerine, and used in conjunction with the 

 bull's-eye, the best position being found for 

 the lens by experiment. As it will not keep 

 ill place unless the microscope be kept ver- 

 tical, a slip of cardboard should be fastened 

 to the slide below the hemispherical lens, 

 or a little gum may be added to the glycer- 

 ine. Unless the gum be perfectly white it 

 had best be avoided, as a yellow tint would 

 ruin definition. 



The paraboloid and spot-lens are some- 

 times used in photo- micrography, but even 

 with the mo^t rapid dry plates, dark ground 

 illuminauon is difficult, and seldom success- 

 ful As it, however, shows many objects to 

 better advantage than any other mode of 

 lighting, the student is recommended to 

 see what results he can gain by its use. • 



LONG FOCUS CAMERA, SUITABLE FOR PHOTO-MICROGRAPHY. 



Lesson TI. — Photographic Apparatus. 



For simple photo-micrographic opera- 

 tions, any ordinary camera may be employ- 

 ed. A quarter-plate camera will answer, 

 but the student is advised to obtain a half- 

 plate or even a whole-plate camera, for, as 

 he advances in skill, he will, perhaps, wish 

 to photograph sections of rocks, or woods, 

 or whole i.. sects, on a larger scale than the 

 smaller camera will allow. A good lens 

 will make a half or whole-plate enlarge- 

 ment of an object without loss of definition. 

 U>ing the eye- piece, and working with low 

 powers, a camera expanding to eighteen 

 inches or two feet will suffice, but fur the 

 higher powers, which cannot well be used 



in conjunction with the eye-piece, a cam- 

 era expanding to four feet, or even six feet, 

 is recommended. The eye-piece cuts off so 

 much light when working with high-power 

 lenses that focussing becomes difficult, if 

 not impossible ; while without it, focussing 

 with a i^.jth inch or -|\;th inch is an easy 

 matter, even when a condenser is not em- 

 ployed. 



If an ordinary camera be employed,* 

 there are none better than those sold under 

 the name of "long focus" cameras. The 

 half- plate size expands from three inches ti 



* Similar photographic apparatus to that men 

 tioned, maybe procured of us of our own manufac- 

 ure.— E & H T. Anthony & Co. 



