PLATE 40. 



Comparison of the resolution produced by objectives 

 of high and low N.A. 



Suitable eye-pieces and camera extension were used to give 

 equal magnifications. 



DIATOM Triceratiam Javus x 620 



B 



Objective 



N.A 



Ocular 



Condenser 



Illuminant 

 Aax. Condenser 



Screen 



Plate ... .. 

 Exposure ... ... 

 Developer 



Zeiss Apo., 16mm 



0.30. 



Zeiss Gomp. x 12. 



Holos, top lens 



removed . 



Zeiss Apo., 3mm. 



0.95. 



Zeiss projection x 4. 

 Holos, stopped down 



to N.A. 0.8. 

 4 amp. arc. 



Biconvex lens, parallel light. 

 Wratten's D + H. Violet light, 4200-4600. 



Imperial N.F. 



30 sec. 5 sec. 



Pyro-soda. 



The magnification produced by the 16mm. objective and x 12 

 ocular is "empty," in that no more detail is visible than could easily 

 be seen at a much less magnification. The objective of high N.A. 

 gives a much greater resolution, and reveals detail that can only be 

 properly seen at a comparatively large magnification. Its penetration 

 is low, and only a small portion of the diatom can be focussed and 

 resolved at one time. 



The D+H screens giving monochromatic violet light were used 

 for resolution; they also diminished the excessive brightness of the 

 image on the ground glass and made focussing easier. 



Photos. W. B. R. 



To follow Plate 39 and page 256. 



