PLATE 39. 



Diatoms. 



A Araclinoidiscus eJirenberghii x 37o 

 B Orthoneis splendida x 620 



Objective Zeiss 16 mm. Apo. N.A. 0.3. 



Ocular Zeiss Compensating, 12. 



Condenser ... Watson's Universal Achromatic. 



Illuminant ... Liliput 4 amp. arc. 



Aux. Condenser Double convex lens, giving parallel beam. 



Screen Wratten's B (green). 



Plate Imperial N.F. 



Exposures ... 3 sec. and 7 sec. 



These are examples of diatoms of moderate thickness, for which 

 it is necessary to employ a low-power objective to give covering power, 

 and combined with a high eye-piece or long extension to give 

 sufficient magnification to show all the detail. The use of a large 

 aperture to resolve fine secondary detail is of less importance. 



Photos. W. B. R. \JofolloLupage256. 



