ZOOLOGY AND BOTANY, MICKOSCOI'V, ETC. 



237 



and the ocular shown in the figure. The magnification of this com- 

 bination is from 3-4 diameters, and the separating power is sufficient to 

 insure under good conditions evaluation to the fourth decimal. This 





illiliinlliJ!'"' 



minium 



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. i !l!!lll!IU!l!l;i 



Fig. 47. 



objective 0' is formed of an achromatic lens combined with a plano- 

 concave lens of the same glass as the hemisphere. This latter lens, 

 whose concave surface has a radius of curvature equal to that of 



