ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 801 



oaicrography or other purposes. Tlio body can be clamped by means of 

 a lever attached to one of the trunnions. The body is specially con- 

 structed to work with Abbe-Zeiss apochromatic objectives, and is 

 fitted with a rackwork draw-tube for lens adjustment ; it will rack out 

 sufficiently to adjust^'hese lenses on the thinnest covers. 



Fig. 98, 



There is the usual rackwork coarse-adjustment. The fine-adjust- 

 ment is a Campbell differential screw. This fine-adjustment, while 

 being very strong, works with great smoothness and delicacy. It is 

 claimed that the diflferential screw solves the difficulty which has always 



1889. 3 K 



