ZOOLOGY AND I50TANY, MICROSCOPY, ETC. 



239 



112 mm. inside and 126 mm. outside the graduations, which are in 

 single degrees. The stage is fitted with centring-screws, and may be 

 removed when it is desired to substitute the plain stage. The mechani- 

 cal stage may be revolved, and the movements for the slide-adjustment 

 are very wide. Graduations are provided for recording the field. The 

 sub-stage is complete in every particular. The lower iris-diaphragm 

 may be revolved, and is actuated by a rack-and-pinion, so that any 

 degree of oblique illumination may be obtained. The condenser stage 

 swings out, leaving an iris-diaphragm in the main stage. The upper 

 iris is removable at will, and the entire substage is focused by a rack- 

 and-pinion. The body-tube is graduated, and is made of aluminium to 



Fig. 42. 



secure lighter weight ; it is extra large for photomicrography. The 

 lower collar is removable for attaching the Micro-Tessar objectives. 

 The coarse-adjustment is by rack-and-pinion, and the fine-adjustment 

 is by the new lever type. Each graduation on the micrometer screw- 

 head, which is divided to give two speeds, equals • 0025 mm. in vertical 

 movement. The new lever fine-adjustment is shown in fig. 42. It is 

 recommended as possessing no lateral motion, which in some types is 

 observable after prolonged usage. The action is direct, and the response 

 to the slightest turn of the micrometer-screw is immediate. The 

 mechanism is entirely incased for the purpose of protection from dust. 



