LARGE MICROSCOPES 39 



The Circuit Stage Van HeurcTc Microscope (Fig. 13). 

 This is one of a series of three models made by Watson 

 based on designs by .the late Dr. Henri Van Heurck, 

 and intended to comprise every movement that can 

 be desired for photomicrography. Being so completely 

 equipped, the stands are very large ; the one figured is 

 the medium size. 



The suspension of the body on a large tripod foot is 

 typical of English stands, and gives a perfectly steady 

 support both horizontally and vertically. The fine 

 adjustment is Watson's well-known lever pattern, 

 giving a movement of ^nV' for each revolution of the 

 milled heads. The coarse adjustment allows of the use 

 of 4" objectives. The stage is very completely equipped 

 with rotating and mechanical movements, and can 

 be fitted with centring screws, verniers, or gradua- 

 tions on the circumference. The substage has centring 

 screws, and is focussed by rack and pinion. In addition 

 a fine adjustment (F) can be fitted if desired. The sub- 

 stage can be turned out of the optical axis for change of 

 condensers, etc. 



The Spencer Microscope, No. 10 (Fig. 14), is an admir- 

 able example of American practice. A similar stand by 

 Bausch and Lomb is shown at Fig. 6. The chief difference 

 between the two is in the position of the milled heads 

 actuating the fine adjustment, which are both lever 

 types, but of different construction. 



The mechanical stage can be removed from the re- 

 volving stage ; the milled heads are on concentric axes 

 one above the other. The revolving stage is covered 

 with vulcanite, and fitted with centring screws and a 

 clamp. "Its edge is graduated in degrees. The tube is 

 50 mm. in diameter. The substage is similar in principle 

 to that of the " Premier," but the Spencer Lens Co. 

 fit a second iris diaphragm between the lenses of their 

 c ondensers. The foot is of the horseshoe form, and 



