184 THE H1>T"KY AND DEVELOPMENT OF THE MICROSCOPE 



:iMr. for thrv are made by most leading opticians. The last mechanical 

 stage we illustrated is by Messrs. R. A: J. Beck, which is illustrated 

 in H-. 117. It ha> vertical rack and pinion and horizontal screw 

 motion- \\itli graduated finer divisions. 



TII .Messrs. ISaiisch and Lomb, however, we are indebted for the 

 int rod i ict ion of an atiaclialile stage in which the iris diaphragm is on 

 the plane of the stage. We illustrate this in fig. 147A. Its use with 

 a condenser we do not c mimend. But especially when the illumina- 



1 "' tchable mechanical stage. (3 full size.) (1895.) 



lion is daylight, and very critical results are not sought, it will lie 



ii-eful, and is admiralilv made. 



V. The sub-Stage is scarcely sec-mid in importance in a first- 

 g microscope to the stage itself. It is intended to receive and 



enable us to use in lln- mpsl efficien.1 manner the optical and other 



apparatus employed to illuminate thr objects .siiital.lv with the 



found needful. Upon this much of the finest 



^ i'b the ] lerii microscope depends. 



ompli-l, this a good sub-stage must have rectangular 

 ,anda rack -and pillion focussing adjustment. 



