1 84 THE HISTOKY AND DEVELOPMENT OF THE MICROSCOPE 



able, for they are made by most leading opticians. The last mechanical 

 stage we illustrated is by Messrs. E,^ & J. Beck, which is illustrated 

 in fig. 147. It has vertical rack and pinion and horizontal screw 

 motions with graduated finer divisions. 



To Messrs. Bausch and Lomb, however, we are indebted for the 

 introduction of an attachable 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 commend. But especially when the illumina- 



FIG. 146. Zeiss's attachable mechanical stage. ( full size.) (1895.) 



tion is daylight, and very critical results are not sought, it will be 

 useful, and is admirably made. 



V. The sub-stage is scarcely second in importance in a first- 

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

 enable us to use in the most efficient manner the optical and other 

 apparatus employed to illuminate the objects suitably with the 

 various powers found needful. Upon this much of the finest 

 critical work with the modern microscope depends. 



To accomplish this a good sub-stage must have rectangular 

 movements, and a rack-and-pinion focussing adjustment. 



