MECHANICAL STAGE 



139 



the pillar. This ensures replacing the stage each time in exactly 

 the same position. Coordinate movements are obtained by the 

 milled wheels T, T. The graduated scales in each instance are 

 supplied with verniers v, v. The object slide is held in position 

 by the fingers F, /; a spiral spring in the joint of F presses it 

 firmly against the corner of the slide. The screws a, a permit 



FIG. 70. Attachable Mechanical Stage. 



changing the distance between F and /, thus providing for the 

 use of object slides or cells of different sizes. 



A more convenient form of removable mechanical stage is 

 shown in Fig. 71. In this type a narrow slot is cut into the micro- 

 scope stage. The opening thus made is provided with beveled 

 grooves at the sides, into which slips a sliding metal plate pro- 

 vided with coordinate movements, M. When a perfectly plain 

 stage is wanted the mechanical stage is removed and a plain 

 black metal plate, P, is inserted in its place. The coordinate 

 movements of the stage are made by rack and pinion actuated 

 through the milled heads H, H'. This stage may be seen in 

 place in Fig. 49. 



