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 
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. 
