244 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK in. 



We will now examine some of the arrangements adopted by 

 makers of compound microscopes. 



As in the simple microscope, we have to deal with it as three 

 principal parts : the optical apparatus, which contains the eye-piece 

 and object-glass, inclosed in a tube ; the stage, which is of 

 various forms, but generally made of a plate pierced with one 



FICJ. 185. Micro.seope with three tubes for simultaneous observers.- 



or more circular openings, on which the glass which carries 

 the object is placed ; lastly, the mirror, which reflects the light 

 on the object. If the object is not transparent, it is lighted from 

 above by means of a lens arranged laterally, and moving in different 

 directions. 



Sometimes the optical tube is vertical (Fig. 181), which of course 



