46 THE MICROSCOPE. 



movable slide carrier is attached to the stage. The more expensive 

 instruments are often provided with a mechanical movement that 

 enables the object to be carried in any desired direction by simply 

 turning two screws located above or at the side of the stage. 



F. Clips These are to hold the glass slide, on which the 

 object is mounted, firmly against the stage. 



O. Mirror. This is one of the optical parts below the stage 

 and is for the purpose of illuminating the object, either by throw- 

 ing light through it, or on it from above. One side of the mirror 

 is usually plane and the other concave. 



P. Mirror Bar. A bar attached to the arm and carrying the 

 mirror. It can usually be swung from side to side to vary the 

 angle of illumination. 



Q. Sub-Stage Ring. Used to support either the diaphragm 

 or some of the optical parts that are used below the stage. It is 

 often attached to the latter but in the more perfect instruments is 

 borne on a separate bar. 



S. Diaphragm. This is a disk provided with numerous 

 apertures, of various sizes, and can be turned to regulate the 

 amount of light coming from the mirror to the object. 



Field of the Hicroscope. This is the clear area seen by look 

 ing into the microscope, and should be perfectly circular, when the 

 instrument is properly lighted. 



