47 



I. Collar. This is a ring which is attached to 

 the draw-tube and is usually provided with a milled 

 edge. 



J. Coarse Adjustment. This is a provision 

 for moving the body quickly back and forth for 

 adjusting the focus approximately. It is done by 

 a sliding rack and stationary pinion (not shown in 

 cut) or a sliding body in an outer sheath. 



K. Milled-Heads. These are attached to the 

 shank of the pinion, which is revolved by means 

 of them and are usually large to give sensitiveness 

 to the movement. They should be placed wide 

 apart so that the fingers may be entirely free from 

 the body. 



L. Fine Adjustment. This is slow moving 

 and serves to get an exact focus. It is attained by 

 a fine screw, provided with a milled head and acts 

 upon the body, either directly or by levers. This 

 as well as the coarse adjustment should be 

 extremely sensitive and should not have the least 

 side or lateral motion. The fact that either of 

 them have it, is evidence of poor workmanship. 



M. Stage. This is the portion on which the 

 object is placed for examination and is usually 

 attached to the arm, although the arm is sometimes 

 attached to the stage. 



