17 



H. Draw-tube. This is that portion of the body 

 which moves in the outer sheath and which receives 

 the eye-piece. It is provided for the purpose of attain- 

 ing different lengths, variations in magnifying power 

 and as a matter of convenience while working. 



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. 



L. Fine Adjustment. This is slow moving and 

 serves to get an exact focus. It is attained by a fine 

 thread, 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 sensi- 

 tive 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 attached to 

 the arm. 



N. Clips. These are two springs which are 

 attached to the upper surface of the stage and 

 serve to hold down the object. 



