135 



scopist cannot too soon learn or too constantly 

 practice. Besides these general warnings, how- 

 ever, certain special cautions should be given to 

 the young microscopist with regard to errors into 

 which he is liable to be led even when the very 

 best instruments are employed." 



How to Set Up the Instrument. Draw the 

 instrument from the case by grasping the base, 

 free it from dust with a large camel's hair brush, 

 1 inch or 1^ inch wide, or by wiping carefully 

 with a chamois skin, or old linen handkerchief. 

 Place the instrument with proper relation to light 

 on the work table, which should be of such height 

 that observations can be made with the utmost 

 possible comfort without straining the neck or 

 compressing the chest. Bear in mind always to 

 sit as upright as possible. 



Bring the draw-tube to standard length by 

 drawing the draw-tube to the length for which the 

 objectives are corrected. Do this by grasping the 

 milled edge of the draw-tube and give it a spiral 

 motion while holding the main tube with the other 

 hand, which will facilitate its easy movement. 

 The objection being, however, that in any but 

 cloth-lined sheaths the polished tube will soon be 

 scratched, especially if not kept very clean. In 

 stands without the graduated tube, a mark or ring 

 is, or should be, provided on it, which should be 

 made to coincide with the upper en4 of main tube, 



