2 STUDIES OF ANIMAL LIFE. 



With one hand hold the stand firmly by the base. 

 With the other slowly raise and lower the tube, 

 at the same time, twisting it toward the right in 

 the sleeve. This method of moving the sliding 

 tube is called the coarse adjustment. (The sliding 

 tube should be kept well cleaned so that it will 

 move easily.) 

 7. The milled head at the top of the column. Measure 

 the distance from the end of the sliding tube 

 to the stage. Turn the milled head three revo- 

 lutions to the right and measure the distance 

 again. This method of moving the sliding tube 

 by means of the milled head is called the fine ad- 

 justment. 



C. Lienses. 



1. The eye-piece, a small metal cylinder with a lens at 



each end. It is placed in the sliding tube at the 

 upper end. Hold the eye-piece to the light and 

 look through it. Observe the circle of bright 

 light. 



2. The objectives, sets of lenses which screw into the 



lower end of the sliding tube. These objectives 

 vary in magnifying power and are usually distin- 

 guished as high power (h.p.) and low power (l.p-). 

 Find three ways of telling one from the other. 

 The following precautions should always be ob- 

 served : — 



Never touch the lens with your fingers. 



To remove dust from the lens, wipe gently with a clean, 

 soft cloth, preferably a piece of old linen. 



If balsam or other adhesive substance is on the lens, do not 

 attempt to clean it yourself, but call the teacher. 



Keep all lenses not in use protected from dust. 



