

2 GENERAL BIOLOGY. 



"-/ 



Objective D, eyepiece 2 magnifies about 240 

 diameters. 



Objective D, eyepiece 4 magnifies about 420 

 diameters. 



To be seen clearly an object must be at a definite 

 distance from the objective. Moving the lenses to 

 the proper place is called focussing. 



For finding the focus there are two adjustments. 

 The coarse adjustment is used especially with the 

 low power ; it may be used also with the high 

 power for finding the approximate focus ; it con- 

 sists in sliding the tube up or down with the 

 fingers. This should always be done with a slight 

 twisting movement. The fine adjustment is effected 

 by means of a screw with a milled head behind the 

 tube. It is used to focus the lens exactly after the 

 object has been brought into view with the coarse 

 adjustment. 



The following rules should be carefully ob- 

 served : 



1. Always examine an object first with the low 



power (AA). 



2. Never use the high power (D) unless the 



object is covered with a cover-glass, Be 

 very careful never to let the objective 

 touch the cover-glass. 



3. Remember that objects can be brought 



clearly into view only by the hand, not 

 by the eye. If the object is not dis- 



