GENERAL DIRECTIONS. 6 



to be examined (Fig. 1, h). These are merely for con- 

 venience and are not always used. 



i. The mirror. The mirror is below the stage (Fig. 1, i). 



k. The milled head. This is at the upper end of the 

 pillar (Fig. 1, A). It is the fine adjustment to raise and 

 lower the body of the microscope and all the parts that the 

 body carries. Turn the milled head slowly and notice the 

 motion of the body of the microscope. 



II. THE OBJECTIVES AND THE EYEPIECES. 



a. There are several objectives and eyepieces, but the 

 objectives most often used are a low power No. 3 and a 

 higher power No. 7. The eyepieces most often used are 

 a low power No. 2 and a higher power No. 4. 



b. The magnifications for the Leitz microscope are 

 approximately as follows : 



c. An object should first be examined with the low 

 power, and afterward studied more carefully with the 

 high power. The lenses must be perfectly clean, since 

 the least dust or cloudiness obscures the image. For 

 wiping the lenses use a soft cloth, first breathing upon 

 the glass in order to dampen it. An old handkerchief is 

 useful. The lenses should never be touched with the 

 fingers, for they are apt to make ineffaceable marks. 



