28 



ELEMENTS OF APPLIED MICROSCOPY. 



phragm is to cut off adventitious light so that all the rays 

 finally reaching the microscope shall come from the 

 immediate vicinity of the object. A little experimentation 

 will show that reducing the diaphragm opening often 

 gives a sharper picture as well as one much less trying 

 to the eyes; in general an opening about the size of the ■ 

 front lens of the objective will yield good results. 



Fig. 19. — ^Abbe Condenser. (After Hager-Mez.) 



Certain opaque objects are best examined by reflected 

 light, and in many cases this method may well be used to 

 supplement the ordinary one, the mirror being turned 

 aside so that no light passes through the stage and the 

 object being illuminated either with the light which nat- 

 urally falls on it or with rays concentrated from above 

 by a lens or mirror. 



3. Focusing.— After the field is well lighted, the next 

 step is to focus on the object, or to so adjust the relation 

 pf the lens systems that a clear image may be formed. 



