the sash of the window may be reflected and show itself 

 in the field as dark bands, or in the case of lamplight 

 the blue portion of the flame may appear as a dark 

 spot. These are only preliminary directions but will 

 suffice for a beginning. There will be little difficulty 

 in obtaining proper illumination at the outset, if one 

 will observe the following : 



Remove the eyepiece and, looking through the back 

 of the objective, have 



Central illumination, 

 Even illumination over the entire field, 

 Mellow illumination. 



Defects in illumination which may not be apparent 

 will show 7 when the eyepiece is replaced. 

 Defective lighting is indicated, 



When dark points or shadows appear in the 



field, 

 When the outlines of an object are bright on 



one side and dark on the other, 

 When the object appears to lie in a glare of 

 light. 



In the first two cases the correction can be made 

 by suitably adjusting the position of the mirror ; in 

 the last by reducing the amount of light by the use 

 of a diaphragm. 



It is now generally conceded that observations with 

 the microscope may be made to any extent without 



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