ILLUMINATION. 9 



should be placed towards the left-hand side of the 

 microscope. But the best way to avoid injuring the 

 sight would be to use both eyes for viewing the 

 objects in turn, although most microscopic observers 

 make use of one eye only for this purpose. 



The structure of many transparent objects can be 

 best seen when the mirror is turned more or less 

 obliquely to one side, so as to view them by oblique 

 light, as it is called : we shall refer to this point here- 

 after. 



As a rule, objects are best seen by transmitted 

 light, or as transparent objects, although it is well to 

 examine objects under both kinds of illumination, 

 i. e. by transmitted and reflected light. 



If during the use of the microscope, after removing 

 the eye from the instrument, the impression of the 

 light remains perceptible to the sight, the light used 

 has been too strong, or its action too long continued ; 

 and the instrument should be at once laid aside for a 

 time. 



