SPECIAL MICROSCOPES 



265 



piece and looking through O c, it will generally be found that the 

 microscopical field is not evenly illuminated : the light should then 

 be lowered or raised until perfectly uniform illumination is 

 obtained. 



The beam of light received by the lens, b, is made to converge, and 



Oc 



M 



FIG. 207. Eeichert's microscope for the examination of metals (1897). 



is reflected downwards, in the direction of the axis of the instrument, 

 by the glass-plate, a. It is then condensed upon the object by the 

 lenses of the objective itself. The illuminated object sends back a 

 portion of the light, which passes through the objective and the plate 

 a, reaching the eye at c. 



The object to be examined should have two parallel surfaces, so 



