196 USE OF THE MICROSCOrE. 



CHAPTEK III. 



OPAQUE OBJECTS. 



Opaque objects may be illuminated in, at least, two different 

 ways ; either by light thrown upon them obliquely by a con- 

 densing lens, or a "side reflector, or else by the silvered cup or 

 Lieburkuhn ; in the latter case, the rays faU upon them more 

 or less perpendicularly. In the first method, and when the 

 object is large, we employ simply the condensing lens or 

 bull's-eye, as it is sometimes called, which has been fully 

 described at pages 122-3-4. The illuminating body, which 

 may be either a candle or an argand lamp, should be situated 

 about a foot or eighteen inches distant from the stage of the 

 microscope, and the condensing lens, with its convex side 

 towards the lamp, placed so near the stage, that all the light 

 falling on it may be brought into a focus upon the object. By 

 turning the convex side of the lens towards the lamp, as 

 shown in fig. 124, in which A B represents the stage, C the 



J' 





Fig. 124. 



glass plate supporting the object a, D E the condensing lens, 

 L the lamp, and r r' r r' diverging rays of light falling upon 



