ACCESSORY INSTRUMENTS. 



127 



Fig. 77. 



half-inch is represented by fig. 77. The rays of light re- 

 flected from the mirror, either in parallel or converging 



lines, are brought into a focus upon 

 an object, placed between it and the 

 mirror, but not too large to inter- 

 cept all the light. The object may 

 either be mounted on glass in the 

 usual manner, or held in the for- 

 ceps, represented in fig. 80; and 

 when too small to fill up the entire 

 field of view, or when transparent, 

 it is necessary to place behind it one 

 of the dark wells represented by fig. 79. Each Lieberkuhn 

 being mounted on a short piece of tube, can be shd up and down 

 on the outside of the object-glass, so that the maximum of illu- 

 mination may be readily obtained. In all the higher powers, 

 the end of the object-glass is turned small, and passes 

 through the aperture in the centre of the Lieberkuhn, but in 

 the lower powers, the distance of the object-glass from the 

 object will allow a Lieberkuhn of sufficient size to be used 

 without the above arrangement. 



Side Reflector. — As a substitute for the Lieberkuhn, Mr. 

 Ross supplies with his microscopes what he terms a side-illu- 

 minator or reflector ; it consists of a concave speculum of a 

 rectangular figure, highly polished and mounted on a jointed 

 arm, as represented by fig. 78; like the small condensing 

 lens, it is attached to some immovable part, or, still better, 

 to the body of the instrument, and parallel rays of light 

 from the lamp are thrown upon it by the bull's-eye 



Fig. 78. 



