82 



THE MICROSCOPE. 



under the highest powers of the microscope (the 1 and ^ 

 inch object-glass) is effected by two reflections. The rays- 



from a lamp rendered pa- 

 rallel by a condensing lens 

 are received on an elliptic 

 reflector, the end of which 

 is cut off a little beyond 

 the focus ; the rays of light 

 converging from this surface 

 are reflected down on the 

 object by a plane mirror 

 attached to the object-glass, 

 and on a level with the outer 

 surface. By such means the 

 structure of the scale of the 

 Podura, and the different 

 characters of its inner and 

 outer surfaces, are rendered 

 distinctly visible. Silver 

 specula, known as Lieber- 

 kuhn's, are much employed, 

 and preferred by some mi- 

 croscopists. The Lieberkuhn 

 is concave, and attached to 

 the object-glasses, from the 

 two-inch to the half-inch, in 

 the manner represented at 

 fig. 47, where a exhibits the 

 lower part of the compound body ; 6 the object-glass, 

 over which is slid a tube and the Lieberkuhn c attached 

 to it ; the rays of light reflected from the mirror are 

 brought to a focus upon an object d, placed between it 

 and the mirror. The object may either be mounted on 

 a slip of glass, or else held in the forceps/; and when too 

 small to fill up the entire field of view, or when trans- 

 parent, it is necessary to place behind it the dark- well e. 



Each Lieberkuhn being mounted on a short piece of 

 tube, can be slid up and down on the outside of the object- 

 glass, so that the maximum of illumination may be readily 

 obtained. In the higher powers the end of the object-glass 

 is turned small enough to pass through the aperture in the 



Fig. 45. 



