154 



MANAGEMENT OF THE MICROSCOPE. 



from the field of the Microscope, that the Compressorium (§ 99) 

 is most useful. 



116. In whatever way the Object is submitted to examination, it 

 must be first brought appi'oximately into position, and supported 

 there, just as if it were in a mounted Slide. The precise mode of 

 effecting this will differ, according to the particular plan of the 

 instrument employed ; thus, in some it is only the ledge itself 

 that slides along the stage ; in others it is a carriage of some kind, 

 whereon the object-slide rests ; in others, again, it is the entire 

 platform itself that moves upon a fixed plate beneath. Having 

 guided his object, as nearly as he can do by the unassisted eye, 

 into its proper place, the Microscopist then brings his light 

 (whether natural or artificial) to bear upon it, by turning the 

 Mirror in such a direction as to reflect upon its under surface the 

 rays which are received by itself from the sky or the lamp. The 

 concave Mirror is that which should always be first employed, the 

 plane being reserved for special purposes ; and it should bring the 

 rays to convergence in or near the plane in which the object lies 

 (Fig. 87). The distance at which it should be ordinarily set 



Fig. 87. 



Arrangement of Microscope for Transparent Objects. 



beneath the Stage, is that at which it brings parallel rays to a focus ; 

 but this distance should be capable of elongation, by the length- 

 ening of the stem to which the Mirror is attached ; since the rays 

 diverging from a lamp at a short distance are not so soon brought 

 to a focus. The correct focal adjustment of the Mirror may be 



