24 



THE STRUCTURE OP 



under his eye, so that he may easily draw its form 

 on a piece of paper placed underneath. (Fig. 11). 



Amongst the ac- 

 cessory apparatus are 

 various arrangements 

 for concentratinof the 



' — 



light on the objects 

 which are placed for 

 examination under 

 the Microscope. One 

 of these combinations 

 is called the achro- 

 matic condenser. This 

 consists of a series 

 of lenses, which are 

 placed between the 

 mirror and the stage, 

 and which may con- 

 sist of an ordinary 

 object-glass. The 

 stages of the larger 

 Fig. n. Camera Lucida, kinds of Microscopes 

 are fitted up with a screw or slide, by which the 

 condenser can be fastened beneath and adjusted 

 to the proper focus for throwing light on the 

 otDJect examined. Instruments have also been in- 

 vented, called illuminators, which are intended to 

 supplement or assist the mirror in throwing light 

 on the object. These are things, hov/ever, about 

 which the begfinner need not trouble himself. 

 Tbey are amongst the apparatus which contribute 

 to the perfection of the Microscope, but are not 

 amongst its necessary accompaniments. 



The same may be said of the ^x)/a?'^5;2?^^ ap~ 

 paratus. The use of polarized light adds greatly 

 to the beautiful appearance of many objects under 

 the Microscope, but it is only in a very few 



i 



