224 



USE OF THE MICROSCOPE. 



same extent, their images will consequently bear the same 

 relation to each other as the bodies themselves. The method 

 of effecting this operation is exhibited by the following figure. 

 In fig. 145 is shown how the rays of light coming from the 

 eye-piece, or from any distant 

 object, are reflected by the prism, 

 in such a manner as to enter the 

 eye, at right angles to their 

 original direction; and as the 

 image of an object is always re- 

 ferred by the eye to a situation 

 in the same direction as that from 

 which the rays entering the eye 

 proceed, the magnified image of 

 the object will be seen on a 

 paper laid on a table beneath the 

 camera, and can there be readily 

 sketched. Supposing, in the pre- ^'S- 145. 



sent case, that the objects under examination be granules of 

 starch, or even blood discs, these can easily be sketched in out- 

 line ; when, therefore, the micrometer is substituted for the 

 starch, its divisions or squares can be drawn over the starch 

 granules, as shown by figs. 146 and 147, the former being 

 squares of 3-J^ of an inch, the latter, ^^V'ff' ^^^> ^^ t^® value 

 of the squares, or divisions of the micrometer, is known, the 

 objects over which the lines are not drawn can also be readily 



Fig. 146. 



Fig. 147. 



