CHAP. III.] 



THE MICROSCOPE. 



245 



lias the merit of simplicity, but this is the very worst position for 

 the optical performance of the human eye. Sometimes it is capable 

 of being inclined obliquely at -various angles (Figs. 180 and 183) ; 

 which is by far the best plan if the workmanship be good ; some- 

 times, indeed, as in Amici's microscope (Fig. 184), it is bent at 



FIG. 186. Arrangement of tubes in Wenham's binocular microsoops. 



right-angles ; the horizontal part incloses the eye-pieces, and the 

 vertical part the object-glass ; at the bend a mirror, inclined at 45, 

 or a prism, reflects the luminous rays coming from the object-glass, 

 and sends them horizontally into the eye-piece. 



Microscopes are also constructed with three bodies, which enables 

 simultaneous observations to be made by three different persons. 

 These instruments are valuable in the study of micrography. 



