USE OF THE CAMERA. 99 



their statements are apt to be equally unreliable and false in 

 other particulars. As will be seen from the above it is advis- 

 able to purchase the lower-angled lenses. The most conven- 

 ient glass ever used by the writer was a J of only 48 angular 

 aperture. 



One criticism which the writer would make on the ordinary 

 objective is the utterly disproportionate length of brass to 

 the optical portion of lenses, making it next to impossible to 

 use low power objectives on the smaller stands. Fig. 34 

 represents one of these lenses drawn from measurements, 

 the shaded part indicating the optical portion and the 

 dotted line showing to what extent it might conveniently be 

 shortened. We commend it to the attention of opticians. 



USE OF THE CAMERA. 



The camera lucida, or camera, as it is commonly called, 

 is one of the most useful microscopic accessories. Two 



FIG. 35. 



forms are offered for sale and are represented in fig. 35 ; the 

 one at the left, A, is the most valuable one, but B is the cheaper. 

 The ray of light coming through the microscope falls upon an 

 inner surface of a glass prism and from thence is reflected 

 directly to the eye as in B, or to a second surface and thence 

 to the eye as in A. At the same time a ray of light coming 



