220 



THE BOOK OF THE LANTERN. 



measurement, the amount of magnification of the image. 

 And this magnification can be carried to any reasonable 

 extent, for the worker is not limited, as he would be if 

 using a camera, by the length to which that camera can 

 be extended. 



But perhaps the simplest arrangement of all is that 

 recently introduced by Messrs. Mawson & Swan, and 

 which is shown at fig. 55. A is a light metal disc, which 



Fig. 55. 



can be screwed on the camera front in place of the ordinary 

 lens. The opening in -its centre is furnished with the 

 regulation microscopic screw, so that any ordinary micro- 

 scopic objective can be readily fixed to it. Upon two 

 horizontal bars, projecting from this metal disc, there 

 slides another similar disc B, also with an opening in the 

 centre. This second disc has fitted to it a pair of small 

 spring clips for the reception of the microscopic slide 

 which it is desired to photograph. Focussing is effected 

 by sliding the disc B to and fro in front of the objective 



