THE CAMERA LUCIDA. 



In this case the rays issuing from the eye-piece of the microscope 

 are reflected twice successively from the two sides of the prism, 

 which are inclined to each other at an angle of 135, as explained 

 in (6). 



According to what has been explained in (8), the observer 

 can vary the magnitude of the picture on the paper by varying 

 the distance of the paper from the prism, without varying the 

 magnifying power of the microscope ; and in this way he can 

 make a tracing of the object on any desired scale. 



192 



