386 Royal Society: — Mr. AY. Crookes on a New A?rangement 



ciently wide to admit of the prisms being; pushed to the side when not 

 wanted, so as to allow the light, after passing through the object- 

 glass, to pass freely up the tube K. A pin at Al enables the prisms 

 to be thrown either in or out of action by a movement of the finger. 

 As the prisms are close above the object-glass, the usual sliding 

 box, carrying the binocular prism and the Nicol's prism (shown at N), 

 may be employed as usual, and the spectrum of any substance mav 

 thus be examined by both eyes simultaneously, either by ordinary 

 light, or when it is under the influence of polarized light. The inser- 

 tion of the prism-box between the object-glass and the body of the 

 microscope does not interfere with the working of the instrument in 

 the ordinary manner. The length of the tube is increased 1 or 2 

 inches, and a little additional rackwork may in some instruments be 

 necessary when using object-glasses of low power. The stereoscopic 

 effect when the Wenham prism is put into action does not appear 

 to be interfered with. 



Fig. 2. 



For ordinary work both these additions may be kept attached to 

 the microscope, the prisms being pushed to the side of the prism- 



