38 



HEAT OR CALORIC. 



The following figures represent the prism and prismatic spectrum. 



Should a ray fall upon 

 a prism, as represented 

 in the figure, in the di- 

 rection of the line, AB; 

 it will, on account of the 

 obliquity of its approach, 

 be refracted towards C, 

 and emerging thence, 

 obliquely to another sur- 

 face of the prism, H C K, 

 it will again be most at- 

 tracted by that portion of the surface towards which it inclines. 

 Consequently, it will be refracted so as to proceed in the direction 

 of CD. 



Thus it must be evident, that two surfaces of the prism have a 

 concurrent influence, in bending the rays from their previous course, 

 while in the pane, the influence of one surface is neutralized by that 

 of the other. 



The lines, L F, and E F, being perpendiculars to the surfaces 

 of the prism, A B L, is the angle of incidence, and, G B C, the 

 angle of refraction, to the surface at which the rays enter the prism. 

 F C B, is the angle of incidence, and E C D, the angle of refrac- 

 tion to the surface, from which the rays emerge. Dr. Hare. 



A TRIANGULAR GLASS PRISM, CONVENIENTLY MOUNTED ON A UNI- 

 VERSAL JOINT. 



This figure represents a triangu- 

 lar glass prism, mounted upon a 

 universal joint, supported by a 

 brass stand, so as to be well qualifi- 

 ed for "the dispersion of light. 



A, The glass prism, supported 

 at each end by a pivot. 



B B, Handles by means of 

 which the pivots are turned, so as 

 to make the prism revolve. 



C C, Ball and socket, forming 

 a joint, upon which the plate D D, 

 may be moved, so as to assume 

 any serviceable position. Dr. Hare. 



Let A B, represent a part of a window shutter of a room, into 

 which light enters only through the hole C. If the light thus enter- 

 ing be received on a screen, a circular spot on it will be made lumi- 



