FUNCTION AND PARTS OF THE MICROSCOPE. 5 
Ray AB, bent toward the normal at B, turns to the right 
and, bent away from the normal to the surface, at C, 
turns to the right still further. If two such prisms are 
Fic. 3.—REFRACTION BY PRISMS. 
placed base to base as in the figure, rays striking them, as 
do the lines AB and AB’, will be bent in opposite direc- 
tions so that they will meet at the point D. The amount 
of bending varies with the angle at the apex of che prism. 
As shown, for example, in Fig. 4, the ray a’b’c’d’ passing 
Fic. 4.—REFRACTION IN Prisms or DirrERFNT ANGLES. 
through a prism of wide angle will suffer greater deflec- 
tion than the ray abcd which meets surfaces to which it 
is more nearly normal. 
