REFRACTION OF LIGHT. 



457 



tion b e, and the eye at e receives the impression of a 

 ray of light proceeding from /. The angle which the 

 ray incident on the refracting surface makes with the 

 perpendicular at the point of incidence, that is, angle a b g 

 in fig. 258, is, as in reflection, called the angle of inci- 

 dence; the angle made by the refracted ray with the 

 same perpendicular, as e b A, in fig. 258, is called the 

 angle of refraction. If rays of light pass from air into 

 water, as in the first experiment, the angle of incidence 

 is greater than the angle of refraction; if the light 



FIG. 259 (4 times real ><?). 



FIG. 260. 



passes from water into air, the angle of incidence is less 

 than the angle of refraction. In general, whatever its 

 direction, the ray makes in water a smaller angle with 

 the perpendicular to the surface than it does in air. 



No refraction seems to take place when light passes 

 through a common window-pane, provided that both 

 surfaces are quite parallel. Let s s in fig. 259 be a 

 section of a pane, and a b the incident ray. At b re- 

 fraction takes place, the direction of the ray is now b c ; 

 at c refraction takes place again, and the direction of 

 the ray is now c d, that is, parallel to its original direc- 



