114 



REFRACTION 



S P 

 FIG. 65. When the ray RO enters 



the water, but, on entering the water, it is bent or refracted 

 and takes the new path OS. The angle AOR is called the 



angle of incidence. The angle 

 POS is called the angle of refrac- 

 tion. 



The angle of refraction is the 

 angle formed by the refracted ray 

 and the perpendicular to the sur- 

 face at the point where the light 

 strikes it. 



When light passes from a rare 

 the water, its path is changed to medium to a denser medium, the 



refracted ray is bent toward the 



perpendicular, so that the angle of refraction is smaller than 

 the angle of incidence. When a ray of light passes from 

 a denser to a rarer medium, the refracted ray is bent away 

 from the perpendicular so that the angle of refraction is 

 greater than the angle of incidence. 



108. How Refraction Deceives Us. Some substances re- 

 fract light more than others ; for example, a stick put in salt 

 water seems more bent than a stick put into fresh water. 

 The power of a medium to bend rays of light or deviate them 

 from their original path is called the refraction of the substance. 

 Refraction is the source of many illusions ; bent rays of 

 light make objects appear 

 where they really are not. 

 A fish at A (Fig. 66) seems 

 to be at B. The end of the 

 stick in Figure 64 seems 

 to be nearer the surface of 

 the water than it really is. 



The light from the sun, moon, and stars can reach us only 

 by passing through the atmosphere, but in Section 76, we 



FIG. 66. A fish at A seems to be at B. 



