REFRACTION 



333 



tact with the atmosphere of the earth. This image is usually large 

 and red. The same thing happens at sunset. 



Refraction in a Prism. Light rays entering glass are bent, since 

 the glass is a medium denser than air. Light rays entering glass 

 made in the form of a prism are bent according to the position the 

 prism is in when the light rays pass through. 



In Fig. 205 it will be seen that the light rays entering the 

 prism are bent so as to be reflected back on the other side of the 

 prism. Use of this is made in in- 

 struments called binoculars. 



The rays of light are made to 

 pass three times the length of a 

 barrel in going from the objective 

 glass to the eyepiece of each bar- 

 rel. Thus, by means of a short 

 tube, the equivalent of a telescope 

 is obtained. 



The prism is used in some head- 

 lights of automobiles for bending 

 the rays of light so that they will 

 fall on the road below the vision 

 of the driver of an approaching 

 automobile. 



Why a Prism Breaks up Sunlight 

 into Colors. Light travels at the 



rate of 186,337 miles per second. This light is composed of many 

 colors, as will be seen by placing a prism in the sunlight and look- 

 ing for the band of color which it produces. 



When light passes at an angle into a denser substance, the ray 

 of light is made to travel more slowly, a fact which causes it to 

 bend. 



As will be seen from the following table, the long red waves vibrate 

 less rapidly, and consequently are made to bend, or are refracted 

 the least, and the shorter waves, which vibrate very rapidly, are 

 refracted the most. 



Scientists know that there are waves of light which we cannot 

 see, as there are no nerves in the eye to be affected by them. The 



FIG. 205. Notice how the prism 

 bends the rays of light, causing 

 the light to travel a great dis- 

 tance. 



