CHAPTER XXXV 



THE EYE 



604. Light. Straight lines of light called rays pass off 

 from objects in all directions. Each ray is supposed to be 

 a vibrating line in a thin 

 substance called ether, 

 which fills all space. 



The vibrations of ether take 

 place many millions of times 

 each second. In sound the air 

 vibrates only a few hundred 

 times. Light travels nearly 

 185,000 miles each second, while 

 sound travels about 1000 feet in 

 the same time. Light waves are 

 from ^fony to TOfcny inch in 

 length, but each sound wave 

 reaches several feet. The length 

 of a wave of light determines its 

 color. Red waves are about 

 twice as long as violet waves. 

 A mixture of all colors produces 



Diagram of light passing from an object. 



It passes in every direction, and, falling 

 upon a screen, produces a confused multi- 



white light, while black is due ! U( ? e of images ' which form only a mass of 



light, but no one clear image, 

 to the absence of light. Colors 



which, like red and green, form white light, are called complementary 

 colors. * 



In passing through glass or other clear substances, rays of light may 

 be bent from their courses. By a properly shaped glass called a lens, 

 rays may be spread apart or may be brought together in a point called 



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