402 A YEAR IN SCIENCE 



ray. Light travels at a velocity of about one hundred 

 and eighty-six thousand miles per second. 



When light rays strike a body, one of three things 

 happens to them: they may enter the body and stop, 

 they may strike its surface and bound back, or they 

 may go through it. If they stop in the substance we 

 say they are absorbed; if they bound back we say they 

 are reflected. If light passes through one substance from 

 another, the light waves are often bent out of a straight 

 line. To this change of direction we give the name 

 refraction. 



Lenses. When light passes from air through glass 

 it is refracted. For purposes of refraction a piece of 

 glass with one or two curved surfaces is frequently 



used. This is called a lens. 

 Lenses are of different 

 forms as shown in Figure 

 Concav^ 182 . When rays of light 



pass through a concave 

 lens, they spread away 

 Fig. 182. A biconvex and a from each other. When 



biconcave lens. 



they pass through a convex 



lens, they are brought toward each other and meet at 

 a point called the focus. 



In the eye the cornea and the lens have convex 

 surfaces. When an object is seen, rays of light pass 

 from every point of it through the cornea and the lens, 

 and are brought to a focus on the retina where an image 

 of the object is formed. 



