Radiant Heat and Light 



143 



In the front of a camera there is a flattened glass ball 

 called the lens. If you were to remove it, the camera 

 would not take 

 any pictures; it 

 would take a 

 blur of light and 

 shade and noth- 

 ing more. 



In front of a 

 moving-picture 

 machine there is a 

 large lens, a piece 

 of glass rounded 

 out toward the 

 middle and thin- FIG. 70. 

 ner toward the 

 edges. If you were to take that lens off while the 

 machine was throwing the motion pictures on the screen, 

 you would have a nicker of light and shade, but no 

 picture. 



It is the lens that forms the pictures in your eye, on 

 a photographic plate or film, and on a moving-picture 

 screen. And a lens is usually just a piece of glass or 

 something glassy, rounded out in such a way as to make 

 all the spreading light that reaches it from one point 

 come together in another point, as shown in Figure 69. 



As you know, when light goes out from anything, as 

 from a candle flame or an incandescent lamp, or from 

 the sun, it goes in all directions. If the light from the 

 point of a candle flame goes in all directions, and if the 

 light from the base of the flame also goes in all directions, 



The light from each point of the candle 

 flame goes out in all directions. 



