130 



HOW WE USE LIGHT 



I 



lighthouses, airplane beacons, and the more common 

 traffic lights. Heliograph signals, made by reflecting a 



beam of sunlight on 

 a mirror, have been 

 sent nearly 200 miles. 

 Light-Using De- 

 vices. Let us think 

 over the things we 

 \\ I ~^--, 



may find at home 

 whose use depends 

 upon light. There is 

 the camera, the opera- 

 glass, the reading 

 glass, and, of course, 

 the mirror and win- 

 By fanning dows. Perhaps there 

 is a magnifying glass, 

 an enlarging mirror, or a bull's-eye flash lamp. Among 

 the toys there might be a kaleidoscope and possibly a 

 stereoscope. If there is a nature lover in the family, 

 you may find bird glasses or field glasses. 



How an Image Is Made by a Pinhole. If you let a 

 small beam of light enter a dark room in which there is 



The Indians used smoke signals. 



the fire puffs of smoke were given off. 



dusty air, you can see that the light travels in a straight 

 line. If a small hole is made in the window shutter on 

 the first floor of a building and the room is dark, people 



