DIRECTION OF LIGHT 



59 



If a candle is held in front of a mirror and we look into 

 the mirror, we see the candle behind it. We know that 

 the candle is not there 

 but that its light is re- 

 flected by the mirror in 

 such a way as to make 

 it appear to corne from 

 behind the mirror. We 

 see the candle by the 

 light the mirror re- 

 flects. 



If we wish to see 

 whether the edge of a 

 board is straight, we 

 sight along it. If we 

 wish to hit an object 

 with a bullet, we bring 

 the rifle barrel into our 

 line of sight. We there- 

 fore feel confident that 

 if light is traveling 



through a uniform medium, such as air usually is, it goes 

 in a straight line. 



Experiment 29. Place a penny in the center of a five -pint tin pan 

 resting on a table. Stand just far enough 

 away so that the outer edge of the penny can 

 be seen over the edge of the pan. Have some 

 one slowly fill the pan with water. How is 

 the visibility of the penny affected ? 



A LAKE MIRROR. 



FIG. 33. 



top of the water, 

 the rod? 



Experiment 30. Fill a battery jar about 

 two thirds full of water. Place a glass rod or 

 stick in the jar. Does the rod appear straight? 

 Pour two or three inches of kerosene on the 

 What effect does this have on the appearance of 



