MIRRORS 51 



each flame, and square this distance ; that is, multiply it by itself. 

 Now divide the square of the distance of the larger candle by 

 the square of the distance of the smaller candle. Suppose the 

 result is 3.5. This would mean that the larger candle has 3.5 

 times as great an illuminating power as the smaller candle. 

 What result do you get? 



6. Now compare the illuminating power of a lamp, or of an 

 electric bulb, with that of the large candle. Instead of the 

 spools, you can use an upright pencil, and instead of putting it 

 between the two sources of light, you can put it to one side, as 

 in Fig. 145, 171, of the text. What is the "candle power" of 

 the lamp or bulb? 



EXERCISE 50 

 MIRRORS 



Apparatus and Materials. Mirror (vertical), two hand mirrors, 

 pencil, plate glass or thick window glass, bottle of water, small candle, 

 silver spoon. 



a. Before a vertical mirror hold an open book, with the pages 

 toward the mirror. How are the letters apparently altered by 

 the reflection? 



6. Lay a mirror, such as a hand glass, on the table before you, 

 and set an- open, upright book behind the mirror. How does the 

 image of the letters differ from the letters themselves? 



c. With a mirror lying flat on the table before you, take a 

 second mirror in both your hands and revolve the mirror slowly, 

 so that first its face and then its back are turned toward you. 

 By changing your distance from the mirror you will find a 

 position in which you can see images of yourself, at one time 

 upright, at another, upside down. Objects behind the mirror 

 will also form images in both upright and inverted positions. 

 You can also get a large number of images of yourself at one 



