Radiant Heat and Light 157 



A mirror that magnifies. A convex lens is not the 

 only thing that can magnify. A concave mirror, which 

 is one that is hollowed out toward the middle, does the 

 same thing. When light is reflected by such a mirror, 

 it acts exactly as if it had gone through a convex lens 

 (Fig. 85). 



Experiment 49. Place the lighted candle and the paper 

 about 4 feet apart, as you did in Experiment 47. Hold a 

 concave mirror back of the candle (so that the candle is 

 between the mirror and the paper) ; then move the mirror 

 back, the mirror casting the reflection of the candle light 

 on the paper, until a clear image of the candle is formed. 



Look at your image in the concave mirror. Does it look 

 larger or smaller than you ? 



How telescopes are made. Astronomers use convex 

 lenses in some of their telescopes ; in others, called 

 reflecting telescopes, they use concave mirrors. Both do 

 the same work, making the moon, the planets, and the 

 sun look much larger than they otherwise would. 



Application 37. Explain how a reading glass makes print 

 look larger; how you can see germs through a microscope; 

 what kind of mirror will magnify; what kind of lens will 

 magnify. 



Inference Exercise 

 Explain the following : 



221. The water that forms rain comes from the ocean, yet the rain 



is not salty. 



222. Iron glows when it is very hot. 



223. You can start a fire with sunlight by holding a reading glass 



at the right distance above the fuel. 



224. Big telescopes make it possible for us to see in detail the sur- 



face structure of the moon. 



225. A room is lighter if it has white walls than if it has dark walls. 



226. Iron is heated by a blacksmith before he shapes it. 



