Radiant Heat and Light 129 



185. Clothes get hot when you iron them. 



1 86. Potatoes fried in deep fat cook more quickly than those 



boiled in water. 



187. If you hold your hand near a vacuum electric lamp globe 



that is glowing, some of the heat will go out to your hand 

 at once. 



1 88. Rubbing silver with fine powder polishes it. 



189. A mosquito can suck your blood. 



190. A hot-water tank becomes hot at the top first, then grad- 



ually heats downward. When you light the gas under 

 an ordinary hot-water heater, the hot water circulates 

 to the top of the boiler, while the cold water from the 

 boiler pushes into the bottom part of the heater, as shown 

 in Figure 59. What causes this circulation? 



SECTION 22. Reflection. 



How is it that you can see yourself in a mirror ? 

 What makes a ring around the moon? 

 Why can we see clouds and not the air? 

 Why is a pair of new shoes or anything smooth usually 

 shiny ? 



If we turn off a switch labeled REFLECTION OF LIGHT 

 on our imaginary switchboard, we think at first that 

 we have accidentally turned off RADIATION again, for 

 once more everything instantly becomes dark around 

 us. We cannot see our hands in front of our faces. 

 Although it is the middle of the day, the sky is jet black. 

 But this time we see bright stars shining in it. And 

 among them is the sun, shining as brightly as ever and 

 dazzling our eyes when we look at it. But its light does 

 no good. When we look down from the sky toward 

 the earth, everything is so black that we should think 

 we were blind if we had not just seen the stars and sun. 



Groping our way along to an electric lamp, we turn 

 it on. It shines brightly, but it does not make any- 



