CHAPTER IV 



HOW THE AIR MOVES AND HOW MUCH WE NEED 



Look at the trees when the wind blows, and see the 

 clouds fly. They show that the air is moving fast, and 

 we say, " The wind is blowing." But in the house the 



MOVEMENT OF THE AIR 



air moves more quietly, though even here the warm air 

 and the cold are always changing places. 



Put a soft feather above a lighted lamp or gas jet and 

 see it fly toward the ceiling. Hot air is lighter than 

 cold air, and it gets so very hot around the lamp that 

 it goes up with a rush, taking the feather with it. Soon, 



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