SOME CHARACTERISTICS OF THE AIR 15 



pushes through the furnace into the chimney and crowds 

 the warmer air upward with sufficient current to enable it to 

 carry the smoke with it. But the incoming cold air is heated 

 as it passes through the fire, so that it is lighter than the out- 

 side air and is in turn forced upward. The movement of the 

 air is therefore continuous. 



14. Importance of air temperature. The temperature of the 

 air is a matter of importance to us all. It has much influence 

 in determining whether our sports shall be tennis, golf, and 

 baseball or coasting and snowballing ; it decides for us whether 

 the water shall invite us to swim or to skate ; it even settles 

 pretty largely the kind of clothing we shall wear, the food 

 we shall eat, and the social activities in which we shall engage. 

 It levies a tax upon us for coal at one time and for ice and 

 electric fans at another. Our whole round of activities in busi- 

 ness and pleasure is very largely regulated by the temperature 

 of the air and the seasonal changes. 



