392 POPULAR LECTURES AND ADDRESSES. 



which he and other founders of the Kinetic 

 Theory of Heat attributed the elastic resistance 

 to compression presented by gases and fluids. 



Imagine, instead of the atoms and molecules 

 of the various substances which constitute the 

 sun's mass, a vast number of elastic globes, 

 like schoolboys' marbles or billiard balls. Con- 

 sider first, anywhere on our earth a few million 

 such balls put into a room, large enough to 

 hold a thousand times their number, with 

 perfectly hard walls and ceiling, but with a real 

 wooden floor ; or, what would be still more 

 convenient for our purpose, a floor of thin 

 elastic sheet steel, supported by joists close 

 enough together to prevent it from drooping 

 inconveniently in any part. Suppose in the 

 beginning the marbles to be lying motionless 

 on the floor. In this condition they represent 

 the atoms of a gas, as for instance, oxygen, 

 nitrogen, or hydrogen, absolutely deprived of 

 heat, and therefore lying frozen, or as molecular 

 dust strewn on the floor of the containing 

 vessel. 



