22 The Cause of Life and Motion 



is toward the body. "When a body, a cannon ball for 

 instance, is suddenly impelled forward, a large propor- 

 tion of these waves are immediately thrown on its 

 posterior side, and they will sustain the ball in its 

 movement until the ball is either brought to a stop by 

 some obstacle or until the waves recover their equili- 

 brium. 



The limit of the ball's flight cannot exceed that 

 which is due to the displaced energy, by any 

 power in the universe applied as an initial im- 

 pulse. Therefore, the limit of flight of any ball 

 may be measured by its displacement of energy, 

 or in other words by its inertia. A ball of cork 

 may be projected with a velocity that would soon 

 exhaust its displaced energy, and in such a case 

 the ball would either be dissipated or it would 

 stop as suddenly in the air, or even in what is 

 called a vacuum, as if it had impinged against a 

 granite wall. If a piece of cork should be 

 placed in the water and allowed to remain there 

 long enough to become soaked through, its dis- 

 placement of energy would become much less 

 than before, and an impulse might be given it by 

 the hand sufficient to exhaust its surrounding 

 energy. And with such an impulse, it would 

 suddenly stop and rebound. If another cork 

 however should be experimented with of pre- 

 cisely the same shape and displacement below 

 the water line, but formed into a thin hollow ves- 

 sel so that a considerable proportion of it should 



