INTELLIGENT BILLIARD BALLS. 



and their speed, and that the amount of energy 

 conveyed can be varied by varying either 

 the mass or the speed. But in the present case 

 we are supposing that only the number that 

 is, the mass of the striking balls is varied, 

 while the hand always moves them up to 

 the striking point so far as possible at the same 

 speed. The velocity of the hand, then, being 

 approximately constant in our trials, the velocity 

 of movement with which the stroke is delivered 

 is constant. The ball which is struck being 

 prevented from moving freely, partly by its 

 own inertia, and partly by that of the balls 

 in front, receives the energy of the striking 

 movement partly in the form of limited move- 

 ment of its whole mass, partly in the form of 

 compression waves transmitted through its 

 substance and that of the other balls. 



For the balls are elastic, and their elasticity, 

 though of much less amplitude than that of 

 indiarubber, is quite as real. This may be 

 easily shown preferably with other people's 

 balls by bouncing them on a stone floor. 



Now the speed with which the wave of com- 

 pression is transmitted depends on the speed 

 of that movement of the striking ball which 

 is transformed into compression waves, and 

 not on the mass, or number of balls, behind it. 

 And the energy of the compression waves is 

 re-transformed at the other end into move- 

 ment of balls whose velocity corresponds to 



39 



