THE ANALYSIS OF BEHAVIOUR 



131 



nerve into the central nervous system. It is there prolonged through 

 an efferent nerve into the effector organ, where it releases energy. 



Now we may try to make a " mechanical model " of this train 

 of events, premising that whatever it may be that occurs in the 

 actual nervous arc it is sure to be (physically) very different 

 from the things that happen when our model is set in action, 

 but that the energy relations in the actual muscle-nerve structures 

 and the parts of the model will be the same. Suppose, then, that 

 a number of billiard balls, a to g, are suspended by threads 

 so that they almost touch each other; let another ball, h, be 

 poised on the end of a tipless cue. Let the end ball, a. be pulled 

 a little to one side, and then let go so that it hits b very gently. 

 Further, we may assume (as it is generally assumed when logical 

 hypotheses or mechanical models are made) that the balls are 

 perfectly elastic (which they 

 nearly are), and that there is 

 no friction in their suspensions. 



The ball a will then com- 

 municate momentum to b, and OO OO Q O O 

 cause b to hit c, c to hit d, and f 6 d C b 

 so on; c will communicate as 

 much energy to d as it received 

 from b, and a wave of 

 mechanical displacement will 

 travel alqng the row. The ball g will hit h with as much force 

 in the blow as a has hit b, and the blow will cause h to roll off 

 its perch and drop to the floor. 



Suppose still further that a has been lifted up J inch; that 

 the weight of each ball is J pound; and that the height of h 

 above the floor is 6 feet. Now, in falling through J inch a does 

 work equal to its weight X the distance through which it falls 

 that is, oVx|=T2 foot-pound. The quantity of energy so 

 represented is " propagated " along the row of balls and com- 

 municated to h, and is just sufficient to push the latter off the 

 end of the cue jon which it is poised. It then falls 6 feet, and 

 so does work equal to 6xJ=2 foot-pounds. Prior to being 

 displaced it had this quantity of potential energy due to its 

 having been lifted from the floor and put in such a position that 

 it was free to fall 6 feet. A small quantity of energy representing 

 T-V foot-pound of work can therefore be propagated without loss, 

 and can release a much larger quantity that is, 2 foot-pounds. 



FIG. 39. 



