-> 



TUK NATURE OF ELECTRICITY. 3o 



as yielding levers to transmit the impulse" along its 

 length. 



If one end of a lever be depressed below a horizon! 

 it receives a forward as well as downward movement, 

 in the arc of a circle, its opposite end receiving an up- 

 ward and backward movement. In this way each suc- 

 cessive portion of the rope oscillates horizontally as 

 well as vertically, modified by the difference between a 

 yielding and a rigid body. 



Let a number of elastic balls be suspended in a 

 straight line in contact with each other. Draw back 

 the outer ball at one end of the line and let it swing 

 against the adjoining ball ; the impulse will be trans- 

 mitted along the line, and the outer ball, at the other 

 end, will swing off to nearly the same distance as that 

 through which the first ball swung, all the others re- 

 maining stationary. 



Here the impulse is transferred from ball to ball by 

 virtue of their elasticity. When number one impinges 

 on number two the impact changes its shape slightly to 

 that of a spheroid; as it resumes its shape it imparts the 

 impulse to number two, by which it is imparted to num- 

 ber three, and so on through the line. But action and 

 reaction being equal and opposite, there is no perceptible 

 movement till the last ball is reached, which swings off, 

 since there is no ball to react against it. The impulse 

 travels, but the line remains stationary. 



Here, also, it will be perceived that there is a radial 

 force acting at right angles to the horizontal force, 

 much the same as would result from a similar impact 

 if each ball were hollow, and its surface composed of an 

 infinite number of semicircles, joined at the points of 

 impact. 



