356 Mr. 0. J. Lodge on a Mechanical Illustration 



It' left to itself long enough, such a jar would be found com- 

 pletely discharged ; and since all the buttons would have pre- 

 served their original distance from one another, there would 

 be no internal charge in any part of the jar ; and residual 

 charge is impossible. The values of the symbols of § 8 for 

 this case are 



/ 1= / 2 =.,. , Pl =p 2 =..., 7 = 7 = •••={, °"=°J 



and after charging it by means of an electromotive force E 

 and leaving it for any time t, the whole charge can be got out 

 of it at once, and its amount will be 



CE e cr. 



3rdly. Some of the buttons may be smoother or may have 

 stronger elastics than others; and in such case they will slide 

 back more quickly than the others and will represent strata of 

 comparatively high conducting-power. Thus in fig. 1, or in 

 II (fig. 2), 3, 5, and 6 are such buttons, especially 5 ; while 

 1, 4, 7, and 8 have remained pretty steady without slipping. 

 What, then, is the condition of the dielectric in this state ? The 

 slipping back of some of the buttons will have relieved the ten- 

 sion on the cord, in other words, will have diminished the differ- 

 ence of potential of the two coatings ; but no motion of the cord 

 has taken place either way because of the clamp at C. In the 

 figure the buttons 1 and 8 have remained tight on the cord; 

 consequently the charges on the two coatings happen to have 

 remained constant ; but charges have appeared in between the 

 strata. For instance, between 3 and 4 there is too much cord; 

 the dielectric is there positively charged ; between 4 and 5 

 it is negatively charged. The difference of potential between 

 the two faces of the stratum 5 has almost vanished. 



§ 4. Now unclamp the screw S, i. e. make metallic contact 

 between the two coatings : a rush of electricity takes place; 

 the buttons spring back, and after a few oscillations take up 

 the position of equilibrium shown in III, fig. 2. They have in 

 fact been all displaced the same distance to the left; and so 

 those which (like 3, 5, and G) had, before discharge, slid almost 

 to their mean position are now displaced beyond it, and the strain 

 in their elastics is acting in the reverse direction to what it did 

 before ; consequently the elastics of 1, 2, 4, 7, and 8 have not 

 been able quite to resume their normal length, but they remain 

 in such a state of strain as to exert as much stress one way as 

 the elastics of 3, 5, and 6 are exerting in the other direction. 

 The jar then appears discharged, but we have not yet got the 

 whole charge out of it. Screw down S again and wait. 



