ELECTRIC POTENTIAL. 19 



glass, or other substance electrified by friction, without 

 reference to the effect on the substance by which it was 

 rubbed. But since action and reaction are equal, it is 

 evident that these two effects must, in some way, equal 

 each other ; that electricity, or its equivalent in some 

 other form of energy, must be produced on the rubber 

 as well as on the substance rubbed. 



To test this, let a piece of flannel, after being used to 

 rub a stick of sealing-wax, touch the disc of electroscope 

 -4, Fig. 4, and the leaves will instantly diverge, showing 

 that the flannel has been electrified. 



Substitute silk, fur, or any other substance used as a 

 rubber, and the same result will follow. Let the various 

 substances rubbed be also tested, and it will be found 

 that electrification has been produced on both rubber 

 and substance rubbed, at the same time, by the same 

 process. 



Now let a rubber, about the same size as the sealing- 

 wax, be prepared, by wrapping a strip of wood in flannel 

 and insulating one end with a piece of india-rubber 

 tube. 



Holding this rubber by the insulated end, let the 

 sealing-wax be rubbed with it ; and, keeping both still 

 in contact, lay them carefully on the disc of the electro- 

 scope, so that both shall touch it at the same instant, 

 and no divergence of the leaves will occur. Now lift 

 off the sealing-wax and they instantty diverge ; replace 

 it and they converge. Lift off the rubber and they 

 diverge, replace it and they converge again. 



Let the experiment be made with any other two sub- 

 stances used to generate electricity by friction, as silk 

 and glass, ebonite and fur, and similar results will be 

 obtained. 



