LIGHT AND ELECTRICITY. 139 



In like manner, wlien the currents have the same direction, they 

 attract each other — that is to say, they tend to approach each other, 

 which woukl increase the living- force if the intensity were maintained. 

 If their directions are opposed they repel one another and tend to 

 sepai\ate, which would again tend to increase the living force were the 

 intensity kept constant. 



Thus, the electrostatic effects would be due to the elasticity of the 

 ether and the electrodynamical phenomena to the living force. Now, 

 ought this elasticity itself to be explained, as Lord Kelvin thinks, by 

 rotations of small parts of the fluid? Different reasons may render 

 this hypothesis attractive; but it plays no essential part in the theory 

 of Maxwell, which is quite independent of it. 



In the same wpy, I have made comparisons with divers mechanisms. 

 But they are only similes, and pretty rough ones. A complete mechan- 

 ical explanation of electrical phenomena is not to be sought in the 

 volumes of Maxwell, but only a statement of the conditions which any 

 such explanation has to satisfy. Precisely what will coufer long life 

 on the work of Maxwell is its being uneutangled with any special 

 mechanical hypothesis. 



