410 Scientific Proceedings, Royal Dublin Society. 



the bands from the wheels entirely : a conductor offering some 

 resistence would be represented by making the bands loose. If 

 the bands be not sufficiently tight on the wheels between a and b, 

 they will slip if the polarisation be carried far enough ; and if the 

 kinetic be much less than the statical friction, the polarisation of 

 the medium will suddenly disappear by the slipping of the bands, 

 and the energy of the polarisation will be converted into heat along 

 the line of slipping. This evidently represents a discharge between 

 the two electrified bodies. Now, observe further that, if the resist- 

 ance to discharge be very small, the momentum of the wheels will 

 carry them beyond their position of complete depolarisation, and a 

 series of oscillations will be set up, the polarisation alternating in 

 opposite directions ; but, of course, ultimately all the energy will 

 disappear as heat along the line of discharge. This exactly repre- 

 sents the discharge between two electrified bodies. If the resist- 

 ance to discharge be small enough, an oscillating discharge is pro- 

 duced which, however, ultimately dies away, all its energy being 

 spent on heating the wire along which the discharge occurs. Now, 

 observe further, the direction in which the energy of the medium 

 flows in to the line of discharge. It comes in in the length of the 

 indiarubber bands, i. «?. in a direction at right angles both to the 

 electric displacement and to the magnetic force, and it comes in at 

 the side of the line of discharge. This is exactly what Professor 

 Poynting has lately shown to be the case in the ether. 



Let us now consider the case of a complete conducting circuit 

 in which there exists an electromotive force at one place, and 

 resistances all round. This can be represented by taking away 

 the bands, or making them loose, along a series of wheels in a 

 circuit, and arranging mechanism for turning the wheels at one 

 part of this circuit, and introducing some friction at all the other 

 parts. Suppose our electromotive force is along the line a b, and 

 that the resistance is introduced by friction along the outside 

 wheels. As I have already explained that I do not intend my 

 model to illustrate the action between matter and ether, any crude 

 mechanism suffices to represent the .electromotive force. The 

 circuit where there are no bands, or loose ones, is our conducting 

 circuit, and the friction to the wheels along it is the resistance 

 of the circuit. Now, if the wheels be driven at any point of the 

 circuit, all the region will be full of wheels turning, for all the 



