AND MODERN PHYSIC'S. 217 



remark " Maxwell does not give a mechanical ex- 

 planation of electricity and magnetism, lie is only 

 concerned to show that such an explanation is 

 possible " is most important 



Wo cannot find in the " Electricity " an answer to 

 tho question What is an electric charge ? Maxwell 

 did not pretend to know, and the attempt to give too 

 great detiniteness to his views on this point is apt to 

 lead to :i misconception of what those views WTO. 



On tho old theories of action at a distance and of 

 electric and magnetic fluids attracting according to 

 known laws, it was easy to be mechanical. It was only 

 necessary to investigate tho manner in which such 

 fluids could distribute themselves so as to bo in equi- 

 librium, and to calculate tho forces arising from the 

 distribution. The problem of assigning such a 

 mechanical structure to the ether as will permit of 

 its exerting tho action which occurs in an electro- 

 magnetic field is a harder one to solve, and till it is 

 solved the question What is an electric charge? 

 must remain unanswered. Still, in order to grasp 

 Maxwell's theory this knowledge is not necessary. 



Tho properties of ether in dielectrics and in con- 

 ductors must be quite different. In a dielectric the 

 ether has the power of storing energy by some change 

 in its configuration or its structure ; in a conductor this 

 power is absent, owing probably to the action of the 

 matter of which the conductor is composed. 



When we arc said to charge an insulated conductor 

 wo really act on tho ether in the neighbourhood of tho 

 body so as to store it with energy ; if there I.KJ another 

 conductor in the field we cannot store energy in tho 





