CHAPTER VI. 



THE STATE OF THE MEDIUM IN THE ELECTROSTATIC FIELD. 



153. THE whole electrostatic theory has so far been based simply upon 

 Coulomb's Law of the inverse square of the distance. We have supposed 

 that one charge of electricity exerts certain forces upon a second distant 

 charge, but nothing has been said as to the mechanism by which this action 

 takes place. In handling this question there are two possibilities open. We 

 may either assume " action at a distance " as an ultimate explanation i.e. 

 simply assert that two bodies act on one another across the intervening 

 space, without attempting to go any further towards an explanation of how 

 such action is brought about or we may tentatively assume that some 

 medium connects the one body with the other, and examine whether it is 

 possible to ascribe properties to this medium, such that the observed action 

 will be transmitted by the medium. Faraday, in company with almost all 

 other great natural philosophers, definitely refused to admit "action at 

 a distance " as an ultimate explanation of electric phenomena, finding such 

 action unthinkable unless transmitted by an intervening medium. 



154. It is worth enquiring whether there is any valid a priori argument which 

 compels us to resort to action through a medium. Some writers have attempted to use 

 the phenomenon of Inductive Capacity to prove that the Energy must reside in the space 

 between the charged plates of a condenser, rather than on the plates themselves for, 

 they say, change the medium between the plates, keeping the plates in the same condition, 

 and the energy is changed. A study of Faraday's molecular explanation of the action in 

 a dielectric will shew that this argument proves nothing as to the real question at issue. 

 It goes so far as to prove that when there are molecules placed between electric charges, 

 these molecules themselves acquire charges, and so may be said to be new stores of energy, 

 but it leaves untouched the question of whether the energy resides in the charges on the 

 molecules or in the ether between them. 



Again, the phenomenon of induction is sometimes quoted against action at a distance 

 a small conductor placed at a point P in an electrostatic field shews phenomena which 

 depend on the electric intensity at P. This is taken to shew that the state of the ether 

 at the point P before the introduction of the conductor was in some way different from 

 what it would have been if there had not been electric charges in the neighbourhood. But 

 all that is proved is that the state of the point P after the introduction of the conductor 

 will be different from what it would have been if there had not been electric charges in 

 the neighbourhood, and this can be explained equally well either by action at a distance or 



