6S2 Prof. L. T. More on Dielectric 



the matter immersed in it. As an illustration, we can make 

 use of the system of glass and liquid dielectrics just described. 

 The lines of electric flux in the aether stretch from one charged 

 armature to the other and may experience, for all we know, 

 the tensions and pressures generally ascribed to them. Since 

 both the glass and the liquid have the same dielectric constant, 

 there is no discontinuity of the lines at the surface of the glass, 

 yet it is supposed to contract in their direction. The only 

 mechanical arrangement I can think of, is to assume that each 

 line does not extend from armature to armature but is like a 

 chain linking particle to particle of the glass. Let us, to be 

 more precise, consider the action of a tension in one of these 

 chain lines on three particles, — one in the surface of the liquid 

 adjoining the glass, a second in the surface of the glass, and 

 the third just within the surface of the glass. Since the 

 dielectric constant is the same in the two substances, the pull 

 on the middle particle is the same in 1 the two directions, and 

 there is no tendency to displacement of the surface of the 

 glass. This is also true for any three particles in the glass, 

 and a contraction does not occur. Of course, where there is 

 a discontinuity of the lines, either in passing from one 

 dielectric to another of a different inductive capacity or from 

 a dielectric to a contiguous conductor, an unbalanced force 

 exists, but that is merely the measure of the attraction of the 

 two charged bodies. It the lines of flux are supposed to pass 

 through ihe glass without being attached to its particles, it 

 is even more difficult to see how the stress in the aether effects 

 the glass. 



If we assume Maxwell's formula for electric stress in the 

 aether, and I know no other adequate, we must not lose sight 

 of a most important fact, that theories involving the aether 

 must always remain purely hypothetical, as we have no 

 possible method of experimentation upon it. And only when 

 matter is immersed in the aether does experimentation become 

 possible. Now all our observation goes to show, that for 

 static and even for kinetic phenomena, at least where the 

 velocity is less than that of light, the aether is unmodified by 

 the presence of matter and does not affect the properties of 

 it : witness the absence of friction between the earth and 

 aether in its motion about the sun ; the Kerr effect of the 

 polarization of transparent matter when electrified ; Brace's 

 experiments on the action of a magnetic field on transparent 

 media showing that the Faraday stresses affect the velocity 

 of light by an amount less than 2*0 x 10 -14 for a c.G.s. 

 unit of intensity per centimetre ; and many others all 

 supporting the doctrine of the independence of aether and 



