630 Mr. W. Sutherland on the 



the Maxwellian specification of the Faraday stress in the 

 aether, when acting as an electrostatic field of intensity F, is 

 a tension F 2 /87r along the lines of force, and a pressure of 

 equal amount in every direction at right angles. Thus the 

 change of the external virial for a volume v occupied by 

 neutrons is — vF 2 /l bV on account of the tension, and 2vF 2 /167r 

 on account of pressure. But by Clausius's equation, if there 

 are no other forces this must represent the change of the 

 kinetic energy in volume v ; so that we find half the energy 

 F 2 /87r, which Maxwell considers to be stored in each unit 

 volume of the electrostatic field, is stored there as kinetic 

 energy of the neutrons, if our simple conception of the action 

 of the neutrons is correct. The other half of the energy 

 must be that which has been put into the field in turning the 

 electric axes of the neutrons so that they have all a positive 

 component of moment in the direction of the field. 



When the aether is not a field of force and the neutrons 

 have their electric axes disposed at random, two cases will 

 arise according as the neutrons have velocities of translation 

 or not. If they have, then on account of the nearer approach 

 of those attracting one another there will be a preponderance 

 of attraction, which will give cohesion to the aether. If, on 

 the other hand, the neutrons have no translatory velocities, 

 but only rotate, then attractions and repulsions will act with 

 the same strength, and there will be no cohesion in the aether 

 on account of its neutrons. Having indicated how the prin- 

 ciples of electric doublets must be applied to the aether as 

 well as to matter, we had better now analyse some of the 

 known laws of molecular force to test, before we proceed 

 farther, whether they are compatible with an origin in the 

 properties of electric doublets. But first to fix ideas we 

 must interpose the following section. 



la. The Mange of Molecular Force. 



For the central force between two small magnets no range 

 can be assigned, and similarly none can be specified for that 

 between two electric doublets by themselves. But in con- 

 sidering a large number of such doublets we find conditions 

 arise which practically fix the range of molecular attraction 

 as a distance of the same order of magnitude as the average 

 distance between two neighbour molecules. We have seen 

 that there are two reasons for the preponderance of attrac- 

 tions over repulsions, namely, an effect analogous to induc- 

 tion by which two approaching doublets tend to pull one 

 another's electric axes into the straight line joining their 



