838 



LORD KELVIN. 



the electric quantifies of the opposite electricities (reckoned according 

 to the old définition of mathematical electrostatics) are equal in the 

 atom and in the electrion. But even if every neutralized separate atom 

 contains just one electrion in stable equilibrium at its centre, it is ob- 

 vious that, when two atoms overlap so far that the centre of one of them 

 is within the spherical boundary of the other, the previons equilibrium 

 of the two electrions is upset, and they must find positions of equili- 

 brium elsewhere than at the centres. Thus in fig. 1 each electrion is at 

 the centre of its atom, and is attracted and repelled with equal forces 

 by the neighbouring atom and electrion at its centre. In fig. 2, if E 



Fig. 1. mg. 2. 



radii 3 and 1 

 C'C = 2'1 CE' = '1458 C£=-0462 



and E' were at the centres C, C\ of the two atoms, E would be repel- 

 led by E' more than it would be attracted by the atom A'. Hence both 

 electrions being supposed free, E will move to the right; and because of 

 its diminished repulsion on E\ E' will follow it in the same direction. 

 The équations of equilibrium of the two are easily written down, not so 

 easily solved without some slight arithmetical artifice. The solution is 

 correctly shown in fig. 2, for the case in which one radius is three times 

 the other, and the distance between the centres is 2*7 times the smaller 

 radius. ] ) The investigation in the footnote- shows that if the atoms are 



*) Calling e the quantity of electricity, vitreous or resinous, in each atom 

 or electrion: X the distance between the centres of the atoms; «, «' the radii of 

 the two atoms; x, x the displacements of the electrions from the centres; X, X' 

 the forces experienced by the electrions; we have 



