844 



LORD KELVIN. 



atom of any sliape whatever and having any arbitrarily given distri- 

 bution of electricity of the opposite kind fixed within it, the greatest 

 quantity of fluid which it can take is exactly equal to its own, and 

 lodges with density equal to its own in every part. Hence if the atom 

 is spherical, and of equal electric density throughout as we have sup- 

 posed it, and if its neutralizing quantum of electrions is a very large 

 number, their configuration of equilibrium will be an assemblage of 

 more and more nearly uniform density from surface to centre, the 

 greater the number. Any Bravais homogeneous assemblage whatever 

 would be very nearly in equilibrium if ail the electrions in a surface- 

 layer of thickness a hundred times the shortest distance from electrion 

 to electrion are held fixed; but the equilibrium would be unstable except 

 in certain cases. It may seem probable that it is stable if the homoge- 

 neous assemblage is of the species which I have calied ] ) equilateral, 

 being that in which each electrion with any two of its twelve next 

 neighbours forms an equilateral triangle. If now ail the electrions in 

 the surface layer are left perfectly free, a slight rearrangement among 

 themselves and still slighter among the neighbouring electrions in the 

 interior will bring the whole multitude (of thousands or millions) to 

 equilibrium. The subject is of extrême interest, geometrical, dynamical 

 and physical, but cannot be pursued further at présent. 



§ 17. To guide our ideas respecting the stable equilibrium of mode- 

 rate numbers of electrions within an atom, remark first that for any 

 number of electrions there may be equilibrium with ail the electrions 

 on one spherical surface concentric with the atom. To prove tins, dis- 

 card for a moment the atom and imagine the electrions, whatever their 

 number, to be attached to ends of equal inextensible strings of which 

 the other ends are fixed to one point C. Every string will be stretched 

 in virtue of the mutual repulsions of the electrions; aud there will be 

 a configuration or configurations of equilibrium with the electrions on 

 a spherical surface. Whatever their number there is essentially at least 

 one configuration of stable equilibrium. Kemark also that there is 

 always a configuration of equilibrium in which ail the strings are in 



x ) „Molecular Tactics of a CrystaV\ § 4, being the Second Kobert Boyle Lec- 

 ture, delivered before the Oxford University Junior Scientifie Club. May, 16, 

 1893 (Clarendon Press, Oxford). 



