848 



LORD KELVIN. 



corners, of a tetrahedron. Froin any case of any number of electrions ail 

 on one spherical surface,, we may pass to another configuration with 

 one more electrion placed at the centre and the proper proportionate 

 increase in the electric strength of the atom. Thus from the cases des- 

 cribed in § 19, we may pass to configurations of equilibrium for seven, 

 nine, eleven, thirteen, and twenty-one electrions. Ail thèse cases, with 

 questions of stability or instability and of the différent amounts of work 

 required to pluck ail the electrions out of the atom and remove them 

 to infinité distances, présent most interesting s abjects for not difficult 

 mathematical work ; and I regret not being able to pursue them at 

 présent. 



§23. Consider now the electric properties of a real body, gaseous, 

 liquid, or solid, consiituted by an assemblage of atoms with their elec- 

 trions. It follows immediately from oui* hypothesis , that in a mona- 

 tomic gas or in any sufnciently sparse assemblage of single atoms, fixed 

 or moving, Faraday's „conducting power for Unes of electric force" , or 

 what is uoiv commonly called the spécifie electro-iiicluctive capacity, or 

 the electro-iuductive perméabilité/, exceeds tmity by titrée limes the ratio 

 of the sum of the volumes of the atoms to the whole volume of space 

 occupied by the assemblage , whether the atoms be monelectrionic or 

 polyelectrionic, and however much the electrion, or group of electrions, 

 within each atom is set to vibrate or rotate with each collision, accor- 

 ding to the kinetic theory of gases. To prove this, consider, in a uniform 

 field of electrostatic force of intensity F, a single atom of radius 

 and, at rest within it, a group of i electrions in stable equilibrium. The 

 action of F produces simply displaceinents of the electrions relatively 

 to the atom, equal and in parallel lines, with therefore no change of 

 shape and no rotation ; and, x denoting the amount of this displacement, 



the équation for the equilibrium of each electrion is —y = F. This 



gives iex = a? F for the electric moment of the electrostatic polari- 

 zation induced in the atom by F. In passing, remark that o>? F is also 

 equal to the electric moment of the polarization produced in an insu- 

 lated unelectrified métal globe of radius a, when brought into an elec- 

 trostatic field of intensity F: and conclude that the electric inductive 

 capacity of a uniformly dense assemblage of fixed metallic globules, so 

 sparse that their mutual influence is negligible, is the same as that of 



