452 Mr. J. H. Jeans on the 



Thus if b is comparable with a, the coefficient k, given by 



C °° —5 

 4tt&= Ee a d^E 



will vary rapidly with slow changes in b/a. 



Fie:. 2. 



y 



Since a is the measure of a subsidiary temperature, a may 

 vary enormously from one substance to another. 



Calculation of Specific Inductive Capacity. 



§ 40. Under a steady field of electric force C every ion at 

 the surface of any atom is in equilibrium under the force, the 

 displacement-potential of the atom to which it belongs, and 

 the potential arising from other atoms. Neglecting the latter, 

 the displacement-potential at every point of the surface of any 

 atom must be E# ; or if R is the radius of the atom, 



E^cosfl (34) 



At all points outside the atom this displacement-potential 

 satisfies Laplace's equation, and it is continuous with (34) 

 at r = R 1 . The general solution is therefore 



E cos dU^/r 2 . 



If there are "Ndv such atoms in a small element of volume dv, 

 the total displacement-potential at an external point will be 



NE cos OU^dv/r 2 or ENR^/r*. 



The specific inductive capacity of a medium composed of 

 such atoms will therefore be given by 



kT2~ NKl ' 



