EQUATIONS OF THE ELECTRICAL FIELD. 555 



In the case of a conductor, on the contrary, the displacement is 

 null, and if c is the specific conductivity of the medium, Ohm's law 

 becomes 



Pc=u t 

 (14) Qc=v, 



Finally, if p is the density of the free electricity at the point in 

 question, we shall have, with a dielectric, the condition 



and, in the case of a conductor, 



TNn ~t\i/ 

 (16) 



The twenty values F, G, H ; P, Q, R; X, Y, Z ; u, v, w; f, g, h; 

 u', v', w' ; p and ^ can be determined from the twenty equations in 

 numbers (2), (10), (n), (12), (13), (14), (15), and (i 6), when the 

 conditions of the problem in each special case are known. 



