Mpher — The Electrical Capacity of Bodies. Ill 



This formula is also the same as would be obtained by inte- 

 grating ( 2) between r and i\. If C represent electrical capacity, 



and we indicate by P = -5- , the perviance of the medium, 

 both (3) and (4) may be written, 



-*- = P = 4*C (5) 



orC =4~V (6) 



This means that the electrical capacity of these bodies de- 

 pends solely on the nature of the medium which surrounds 

 them, and upon the characterizing dimensions of that portion 

 of the medium which carries the field of force. Or in other 

 words, the capacity depends solely on the perviance for the 

 flow of induction from the body, of that part of the surround- 

 ing medium which carries the field of force. 



The energy of the electrification is 



_ _ Q 2 _ (4 » Q) 2 R 



W _ 2C " 8* (7) 



If the flow of force or induction which we have treated as a 

 current in applying Ohm's law, be denoted by I, the last 

 equation becomes 



0^ PR 

 W ~~ 2<J ~~ 8* («) 



The first member of this equation is the potential energy 

 of an electrification, which is in equilibrium. The second 

 member represents the same quantity, in terms, which, in 

 form, are precisely like the expression for power, or work 

 per second, done on a conductor having a resistance R, by a 

 current of electricity I. In the electrical conductor, this 

 expression represents the heat generated per second in the 

 conductor. In the dielectric through which the flow of force 

 takes place no heat is developed, but a condition of stress is 

 maintained. 



