CHAPTER II. 

 ELECTEIC INERTIA. 



WHATEVER a charge may be, and whatever the 

 physical constitution of the ether, it must be able 

 to maintain electric lines and magnetic lines 

 separately, and to transmit energy wherever both 

 sets of lines coexist and cross each other. 



An accelerated charge is equivalent to a changing 

 current, for dC/dt may be written d 2 e/dt 2 . When- 

 ever a current changes it is well known that an E.M.F. 

 of self-induction is set up, equal to LdC/dt; and 

 this electrical equation E = L e corresponds to the 

 mechanical equation F = ra x, Newton's second law. 



Considered from the point of view of a current as 

 constituted by a moving charge, this self-induced or 

 reaction E.M.F. corresponds or is analogous to a mass- 

 acceleration. And the electrical acceleration is 

 opposed by the E.M.F., just as the acceleration of 

 matter is opposed by its mechanical inertia. The 

 coefficient of the electric acceleration commonly 

 denoted by L represents therefore an inertia term, 

 and is properly called 'electric inertia.' 



By Lenz's law the effect of induction is always 

 to oppose the cause which is producing it. In the 

 present case the * cause' is the acceleration or retarda- 

 tion of the moving charge ; and so, in each case, this 



