136 Dr. 0. J. Lodge on Intermittent Currents 



for the current in a solitary primary circuit, as it evidently 

 ought to do ; and there is nothing new to be said about it. 



But the value of j, the current induced in the secondary 

 circuit, becomes 



^w^m (eh ~*°- • • • (28) 



To find the induced current at instantaneous break in the 

 special case now being considered, we must put 8= go , and 

 we get 



££•-'" w 



which is the recognized value for it (see Chrystal, ' Encyc. 



TVT TT 

 Brit.' equation (41)). Its initial or maximum value is 7- . p5 

 and it rapidly dies away. 



To find the induced current at "make " we must put K=qo ; 

 and then (28) becomes 



MTT1 s, r 



'--•CraByfr" 1 - e_f< >- • • • ( 30 > 



This, therefore, begins at zero, rises to a maximum after the 

 lapse of time 



LI . Lr 



^Lr^m^m' 



and then dies away. 



If the primary and secondary circuits are similar, so that 



S r 



L = r 



the expression for the induced current at make simplifies, 

 becoming 



>— 5** < 31 > 



14. Case 2. — When the primary and secondary circuits 

 are wound side by side, so that the coefficient of mutual induc- 

 tion nearly equals the coefficient of self-induction of either — 

 in other words, so that L = Z=M. 



For this case (see equations 22 and 25), 

 4'rS 

 Xss ( r _g)3 » and a=^ = co ; 



but if we put L— M= a small quantity z 9 say, and then pro- 

 ceed to the limit, we shall find a finite value for the difference 



