548 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



there cannot be any impulsive change of the induction flux when 

 the inductance is suddenly increased. A glance at the figure shows, 

 however, that the rate of increase of the induction suddenly becomes 

 much greater than it was just before the change. 



Curve ODE of Figure 7 shows the manner of growth of the current 

 in another simple circuit of fixed inductance, 4X. If, at the time OW, 

 when the current has attained half its final strength, and the induction 



Figure 6. The line ONJ represents the current in a circuit of inductance L 

 without iron. OPT shows the form of the current in the same circuit when 

 the inductance has been increased to 4L. ONFG is the current when the 

 inductance is suddenly changed from L to 4L at the time OU. 



flux through the circuit is represented on the scale indicated by 

 equation by OABD, the inductance be suddenly changed to L, the 

 current suddenly becomes four times as strong as it was and tlien falls 

 in a manner shown by the curve ST. The flux through the circuit just 

 after the change is already twice as large as it will be eventually when 

 the current reaches its final value, OA, and it decreases by an amount 

 represented by the area BST, which is half the area AODB. Just 

 before the change the flux was increasing with the time at a rate 

 represented by the length of the line BD ; just after the change it 

 decreases at a rate represented by the line BS, which is twice as long 

 asDB. 



In the case of a circuit which does not contain iron, an increase of 



