COMPARISON OF SELF-INDUCTION AND MUTUAL INDUCTION. 511 



while the difference of potential between the summits A and D is 

 equal to a'a!. 



Complete equilibrium requires the two conditions 



dt dt 



As I = a + a', it follows that 

 L 



M 



-B)- 



As the coefficient L is essentially positive, M must be negative, 



E 

 II H 



and therefore the two currents must be in opposite directions in the 

 two coils. We should, further, have L > - M. 



As the branches of the bridge have no induction of their own, 

 and are first adjusted for the permanent regime, we may adjust the 

 effects of induction in several ways : 



i st. The value of M is varied by changing the relative position 

 of the two coils, until the variable currents are in equilibrium. 



2nd. M being supposed constant, and smaller than L in absolute 

 value, the two resistances are modified in the same ratio, until equili- 

 brium is obtained. 



3rd. Between the points A and B, at which the battery termi- 

 nates, a shunt of resistance c is introduced which has no induction 

 of its own. 



