34^ COMPARISON OF RESISTANCES. 



receives a swing proportional to the integral idt extended to the 

 whole duration of the change. 



Each of the terms of this integral which does not depend on /, 



Cda 



such as L a dt, is equal to L a (a 2 -a 1 ), a x and a 2 being the 

 J dt 



initial and final intensities. This term is zero when the intensity 

 is the same at the two limits. 



This would particularly be the case for terms relating to all 

 branches of the network if, instead of a constant electromotive 

 force E, we introduce in the branch R a transient electromotive 

 force like that obtained in closing and then quickly opening the 

 circuit of a battery, or by the displacement of an adjacent magnet,' 

 or, lastly, by the rotation of a circuit. The condition of equilibrium 

 of the bridge being realised, the needle remains stationary in the 

 two cases, for the intensity / is null at the two limits. 



951. When a constant electromotive force E is introduced in 

 the branch R, the diagonals being always conjugate, all the currents 

 are at first zero at the moment the circuit is closed, and finally, from 

 equations (22), acquire the values 



a 



-, 



The swing of the needle is proportional to 



MN a a ' 



Taking into consideration that ab { ' = &a', this expression may be 

 written 



