512 CONSTANTS OF COILS. 



The intensity y of the current which passes through the shunt 

 satisfies equations 



The condition of equilibrium for the variable state remains 

 the same, and gives 



f 



M = 0, 

 \ c / 



or 



L (a a+b 



The discussion of the equations shows that the relative error 



for the ratio - - is about 100 times that made in adjusting the 

 -L* 



resistances.* To obtain the greatest precision of which the method 

 is susceptible, the galvanometer should be 100 to 1000 times more 

 sensitive for transient than for permanent currents. It is advan- 

 tageous to produce a permanent state by means of a rotating 

 commutator. 



1099. COMPARISON OF A CAPACITY WITH A COEFFICIENT OF 

 INDUCTION. By using repeated discharges, a capacity may be 

 compared with a coefficient of mutual induction (1063). By the 

 method of equilibrium we may also determine the ratio of a ca- 

 pacity to the coefficient of self-induction L of a coil. Place the 

 coil in the branch AD of Wheatstone's bridge (Fig. 235) and the 

 condenser F as a shunt on the branch CB. The condition that 

 there is no current in the galvanometer is that the two points CD 

 are at the same potential. If V is the difference of potential of the 

 two armatures at a given time, this condition gives the two equations 



T da! 

 aa = aa +L- , 



at 



* M. BRILLOUIN. Loc. at., p. 348. 



