of the Coefficients of Induction. 



463 



E. 



P- 



First Swing 

 (mean). 







•008 



293-5 



1000 



•019 



291-2 



5000 



•064 



269-0 



10000 



•120 



234-0 



50000 



•568 



105-5 



100000 



1-128 



61-5 



200000 



2-248 



36-0 



300000 



3-368 



25-0 



Thus, for the particular galvanometer tested, the throw 

 produced by a given discharge when the time-constant is one 

 tenth of the period is only about 80 per cent, of that produced 

 by the instantaneous discharge of the same quantity ; and 

 when the time-constant is equal to the period, the throw is 

 only about 20 per cent, of the corresponding throw for 

 instantaneous discharge. Experiments since made with a 

 high-resistance Thomson astatic galvanometer, with a period 

 of 10 seconds, have yielded practically the same results. In 

 the actual experiments on the Ferranti field-magnet coils, it 

 would have been possible to interpret the meaning of the 

 galvanometer-swings if the time-constant of discharge had 

 had any fixed value, or if this value had been known ; but 

 the resistances and self-induction were continually varying, 

 and the self-induction was always unknown. It would pro- 

 bably have been impossible even to compare the results with 

 each other had it not been for the fact that, as the currents 

 increased, the resistance and self-induction of the circuit 

 diminished simultaneously, so that the time-constant of dis- 

 charge tended to remain fixed in value. 



11. The experiments on the dynamo coils were carried out 

 by Messrs. Rossiter and Watney together with the writer. 



The electromotive force used was obtained from accu- 

 mulators, and amounted to about 100 volts. The bridge 

 was kept balanced for steady currents. The only resistance 

 altered was that in the battery-circuit. The currents were 

 changed by switching resistances into or out of the battery- 

 circuit. If Q is the quantity of electricity discharged through 

 the galvanometer when the current in the coil changes from 



C, to C 9 



L 1= K 



Q 



Ci — c 2 



where K is a function of resistances only, and is independent of 

 the resistance of the battery branch when the bridge is balanced 



