On tlie Comparison of Two Self-Inductit 



609 



resistance CE is equal to the resistance ED. If the resistance 

 in the arm DF is equal to that in CE there will be no per- 

 manent current in the galvanometer, and if the self-induction 

 in DF is equal to that in CF, there will be no transient 

 current when the battery key is put down after the galva- 

 nometer key. The method consists in varying S and R till 

 both these conditions are fulfilled. 



Denoting the resistances of A and B by X and Y, and 

 their coefficients of self-induction by L and N, we have, then, 



~ = (l+JY, and 



xs 



x+s 



, =Y+n. 



xs 



It is possible that Y may be greater than v- ^ : and, in 



that case, the resistance R should be in CF in series with the 

 system consisting of A and S. Any inconvenience of moving 

 the variable resistance R from DF to CE will be avoided by 

 having variable resistances in both arms. 



The following experiment will illustrate the ease with 

 which the adjustment can be made. 



Resistance of A- 109*3 ohms. 

 Resistance of B= 14*5 ohms. 



E in ohms. 



S in ohms. 



Kick on taking out 

 Battery Key. 







167 



Eight- 



10 



31-5 



Eight. 



20 



50 



Eight. 



30 



75 



Eight. 



40 



109 



Eight. 



50 



157 



Eight. 



60 



233 



Eight. 



70 



371 



Eight, but small. 



80 



697 



Lett. 



72 



414 



Eight, one division. 



73 



434 



No kick. 



74 



465 



Left, one division. 



X the coefficient of self-induction of B is therel 



to 



ore equa. 



434 2 L L -i. 56 * 



(434+109-3) 2 ' N 



* Very careful measurements by Mr. VV. G. Griffith of the self- 

 inductances of these coils, in which Lord Kayleich's method was used, 

 gaie ; for A, Q'236 henry, and, forB, 0-151 henry. 



