232 Prof. C. Niven on Determining and Comparing 

 resistance of each coil, 



. G S Gq ' 

 the total flow through both coils 



and this will be a maximum when 



(R + G + c)(2B + R + F + c)/Gis a minimum, 

 that is, when 



G 2 =(R + c)(2B + R + c). 



§ 4. To Compare two Coefficients of Self-induction. 



The following method, which is a modification of Maxwell's, 

 was suggested by the one which follows and by that given 

 in § 5. 



Method I. — Wheatstone's-bridge arrangement. The coil 

 L, whose resistance is y v is first balanced by resistances a ly b, d 

 for steady currents ; a ] is then placed in series with the second 



coil (N), whose resistance suppose = a 2 , and is balanced by 

 putting 7 2 in series with ^ ; « 1? y 2j b, d being supposed to 

 have no appreciable self-induction. The conditions for this 

 are 



a i/Yi = a 2/72 = £/d- 



When these conditions are accurately satisfied no steady cur- 

 rent should pass through the galvanometer, whether P and Q 

 are connected by a wire or not. If the second adjustment 

 should throw the first slightly out, the right position of Q, 

 P being kept fixed, may be easily got by making the first 

 part of « 2 and the last part of u x parts of the same wire, along 

 which we may have sliding contact. Kohlrausch's form of 

 the bridge is convenient for this purpose. It is also desirable 

 in most cases to interpolate a resistance into ji besides that of 

 the coil itself. 



A resistance S is then placed in PQ till no " kick " is given 

 on making contact. Our equations in this case are 



