236 Prof. C. Niven on Determining and Comparing 

 If x — u=<y, 



(a + c + G)y + a + c. u— az=— Li? . 

 From which we obtain, eliminating u t z and putting 

 x = z b/(b + d), 



z =E(b + d)/(B.b + d + d.a + b), 



B (ej±g^Ly)) 



(« + c+G.5 + aGr.l + -^-J(B.6 + rf + d.a + 6) 



B, it must be remembered, includes the resistance of one of 

 the coils as well as that of the battery. 



R includes the resistance of the other coil of the pair, with 

 the additional resistance necessary to neutralize the kick of 

 the galvanometer. For example, the coefficient of induction 

 of a certain pair of coils used for experimental purposes was 

 compared with the coefficient of self-induction of the field- 

 magnets of an old dynamo of the Ladd pattern. The resist- 

 ance of one of the coils (that put as a shunt to the galvano- 

 meter) was 10*5 ohms, c>=l'79 = «i, a=b= 1000, and an 

 additional resistance of 167 ohms was required for a balance ; 



L/M- ( 1001 ' 79 > 2 -5-65 

 hlM - 1000x177-5 -8b& - 



On the Use of Shunts in finding Coefficients of Mutual 

 Induction. 



Let R=R 1 + R / ; where R x is the resistance of the coil 

 proper, W the added resistance, and let R 2 be the resistance 

 of the second coil of the pair ; then it is easy to see that if we 

 shunt part of the current passing through R 2 into a shunt S, 

 the coefficient of mutual induction will be diminished in the 

 ratio 



S:R 2 + S. 



A precisely similar rule may be proved to hold good as the 

 result of shunting part of the current through R : into a 

 shunt S. 



