Coefficients of Induction. 



335 



The first is the condition for no permanent current; and 

 the second, which is the condition for no instantaneous 

 current, gives the formula 



L=K{r»(R+S) + EQ}. 



If we make r= 0, we get Maxwell's formula. The practical 

 method immediately suggested by the above expression for L 

 is to obtain a permanent balance in the ordinary w T ay, and 

 then to adjust r and, if possible, K till there is no motion of 

 the galvanometer-needle. Or if, as in Maxwell's method, 

 values of P, Q, R have been obtained, so that there is only a 

 small throw of the needle when the battery-circuit is made or 

 broken, the final adjustment may be quickly and accuratelv 

 made by introducing an adjustable resistance r, and in doing 

 this a telephone may be employed instead of the galvanometer. 

 It is clear that, if we do this, R and Q must be such that 

 KRQ<L. 



However, we may make the rough adjustment, having first 

 placed a small resistance between N and B, and subsequently 

 adjust this till there is no kick of the galvanometer-needle 

 or no sound in the telephone. 



In order to find the relative values of the various resist- 

 ances which will make the sensitiveness of the final adjust- 

 ment greatest, we will calculate the quantity of electricitv 

 q which passes through the galvanometer on making or 

 breaking the battery -circuit after the adjustment for no 

 permanent current has been made. 



Fio:. 4. 



Consider the system of conductors in fig. 4 as made up 

 of the circuits DAB, DBC, MADG, and the condenser-circuit 



