Electrical measurementsA laboratory manual . 50. Example. To compare the Two Coils of Art. 118 with the Standard of standard was inserted in the arm i?i, together with anadditional non-inductive resistance, the latter being added in order to increase the ratio -^, so as to brino the induction inthe arm B^ within the limits of the standard. Coil. ^2 R\ Zj (Standard). L-2 Smaller. Larger. Two opposedin series. S ( \ \ 121. Nivens Method
Electrical measurementsA laboratory manual . 50. Example. To compare the Two Coils of Art. 118 with the Standard of standard was inserted in the arm i?i, together with anadditional non-inductive resistance, the latter being added in order to increase the ratio -^, so as to brino the induction inthe arm B^ within the limits of the standard. Coil. ^2 R\ Zj (Standard). L-2 Smaller. Larger. Two opposedin series. S ( \ \ 121. Nivens Method of comparing Two Self-In-ductances.^— The inductance of Ri is to be comparedwith that of R^ (Fig. 121). First connect Ri in a Wheat-stones bridge with three non-inductive resistances Ro, R5,and Rq and obtain a balance for steady currents. Then addthe inductive resistance R^ in series with Ro and balanceagain for steady currents by adding a proportional non-inductive resistance to Ri. Finally connect E and F by ^ Phil. Mag., Sept., SELF-INBUCTION AND MUTUAL INDUCTION. 259 means of the resistance i^r, and vary it till the galva-nometer shows no deflection on mak- c ing and breakingthe battery cir-cuit. Call the quan-tity of electricitywhich has passedthrong h eachbranch of the cir-cuit q^ with the proper subscript, at the time t after closing the circuit,and let Q with the corresponding subscripts represent thequantities for the several branches when the current hasreached a steady state, after an interval T, reckoned fromthe time when the circuit is closed. Then the current is represented by —^ and this is zero for each branch when t is zero. It is also zero for the two cross branches i^7,i^s, when the steady state has been reached. The potential difference between C and D at any timet is the same by the four paths. Hence Fig. 121. at dt dqc, _ -pfdqdtj^dq, ^ j^d^ _ J, dq., _ d-q, dq^ d-q^ E ^ -\- L —^ = i?4 -^ + X dt dt- dt df dt dt dt at at- at dt- dt . . (1) Inte
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