Page:A Treatise on Electricity and Magnetism - Volume 2.djvu/389

757.] a third method. Beginning with an arrangement in which the transient current due to self-induction is slightly in excess of that due to mutual induction, we may get rid of the inequality by inserting a conductor whose resistance is $$W$$ between $$A$$ and $$Z$$. The condition of no permanent current through the galvanometer is not affected by the introduction of $$W$$. We may therefore get rid of the transient current by adjusting the resistance of $$W$$ alone. When this is done the value of $$L$$ is

757.] Insert the coils in two adjacent branches of Wheatstone's Bridge. Let $$L$$ and $$N$$ be the coefficients of self-induction of the coils inserted in $$P$$ and in $$R$$ respectively, then the condition of no galvanometer current is

Hence, by a proper adjustment of the resistances, both the permanent and the transient current can be got rid of, and then the ratio of $$L$$ to $$N$$ can be determined by a comparison of the resistances.