Universal curve for determining sensitivity of ballistic galvanometers under all conditions of circuit resistance.—On closed circuit, the throws produced by a given discharge depend on the circuit resistance because of its effect on the damping. No simple relation between sensitivity and circuit resistance is known which is applicable to a wide range of instruments and damping. However if sensitivity is expressed as a fraction of undamped sensitivity, and circuit resistance as a fraction of critical damping resistance, a general mathematical relation between these two quantities is obtained which is true for all moving-coil type instruments. Numerical data are given and also the curve. A special damping coil may be treated as an equivalent parallel circuit, and the joint effect determined accordingly. The accuracy is limited only by the precision of measurement of undamped sensitivity and critical damping resistance, as no approximations are involved in the derivation.

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