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<p>This paper gives the theory and description of some two-circuit electrodynamometers, with standarised shunts, built at the Bureau of Standards and used for measuring alternating currents. When the instruments are compensated for the resultant inductance and capacity of the moving-coil circuit, they have the same constant for alternating current as for direct, and may therefore be calibrated by direct currents. The author first shows that in an instrument in which the self-inductance of the moving-coil circuit and the mutual inductance of the two circuits are both zero, while eddy currents in the region of the moving coils, and capacity in the resistance, a
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<br>Subjects: alternating-current research; apparatus and instruments; measurements and use of instruments; Condensed matter; electronic structure, electrical, magnetic, and optical properties</div>
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