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The natural frequency of a circuit depends upon inductance and capacitance and is modified by resistance and conductance in the circuit. When the inductance consists of a coil which has an iron magnetic circuit, the effective value of the inductance of the coil becomes a variable. The change in the value of the inductance is attributed to eddy currents induced in the iron. The eddy currents vary with the conductivity and permeability of the iron and the thickness of the laminations. Otherdoi:10.1109/jrproc.1919.217417 fatcat:57olruodmfhefjltdkje5esp4u