The self-inductance of a toroidal coil of rectangular section

Abstract

One of the most carefully constructed standards of self-inductance ever made is that described some years ago by Prof. Frohlich, of Budapest.^ It consists of a large marble ring of rectangular section, very accurately ground and measured, and wound with a single layer of fine silk-covered wire. Bach turn of the wire lies in a plane passing through the axis of the ring, the wires being wound as closely as possible on the inner surface of the ring and uniformly spaced on the outer surface. Taking account of the magnetic field within the space occupied by the wire as well as the space within the marble core, Prof. Frohlich obtained the following expression for the self-inductance of the coil :