A classical electromagnetic model of the hydrogen atom was introduced in the author's previous paper, A Unified Theory of Physics. The model consists of a spinning spherical proton and a revolving electron ring. Spectral radiation results from resonant vibrations of the electron and proton. The model behaves like a transformer in which there is no ohmic loss. The proton spin and the electron ring rotation form the primary and secondary currents. The mutual inductance stores some of the atoms ’ energy. One of the forces required to establish the stable state and to yield the required free-vibrational frequencies is supplied by an interaction between the primary and secondary currents. Its computation involves the gradient of the mutual inductance, the variation of mutual inductance with distance.