= Magnetic polarizability of a perfectly conducting sphere
{title2=$\mathbf m=-2\pi a^3\mathbf H_{\rm inc}$}
In the small-sphere oscillatory-field limit, <surface current density> excludes the changing <magnetic field>. Adding a central magnetic dipole to a uniform applied field and imposing zero normal field at the sphere gives $\mathbf m=-2\pi a^3\mathbf H_{\rm inc}$. The minus sign expresses <diamagnetism>; it does not make this dipole's backward radiation cancel the electric contribution.<Electromagnetic Fields and Energy by Hermann A. Haus and James R. Melcher>[section 8.4, Example 8.4.3]{ref}
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