= Geselowitz formula
{c}
{title2=$\mathbf B=\mathbf B^p-\frac{\mu_0\sigma}{4\pi}\int_S u\,\mathbf n'\times\frac{\mathbf r-\mathbf r'}{|\mathbf r-\mathbf r'|^3}\,dS'$}
For a homogeneous <volume conductor> with an insulating boundary $S$, the <Geselowitz formula> expresses the exterior <magnetic field> as the primary <Biot-Savart law> field minus a surface contribution from the induced <electric potential>. For a <current dipole>, $\mathbf B^p=\mu_0\mathbf Q\times(\mathbf r-\mathbf r_0)/(4\pi|\mathbf r-\mathbf r_0|^3)$. On a spherical boundary, $\mathbf n'$ is parallel to $\mathbf r'$, so the surface term has zero radial component at the observation point.
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