In their paper "Conformally flat Manifolds, Kleinian Groups and Scalar Curvature", Schoen and Yau repeatedly use the term "Newtonian capacity" for a subset of $S^n$.
I know the following definition: If $\Omega$ is a Riemannian manifold with boundary, then the capacity of a subset $K$ of the interior of $\Omega$ is the infimum over $$E(u) = \int_\Omega |d u|^2,$$ where $u$ varies over all $C^1$ functions with $u \equiv 1$ on $K$ and $u\equiv 0$ on $\partial M$.
However, setting $\Omega = S^n$ does not make sense since $\Omega$ does not have a boundary. So does anybody have an idea how this is meant?