  Let $\ell$ be a fixed vertical lattice line of the unit triangular lattice in
the plane, and let $\Cal H$ be the half plane to the left of $\ell$. We
consider lozenge tilings of $\Cal H$ that have a triangular gap of side-length
two and in which $\ell$ is a free boundary - i.e., tiles are allowed to
protrude out half-way across $\ell$. We prove that the correlation function of
this gap near the free boundary has asymptotics $\frac{1}{4\pi r}$,
$r\to\infty$, where $r$ is the distance from the gap to the free boundary. This
parallels the electrostatic phenomenon by which the field of an electric charge
near a conductor can be obtained by the method of images.
