  We discuss the $E1$ and $M1$ spontaneous decay rates of the an emitter
residing inside of a real cavity carved out of a vast, uniform, homogenous,
isotropic, linear, lossless, dispersionless, and continuous medium. The ratio
of the medium rate to vacuum rate is given by $\Gamma_m/\Gamma_0 = [G(u)]^2 n^3
/ u$, where $G(u) = 3u/(2u+1)$ is the local field correction factor, $n =
\sqrt{\epsilon\mu/(\epsilon_0\mu_0)}$ is the index of refraction of the medium,
$\epsilon(\epsilon_0)$ is the electric permitivity of the medium (vacuum),
$\mu(\mu_0)$ is the magnetic permeability of the medium (vacuum), and $u =
\epsilon/\epsilon_0$ for $E1$ transitions or $u = \mu_0/\mu$ for $M1$
transitions.
