  The finite temperature Casimir free energy is calculated for a dielectric
ball of radius $a$ embedded in an infinite medium. The condition
$\epsilon\mu=1$ is assumed for the inside/outside regions. Both the Green
function method and the mode summation method are considered, and found to be
equivalent. For a dilute medium we find, assuming a simple "square" dispersion
relation with an abrupt cutoff at imaginary frequency $\hat \omega= \omega_0$,
the high temperature Casimir free energy to be negative and proportional to
$x_0 \equiv \omega_0 a$. Also, a physically more realistic dispersion relation
involving spatial dispersion is considered, and is shown to lead to comparable
results.
