  The Casimir energy of a solid ball placed in an infinite medium is calculated
by a direct frequency summation using the contour integration. It is assumed
that the permittivity and permeability of the ball and medium satisfy the
condition $\epsilon_1 \mu_1=\epsilon_2\mu_2$. Upon deriving the general
expression for the Casimir energy, a dilute compact ball is considered
$(\epsilon_1 -\epsilon_2)^2/(\epsilon_1+\epsilon_2)^2\ll 1$. In this case the
calculations are carried out which are of the first order in $\xi ^2$ and take
account of the five terms in the Debye expansion of the Bessel functions
involved. The implication of the obtained results to the attempts of explaining
the sonoluminescence via the Casimir effect is shortly discussed.
