  We consider a system of particles confined in a box $\La\subset\R^d$
interacting via a tempered and stable pair potential. We prove the validity of
the cluster expansion for the canonical partition function in the high
temperature - low density regime. The convergence is uniform in the volume and
in the thermodynamic limit it reproduces Mayer's virial expansion providing an
alternative and more direct derivation which avoids the deep combinatorial
issues present in the original proof.
