  The relativistic Maxwell-Boltzmann distribution for the system of $N$ events
with motion in space-time parametrized by an invariant ``historical time''
$\tau $ is considered without the simplifying approximation $m^2\cong M^2$,
where $M$ is a given intrinsic property of the events. The relativistic mass
distribution is obtained and the average values of $m$ and $m^2$ are
calculated. The average value of the energy in nonrelativistic limit gives a
correction of the order of 10\% to the Dulong-Petit law. Expressions for the
pressure and the density of events are obtained and the ideal gas law is
recovered.
