  The statistical mechanics of an ideal gas of point particles moving in a time
independent background metric with $g_{0j}\neq 0$ is investigated. An explicit
calculation shows that when there is no background electrostatic or
magnetostatic field the thermodynamic pressure, energy density, and thermally
averaged energy-momentum tensor depend on temperature and chemical potential
only through the ratios $T_{0}/\sqrt{g_{00}}$ and $\mu_{0}/\sqrt{g_{00}}$. A
background magnetostatic field does not change this, however with a background
electrostatic field the previous results are multiplied by a factor
$\exp(-eA_{0}/T_{0})$, which is an exception to the strict Tolman-Ehrenfest
rule because the system is open.
