  We investigate a Boltzmann gas at equilibrium with its center of mass moving
on a circular geodesics in the Schwarzschild field. As a consequence of
Tolman's law we find that a central comoving observer measures oscillations of
the temperature and of other thermodynamic quantities with twice the
frequencies that are known from test-particle motion. We apply this scheme to
the gas dynamics in the gravitational fields of the planets of the Solar System
as well as to strong-field configurations of neutron stars and black holes.
