  We study the configurational probability distribution of a mono-atomic gas
with a finite number of particles N in the micro-canonical ensemble. We give
two arguments why the thermodynamic entropy of the configurational subsystem
involves Renyi's entropy function rather than that of Tsallis. The first
argument is that the temperature of the configurational subsystem is equal to
that of the kinetic subsystem. The second argument is that the instability of
the pendulum, which occurs for energies close to the rotation threshold, is
correctly reproduced.
