  The thermal instability with a piecewise power law cooling function is
investigated using one- and three-dimensional simulations with periodic and
shearing-periodic boundary conditions in the presence of constant thermal
diffusion and kinematic viscosity coefficients. Consistent with earlier
findings, the flow behavior depends on the average density, <rho>. When
$\bra{\rho}$ is in the range 1-5 x 10^{-24} g cm^{-3} the system is unstable
and segregates into cool and warm phases with temperatures of roughly 100 and
10^4 K, respectively. However, in all cases the resulting average pressure <p>
is independent of <rho> and just a little above the minimum value. For a
constant heating rate of 0.015 erg g^{-1} s^{-1}, the mean pressure is around
24 x 10^{-14} dyn (corresponding to p/k_B ~ K cm^{-3}). Cool patches tend to
coalesce into bigger ones. In all cases investigated there is no sustained
turbulence, which is in agreement with earlier results. Simulations in which
turbulence is driven by a body force show that when rms velocities of between
10 and 30 km/s are obtained, the resulting dissipation rates rates are
comparable to the thermal energy input rate. The resulting mean pressures are
then about 30 x 10^{-14} dyn, corresponding to p/k_B ~ 2170 K cm^{-3}. This is
comparable to the value expected for the Galaxy. Differential rotation tends to
make the flow two-dimensional, that is, uniform in the streamwise direction,
but this does not lead to instability.
