  The effects of thermal coupling between two thin liquid layers, separated by
a gas layer, are discussed. The liquid layers undergo long-wavelength
instabilities driven by gravitational and thermocapillary stresses. To study
the dynamics, both a linear stability analysis and a full numerical solution of
the thin-film equations are performed. The results demonstrate that the
stability properties of the combined system differ substantially from the case
where both layers evolve independently from each other. Most prominently,
oscillatory instabilities, not present in single-liquid layer configurations,
may occur.
