Suppression of dripping from a ceiling

An isothermal layer suspended from a surface is gravitationally (Rayleigh-T aylor) unstable. We find that, when a vertical temperature difference Delta T above a critical value (DeltaT)(c) is imposed across the liquid-gas layer system (heated from below), the restoring force provided by the temperatur e-dependent surface tension (thermocapillarity) can stabilize the layer. Ou r measurements of the most unstable wave number for DeltaT < (<Delta>T)(c) agree well with our linear stability analysis. The instability occurs at lo ng wavelengths: the most unstable wavelength at (DeltaT)(c) is infinite.