  Using atomic force microscopy on silica and float glass surfaces, we give
evidence that the roughness of melted glass surfaces can be quantitatively
accounted for by frozen capillary waves. In this framework the height spatial
correlations are shown to obey a logarithmic scaling law; the identification of
this behaviour allows to estimate the ratio $kT\_F/\pi\gamma$ where $k$ is the
Boltzmann constant, $\gamma$ the interface tension and $T\_F$ the temperature
corresponding to the ``freezing'' of the capillary waves. Variations of
interface tension and (to a lesser extent) temperatures of annealing treatments
are shown to be directly measurable from a statistical analysis of the
roughness spectrum of the glass surfaces.
