We report x-ray reflectivity measurements of liquid mercury between -36 deg
rees C and +25 degrees C. The surface structure can be described by a layer
ed density profile convolved with a thermal roughness sigma(Tau). The layer
ing has a spacing of 2.72 Angstrom and an exponential decay length of 5.0 A
ngstrom. Surprisingly, sigma(Tau) is found to increase considerably faster
with temperature than the root Tau behavior predicted by capillary wave the
ory, in contrast with previous measurements on Ga and dielectric liquids. [
S0163-1829(98)52144-3]