SURFACE-LAYERS ON ICE

There is a widespread opinion that ice surfaces are covered by a liqui d layer at equilibrium, and several treatments of the ice surface desc ribe it as a homogeneous layer with a definable thickness. Arguments a re presented that the ice surface cannot have a homogeneous surface la yer and that representations of it that use such a layer are not usefu l approximations. No part of the transition layer on ice can be homoge neous except at a triple point without violating the phase rule. Some experiments suggest the existence of a surprisingly thick transition r egion at ice surfaces, but others do not. Water apparently does not co mpletely wet ice, since its contact angle on ice close to the triple p oint appears not to be zero, and sharply faceted growth forms of ice f rom the vapor close to the melting point also suggest the absence of a thick, liquid, surface transition region.