The freezing of capillary waves on glycerol surfaces is studied by in situ x-ray reflectivity measurements. A wide temperature range around the calorimetric glass transition temperature at T g Ϸ186 K is investigated. For TϾ250 K the obtained surface roughness as a function of the temperature differs significantly from the value predicted by the classical capillary waves theory. Below the temperature TϷ250 K the magnitude of the roughness remains constant. Furthermore, a large hysteresis, i.e.,

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... large difference of the roughnesses measured during cooling and heating of the sample, is observed. These findings are discussed in terms of viscosity effects.