A simple method is described whereby a crystal mounted in the usual way on an oscillation goniometer may be maintained at a temperature of -30 to 60°C for at least an hour. Liquid air in a vacuum flask is boiled by electrical heating and the cold gas is conveyed to the crystal through a well-lagged rubber tube ending in a glass tube supported about 3 mm above the crystal. The temperature may be varied by adjusting the rate of boiling of the liquid air. No precautions against ice formation are necessary.