The rates of evaporation of ice spheres, 0·3-1·8 mm radius, have been measured by direct weighing in air streams of 25-100 cm sec-1 at -3°C and -12°C and over a range of Reynolds numbers of 10-200. The experimental results may be represented in terms of heat and mass transfer coefficients of the form (Nu) = 1·88 + 0·66 (Pr)1/3 (Re)1/2 and (Sh) = 1·88 + 0·66 (Sc)1/3 (Re)1/2 where (Nu), (Pr), (Sh), (Sc) and (Re) are respectively the Nusselt, Prandtl, Sherwood, Schmidt and Reynolds numbers, provided that the diffusion coefficients of water vapour in air are about 7% lower than those given in the International Critical Tables. These results are consistent with those quoted by some other workers for evaporating water drops.

Some measurements on snow crystals in the form of hexagonal plates and dendritic stellar crystals reveal the influence of geometrical shape on their rates of evaporation.