XXIX. The growth of ice crystals from the vapour

The growth and evaporation of single ice crystals have been studied in relation to the temperature and supersaturation of the environment. The sequence of crystal forms which occurs in clouds as the temperature falls from 0°c to - 40°c has been reproduced in these experiments. Measurements of the growth rates of individual faces of crystals growing under fixed environmental conditions reveal that dR 2 /dt=const. where R is a linear crystal dimension, but the growth rates of basal and prism faces are different to a degree depending mainly on the temperature. At constant temperature, dR 2 /dt varied as the square of the supersaturation σ over the range of σ studied. A critical supersaturation for growth was found which varied in an apparently random manner from face to face, there being no systematic difference between the values for the prism and basal faces. The crystal habit, denned by limiting values of the axis/diameter ratio, was found to be controlled very largely by the temperature, the supersaturation having a much smaller, non-systematic effect.