The influence of temperature and supersaturation on the habit of ice crystals grown from the vapour

Ice crystals, growing on a fibre in a water-vapour diffusion cloud chamber under conditions in which the temperature and supersaturation of the environment can be varied indepen­dently, undergo the following transitions of habit in the temperature range 0 to —30°C: plates→needless→hollow prismatic columns→plates→dendritic crystals→plates→prismatic columns. These changes of habit are controlled mainly by the temperature of the environ­ment, large variations of supersaturation influencing only secondary features such as the development of dendritic forms. When crystals growing at a particular temperature are suddenly transferred into a different environment, further growth follows the habit charac­teristic of the new conditions; this allows the production of crystals of composite habit. In contradiction to a recent report by Nakaya, the crystal habit does not appear to be influenced by the presence or absence of atmospheric aerosols, but small quantities of organic vapours, e. g. camphor and isobutyl alcohol, modify the habit to an extent depending upon their concentration.