The polar properties of single crystals of ice

Abstract

Although the crystallography of ice has been the subject of much study,* there is still no general agreement upon it. This is due chiefly to the fact that in the absence of authentic single crystals of ice with well-defined natural faces, the available material has been limited to specimens formed under uncontrolled and in most cases obviously complex conditions. The approach by way of the X-ray analysis of structure has now reached substantial conclusions in the work of Barnes, and it remains to compare these conclusions with observations on single crystals of ice of simple forms, grown under controlled conditions. Such crystals, of microscopic size, have now been made and photographed, and the figures of Plate 7 reproduce some photographs of collections and individuals which seem most significant for the present study. The crystals were photographed as they lay on a glass plate which had been ruled with lines 0·01 cm. apart, thereby supplying the photographs with a linear scale. The optical system was similar to that of a microscope as ordinarily used, when the object is viewed by light from a source about 25 cm. distant, traversing the slide from below. Figs. 1 to 4 inclusive, which have been enlarged 55 diameters, show four successive stages in the growth of a collection of crystals. Most of the individuals are seen to pass through these stages with a proportional increase in all their dimensions, and without any perceptible change of shape— an observation which gives strong support to the view that they are monocrystalline.