Ice Crystallites

Abstract

THE interesting facts recorded by your correspondent C. M. Irvine on p. 31 recall some unrecorded observations of my own. On several occasions during recent winters I have observed these crystallographic forms of ice on a gravel walk by the side of my lawn, in places where, owing to faulty gradients, the water does not completely drain away at the surface, and the ground just below the surface is in consequence more saturated with water than at other spots. The acicular ice forms have appeared in bundles standing up between the pebbles and capped by earthy material, just as described by Mr. Irvine, and in previous communications to NATURE by Mr. B. Woodd Smith (see his letter on p. 79). The nature of the soil agrees with that described by these two observers, so far as permeability to water is concerned; and I think they appeared on the occurrence of clear frosty weather after a thaw and melting of previous snow. My observations, however, extended further than theirs appear to have done. I was at the time pursuing the study of the glassy acicular crystallites of sulphur (which are erroneously described as “crystals” in most textbooks on chemistry). These, on examination with polarized light (as I have described elsewhere) are found to be destitute of any crystalline internal structure (in fact truly vitreous or isotropic masses in spite of their crystallographic outlines); such structure developing, as devitrification proceeds, by crystallization in the orthorhombic system, to which the outlines of the crystallites do not conform.