I.—The Structure of Glacier Ice

Extract

In the Geological Magazine for April, 1895, p. 152, the results of some observations made by Mr. George Fletcher, F.G.S., and myself on the structure of glacier ice were given.

Thin plates of ice were made by cutting and melting, and then examined in polarized light. In all cases it was found that the individual crystals were in close contact, there being no evidence of the presence of a eutectic separating them. The crystals in the same piece varied very greatly in size, and had very irregular outlines.

As the sections which we figured were in all cases drawn by hand, I thought it advisable to construct a special form of instrument with which to obtain actual photographs of thin sections of glacier ice. The instrument eventually used consisted of two bundles of thin glass plates, one being used as a polarizer and the other as an analyser. They were fixed vertically above each other, and between them was the glass stage upon which the thin ice sections rested. Below the analyser was a small lens throwing the image of the ice section upon a photographic plate.

Last Summer, accompanied by Mr. H. Arnold-Bemrose, M.A., F.G.S., who kindly assisted me in the matter, I visited the Furka Pass, and we obtained photographs of the ice of the Rhône Glacier.

Figs. 1 and 2 are full-sized photographs of thin slices of ice. Samples with small crystals were selected, so as to bring many crystals within the limits of the field. The ice section was about 03 inch thick, and where the surface between two crystals is at an angle with the glass plate upon which the ice section rested, interference fringes are consequently to be seen.