A Frenchman who was present in the room in which the Chemical Section of the British Association met at Bath, and heard a paper which I read there on this prismatic structure, suggested that it was probably something akin to the rhomboidal form assumed by dried mud; and I have since been struck by the great resemblance to it, as far as the surface goes, which the pits of mud left by the coprolite-workers near Cambridge offer, of course on a very large scale. This led me to suppose that the intense dryness which would naturally be the result of the action of some weeks or months of great cold upon subterranean ice might be one of the causes of its assuming this form, and the observations at Jena would rather confirm than contradict this view: competent authorities, however, seem inclined to believe that warmth, and not cold, is the producing cause.
Professor Tyndall found, in the course of his experiments on the discs and flowers produced in the interior of a mass of ice by sending a warm ray through the mass, that the pieces of ice were in some cases traversed by hazy surfaces of discontinuity, which divided the apparently continuous mass into irregular prismatic segments. The intersections of the bounding surfaces of these segments with the surface of the slab of ice formed a very irregular network of lines. I am inclined, however, to think that the irregularity in these cases proved to be so much greater than that observed in the glacieres, that this interior prismatic subdivision must be referred to some different cause.
[Footnote 196: The continued extrication of latent heat by ice, as it is cooled a few degrees below 32 deg. F., appears to indicate a molecular change subsequent to the first freezing.—Phil. Trans., as quoted in the next note.]
[Footnote 197: See the paper ’On Liquid Diffusion as applied to Analysis,’ by the Master of the Mint (Phil. Trans. 1861, p. 222).]
[Footnote 198: Compare the description of one of the hollow stalagmites I explored in the Schafloch, p. 145.]
[Footnote 199: Professor Tyndall has pointed out that, owing to the want of perfect homogeneity, some parts of a block of ice exposed to a temperature of 32 deg. F. will melt, while others remain solid (Phil. Trans. 1858, p. 214). He also arrived at the conclusion (p. 219) that heat could be conducted through the substance of a mass, and melt portions of the interior, without visible prejudice to the solidity of the other parts of the mass.]
[Footnote 200: Journal des Mines, xxxiii. 157. See also an English translation of his account in the second volume of the Edinburgh Journal of Science.]
[Footnote 201: It is to be hoped that the accuracy of his scientific descriptions exceeds that of his topographical information; for he states that the glaciere is two leagues from Valence, whereas it cost me six hours’ drive on a level road, and five and a half hours’ walking and climbing, to reach it from that town.]