Chemical Causes.—Non-scientific persons, on first hearing of glacière caves, almost always suggest that to form the ice there must be salts in the rocks. Probably they connect unconsciously in their minds “ice caves” and “ice cream.”
Chemical causes, however, have never appealed to scientific men.[48] There are only two places I know of where salt is reported. One is the Ice Spring in Oregon, which is said to be slightly saline in taste; the other is the Cave of Illetzkaya-Zatschita, where the gypsum hillock, in which the ice is found, overlies a bed of rock salt. Repeated experiments in letting lumps of glacière ice melt in my mouth have convinced me personally that in all cases the water is exceedingly pure and sweet, a fact mentioned in the very first notice extant about glacières, the letter of Benigne Poissenot in 1586, who speaks of the deliciousness of the water in Chaux-les-Passavant. To sum this matter up briefly, it can be safely asserted that all causes, which would fall under the head of “Chemical causes,” must be entirely eliminated as possible cold producers.
[48] See Part IV.: Billerez, [page 270]; Hacquet, [page 271].
Waves of Heat and Cold.—While Sir Roderick Murchison was studying the geology of Russia,[49] he visited Illetzkaya-Zatschita and was puzzled to account for the ice formations. He thought, at first, that they were due to the presence of salt, but recognizing that this was not correct he submitted the case to Sir John Herschel, who, rejecting the evaporation or condensation of vapor as the cause, argued that the ice was due to waves of heat and cold, and that at certain depths in the interior, the cold wave arrived in mid-summer and the heat in mid-winter. Murchison declined to assent to this doctrine, asking why one cave should present this exceptional occurrence, when the numerous other rents and openings in the same hillock were free from ice. The impossibility of the heat and cold wave theory was so completely shown by Murchison’s objection, that it has never again been brought forward.
[49] The Geology of Russia and the Ural Mountains, vol. I., pages 184-198.
Capillary or Compressed Air Theory.—The possibility of compressed air causing subterranean ice to form seems to have been first authoritatively formulated by Mr. N. M. Lowe, of Boston.[50] His theory in brief is this:—Bubbles of air drawn into water flowing down through fissures in rocks are liable to a continually increasing pressure. When the air has reached the bottom and is liberated in the cave, it will be from a pressure equal to the height of the column of water, and it will have lost by connection in the mass through which the conduit passes, the heat due to its compression; and on being liberated, it will immediately absorb from the air and the water in the cave, the heat which it has lost in its downward passage.
[50] Science Observer. Boston, 1879, vol. II., page 57. See Part IV.: Silliman, [page 279]; Olmstead, [page 282].
Several scientific observers have rallied to this idea.[51] One of the Hungarian residents at Dóbsina, a doctor, whose opportunities for observations are unrivalled, told me—if I understood him correctly—that he believed in the capillary theory.