The Summer’s Heat Theory.—The natives and peasants in the neighborhood of glaciÈre caves generally believe that the ice of caves is formed in summer and melts in winter. I have met with this belief everywhere in Europe; in the Eifel, Jura, Swiss Alps, Tyrolese Alps, and Carpathians: and also occasionally in the United States. Peasants and guides tell you with absolute confidence: “The hotter the summer the more ice there is.” The strange thing is that any number of writers[46]—sometimes scientific men—have accepted the ideas and statements of the peasants about the formation of ice in summer, and have tried to account for it.

The belief of the peasants is founded on the fact that they scarcely ever go to any cave except when some tourist takes them with him, and, therefore, they rarely see one in winter, and their faith is not based on observation. It is, however, founded on an appearance of truth: and that is on the fact that the temperatures of glaciÈre caves, like that of other caves or that of cellars, are colder in summer than the outside air, and warmer in winter than the outside air. Possessing neither reasoning powers nor thermometers, the peasants simply go a step further and say that glaciÈre caves are cold in summer and hot in winter.

Professor Thury tells a story to the point. He visited the Grand Cave de Montarquis in mid-winter. All the peasants told him there would be no use going, as there would be no ice in the cave. He tried to find even one peasant who had been to the cave in winter, but could not. He then visited it himself and found it full of hard ice. On his return he told the peasants of his discovery. They were staggered at first, finally one exclaimed: “It makes no difference; in genuine glaciÈres there is no ice in winter.”

It will be difficult, probably, to eradicate this belief and the consequent theories among the uneducated people in the vicinity of glaciÈre caves, for their imperfect observations will keep it alive. In refutation, it may be said that the winter’s cold theory is the direct opposite of the summer’s heat theory, and that all the observations and all the facts which prove the one, disprove the other.

Within two or three years, however, the formation of small quantities of ice has been observed during the summer months in one or two caves. This has taken place in mountain caves situated at a high altitude at times when the air outside has dropped below freezing point during the night. There is, therefore, nothing inconsistent in this fact with the winter’s cold theory: indeed it is only a widening of it in the meaning of the word winter.[47]

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.”

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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.

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.

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.

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.

There are many facts, however, which militate against the compressed air theory as applied to caves. Almost all caves receive some drip through fissures, and yet there are many thousands of caves which never contain ice, and whose temperature scarcely varies the year round. Especially against the theory is the fact that glaciÈre caves are never known in hot countries. If the theory were correct we should, for instance, sometimes find ice in such caves as those of Yucatan described by Mr. Mercer.[52]

There are also some mechanical difficulties in the way. Mr. John Ritchie[53] touches them when he says: “If the passage through which the water flows down is at all tubular the column will be subjected to the usual hydrostatic pressure.” The word tubular is the hard one to answer. Limestone rock fissures are certainly not tubular. They have all sorts of shapes and angles and corners, every one of which would interfere with anything like a regular pressure.

This latter objection would not apply to borings in mines. I have been assured that in some borings in Western mines ice has been formed by pressure, and there may be truth in this, although I doubt it, as I have yet to hear of ice in any mines in warm latitudes. Mr. John Ritchie[54] has suggested, also, that if compressed air does not perhaps act strongly enough to form ice, yet it may help in keeping the temperature low and aid in the formation of draughts in caves and boulder heaps. At present, however, I can see no reason to think that the ice in caves is due to compressed air.[55]