_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. [51] See B. Schwalbe, _Ueber Eishöhlen und Eislöcher_, page 56. 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] [52] _The Hill Caves of Yucatan._