In the _Histoire de l'Académie Royale des Sciences_, 1686, Tome II., pages 2, 3, there is an account, with no author's name, of Chaux-les-Passavant. The memoir states that in winter the cave is filled with thick vapors and that after some trees were cut down near the entrance, the ice was less abundant than formerly: that people come for ice with carts and mules, but that the ice does not become exhausted, for one day of great heat forms more ice than could be carried away in eight days in carts and wagons: and that when a fog forms in the cave, there is assuredly rain the following day, and that the peasants in the neighborhood consult this curious "almanac" to know the weather which is coming. Freiherr Valvasor, in 1689, wrote about some of the glacières of the Krain.[72] [72] See Part III.: pages 238, 239. Behrens, in 1703, thought it was colder in summer than in winter in the caves near Questenberg in the Harz. M. de Billerez, in 1712, writes that at Chaux-les-Passavant it is really colder in summer than in winter; and that the ice is harder than river ice, and this he thinks is due to the presence of a nitrous or ammoniacal salt, which he says he found in the rocks. M. de Boz made four trips to Chaux-les-Passavant on the 15th of May and 8th of November, 1725; and the 8th of March and 20th of August, 1726. His memoir says that his observations tend to disprove those of M. de Billerez, and that "the cause for the great cold, which is less great in summer, although always remaining, is quite natural." He cites as causes for the ice the exposure to the north-north-east; the rock portal sheltering the entrance, and all the forest covering the surrounding lands; and adds that some veracious persons told him that since some of the big trees above the grotto had been cut down there was less ice than before. He found no traces of salt, nor any springs, and that the water supply came from the rains and melted snows filtering through the ground. In 1739, Matthias Bel published his curious account of Szilize.[73] [73] See Part III.: page 254. J. N. Nagel, a Vienna mathematician, visited the Ötscher in 1747. He concluded that the ice was made in winter and preserved in summer as in an ice house.