It may be remembered that I found one very beautiful column, far higher than any of those mentioned by Dr. Oudot, and higher than those which M. Billerez saw, formed upon the trunk and branches of a fir-tree.  I have now no doubt that the peculiar shape of another—­the largest of the three columns which were in the cave at the time of my visit—­is due to the fact of its being a collection of several smaller columns, which have in course of time flowed into one as they increased separately in bulk, and that its height has been augmented by a device similar to that adopted by Dr. Oudot.  The two magnificent capitals which this column possessed, as well as the numerous smaller capitals which sprang from its sides, will thus be completely accounted for.

One more account may be mentioned, before I proceed to the theory which has found most favour in Switzerland of late years.  M. Cadet published some Conjectures on the formation of the ice in this cavern, in the Annales de Chimie, Nivose, an XI.[188] He saw the cave in the end of September 1791, and found very little ice—­not a third of what there had been a month before, according to the account of his guide.  The limonadier of a public garden in Besancon informed him that the people of that town resorted to the glaciere for ice when the supplies of the artificial ice-houses failed, and that they chose a hot day for this purpose, because on such days there was more ice in the cave.  Ten chars would have been sufficient to remove all the ice M. Cadet found, and the air inside the cave seemed to be not colder than the external air; but, nevertheless, M. Cadet believed the old story of the greater abundance of ice in summer than in winter, and he attempted to account for the phenomenon.

The ground above and near the cave is covered with beech and chestnut trees, and thus is protected from the rays of the sun.  The leaves of these trees give forth abundant moisture, which has been pumped up from their roots; and as this moisture passes from the liquid to the gaseous state, it absorbs a large quantity of caloric.  Thus, throughout the summer, the atmosphere is incessantly refrigerated by the evaporation produced by the trees round the cave; whereas in winter no such process goes on, and the cave assumes a moderate temperature, such as is usually found in ordinary caves.  Unfortunately for M. Cadet’s theory, the facts are not in accordance with his imaginary data, nor yet with his conclusions.  He adds, on the authority of one of his friends, that the intendant of the province, M. de Vanolles, wishing to preserve a larger amount of ice in the cave, built up the entrance with a wall 20 feet high, in which a small door was made, and the keys were left in the hands of the authorities of the neighbouring village, with orders that no ice should be removed.  The effect of this was, that the ice diminished considerably, and they were obliged to pull down the wall again.  M. Cadet saw the remains of the wall, and the story was confirmed by the Brothers of Grace-Dieu.  It would be very interesting to know at what season this wall was built, and when it was pulled down.  If my ideas on the subject of ice-caves are correct, it would be absolutely fatal to shut out the heavy cold air of winter from the grotto.