The first mention I have found of this cave is contained in an old history of the Franche Comté of Burgundy, published at Dôle in 1592, to which reference has been already made. Gollut, the author, speaks more than once of a glacière in his topographical descriptions, and in a short account of it he states that it lay near the village of Leugné, which I find marked in the Delphinal Atlas very near the site of the Chartreuse of Grâce-Dieu; so that there can be no doubt that his glacière was the same with that which now exists. His theory was, that the dense covering of trees and shrubs protected the soil and the surface-water from the rays of the sun, and so the cold which was stored up in the cave was enabled to withstand the attacks of the heat of summer.[[175]] In the case of many of the glacières, there can be no doubt that this idea of winter cold being so preserved, by natural means, as to resist the encroachments of the hotter seasons, is the true explanation of the phenomenon of underground ice.
The next account of this glacière is found in the History of the Royal Academy of Sciences (French), under the year 1686,[[176]] but no theory is there suggested. The writer of the account states that in his time the floor of the cave was covered with ice, and that ice hung from the roof in festoons. In winter the cave was full of thick vapours, and a stream of water ran through it. The ice had for long been less abundant than in former times, in consequence of the felling of some trees which had stood near the entrance.
The Academy received in the same year another letter on this subject, confirming the previous account, and adding some particulars. From this it would seem that people flocked from all sides to the glacière with waggons and mules, and conveyed the ice through the various parts of Burgundy, and to the camp of the Saone; not thereby diminishing the amount of ice, for one hot day produced as much as they could carry away in eight days. The ice seemed to be formed from a stream which ran through the cave and was frozen in the summer only. The writer of this second account saw vapours in the glacière (the editor of the Histoire de l'Académie does not say at what season the visit to the cave took place), and was informed that this was an infallible sign of approaching rain; so much so, that the peasants were in the habit of determining the coming weather by the state of the grotto.
In 1712, M. Billerez, Professor of Anatomy and Botany in the University of Besançon, communicated to the Academy[[177]] an account of a visit made by him to this cave in September 1711. He found 3 feet of ice on the floor of the cave, in a state of incipient thaw, and three pyramids, from 15 to 20 feet high and 5 or 6 feet in diameter, which had been already considerably reduced in size by thaw. A vapour was beginning to pass out from the cave, at the highest part of the arch of entrance; a phenomenon which, he was told, continued through the winter, and announced or accompanied the departure of the ice: nevertheless, the cold was so great that he could not remain in the glacière more than half an hour with any sort of comfort. The thermometer stood at 60° outside the cave, and fell to 10°[[178]] when placed inside; but thermometrical observations of that date were so vague as to be useless for present purposes. The ice appeared to be harder than the ordinary ice of rivers, less full of air-bubbles, and more difficult to melt.
M. Billerez enunciated a new theory to account for the phenomena presented by the cave. He observed that the earth in the immediate neighbourhood, and especially above the roof of the grotto, was full of a nitrous or ammoniac salt, and he accordingly suggested that this salt was disturbed by the heat of summer and mingled itself with the water which penetrated by means of fissures to the grotto, and so the cave was affected in the same way as the smaller vessel in the ordinary preparation of artificial ice. He had heard that some rivers in China freeze in summer from the same cause.[[179]]
In 1726, a further communication was made to the Academy by M. des Boz,[[180]] Royal Engineer, describing four visits which he had made to the grotto near Besançon at four different seasons of the year, viz., in May and November 1725, and in March and August 1726. In all cases he found the air in the cave colder than the external air,[[181]] and its variations in temperature corresponded with the external variations, the cold being greater in winter than in summer.
M. des Boz ascribed the existence of ice in the cave to natural causes. The opening being towards the north-east, and corresponding with a gorge in the hills opposite, running in the same direction, none but cold winds could reach the mouth of the grotto. Moreover, the soil above was so thickly covered with trees and brushwood, that the rays of the sun could not reach the earth, much less the rock below. Credible persons asserted that since some of the trees had been felled, there had not been so much ice in the cave.
In order to test the presence of salt, M. des Boz melted some of the ice, and evaporated the resulting water, but found no taste of salt in the matter which remained.[[182]] He denied the existence of the spring of water which previous accounts had mentioned, and believed that the water which formed the ice came solely from melted snow, and from the fissures of the rock.
In 1727, the Duc de Lévi caused the whole of the ice to be removed from the cave, for the use of the army of the Saone, which he commanded. In 1743 the ice had formed again, and the grotto was subjected to a very careful investigation by M. de Cossigny, chief engineer of Besançon, in the months of August and October.[[183]] The thermometer he used had been presented to him by the Academy, and was very probably constructed by M. de Réaumur himself, for de Cossigny's account was sent through M. de Réaumur to the Academy, but still the observations made with it cannot be considered very trustworthy. On the 8th of August, at 7.30 A.M., the temperature in the cave was 1/2° above the zero point of this thermometer, and at 11.30 A.M. it had risen to 1° above zero. On the 17th of October, at 7 A.M., the thermometer stood at 1/2°, and at 4 P.M. it gave the same register.
M. de Cossigny found that the entrance to the cave was rather more than 150 feet above the Abbey of Grâce-Dieu, and about half a league distant by the ordinary path. A great part of his account is occupied by contradictions of previous accounts, especially in the matter of dimensions,[[184]] The people of Besançon had urged him to stay only a short time in the cave, because of the sulphureous and nitrous exhalations, but he detected no symptoms of anything of that kind. The most curious thing which he saw was the soft earth which lay, and still lies, at the bottom of the long slope of ice by which the descent is made; and he subjected this to various chemical tests and processes, but could not find that it contained anything different from ordinary earth.[[185]]