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,[181] 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,[182] and its variations in temperature corresponded with the external variations, the cold being greater in winter than in summer.