In 1727, the Duc de Levi 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 Besancon, 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 Reaumur himself, for de Cossigny’s account was sent through M. de Reaumur 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 deg. above the zero point of this thermometer, and at 11.30 A.M. it had risen to 1 deg. above zero.  On the 17th of October, at 7 A.M., the thermometer stood at 1/2 deg., 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 Grace-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 Besancon 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]

When M. de Cossigny visited the cave, there were thirteen or fourteen columns of ice, from 6 to 8 feet high, and he was in consequence inclined to doubt the accuracy of the statement of M. Billerez, that in his time (1711) there were three columns only, from 15 to 20 feet high.  But my own observation of the shape of the columns suggested that the largest of all was probably an amalgamation of several others; so that it is not unreasonable to suppose that after the Duc de Levi removed the large columns seen by M. Billerez, a number of smaller columns were formed on the old site, and that these had not become large enough to amalgamate in 1743.

Not satisfied with these visits of August and October, M. de Cossigny visited the cave in April 1745.  He found the temperature at 5 A.M. to be exactly at the freezing point, and at noon it had risen 1 deg..  From this he concluded that the stories of the greater cold in the cave during the summer, as compared with the winter, were false.