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.[183] 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]