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 Besancon 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.
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.
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