The effect of this was, that the ice diminished considerably,
and they were obliged to pull down the wall again. M. Cadet saw the
remains of the wall, and the story was confirmed by the Brothers of
Grace-Dieu. It would be very interesting to know at what season this
wall was built, and when it was pulled down. If my ideas on the
subject of ice-caves are correct, it would be absolutely fatal to shut
out the heavy cold air of winter from the grotto.
In 1822, M.A. Pictet, of Geneva, took up the question of natural
glacieres, and read a paper before the Helvetic Society of Natural
Sciences,[189] describing his visits to the caves of the Brezon and the
Valley of Reposoir. In order to explain the phenomena presented by those
caves, M. Pictet adopted De Saussure's theory of the principle of
_caves-froides_, rendering it somewhat more precise, and extending it
to meet the case of ice-caves. It is well known that, in many parts of
the world, cold currents are found to blow from the interstices of
rocks; and these are utilised by neighbouring proprietors, who build
sheds over the fissures, and so secure a cool place for keeping meat,
&c.
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