air, strong enough to incline the flame of a
candle 45 deg., M. Thury found a gentle current passing from the cave into
the fissure, sufficient only to incline the flame 10 deg., and near the
entrance 8 deg., while in the entrance itself no current was perceptible at
4 P.M.

M. Thury remarks that less current was to be expected in winter than in
summer, because the upper ends of the fissures would be probably choked
with snow, and their lower ends with ice. It is evident that the current
which passes up into the fissure in winter, is favourable to the
introduction of the colder air from without; while the opposite current
in summer keeps up a supply of cold air in the cave, and so increases
its powers of resisting the attempts of the heated external air to make
a partial entrance. Both these currents, then, favour the glacial
conditions of the cave, and to some extent counterbalance the
disadvantages of its situation: viz., its aspect, towards the
south-east; the large size of its opening to the air, and the absence of
all shelter near the mouth, such as is so often provided by trees or
rocks. The small depth of the cave, scarcely amounting to 18 feet below
the level of the entrance, is also a great disadvantage.

The people of Pralong asked, on the return of the party, what had been
found in the _grand' cave_, and the answer reduced them to silence for a
few moments. Their prejudices, however, were invincible, and they
persisted in their belief that a true glaciere ought to have no ice in
it in the winter. M. Thury did not enquire from what source they drew
their ideas of a true glaciere.

There is a book, in three volumes, on the 'Glacieres of the Alps,' by M.
Bourrit, dedicated to Buffon, in which is a description of the Valley of
Reposoir; but no mention whatever is made of the _grand' cave_. Indeed,
M. Bourrit merely meant by _glaciere_, a glacial district, something
more extensive than a _glacier_, and he had evidently no knowledge of
the existence of caves containing ice.

FOOTNOTES:

[Footnote 77: Premiere Serie, t. xx. pp. 261, &c.]

[Footnote 78: Less than 1/2 deg. C., he says.]

[Footnote 79: _Bibl. Univ. de Geneve_, Premiere Serie, t. xxv. pp. 224,
&c.]

[Footnote: 80: _Bibl. Univ_. l.c.]

* * * * *

CHAPTER XIII.

LA BORNA DE LA GLACE, IN THE DUCHY OF AOSTA.

The Chanoine Carrel, of Aosta, whose name is so well and so favourably
known to Alpine men