those which I obtained as the result of careful measurement. The latest
description of a visit to the glacière states a fact which probably will
be held to explain, the present excess of height above that of earlier
times.[37] The citizen Girod-Chantrans, who wrote this description, had
procured the notes of a medical man living in the neighbourhood, from
which it seemed that Dr. Oudot made the experiment, in 1779, of fixing
stakes of wood in the heads of the columns, then from 4 to 5 feet high,
and found that these stakes were the cause of a very large increase in
the height of the columns, ice gathering round them in pillars a foot
thick. So that it is not improbable that the largest of the three masses
of the present day owes its height, and its peculiar form, to a series
of stakes fixed from time to time in the various heads formed under the
fissures in the roof, though nothing but the most solid ice can now be
seen. It would be very interesting to try this experiment in one of the
caves where, without any artificial help, such immense masses of ice are
formed; and by this means columns might, in the course of a year or two,
be raised to the very roof. Further details on this subject will be
given hereafter.

There was no perceptible draught of air in any part of the cave, and the
candles burned steadily through the whole time of my visit, which
occupied more than two hours. The centre was sufficiently lighted by the
day; but in the western corner, and behind the largest column,
artificial light was necessary. The ice itself did not generally show
signs of thawing, but the whole cave was in a state of wetness, which
made the process of measuring and investigating anything but pleasant.
I had placed two thermometers at different points on my first
entrance--one on a drawing-board on a large stone in the middle of the
pond of water which has been mentioned, and the other on a bundle of
pencils at the entrance of the end chapel, in a part of the cave where