her the transformation of
snow into ice be the result of pressure only, or, as I believe, quite as
much the result of successive thawings and freezings, these structural
features can equally be produced, and exhibit these relations to one
another. It may be, moreover, that, when the glacier is at a temperature
below 32 deg., its motion produces extensive fissuration throughout the
mass.

Now that water pervades this net-work of fissures in the glacier to a
depth not yet ascertained, my experiments upon the glacier of the Aar
have abundantly proved; and that the fissures themselves exist at a
depth of two hundred and fifty feet I also know, from actual
observation. All this can, of course, take place, even if the internal
temperature of the glacier never should fall below 32 deg. Fahrenheit; and
it has actually been assumed that the temperature within the glacier
does not fall below this point, and that, therefore, no phenomena,
dependent upon a greater degree of cold, can take place beyond a very
superficial depth, to which the cold outside may be supposed to
penetrate. I have, however, observed facts which seem to me
irreconcilable with this assumption. In the first place, a
thermometrograph indicating -2 deg. Centigrade, (about 28 deg. Fahrenheit,) at a
depth of a little over two metres, that is, about six feet and a half,
has been recovered from the interior of the glacier of the Aar, while
all my attempts to thaw out other instruments placed in the ice at a
greater depth utterly failed, owing to the circumstance, that, after
being left for some time in the glacier, they were invariably frozen up
in newly formed water-ice, entirely different in its structure from the
surrounding glacier-ice. This freezing could not have taken place, did
the mass of the glacier never fall below 32 deg. Fahrenheit. And this is not
the only evidence of hard frost in the interior of the glaciers. The
innumerable large walls of water-ice, which may be seen intersecting
their mass in every direction and to any depth thus far reached, show
that water freezes in their interior. It cannot be objected, that this
is merely the result of pressure; since the thin fluid seams, exhibited
under pressure in the interesting experiments of Dr. Tyndall, and
described in his work under the head of Crystallization and Internal
Liquefaction, cannot be compared to the large, irregular masses of
water-ice found in the interior of the glacier, to which I here