allude.

In the absence of direct thermometric observations, from which the
lowest internal temperature of the glacier could be determined with
precision in all its parts, we are certainly justified in assuming that
every particle of water-ice found in the glacier, the formation of which
cannot be ascribed to the mere fact of pressure, is due to the influence
of a temperature inferior to 32 deg. Fahrenheit at the time of its
consolidation. The fact that the temperature in winter has been proved
by actual experimentation to fall as low as 28 deg. Fahrenheit, that is,
four degrees below the freezing-point at a depth of six feet below a
thick covering of snow, though not absolutely conclusive as to the
temperature at a greater depth, is certainly very significant.

Under these circumstances, it is not out of place to consider through
what channels the low temperature of the air surrounding the glacier may
penetrate into the interior. The heavy cold air may of course sink from
the surface into every large open space, such as the crevasses, large
fissures, and _moulins_ or mill like holes to be described in a future
article; it may also penetrate with the currents which ingulf themselves
under the glacier, or it may enter through its terminal vault, or
through the lateral openings between the walls of the valley and the
ice. Indeed, if all the spaces in the mass of the glacier, not occupied
by continuous ice, could be graphically represented, I believe it would
be seen that cold air surrounds the glacier-ice itself in every
direction, so that probably no masses of a greater thickness than that
already known to be permeable to cold at the surface would escape this
contact with the external temperature. If this be the case, it is
evident that water may freeze in any part of the glacier.

To substantiate this position, which, if sustained, would prove that the
dilatation of the mass of the glacier is an essential element of its
motion, I may allude to several other well-known facts. The loose snow
of the upper regions is gradually transformed into compact ice. The
experiments of Dr. Tyndall prove that this may be the result of
pressure; but in the region of the _neve_ it is evidently owing to the
transformation of the snow-flakes into ice by repeated melting and
freezing, for it takes place in the uppermost layers of the snow, where
pressure can have no such effect, as well as in its deeper beds. I take
it for granted, also,