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.
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