It is
admitted by all, that the waste of a glacier at its surface, in
consequence of evaporation and melting, amounts to about nine or ten
feet in a year. At this rate of diminution, a glacier, even one thousand
feet in thickness, could not advance during a single century without
being exhausted. The water supplied by infiltration no doubt repairs the
loss to a great degree. Indeed, the lower part of the glacier must be
chiefly maintained from this source, since the annual increase from the
fresh accumulations of snow is felt only above the snow-line, below
which the yearly snow melts away and disappears. In a complete theory
of the glaciers, the effect of so great an accession of plastic material
cannot be overlooked.
I now come to some points in the structure of the glacier, the
consideration of which is likely to have a decided influence in settling
the conflicting views respecting their motion. The experiments of
Faraday concerning regelation, and the application of the facts made
known by the great English physicist to the theory of the glaciers, as
first presented by Dr. Tyndall in his admirable work, show that
fragments of ice with most surfaces are readily reunited under pressure
into a solid mass.
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