These
causes, of course, modify the ice itself, while they contribute to the
motion. Further investigations are required to ascertain in what
proportion these different influences contribute to the general result,
and at what time and under what circumstances they modify most directly
the motion of the glacier.
That a glacier cannot be altogether compared to a river, although there
is an unmistakable analogy between the flow of the one and the onward
movement of the other, seems to me plain,--since the river, by the
combination of its tributaries, goes on increasing in bulk in
consequence of the incompressibility of water, while a glacier gradually
thins out in consequence of the packing of its mass, however large and
numerous may be its accessions. The analogy fails also in one important
point, that of the acceleration of speed with the steepness of the
slope. The motion of the glacier bears no such direct relation to the
inclination of its bed. And though in a glacier, as in a river, the axis
of swiftest motion is thrown alternately on one or the other side of the
valley, according to its shape and slope, the very nature of ice makes
it impossible that eddies should be formed in the glacier, and the
impressive feature of whirlpools is altogether wanting in them.
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