s flow of the icy stream, filled me with
admiration." (Travels in the Alps, p. 133.) In order to explain this
remarkable regularity of motion, and its obedience to laws so strictly
analogous to those of fluids, the same writer proposed the theory that
the ice, instead of being solid and compact, is a viscous or plastic
body, capable of yielding to great pressure, and the more so in
proportion as its temperature is higher, and as it approaches more
nearly to the melting point. He endeavors to show that this hypothesis
will account for many complicated phenomena, especially for a ribboned
or veined structure which is everywhere observable in the ice, and might
be produced by lines of discontinuity, arising from the different rates
at which the various portions of the semi-rigid glacier advance and pass
each other. Many examples are adduced to prove that a glacier can model
itself to the form of the ground over which it is forced, exactly as
would happen if it possessed a certain ductility, and this power of
yielding under intense pressure, is shown not to be irreconcilable with
the idea of the ice being sufficiently compact to break into fragments,
when the strain upon its parts is excessive; as where the glacier turns
a sharp angle, or descends upon a rapid or convex slope. The increased
velocity in summer is attributed partly to the greater plasticity of the
ice, when not exposed to intense cold, and partly to the hydrostatic
pressure of the water in the capillary tubes, which imbibe more of this
liquid in the hot season.

On the assumption of the ice being a rigid mass, Mr. Hopkins attributed
the more rapid motions in the centre to the unequal rate at which the
broad stripes of ice, intervening between longitudinal fissures,
advance; but besides that there are parts of the glacier where no such
fissures exist, such a mode of progression, says Mr. Forbes, would cause
the borders of large transverse rents or "crevasses," to be jagged like
a saw, instead of being perfectly even and straight-edged.[289] An
experiment recently made by Mr. Christie, secretary to the Royal
Society, appears to demonstrate that ice, under great pressure,
possesses a sufficient degree of moulding and self-adapting power to
allow it to be acted upon, as if it were a pasty substance. A hollow
shell of iron an inch and a half thick, the interior being ten inches in
diameter, was filled with water, in the course of a severe winter, and
exposed to th