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observations already collected long ago to corroborate this
fact. It has long been a subject of discussion, whether the
ice is a brittle or a plastic substance. All observers agree,,
that pure ice, taken far below zero under ordinary pressure,
is not plastic at all. But we nevertheless must confess, that
ice in the vicinity of 0° somehow or other can behave like a
plastic body, in order to account for a great many well known
facts and in the first place for the movement of the glaciers.
We may f. ex. attribute the fact, that two blocks of ice, which
are brought into contact in a warm room, immediately adhere
to each other like wax, to the peculiar molecular state of the
ice jjar/ticles at the free surfaces, which by their contact are
brought into altered conditions of cohesion, or we may ascribe
this and similar phenomena to a regelation, i. e. a temporary
melting process, caused by the lowering of the melting point
by pressure and restoration of the initial state of aggregation,
as soon as the pressure ceases; we may, in short, declare the
plastic condition of the ice at its melting point to depend on
an apparent instead of a real toughness of its substance —
but we still can not deny such observations, which plainly
show us, that every kind of ice, which we may test, softens,
before melting.
In his admirable researches on the latent heat of melting
bodies, Person 1 observed some irregularities in the specific
heat of ice below zero, which led him to adopt the theory,,
that the ice does not melt at once at a fixed temperature, but
already some degrees below the melting point begins to weaken.
The mechanical softening of pure ice below zero has been
testified by many observers. It will suffice to cite a few lines
from a paper by Pfaff entitled »Versuche über die Plasticitftt
des Eises».2
»Es geht aus meinen Versuchen hervor, dass auch der
geringste Druck hinreicht, um Eistheilchen zu verschieben,
wenn er anhaltend wirkt und die Temperatur des Eises und der
Umgebung nahe dem Schmelzpunkte ist.»
»Es ergiebti sich, dass das Eis sich nahe seinem
Schmelzpunkte in der That wie Wachs verhält und bei einem Drucke
von nur zwei Atmosphären sich so nachgiebig zeigt, dass z. B.
ein hohler Cylinder von Eisen von 11.5 m.m. Durchmesser und
1.7 Wandstärke in zwei Stunden bei einer Temperatur zwischen
— 1 und O.5 Grad 3 m.m. tief in das Eis eindrang. Welchen
’ C. R. XXX p. 526.
2 Pogg. Ann. CLIV 1875.
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