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kind of ice, which is formed directly by the freezing of the
water of the open ocean, before it lias been subject to the
thawing influence of the weather in the spring or of the arctic
summer.
The reports of arctic explorers, who have passed winters
in the midst of the polar ice, abound in descriptions of the
terrors caused by the pressure of the pack-ice. A ship, fettered
for the winter within the boundaries of tlio pack-ice of the
open sea, seems to be doomed to ultimate destruction. The
■danger of the situation lies in the incessantly renewed rifts
in the ice: 1 »The ice is broken up and limed together again
into now combinations of the debris by the united efforts of
the winds and sea-currents, as well as by the influence of the
cold, which causes the ice to contract its volume and thus
gives birth to innumerable rifts. By sudden fall of temperature
these rifts increase in number astoundingly. if the snow is
swept away in the spring, there will scarcely be found a
square-meter, which is destitute of such rifts» ...........
If the pack-ice of the open sea possessed the property of
regular expansion, which characterizes the pure ice, it would
be wholly incomprehensible to us, how the rifts can he formed
so abundantly or give birth to such pernicious effects. But
a glance at the curve of volumes of sample V and VI will
give us a clue, how to explain the breaking up of
innumerable rifts in the ice by a sudden full of temperature.
Suppose the ice to have been formed by freezing of
ocean-water of ordinary saltness, then the variations of its volumes
will be approximately represented either by V or VI. A
sudden fall of temperature only affects the upper layers of
the ice, while that part of the ice submerged into, or in
contact with the water, retains the constant temperature of its
freezing point i. e. —1° or —2" C. From the graphic
illustration we see, that instead of being contracted by /lie cold the
volume of Hie ice increases extraordinarily. Between —2° and —;5" (’
ice of the type V will expand O.ooss, and between —4".<t and
— 6°,4 C ice of the same kind as VI expands its volume O.0029B7.
Such extraordinary variations of volume, which are contrary
to all former notions of the behavior of the ice, can not be
compared to the ordinary expansion or contraction by heat
of any liquid or solid body, but will only bear comparison
with the changes of volume effected by temperature in gaseous
bodies. The effect will be a hard strain upon the upper
1 The following description ¡h taken principally from Weypreclit.
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