It may
be, he adds, that this structure is in the first place determined by the
act of freezing, but it does not develop itself until the ice thaws.
M. Hassenfratz observed an appearance in ice on the Danube at
Vienna[208] corresponding to that described at Jena. He gives no
information as to the state of the weather or the temperature at the
time, nor any of the circumstances under which the ice came under his
notice. One of the masses of ice which he describes was crystallised in
prisms of various numbers of sides: of these prisms the greater part
were hexahedral and irregular. Another mass was composed of prisms in
the form of truncated pyramids; and in another he found quadrilateral
and octahedral prisms, the former splitting parallel to the faces, and
also truncated pyramids with five and six sides. He adds, that he had
frequently seen in the upper valleys tufts of ice growing, as it were,
out of the ground, and striated externally, but had never succeeded in
discovering any internal organisation, until one evening in a time of
thaw, when he found by means of a microscope that the striated tufts of
ice had assumed the same structure on a small scale as that which he had
observed on the Danube.
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