The
side-planes had a rounded, wrinkled appearance; and their mutual
inclinations--as far as could be determined--were from 105 deg. to 115 deg., and
from 66 deg. to 75 deg.. When these ice-pillars were examined by means of
polarised light, they were found to possess a feeble double-refracting
power.
The writer of the article in Poggendorff suggests a question which he
was not sure how to answer:--Is this appearance in correspondence with
the original formation of the ice, or does it only appear under slow
thaw?
It is worthy of remark, that from the 1st to the 11th of February the
thermometer was never higher than 22 deg..8 F., and during that time fell as
low as 21 deg. below zero, i.e. 43 deg. below the freezing point.
Professor Tyndall has informed me that in the winters of 1849, 1850,
1851, he found the banks of a river in Germany loaded with massive
layers of drift-ice, in a state of thaw, and was struck by the fact that
every layer displayed the prismatic structure described above, the axes
of the prisms being at right angles to the surfaces of freezing.
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