While I was surveying, the ice, which was sixteen inches thick,
undulated under a slight wind like water. It is well known that a
level cannot be used on ice. At one rod from the shore its greatest
fluctuation, when observed by means of a level on land directed
toward a graduated staff on the ice, was three quarters of an inch,
though the ice appeared firmly attached to the shore. It was
probably greater in the middle. Who knows but if our instruments
were delicate enough we might detect an undulation in the crust of
the earth? When two legs of my level were on the shore and the
third on the ice, and the sights were directed over the latter, a
rise or fall of the ice of an almost infinitesimal amount made a
difference of several feet on a tree across the pond. When I began
to cut holes for sounding there were three or four inches of water
on the ice under a deep snow which had sunk it thus far; but the
water began immediately to run into these holes, and continued to
run for two days in deep streams, which wore away the ice on every
side, and contributed essentially, if not mainly, to dry the surface
of the pond; for, as the water ran in, it raised and floated the
ice.
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