An observation made a few years since at Odessa, after an
earthquake which happened during the night, suggests a simple
instrument by which the direction of the shock may be determined.
A glass vase, partly filled with water, stood on the table of
a room in a house at Odessa; and, from the coldness of the glass,
the inner part of the vessel above the water was coated with dew.
Several very perceptible shocks of an earthquake happened between
three and four o'clock in the morning; and when the observer got
up, he remarked that the dew was brushed off at two opposite
sides of the glass by a wave which the earthquake had caused in
the water. The line joining the two highest points of this wave
was, of course, that in which the shock travelled. This
circumstance, which was accidentally noticed by an engineer at
Odessa,(4*) suggests the plan of keeping, in countries subject to
earthquakes, glass vessels partly filled with treacle, or some
unctuous fluid, so that when any lateral motion is communicated
to them from the earth, the adhesion of the liquid to the glass
shall enable the observer, after some interval of time, to
determine the direction of the shock.
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