Light Science for Leisure Hours: A series of familiar essays on scientific subjects, natural phenomena, &c.Proctor, Richard A. (Richard Anthony)
Science
Light Science for Leisure Hours: A series of familiar essays on scientific subjects, natural phenomena, &c.
Proctor, Richard A. (Richard Anthony)
Science
Such were among the phenomena presented in the region where the
earthquake itself was felt. It will be seen at once that within this
region, or rather along that portion of the sea-coast which falls
within the central region of disturbance, the true character of the
sea-wave generated by the earthquake could not be recognised. If a rock
fall from a lofty cliff into a comparatively shallow sea, the water
around the place where the rock has fallen is disturbed in an irregular
manner. The sea seems at one place to leap up and down; elsewhere one
wave seems to beat against another, and the sharpest eye can detect
no law in the motion of the seething waters. But presently, outside
the scene of disturbance, a circular wave is seen to form, and if the
motion of this wave be watched, it is seen to present the most striking
contrast to the turmoil and confusion at its centre. It sweeps onwards
and outwards in a regular undulation. Gradually it loses its circular
figure (unless the sea-bottom happens to be unusually level), showing
that although its motion is everywhere regular, it is not everywhere
equally swift. A wave of this sort, though incomparably vaster, swept
swiftly away on every side from the scene of the great earthquake near
the Peruvian Andes. It has been calculated that the width of this wave
varied from one million to five million feet, or roughly, from 200
to 1,000 miles, while, when in mid-Pacific, the length of the wave,
measured along its summit in a widely-curved path from one side to
another of the great ocean, cannot have been less than 8,000 miles.
We cannot tell how deep-seated was the centre of subterranean action;
but there can be no doubt it was very deep indeed, because otherwise
the shock felt in towns separated from each other by hundreds of miles
could not have been so nearly contemporaneous. Therefore the portion of
the earth’s crust upheaved must have been enormous, for the length of
the region where the direct effects of the earthquake were perceived is
estimated by Professor Von Hochstetter at no less than 240 miles. The
breadth of the region is unknown, because on one side the slope of the
Andes and on the other the ocean concealed the motion of the earth’s
crust.
Public-domain text, read in full here on John Shaqi.
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