d form, and then topples upon the
land. Those vessels which are not at once crushed down by the blow are
generally hurled far inland by the rush of waters. In the great
Jamaica earthquake of 1692 a British man-of-war was borne over the
tops of certain warehouses and deposited at a distance from the shore.

Owing to the fact that water is a highly elastic material, the shocks
transmitted to it from the bottom are sent onward with their energy
but little diminished. While the impulse is very violent, these
oscillations may prove damaging to shipping. The log-books of mariners
abound in stories of how vessels were dismasted or otherwise badly
shaken by a sudden blow received in the midst of a quiet sea. The
impression commonly conveyed to the sailors is that the craft has
struck upon a rock. The explanation is that an earthquake jar, in
traversing the water, has delivered its blow to the ship. As the speed
of this jarring movement is very much greater than that of any
ordinary wave, the blow which it may strike may be most destructive.
There seems, indeed, little reason to doubt that a portion of the
vessels which are ever disappearing in the wilderness of the ocean are
lost by the crushing effect of these quakings which pass through the
waters of the deep.

We have already spoken of the earthquake shock as an oscillation. It
is a quality of all bodies which oscillate under the influence of a
blow, such as originates in earthquake shocks, to swing to and fro,
after the manner of the metal in a bell or a tuning fork, in a
succession of movements, each less than the preceding, until the
impulse is worn out, or rather, we should in strict sense say,
changed to other forms of energy. The result is, that even in the
slightest earthquake shock the earth moves not once to and fro, but
very many times. In a considerable shock the successive diminishing
swingings amount to dozens before they become so slight as to elude
perception. Although the first swaying is the strongest, and generally
the most destructive, the quick to-and-fro motions are apt to continue
and to complete the devastation which the first brings about. The
vibrations due to any one shock take place with great rapidity. They
may, indeed, be compared to those movements which we perceive in the
margin of a large bell when it has received a heavy blow from the
clapper. The reader has perhaps seen that for a moment the rim of the
bell vibrates with such rapidity that