d bodies, to imagine them capable of transmitting, with
such extreme velocity, motions analogous to tidal waves, it seems
nevertheless certain that such undulations are produced, and it is
supposed that when the shock passes a given point, each particle of the
solid earth describes an ellipse in space. The facility with which all
the particles of a solid mass can be made to vibrate may be illustrated,
says Gay Lussac, by many familiar examples. If we apply the ear to one
end of a long wooden beam, and listen attentively when the other end is
struck by a pin's head, we hear the shock distinctly; which shows that
every fibre throughout the whole length has been made to vibrate. The
rattling of carriages on the pavement shakes the largest edifices; and
in the quarries underneath some quarters in Paris, it is found that the
movement is communicated through a considerable thickness of rock.[689]

The great sea-wave originating directly over the centre of disturbance
is propagated, as Michell correctly stated, in every direction, like the
circle upon a pond when a pebble is dropped into it, the different rates
at which it moves depending (as he also suggested) on variations in the
depth of the water. This wave of the sea, says Mr. Mallet, is raised by
the impulse of the shock immediately below it, which in great
earthquakes lifts up the ground two or three feet perpendicularly. The
velocity of the shock, or earth-wave, is greater because it "depends
upon a function of the elasticity of the crust of the earth, whereas the
velocity of the sea-wave depends upon a function of the depth of the
sea."

"Although the shock in its passage under the deep ocean gives no trace
of its progress, it no sooner gets into soundings or shallow water, than
it gives rise to another and smaller wave of the sea. It carries, as it
were, upon its back, this lesser aqueous undulation; a long narrow ridge
of water which corresponds in form and velocity to itself, being pushed
up by the partial elevation of the bottom. It is this small wave, called
technically the 'forced sea-wave,' which communicates the
earthquake-shock to ships at sea, as if they had struck upon a rock. It
breaks upon a coast at the same moment that the shock reaches it, and
sometimes it may cause an apparent slight recession from the shore,
followed by its flowing up somewhat higher than the usual tide mark:
this will happen where the beach is very sloping, as is usual where the
se