d well
the effects of great sea-waves rolling in-shore after the shock, did not
establish any clear relation between the two.[A]

Hitherto no one appears to have formed any clear notion as to what an
Earthquake is--that is to say, any clear idea of what is the nature of
the movement constituting the shock, no matter what may be the nature or
origin of the movement itself. The first glimmering of such an idea, so
far as my reading has enabled me to ascertain, is due to the penetrating
genius of Dr. Thomas Young, who, in his "Lectures on Natural
Philosophy," published in 1807, casually suggests the probability that
earthquake motions are vibratory, and are analogous to those of
sound.[B] This was rendered somewhat more definite by Gay Lussac, who,
in an able paper "On the Chemical Theories of Volcanoes," in the
twenty-second volume of the "Annales de Chemie," in 1823, says: "En un
mot, les tremblements de terre ne sont que la propagation d'une
commotion a travers la masse de la terre, tellement independante des
cavites souterraines qu'elle s'entendrait, d'autant plus loin que la
terre serait plus homogene."

These suggestions of Young and of Gay Lussac, as may be seen, only refer
to the movement in the more or less solid crust of the earth. But two,
if not three, other great movements were long known to frequently
accompany earthquake shocks--the recession of the sea from the shore
just about the moment of shock--the terrible sounds or subterraneous
growlings which sometimes preceded, sometimes accompanied, and sometimes
followed the shock--and the great sea-wave which rolls in-shore more or
less long after it, remained still unknown as to their nature. They had
been recognised only as concomitant but unconnected phenomena--the more
inexplicable, because sometimes present, sometimes absent, and wholly
without any known mutual bearing or community of cause.

On the 9th February, 1846, I communicated to the Royal Irish Academy my
Paper, "On the Dynamics of Earthquakes," printed in Vol. XXI., Part I.,
of the Transactions of that Academy, and published the same year in
which it was my good fortune to have been able to colligate the observed
facts, and bringing them together under the light of the known laws of
production and propagation of vibratory waves in elastic, solid, liquid
and gaseous bodies, and of the production and propagation of liquid
waves of translation in water varying in depth, to prove that all the
phenom