has, I believe, been anywhere
given.

The appendix to the Report comprises the entire bibliography of
Earthquakes collected during those researches, and a concluding chapter
on desiderata, and inquiries as to ill-understood phenomena supposed to
be connected with Earthquakes.

* * * * *

In 1849-50, I was honoured by the request to draw up the article
"Earthquake Phenomena," which has appeared in the first and subsequent
editions of the "Admiralty Manual of Scientific Inquiry." Originally the
subject was intended to have formed part of the article on Geology,
entrusted to Mr. Darwin, who consulted me upon the subject; and upon my
representing how much Earthquakes had, within a short time, become
matter for the mathematician and physicist, he, with a singleness of eye
to science which it is but just to place on record, took the necessary
steps with the Admiralty authorities that Earthquakes should form a
separate article, and advised its being placed, as it was, in my hands.
To record this will, I believe, be sufficient justification for my
reference to this article, in which a good deal of information as to
Seismometry is to be found.

* * * * *

By recurring to Mr. Hopkins's Report on Earthquake Theory, before
remarked upon ("Report of British Association, 1847"), it will be seen
that the solutions of the problems which he there gives for finding the
depth of focus of shock are founded upon the _velocity of propagation_
of the wave in the interior of the mass, the _apparent horizontal
velocity_ and the _horizontal direction of propagation_ at any proposed
point being known (p. 82).

By this it appears plainly that at that time Mr. Hopkins supposed that
it was the _velocity of translation_ of the wave of shock that did the
mischief, and not the _velocity of the wave particle_, or wave itself.
And, further, that the former might be obtained by reference simply to
the modulus of elasticity of the rock of any given formation, as,
indeed, was my own earliest view when I produced my "Dynamics of
Earthquake" in 1846. From the remarks already made as to the vast
difference between the actual transit velocity in more or less
discontinuous rocks--such as they occur in Nature--it will be equally
obvious that Mr. Hopkins's methods, as above mentioned, are
impracticable, even were there no confusion between the velocity of
translation of the wave and that of the