bases of the Calabrian Obelisks) which had been supposed due to
such, were but resolved motions, due to the transit rectilinearly of the
shock.

This removed one apparent stumbling block to the true theory.

Incidentally also it was shown that from the observed elements of the
movement of the elastic wave of shock at certain points--by suitable
instruments--the position and depth of the _focus_, or centre of
impulse, might be inferred.

In the same volume ("Transactions of the Royal I. Academy," XXI.) I gave
account, with a design to scale, for the first self-registering and
recording seismometer ever, to my knowledge, proposed. In some respects
in principle it resembles that of Professor Palmieri, of which he has
made such extended use at the Vesuvian Observatory, though it differs
much from the latter in detail. In June, 1847, Mr. Hopkins, of
Cambridge, read his Report, "On the Geological Theories of Elevation and
Earthquakes," to the British Association--requested by that body the
year before--and printed in its Reports for that year.

The chief features of this document are a digest of Mr. Hopkins's
previously published "Mathematical Papers" on the formations of
fissures, etc., by elevations and depressions, and those on the
thickness of the earth's crust, based on precession, etc., which he
discusses in some relations to volcanic action.

This extends to forty-one pages, the remaining eighteen pages of the
Report being devoted to "Vibratory Motions of the Earth's Crust produced
by Subterranean Forces--Earthquakes."

The latter consists mainly of a _resume_ of the acknowledged laws, as
delivered principally by Poisson, of formation and propagation of
elastic waves and of liquid waves, by Webers, S. Russel and others--the
original matter in this Report is small--and as respects the latter
portion consists mainly in some problems for finding analytically the
position or depth of the centre of disturbance when certain elements of
the wave of shock are given, or have been supposed registered by
seismometric instruments, such as that described by myself, and above
referred to.[D] At the time my original Paper "On the Dynamics of
Earthquakes" was published, there was little or no _experimental_
knowledge as to the actual velocity of transit of waves--analogous to
those of sound, but of greater amplitude--through elastic solids. The
velocity as deduced from theory, the solid being assumed quite
_homogeneous_ and _co