t forth its commission of its learned members to examine into
the effects, they had spread around them in sad profusion all that was
necessary to have enabled them to arrive at a true notion of the nature
of the shock, and thence a sound explanation of the varied and great
secondary effects they witnessed, and of which they have left us the
records in their Report, and the engravings illustrative of it. But we
look in vain for any light; the things seen, often with distortion or
exaggeration, are heaped together as in the phantasmagoria of a wild
and terrible dream, from which neither order nor conclusion follow.

Why was this? Why were these eminent _savants_ no more successful in
explaining what they saw than the ignorant peasants they found in the
Calabrian mountains?

Because physical science itself was not sufficiently advanced, no doubt;
but also because they had no notion of applying such science as they
had, to the very central point itself of the main problem before them,
freed from all possible adventitious conditions, and so, as it were,
attacking it in the rear. How different might have been the result of
their labours, had they begun by asking themselves, What is an
earthquake? Can we not try to find out what it _is_ by observing and
_measuring_ what it has done? We see the converse mode of dealing with
Nature in Torricelli. "Nature abhors a vacuum," was told him, as the
wisdom of his day. Possibly: but her abhorrence is limited, for I find
it is _measured_ by the pressure of a column of water of thirty-four
feet in height. We need not pursue the story with Pascal, up to the top
of the Puy de Dome.

This lesson is instructive generally to all investigators, and
particularly here; for Vulcanology, to which we are about now to turn,
has occupied until almost to-day much the same position that Seismology
did in those of the Neapolitan Commissioners.

Whole libraries have been written with respect to it dealing with
_quality_, but _measure_ and _quantity_ remain to be applied to it.

To a very preponderant class in the civilised world no knowledge is of
much interest or value that does not point to what is called a
"practical result," one measurable into utility or coin. I do not stop
to remark as to the bad or as to certain good results of this tendency
of mind; but I may venture to point out to all, that the exact knowledge
of the nature of earthquake motion, even during the short time that it
has become