the cloud
in Tuscany having been produced by any other kind of exhalations from
the earth; we may venture to believe, that an immense cloud of ashes,
mixed with pyritical dust, and with numerous particles of iron, having
been projected from Vesuvius to a most prodigious height, became
afterwards condensed in its descent;--took fire, both of itself, as well
as by means of the electric fluid it contained;--produced many
explosions;--melted the pyritical, and metallic, and argillaceous
particles, of which the ashes were composed;--and, by this means, had a
sudden crystallization, and consolidation of those particles taken
place, which formed the stones of various sizes, that fell to the
ground: _but did not harden the clayey ashes so rapidly as the metallic
particles crystallized_; and, therefore, gave an opportunity for
_impressions to be made_ on the surfaces of some of the stones, as they
fell, by means of the impinging of the others.

Nor does it appear to me, to be any solid objection to this conclusion,
either that Vesuvius was so far distant; or that the cloud came from the
north.

For, if we examine Sir William Hamilton's account of the very eruption
in question,[D] we shall find, that he had reason to conclude, that the
_pine-like_ cloud of ashes projected from Vesuvius, at one part of the
time during this eruption, was twenty-five or thirty miles in height;
and, if to this conclusion we add, not only that some ashes actually
were carried to a greater distance than _two hundred miles_;[E] but
that, when any substance is at a vast height in the atmosphere, a very
small variation of the direction of its course, causes a most prodigious
variation in the extent of the range of ground where it shall fall;
(just as the least variation in the angle, at the vertex of an
_isosceles_ triangle, causes a very great alteration in the extent of
its base;) we may easily perceive, not only the possibility, but the
probability, that the ashes in question, projected to so vast an height,
were first carried even beyond _Siena_ in Tuscany, northward; and then
brought back, by a contrary current of wind, in the direction in which
they fell.

Sir William Hamilton himself formed somewhat this sort of conclusion, on
receiving the first intimation of this shower of stones from the Earl of
Bristol.[F]

I cannot therefore but allow my own conclusion to carry conviction with
it to my own mind; and to send it forth into the world; as a