And I have met with many instances, wherein it appears unquestionably, that all these kind of processes in nature are going on continually: and that extraneous substances are actually inclosed, and continually inclosing, which could not be antediluvian; but must have been recent.
To these short premises, I must beg leave to add; that in two papers formerly printed in the Philosophical Transactions,[B] I endeavoured, by some very remarkable instances, to prove, that iron, wherever it comes into combination with any substances that are tending to consolidation, hastens the process exceedingly;—and also renders the hardness of the body much greater.
And I have also endeavoured, elsewhere,[C] to shew, in consequence of conclusions deduced from experiments of the most unquestionable authority, that air, in its various shapes and modifications, is indeed itself the great consolidating fluid, out of which solid bodies are composed; and by means of which the various attractions take place, which form all the hard bodies, and visible substances upon earth.
From all these premises then, it was impossible for me not to be led to conclude; that we have, in this august phænomenon of the fall of stones from the clouds, in Tuscany, an obvious proof, as it were before our eyes, of the combined operation of those very powers, and processes, to which I have been alluding.
It is well known; that pyrites, which are composed of iron, and sulphur, and other adventitious matter, when laid in heaps, and moistened, will take fire.
It is also well known, that a mixture of pyrites of almost any kind, beaten small, and mixed with iron filings and water, when buried in the ground will take fire; and produce a sort of artificial volcano. And, surely then, wherever a vast quantity of such kind of matter should at any time become mixed together, as flying dust, or ashes; and be by any means condensed together, or compressed, the same effect might be produced, even in the atmosphere and air.
Instead, therefore, of having recourse to the supposition, of 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]