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semidiameter of the earth. And the vast sphere beyond this depth, in diameter 6,451,538 fathoms, may probably be only filled with air ; which will be here greatly condensed, and much heavier than the heaviest bodies we know in nature. But it is found by experiment, that, the more air is compressed, the more does the same degree of heat increase its spring, and the more capable does it render it of a violent effect; and that, for instance, the degree of heat of boiling water increases the spring of the air above what it has in its natural state, in our climate, by a quantity equal to a third of the weight wherewith it is pressed. Whence we may conclude, that a degree of heat, which on the surface of the earth will only have a moderate effect, may be capable of a very violent one below. And, as we are assured, that there are in nature degrees of heat much more considerable than that of boiling water, it is very possible there may be some whose violence, further assisted by the exceeding weight of the air, may be more than sufficient to break and overturn this solid orb of 43,528 fathoms; whose weight, compared to that of the included air, would be but a trifle.
Chemistry furnishes us a method of making artificial earthquakes, which shall have all the great effects of natural ones; which, as it may illustrate the process of nature in the production of these terrible phenomena under ground, we shall here add.
To twenty pounds of iron filings, add as many of sulphur; mix, work, and temper the whole together with a little water, so as to form a mass, half moist and half dry. This being buried three or four feet under ground, in six or seven hours time, will have a prodigious effect; the earth will begin to tremble, crack, and smoke, and fire and flame burst through.
Such is the effect even of the two cold bodies in
cold ground; there only wants a sufficient quantity of this mixture to produce a true Ætna. If it were supposed to burst out under the sea, it would produce a spout; and, if it were in the clouds, the effect would be thunder and lightning.
An earthquake is defined to be a vehement shake, or agitation, of some considerable place, or part of the earth, from natural causes; attended with a huge noise like thunder, and frequently with an eruption of water, or fire, or smoke, or winds, &c.
They are the greatest and most formidable phenomena of nature. Aristotle and Pliny distinguish two kinds, with respect to the manner of the shake, viz. a tremor and a pulsation ; the first being horizontal, in alternate vibrations, compared to the shaking of a person in an ague. The second perpendicular, up and down, their motion resembling that of boiling.
Agricola increases the number, and makes four kinds; which Albertus Magnus again reduces to three, viz. inclination, when the earth librates alternately from right to left, by which mountains have been sometimes brought to meet, and clash against each other ; pulsation, when it beats up and down, like an artery; and trembling, when it shakes and totters every way, like a flame.
The Philosophical Transactions furnish us with abundance of histories of earthquakes; particularly one at Oxford, in 1665, by Dr. Wallis and Mr. Boyle. Another at the same place in 1683, by Mr. Pigot. Another in Sicily, in 1692-3, by Mr. Hartop, Father Alessandro Burgos and Vin. Bonajutus, which last is one of the most terrible ones in all history.
It shook the whole island ; and not only that, but Naples and Malta shared in the shock. It was of the second kind mentioned by Aristotle and Pliny, viz. a
perpendicular pulsation or succussion. It was impossible, says the noble Bonajutus, for anybody in this country to keep on their legs, on the dancing earth; nay, those that lay on the ground, were tossed from side to side, as on a rolling billow; high walls leaped from their foundations several paces.
The mischief it did is amazing; almost all the buildings in the countries were thrown down. Fifty-four cities and towns, besides an incredible number of villages, were either destroyed or greatly damaged. We shall only instance the fate of Catania, one of the most famous, ancient, and flourishing cities in the kingdom; the residence of several monarchs, and a university. "This once famous, now unhappy Catania,” to use words of Father Burgos, “had the greatest share in the tragedy. Father Antonio Serovita, being on his way thither, and at the distance of a few miles, observed a black cloud, like night, hovering over the city; and there arose from the mouth of Mongibello great spires of flame, which spread all around. The sea all of a sudden began to roar, and rise in billows; and there was a blow, as if all the artillery in the world had been at once discharged. The birds flew about astonished, the cattle in the fields ran crying, &c. His and his companion's horse stopped short, trembling; , so that they were forced to alight. They were no sooner off, but they were lifted from the ground above two palms. When casting his eyes towards Catania, he with amazement saw nothing but a thick cloud of dust in the air. This was the scene of their calamity; for of the magnificent Catania, there is not the least footstep to be seen." Bonajutus assures us, that, of '18,914 inhabitants, 18,000 perished therein. The same author, from a computation of the inhabitants, before and after
the earthquake, in the several cities and towns, finds that near 60,000 perished out of 254,900.
Jamaica is remarkable for earthquakes. The inhabitants, Dr. Sloane informs us, expect one every year. That author gives us the history of one in 1687; another horrible one, in 1692, is described by several anonymous authors. In two minutes time it shook down and drowned nine tenths of the town of Port Royal. The houses sunk outright, thirty or forty fathoms deep. The earth opening swallowed up people, and they rose in other streets; some in the middle of the harbour, and yet were saved; though there were two thousand people lost, and one thousand acres of land sunk. All the houses were thrown down throughout the island. One Hopkins had his plantation removed half a mile from its place. Of all wells, from one fathom to six or seven, the water flew out at the top with a vehement motion. While the houses on the one side of the street were swallowed up, on the other they were thrown on heaps; and the sand in the street rose like waves in the sea, lifting up everybody that stood on it, and immediately dropping down into pits; and at the same instant, a flood of waters breaking in rolled them over and over; some catching hold of beams and rafters, &c. Ships and sloops in the harbour were overset and lost; the Swan frigate particularly, by the motion of the sea, and sinking of the wharf, was driven over the tops of many houses.
It was attended with a hollow rumbling noise like that of thunder. In less than a minute three quarters of the houses, and the ground they stood on, with the inhabitants, were all sunk quite under water; and the little part left behind was no better than a heap of rubbish. The shake was so violent, that it threw people down on their knees, or their faces, as they were running about for shelter. The ground heaved and swelled like a rolling sea, and several houses, still standing, were shuffled and moved some yards out of their places. A whole street is said to be twice as broad now as before; and in many places the earth would crack, and open, and shut, quick and fast. Of which openings, two or three hundred might be seen at a time; in some whereof, the people were swallowed up; others the closing earth caught by the middle, and pressed to death; in others, the heads only appeared. The larger openings swallowed up houses; and out of some would issue whole rivers of waters, spouted up a great height into the air, and threatening a deluge to that part the earthquake spared. The whole was at
. tended with stenches and offensive smells, the noise of falling mountains at a distance, &c., and the sky in a minute's time was turned dull and reddish, like a glowing oven. Yet, as great a sufferer as Port Royal
, was, more houses were left standing therein than on the whole island beside. Scarce a planting-house or sugar-work was left standing in all Jamaica. part of them were swallowed up, houses, people, trees, and all at one gape; in lieu of which, afterwards appeared great pools of water, which, when dried up,, left nothing but sand, without any mark that ever tree or plant had been thereon.
Above twelve miles from the sea, the earth gaped and spouted out, with a prodigious force, vast quantities of water into the air; yet the greatest violences were among the mountains and rocks; and it is a general opinion, that, the nearer the mountains, the greater the shake; and that the cause thereof lay there. Most of the rivers were stopped up for twenty-four hours by the falling of the mountains, till, swelling up, they found themselves new tracts and channels, tearing up in their