Читать книгу The Works of Benjamin Franklin, Volume 2 - Бенджамин Франклин - Страница 16

The late earthquake felt here, and probably in all the neighbouring provinces, having made many people desirous to know what may be the natural cause of such violent concussions, we shall endeavour to gratify their curiosity by giving them the various opinions of the learned on that head.

Here naturalists are divided. Some ascribe them to water, others to fire, and others to air; and all of them with some appearance of reason. To conceive which, it is to be observed that the earth everywhere abounds in huge subterraneous caverns, veins, and canals, particularly about the roots of mountains; that of these cavities, veins, &c., some are full of water, whence are composed gulfs, abysses, springs, rivulets; and others full of exhalations; and that some parts of the earth are replete with nitre, sulphur, bitumen, vitriol, &c. This premised:

1. The earth itself may sometimes be the cause of its own shaking; when the roots, or basis of some large mass being dissolved or worn away by a fluid underneath, it sinks into the same and with its weight occasions a tremor of the adjacent parts, produces a noise, and frequently an inundation of water.

2. The subterraneous waters may occasion earthquakes by their overflowing, cutting out new courses, &c. Add that the water, being heated and rarefied by the subterraneous fires, may emit fumes, blasts, &c., which, by their action either on the water or immediately on the earth itself, may occasion great succussions.

3. The air may be the cause of earthquakes; for, the air being a collection of fumes and vapors raised from the earth and water, if it be pent up in too narrow viscera of the earth, the subterraneous or its own native heat rarefying and expanding it, the force wherewith it endeavours to escape may shake the earth; hence there arise divers species of earthquakes, according to the different position, quantity, &c., of the imprisoned aura.

Lastly, fire is a principal cause of earthquakes: both as it produces the aforesaid subterraneous aura or vapors; and as this aura or spirit, from the different matter and composition whereof arise sulphur, bitumen, and other inflammable matters, takes fire either from other fire it meets withal, or from its collision against hard bodies, or its intermixture with other fluids; by which means bursting out into a greater compass the place becomes too narrow for it, so that pressing against it on all sides the adjoining parts are shaken, till, having made itself a passage, it spends itself in a volcano or burning mountain.

But to come nearer to the point. Dr. Lister is of opinion that the material cause of thunder, lightning, and earthquakes is one and the same—viz., the inflammable breath of the pyrites, which is a substantial sulphur and takes fire of itself.

The difference between these three terrible phenomena he takes only to consist in this: that this sulphur, in the former, is fired in the air, and in the latter under ground. Which is a notion that Pliny had long before him; “Quid enim,” says he, “aliud est in terrâ tremor, quam in nube tonitru?”

This he thinks abundantly indicated by the same sulphurous smell being found in any thing burnt with lightning, and in the waters, &c., cast up in earthquakes, and even in the air before and after them.

Add that they agree in the manner of the noise, which is carried on as in a train fired; the one, rolling and rattling through the air, takes fire as the vapors chance to drive; as the other fired under ground, in like manner, moves with a desultory noise.

Thunder, which is the effect of the trembling of the air, caused by the same vapors dispersed through it, has force enough to shake our houses; and why there may not be thunder and lightning under ground, in some vast repositories there, I see no reason; especially if we reflect that the matter which composes the noisy vapor above us is in much larger quantities under ground.

That the earth abounds in cavities, everybody allows; and that these subterraneous cavities are, at certain times and in certain seasons, full of inflammable vapors, the damps in mines sufficiently witness, which fired do every thing as in an earthquake, save in a lesser degree.

Add that the pyrites alone, of all the known minerals, yields this inflammable vapor, is highly probable; for that no mineral or ore whatsoever is sulphurous, but as it is wholly, or in part, a pyrites; and that there is but one species of brimstone which the pyrites naturally and only yields. The sulphur vive, or natural brimstone, which is found in and about the burning mountains, is certainly the effects of sublimation; and those great quantities of it, said to be found about the skirts of volcanoes, is only an argument of the long duration and vehemence of those fires. Possibly the pyrites of the volcanoes or burning mountains may be more sulphurous than ours; and indeed it is plain that some of ours in England are very lean and hold but little sulphur; others again very much; which may be one reason why England is so little troubled with earthquakes, and Italy, and almost all round the Mediterranean Sea, so very much; though another reason is the paucity of pyrites in England.

Comparing our earthquakes, thunder, and lightning with theirs, it is observed that there it lightens almost daily, especially in summer-time; here seldom: there thunder and lightning is of long duration, here it is soon over: there the earthquakes are frequent, long, and terrible, with many paroxysms in a day, and that for many days; here very short, a few minutes, and scarce perceptible. To this purpose the subterraneous caverns in England are small and few compared to the vast vaults in those parts of the world; which is evident from the sudden disappearance of whole mountains and islands.

Dr. Woodward gives us another theory of earthquakes. He endeavours to show that the subterraneous heat or fire (which is continually elevating water out of the abyss to furnish the earth with rain, dew, springs, and rivers), being stopped in any part of the earth, and so diverted from its ordinary course by some accidental glut or obstruction in the pores or passages through which it used to ascend to the surface, becomes, by such means, preternaturally assembled in a greater quantity than usual into one place, and therefore causeth a great rarefaction and intumescence of the water of the abyss, putting it into great commotions and disorders, and at the same time making the like effort on the earth, which, being expanded upon the face of the abyss, occasions that agitation and concussion we call an earthquake.

This effort in some earthquakes, he observes, is so vehement that it splits and tears the earth, making cracks and chasms in it some miles in length, which open at the instant of the shock, and close again in the intervals betwixt them; nay, it is sometimes so violent that it forces the superincumbent strata, breaks them all throughout, and thereby perfectly undermines and ruins the foundation of them; so that, these falling, the whole tract, as soon as the shock is over, sinks down into the abyss and is swallowed up by it; the water thereof immediately rising up and forming a lake in the place where the said tract before was. That this effort being made in all directions indifferently, the fire, dilating and expanding on all hands, and endeavouring to get room and make its way through all obstacles, falls as foul on the waters of the abyss beneath as on the earth above, forcing it forth which way soever it can find vent or passage, as well through its ordinary exits, wells, springs, and the outlets of rivers, as through the chasms then newly opened, through the camini or spiracles of Ætna or other neighbouring volcanoes, and those hiatuses at the bottom of the sea, whereby the abyss below opens into it and communicates with it. That, as the water resident in the abyss is, in all parts of it, stored with a considerable quantity of heat, and more especially in those where those extraordinary aggregations of this fire happen, so likewise is the water which is thus forced out of it; insomuch that when thrown forth and mixed with the waters of wells or springs of rivers and the sea, it renders them very sensibly hot.

He adds that though the abyss be liable to those commotions, in all parts, yet the effects are nowhere very remarkable except in those countries which are mountainous, and consequently stony or cavernous underneath, and especially where the disposition of the strata is such that those caverns open into the abyss, and so freely admit and entertain the fire, which, assembling therein, is the cause of the shock; it naturally steering its course that way where it finds the readiest reception, which is towards those caverns. Besides, that those parts of the earth which abound with strata of stone or marble, making the strongest opposition to this effort, are the most furiously shattered and suffer much more by it than those which consist of gravel, sand, and the like laxer matter, which more easily give way and make not so great resistance. But, above all, those countries which yield great store of sulphur and nitre are by far the most injured by earthquakes; those minerals constituting in the earth a kind of natural gun-powder, which, taking fire upon this assemblage and approach of it, occasions that murmuring noise, that subterraneous thunder, which is heard rumbling in the bowels of the earth during earthquakes, and by the assistance of its explosive power renders the shock much greater, so as sometimes to make miserable havoc and destruction.

And it is for this reason that Italy, Sicily, Anatolia, and some parts of Greece have been so long and often alarmed and harassed by earthquakes; these countries being all mountainous and cavernous, abounding with stone and marble and affording sulphur and nitre in great plenty.

Further, that Ætna, Vesuvius, Hecla, and the other volcanoes are only so many spiracles, serving for the discharge of this subterraneous fire when it is thus preternaturally assembled. That where there happens to be such a structure and conformation of the interior parts of the earth, as that the fire may pass freely and without impediment from the caverns wherein it assembles unto those spiracles, it then readily gets out from time to time without shaking or disturbing the earth; but where such communication is wanting, or passage not sufficiently large and open, so that it cannot come at the spiracles, it heaves up and shocks the earth with greater or lesser impetuosity according to the quantity of fire thus assembled, till it has made its way to the mouth of the volcano. That therefore there are scarce any countries much annoyed by earthquakes but have one of these fiery vents, which are constantly in flames when any earthquake happens, as disgorging that fire which, whilst underneath, was the cause of the disaster. Lastly, that were it not for these diverticula, it would rage in the bowels of the earth much more furiously and make greater havoc than it doth.

We have seen what fire and water may do; and that either of them are sufficient for all the phenomena of earthquakes; if they should both fail, we have a third agent, scarce inferior to either of them; the reader must not be surprised when we tell him it is air.

Monsieur Amontons, in his Mémoires de l’Académie des Sciences, An 1703, has an express discourse to prove that on the foot of the new experiments of the weight and spring of the air, a moderate degree of heat may bring the air into a condition capable of causing earthquakes. It is shown that at the depth of 43,528 fathoms below the surface of the earth, air is only one fourth less heavy than mercury. Now this depth of 43,528 fathoms is only a seventy-fourth part of the 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 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 vibrates 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 round. 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 pile 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 water spouted up a great height into the air, and threatening a deluge to that part the earthquake spared. The whole was attended 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. A great 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.

About 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 passage trees, &c. After the great shake, those people who escaped got on board ships in the harbour, where many continued above two months; the shakes all that time being so violent, and coming so thick, sometimes two or three in an hour, accompanied with frightful noises, like a ruffling wind, or a hollow, rumbling thunder, with brimstone blasts, that they durst not come ashore. The consequence of the earthquake was a general sickness, from the noisome vapors belched forth, which swept away above three thousand persons.

After the detail of these horrible convulsions, the reader will have but little curiosity left for the less considerable phenomena of the earthquake at Lima, in 1687, described by Father Alvarez de Toledo, wherein above five thousand persons were destroyed; this being of the vibratory kind, so that the bells in the church rung of themselves; or that at Batavia in 1699, by Witsen; that in the north of England in 1703, by Mr. Thoresby; or, lastly, those in New England in 1663 and 1670, by Dr. Mather.