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the air being a collection of fumes and vapours 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 arises 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 vapours, 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 fuids; 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 the sulphur in the former is fired in the air, and in the latier under ground. Which is a notion Pliny had long before him : “Quid enim,” says he,“ aliud est in terrà tremor, quam in nube tonitru ?” For wherein does the trembling of the earth differ from that occasioned by thunder in the clouds ?
This he thinks abundantly indicated by the same sulphurous smell being found in anything burned 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 vapours 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 vapours 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 vapour 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 vapours, the damps in mines sufficiently witness, which, fired, do rything as in an earthquake, save in a lesser degree.
Add that the pyrites alone, of all the known minerals, yields this inflammable vapour, 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 some reason why England is so little troubled with earthquakes, and Italy, and almost all round the Mediterranean Sea, so 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 parox. ysms 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 isl. ands.
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, maing cracks and chasms in it some miles in length, which open at the instant of the shock, and close again in the intervals between them; nay, it is sometimes so violent that it forces the superincumbent strata, breaks them all throughout, and thereby per
fectly undermines and ruins the foundation of them;. so that, these failing, 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 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 gunpowder, 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.
Farther, 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 part 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,