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No. IV. Price SIXPENCE.-Published by HUNT AND CLARKE, 4, York Street, Covent Garden, London.

PROBABLE CAUSE OF VOLCANOS AND EARTHQUAKES.

(From Professor Silliman's American Journal of Science, for October.)

THE air of the atmosphere at the surface of the earth will support, in barometer tubes, mercury at 30 inches,

or

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fresh water at 33 feet, and sea water at about 32 feet. It is 828 times lighter than fresh water, :: 0,00120: 1. And because fresh water is to sea water as 1000 is to 1029, so air is 853 times lighter than sea water, or :: 0,00118: 1. But for reasons to be explained in the course of this article, we will assume that air is only 800 times lighter than sea water, :: 0,00125: 1. This being granted, let us suppose that a bell, suspended by a metallic chain, and full of atmospheric air, is plunged into the ocean; the air contained in it will be compressed more and more as it descends, and consequently its density will be increased in proportion to the depth it penetrates. The following table will show the ratio of the condensation compared with the depth of

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lation the depth at which that precise point is obtained, we shall find twenty-five thousand six hundred feet, or about four miles and seven-eighths, equal to the pressure of eight hundred atmospheres.

Thence it follows, that at the depth of four miles and seven-eighths the air would be compressed in the bell to the same density with the sea water.

But now, when arrived at this point, if we plunge the bell more and more into the sea, the density will still increase, and will soon exceed that of the surrounding water; at that moment what will become of the bubble of air contained in the bell, if even we suppose it to be upset?

Will it come up and break at the surface? It cannot, for, by the supposition, it is heavier than its own volume of water; on the contrary, it must descend to the bottom, with an increased velocity; for its density will increase as it sinks, and it must remain at the bottom of the sea, just as a stone itself would do.

I request the reader to stop here, and reflect one moment; the novelty of the assertion, that a bubble of air is precipitated to the bottom of the sea, instead of rising to its surface, merits to be examined with attention before it is admitted; if it can be destroyed, either by argument or experiment, the re mainder of this article becomes useless, for all that follows is in the form of corollaries from this first principle; but if, after a close and severe examination, the reader, as well as myself, is convinced of its truth, let us then proceed together.

If a series of bells, similar to the one just described, were constantly in operation through the whole extent of the ocean, there would

soon be, under the water of the sea, a layer of compressed air of its whole extent. But has nature provided for such an apparatus? Yes, she has, with the simplicity, ease, grandeur, and efficacy that she shows in all her operations; let us merely study her laws, and we shall soon discover it.

Let us take a glass of water from a running spring; let us expose it for some time to the light and heat of the sun; we shall soon observe bubbles rising from every part of the water, collecting at the surface, and breaking the one after the other. Let us put some of the same water into a convenient vessel by the fire, and we shall again observe a rising of bubbles before the moment of ebullition; and, still better, let us put some of it into a glass under the receiver of an airpump, and produce a vacuum, when the bubbles will rise with great celerity; let us collect the air thus disengaged, and we shall find its quantity a little above four per cent. in bulk of the water under experiment.

The water of the sea, always under full atmospheric pressure, is constantly agitated by the wind, and, being divided at its surNo. IV. NOVEMBER 22, 1828.

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face into waves and breakers, it so multiplies its points of contact with the atmospheric air, that it, of course, absorbs all that its affinity for it, under these circumstances, allows. Moreover, all rain water being divided into drops, the most favourable condition for its combination, brings down water perfectly saturated with air, and the whole quantity of rain that falls on the globe goes ultimately to the sea, whether it falls directly into it, or whether it is carried to it by rivers flowing down and renewing constantly their surfaces, all which circumstances unite to supply the sea with a new and perpetual addition of combined atmospheric air; it may then be admitted that the sea water is completely saturated with this fluid.

We have seen, in one of the preceding paragraphs, that the affinity of the air for water is very weak. Is it a chemical combination, or merely an affinity of cohesion? It matters not which opinion we form in that respect, for true it is, that the least change in the temperature, or in the relative densities, destroys their union. We have just seen that in spring water, by the mere subtraction of the atmospheric pressure, the air resumes its gaseous form, and then, from its relative levity, separates from the water, and ascends and breaks into bubbles at its surface. Now, below the depth of twenty-five thousand six hundred feet, the air is denser than the water; and if a density different from that of the water in minus has been sufficient to operate their disunion, a similar difference in plus must produce the same effect. A bubble of air, under the pressure of eight hundred atmospheres, small as we may conceive it, is still a bubble of air, and its density being superior to that of the medium in which it is placed, it must plunge to the bottom, performing exactly what we have ascertained to be the case with the bell. I conceive that these bubbles collect together in sinking, just as they do in rising, making a constant shower at the bottom of the sea, to supply the constant consumption of it, as we shall soon have occasion to state.

Until this moment we have called the air absorbed by water atmospheric air; which, according to the multiplied experiments made on it, appears to be a compound of 24 oxygen, 75 azote, and I carbonic acid gas; total 100. Whereas, the air absorbed by water, although a compound of the three same gases, contains them in different proportions. The analysis of the air contained in spring water has been made at different times, in different places, and by different persons, and, consequently, the results are all different and uncertain. The analysis of the air contained in rain water, river water, and particularly sea water, should be the object of our immediate researches, as going more directly to our purpose; but I could not find any publication on this subject. To

arrive at any positive result would require no small trouble, and meet with many difficulties, as the analysis should be performed at sea, in different latitudes, and upon water taken at various depths. It is probable, however, from what information we can collect, that the relative proportion of the three gases is altered; that the absorbed air contains more carbonic acid, less azote, and the same relative quantity of oxygen, which alteration must increase its density. These considerations have induced us, in the foregoing table, to represent the density of the air and water by the numbers 800 and 1, instead of 853 and 1. This is the explanation we have promised to give.

The depth of the sea water is not a varia. ble, it is an absolute quantity; a measure which will be determined to a foot by calculation as soon as we have exactly the relation of the three gases it contains. By our computation, which is, however, not far from the truth, we found it twenty-five thousand six hundred feet, or four miles and seven-eighths; but whatever be the depth, at the point of contact, the air must be exactly of the same density with the water. It cannot be more or less; for, if it were less, it would rise to the surface; if it were more, a new quantity of it would shower again through the water.

Air compressed under such an immense weight must have a tremendous force of elasticity. It is superior to any thing we have as yet produced in our most powerful engines, not excepting Perkins's high pressure steam artillery; so that, if we conceive a tube of sufficient length and resistance to open a communication through the sea between that immense reservoir of compressed air and our atmosphere, the projectiles placed in this tube would acquire a velocity several times greater than that of a cannon ball; this air then must penetrate, under ground at four miles and seven-eighths below the surface of the earth, through the crevices of the rocks, and in all the subterranean vacuities which communicate with each other, or with the general reservoir of air. And if it meets there, or rather, when it meets there combustible substances, as bitumen, sulphur, coal, &c. a conflagration must ensue, which is constantly supplied with a new quantity of blowing air, forced by the pressure of the sea, as if by a permanent forge bellows. The air, after having supported combustion, rarefied by the heat, opens its way, and issues by apertures at the summit of volcanic mountains, which we have called craters, as it does in common chimneys at the top of the flues. Such is our conception of these subterranean fires called volcanoes, considered in their quiet and peaceful operation.

It would be difficult to conceive how combustion should be constantly supported under ground without a constant supply of

air; and we do not perceive how that air would be brought into those subterranean cavities, except by the means just suggested; we see no hole or opening which might be considered as a draught for the passage of air; on the contrary, all the apertures observed emit gases that may be considered as the result of the conflagration of combustible bodies, and decomposition of water by fire. We see smoke ascending from the top of volcanic mountains, and all these phenomena seem to speak in favour of our hypothesis.

We do not think it necessary to enlarge on the various products of these subterranean fires; a great deal has been said and published on this subject; the formation of carbonic acid; its emission in its natural gaseous state; its combination with lime, magnesia, metallic oxides, &c.; its abundance in mineral waters; the flowing of hot water springs, either simple or sulphurous; the rushing out of hydrogen gas, sulphuretted or carburetted: these results are the natural effects of these permanent fires, considered in their quiet state.

Now, it is time to present our readers with the complement of the theory by the spectacle of an eruption. A large volcano may be considered as a whole coalery on fire, several miles and perhaps several hundred miles in extent, five miles under ground, that is to say, under the inferior level of the sea water; coals, bitumen, sulphur, &c. are constantly burning; minerals, sand, and stones are melting, vitrifying, and running at the bottom of the cavern in the shape of lava, of which it forms a permanent lake in fusion, just as melted iron is collected at the bottom of a casting furnace. These things being in this situation, if a sudden vacuum is produced, what will happen? But I may be stopped here, and be asked, how can a sudden vacuum be produced? I see many causes why it may, but the most simple and natural, and consequently the least objectionable one, is, that after a certain time, a number of years that cannot be foreseen, for it is not periodical, a layer of the coal being burnt, reduced to ashes, the mineral to lava, the ground above, no longer supported, crumbles down, with a rumbling noise; a new surface of cold ground is put in contact with the overheated air and vapours, and a sudden condensation is produced; a partial vacuum follows: it is so sudden, that it communicates a tremor to the surrounding ground, which is felt as the first shock of an earthquake. This vacuum produces in its turn a violent aspiration, that brings down the water of the sea itself, and of all the streams that may communicate with that furnace. Then, a reverse effect is produced; water coming in contact with the melted lava and the burning coals, is acted upon in two different ways; a part is vaporised, and

another part decomposed: steam and hydrogen gas are produced in immense abundance; these fluids must open their passage; water is repulsed back into the sea, which rises above its natural level, under the appearance of a huge tide or wave; another part may be thrown off through the gaping ground, and even may issue mixed with the flames of the mountains. In the meanwhile, new shocks are felt, until the weakest point has yielded to the combined powers of the steam and gases, actuated by the heat and a pressure of eight hundred atmospheres. Generally, the former crater, filled in part with loose stones, lava, and ashes of the preceding eruption, is the weakest point; all is thrown up; a column of fire, produced by the burning hydrogen, is raised to the clouds; ashes, the result perhaps of twenty years' combustion, in sufficient quantity to bury villages and cities, and stones of all sizes, loosened, are projected to an immense distance; and, finally, the lava, swept away by the steam, gases, and blowing air, is raised up to the summit of the crater, or runs on one side of the mountain, after having broken open a passage by its enormous mass and weight. When the steam and gases are exhausted, when the lava has flowed out for some time, the eruption decreases, and finally is stopped, because the column of lava in the crater, being of a density superior to the water of the sea, chokes the passage, and the volcano must then resume its quiet operation.

But why should I endeavour to describe what must happen? Let us rather ascertain what has happened, and see whether the facts recorded agree with the theory here presented.

One of the first historians who gives an account of Vesuvius, is, I believe, Pliny the younger. We read in his Epist. xx. lib. vi. these remarkable words:

"Preterea mare in se resorberi et tremore terræ quasi repelli videbamus. Certè processerat littus, multa animalia maris siccis arenis detinebat. Ab altero latere nubes atra et horrenda ignei spiritûs tortis vibratisque discursibus rupta, in longas flammarum figuras dehiscebat; fulgoribus illæ et similes et majores erant.'

The retreat of the sea, and its sudden return by the effect of the elasticity of the fluids, seems to be one of the best ascertained facts.

Eruption of Vesuvius, 1730, by Nicholas

Cyrillus, Phil. Trans. vol. 37.

"March 8th. Vesuvius sends forth a great smoke and stream of fire, with hollow rumbling. 9th. The following night Vesuvius thundered as it were twice. 10th, 11th, 12th. The clouds hide the smoke and fire. 13th. Smoke lessened. 14th. In the evening, after eight o'clock, the fire arose to a vast height.

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"The mighty concussion was felt precisely at the same instant of time, being about half an hour after twelve at noon. Let us reflect on the vast extent of this trembling, one hundred miles in length, and forty in breadth, which amount to four thousand square miles in surface. That this should be put into such an agitation in one moment, is such a prodigy, as we would never believe, did we not know it to be a fact, from our own senses."

The astonishment of the writer of this paragraph would have ceased, if he had conceived, as ourselves, that the vacuum produced in a receiver is almost instantaneous in all its parts, whatever be its extent, or is filled as instantaneously, because steam and gases rush into a vacuum at the rate of thirteen hundred and five feet in a second of time, under the pressure of one atmosphere: what then must it be under eight hundred? The following extracts will come again in support of this assertion.

Account of an Earthquake at Lisbon, November 1st, 1755. Dr. Wolfal. Phil. Trans. vol. 49.

"Soon after the shock (forty minutes past nine), which was near high water, the tide rose forty feet higher, in an instant, than was ever known, and as suddenly subsided."

The same at Cadiz, November 1st, 1755. Benjamin Bewick. Phil. Trans. vol. 49. "Just before ten, the whole town was shaken with a violent earthquake-they saw rolling towards the city a tide of the sea, which passed over the parapet of sixty feet above the ordinary level of the water-the waves came in this manner four or five times, but with less force each time."

At Arzila," it happened about the same time."

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We have expatiated with some details upon the dreadful earthquake which was so fatal to Lisbon in 1755, destroyed whole cities in Europe and in Africa, cost the lives perhaps of one hundred thousand human beings, and was felt upon a surface of more than one million square miles at the same moment. We have taken into consideration particularly its effects upon the water of the sea. The detonation took place under ground, or rather under the sea, in that space which we suppose filled with condensed air, below its inferior level. If we should wish to locate precisely the centre of concussion, judging from its intensity and direction, it seems to be, between the Azores, Madeira, and the continent. The sea was swelled at the same moment from the thirtieth degree of latitude to the fiftieth, that is to say, on the coast of Africa from Morocco up to Tangier, on the coasts of Spain and Portugal, France, Hamburg, the coast of England, and even to the north of Scotland. However, a fact observed by Captain Affleck, of the Advice man-of-war, then at Antigua, and recorded in the Philosophical Transactions, vol. 49, surpasses in wonder even all this:

"On the first of November last, you had a remarkable flux and reflux of the sea at Portsmouth, and other parts of the coast, which was agitated in like manner at the same time, on the coast of America, and all these islands."

If by the words "same time" is meant the same hour, it is in fact three hours later, on account of the difference of longitude, and the distance between the point of explosion across the Atlantic to the Antilles, being about four thousand miles, and will give a velocity of two thousand and forty feet in a second of time. This velocity cannot be that of a wave of water; it must be, it can fluid or gas of a greater density than atmos be, but a velocity of percussion in an elastic pheric air. This fact, and similar ones, will enable us one day to give not only a mathematical demonstration of the existence of such a fluid under the sea, but also to calculate exactly its density.

Let us proceed in our investigation.

Earthquake in Calabria, 1638.

In Goldsmith's History of the Earth, is an account of that great convulsion of nature, translated from the celebrated Father Kircher, from which we extract the two following observations:

The Gulf of Charybdis, which we approached, seemed whirled round in such a manner as to form a vast hollow, verging to a point in the centre."

And afterwards:

"The sea itself seemed to wear a very unusual appearance. Those who have seen a lake in a violent shower of rain, covered all over with bubbles, will conceive some idea of

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"Just at the time of the second shock, the sea retired from the land, all along the coast, leaving its bottom dry for a considerable distance, and in a few minutes it returned again with great fury, and overflowed the shores. In many places the earth gaped prodigiously. Out of all these openings sprung forth a great quantity of water, which drowned the neighbouring places. This last (shake) was stupendous beyond imagination, the fiery eruption of the burning Etna throwing out a prodigious quantity of flames, stones, and ashes, &c."

Earthquakes in the two Calabrias, Messina, &c. 1783. By Sir Wm. Hamilton. Phil. Trans. vol. 73.

"A shock had raised and agitated the sea so violently, that the waves went furiously three miles inland, and swept off in its return two thousand four hundred and seventy three of the inhabitants of Scilla, &c. "At the moment of the earthquake the river disappeared, and returning soon after, overflowed, &c.

"The officer who commanded in the citadel (Messina), assured me that, on the fifth of February, and the three following days, the sea, about a quarter of a mile from that fortress, rose and boiled with a most horrid noise, &c."

Eruption of Mount Vesuvius, June 12th, 1794. Sir William Hamilton, Phil.

Trans. vol.-.

"The classical accounts of the eruption of Vesuvius, which destroyed Herculaneum and Pompei, and many of the existing printed accounts of its great eruption in 1631, might pass for an account of the late eruption, by only changing the date, and omitting the circumstance of the retreat of the sea from the shore, which happened in both those great eruptions, and not in this, &c."

The water of the sea not retiring from the coast in this eruption seems to be an anomaly. Whether the suction or aspiration was performed too slowly, or too far from the shore to be observed, or whether it did not take place at all from the sea, still we are in no apprehension of seeing an eruption without the presence of water; for, in the same relation, a few lines lower, we read:

"The water at the great fountain at Torre del Greco began to decrease some days before the eruption. It was necessary in all the other wells of the town and its neighbourhood to lengthen the ropes daily to reach the water, and some of the wells became quite dry."

"Subterranean noises were heard at Resina for two days before the eruption. Soon after the beginning of it, ashes fell thick at the foot of the mountain-and though there were not at that time any clouds in the air, the ashes were wet, accompanied with large drops of water, which were to the taste very salt.

"After some time, the lava ran in abundance, freely and with great velocity. The frequent falling of the huge stones and scoriæ, which were thrown up to an incredible height, from some of the new mouths, one of which, having been since measured, was ten feet high, and thirty-five in circumference, &c.

"It is impossible that any description can give an idea of this fiery scene, or of the horrid noises that attended this great operation of nature. It was a mixture of the loudest thunder with incessant reports, like those from a numerous heavy artillery, accompanied by a continual hollow murmur, like that of the roaring of the ocean during a violent storm; and, added to these, was another blowing noise, which brought to my mind that noise which is produced by the action of enormous bellows at the furnace of the Carron iron foundry in Scotland, and which it perfectly resembled, &c."

If this last paragraph had been written with the direct intention of supporting our theory, could Sir Wm. Hamilton have made use of other expressions?

We will here recapitulate in a few words the whole of the hypothesis. We have en

deavoured to establish-that the surface of

the earth, as deep as four miles and seveneighths, is the domain of water; that it cannot penetrate deeper, as it there meets with a fluid denser than itself; that either in the open sea, or between the crevices of the rocks and ground at that depth, is its inferior level; that at the surface of the earth, fresh water ascends higher than the superior level of the sea, in proportion to its relative levity, and the depth at which they come in contact. Below four miles and seveneighths is condensed air which supports the combustion of inflammable bodies, and keeps in activity those subterranean fires, the immediate cause of earthquakes and volcanos; that it ceases to be problematical how these fires under ground are not smothered for want of oxygen, and how those under the sea are not extinguished by its water; that we now may account for volcanic islands suddenly rising or disappearing; that it also explains why earthquakes, without any outward explosion, extend to a greater distance,

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