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truth between us, I will send you my present that happened in cold weather, in the Downs, thoughts, with some observations on your described by Mr. Gordon in the Transactions, reasons on the accounts in the Transactions, was, for that reason, thought extraordinary; and on other relations I have met with. but he remarks withal, that the weather, Perhaps, while I am writing, some new light though cold when the spout appeared, was may strike me, for I shall now be obliged to soon after much colder: as we find it, comconsider the subject with a little more atten- monly, less warm after a whirlwind. tion.

I agree with you, that, by means of a vacuum in a whirlwind, water cannot be supposed to rise in large masses to the region of the clouds; for the pressure of the surrounding atmosphere could not force it up in a continued body, or column, to a much greater height, than thirty feet. But if their really is a vacuum in the centre, or near the axis of whirlwinds, then, I think, water may rise in such vacuum to that height, or to a less height, as the vacuum may be less perfect.

You agree, that the wind blows every way towards a whirlwind, from a large space round. An intelligent whale-man of Nantucket, informed me that three of their vessels, which were out in search of whales, happening to be becalmed, lay in sight of each other, at about a league distance, if I remember right, nearly forming a triangle: after some time, a water-spout appeared near the middle of the triangle, when a brisk breeze of wind sprung up, and every vessel made sail; and then it appeared to them all, by the I had not read Stuart's account, in the setting of the sails, and the course each vessel Transactions, for many years, before the re- stood, that the spout was to the leeward of ceipt of your letter, and had quite forgot it; every one of them; and they all declared it but now, on viewing his draughts, and consi- to have been so, when they happened afterdering his descriptions, I think they seem to wards in company, and came to confer about favour my hypothesis; for he describes and it. So that in this particular likewise, whirldraws columns of water, of various heights, winds and water-spouts agree. terminating abruptly at the top, exactly as water would do, when forced up by the pressure of the atmosphere into an exhausted tube. I must, however, no longer call it my hypothesis, since I find Stuart had the same thought, though somewhat obscurely expressed, where he says, "he imagines this phenomenon may be solved by suction (improperly so called) or rather pulsion, as in the application of a cupping glass to the flesh, the air being first voided by the kindled flax." In my paper, I supposed a whirlwind and a spout to be the same thing, and to proceed from the same cause; the only difference between them being, that the one passes over land, the other over water. I find, also, in the Transactions, that M. de la Pryme was of the same opinion; for he there describes two spouts, as he calls them, which were seen at different times, at Hatfield, in Yorkshire, whose appearances in the air were the same with those of the spouts at sea, and effects the same with those of real whirlwinds.

Whirlwinds have generally a progressive, as well as a circular motion; so had what is called the spout, at Topsham, as described in the Philosophical Transactions, which also appears, by its effects described, to have been a real whirlwind. Water-spouts have, also, a progressive motion; this is sometimes greater, and sometimes less; in some violent, in others barely perceivable. The whirlwind at Warrington continued long in AcrementClose.

Whirlwinds generally arise after calms and great heats: the same is observed of water-spouts, which are, therefore, most frequent in the warm latitudes. The spout

But, if that which appears a water-spout at sea, does sometimes, in its progressive motion, meet with and pass over land, and there produce all the phenomena and effects of a whirlwind, it should thence seem still more evident, that a whirlwind and a spout are the same. I send you, herewith, a letter from an ingenious physician of my acquaintance, which gives one instance of this, that fell within his observation.

A fluid, moving from all points horizontally, towards a centre, must, at that centre, either ascend or descend. Water being in a tub, if a hole be opened in the middle of the bottom, will flow from all sides to the centre, and there descend in a whirl. But, air flowing on and near the surface of land or water, from all sides, towards a centre, must at that centre ascend; the land or water hindering its descent.

If these concentring currents of air be in the upper region, they may, indeed, descend in the spout or whirlwind; but then, when the united current reached the earth or water, it would spread, and, probably, blow every way from the centre. There may be whirlwinds of both kinds, but from the commonly observed effects, I suspect the rising one to be the most common: when the upper air descends, it is, perhaps, in a greater body, extending wider, as in our thunder-gusts, and without much whirling; and, when air descends in a spout, or whirlwind, I should rather expect it would press the roof of a horse inwards, or force in the tiles, shingles, or thatch, force a boat down into the water, or a piece of timber into the earth, than that it would lift them up, and carry them away.

per.

It has so happened, that I have not met with I would only first beg to be allowed two or any accounts of spouts, that certainly descend- three positions, mentioned in my former paed; I suspect they are not frequent. Please to communicate those you mention. The apparent dropping of a pipe from the clouds towards the earth or sea, I will endeavour to explain hereafter.

The augmentation of the cloud, which, as am informed, is generally, if not always the case, during a spout, seems to show an ascent, rather than a descent of the matter of which such cloud is composed; for a descending spout, one would expect, should diminish a cloud. I own, however, that cold air descending, may, by condensing the vapours in a lower region, form and increase clouds; which, I think, is generally the case in our common thundergusts, and, therefore, do not lay great stress on this argument.

Whirlwinds and spouts, are not always, though most commonly, in the day time. The terrible whirlwind, which damaged a great part of Rome, June 11, 1749, happened in the night of that day. The same was supposed to have been first a spout, for it is said to be beyond doubt, that it gathered in the neighbouring sea, as it could be tracked from Ostía to Rome. I find this is in Père Boschovich's account of it, as abridged in the Monthly Review for December, 1750.

1. That the lower region of air is often more heated, and so more rarefied, than the upper; consequently, specifically lighter. The coldness of the upper region is manifested by the I hail which sometimes falls from it in a hot day. 2. That heated air may be very moist, and yet the moisture so equally diffused and rarefied, as not to be visible, till colder air mixes with it, when it condenses, and becomes visible. Thus our breath, invisible in summer, becomes visible in winter.

Now let us suppose a tract of land, or sea, of perhaps sixty miles square, unscreened by clouds, and unfanned by winds, during great part of a summer's day, or, it may be, for several days successively; till it is violently heated, together with the lower region of air in contact with it, so that the said lower air becomes specifically lighter than the superincumbent higher region of the atmosphere, in which the clouds commonly float: let us suppose, also, that the air surrounding this tract has not been so much heated during those days, and therefore remains heavier. The consequence of this should be, as I conceive, that the heated lighter air, being pressed on all sides, must ascend, and the heavier descend; and, as this In that account, the whirlwind is said to rising cannot be in all parts, or the whole area have appeared as a very black, long, and lofty of the tract at once, for that would leave too cloud, discoverable, notwithstanding the dark- extensive a vacuum, the rising will begin ness of the night, by its continually lightning precisely in that column that happens to be or emitting flashes on all sides, pushing along the lightest, or most rarefied; and the warm with a surprising swiftness, and within three air will flow horizontally from all points to or four feet of the ground. Its general effects this column, where the several currents meeton houses, were stripping off the roofs, blow-ing, and joining to rise, a whirl is naturally ing away chimneys, breaking doors and windows, forcing up the floors, and unpaving the rooms (some of these effects seem to agree well with a supposed vacuum in the centre of the whirlwind) and the very rafters of the And, as the several currents arrive at this houses were broken and dispersed, and even central rising column, with a considerable dehurled against houses at a considerable dis-gree of horizontal motion, they cannot sudtance, &c.

formed, in the same manner as a whirl is formed in the tub of water, by the descending fluid flowing from all sides of the tub, to the hole in the centre.

denly change it to a vertical motion; thereIt seems, by an expression of Père Boscho- fore as they gradually, in approaching the vich's, as if the wind blew from all sides to- whirl, decline from right curved or circular wards the whirlwind; for, having carefully lines, so, having joined the whirl, they asobserved its effects, he concludes of all whirl-cend by a spiral motion, in the same manner winds, "that their motion is circular, and their action attractive."

He observes, on a number of histories of whirlwinds, &c. "that a common effect of them is, to carry up into the air, tiles, stones, and animals themselves, which happen to be in their course, and all kinds of bodies unexceptionably, throwing them to a considerable distance, with great impetuosity."

Such effects seem to show a rising current of air.

I will endeavour to explain my conceptions of this matter by figures, representing a plan and an elevation of a spout or whirlwind.

as the water descends spirally through the hole in the tub before-mentioned.

Lastly, as the lower air, and nearest the surface, is most rarefied by the heat of the sun, that air is most acted on by the pressure of the surrounding cold and heavy air, which is to take its place; consequently, its motion towards the whirl is swiftest, and so the force of the lower part of the whirl, or trump, strongest, and the centrifugal force of its particles greatest; and hence the vacuum round the axis of the whirl should be greatest near the earth or sea, and be gradually diminished as it approaches the region of the clouds, till

it ends in a point, as at P, Fig. II. in the plate, | low, broad cone, whose top gradually rises forming a long and sharp cone.

In Fig. I. which is a plan or ground-plat of a whirlwind, the circle V. represents the central vacuum.

Between a aa a and b b b b I suppose a body of air, condensed strongly by the pressure of the currents moving towards it, from all sides without, and by its centrifugal force from within, taoving round with prodigious swiftness, (having, as it were, the entire momenta of all the currents

united in itself) and with a power equal to its swiftness and density.

It is this whirling body of air between a a a a and b b b b that rises spirally; by its force it tears buildings to pieces, twists up great trees by the roots, &c. and, by its spiral motion, raises the fragments so high, till the pressure of the surrounding and approaching currents diminishing, can no longer confine them to the circle, or their own centrifugal force increasing, grows too strong for such pressure, when they fly off in tangent lines, as stones out of a sling, and fall on all sides, and at great distances.

If it happens at sea, the water under and between a aa a and b b b b will be violently agitated and driven about, and parts of it raised with the spiral current, and thrown about so as to form a bush-like appearance. This circle is of various diameters, sometimes very lage. If the vacuum passes over water, the water may rise in it in a body, or column, to near the height of thirty-two feet. If it passes over houses, it may burst their windows or walls outwards, pluck off the roofs, and pluck up the floors, by the sudden rarefaction of the air contained within such buildings; the outward pressure of the atmosphere being suddenly taken off; so the stopped bottle of air bursts under the exhausted receiver of the air pump.

Fig. II. is to represent the elevation of a water-spout, wherein I suppose PPP to be the cone, at first a vacuum, till W W, the rising column of water, has filled so much of it. SSSS, the spiral whirl of air, surrounding the vacuum, and continued higher in a close column after the vacuum ends in the point P, till it reaches the cool region of the air. B B, the bush described by Stuart, surrounding the foot of the column of water.

Now, I suppose this whirl of air will, at first be as invisible as the air itself, though reaching, in reality, from the water, to the region of cool air, in which our low summer thunder-clouds commonly float: but presently it will become visible at its extremities. At its lower end, by the agitation of the water, under the whirling part of the circle, between P and S forming Stuart's bush, and by the swelling and rising of the water, in the beginning vacuum, which is, at first, a small, VOL. II.... 2 U

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and sharpens, as the force of the whirl increases. At its upper end it becomes visible, by the warm air brought up to the cooler region, where its moisture begins to be condensed into thick vapour, by the cold, and is seen first at A, the highest part, which being now cooled, condenses what rises next at B, which condenses that at C, and that condenses what is rising at D, the cold operating by the contact of the vapours faster in a right line downwards than the vapours can climb in a spiral line upwards; they climb, however, and as by continual addition they grow denser, and, consequently, their centrifugal force greater, and being risen above the concentrating currents that compose the whirl, fly off, spread, and form a cloud.

It seems easy to conceive, how, by this successive condensation from above, the spout appears to drop or descend from the cloud, though the materials of which it is composed are all the while ascending.

The condensation of the moisture, contained in so great a quantity of warm air as may be supposed to rise in a short time in this prodigiously rapid whirl, is perhaps, sufficient to form a great extent of cloud, though the spout should be over land, as those at Hatfield; and if the land happens not to be very dusty, perhaps the lower part of the spout will scarce become visible at all; though the upper, or what is commonly called the descending part be very distinctly seen.

The same may happen at sea, in case the whirl is not violent enough to make a high vacuum, and raise the column, &c. In such case, the upper part A, B, C, D only will be visible, and the bush, perhaps, below.

But if the whirl be strong, and there be much dust on the land, and the column W W be raised from the water, then the lower part becomes visible, and sometimes even united to the upper part. For the dust may be carried up in the spiral whirl, till it reach the region where the vapour is condensed, and rise with that even to the clouds: and the friction of the whirling air, on the sides of the column W W, may detach great quantities of its water, break it into drops, and carry them up in the spiral whirl mixed with the air; the heavier drops may, indeed, fly off, and fall, in a shower, round the spout; but much of it will be broken into vapour, yet visible; and thus, in both cases, by dust at land, and by water at sea, the whole tube may be darkened and rendered visible.

As the whirl weakens, the tube may (in appearance) separate in the middle; the column of water subsiding, and the superior condensed part drawing up to the cloud. Yet still the tube, or whirl of air, may remain entire, the middle only becoming invisible, as not containing visible matter.

Dr. Stuart says, "It was observable of all the spouts he saw, but more perceptible of the great one; that, towards the end, it began to appear like a hollow canal, only black in the borders, but white in the middle; and though at first it was altogether black and opaque, yet, now, one could very distinctly perceive the sea water to fly up along the middle of this canal, as smoke up a chimney."

And Dr. Mather, describing a whirlwind, says, "a thick dark small cloud arose, with a pillar of light in it, of about eight or ten feet diameter, and passed along the ground in a tract not wider than a street, horribly tearing up trees by the roots, blowing them up in the air like feathers, and throwing up stones of great weight to a considerable height in the air, &c."

These accounts, the one of water-spouts, the other of a whirlwind, seem, in this particular, to agree; what one gentleman describes as a tube, black in the borders, and white in the middle, the other calls a black cloud, with a pillar of light in it; the latter expression has only a little more of the marellous, but the thing is the same; and it seems not very difficult to understand. When Dr. Stuart's spouts were full charged, that is when the whirling pipe of air was filled between a a a a and b b b b, Fig. I. with quantities of drops, and vapour torn off from the column W W Fig. II, the whole was rendered

Vac.

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so dark, as that it could not be seen through, nor the spiral ascending motion discovered; but when the quantity ascending lessened, the pipe became more transparent, and the ascending motion visible. For by inspection of the figure given in this page, representing a section of our spout, with the vacuum in the middle, it is plain that if we look at such a hollow pipe in the direction of the arrows, and suppose opaque particles to be equally mixed in the space between the two circular lines, both the part between the arrows a and b, and that between the arrows c and d, will appear much darker than that between b and c, as there must be many more of those opaque particles in the line of vision across the sides, than across the middle. It is thus that a hair in a microscope evidently appears to be a pipe,

the sides showing darker than the middle. Dr. Mather's whirl was probably filled with dust, the sides were very dark, but the vacuum within rendering the middle more transparent, he calls it a pillar of light.

It was in this more transparent part, between b and c, that Stuart could see the spiral motion of the vapours, whose lines on the nearest and farthest side of the transparent part crossing each other, represented smoke ascending in a chimney; for the quantity being still too great in the line of sight through the sides of the tube, the motion could not be discovered there, and so they represented the solid sides of the chimney.

When the vapours reach in the pipe from the clouds near to the earth, it is no wonder now to those who understand electricity, that flashes of lightning should descend by the spout, as in that of Rome.

But you object, if water may be thus carried into the clouds, why have we not salt rains? The objection is strong and reasonable, and I know not whether I can answer it to your satisfaction. I never heard but of one salt rain, and that was where a spout passed pretty near a ship, so I suppose it to be only the drops thrown off from the spout, by the centrifugal force (as the birds were at Hatfield) when they had been carried so high as to be above, or to be too strongly centrifugal, for the pressure of the concurring winds surrounding it: and, indeed, I believe there can be no other kind of salt rain; for it has pleased the goodness of God so to order it, that the particles of air will not attract the particles of salt, though they strongly attract water.

Hence, though all metals, even gold, may be united with air, and rendered volatile, salt remains fixt in the fire, and no heat can force it up to any considerable height, or oblige the air to hold it. Hence, when salt rises, as it will a little way, into air with water, there is instantly a separation made; the particles of water adhere to the air, and the particles of solt fall down again, as if repelled and forced off from the water by some power in the air; or, as some metals, dissolved in a proper menstruum, will quit the solvent when other matter approaches, and adhere to that, so the water quits the salt, and embraces the air; but air will not embrace the salt, and quit the water, otherwise our rains would indeed be salt, and every tree and plant on the face of the earth be destroyed, with all the animals that depend on them for subsistence-He who hath proportioned and given proper qualities to all things, was not unmindful of this. Let us adore Him with praise and thanksgiving.

By some accounts of seamen, it seems the column of water W W, sometimes falls suddenly; and if it be, as some say, fifteen or twenty yards diameter, it must fall with great

force, and they may well fear for their ships. | By one account, in the Transactions, of a spout that fell at Colne, in Lancashire, one would think the column is sometimes lifted off from the water, and carried over land, and there let fall in a body; but this, I suppose, happens rarely.

Stuart describes his spouts as appearing no bigger than a mast, and sometimes less; but they were seen at a league and a half dis

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I think I formerly read in Dampier, or some other voyager, that a spout, in its progressive motion, went over a ship becalmed, on the coast of Guinea, and first threw her down on one side, carrying away her foremast, then suddenly whipped her up, and threw her down on the other side, carrying away her mizen-mast, and the whole was over in an instant. I suppose the first mischief was done by the fore-side of the whirl, the latter by the hinder-side, their motion being contrary.

I suppose a whirlwind, or spout, may be stationary, when the concurring winds are equal; but if unequal, the whirl acquires a progressive motion, in the direction of the strongest pressure.

When the wind that gives the progressive motion becomes stronger below than above, or above than below, the spout will be bent, and, the cause ceasing, straiten again.

Your queries, towards the end of your paper, appear judicious, and worth considering. At present I am not furnished with facts sufficient to make any pertinent answer to them; and this paper has already a sufficient quantity of conjecture.

Your manner of accommodating the accounts to your hypothesis of descending spouts is, I own, ingenious, and perhaps that hypothesis may be true. I will consider it farther, but, as yet, I am not satisfied with it, though hereafter I may be.

Here you have my method of accounting for the principal phenomena, which I submit to your candid examination.

And as I now seem to have almost written

I had often seen water-spouts at a distance, and heard many strange stories of them, but never knew any thing satisfactory of their nature or cause, until that which I saw at Antigua; which convinced me that a waterspout is a whirlwind, which becomes visible in all its dimensions by the water it carries up with it.

There appeared not far from the mouth of the harbour of St. John's, two or three water-spouts, one of which took its course up the harbour. Its progressive motion was slow and unequal, not in a strait line, but, as it were, by jerks or starts. When just by the wharf, I stood about one hundred yards from it. There appeared in the water a circle of about twenty yards diameter, which, to me, had a dreadful, though pleasing appearance. The water in this cir cle was violently agitated, being whisked about, and carried up into the air with great rapidity and noise, and reflected a lustre, as if the sun shined bright on that spot, which was more conspicuous, as there appeared a dark circle around it. When it made the shore, it carried up with the same violence shingles, staves,* large picces of the roofs of houses, &c. and one small wooden house it lifted entire from the foundation on which it stood, and carried it to the distance of fourteen feet, where it settled without breaking or oversetting; and, what is remarkable, though the whirlwind moved from west to cast, the house moved from east to west.Two or three negroes and a white woman, were killed by the fall of timber, which it carried up into the air and dropped again. After passing through the town, I believe it was soon dissipated; for, except tearing a large limb from a tree, and part of the cover of a sugar work near the town, I do not remember any further damage done by it. I conclude, wishing you success in your inquiry.

W. MERCER.

Dr. Perkins to Dr. Franklin.

a book, instead of a letter, you will think it Shooting Stars.-Read at the Royal Society,

high time I should conclude; which I beg leave to do, with assuring you that I am, &c. B. FRANKLIN.

Dr. Mercer to Dr. Franklin. Description of a Water-spout at Antigua.Read at the Royal Society, June 24, 1756.

NEW-BRUNSWICK, November 11, 1752.

I AM favoured with your letter of the 2d instant, and shall, with pleasure, comply with your request, in describing (as well as my memory serves me) the water-spout I saw at Antigua; and shall think this, or any other service I can do, well repaid, if it contributes to your satisfaction in so curious a disquisition.

July 8, 1756.

BOSTON, May 14, 1753.

I RECEIVED your letter of April last, and thank you for it. Several things in it make make me at a loss which side the truth lies on, and determine me to wait for farther evidence.

As to shooting-stars, as they are called, I know very little, and hardly know what to say. I imagine them to be passes of electric fire from place to place in the atmosphere, perhaps occasioned by accidental pressures of a non-electric circumambient fluid, and so by

might be lying in quantities on the wharf, for sale, as brought from the northern colonies.—B. F.

*I suppose shingles, staves, timber, and other lumber

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