Abbildungen der Seite

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.

You agree, that the wind blows every way I agree with you, that, by means of a va- towards a whirlwind, from a large space cuum in a whirlwind, water cannot be sup- round. An intelligent whale-man of Nanposed to rise in large masses to the region of tucket, informed me that three of their vesthe clouds; for the pressure of the surround-sels, which were out in search of whales, ing atmosphere could not force it up in a con- happening to be becalmed, lay in sight of tinued body, or column, to a much greater each other, at about a league distance, if I height, than thirty feet. But if their really remember right, nearly forming a triangle: is a vacuum in the centre, or near the axis of after some time, a water-spout appeared near whirlwinds, then, I think, water may rise in the middle of the triangle, when a brisk breeze such vacuum to that height, or to a less height, of wind sprung up, and every vessel made as the vacuum may be less perfect.

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 But, if that which appears a water-spout at water would do, when forced up by the pres- sea, does sometimes, in its progressive motion, sure of the atmosphere into an exhausted tube. meet with and pass over land, and there pro

I must, however, no longer call it my hy. duce all the phenomena and effects of a whirlpothesis, since I find Stuart had the same wind, it should thence seem still more evident, thought, though somewhat obscurely express that a whirlwind and a spout are the same. ed, where he says, “he imagines this phe- I send you, herewith, a letter from an ingenomenon may be solved by suction (impro- nious physician of my acquaintance, which perly so called) or rather pulsion, as in the gives one instance of this, that fell within his application of a cupping glass to the flesh, observation. the air being first voided by the kindled flax." A fluid, moving from all points horizontally,

In my paper, I supposed a whirlwind and towards a centre, must, at that centre, either a spout to be the same thing, and to proceed ascend or descend. Water being in a tub, if from the same cause; the only difference be- a hole be opened in the middle of the bottom, tween them being, that the one passes over will flow from all sides to the centre, and there land, the other over water. I find, also, in descend in a whirl. But, air flowing on and the Transactions, that M. de la Pryme was near the surface of land or water, from all of the same opinion; for he there describes sides, towards a centre, must at that centre two spouts, as he calls them, which were seen ascend; the land or water hindering its deat different times, at Hatfield, in Yorkshire, scent. whose appearances in the air were the same If these concentring currents of air be in with those of the spouts at sea, and effects the the upper region, they may, indeed, descend same with those of real whirlwinds.

in the spout or whirlwind; but then, when Whirlwinds have generally a progressive, the united current reached the earth or waas well as a circular motion ; so had what is ter, it would spread, and, probably, blow evecalled the spout, at Topsham, as described in ry way from the centre. There may be the Philosophical Transactions, which also whirlwinds of both kinds, but from the comappears, by its effects described, to have been monly observed effects, I suspect the rising a real whirlwind. Water-spouts have, also, one to be the most common: when the upper a progressive motion ; this is sometimes air descends, it is, perhaps, in a greater body, greater, and sometimes less; in some violent, extending wider, as in our thunder-gusts, and in others barely perceivable. The whirlwind without much whirling; and, when air deat Warrington continued long in Acrement- scends in a spout, or whirlwind, I should raClose.

ther expect it would press the roof of a horise Whirlwinds generally arise after calms inwards, or force in the tiles, shingles, or anil great heats: the same is observed of thatch, force a boat down into the water, or a water-spouts, which are, therefore, most fre- piece of timber into the earth, than that it . quent in the warm latitudes. The spout would lift them up, and carry them away.

It has so happened, that I have not met with I would only first beg to be allowed two of any accounts of spouts, that certainly descend- three positions, mentioned in my former paed; I suspect they are not frequent. Please per. to communicate those yon mention. The ap- 1. That the lower region of air is often more parent dropping of a pipe from the clouds to heated, and so more rarefied, than the upper; wards the earth or sea, I will endeavour to consequently, specifically lighter. The coldexplain hereafter.

ness of the upper region is manifested by the The augmentation of the cloud, which, as I hail which sometimes falls from it in a hot day. am informed, is generally, if not always the 2. That heated air may be very moist, and case, during a spout, seems to show an ascent, yet the moisture so equally diffused and rarerather than a descent of the matter of which fied, as not to be visible, till colder air mixes such cloud is composed; for a descending spout, with it, when it condenses, and becomes visione would expect, should diminish a cloud. Ible. Thus our breath, invisible in summer, own, however, that cold air descending, may, becomes visible in winter. by condensing the vapours in a lower region, Now let us suppose a tract of land, or sea, form and increase clouds; which, I think, is of perhaps sixty miles square, unscreened by generally the case in our common thunder-clouds, and unfanned by winds, during great gusts, and, therefore, do not lay great stress part of a summer's day, or, it may be, for seveon this argument.

ral days successively; till it is violently beated, Whirlwinds and spouts, are not always, together with the lower region of air in conthough most commonly, in the day time. The tact with it, so that the said lower air becomes terrible whirlwind, which damaged a great specifically lighter than the superincumbent part of Rome, June 11, 1749, happened in the higher region of the atmosphere, in which the night of that day. The same was supposed clouds commonly float: let us suppose, alao, to have been first a spout, for it is said to be that the air surrounding this tract has not been beyond doubt, that it gathered in the neigh- so much heated during those days, and therebouring sea, as it could be tracked from Ostia fore remains heavier. The consequence of to Rome. I find this is in Père Boschovich's this should be, as I conceive, that the heated account of it, as abridged in the Monthly Re- lighter air, being pressed on all sides, must view for December, 1750.

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 meet. on houses, were stripping off the roofs, blow-ing, and joining to rise, a whirl is naturally ing away chimneys, breaking doors and win-formed, in the same manner as a whirl is dows, forcing up the floors, and unpaving the formed in the tub of water, by the descending rooms (some of these effects seem to agree fluid flowing from all sides of the tub, to the well with a supposed vacuum in the centre hole 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.

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 as the water descends spirally through the hole action attractive."

in the tub before-mentioned. He observes, on a number of histories of Lastly, as the lower air, and nearest the whirlwinds, &c. “that a common effect of surface, is most rarefied by the heat of the them is, to carry up into the air, tiles, stones, sun, that air is most acted on by the pressure and animals themselves, which happen to be of the surrounding cold and heavy air, which in their course, and all kinds of bodies unex- is to take its place; consequently, its motion ceptionably, throwing them to a considerable towards the whirl is swiftest, and so the force distance, with great impetuosity.”

of the lower part of the whirl, or trump, Such effects seem to show a rising current strongest, and the centrifugal force of its parof air.

ticles greatest; and hence the vacuum round I will endeavour to explain my conceptions the axis of the whirl should be greatest near of this matter by figures, representing a plan the earth or sea, and be gradually diminished and an elevation of a spout or whirlwind 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.

and sharpens, as the force of the whirl inIn Fig. I. which is a plan or ground-plat of creases. . At its upper end it becomes visible, a whirlwind, the circle V. represents the cen- by the warm air brought up to the cooler retral vacuum.

gion, where its moisture begins to be conBetween a aa a and bbbb I suppose a densed into thick vapour, by the cold, and is body of air, condensed strongly by the pres- seen first at A, the highest part, wbich being sure of the corrents moving towards it, from now cooled, condenses what rises next at B, all sides without, and by its centrifugal force which condenses that at C, and that confrom within, joving round with prodigious denses whai is rising at D, the cold operating swiftness, (having, as it were, the entire mo- by the contact of the vapours faster in a right menta of all the currents - .-

line downwards than the vapours can climb united in itself) and with a power equal to in a spiral line upwards; they climb, however, its swiftness and density.

and as by continua) addition they grow denser, It is this whirling body of air between and, consequently, their centrifugal force a aa a and b b b b that rises spirally; by its greater, and being risen above the concenforce it tears buildings to pieces, twists up trating currents that compose the whirl, fly great trees by the roots, &c. and, by its spiral off, spread, and form a cloud. motion, raises the fragments so high, till the It seems easy to conceive, how, by this sucpressure of the surrounding and approaching cessive condensation from above, the spout apcurrents diminishing, can no longer confine pears to drop or descend from the cloud, them to the circle, or their own centrifugal though the materials of which it is composed force increasing, grows tvo strong for such are all the while ascending. pressure, when they fly off in tangent lines, The condensation of the moisture, containas stones out of a sling, and fall on all sides, ed in so great a quantity of warm air as may and at great distances.

be supposed to rise in a short time in this proIf it happens at sea, the water under and digiously rapid whirl, is perhaps, sufficient to between a a a a and b b b b will be violently form a great extent of cloud, though the spout agitated and driven about, and parts of it should be over land, as those at Hatfield; and raised with the spiral current, and thrown if the land happens not to be very dusty, perabout so as to form a bush-like appearance. | haps the lower part of the spout will scarce

This circle is of various diameters, some- become visible at all; though the upper, or :imes very lage. If the vacuum passes over what is commonly called the descending part water, the water may rise in it in a body, or be very distinctly seen. column, to near the height of thirty-two feet. The same may happen at sea, in case the If it passes over houses, it may burst their whirl is not violent enough to make a high windows or walls outwards, pluck off the vacuum, and raise the column, &c. In such roofs, and pluck up the floors, by the sudden case, the upper part A, B, C, D only will be rarefaction of the air contained within such visible, and the bush, perhaps, below. buildings; the outward pressure of the at- ! But if the whirl be strong, and there be mosphere being suddenly taken off; so the much dust on the land, and the column WW stopped bottle of air bursts under the exhausted be raised from the water, then the lower part receiver of the air pump.

| becomes visible, and sometimes even united Fig. II. is to represent the elevation of a to the upper part. For the dust may be carwater-spout, wherein I suppose P P P to be ried up in the spiral whirl, till it reach the rethe cone, at first a vacuum, till W W, the gion where the vapour is condensed, and rise rising column of water, has filled so much of with that even to the clouds: and the friction it. SSSS, the spiral whirl of air, surround of the whirling air, on the sides of the column ing the vacuum, and continued higher in a W W, may detach great quantities of its close column after the vacuum ends in the water, break it into drops, and carry them up point P, till it reaches the cool region of the in the spiral whirl mixed with the air ; the air. B B, the bush described by Stuart, sur-heavier drops may, indeed, ily off, and fall, in rounding the foot of the column of water. a shower, round the spout; but much of it

Now, I suppose this whirl of air will, at will be broken into vapour, yet visible; and first be as invisible as the air itself, though thus, in both cases, by dust at land, and by reaching, in reality, from the water, to the water at sea, the whole tube may be darkened region of cool air, in which our low summer and rendered visible. " thunder-clouds commonly float: but presently As the whirl weakens, the tube may (in it will become visible at its extremities. At appearance) separate in the middle; the coits lower end, by the agitation of the water,lumn of water subsiding, and the superior under the whirling part of the circle, between condensed part drawing up to the cloud. Yet P and S forming Stuart's bush, and by the still the tube, or whirl of air, may remain enswelling and rising of the water, in the be- tire, the middle only becoming invisible, as ginning vacuum, which is, at first, a small, not containing visible matter. VOL. II. ... 20


Dr. Stuart says, “ It was observable of all the sides showing darker than the middle. Dr. the spouts he saw, but more perceptible of the Mather's 'whirl was probably filled with dust, great one; that, towards the end, it began to the sides were very dark, but the vacuum appear like a hollow canal, only black in the within rendering the middle more transpaborders, but white in the middle; and though rent, he calls it a pillar of light. at first it was altogether black and opaque, It was in this more transparent part, beyet, now, one could very distinctly perceive tween b and c, that Stuart could see the spithe sea water to fly up along the middle of ral motion of the vapours, whose lines on the this canal, as smoke up a chimney."

nearest and farthest side of the transparent And Dr. Mather, describing a whirlwind, part crossing each other, represented smoke says, " a thick dark small cloud arose, with a ascending in a chimney; for the quantity bepillar of light in it, of about eight or ten feet ing still too great in the line of sight through diameter, and passed along the ground in a the sides of the tube, the motion could not be tract not wider than a street, horribly tearing discovered there, and so they represented the up trees by the roots, blowing them up in the solid sides of the chimney. air like feathers, and throwing up stones of When the vapours reach in the pipe from the great weight to a considerable height in the clouds near to the earth, it is no wonder now air, &c."

to those who understand electricity, that flashThese accounts, the one of water-spouts, es of lightning should descend by the spout," the other of a whirlwind, seem, in this par- as in that of Rome. ticular, to agree; what one gentleman de- But you object, if water may be thus carried scribes as a tube, black in the borders, and into the clouds, why have we not salt rains ? white in the middle, the other calls á black The objection is strong and reasonable, and I cloud, with a pillar of light in it; the latter know not whether I can answer it to your saexpression has only a little more of the mar- tisfaction. I never heard but of one salt rain, mllous, but the thing is the same; and it and that was where a spout passed pretty near seems not very difficult to understand. When a ship, so I suppose it to be only the drops Dr. Stuart's sponts were full charged, that is thrown off from the spout, by the centrifugal when the whirling pipe of air was filled be- force (as the birds were at Hatfield) when tween a a a a and 666b, Fig. I. with quan- they had been carried so high as to be above, tities of drops, and vapour torn off from the co- or to be too strongly centrifugal, for the pres. lumn W W Fig. II, the whole was rendered sure 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, thongh 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 I will a little way, in to air with water, there is instantly a separation made; the particles of water adhere to the air, and the particles of

s'ilt fall down again, as if repelled and forced so dark, as that it could not be seen through, off from the water by some power in the air; nor the spiral ascending motion discovered ; or, as some metals, dissolved in a proper menbut when the quantity ascending lessened, the struum, will quit the solvent when other matpipe became more transparent, and the ascena. ter approaches, and adhere to that, so the waing motion visible. For by inspection of the ter quits the salt, and embraces the air; but figure given in this page, representing a sec- air will not embrace the salt, and quit the tion of our spout, with the vacuum in the mid- water, otherwise our rains would indeed be dle, it is plain that if we look at such a hollow salt, and every tree and plant on the face of pipe in the direction of the arrows, and sup- the earth be destroyed, with all the animals pose opaque particles to be equally mixed in that depend on them for subsistence- He the space between the two circular lines, who hath proportioned and given proper qua. both the part between the arrows a and b, and lities to all things, was not unmindful of this. that between the arrows c and d, will appear Let us adore Him with praise and thanksgivmuch darker than that between b and c, as ing.

" C, asing. there must be many more of those opaque par By some accounts of seamen, it seems the ticles in the line of vision across the sides, column of water W W , sometimes falls sudthan across the middle. It is thus that a hair denly; and if it be, as some say, fifteen or in a microscope evidently appears to be a pipe, twenty yards diameter, it must fall with great

[ocr errors]


force, and they may well fear for their ships. I had often seen water-spouts at a distance, By one account, in the Transactions, of a and heard many strange stories of them, but spout that fell at Colne, in Lancashire, one never knew any thing satisfactory of their nawould think the column is sometimes lifted ture or cause, until that which I saw at Anoff from the water, and carried over land, and tigua; which convinced me that a waterthere let fall in a body; but this, I suppose, spout is a whirlwind, which becomes visible happens rarely.

in all its dimensions by the water it carries up Stuart describes his spouts as appearing no with it. bigger than a mast, and sometimes less; but There appeared not far from the mouth of the they were seen at a league and a half dis-harbour of St. John's, two or three water-spouts, tance.

one of which took its course up the harbour. Its I think I formerly read in Dampier, or some progressive motion was slow and unequal, not other voyager, that a spout, in its progressive in a strait line, but, as it were, by jerks or motion, went over a ship becalmed, on the starts. When just by the wharf, I stood about coast of Guinea, and first threw her down on one hundred yards from it. There appeared one side, carrying away her foremast, then in the water a circle of about twenty yards suddenly whipped her up, and threw her diameter, which, to me, had a dreadful, though down on the other side, carrying away her pleasing appearance. The water in this cir mizen-mast, and the whole was over in an in-cle was violently agitated, being whisked stant. I suppose the first mischief was done about, and carried up into the air with great by the fore-side of the whirl, the latter by the rapidity and noise, and reflected a lustre, as hinder-side, their motion being contrary. if the sun shined bright on that spot, which

I suppose a whirlwind, or spout, may be was more conspicuous, as there appeared a stationary, when the concurring winds are dark circle around it. When it made the equal; but if unequal, the whirl acquires a shore, it carried up with the same violence progressive motion, in the direction of the shingles, staves,* large picces of the roofs of strongest pressure.

houses, &c. and one small wooden house it When the wind that gives the progressive lifted entire from the foundation on which it motion becomes stronger below than above, stood, and carried it to the distance of fouror above than below, the spout will be bent, teen feet, where it settled without breaking and, the cause ceasing, straiten again, or oversetting; and, what is remarkable,

Your queries, towards the end of your pa- though the whirlwind 'moved from west to per, appear judicious, and worth considering. cast, the house moved from east to west.At present I am not furnished with facts suff- Txo or three negroes and a white woman, cient to make any pertinent answer to them were killed by the fall of timber, which it carand this paper has already a sufficient quan- ried up into the air and dropped again. After tity of conjecture.

passing through the town, I believe it was Your manner of accommodating the ac- soon dissipated; for, except tearing a large counts to your hypothesis of descending spouts limb frorn a tree, and part of the cover of a is, I own, ingenious, and perhaps that hypo- sugar work near the town, I do not remember thesis may be true. I will consider it farther, any further damage done by it. I conclude, but, as yet, I am not satisfied with it, though wishing you success in your inquiry. . hereafter I may be.

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

Dr. Perkins to Dr. Franklin. And as I now seem to have almost written a book, instead of a letter, you will think it

Shooting Stars.--Read at the Royal Society,

July 8, 1756. high time I should conclude; which I beg/ leave to do, with assuring you that I am, &c. 1

Boston, May 14, 1753. B. FRANKLIN.

I 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 Dr. Mercèr to Dr. Franklin.

on, and determine me to wait for farther evi. Description of a Water-spout at Antigun.--Read dence. at the Royal Society, June 21, 1756.

As to shooting-stars, as they are called, I New-BRUNSWICK, November 11, 1732. know very little, and hardly know what to I Am favoured with your letter of the 2d in-say. I imagine them to be passes of electric stant, and shall, with pleasure, comply with fire from place to place in the atmosphere, your request, in describing (as well as my perhaps occasioned by accidental pressures of memory serves me) the water-spout I saw at a non-electric circumambient fluid, and so by Antigua; and shall think this, or any other service I can do, well repaid, if it contributes

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

might be lying in quantities on the wharf, for sale, as to your satisfaction in so curious a disquisition. I brought from the northern colonies.-B. F.

« ZurückWeiter »