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freeze as the earth, rather moderate than increase the coldness of our winter winds.

The air over the sea being warmer, and therefore lighter in winter than the air over the frozen land, may be another cause of our general N. W. winds, which blow off to sea at right_angles from our North-American coast. The warm light sea air rising, the heavy cold land air pressing into its place. Heavy fluids descending, frequently form eddies, or whirlpools, as is seen in a funnel, where the water acquires a circular motion, receding every way from a centre, and leaving a vacancy in the middle, greatest above, and lessening downwards, like a speaking trumpet, its big end upwards.

Air descending, or ascending, may form the same kind of eddies, or whirlings, the parts of air acquiring a circular motion, and receding from the middle of the circle by a centrifugal force, and leaving there a vacancy; if descending, greatest above, and lessening downwards; if ascending, greatest below, and lessening upwards; like a speaking trumpet, standing its big end on the ground,

When the air descends with a violence in some places, it may rise with equal violence in others, and form both kinds of whirlwinds. The air in its whirling motion receding every way from the centre or axis of the trumpet leaves there a vacuum, which cannot be filled through the sides, the whirling air, as an arch, preventing; it must then press in at the open ends.

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The greatest pressure inwards must be at the lower end, the greatest weight of the rounding atmosphere being there. The air entering rises within, and carries up dust, leaves, and even heavier bodies that happen in its way, as the eddy, or whirl, passes over land. If it passes over water, the weight of the surrounding atmosphere forces up the water into the vacuity, part of which, by degrees, joins with the whirling air, and adding weight and receiving accelerated motion, recedes still farther from the centre or axis of the trump, as the pressure lessens; and at last, as the trump widens, is broken into small particles, and so united with air as to be supported by it, and become black clouds at the top of the trump.

Thus these eddies may be whirlwinds at land, water-spouts at sea. A body of water so raised, may be suddenly let fall, when the motion, &c. has not strength to support it, or the whirling arch is broken so as to admit the air falling in the sea, it is harmless, unless ships happen under it; but if in the progressive motion of the whirl it has moved from the sea, over the land, and then breaks, sudden, violent, and mischievous torrents are the consequences.

Perkins of Boston to Dr. Franklin.

On Water-Spouts.-Read at the Royal Society, June 3, 1756.

BOSTON, October 16, 1752.

I FIND by a word or two in your last,* that you are willing to be found fault with; which authorizes me to let you know what I am at a loss about in your papers, which is only in the article of the water-spout. I am in doubt whether water in bulk, or even broken into drops, ever ascends into the region of the clouds per vorticem; i. e. whether there be, in reality, what I call a direct water-spout. I make no doubt of direct and inverted whirlwinds; your description of them, and the reason of the thing, are sufficient. I am sensible too, that they are very strong, and often move considerable weights. But I have not met with any historical accounts that seem exact enough to remove my scruples concerning the ascent above said.

Descending spouts (as I take them to be) are many times seen, as I take it, in the calins, between the sea and land trade-winds on the coast of Africa. These contrary winds, or diverging, I can conceive may occasion them, as it were by suction, making a breach in a large cloud. But I imagine they have, at the same time, a tendency to hinder any direct or rising spout, by carrying off the lower part of the atmosphere as fast as it begins to rarefy; and yet spouts are frequent here, which strengthens my opinion, that all of them descend.

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But however this be, I cannot conceive a force producible by the rarefication and condensation of our atmosphere, in the circumstances of our globe, capable of carrying water, in large portions, into the region of the clouds. Supposing it to be raised, it would be too heavy to continue the ascent beyond a considerable height, unless parted into small drops; and even then, by its centrifugal force, from the manner of conveyance, it would be flung out of the circle, and fall scattered, like rain.

But I need not expatiate on these matters to you. I have mentioned my objections, and, as truth is my pursuit, shall be glad to be informed. I have seen few accounts of these whirl or eddy winds, and as little of the spouts; and these, especially, lame and poor things to obtain any certainty by. If you know any thing determinate that has been observed, I shall hope to hear from you; as also of any mistake in my thoughts. I have nothing to object to any other part of your

* A Letter on Inoculation, which is transferred to a subsequent part of this volume, that the papers on meteorological subjects may not be interrupted.

suppositions: and as to that of the tradewinds, I believe nobody can.

P. S. The figures in the Philosophical Transactions show, by several circumstances, that they all descended, though the relators seemed to think they took up water.*

On the place of this spattering, arises the appearance of a bush, into the centre of which the spout comes down. This bush I take to be formed by a spray, made by the force of these drops, which being uncommonly large and descending with unusual force by a stream of wind descending from the cloud Dr. Perkins to Dr. Franklin.-Read at the which wind being repulsed by the surface of with them, increases the height of the spray: Royal Society, June 24, 1756.

BOSTON, October 23, 1752.

the waters rebounds and spreads; by the first rising the spray higher than it otherwise would go; and by the last making the top of the bush appear to bend outwards (i. e.) the cloud of spray is forced off from the trunk of the spout, and falls backward.

with the wind I mentioned, by their descent, which beat back the rising spray in the centre.

In the enclosed, you have all I have to say of that matter. It proved longer than I expected, so that I was forced to add a cover to it. I confess it looks like a dispute; but that is quite contrary to my intentions. The sinThe bush does the same where there is no cerity of friendship and esteem were my appearance of a spout reaching it; and is demotives; nor do I doubt your scrupling the pressed in the middle, where the spout is exgoodness of the intention. However, I must pected. This, I imagine, to be from numerconfess, I cannot tell exactly how far I was ac-ous drops of the spout falling into it, together tuated by hopes of better information, in discovering the whole foundation of my opinion, which, indeed, is but an opinion, as I am very much at a loss about the validity of the reasons. I have not been able to differ from you in sentiment concerning any thing else in your Suppositions. In the present case I lie open to conviction, and shall be the gainer when informed. If I am right, you will know The pillar of water, as they call it, from its that, without my adding any more. Too much likeness, I suppose to be only the end of the said on a merely speculative matter, is but a spout immersed in the bush, a little blackrobbery committed on practical knowledge.ened by the additional cloud, and perhaps, apPerhaps I am too much pleased with these pears to the eye beyond its real bigness, by a dry notions: however, by this you will see refraction in the bush, and which refraction that I think it unreasonable to give you more may be the cause of the appearance of setrouble about them, than your leisure and in-paration, betwixt the part in the bush, and clination may prompt you to.—I am, &c.

Since my last I considered, that, as I had begun with reason of my dissatisfaction about the ascent of water in spouts, you would not be unwilling to hear the whole I have to say, and then you will know what I rely upon.

What occasioned my thinking all spouts descend, is that I found some did certainly do 80. A difficulty appeared concerning the ascent of so heavy a body as water, by any force I was apprized of as probably sufficient. And, above all, a view of Mr. Stuart's portraits of spouts, in the Philosophical Transactions.

Some observations on these last will include the chief part of my difficulties.

Mr. Stuart has given us the figures of a number observed by him in the Mediterranean; all with some particulars which make for my opinion, if well drawn.

The great spattering, which relators mention in the water where the spout descends, and which appears in all his draughts, I conceive to be occasioned by drops descending very thick and large into the place.

This circumstance, of the bush bending outwards at the top, seems not to agree with what I call a direct whirlwind, but consistent with the reversed; for a direct one would sweep the bush inwards; if, in that case, any thing of a bush would appear.

that above it. The part in the bush is cylindrical, as it is above (i. e.) the bigness the same from the top of the bush to the water. Instead of this shape, in case of a whirlwind, it must have been pyramidical.

Another thing remarkable, is, the curve in some of them: this is easy to conceive, in case of descending parcels of drops through various winds, at least till the cloud condenses so fast as to come down, as it were, uno rivo. But it is harder to me to conceive it in the ascent of water, that it should be conveyed along, secure of not leaking or often dropping through the under side, in the prone part: and, should the water be conveyed so swiftly, and with such force, up into the cloud, as to prevent this, it would, by a natural disposition to move on in a present direction, presently straiten the curve, raising the shoulder very swiftly, till lost in the cloud.

Over every one of Stuart's figures, I see a cloud: I suppose his clouds were first, and then the spout; I do not know whether it be so with all spouts, but suppose it is. Now, if whirlwinds carried up the water, I should ex*Two engraved representations of water-spouts, from pect them in fair weather, but not under a the Philosophical Transactions, are given in this edition, the better to illustrate the plate on the same sub-cloud; as is observable of whirlwinds; they ject, by Dr. Franklin. come in fair weather, not under the shade of

I overlooked, in its proper place, Stuart's No. 11, which is curious for its inequalities, and, in particular, the approach to breaking, which, if it would not be too tedious, I would have observed a little upon, in my own way, as, I think, this would argue against the ascent, &c. but I must pass it, not only for the reason mentioned, but want of room besides.

a cloud, nor in the night: since shade cools | and so might be called air-spouts, if they were the air: but, on the contrary, violent winds objects of sight? often descend from the clouds; strong gusts which occupy small spaces: and from the higher regions, extensive hurricanes, &c. Another thing is the appearance of the spout coming from the cloud. This I cannot account for on the notion of a direct spout, but in the real descending one, it is easy. I take it, that the cloud begins first of all to pour out drops at that particular spot, or foramen; and, when that current of drops increases, so as to force down wind and vapour, the spout becomes so far as that goes opaque. I take it, that no clouds drop spouts, but such as make very fast, and happen to condense in a particular spot, which perhaps is coldest, and gives a determination downwards, so as to make a passage through the subjacent atmosphere.

If spouts ascend, it is to carry up the warm rarefied air below, to let down all and any that is colder above; and, if so, they must carry it through the cloud they go into (for that is cold and dense, I imagine) perhaps far into the higher region, making a wonderful appearance at a convenient distance to observe it, by the swift rise of a body of vapour, above the region of the clouds. But as this has never been observed in any age, if it be supposable that is all.

I cannot learn by mariners, that any wind blows towards a spout more than any other way; but it blows towards a whirlwind, for a large distance round.

I suppose there has been no instance of the water of a spout being salt, when coming across any vessel at sea. I suppose too, that there have been no salt rains; these would make the case clear.

I suppose it is from some unhappy effects of these dangerous creatures of nature, that sailors have an universal dread on them, of breaking in their deck, should they come across them.

I imagine spouts, in cold seasons, as Gordon's in the Downs, prove the descent.

Query. Whether there is not always more or less cloud, first, where a spout appears?

Whether they are not, generally, on the borders of trade-winds; and whether this is for, or against me?

Whether there be any credible account of a whirlwind's carrying up all the water in a pool, or small pond: as when shoal, and the banks low, a strong gust might be supposed to blow it all out?

Whether a violent tornado, of a small extent, and other sudden and strong gusts, be not winds from above, descending nearly perpendicular; and, whether many that are called whirlwinds at sea, are any other than these,

As to Mr. Stuart's ocular demonstration of the ascent in his great perpendicular spout, the only one it appears in, I say, as to this, what I have written supposes him mistaken, which, yet, I am far from asserting.

The force of an airy vortex, having less influence on the solid drops of water, than on the interspersed cloudy vapours, makes the last whirl round swifter, though it descend slower: and this might easily deceive, without great care, the most unprejudiced person.

To Dr. Perkins.

Water-spouts and Whirlwinds compared.—Read
at the Royal Society, June 24, 1753.
PHILADELPHIA, Feb. 4, 1753.
I OUGHT to have written to you, long since,
in answer to yours of October 16, concerning
the water-spout; but business partly, and
partly a desire of procuring further informa-
tion by inquiry among my seafaring acquaint-
ance, induced me to postpone writing, from
time to time, till I am now almost ashamed to
resume the subject, not knowing but you may
have forgot what has been said upon it.

Nothing certainly, can be more improving to a searcher into nature, than objections judiciously made to his opinion, taken up, perhaps, too hastily: for such objections oblige him to re-study the point, consider every cir cumstance carefully, compare facts, make experiments, weigh arguments, and be slow in drawing conclusions. And hence a sure advantage results; for he either confirms a truth, before too slightly supported; or discovers an error, and receives instruction from the objector.

In this view I consider the objections and remarks you sent me, and thank you for them sincerely: but, how much soever my inclinations lead me to philosophical inquiries, I am so engaged in business, public and private, that those more pleasing pursuits are frequently interrupted, and the chain of thought necessary to be closely continued in such disquisitions, is so broken and disjointed, that it is with difficulty I satisfy myself in any of them: and I am now not much nearer a conclusion, in this matter of the spout, than when I first read your letter.

Yet, hoping we may, in time, sift out the

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 I 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.

every one of them; and they all declared it to have been so, when they happened afterwards in company, and came to confer about it. So that in this particular likewise, whirlwinds and water-spouts agree.

You agree, that the wind blows every way towards a whirlwind, from a large space round. An intelligent whale-man of Ñantucket, 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; but now, on viewing his draughts, and considering his descriptions, I think they seem to favour my hypothesis; for he describes and draws columns of water, of various heights, 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 proI 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." 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

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 house 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 to wards 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.

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, 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, also, 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 to Rome. I find this is in Père Boschovich's account of it, as abridged in the Monthly Review for December, 1750.

fore 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. 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 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.

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.

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

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