Benjamin Franklin Papers

From Benjamin Franklin to John Perkins, 4 February 1753

To John Perkins

Draft: American Philosophical Society2

Philada. Feb. 4. 1753

Dear Sir

I ought to have wrote to you long since, in Answer to yours of Oct. 16. concerning the Water Spout:3 But Business partly, and partly a Desire of procuring further Information by Inquiry among my Seafaring Acquaintance, induc’d me to postpone Writing from time to time, till I am now almost asham’d 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 Opinions, taken up perhaps too hastily: For such Objections oblige him to restudy the Point, consider every Circumstance 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 engag’d in Business public and private, that those more pleasing pursuits are frequently interrupted, and the Chain of Thought necessary to be closely continu’d in such Disquisitions, 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 Thoughts with some Observations on your Reasons, on the Accounts in the Transactions, and other Relations I have met with. Perhaps while I am writing some new Light may strike me—for I shall now be oblig’d to consider the Subject with a little more Attention. I agree with you, that by means of a Vacuum in a Whirlwind, Water cannot be suppos’d 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 continu’d Body or Column to a much greater Height than thirty feet: But if there really is a Vacuum in the Center or near the Axis of Whirlwinds, then I think Water may rise in such Vacuum to that Height or to less Height as the Vacuum may be less perfect.

I had not read Stuart’s Account in the Transactions4 for many Years before the receipt of your Letter and had quite forgot it; but now, on Viewing his Drafts, 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 Water would do when forc’d 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 tho’ somewhat obscurely express’d, where he says, “he imagines this Phaenomenon may be solv’d by Suction (improperly so call’d) 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 Mr. 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.5

Whirlwinds have generally a progressive as well as a circular Motion; so had what is called the Spout at Topsham; See the Account of it in the Transactions;6 which also appears by its Effects described to have been a real Whirlwind. Water Spouts have likewise a progressive Motion. Tho’ this is sometimes greater and sometimes less, in some violent, in others barely perceivable. The Whirlwind at Warrington continu’d long in Acrement Close.7

Whirlwinds generally arise after Calms and great Heats: The same is observ’d of Water Spouts, which are therefore most frequent in the warm Latitudes. The Spout that happen’d in Cold Weather in the Downs, describ’d by Mr. Gordon, in the Transactions,8 was for that reason thought extraordinary, but he remarks withal, that the Weather tho’ cold when the Spout appeared, was soon after much colder; as we find it commonly less warm after a Whirlwind.

You agree that the Wind blows every way towards a Whirlwind from a large Space round; An intelligent Whaleman 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 also sprang up; and every Vessel made Sail and then it appeared to them all by the Setting of the Sails and the Course each Vessel stood, that the Spout was to Leeward of every one of them, and they all declar’d it to have been so when they happen’d afterwards in Company and came to confer about it. So that in this Particular likewise, Whirlwinds and Waterspouts agree.

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 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.9

A Fluid moving from all Points horizontally towards a Center, must at that Center either ascend or descend. Water being in a Tub, if a Hole be open’d in the Middle of the Bottom, will flow from all Sides to the Center, and there descend in a Whirl. But Air flowing on and near the Surface of Land or Water from all Sides toward a Center, must at that Center 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 reach’d the Earth or Water it would spread and probably blow every way from the Center: There may be Whirlwinds of both kinds, but from the common observ’d Effects, I suspect the Rising one to be the most common; and that when the upper Air descends, tis perhaps in a greater Body, extending wider and without much whirling as in our Thunder Gusts. 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.

It has so happen’d that I have not met with any Accounts of Spouts, that certainly descended. 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 I am inform’d 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 descending cold Air, may by Condensing the Vapours of a lower Region form and increase Clouds, which I think is generally the Case in our common Thunder Gusts, and therefore do not lay great Stress on this Argument.

Whirlwinds and Spouts are not always tho’ most commonly in the Day-time. The terrible Whirlwind which damag’d a great Part of Rome June 11. 1749 happen’d 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 Ostia to Rome. I find this in Pere Boschovich’s Account of it, as abridg’d in the Monthly Review for December 1750.1

In that Account the Whirlwind is said to have appear’d as a very black long and lofty Cloud, (discoverable notwithstanding the Darkness of the Night by its continually lightning or emitting Flashes on all Sides) pushing along with a surprizing Swiftness, and within 3 or 4 feet of the Ground. Its general Effects on Houses, were stripping off the Roofs, blowing 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 Center of the Whirlwind;]2 and the very Rafters of the Houses were broke and dispersed, and even hurled against Houses at a considerable Distance, &c.

It seems by an Expression of Pere Boschovich’s as if the Wind blew from all sides towards this Whirlwind for having carefully observ’d its Effects he concludes of all Whirlwinds “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 unexceptionally, 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.3

I would only first beg to be allowed two or three Positions mentioned in my former Paper.

1st. That the lower Region of Air is often more heated and so more rarified, than the upper; consequently specifically lighter. The Coldness of the upper Region is manifested by the Hail which sometimes falls from it in a hot Day:

2dly. That heated Air may be very moist, and yet the Moisture so equally diffus’d and rarified, 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 60 Miles square unscreen’d by Clouds and unfann’d by Winds during great Part of a Summer’s Day, or it may be for several Days successively till ’tis 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 imagine that the heated lighter Air being press’d on all Sides must ascend, and the heavier descend; and as this Rising cannot be in all Parts or the whole Area of the Tract at once, for that would leave too extensive a Vacuum, the Rising will begin precisely in that Column that happens to be the lightest or most rarified; and the warm Air will flow horizontally from all Points to this Column, where the several Currents meeting and joining to rise, a Whirl is naturally 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 Center.

And as the several Currents arrive at this central rising Column with a considerable Degree of horizontal Motion, they cannot suddenly change it to a vertical Motion, therefore as they gradually in approaching the Whirl decline from right to curve or circular Lines, so having join’d the Whirl they ascend by a spiral Motion; in the same Manner as the Water descends spirally thro’ the Hole in the Tub before-mentioned.

Lastly, as the lower Air and nearest the Surface, is most rarified 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 diminish’d as it approaches the Region of the Clouds, till it ends in a Point, as at A in Fig II. forming a long and sharp Cone.

In Fig I. which is a Plan or Ground Plot of a Whirlwind, the Circle V represents the central Vacuum.

Between aaaa and bbbb I suppose a Body of Air condens’d strongly by the Pressure of the Currents moving towards it from all sides without, and by its Centrifugal Force from within; moving round with prodigious Swiftness, (having as it were the 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 aaaa and bbbb 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 encreasing 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 between aaaa and bbbb will be violently agitated and driven about, and parts of it raised with the spiral Current, and thrown about so as to form a Bushlike Appearance.

This Circle is of various Diameters, sometimes very large.

If the Vacuum passes over Water the Water may rise in it in a Body or Column to near the Height of 32 feet. If it passes over Houses, it may burst their Windows or Walls outwards, pluck off the Roofs and blow up the Floors, by the Sudden Rarefaction of the Air contain’d within such Buildings, the outward Pressure of the Atmosphere being suddenly taken off; So the stop’d 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 WW the rising Column of Water has fill’d so much of it. SSSS the Spiral Whirl of Air surrounding the Vacuum and continu’d higher in a close Column after the Vacuum ends in the Point P. till it reach the cool Region of the Air. B.B. the Bush describ’d 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 tho’ 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 low broad Cone whose Top gradually rises 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 condens’d into thick Vapour by the Cold, and is seen first at A. the highest Parts, which being now cool’d, 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 themselves 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, they flie 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, tho’ the Materials of which it is composed are all the while ascending.

The Condensation of the Moisture contain’d in so great a Quantity of warm Air as may be suppos’d to rise in a short Time in this prodigiously rapid Whirl, is perhaps sufficient to form a great Extent of Cloud, tho’ 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; Tho’ the upper or what is commonly call’d 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 ABCD only will be visible, and the Bush perhaps below.

But if the Whirl be strong, and there be much Dust on the Land, or the Column WW be rais’d 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 condens’d, and rise with that even to the Clouds. And the Friction of the Whirling Air on the Sides of the Column WW may detach great Quantities of its Water, break it into Drops and carry them up in the Spiral Whirl mix’d 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 darkned and render’d visible.

As the Whirl weakens, the Tube may (in Appearance) separate in the Middle; the Column of Water subsiding, and the superior condens’d 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 tho’ 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 Smoak 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 8 or 10 foot 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.”4

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 marvellous, but the Thing is the same. And it seems not very difficult to understand. When Dr. Stuarts Spouts were full charg’d; that is, when the whirling Pipe of Air was filled, between aaaa and bbbb [Fig. I], with Quantities of Drops and Vapour torn off from the Column WW [Fig. II], the whole was render’d so dark as that it could not be seen thro’, nor the spiral ascending Motion discover’d; but when the Quantity ascending lessen’d, the Pipe became more transparent, and the ascending Motion visible. For by Inspection of this Figure in the Margin 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 opacous Particles to be equally mix’d 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 shewing darker than the Middle. Dr. Mather’s Whirl was probably fill’d 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 this transparent Part crossing each other, represented Smoke ascending in a Chimney; for the Quantity being still too great in the Line of Sight thro’ the Sides of the Tube, the Motion could not be discover’d 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 at Rome.

But you object, If Water may be thus carried into the Clouds, why have we no 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; tho’ they strongly attract Water. Hence tho’ all Metals, even Gold, may be united with Air and render’d volatile, Salt remains fix’d 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 Salt fall down again, as if repell’d and forc’d off from the Water by some Power in the Air: Or as some Metals dissolv’d 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 destroy’d, 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 WW sometimes falls suddenly, and if it be as some say 15 or 20 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 Coln 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 at a League and half Distance.

I think I formerly read in Dampier,5 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, whipt 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 foreside 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.

Where 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 furnish’d 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 satisfy’d with it, tho’ hereafter I may be. Here you have my Method of Accounting for the principal Phaenomena, which I submit to your candid Examination. If my Hypothesis is not the Truth itself, it is least as naked: For I have not with some of our learned Moderns disguis’d my Nonsense in Greek, cloth’d it in Algebra, or adorn’d it with Fluxions.6 And as I now seem to have almost written a Book instead of a Letter, you will think it high time I should conclude, which I beg Leave to do with assuring you that I am most sincerely, Dear Sir Your obliged Friend and humble Servant.

[Note numbering follows the Franklin Papers source.]

2Printed as Letter XX in Exper. and Obser., 1769 and 1774. Read in the Royal Society, June 24, 1756.

3See above, p. 358.

4Alexander Stuart, “Part of a Letter … concerning some Spouts he observed in the Mediterranean,” Phil. Trans., XXIII (1702–03), 1077–80.

5Abraham de la Pryme, “Part of a Letter … concerning a Spout … in Yorkshire,” ibid., 1248–9; “Part of a Letter … concerning a Spout … in Hatfield,” ibid., 1331–2.

6Ibid., XIX (1695–97), 28.

7Ibid., XVIII (1694), 192.

8Rev. Patrick Gordon, “Part of a Letter … concerning a Water-spout observed in the Downs,” ibid., XXII (1700–01), 805–6.

9See above, p. 378.

1Monthly Review, IV (1750), 148.

2Brackets in MS; parentheses in printed versions.

3The diagram that must have accompanied this letter is now missing. It was reproduced in Exper. and Obser., 1769, facing p. 226; see below, p. 435.

4Cotton Mather, “An Extract of Several Letters … to Richard Waller,” Phil. Trans., XXIX (1714–16), 70.

5See immediately below.

6This sentence was omitted from the printed versions. In the MS BF had first written after “adorned it with Fluxians”: “You have it in puris naturalibus. I cannot however help laughing at my own Presumption, in attempting to explain them.” But he clearly struck out some of this, and may have meant to cancel all.

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