To John Perkins
Dear Sir Philada. Feb. 4. 1753
I ought to have wrote to you long since, in Answer to yours of Oct. 16. concerning the Water Spout: 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 Transactions 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.
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; 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.
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, 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.
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.
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;] 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.
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.