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Air moderately heated will support a great
Thus, supposing the er quantity of water invisibly than cold air ; 0 0 O particles A B C D, and for its particles being by heat repelled to a F
o the other near them greater distance from each other, thereby O
O to be at the distance more easily keep the particles of water that
caused by their mutual are annexed to them from running into cohe- 0 0 0 repellency(confined by sions that would obstruct, refract, or reflect
their common gravity) the light.
0 0 0 O if a would descend to Hence when we breathe in warm air,
E, it must pass between though the same quantity of moisture may be B and c; when it comes between B and c, taken up from the lungs, as when we breathe it will be nearer to them than before, and in cold air
, yet that moisture is not so visible. must either have pushed them nearer to f Water being extremely heated, i. e. to the and G, contrary to their mutual repelleney, degree of boiling, its particles in quitting it so or pass through by a force exceeding its rerepel each other, as to take up vastly more pellency with them. It then approaches D, space than before, and by that repellency sup- and, to move it out of the way, must act on port themselves, expelling the air from the it with a force sufficient to overcome its respace they occupy. That degree of heat be- pellency with the two next lower particles, ing lessened, they again mutually attract, by which it is kept in its present situation. and having no air particles mixed to adhere Every particle of air, therefore, will bear to, by which they might be supported and any load inferior to the force of these repulkept at a distance, they instantly fall, coalesce, sions. and become water again.
Hence the support of fogs, mists, clouds. The water commonly diffused in our at- Very warm air, clear, though supporting a mosphere never receives such a degree of heat very great quantity of moisture, will grow from the sun, or other cause, as water has turbid and cloudy on the mixture of colder when boiling; it is not, therefore, supported air, as foggy turbid air will grow clear by by such heat, but by adhering to air. warming
Water being dissolved in, and adhering to Thus the sun shining on a morning fog, air, that air will not readily take up oil, be- dissipates it; clouds are seen to waste in a cause of the mutual repellency between wa- sun-shiny day. ter and oil.
But cold condenses and renders visible the Hence cold oils evaporate but slowly, the vapour : a tankard or decanter filled with air having generally a quantity of dissolved cold water will condense the moisture of water.
warm clear air on its outside, where it beOil being heated extremely, the air that comes visible as dew, coalesces into drops, approaches its surface will be also heated ex- descends in little streams. tremely ; the water then quitting it, it will The sun heats the air of our atmosphere attract and carry off the oil, which can now most near the surface of the earth; for there, adhere to it. Hence the quick evaporation besides the direct rays, there are many reof oil heated to a great degree.
flections. Moreover, the earth itself being Oil being dissolved in air, the particles to heated, communicates of its heat to the which it adheres will not take up water. neighbouring air.
Hence the suffocating nature of air impreg. The higher regions, having only the direct nated with burnt grease, as from snuffs of rays of the sun passing through them, are candles and the like. A certain quantity of comparatively very cold. Hence the cold moisture should be every moment discharged air on the tops of mountains, and snow on and taken away from the lungs; air that has some of them all the year, even in the torrid been frequently breathed, is already over
Hence hail in summer. loaded, and, for that reason, can take no more, If the atmosphere were, all of it (both so will not answer the end. Greasy air re- above and below) always of the same temper fuses to touch it. In both cases suffocation as to cold or heat, then the upper air would for want of the discharge.
always be rarer than the lower, because the Air will attract and support many other pressure on it is less; consequently lighter, substances.
and therefore would keep its place. A particle of air loaded with adhering wa- But the upper air may be more condensed ter, or any other matter, is heavier than be- by cold, than the lower air by pressure; the fore, and would descend.
lower more expanded by heat, than the upThe atmosphere supposed at rest, a loaded per for want of pressure. In such case the descending particle must act with a force on upper air will become the heavier, the lower the particles it passes between, or meets the lighter. with, sufficient to overcome, in some degree, The lower region of air being heated and their mutual repellency, and push them nearer expanded heavés up, and supports for some time to each other.
the colder heavier air above, and will conti
nue to support it while the equilibrium is kept. fied by the sun, rises. Its place is supplied Thus water is supported in an inverted open by air from northern and southern latitudes, glass, while the equilibrium is maintained by which coming from parts wherein the earth the equal pressure upwards of the air below; and air had less motion, and not suddenly acbut the equilibrium by any means breaking; quiring the quicker motion of țhe equatorial the water descends on the heavier side, and earth, appearsan east wind blowing westward; the air rises into its place.
the earth moving from west to east, and slipThe lifted heavy cold air over a heated ping under the air.* country, becoming by any means unequally Thus, when we ride in a calm, it seems a supported, or unequal in its weight, the hea- wind against us : if we ride with the wind, viest part descends first, and the rest follows and faster, even that will seem a small wind impetuously. Hence gusts after heats, and against us. hurricanes in hot climates. Hence the air of The air rarefied between the tropics, and gusts and hurricanes is cold, though in hot rising, must flow in the higher region north climates and seasons; it coming from above. and south. Before it rose, it had acquired
The cold air descending from above, as it the greatest motion the earth's rotation could penetrates our warm region full of watery par- give it. It retains some degree of this moticles, condenses them, renders them visible, tion, and descending in higher latitudes, forms a cloud thick and dark, overcasting where the earth's motion is less, will appear sometimes, at once, large and extensive; a westerly wind, yet tending towards the sometimes, when seen at a distance, small at equatorial parts, to supply the vacancy occafirst, gradually increasing; the cold edge, or sioned by the air of the lower regions towing surface of the cloud, condensing the vapours thitherwards. next it, which form smaller clouds that join Hence our general cold winds are about it, increase its bulk, it descends with the wind north west, our summer cold gusts the sanie. and its acquired weight, draws nearer the The air in sultry weather, though not earth, grows denser with continual additions cloudy, has a kind of haziness in it, which of water, and discharges heavy showers. makes objects at a distance appear dull and
Small black clouds thus appearing in a clear indistinct. This haziness is occasioned by sky, in hot climates, portend storms, and warn the great quantity of moisture equally diffused seamen to hand their sails.
in that air. When, by the cold wind blowing The earth, turning on its axis in about down among it, it is condensed into clouds, twenty-four hours, the equatorial parts must and fulls in rain, the air becomes purer and move about fitteen miles in each minute; clearer. Hence, after gusts, distant objects in northern and southern latitudes this mo- appear distinct, their figures sharply termition is gradually less to the poles, and there nated. nothing.
Extreme cold winds congeal the surface of If there was a general calm over the face the earth, by carrying off its fire. Warm of the globe, it must be by the air's moving winds afterwards blowing over that frozen in every part as fast as the earth or sea it surface will be chilled by it. Could that
frozen surface be turned under, and warmer He that sails, or rides, has insensibly the turned up from beneath it, those warm winds same degree of motion as the ship or coach would not be chilled so much. with which he is connected. If the ship The surface of the earth is also sometimes strikes the shore, or the coach stops suddenly, much heated by the sun : and such heated surthe motion continuing in the man, he is thrown face not being changed heats the air that forward. If a man were to jump from the moves over it. land into a swift sailing ship, he would be Seas, lakes, and great bodies of water, agithrown backward (or towards the stern) not tated by the winds, continually change surhaving at first the motion of the ship. faces; the cold surface in winter is turned
He that travels by sea or land, towards the under by the rolling of the waves, and a equinoctial, gradually acquires motion ; from warmer turned up; in summer, the warm is it, loses.
turned under, and colder turned up. Hence But if a man were taken up from latitude the more equal temper of sea-water, and the 40 (where suppose the earth's surface to move air over it. Hence, in winter, winds from the twelve miles per minute) and immediately sea seem warm, winds from the land cold. set down at the equinoctial
, without chang- In summer the contrary. ing the motion he had, his heels would be Therefore the lakes north-west of us, as struck up, he would fall westward. If taken they are not so much frozen, nor so apt to up from the equinoctial, and set down in lati
* See a paper on this subject, by the late ingenious tude 40, he would fall eastward.
Mr. Hadley, in the Philosophical Transactions, where. The air under the equator, and between in this hypothesis for explaining the trade-winds first the tropics, being constantly heated and rare
appeared. | In Pennsylvania.
freeze as the earth, rather moderate than in- Perkins of Boston to Dr. Franklin. crease the coldness of our winter winds.
The air over the sea being warmer, and On Water-Spouts.--Read at the Royal Society, therefore lighter in winter than the air over
June 3, 1756. the frozen land, may be another cause of our
Boston, October 16, 1752. general N. W. winds, which blow off to sea at right angles from our North-American I FIND by a word or two in your last,* that coast. The warm light sea air rising, the you are willing to be found fault with; which heavy cold land air pressing into its place.
authorizes me to let you know what I am at a Heavy fluids descending, frequently form loss about in your papers, which is only in the eddies, or whirlpools, as is seen in a funnel, article of the water-spout. I am in doubt where the water acquires a circular motion, whether water in bulk, or even broken into receding every way from a centre, and leav- drops, ever ascends into the region of the ing a vacancy in the middle, greatest above, clouds per vorticem ; i. e. whether there be, and lessening downwards, like a speaking in reality, what I call a direct water-spout. trumpet, its big end upwards.
I make no doubt of direct and inverted whirlAir descending, or ascending, may form the winds; your description of them, and the reasame kind of eddies, or whirlings, the parts of son of the thing, are sufficient. I am sensible air acquiring a circular motion, and receding too, that they are very strong, and often move from the middle of the circle by a centrifu- considerable weights. But I have not met gal force, and leaving there a vacancy; if de- with any historical accounts that seem exact scending, greatest above, and lessening down- enough to remove my scruples concerning the wards; if ascending, greatest below, and les ascent above said. sening upwards; like a speaking trumpet,
Descending spouts (as I take them to be) standing its big end on the ground.
are many times seen, as I take it, in the calins, When the air descends with a violence in between the sea and land trade-winds on the some places, it may rise with equal violence coast of Africa. These contrary winds, or in others, and form both kinds of whirlwinds. diverging, I can conceivę may occasion them,
The air in its whirling motion receding as it were by suction, making a breach in a every way from the centre or axis of the large cloud. But I imagine they have, at trumpet leaves there a vacuum, which can- the same time, a tendency to hinder any dinot be filled through the sides, the whirling rect or rising spout, by carrying off the lower air, as an arch, preventing ; it must then press part of the atmosphere as fast as it begins to in at the open ends.
rarefy; and yet spouts are frequent here, which The greatest pressure inwards must be at strengthens my opinion, that all of them de. the lower end, the greatest weight of the sur
scend. rounding atmosphere being there. The air
But however this be, I cannot conceive a entering rises within, and carries up dust
, force producible by the rarefication and conleaves, and even heavier bodies that happen in densation of our atmosphere, in the circumits way, as the eddy, or whirl, passes over land. stances of our globe, capable of carrying wa
If it passes over water, the weight of the ter, in large portions, into the region of the surrounding atmosphere forces up the water clouds. Supposing it to be raised, it would into the vacuity, part of which, by degrees, be too heavy to continue the ascent beyond joins with the whirling air, and adding weight a considerable height, unless parted into and receiving accelerated motion, recedes small drops; and even then, by its centrifugal still farther fromngthe centre or axis of the force, from the manner of conveyance, it trump, as the pressure lessens; and at last, would be flung out of the circle, and fall as the trump widens, is broken into small
scattered, like rain. ticles, and so united with air as to be support
But I need not expatiate on these matters ed by it, and become black clouds at the top to you. I have mentioned my objections, of the trump
and, as truth is my pursuit, shall be glad to Thus these eddies may be whirlwinds at be informed. I have seen few accounts of land, water-spouts at sea. A body of water these whirl or eddy winds, and as little of the so raised, may be suddenly let fall, when the spouts; and these, especially, lame and poor motion, &c. has not strength to support it, or things to obtain any certainty by. If you the whirling arch is broken so as to admit the know any thing determinate that has been air: falling in the sea, it is harmless, unless observed, I shall hope to hear from you; as ships happen under it; but if in the progres- also of any mistake in my thoughts. I have sive motion of the whirl it has moved from the nothing to object to any other part of your sea, over the land, and then breaks, sudden, violent, and mischievous torrents are the con- subsequent part of this volume, that the papers on me
* A Letter on Inoculation, which is transferred to a sequences.
teorological subjects may not be interrupied.
suppositions: and as to that of the trade- ! On the place of this spaitering, arises the winds, I believe nobody can.
appearance of a bush, into the centre of which P. S. The figures in the Philosophical the spout comes down. This bush I take to Transactions show, by several circumstances, be formed by a spray, made by the force of that they all descended, though the relators these drops, which being uncommonly large seemed to think they took up water.* and descending with unusual force by a
stream of wind descending from the cloud
with them, increases the height Dr. Perkins to Dr. Franklin.-Read at the which wind being repulsed by the surface of Royal Society, June 24, 1756.
the waters rebounds and spreads; by the first Boston, October 23, 1752.
rising the spray higher than it otherwise In the enclosed, you have all I have to say would go ; and by the last making the top of of that matter. It proved longer than I ex- the bush appear to bend outwards (i. e.) the pected, so that I was forced to add a cover to cloud of spray is forced off from the trunk of it. I confess it looks like a dispute ; but that the spout, and falls backward. is quite contrary to my intentions. The sin
The 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 dis- with the wind I mentioned, by their descept, covering the whole foundation of my opinion, which beat back the rising spray in the centre. which, indeed, is but an opinion, as I am This circumstance, of the bush bending very much at a loss about the validity of the outwards at the top, seems not to agree with reasons. I have not been able to differ from what I call a direct whirlwind, but consistent you in sentiment concerning any thing el:e with the reversed; for a direct one would in your Suppositions. In the present case I sweep the bush inwards; if, in that case, any lie open to conviction, and shall be the gainer thing of a bush would appear. 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. that above it. · The part in the bush is cy
Since my last I considered, that, as I had lindrical, as it is above (i. e.) the bigness begun with reason of my dissatisfaction about the same from the top of the bush to the wathe ascent of water in spouts, you would not ter. Instead of this shape, in case of a whirlbe unwilling to hear the whole I have to say, wind, it must have been pyramidical. and then you will know what I rely upon. Another thing remarkable, is, the curve in
What occasioned my thinking all spouts some of them : this is easy to conceive, in descend, is that I found some did certainly do case of descending parcels of drops through so. A difficulty appeared concerning the as- various winds, at least till the cloud condenses cent of so heavy a body as water, by any force so fast as to come down, as it were, uno rivo. I was apprized of as probably sufficient. And, But it is harder to me to conceive it in the above all, a view of Mr. Stuart's portraits of ascent of water, that it should be conveyed spouts, in the Philosophical Transactions. along, secure of not leaking or often dropping
Some observations on these last will in- through the under side, in the prone part : clude the chief part of my difficulties. and, should the water be conveyed so swiftly,
Mr. Stuart has given us the figures of a and with such force, up into the cloud, as to number observed by him in the Mediterra- prevent this, it would, by a natural disposition nean; all with some particulars which make to move on in a present direction, presently for my opinion, if well drawn.
straiten the curve, raising the shoulder very The great spattering, which relators men- swiftly, till lost in the cloud. tion in the water where the spout descends, Over every one of Stuart's figures, I see a and which appears in all his draughts, I con- cloud : I suppose his clouds were first, and ceive to be occasioned by drops descending then the spont; I do not know whether it be very thick and large into the place.
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 & the Philosophical Transactions, are given in this edi: 1 cloud; as is observable of whirlwinds; they tion, the beiter to illustrate the plate on the same subject, by Dr. Franklin.
come in fair weather, not under the shade of 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 I overlooked, in its proper place, Stuart's which occupy small spaces: and from the No. 11, which is curious for its inequalities, higher regions, extensive hurricanes, &c. and, in particular, the approach to breaking,
Another thing is the appearance of the which, if it would not be too tedious, I would sport coming from the cloud. This I cannot have observed a little upon, in my own way, account for on th notion of a direct spout, as, I think, this would argue against the asbut in the real descending one, it is easy. I cent, &c. but I must pass it, not only for take it, that the cloud begins first of all to the reason mentioned, but want of room bepour out drops at that particular spot, or fora- sides. men; and, when that current. of drops in- As to Mr. Stuart's ocular demonstration of creases, so as to force down wind and vapour, the ascent in his great perpendicular spout, the spout becomes so far as that goes opaque. the only one it appears in, 1 say, as to this, I take it, that no clouds drop spouts, but such what I have written supposes him inistaken, as make very fast, and happen to condense in which, yet, I am far from asserting. a particular spot, which perhaps is coldest, The force of an airy vortex, having less and gives a determination downwards, so as influence on the solid drops of water, than on to make a passage through the subjacent at the interspersed cloudy vapours, makes the mosphere.
last whirl round swifter, though it descend If spouts ascend, it is to carry up the warm slower: and this might easily deceive, withrarefied air below, to let down all and any out great care, the most unprejudiced person. that is colder above; and, if so, they must carry it through the cloud they go into (for
To Dr. Perkins. that is cold and dense, I imagine) perhaps far into the higher region, making a wonderful Water-spouts and IThirluinds compared.-- Read appearance at a convenient distance to observe at the Royal Society, June 24, 1.53. it, by the swift rise of a body of vapour, above
PHILADELPHIA, Feb. 4. 1753. the region of the clouds. But as this has never I ought to have written to you, long since, been observed in any age, if it be supposable in answer to yours of October 16, concerning that is all.
the water-spout; but business partly, and I cannot learn by mariners, that any wind partly a desire of procuring further informablows towards a spout more than any other tion by inqury among my seafaring acquaintway; but it blows towards a whirlwind, for a ance, induced me to postpone writing, from large distance round.
time to time, till I am now almost ashamed to I suppose there has been no instance of the resume the subject, not knowing but you may water of a spout being salt, when coming have forgot what has been said upon it. across any vessel at sea. I suppose too, that Nothing certainly, can be more improving there have been no salt rains; these would to a searcher into nature, than objections jumake the case clear,
diciously made to his opinion, taken up, perI suppose it is froin some unhappy effects haps, too hastily: for such objections oblige of these dangerous creatures of nature, that him to re-study the point, consider every cirsailors have an universal dread on them, of cumstance carefully, compare facts, make exbreaking in their deck, should they come periments, weigh arguments, and be slow in across them.
drawing conclusions. And hence a sure adI imagine spouts, in cold seasons, as Gor- vantage results; for he either confirms a don's in the Downs, prove the descent. truth, before too slightly supported; or disco
Qirery. Whether there is not always vers an error, and receives instruction from more or less cloud, first, where a spout ap- the objector. perrs?
In this view I consider the objections and Whether they are not, generally, on the remarks you sent me, and thank you for them borders of trade-winds; and whether this is sincerely: but, how much soever my inclinafor, or against me ?
tions lead me to philosophical inquiries, I am Whether there be any credible account so engaged in business, public and private, of a whirlwind's carrying up all the water in that those more pleasing pursuits are frequenta pool, or small pond: as when shoal, and the ly interrupted, and the chain of thought nebanks low, a strong gust might be supposed to cessary to be closely continued in such disblow it all out?
quisitions, is so broken and disjointed, that it Whether a violent tornado, of a small ex- is with difficulty I satisfy myself in any of tent, and other sudden and strong gusts, be them: and I am now not much nesrer a connot winds from above, descending nearly per- clusion, in this matter of the spout, ihan when pendicular; and, whether many that are call. I first read your letter. ed whirlwinds at sea, are any other than these, Yet, hoping we may, in time, sift out the