Air moderately heated will support a greater quantity of water invisibly than cold air; for its particles being by heat repelled to a F greater distance from each other, thereby O more easily keep the particles of water that are annexed to them from running into cohe-O sions that would obstruct, refract, or reflect the light. Hence when we breathe in warm air, though the same quantity of moisture may be taken up from the lungs, as when we breathe in cold air, yet that moisture is not so visible. Water being extremely heated, i. e. to the degree of boiling, its particles in quitting it so repel each other, as to take up vastly more space than before, and by that repellency support themselves, expelling the air from the space they occupy. That degree of heat being lessened, they again mutually attract, and having no air particles mixed to adhere to, by which they might be supported and kept at a distance, they instantly fall, coalesce, and become water again. The water commonly diffused in our atmosphere never receives such a degree of heat from the sun, or other cause, as water has when boiling; it is not, therefore, supported by such heat, but by adhering to air. Water being dissolved in, and adhering to air, that air will not readily take up oil, because of the mutual repellency between water and oil. Hence cold oils evaporate but slowly, the air having generally a quantity of dissolved water. Oil being heated extremely, the air that approaches its surface will be also heated extremely; the water then quitting it, it will attract and carry off the oil, which can now adhere to it. Hence the quick evaporation of oil heated to a great degree. Oil being dissolved in air, the particles to which it adheres will not take up water. Hence the suffocating nature of air impreg nated with burnt grease, as from snuffs of candles and the like. A certain quantity of moisture should be every moment discharged and taken away from the lungs; air that has been frequently breathed, is already overloaded, and, for that reason, can take no more, so will not answer the end. Greasy air refuses to touch it. In both cases suffocation for want of the discharge. Air will attract and support many other substances. A particle of air loaded with adhering water, or any other matter, is heavier than before, and would descend. The atmosphere supposed at rest, a loaded descending particle must act with a force on the particles it passes between, or meets with, sufficient to overcome, in some degree, their mutual repellency, and push them nearer to each other. E Thus, supposing the particles A B C D, and the other near them O to be at the distance caused by their mutual repellency (confined by their common gravity) O O O if A would descend to E, it must pass between в and c; when it comes between B and C, it will be nearer to them than before, and must either have pushed them nearer to F and e, contrary to their mutual repellency, or pass through by a force exceeding its repellency with them. It then approaches D, and, to move it out of the way, must act on it with a force sufficient to overcome its repellency with the two next lower particles, by which it is kept in its present situation. Every particle of air, therefore, will bear any load inferior to the force of these repul sions. Hence the support of fogs, mists, clouds. Very warm air, clear, though supporting a very great quantity of moisture, will grow turbid and cloudy on the mixture of colder air, as foggy turbid air will grow clear by warming. Thus the sun shining on a morning fog, dissipates it; clouds are seen to waste in a sun-shiny day. But cold condenses and renders visible the vapour: a tankard or decanter filled with cold water will condense the moisture of warm clear air on its outside, where it becomes visible as dew, coalesces into drops, descends in little streams. The sun heats the air of our atmosphere most near the surface of the earth; for there, besides the direct rays, there are many reflections. Moreover, the earth itself being heated, communicates of its heat to the neighbouring air. The higher regions, having only the direct rays of the sun passing through them, are comparatively very cold. Hence the cold air on the tops of mountains, and snow on some of them all the year, even in the torrid zone. Hence hail in summer. If the atmosphere were, all of it (both above and below) always of the same temper as to cold or heat, then the upper air would always be rarer than the lower, because the pressure on it is less; consequently lighter, and therefore would keep its place. But the upper air may be more condensed by cold, than the lower air by pressure; the lower more expanded by heat, than the upper for want of pressure. In such case the upper air will become the heavier, the lower the lighter. The lower region of air being heated and expanded heaves up, and supports for some time 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 the equatorial the water descends on the heavier side, and earth, appears an east wind blowing westward; the air rises into its place. the earth moving from west to east, and slipping under the air.* The lifted heavy cold air over a heated country, becoming by any means unequally supported, or unequal in its weight, the heaviest part descends first, and the rest follows impetuously. Hence gusts after heats, and hurricanes in hot climates. Hence the air of gusts and hurricanes is cold, though in hot climates and seasons; it coming from above. The cold air descending from above, as it penetrates our warm region full of watery particles, condenses them, renders them visible, forms a cloud thick and dark, overcasting sometimes, at once, large and extensive; sometimes, when seen at a distance, small at first, gradually increasing; the cold edge, or surface of the cloud, condensing the vapours next it, which form smaller clouds that join it, increase its bulk, it descends with the wind and its acquired weight, draws nearer the earth, grows denser with continual additions of water, and discharges heavy showers. Small black clouds thus appearing in a clear sky, in hot climates, portend storms, and warn seamen to hand their sails. The earth, turning on its axis in about twenty-four hours, the equatorial parts must move about fifteen miles in each minute; in northern and southern latitudes this motion is gradually less to the poles, and there nothing. If there was a general calm over the face of the globe, it must be by the air's moving in every part as fast as the earth or sea it covers. He that sails, or rides, has insensibly the same degree of motion as the ship or coach with which he is connected. If the ship strikes the shore, or the coach stops suddenly, the motion continuing in the man, he is thrown forward. If a man were to jump from the land into a swift sailing ship, he would be thrown backward (or towards the stern) not having at first the motion of the ship. He that travels by sea or land, towards the equinoctial, gradually acquires motion; from it, loses. But if a man were taken up from latitude 40 (where suppose the earth's surface to move twelve miles per minute) and immediately set down at the equinoctial, without changing the motion he had, his heels would be struck up, he would fall westward. If taken up from the equinoctial, and set down in latitude 40, he would fall eastward. The air under the equator, and between the tropics, being constantly heated and rare Thus, when we ride in a calm, it seems a wind against us: if we ride with the wind, and faster, even that will seem a small wind against us. The air rarefied between the tropics, and rising, must flow in the higher region north and south. Before it rose, it had acquired the greatest motion the earth's rotation could give it. It retains some degree of this motion, and descending in higher latitudes, where the earth's motion is less, will appear a westerly wind, yet tending towards the equatorial parts, to supply the vacancy ocċasioned by the air of the lower regions flowing thitherwards. Hence our general cold winds are about north west, our summer cold gusts the same. The air in sultry weather, though not cloudy, has a kind of haziness in it, which makes objects at a distance appear dull and indistinct. This haziness is occasioned by the great quantity of moisture equally diffused in that air. When, by the cold wind blowing down among it, it is condensed into clouds, and falls in rain, the air becomes purer and clearer. Hence, after gusts, distant objects appear distinct, their figures sharply terminated. Extreme cold winds congeal the surface of the earth, by carrying off its fire. Warm winds afterwards blowing over that frozen surface will be chilled by it. Could that frozen surface be turned under, and warmer turned up from beneath it, those warm winds would not be chilled so much. The surface of the earth is also sometimes much heated by the sun and such heated surface not being changed heats the air that moves over it. Seas, lakes, and great bodies of water, agitated by the winds, continually change surfaces; the cold surface in winter is turned under by the rolling of the waves, and a warmer turned up; in summer, the warm is turned under, and colder turned up. Hence the more equal temper of sea-water, and the air over it. Hence, in winter, winds from the sea seem warm, winds from the land cold. In summer the contrary. Therefore the lakes north-west of us, as they are not so much frozen, nor so apt to *See a paper on this subject, by the late ingenious Mr. Hadley, in the Philosophical Transactions, wherein this hypothesis for explaining the trade-winds first appeared. In Pennsylvania. 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. Perkins of Boston to Dr. Franklin. On Water-Spouts.-Read at the Royal Society, 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. 1 make no doubt of direct and inverted whirl- Descending spouts (as I take them to be) 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 ticles, and so united with air as to be supported by it, and become black clouds at the top of the trump. par 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. 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 and, as truth is my pursuit, shall be glad to to you. I have mentioned my objections, 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 trade- ! On the place of this spattering, arises the winds, 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.* 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 with them, increases the height of the spray : Dr. Perkins to Dr. Franklin.-Read at the which wind being repulsed by the surface of 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. The bush does the same where there is no appearance of a spout reaching it; and is depressed in the middle, where the spout is expected. This, I imagine, to be from numerous drops of the spout falling into it, together 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 sincerity of friendship and esteem were my motives; nor do I doubt your scrupling the goodness of the intention. However, I must confess, I cannot tell exactly how far I was actuated 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 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 dry notions: however, by this you will see that I think it unreasonable to give you more trouble about them, than your leisure and inclination may prompt you to.-I am, &c. I 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 SO. 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. *Two engraved representations of water-spouts, from the Philosophical Transactions, are given in this edition, the better to illustrate the plate on the same subject, by Dr. Franklin. 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. pears to the eye beyond its real bigness, by a refraction in the bush, and which refraction may be the cause of the appearance of separation, betwixt the part in the bush, and 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 expect them in fair weather, but not under a cloud; as is observable of whirlwinds; they come in fair weather, not under the shade of a cloud, nor in the night: since shade cools the air: but, on the contrary, violent winds 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, and so might be called air-spouts, if they were objects of sight? 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. 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 information by inquiry among my seafaring acquaintance, 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 |