Imágenes de página
PDF
ePub

small vent, or by drawing the cork of a bottle.

To Peter Collinson. Dr. Boerhaave says, that the steam issuing

Account of a Whirlwind in Maryland. from fermenting liquors received through a very small vent-hole, into the nose, will kill

PAILADELPHIA, Aug. 25, 1755. as suddenly and certainly as lightning That As you have my former papers on whirl. · air is generated by fermentation, I think you winds, &c. I now send you an account of one will find fully proved in Dr. Hales's Analysis which I had lately an opportunity of seeing of the Air, in his Vegetable Statics. If you and examining myself, have not read the book, you have a new plea Being in Maryland, riding with colonel sure to come.

Tasker, and some other gentlemen, to his The solution you give to the objection I country seat, where I and my son were enmade from the contrary winds blowing from tertained by that amiable and worthy man the opposite sides of the mountains, from there with great hospitality and kindness, we saw, being eddies, does not please me, because the in the vale below us, a small whirlwind beginextent of these winds is by far too large to be ning in the road, and showing itself by the occasioned by any eddy. It is forty miles dust it raised and contained. It appeared in from New York to our mountains, through the form of a sugar-loaf, spinning on its point, which Hudson's River passes. The river moving up the hill towards us, and enlarging runs twelve miles in the mountains, and from as it came forward. When it passed by us, the north side of the mountains it is about its smaller part near the ground appeared no ninety miles to Albany. I have myself been bigger than a common barrel, widening upon board a vessel more than once, when we wards, it seemed, at forty or fifty feet high, have had a strong northerly wind against us, to be twenty or thirty feet in diameter. The all the way from New York, for two or three rest of the company stood looking after it, but days. We have met vessels from Albany, my curiosity being stronger, I followed it, who assured us, that, on the other side of the riding close by its side, and observed its lickmountains, they had, at the same time, a ing up, in its progress, all the dust that was strong continued southerly wind against them; under its smaller part. As it is a common opiand this frequently happens.

nion that a shot, fired through a water-spout, I have frequently seen, both on the river, will break it, I tried to break this little whirlin places where there could be no eddy-winds wind, by striking my whip frequently through and on the open sea, two vessels sailing with it, but without any effect. Soon after, it quitcontrary winds, within half a mile of each ted the road and took into the woods, growing other; but this happens only in easy winds, every moment larger and stronger, raising, and generally calm in other places near these instead of dust, the old dry leaves with which winds.

the ground was thick covered, and making a You have, no doubt, frequently observed a great noise with them and the branches of the single cloud pass, from which a violent gust trees, bending some tall trees round in a circle of wind issues, but of no great extent. I have swiftly and very surprisingly, though the proobserved such a gust make a lane through gressive motion of the whirl was not so swift the woods, of some miles in length, by laying but that a man on foot might have kept pace the trees flat to the ground, and not above with it, but the circular motion was amazingly eight or ten chains in breadth. Though the rapid. By the leaves it was now filled with, violence of the wind be in the same direction I could plainly perceive that the current of in which the cloud moves and precedes it, yet air they were driven by moved upwards in a wind issues from all sides of it; so that sup spiral line; and when I saw the passing whirl posing the cloud moves south-easterly, those continue entire, after leaving the trunks and on the north-east side of it feel a south-west bodies of large trees which it had enveloped, wind, and others on the south-west side, a I no longer wondered that my whip had no north-east. And where the cloud passes over effecton it in its smaller state. Iaccompanied we frequently have a south-east wind from it about three quarters of a mile, till some the hinder part of it, but none violent, except limbs of dead trees, broken off by the whirl, the wind in the direction in which the cloud flying about, and falling near me, made me moves. To show what it is which prevents more apprehensive of danger : and then I stopthe wind from issuing out equally on all sides ped, looking at the top of it as it went on, is not an easy problem to me, and I shall not which was visible, by means of the leaves conattempt to solve it; but when you shall show tained in it, for a very great height above the what it is which restrains the electrical fluid trees. Many of the leaves, as they got loose from spreading itself in the air surrounding it, from the upper and widest part, were scattered when it rushes with great violence through in the wind; but so great was their height in the air along, or in the conductor, for a great the air, that they appeared no bigger than flies. extent in length, then I may hope to explain My son, who was, by this time, come up the other problem, and remove the difficulty with me, followed the whirlwind till it left the we have in conceiving it.

woods, and crossed an old tobacco-field, where,

[ocr errors]

1

[ocr errors]

1

[ocr errors]
[ocr errors]
[ocr errors]

finding neither dust nor leaves to take up, it E. of Philadelphia about four hundred miles. gradually became invisible below, as it went This puzzled me, because the storm began away over that field. The course of the ge- with us so soon as to prevent any observation, neral wind then blowing was along with us and being a north-east storm, I imagined it as we travelled, and the progressive motion of must have begun rather sooner in places far. the whirlwind was in a direction nearly oppo- ther to the north-eastward than it did at Phisite, though it did not keep a strait line, nor ladelphia. I therefore mentioned it in a letter was its progressive motion uniform, it making to my brother, who lived at Boston; and he

little sallies on either hand as it went, pro- informed me the storm did not begin with i ceeding sometimes faster, and sometimes them till near eleven o'clock, so that they had

slower, and seeming sometimes for a few a good observation of the eclipse; and upon seconds almost stationary, then starting for comparing all the other accounts I received wards pretty fast again. When we rejoined from the several colonies, of the time of bethe company, they were admiring the vast ginning of the same storm, and since that of height of the leaves now brought by the com- other storms of the same kind, I found the be

mon wind, over our heads. These leaves ac- ginning to be always later the farther northi companied us as we travelled, some falling eastward. I have not my notes with me

now and then round about us, and some not here in England, and cannot, from memory, I reaching the ground till we had gone near say the proportion of time to distance, but I

three miles from the place where we first saw think it is about an hour to every hundred the whirlwind begin. Upon my asking co- miles. lonel Tasker if such whirlwinds were com From thence I formed an idea of the cause mon in Maryland, he answered pleasantly, of these storms, which I would explain by a No, not at all common, but we got this on familiar instance or two.—Suppose a long

purpose to treat Mr. Franklin.-And a very canal of water stopped at the end by a gate. i high treat it was too. B. FRANKLIN. The water is quite at rest till the gate is open,

then it begins to move out through the gate ;

the water next the gate is first in motion, and Alexander Small, London.

moves towards the gate; the water next to On the North-east Storms in North America. that first water moves next, and so on suc

May 12, 1760. cessively, till the water at the head of the caa AGREEABLE to your request, I send you my nal is in motion, which is last of all. In this reasons for thinking that our north-east storms case all the water moves indeed towards the in North America begin first, in point of time, gate, but the successive times of beginning in the south-west parts: that is to say, the motion are the contrary way, viz. from the

air in Georgia, the farthest of our colonies to gate backwards to the head of the canal. ! the south-west, begins to move south-westerly Again, suppose the air in a chamber at rest,

before the air of Carolina, which is the next no current through the room till you make a

colony north-eastward; the air of Carolina, fire in the chimney. Immediately the air in | has the same motion before the air of Vir: the chimney being rarefied by the fire rises ;

ginia, which lies still more north east-ward; the air next the chimney flows in to supply į and so on north-easterly through Pennsylva- its place, moving towards the chimney; and, i nia, New York, New England, &c. quite to in consequence, the rest of the air succesNewfoundland.

sively, quite back to the door. Thus to proThese north-east storms are generally very

duce our north-east storms, I suppose some violent, continue sometimes two or three days, great heat and rarefaction of the air in or and often do considerable damage in the hår- about the gulph of Mexico; the air thence bours along the coast. They are attended rising has its place supplied by the next more with thick clouds and rain.

northern, cooler, and therefore denser and What first gave me this idea, was the fol- heavier, air; that, being in motion, is followed lowing circumstance. About twenty years by the next more northern air, &c. in a suc

ago, a few more or less, I cannot from my me- cessive current, to which current our coast | mory

be certain, we were to have an eclipse of and inland ridge of mountains give the directhe moon at Philadelphia, on a Friday evening, tion of north-east as they lie N. E. and S. W. about nine o'clock. I intended to observe it, This I offer only as an hypothesis to account but was prevented by a north-east storm, which for this particular fact; and perhaps, on farcame on about seven, with thick clouds as ther examination, a better and truer may be usual, that quite obscured the whole hemis- found. I do not suppose all storms generated phere. Yet when the post brought us the in the same manner. Our north-west thunder Boston newspaper, giving an account of the gusts in America, I know are not; but of effects of the same storm in those parts, I them I have written my opinion fully in a found the beginning of the eclipse had been pages which you have seen. well observed there, though Boston lies N.

B. FRANKLIN.

[ocr errors]

To Dr. Percival, Manchester. distance, and the day shortest, but some time Meteorological Imaginations and Conjectures.*

after that period, according to the English

proverb, which says, “as the day lengthens, THERE seems to be a region higher, in the the cold strengthens;" the causes of refrigeair over all countries, where it is always win ration continuing to operate, while the sun ter, where frost exi-ts continually, since in the returns too slowly, and his force continues too inidst of summer, on the surface of the earth, weak to counteract them. ice falls often from above in the form of hail. During several of the summer months of the

Hailstones, of the great weight we some year 1783, when the effects of the sun's rays times find them, did not probably acquire their to heat the earth in these northern regions magnitude before they began to descend. The should have been the greatest, there existed air being eight hundred times rarer than wa- a constant fog over all Europe, and great part ter, is unable to support it but in the shape of of North America. This fog was of a pervapour, a state in which its particles are sepa- manent nature: it was dry, and the rays of rated. As soon as they are condensed by the the sun seemed to have little effect towards cold of the upper region, so as to form a drop, dissipating it, as they easily do a moist fog, that drop begins to fall. If it freezes into a arising from water. They were indeed rengrain of ice, that ice descends. In descend- dered so faint in passing through it, that when ing, both the drop of water and the grain of collected in the focus of a burning glass, they ice are augmented by particles of the vapour would scarce kindle brown paper. Of course, they pass through in falling, and which they their summer effect in heating the earth was condense by coldness, and attach to them- exceedingly diminished. selves.

Hence the surface was early frozen. It is possible that, in summer, much of what Hence the first snows remained on it unis rain, when it arrives at the surface of the melted, and received continual additions. earth, might have been snow when it began Hence perhaps the winter of 1783-4, was its descent; but being thawed, in passing more severe than any that had happened for through the warm air near the surface, it is many years. changed from snow into rain.

The cause of this universal fog is not yet How immensely cold must be the original ascertained. Whether it was adventitious to particle of hail, which forms the centre of the this earth, and merely a smoke proceeding future hailstone, since it is capable of commu- from the consumption by fire of soine of those nicating sufficient cold, if I may so speak, to great burning balls or globes which we hapfreeze all the mass of vapour condensed round pen to meet with in our rapid course round it, and form a lump of perhaps six or eight the sun, and which are sometimes seen to ounces in weight !

kindle and be destroyed in passing our atmoWhen, in summer time, the sun is high, sphere, and whose smoke might be attracted and continues long every day above the ho- and retained by our earth; or whether it was rizon, his rays strike the earth more directly the vast quantity of smoke, long continuing and with longer continuance, than in the to issue during the summer from Hecla, in winter; hence the surface is more heated, and Iceland, and that other volcano which arose to a greater depth, by the effect of those rays. out of the sea near that island, which smoke

When rain falls on the heated earth, and might be spread by various winds over the soaks down into it, it carries down with it a northern part of the world, is yet uncertain. great part of the heat, which by that means It seems however worth the inquiry, whedescends still deeper.

ther other hard winters, recorded in history, The mass of earth, to the depth of perhaps were preceded by similar permanent and thirty feet, being thus heated to a certain de widely extended summer fogs. Because, if gree, continues to retain its heat for some found to be so, men might from such fogs contime. Thus the first snows that fall in the jecture the probability of a succeeding hard beginning of winter, seldom lie long on the winter, and of the damage to be expected by surface, but are soon melted, and soon absorb- the breaking up of frozen rivers in the spring; ed. After which, the winds that blow over and take such measures as are possible and the country on which the snows had fallen, practicable, to secure themselves and effects are not rendered so cold as they would have from the mischiefs that attended the last. been, by those snows, if they had remained, Passy, May, 1784. and thus the approach of the severity of winter is retarded; and the extreme degree of its cold is not always at the time we might ex To Dr. Lining, at Charleston. pect it, viz. when the sun is at its greatest On Cold produced by Evaporation, * This paper was inserted in the Memoirs of the Li.

NEW YORK, April 14, 1757. terary and Philosophical Society of Manchester, Vol. IL. page 378. It was communicated by Dr. Percival, and of a line from you; and, indeed, the troubles

It is a long time since I had the pleasure read December 22, 1784.

of our country, with the hurry of business Igers with one hand, and a piece of wood, of have been engaged in on that account, have the same dimensions, with the other, and bring made me so bad a correspondent, that I both at the same time to the flame of a candle, ought not to expect punctuality in others. you will find yourself obliged to drop the dol

But being about to embark for England, I lar before you drop the wood, because it concould not quit the continent without paying ducts the heat of the candle sooner to your my respects to you, and, at the same time, flesh. Thus, if a silver tea-pot had a handle taking leave to introduce to your acquaint- of the same metal, it would conduct the heat ance a gentleman of learning and merit, colo- from the water to the hand, and become t90 nel Henry Bouquet, who does me the favour hot to be used; we therefore give to a metal to present you this letter, and with whom I am tea-pot a handle of wood, which is not so good sure you will be much pleased.

a conductor as metal. But a china or stone Professor Simpson, of Glasgow, lately com- tea-pot being in some degree of the nature of municated to me some curious experiments glass, which is not a good conductor of heat, of a physician of his acquaintance, by which may have a handle of the same stuff. Thus, it appeared, that an extraordinary degree of also, a damp moist air shall make a man more cold, even to freezing, might be produced by sensible of cold, or chill him more, than a dry evaporation, I have not had leisure to repeat air that is colder, because a moist air is fitter and examine more than the first and easiest to receive and conduct away the heat of his of them, viz. Wet the ball of a thermome- body. This fluid, entering bodies in great ter by a feather dipt in spirit of wine, which quantity, first expands them, by separating has been kept in the same room, and has, of their parts a little, afterwards, by farther secourse, the same degree of heat or cold. The parating their parts, it renders solids fluid, mercury sinks presently three or four degrees, and at length dissipates their parts in air, and the quicker, if during the evaporation Take this fluid from melted lead, or from wayou blow on the ball with bellows; a second ter, the parts cohere again, the first grows wetting and blowing, when the mercury is solid, the latter becomes ice: and this is down, carries it yet lower. I think I did not sooner done by the means of good conductors. get it lower than five or six degrees from Thus, if you take, as I have done, a square bar where it naturally stood, which was at that of lead, four inches long, and one inch thick, time sixty. But it is said, that a vessel of together with three pieces of wood planed to water being placed in another somewhat the same dimensions, and lay them on a larger, containing spirit, in such a manner smooth board, fixt so as not to be easily sepam that the vessel of water is surrounded with rated or moved, and pour into the cavity they the spirit, and both placed under the receiver form, as much melted lead as will fill it, you of an air pump; on exhausting the air, the will see the melted lead chill, and become spirit, evaporating, leaves such a degree of firm, on the side next the leaden bar, some cold as to freeze the water, though the ther- time before it chills on the other three sides mometer, in the open air, stands inany degrees in contact with the wooden bars, though beabove the freezing point.

fore the lead was poured in, they might all be I know not how this phenomena is to be supposed to have the same degree of heat or accounted for, but it gives me occasion to coldness, as they had been exposed in the mention some loose notions relating to heat same room to the same air. You will likeand cold, which I have for some time enter- wise observe, that the leaden bar, as it has tained, but not yet reduced into any form. cooled the melted lead more than the wooden Allowing common fire, as well as electrical, bars have done, so it is itself more heated by to be a fluid capable of permeating other bo- the melted lead. There is a certain quantidies, and seeking an equilibrium, I imagine ty of this fluid called fire, in every living husome bodies are better fitted by nature to be man body, which fluid, being in due proporconductors of that fluid than others; and, that, tion, keeps the parts of the flesh and blood at generally, those which are the best conduct- such a just distance from each other, as that ors of the electric fluid, are also the best con- the flesh and nerves are supple, and the blood ductors of this; and è contra.

fit for circulation. If part of this due proporThus a body which is a good conductor of tion of fire be conducted away, by means of a fire readily receives it into its substance, and contact with other bodies, as air, water, or conducts it through the whole to all the parts, metals, the parts of our skin and flesh that as metals and water do; and if two bodies, come into such contact first, draw more near both good conductors, one heated, the other together than is agreeable, and give that senin its common state, are brought into contact sation which we call cold; and if too much with each other, the body which has most fire be conveyed away, the body stiffens, the blood readily communicates of it to that which had ceases to flow, and death ensues. On the least, and that which had least readily re- other hand, if too much of this fluid be comceives it, till an equilibrium is produced. municated to the flesh, the parts are separatThus, if you take a dollar between your fin- led too far, and pain ensues, as when they are

separated by a pin or lancet. The sensation preparing for distillation, wherein there is a that the separation by fire occasions, we call separation of the spirituous, from the watery heat or burning. My desk on which I now and earthy parts. And it is remarkable, that write, and the lock of my desk, are both ex- the liquor in a distiller's vat, when in its posed to the same temperature of the air, highest and best state of fermentation, as I and have therefore the same degree of heat have been informed, has the same degree of or cold: yet if I lay my hand successively on heat with the human body: that is, about 94 the wood and on the metal, the latter feels or 96. much the coldest, not that it is really so, but Thus, as by a constant supply of fuel in a being a better conductor, it more readily than chimney, you keep a warm room, so, by a the wood takes away and draws into itself the constant supply of food in the stomach, you fire that was in my skin.. Accordingly if I keep a warm body; only where little exercise lay one hand, part on the lock, and part on is used, the heat may possibly be conducted the wood, and after it had laid on some time, away too fast; in which case such materials I feel both parts with my other hand, I find are to be used for cloathing and bedding, the part that has been in contact with the lock, against the effects of an immediate contact of very sensibly colder to the touch than the the air, as are, in themselves, bad conductors part that lay on the wood. How a living of heat, and consequently, prevent its being animal obtains its quantity of this fluid called communicated through their substance to the fire, is a curious question. I have shown, air. Hence, what is called warmth in wool, that some bodies (as metals) have a power of and its preference on that account, to linen; attracting it stronger than others; and I have wool not being so good a conductor : and sometimes suspected, that a living body had hence all the natural coverings of animals, to some power of attracting out of the air, or keep them warm, are such as retain and conother bodies, the heat it wanted. Thus me- fine the natural heat in the body, by being tals hammered, or repeatedly bent, grow hot bad conductors, such as wool, hair, feathers, in the beat or hammered part. But when I and the silk by which the silkworm, in its consider that air, in contact with the body, tender embryo state, is first cloathed. Cloath"cools it; that the surrounding air is rather ing, thus considered, does not make a man heated by its contact with the body; that warm by giving warmth, but by preventing every breath of cooler air drawn in, carries the too quick dissipation of the heat produced off part of the body's heat when it passes out in his body, and so occasioning an accumuagain; that therefore there must be in the lation. body a fund for producing it, or otherwise the There is another curious question I will animal would soon grow cold: I have been just venture to touch upon, viz. Whence rather inclined to think, that the fluid fire, as arises the sudden extraordinary degree of well as the fluid air, is attracted by plants in cold, perceptible on mixing some chemical their growth, and becomes consolidated with liquors, and even on mixing salt and snow, the other materials of which they are formed, where the composition appears colder than the and makes a great part of their substance: coldest of the ingredients? I have never seen that when they come to be digested, and to the chemical mixtures made, but salt and snow suffer in the vessels a kind of fermentation, I have often mixed myself, and am fully satispart of the fire, as well as part of the air, re- fied that the composition feels much colder to covers its fluid active state again, and diffuses the touch, and lowers the mercury in the itself in the body digesting and separating it: thermometer more than either ingredient that the fire so reproduced, by digestion and would do separately. I suppose, with others, separation continually leaving the body, its that cold is nothing more than the absence of place is supplied by fresh quantities, arising heat or fire. Now if the quantity of fire befrom the continual separation. That what- fore contained or diffused in the snow and ever quickens the motion of the fluids in an salt was expelled in the uniting of the two animal quickens the separation, and repro- matters, it must be driven away either through duces more of the fire; as exercise. That all the air or the vessel containing them. If it the fire emitted by wood, and other combusti- is driven off through the air, it must warm bles, when burning existed in them before, in the air, and a thermometer held over the a solid state, being only discovered when se- mixture, without touching it

, would discover parating. That some fossils, as sulphur, sea the heat, by the rising of the mercury, as it coal, &c. contain a great deal of solid fire; must, and always does in warm air. and that, in short, what escapes and is dissi This, indeed, I have not tried, but I should pated in the burning of bodies, besides water guess it would rather be driven off through and earth, is generally the air and fire that the vessel, especially if the vessel be metal, before made parts of the solid. Thus I ima- as being a better conductor than air; and so gine that animal heat arises by or from a kind one should find the bason warmer after such of fermentation in the juices of the body, in mixture. But, on the contrary, the vesse) the same manner as heat arises in the liquors grows cold, and even water, in which the

« AnteriorContinuar »