Imágenes de página
PDF
ePub

electrified, joins with the natural repulsion of the air, to force its particles to a greater distance, whereby the triangles are dilated, and the air rises, carrying up with it the water.

20. If the particles of water bring with them portions of both sorts of fire, the repulsion of the particles of air is still more strengthened and increased, and the triangles farther enlarged.

21. One particle of air may be surrounded by twelve particles of water of equal size with itself, all in contact with it; and by more added to those.

22. Particles of air, thus loaded would be drawn nearer together by the mutual attraction of the particles of water, did not the fire, common or electrical, assist their repulsion.

23. If air, thus loaded, be compressed by adverse winds, or by being driven against mountains, &c., or condensed by taking away the fire that assisted it in expanding; the triangles contract, the air with its water will descend as a dew; or, if the water surrounding one particle of air comes in contact with the water surrounding another, they coalesce and form a drop, and we have rain.

24. The sun supplies (or seems to supply) common fire to vapours, whether raised from earth or sea.

wards the mountains and towards each other. If the air was not much loaded, it only falls in dews on the mountain tops and sides, forms springs, and descends to the vales in rivulets, which, united, make larger streams and rivers. If much loaded, the electrical fire is at once taken from the whole cloud; and, in leaving it, flashes brightly and cracks loudly; the particles instantly coalescing for want of that fire, and falling in a heavy shower.

30. When a ridge of mountains thus dams the clouds, and draws the electrical fire from the cloud first approaching it; that which next follows, when it comes near the first cloud, now deprived of its fire, flashes into it, and begins to deposite its own water; the first cloud again flashing into the mountains; the third approaching cloud, and all succeeding ones, acting in the same manner as far back as they extend, which may be over many hundred miles of country.

31. Hence the continual storms of rain, thunder, and lightning on the east side of the Andes, which running north and south, and being vastly high, intercept all the clouds brought against them from the Atlantic ocean by the trade winds, and oblige them to deposite their waters, by which the vast rivers Amazons, La Plata, and Oroonoko are form25. Those vapours, which have both common ed, which return the water into the same sea and electrical fire in them, are better support-after having fertilized a country of very great ed than those which have only common fire in them; for when vapours rise into the coldest region above the earth, the cold will not diminish the electrical fire, if it doth the com

mon.

extent.

32. If a country be plain, having no mountains to intercept the electrified clouds, yet it is not without means to make them deposite their water. For if an electrified cloud, coming from the sea, meets in the air a cloud raised from the land, and therefore not electrified, the first will flash its fire into the latter, and thereby both clouds shall be made suddenly to

26. Hence clouds, formed by vapours raised from fresh waters within land, from growing vegetables, moist earth, &c. more speedily and easily deposite their water, having but little electrical fire to repel and keep the par-deposite water. ticles separate. So that the greatest part of the water raised from the land, is let fall on the land again; and winds blowing from the land to the sea are dry; there being little use for rain on the sea, and to rob the land of its moisture, in order to rain on the sea, would not appear reasonable.

27. But clouds, formed by vapours raised from the sea, having both fires, and particularly a great quantity of the electrical, support their water strongly, raise it high, and being moved by winds, may bring it over the middle of the broadest continent from the middle of the widest ocean.

28. How these ocean clouds, so strongly supporting their water are made to deposite it on the land where it is wanted is next to be considered.

29. If they are driven by winds against mountains, those mountains being less electrified attract them, and on contact take away their electrical fire (and being cold, the common fire also ;) hence the particles close to

33. The electrified particles of the first cloud close when they lose their fire; the particles of the other clouds close in receiving it: in both, they have thereby an opportunity of coalescing into drops.-The concussion, or jerk given to the air, contributes also to shake down the water, not only from those two clouds, but from others near them. Hence the sudden fall of rain immediately after flashes of lightning.

34. To show this by an easy experiment: take two round pieces of pasteboard two inches diameter; from the centre circumference of each of them suspend by fine silk threads eighteen inches long, seven small balls of wood, or seven peas equal in goodness: so will the balls appending to each pasteboard, form equal equilateral triangles, one ball being in the centre, and six at equal distances from that, and from each other; and thus they represent particles of air. Dip both sets in water, and some adhering to each ball, they will representair loaded. Dexterously electrify one

set, and its balls will repel each other to a greater distance, enlarging the triangles. Could the water supported by seven balls come into contact, it would form a drop or drops so heavy as to break the cohesion it had with the balls, and so fall. Let the two sets then represent two clouds, the one a sea cloud electrified, the other a land cloud. Bring them within the sphere of attraction, and they will draw towards each other, and you will see the separated balls close thus; the first electrified ball that comes near an unelectrified ball by attraction joins it, and gives it fire; instantly they separate, and each flies to another ball of its own party, one to give, the other to receive fire; and so it proceeds through both sets, but so quick as to be in a manner instantaneous. In the cohesion they shake off and drop their water which repre

sents rain.

35. Thus when sea and land clouds would ́pass at two great a distance for the flash, they are attracted towards each other till within that distance; for the sphere of electrical attraction is far beyond the distance of flashing. 36. When a great number of clouds from the sea meet a number of clouds raised from the land, the electrical flashes appear to strike in different parts; and as the clouds are jostled and mixed by the winds, or brought near by the electrical attraction, they continue to give and receive flash after flash, till the electrical fire is equally dissolved.

When the air, with its vapours raised from the ocean between the tropics, comes to descend in the polar regions and to be in contact with the vapours arising there, the electrical fire they brought begins to be communicated, and is seen in clear nights, being first visible where it is first in motion, that is, where the contact begins, or in the most northern part; from thence the streams of light seem to shoot southerly, even up to the zenith of northern countries. But though the light seems to shoot from the north southerly, the progress of the fire is really from the south northerly, its motion beginning in the north, being the reason that it is there seen first.

For the electrical fire is never visible but when in motion, and leaping from body to body, or from particle to particle through the air. When it passes through dense bodies it is unseen. When a wire makes part of the circle, in the explosion of the electrical phial, the fire, though in great quantity, passes in the wire invisibly; but in passing along a chain, it becomes visible as it leaps from link to link. In passing along leaf gilding it is visible: for the leaf-gold is full of pores; hold a leaf to the light and it appears like a net, and the fire is seen in it leaping over the vacancies.-And as when a long canal filled with still water is opened at one end, in order to be discharged, the motion of the water begins first near the opened end, and proceeds towards the close end, though the water itself moves from the close towards the opened end: so the electrical fire discharged into the polar regions, perhaps from a thousand leagues length of vapourised air, appears first where it is first in motion, i. e. in the most northern part, and the appearance proceeds southward, though the fire really moves northward. This is supposed to account for the au

37. When the gun-barrel, (in electrical experiments) has but little electrical fire in it, you must approach it very near with your knuckle before you can draw a spark. Give it more fire, and it will give a spark at a greater distance. Two gun-barrels united, and as highly electrified, will give a spark at a still greater distance. But if two gun-barrels electrified will strike at two inches dis-rora borealis. tance, and make a loud snap, to what a great distance may 10,000 acres of electrified cloud strike and give its fire, and how loud must be that crack?

41. When there is great heat on the land, in a particular region (the sun having shone on it perhaps several days, while the surrounding countries have been screened by clouds) 38. It is a common thing to see clouds at the lower air is rarified and rises, the cooler different heights passing different ways, denser air above descends; the clouds in that which shows different currents of air one un-air meet from all sides, and join over the heatder the other. As the air between the tropics ed place; and if some are electrified, others is rarified by the sun, it rises, the denser north-not, lightning and thunder succeed, and showern and southern air pressing into its place. ers fall. Hence thunder-gusts after heats, and The air so rarified and forced up, passes north-cool air after gusts; the water and the clouds ward and southward, and must descend in the that bring it, coming from a higher and therepolar regions, if it has no opportunity before, fore a cooler region. that the circulation may be carried on.

39. As currents of air, with the clouds therein, pass different ways, it is easy to conceive how the clouds, passing over each other, may attract each other, and so come near enough for the electrical stroke. And also how electrical clouds may be carried within land very far from the sea, before they have an opportunity to strike.

42. An electrical spark, drawn from an irregular body at some distance is scarcely ever strait, but shows crooked and waving in the air. So do the flashes of lightning; the clouds being very irregular bodies.

43. As electrified clouds pass over a country, high hills and high trees, lofty towers, spires, masts of ships, chimneys, &c., as so many prominences and points, draw the elec

trical fire, and the whole cloud discharges | nor altogether from agitated fire in the methere.

tals. For as whatever body can insinuate itself between the particles of metal, and overcome the attraction by which they cohere (as sundry menstrua can) will make the solid become a fluid, as well as fire, yet without heating it: so the electrical fire, or lightning, creating a violent repulsion between the particles of the metal it passes through, the metal is fused..

44. Dangerous, therefore, is it to take shelter under a tree, during a thunder-gust. It has been fatal to many, both men and beasts. 45. It is safer to be in the open field for another reason. When the clothes are wet, if a flash in its way to the ground should strike your head, it may run in the water over the surface of your body; whereas, if your clothes were dry, it would go through the body, 54. If you would, by a violent fire, melt off because the blood and other humours, con- the end of a nail, which is half driven into a taining so much water, are more ready con- door, the heat given the whole nail, before a ductors. part would melt, must burn the board it sticks Hence a wet rat cannot be killed by the ex-in; and the melted part would burn the floor ploding electrical bottle, when a dry rat may.* it dropped on. But if a sword can be melted 46. Common fire is in all bodies, more or in the scabbard, and money in a man's pocket less, as well as electrical fire. Perhaps they by lightning, without burning either, it must may be different modifications of the same be a cold fusion.* element; or they may be different elements. The latter is by some suspected.

47. If they are different things, yet they may and do subsist together in the same body. 48. When electrical fire strikes through a body, it acts upon the common fire contained in it, and puts that fire in motion; and if there be a sufficient quantity of each kind of fire, the body will be inflamed.

49. When the quantity of common fire in the body is small, the quantity of the electrical fire (or the electrical stroke) should be greater if the quantity of common fire be great, less electrical fire suffices to produce the effect.

50. Thus spirits must be heated before we can fire them by the electrical spark. If they are much heated, a small spark will do; if not, the spark must be greater.

51. Till lately we could only fire warm vapours: but now we can burn hard dry rosin. And when we can procure greater electrical sparks, we may be able to fire not only unwarmed spirits, as lightning does, but even wood, by giving sufficient agitation to the common fire contained in it, as friction we know will do.

52. Sulphureous and inflammable vapours, arising from the earth, are easily kindled by lightning. Besides what arise from the earth, such vapours are sent out by stacks of moist hay, corn, or other vegetables, which heat and reek. Wood, rotting in old trees or buildings, does the same. Such are therefore easily

and often fired.

[blocks in formation]

55. Lightning rends some bodies. The electrical spark will strike a hole through a quire of strong paper.

56. If the source of lightning, assigned in this paper be the true one, there should be little thunder heard at sea from land. And accordingly, some old sea-captains, of whom inquiry has been made, do affirm, that the fact agrees perfectly with the hypothesis; for that in crossing the great ocean, they seldom meet with thunder till they come into soundings; and that the islands far from the continent have very little of it. And a curious observer, who lived thirteen years at Bermudas, says, there was less thunder there in that whole time than he has sometimes heard in a month at Carolina.

To Peter Collinson, London.

Introductory Letter to some additional Papers.

PHILADELPHIA, July 29, 1750.

As you first put us on electrical experiments, by sending, to our Library Company a tube, with directions how to use it; and as our honourable proprietary enabled us to carry those experiments to a greater height, by his generous present of a complete electrical apparatus; it is fit that both should know, from time to time, what progress we make. It was in this view I wrote and sent you my former papers on this subject, desiring, that as I had not the honour of a direct correspondence with that bountiful benefactor to our library, they might be communicated to him through your hands. In the same view I write and send you this additional paper. If it happens to bring you nothing new, (which may well be, considering the number of ingenious men in

*These facts, though related in several accounts, are now doubted; since it has been observed that the parts of a bell-wire which fell on the floor, being broken and partly melted by lightning, did actually burn into the boards. (See Philosophical Transactions, vol. li. part i.) And Mr. Kinnersley has found that a fine iron wire melted by electricity, has had the same effect.

Europe, continually engaged in the same re- 7. But in common matter there is (genersearches) at least it will show, that the in-ally) as much of the electrical as it will construments put into our hands are not neglected; and that if no valuable discoveries are made by us, whatever the cause may be, it is not want of industry and application.—I am, sir, your much obliged humble servant,

B. FRANKLIN.

Opinions and conjectures, concerning the
Properties and Effects of the electrical
Matter, and the Means of preserving
Buildings, Ships, &c. from Lightning,
arising from Experiments and Observa-
tions made at Philadelphia, 1749-Golden
Fish.-Extraction of effluvial Virtues by
Electricity impracticable.

1. THE electrical matter consists of particles extremely subtile, since it can permeate common matter, even the densest metals, with such ease and freedom as not to receive any perceptible resistance.

2. If any one should doubt whether the electrical matter passes through the substance of bodies, or only over and along their surfaces, a shock from an electrified large glass jar, taken through his own body, will probably convince him.

tain within its substance. If more is added, it lies without upon the surface, and forms what we call an electrical atmosphere; and then the body is said to be electrified.

8. It is supposed, that all kinds of common matter do not attract and retain the electrical, with equal strength and force, for reasons to be given hereafter: and that those called electrics per se, as glass, &c. attract and retain it strongest, and contain the greatest quantity.

9. We know that the electrical fluid is in common matter, because we can pump it out by the globe or tube. We know that common matter has near as much as it can contain, because, when we add a little more to any portion of it, the additional quantity does not enter, but forms an electrical atmosphere.And we know that common matter has not (generally) more than it can contain, otherwise, all loose portions of it would repel each other, as they constantly do when they have electric atmospheres.

10. The beneficial uses of this electric fluid in the creation we are not yet well acquainted with, though doubtless such there are, and those very considerable; but we may see some pernicious consequences that would attend a much greater proportion of it. For, had this globe we live on, as much of it in

3. Electrical matter differs from common matter in this, that the parts of the latter mutually attract, those of the former mutually repel each other. Hence the appearing di-proportion as we can give to a globe of iron, vergency in a stream of electrified effluvia.

4. But though the particles of electrical matter do repel each other, they are strongly attracted by all other matter.*

wood or the like, the particles of dust and other light matters that get loose from it, would by virtue of their separate electrical atmospheres, not only repel each other, but 5. From these three things, the extreme be repelled from the earth, and not easily be subtilty of the electrical matter, the mutual brought to unite with it again; whence our repulsion of its parts, and the strong attraction air would continually be more and more clogbetween them and other matter, arise this ef-ged with foreign matter, and grow unfit for fect, that, when a quantity of electrical mat- respiration. This affords another occasion ter is applied to a mass of common matter, of for adoring that wisdom which has made all any bigness or length, within our observation things by weight and measure! (which hath not already got its quantity) it is immediately and equally diffused through the

whole.

11. If a piece of common matter be suspended entirely free from electrical matter, and a single particle of the latter be brought 6. Thus, common matter is a kind of spunge nigh, it will be attracted and enter the body to the electrical fluid. And as a spunge would and take place in the centre, or where the atreceive no water, if the parts of water were traction is every way equal. If more partinot smaller than the pores of the spunge; and cles enter, they take their places where the even then but slowly, if there were not a mu-balance is equal between the attraction of the tual attraction between those parts and the parts of the spunge; and would still imbibe it faster, if the mutual attraction among the parts of the water did not impede, some force being required to separate them; and fastest, if, instead of attraction, there were a mutual repulsion among those parts, which would act in conjunction with the attraction of the spunge: so is the case between the electrical and common matter.

common matter, and their own mutual repulsion. It is supposed they form triangles, whose sides shorten as their number increases; till the common matter has drawn in so many, that its whole power of compressing those triangles by attraction, is equal to their whole power of expanding themselves by repulsion; and then will such piece of matter receive no more.

12. When part of this natural proportion

* See the ingenious Essays on Electricity, in the of electrical fluid is taken out of a piece of

Transactions, by Mr. Ellicot.

common matter, the triangles formed by the

tual repulsion of the parts, until they occupy the whole piece.

remainder, are supposed to widen by the mu- | an electrical atmosphere communicated to it, and we consider every side as a base on which the particles rest, and by which they are attracted, one may see, by imagining a line from A to F, and another from E to G, that the portion of the atmosphere included in F, A, E, G, has the line A, E, for its basis. So the portion of atmosphere included in H, A, B, I, has the line A, B for its basis. And like

13. When the quantity of electrical fluid, taken from a piece of common matter, is restored again, it enters the expanded triangles, being again compressed till there is room for the whole.

14. To explain this: take two apples, or two balls of wood or other matter, each hav-wise the portion included in K, B, C, L, has ing its own natural quantity of the electrical B, C, to rest on; and so on the other side of fluid. Suspend them by silk lines from the the figure. Now if you would draw off this ceiling. Apply the wire of a well-charged atmosphere with any blunt, smooth body, and phial, held in your hand, to one of them (A approach the middle of the side A, B, you Fig. 7,) and it will receive from the wire a must come very near, before the force of quantity of the electrical fluid; but will not your attractor exceeds the force or power with imbibe it, being already full. The fluid there- which that side holds its atmosphere. But fore will flow round its surface, and form an | there is a small portion between I, B, K, that electrical atmosphere. Bring A into contact has less of the surface to rest on, and to be with B, and half the electrical fluid is com- attracted by, than the neighbouring portions, municated, so that each has now an electrical while at the same time there is a mutual reatmosphere, and therefore they repel each pulsion between its particles, and the particles other. Take away these atmospheres, by touch- of those portions; therefore here you can get ing the balls, and leave them in their natural it with more ease, or at a greater distance. state; then having fixed a stick of sealing-wax Between F, A, H, there is a larger portion to the middle of the phial to hold it by, apply that has yet a less surface to rest on, and to the wire to A, at the same time the coating attract it; here, therefore, you can get it touches B. Thus will a quantity of the elec-away still more easily. But easiest of all trical fluid be drawn out of B, and thrown on A. So that A will have a redundance of this fluid, which forms an atmosphere round, and B an exactly equal deficiency. Now, bring these balls again into contact, and the electrical atmosphere will not be divided between A and B, into two smaller atmospheres as before; for B will drink up the whole atmosphere of A, and both will be found again in their natural state.

15. The form of the electrical atmosphere is that of the body it surrounds. This shape may be rendered visible in a still air, by raising a smoke from dry rosin dropt into a hot tea-spoon under the electrified body, which will be attracted, and spread itself equally on all sides, covering and concealing the body.* And this form it takes, because it is attracted by all parts of the surface of the body, though it cannot enter the substance already replete. Without this attraction, it would not remain round the body, but dissipate in the air.

16. The atmosphere of electrical particles surrounding an electrified sphere, is not more disposed to leave it, or more easily drawn off from any one part of the sphere than another, because it is equally attracted by every part. But that is not the case with bodies of any other figure. From a cube it is more easily drawn at the corners than at the plain sides, and so from the angles of a body of any other form, and still most easily from the angle that is most acute. Thus, if a body shaped as A, B, C, D, E, in Fig. 8, be electrified, or have

* See the second letter of date July 11, 1747.

between L, C, M, where the quantity is largest, and the surface to attract and keep it back the least. When you have drawn away one of these angular portions of the fluid, another succeeds in its place, from the nature of fluidity, and the mutual repulsion beforementioned; and so the atmosphere continues flowing off at such angle, like a stream, till no more is remaining. The extremities of the portions of atmosphere over these angular parts, are likewise at a greater distance from the electrified body, as may be seen by the inspection of the above figure; the point of the atmosphere of the angle C, being much farther from C than any other part of the atmosphere over the lines C, B, or B, A: and, besides the distance arising from the nature of the figure, where the attraction is less, the particles will naturally expand to a greater distance by their mutual repulsion. On these accounts we suppose electrified bodies discharge their atmospheres upon unelectrified bodies more easily, and at a greater distance from their angles and points than from their smooth sides.-Those points will also discharge into the air, when the body has too great an electrical atmosphere, without bringing any non-electric near, to receive what is thrown off: for the air, though an electric per se, yet has always more or less water and other nonelectric matters mixed with it: and these attract and receive what is so discharged.

17. But points have a property, by which they draw on, as well as throw off the elec trical fluid, at greater distances than blunt bodies can. That is, as the pointed part of an

« AnteriorContinuar »