Imágenes de página
PDF
ePub
[ocr errors]
[ocr errors]

In September 1752, I erected an iron rod | and, having placed them properly, I beheld, ! to draw the lightning down into my house, in with great surprise and pleasure, the cork bali

order to make some experiments on it, with play briskly between them; and was convinc

two bells to give notice when the rod should ed that one bottle was electrised negatively. i be electrified; a contrivance obvious to every I repeated this experiment several times i electrician,

during the gust, and in eight succeeding I found the bells rang sometimes when gusts, always with the same success; and be there was no lightning or thunder, but only a ing of opinion (for reasons I formerly gave in | dark cloud over the rod; that sometimes af- my letter to Mr. Kinnersley, since printed in

ter a flash of lightning they would suddenly London) that the glass globe electrises posi| stop; and at other times, when they had not lively, I concluded that the clouds are always

rang before, they would, after a flash, sudden- electrised negatively, or have always in them

ly begin to ring; that the electricity was less than their natural quantity of the electric | sometimes very faint, so that when a small fluid.

spark was obtained, another could not be got Yet notwithstanding so many experiments, for some time after; at other times the sparks it seems I concluded too soon ; for at last, would follow extremely quick, and once I had June the 6th, in a gust which continued from a continual stream from bell to bell, the size five o'clock, P. M. to seven, I met with one of a crow quill: even during the same gust cloud that was electrised positively, though there were considerable variations.

several that passed over my rod before, during In the winter following I conceived an ex- the same gust, were in the negative state. periment, to try whether the clouds were This was thus discovered. electrified positively or negatively; but my I had another concurring experiment, which pointed rod, with its apparatus, becoming out I often repeated, to prove the negative state of order, I did not refit it till towards the of the clouds, viz. while the bells were ring. spring, when I expected the warm weather ing, I took the phial charged from the glass would bring on more frequent thunder-clouds. globe, and applied its wire to the erected rod,

The experiment was this: to take two phi- considering, that if the clouds were electrisals; charge one of them with lightning from ed positively, the rod which received its electhe iron rod, and give the other an equal tricity from them must be so too; and then charge by the electric glass globe, through the additional positive electricity of the phial the prime conductor: when charged, to place would make the bells ring faster :--but, if the them on a table within three or four inches clouds were in a negative state, they must of each other, a small cork ball being suspend- exhaust the electric fluid from my rod, and ed by a fine silk thread from the ceiling, so bring that into the same negative state with as it might play between the wires. If both themselves, and then the wire of a positively bottles then were electrified positively, the charged phial, supplying the rod with what it ball being attracted and repelled by one, wanted (which it was obliged otherwise to must be also repelled by the other. If the draw from the earth by means of the penduone positively, and the other negatively; then lous brass ball playing between the two bells) the ball would be attracted and repelled al- the singing would cease till the bottle was ternately by each, and continue to play be discharged. tween them as long as any considerable charge In this manner I quite discharged into the remained.

rod several phials, that were charged from Being very intent on making this experi- the glass globe, the electric fluid streaming ment, it was no small mortification to me, that from the wire to the rod, till the wire would I happened to be abroad during two of the receive no spark from the finger; and, dur. greatest thunder-storms we had early in the ing this supply, to the rod from the phial, the spring, and though I had given orders in my bells stopped ringing; but by continuing the family, that if the bells rang when I was from application of the phial wire to the rod, I exhome, they should catch some of the lightning hausted the natural quantity from the inside for me in electrical phials, and they did so, yet surface of the same phials, or, as I call it, it was mostly dissipated before my return, and charged them negatively. in some of the other gusts, the quantity of Ať length, while I was charging a phial by lightning I was able to obtain was so small, my glass globe, to repeat this experiment, my and the charge so weak, that I could not sa- bells, of themselves, stopped ringing, and aftisfy myself: yet I sometimes saw what ter some pause, began to ring again.-But heightened my suspicions, and inflamed my now, when I approached the wire of the curiosity.

charged phial to the rod, instead of the usual At last, on the 12th of April, 1753, there stream that I expected from the wire to the being a smart gust of some continuance, Irod, there was no spark; not even when I charged one phial pretty well with lightning, brought the wire and the rod to touch; yet and the other equally, as near as I could the bells continued ringing vigorously, which judge, with electricity from my glass globe; / proved to me, that the rod was then positively

electrified, as well as the wire of the phial, That this natural quantity is not the same and equally so; and consequently, that the in all kinds of common matter under the particular cloud then over the rod was in same dimensions, nor in the same kind of the same positive state. This was near the common matter in all circumstances; but a end of the gust.

solid foot, for instance, of one kind of common But this was a single experiment, which, matter, may contain more of the electric fluhowever, destroys my first too general con- id than a solid foot of some other kind of clusion, and reduces me to this: That the common matter; and a pound weight of the clouds of a thunder-gust are most commonly same kind of common matter may, when in a negative state of electricity, but some- in a rarer state, contain more of the electric times in a positive state.

fluid than when in a denser state. The latter I believe is rare; for though 1 For the electric fluid, being attracted by soon after the last experiment set out on a any portion of common matter, the parts of journey to Boston, and was from home most that fluid, (which have among themselves a part of the summer, which prevented my mutual repulsion) are brought so near to each making farther trials and observations; yet other by the attraction of the common matter Mr. Kinnersley returning from the islands that absorbs them, as that their repulsion is just as I left home, pursued the experiments equal to the condensing power of attraction in during my absence, and informs me that he common matter; and then such portion of always found the clouds in the negative state. common matter will absorb no more.

So that, for the most part, in thunder Bodies of different kinds having thus atstrokes, it is the earth that strikes into the tracted and absorbed what I call ther natural clouds, and not the clouds that strike into the quantity, i. e. just as much of the electric fluearth.

id as is suited to their circumstances of denThose who are versed in electric experi- sity, rarity, and power of attracting, do not ments, will easily conceive, that the effects then show any signs of electricity among each and appearances must be nearly the same in other. either case; the same explosion, and the same And if more electric fluid be added to one flash between one cloud and another, and be- of these bodies, it does not enter, but spreads tween the clouds and mountains, &c. the on the surface, forming an atmosphere; and same rending of trees, walls, &c. which the then such body shows signs of electricity. electric fluid meets with in its passage, and I have in a former paper compared common the same fatal shock to animal bodies; and matter to a sponge, and the electric fluid to that pointed rods fixed on buildings, or masts water: I beg leave once more to make use of ships, and communicating with the earth of the same comparison, to illustrate farther or sea, must be of the same service in restor- my meaning in this particular. ing the equilibrium silently between the When a sponge is somewhat condensed by earth and clouds, or in conducting a flash or being squeezed between the fingers, it will stroke, if one should be, so as to save harmless not receive and retain so much water as when the house or vessel : for points have equal in its more loose and open state. power to throw off, as to draw on the electric If more squeezed and condensed, some of fire, and rods will conduct up as well as the water will come out of its inner parts, down.

and flow on the surface. But though the light gained from these ex If the pressure of the fingers be entirely periments makes no alteration in the practice, removed, the sponge will not only resume it makes a considerable one in the theory. what was lately forced out, but attract an adAnd now we as much need an hypothesis to ditional quantity, explain by what means the clouds become As the sponge in its rarer state will natunegatively, as before to show how they be- rally attract and absorb more water, and in its came positively electrified.

denser state will naturally attract and absorb I cannot forbear venturing some few con- less water; we may call the quantity it atjectures on this occasion; they are what oc- tracts and absorbs in either state, its natural cur to me at present, and though future dis- quantity, the state being considered. coveries should prove them not wholly right, Now what the sponge is to water, the yet they may in the mean time be of some same is water to the electric fluid. use, by stirring up the curious to make more When a portion of water is in its common experiments, and occasion more exact disqui- dense state, it can hold no more electric Auid sitions.

than it has: if any be added, it spreads on the I conceive then, that this globe of earth and surface. water, with its plants, animals, and buildings, When the same portion of water is rarified have diffused throughout their substance, a into vapour, and forms a cloud, it is then caquantity of the electric fluid, just as much as pable of receiving and absorbing a much they can contain, which I call the natural greater quantity ; there is room for each parquantity.

ticle to have an electric atmosphere.

Thus water, in its rarified state, or in the can, I gave it a spark, which flowed round in form of a cloud, will be in a negative state of an electric atmosphere; and the lock of cotton electricity ; it will have less than its natural was repelled from the side of the can to the quantity; that is, less than it is naturally ca- distance of about nine or ten inches. The pable of attracting and absorbing in that state. can would not then receive another spark

Such a cloud then, coming so near the from the wire of the phial: but as I gradually earth as to be within the striking distance, drew up the chain, the atmosphere of the can will receive from the earth a flash of the elec- diminished by flowing over the rising chain, tric fluid; which flash, to supply a great ex- and the lock of cotton accordingly drew nearer tent of cloud, must sometimes contain a very and nearer to the can; and then, if I again great quantity of that fluid.

brought the phial wire near the can, it would Or such a cloud, passing over woods of tall receive another spark, and the cotton fly off trees, may from the points and sharp edges of again to its first distance; and thus, as the their moist top leaves, receive silently some chain was drawn higher, the can would resupply.

ceive more sparks; because the can and exA cloud being by any means supplied from tended chain were capable of supporting a the earth, may strike into other clouds that greater atmosphere than the can with the have not been supplied, or not so much sup- chain gathered ap into its belly. And that plied ; and those to others, till an equilibrium the atmosphere round the can was diminished is produced among all the clouds that are by raising the chain, and increased again by within striking distance of each other. lowering it, is not only agreeable to reason,

The cloud thus supplied having parted with since the atmosphere of the chain must be much of what it first received, may require drawn from that of the can, when it rose, and and receive a fresh supply from the earth, or returned to it again when it fell; but was from some other cloud, which by the wind is also evident to the eye, the lock of cotton albrought into such a situation as to receive it ways approaching the can when the chain was more readily from the earth.

drawn up, and receding when it was let down Hence repeated and continual strokes and again. flashes till the clouds have all got nearly their Thus we see that increase of surface makes natural quantity as clouds, or till they have a body capable of receiving a greater electric descended in showers, and are united again atmosphere: but this experiment does not, I with this terraqueous globe, their original

. own, fully demonstrate my new hypothesis; Thus, thunder-clouds are generally in a for the brass and silver still continue in their negative state of electricity compared with solid state, and are not rarified into vapour, as the earth, agreeable to most of our experi- the water is in clouds. Perhaps some future ments; yet as by one experiment we found a experiments on vapourised water may set this cloud clectrised positively, I conjecture that matter in a clearer light. in that case, such cloud, after having received One seemingly material objection arises to what was, in its rare state, only its natural the new hypothesis, and it is this: if water, quantity, became compressed by the driving in its rarified state, as a cloud, requires, and winds, or some other means, so that part of will absorb more of the electric fluid than what it had absorbed was forced out, and form- when in its dense state as water, why does it ed an electric atmosphere around it in its den- not acquire from the earth all it wants at the ser state. Hence it was capable of commu- instant of its leaving the surface, while it is nicating positive electricity to my rod. yet near, and but just rising in vapour ? To

To show that a body in different circum- this difficulty I own I cannot at present give stances of dilatation and contraction is capable a solution satisfactory to myself: I thought, of receiving and retaining more or less of the however, that I ought to state it in its full electric fluid on its surface, I would relate the force, as I have done, and submit the whole to following experiment: I placed a clean wine examination. glass on the floor, and on it a small silver can. And I would beg leave to recommend it to In the can I put about three yards of brass the curious in this branch of natural philoso chain; to one end of which I fastened a silk phy, to repeat with care and accurate obserthread, which went right up to the ceiling, vation the experiments I have reported in this where it passed over a pulley, and came down and former papers relating to positive and again to my hand, that I might at pleasure negative electricity, with such other relative draw the chain up out of the can, extending ones as shall occur to them, that it may be it till within a foot of the ceiling, and let it certainly known whether the electricity comgradually sink into the can again. From the municated by a glass globe, be really positive. ceiling, by another thread of fine raw silk, 1 And also I would request all who may have an suspended a small light lock of cotton, so as opportunity of observing the recent effects of that when it hung perpendicularly, it came in lightning on buildings, trees, &c. that they contact with the side of the can. Then ap- would consider them particularly with a view proaching the wire of a charged phial to the to discover the direction. But in these ex

aminations, this one thing is always to be un- little more than the colour of gold, and on an derstood, viz. that a stream of the electric fluid octavo book is not in the whole an inch square, passing through wood, brick, metal, &c. while and therefore not the thirty-sixth part of a such fluid passes in small quantity, the mu- grain, according to M. Reaumur; yet it is tually repulsive power of its parts is confined sufficient to conduct the charge of five large and overcome by the cohesion of the parts of jars, and how many more I know not. Now, the body it passes through, so as to prevent I suppose a wire of a quarter of an inch diaan explosion ; but when the fluid comes in a meter to contain about five thousand times as quantity too great to be confined by such co much metal as there is in that gold line, and hesion, it explodes, and rends or fuses the body if so, it will conduct the charge of twenty-five that endeavoured to confine it. If it be wood, thousand such glass jars, which is a quantity, brick, stone, or the like, the splinters will fly I imagine, far beyond what was ever contained off on that side where there is least resistance. in any one stroke of natural lightning. But And thus, when a hole is struck through paste- a rod of half an inch diameter would conduct board by the electrified jar, if the surfaces of four times as much as one of a quarter. the pasteboard are not confined or compressed, And with regard to conducting, though a there will be a bur raised all round the hole certain thickness of metal be required to conon both sides the pasteboard ; but if one side duct a great quantity of electricity, and, at the be confined, so that the bur cannot be raised same time, keep its own substance firm and on that side, it will be all raised on the other, unseparated; and a less quantity, as a very which way soever the fluid was directed. For small wire for instance, will be destroyed by the bur round the outside of the hole, is the the explosion; yet such small wire will have effect of the explosion every way from the answered the end of conducting that stroke, centre of the stream, and not an effect of the though it becomes incapable of conducting direction.

another. And considering the extreme rapiIn every stroke of lightning, I am of opi- dity with which the electric fluid moves withnion that the stream of the electric fluid, out exploding, when it has a free passage, or moving to restore the equilibrium between the complete metal communication, I should think cloud and the earth, does always previously a vast quantity would be conducted in a short find its passage, and mark out, as I may say, time, either to or from a cloud, to restore its its own course, taking in its way all the con- equilibrium with the earth, by means of a very ductors it can find, such as metals, damp walls, small wire: and therefore thick rods should moist wood, &c. and will go considerably out seem not so necessary:~However, as the of a direct course, for the sake of the assist- quantity of lightning discharged in one stroke, ance of good conductors; and that, in this cannot well be measured, and, in different course, it is actually moving, though silently strokes, is certainly very various, in some and imperceptibly, before the explosion, in much greater than others; and as iron (the and among the conductors: which explosion best metal for the purpose, being least apt to happens only when the conductors cannot dis- fuse) is cheap, it may be well enough to procharge it as fast as they receive it, by reason vide a larger canal to guide that impetuous of their being incomplete, disunited, too small, blast than we may imagine necessary : for, or not of the best materials for conducting though one middling wire may be sufficient, Metalline rods, therefore, of sufficient thick- two or three can do no harm. And time, ness, and extending from the highest part of with careful observations well compared, will an edifice to the ground, being of the best at length point out the proper size to greater materials and complete conductors, will, I certainty. think, secure the building from damage, either Pointed rods erected on edifices may likeby restoring the equilibrium so fast as to pre-wise often prevent a stroke, in the following vent a stroke, or by conducting it in the sub- manner: an eye so situated as to view horistance of the rod as far as the rod goes, so that zontally the under side of a thunder-cloud, there shall be no explosion but what is above will see it very ragged, with a number of seits point, between that and the clouds. parate fragments, or petty clouds, one under

If it be asked, what thickness of a metalline another, the lowest sometimes not far from the rod may be supposed sufficient ? In answer, I earth. These, as so many stepping stones, aswould remark, that five large glass jars, such sist in conducting a stroke between the cloud as I have described in my former papers, dis- and a building. To represent these by an excharge a very great quantity of electricity, periment, take two or three locks of fine loose which nevertheless will be all conducted cotton, connect one of them with the prime round the corner of a book, by the fine fillet- conductor by a fine thread of two inches ing of gold on the cover, it following the gold (which may be spun out of the same lock by the farthest way about, rather than take the the fingers) another to that, and the third to shorter course through the cover, that not be the second, by like threads.-Turn the globe ing so good a conductor. Now in this line of and you will see these locks extend themselves gold, the metal is so extremely thin as to be towards the table (as the lower small clouds

nomena.

EXPERIMENT I.

do towards the earth) being attracted by it: I used. When your bells are ringing, pass & but on presenting a sharp point erect under rubbed tube by the edge of the bell

, connectthe lowest, it will shrink up to the second, the ed with your pointed rod : if the cloud is then second to the first, and all together to the in a negative state, the ringing will stop; if prime conductor, where they will continue as in a positive state, it will continue, and perhaps long as the point continues under them. May be quicker. Or, suspend a very small corknot, in like manner, the small electrised clouds, ball by a fine silk thread, so that it may hang whose equilibrium with the earth is soon re- close to the edge of the rod-bell: then whenstored by the point, rise up to the main body, ever the bell is electrified, whether posiand by that means occasion so large a vacan- tively or negatively, the little ball will be recy, as that the grand cloud cannot strike in pelled, and continue at some distance from that place?

the bell. Have ready a round headed glass These thoughts, my dear friend, are many stopper of a decanter, rub it on your side till of them crude and hasty; and if I were mere- it is electrified, then present it to the corkly ambitious of acquiring some reputation in ball. If the electricity in the ball is positive, philosophy, I ought to keep them by me, till it will be repelled from the glass stopper as corrected and improved by time, and farther well as from the bell. If negative it will fly experience. But since even short hints and to the stopper.

B. FRANKLIN. imperfect experiments in any new branch of science, being communicated, have oftentimes a good effect, in exciting the attention of the ingenious to the subject, and so become the

Electrical Experiments. occasion of more exact disquisition, and more With an attempt to account for their several phecomplete discoveries, you are at liberty to

Together with some observations on communicate this paper to whom you please ;

thunder-clouds, in further confirmation of Dr. it being of more importance that knowledge

Franklin's observations on the positive and should increase, than that your friend should

negative electrical state of the clouds, by John

Canton, M. A. and F. R. S. be thought an accurate philosopher.

Dec. 6, 1753. B. FRANKLIN.

From the ceiling, or any convenient part

of a room, let two cork-balls, each about the To Peter Collinson.

bigness of a small pea, be suspended by linen Additional proofs of the positive and negative threads of eight or nine inches in length, so

state of Electricity in the Clouds.New method as to be in contact with each other. Bring the of ascertaining it.

excited glass tube under the balls, and they PHILADELPHIA, April 18, 1754.

will be separated by it, when held at the dis SINCE September last, having been abroad tance of three or four feet; let it be brought on two long journies, and otherwise much en- nearer, and they will stand farther apart; engaged, I have made but few observations on tirely withdraw it, and they will immediately the positive and negative state of electricity come together. This experiment may be in the clouds. But Mr. Kinnersley kept his made with very small brass balls hung by silrod and bells in good order, and has made ver wire; and will succeed as well with sealmany.

ing wax made electrical, as with glass. Once this winter the bells rang a long time during a fall of snow, though no thunder was heard, nor lightning seen. Sometimes the If two cork-balls be suspended by dry silk flashes and cracks of the electric matter be- threads, the excited tube must be brought tween bell and bell were so large and loud within eighteen inches before they will repel as to be heard all over the house: but by all each other; which they will continue to do, his observations, the clouds were constant for some time, after the tube is taken away. ly in a negative state, till about six weeks As the balls in the first experiment are not ago, when he found them once to change in a insulated, they cannot properly be said to be few minutes from the negative to the positive. electrified: but when they hang within the About a fortnight after that, he made another atnosphere of the excited tube, they may atobservation of the same kind; and last Mon- tract and condense the electrical fluid round day afternoon, the wind blowing hard at S. E. about them, and be separated by the repuland veering round to N. E. with many thick sion of its particles. It is conjectured also, driving clouds, there were five or six succes- that the balls at this time contain less than sive changes from negative to positive, and their common share of the electrical fluid, on from positive to negative, the bells stopping a account of the repelling power of that which minute or two between every change. Be surrounds them; though some, perhaps, is sides the methods mentioned in my paper continually entering and passing through the of September last, of discovering the electri- threads. And if that be the case, the reason cal state of the clouds, the following may be is plain why the balls huog, by silk, in the VOL. II. ...20

25

EXPERIMENT II.

« AnteriorContinuar »