Abbildungen der Seite
PDF
EPUB

53. Metals are often melted by lightning, though perhaps not from heat in the lightning, nor altogether from agitated fire in the metals. 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.

54. If you would, by a violent fire, melt.off the end of a nail, which is half driven into a door, the heat given the whole nail, before a part would melt, must burn the board it sticks in; and the melted part would burn the floor it dropped on. But, if a sword can be melted in the scabbard, and money in a man's pocket by lightning, without burning either, it must be a cold fusion.*

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 far from land. And accordingly some old seacaptains, 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.

* These facts, though related in several accounts, are now doubted; sinee 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.

TO PETER COLLINSON.

Accumulation of the Electrical Fire proved to be in the electrified Glass. Effect of Lightning on the Needle of Compasses explained. Gunpowder fired by the Electric Flame.

Philadelphia, 27 July, 1750.

Sir,

Mr. Watson, I believe, wrote his Observations on my last paper in haste, without having first well considered the experiments, related ^ 17,* which still appear to me decisive in the question, Whether the accumulation of the electrical fire be in the electrified glass, or in the non-electric matter connected urith the glass? and to demonstrate that it is really in the glass.

As to the experiment that ingenious gentleman mentions, and which he thinks conclusive on the other side, I persuade myself he will change his opinion of it, when he considers, that, as one person applying the wire of the charged bottle to warm spirits, in a spoon held by another person, both standing on the floor, will fire the spirits, and yet such firing will not determine whether the accumulation was in the glass or the non-electric; so the placing another person between them, standing on wax, with a basin in his hand, into which the water from the phial is poured, while he at the instant of pouring presents a finger of his other hand to the spirits, does not at all alter the case; the stream from the phial,

• See the paper entitled, Farther Experiments, &c.

the side of the basin, with the arms and body of the person on the wax, being altogether but as one long wire, reaching from the internal surface of the phial to the spirits.

June 29th, 1751. In Captain Waddell's account of the effects of lightning on his ship, I could not but take notice of the large comazants, (as he calls them), that settled on the spintles at the top-mast heads, and burned like very large torches (before the stroke). According to my opinion, the electrical fire was then drawing off", as by points, from the cloud; the largeness of the flame betokening the great quantity of electricity in the cloud; and, had there been a good wire communication from the spintle heads to the sea> that could have conducted more freely than tarred ropes, or masts of turpentine wood, I imagine there would either have been no stroke, or, if a stroke, the wire would have conducted it all into the sea without damage to the ship.

His; compasses lost the virtue of the loadstone, or the poles were reversed, the north point turning to the south. By electricity we have (here at Philadelphia) frequently given polarity to needles, and reversed it at pleasure. Mr. Wilson, at London, tried it on too large masses, and with too small force.

A shock from four large glass jars, sent through a fine sewing-needle, gives it polarity, and it will traverse when laid on water. If the needle, when struck, lies east and west, the end entered by the electric blast points north. If it lies north and south, the end that lay towards the north will continue to point north when placed on water, whether the fire entered at that end, or at the contrary end.

The polarity given is strongest when the needle is struck lying north and south; weakest, when lying east and west. Perhaps if the force was still greater, the south end, entered by the fire (when the needle lies north and south) might become the north, otherwise it puzzles us to account for the inverting of compasses by lightning; sinqe their needles must always be found in ,thdt situation, and by our little experiments, whether the blast entered the north and went out at the south end of the needle, or the contrary, still the end that lay to the north should continue to point north.

In these experiments the ends of the needle are sometimes finely blued, like a watch-spring, by the electric flame. This color, given by the flash from two jars only, will wipe off; but four jars fix it, and frequently melt the needles. I send you some, that have had their heads and points melted off by our mimic lightning; and a pin, that had its point melted off, and some part of its head and neck run. Sometimes the surface on the body of the needle is also run, and appears blistered when examined by a magnifying-glass. The jars I make use of hold seven or eight gallons, and are coated and lined with tin-foil; each of them takes a thousand turns * of a globe nine inches diameter to charge it.

•I send you two specimens of tin-foil melted between glass, by the 'force of two jars only.

I have not heard that any of your European electricians have ever been able to fire gunpowder by the electric flame. We do it here in this manner; a small cartridge is filled with dry powder, hard rammed, so^ as to bruise some of the grains; two pointed wires are then thrust in, one at each end, the points approaching

* The cushion being afteswards cevered with a long flap of buckskin; which might cling to the globe, and care being taken to keep that flap of a due temperature, between too dry and too moist, we found so much more of the electric fluid was obtained, as that one hundred and fifty turns were sufficient. 1753.

Vol. v. 29

each other in the middle of the cartridge till within the distance of half an inch ; then, the cartridge being placed in the circuit, when the four jars are discharged, the electric flame leaping from the point of one wire to the point of the other, within the cartridge amongst the powder, fires it, and the explosion of the powder is at the same instant with the crack of the discharge. Yours, &c.

B. Franklin.

[graphic]

TO PETER COLLlNSON.

Introductory Letter to some additional Papers.

PhUadelphia, 29 July, 1750.

Sir,

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 honorable 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 honor 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 Europe, continually engaged in the same researches,) at least it will show, that the instruments 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.

« ZurückWeiter »