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pelling it in all directions, raise the column and thickest part may not be sensibly warmer in the tube K, up to d, or thereabouts; and than before. the charge of the above-mentioned case of And when trees or houses are set on fire bottles will raise it to the top of the tube.-- by the dreadful quantity which a cloud, or the Upon the air's coalescing, the column, by its earth, sometimes discharges, must not the heat, gravity, instantly subsides, till it is in equili- by which the wood is first kindled, be
genebrio with the rarefied air; it then gradually rated by the lightning's violent motion, descends as the air cools, and settles where through the resisting combustible matter ? it stood before. By carefully observing at If lightning, by its rapid motion, produces what height above the gage-wire b, the de- heat in itself; as well as in other bodies (and scending column first stops, the degree of that it does I think is evident from some of rarefaction is discovered, which, in great ex- the foregoing experiments made with the plosions, is very considerable.
thermometer) then its sometimes singeing the I hung in the thermometer, successively, a hair of animals killed by it, may easily be acstrip of wet writing paper, a wet flaxen and counted for. And the reasons of its not alwoollen thread, a blade of green grass, a fila- ways doing so, may, perhaps, be this: the ment of green wood, a fine silver thread, a quantity, though sufficient to kill a large anivery small brass wire, and a strip of gilt pa- mal, may sometimes not be great enough, or per; and found that the charge of the above- not have met with resistance enough, to bementioned glass jar, passing through each of come, by its motion, burning hot. these, especially the last, produced heat We find that dwelling-houses, struck with enough to rarefy the air very perceptibly. lightning, are seldom set on fire by it; but
I then suspended, out of the thermometer, when it passes through barns, with hay or a piece of small harpsichord wire, about twen- straw in them, or store-houses, containing ty-four inches long, with a pound weight at large quantities of hemp, or such like matter, the lower end, and sent the charge of the they seldom, if ever, escape a conflagration; case of five and thirty bottles through it, which may, perhaps, be owing to such comwhereby I discovered a new method of wire-bustibles being apt to kindle with a less dedrawing. The wire was red hot the whole gree of heat than is necessary to kindle wood. length, well annealed, and above an inch We had four houses in this city, and a veslonger than before. A second charge melted sel at one of the wharfs, struck and damaged it; it parted near the middle, and measured, by lightning last summer. One of the houses when the ends were put together, four inches was struck twice in the same storm. But I longer than at first. This experiment, I re- have the pleasure to inform you, that your member, you proposed to me before you left method of preventing such terrible disasters, Philadelphia; but I never tried it till now. has, by a fact which had like to have escaped That I might have no doubt of the wire's be our knowledge, given a very convincing proof ing hot as well as red, I repeated the experi- of its great utility, and is now in higher rement on another piece of the same wire en- pute with us than ever. s compassed with a goose-quill, filled with loose Hearing, a few days ago, that Mr. William grains of gunpowder; which took fire as rea- West, merchant in this city, suspected that dily as if it had been touched with a red hot the lightning in one of the thunder-storms poker. Also tinder, tied to another piece of last summer had passed through the iron conthe wire, kindled by it. I tried a wire about ductor, which he had provided for the securithree times as big, but could produce no such ty of his house; I waited on him, to inquire effects with that.
what ground he might have for such suspiHence it appears that the electric fire, cion. Mr. West informed me, that his famithough it has no sensible heat when in a state ly and neighbours were all stunned with a of rest, will, by its violent motion, and the re- very terrible explosion, and that the flash and sistance it meets with, produce heat in other crack were seen and heard at the same inbodies when passing through them, provided stant. Whence he concluded, that the lightthey be small enough. A large quantity will ning must have been very near, and, as no pass through a large wire, without producing house in the neighbourhood had suffered by it, any sensible heat; when the same quantity that it must have passed through his conductpassing through a very small one, being there or. Mr. White, his clerk, told me that he confined to a narrower passage, the particles was sitting at the time, by, a window about crowding closer together, and meeting with two feet distant from the conductor, leaning greater resistance, will make it red hot, and against the brick wall with which it was even melt it.
in contact; and that he felt a smart sensation Hence lightning does not melt metal by a like an electric shock, in that part of the bocold fusion, as we formerly supposed; but, dy which touched the wall. Mr. West furwhen it passes through the blade of a sword, ther informed me, that a person of undoubted if the quantity be not very great, it may heat veracity assured him, that, being in the door the point so as to melt it, while the broadest of an opposite house, on the other side of WaVOL. II. ...2 Q
ter-street (which you know is but narrow) he your acceptance of the best representation I saw the lightning diffused over the pavement can give of it, which you will find by the side which was then very wet with rain, to the of the thermometer, drawn in its full dimendistance of two or three yards from the foot sions as it now appears. The dotted lines of the conductor; and that another person of above are intended to show the form of the very good credit told him, that he being a wire before the lightning melted it. few doors off on the other side of the street, And now, sir, I most heartily congratulate saw the lightning above, darting in such di- you on the pleasure you must have in finding rection that it appeared to him to be directly your great and well grounded expectations so over that pointed rod.
far fulfilled. May this method of security Upon receiving this information, and being from the destructive violence of one of the desirous of further satisfaction, there being no most awful powers of nature meet with such traces of the lightning to be discovered in the further success, as to induce every good and conductor, as far as we could examine it be greatful heart to bless God for the important low, I proposed to Mr. West our going to the discovery! May the benefit thereof be diftop of the house, to examine the pointed rod, fused over the whole globe! May it extend to assuring him, that if the lightning had passed the latest posterity of mankind, and make the through it, the point must have been melted ; name of FRANKLIN, like that of NEW. and to our great satisfaction, we found it so. TON, immortal. This iron rod extended in height about nine
EBEN. KINNERSLEY. feet and a half above a stack of chimnies to which it was fixed (though I suppose
three or four feet would have been sufficient.) It was
To Mr. Kinnersley. somewhat more than half an inch diameter in Answer to some of the foregoing subjects.—How the thickest part, and tapering to the upper
long the Leyden bottle may be kept charged.end. The conductor, from the lower end of
Heated glass rendered permeable by the electric fluid.
Electrical attraction and repulsion.it to the earth, consisted of square iron nail
Reply to other subjects in the preceding paper. rods, not much above a quarter of an inch Numerous ways of kindling fire.-Explo thick, connected together by interlinking sion of water.--Knobs and points. joints. It extended down the cedar roof to
LONDON, February 20, 1762. the eaves, and from thence down the wall
I RECEIVED your ingenious letter of the of the house, four story and a half, to the 12th of March last, and thank you cordially pavement in Water-street, being fastened to for the account you give me of the new exthe wall in several places by small iron hooks.periments you have lately made in electriThe lower end was fixed to a ring in the top city. It is a subject that still affords me pleaof an iron stake that was drove about four or sure, though of late I have not much attendfive feet into the ground.
ed to it. The above-mentioned iron rod had a hole Your second experiment, in which you atin the top of it, about two inches deep, where tempted, without success, to communicate in was inserted a brass wire, about two lines positive electricity by vapour ascending from thick, and when first put there, about ten the electrised water, reminds me of one I inches long, terminating in a very acute formerly made, to try if negative electricity point; but now its whole length was no more might be produced by evaporation only. I than seven inches and a half
, and the top very placed a large heated brass plate, containing blunt. Some of the metal appears to be mis- four or five square feet on an electric stand: sing, the slenderest part of the wire being, as a rod of metal, about four feet long, with a I suspect, consumed into smoke. But some bullet at its end, extended from the plate ho of it, where the wire was a little thicker, be- rizontally. A light lock of cotton, suspended ing only melted by the lightning, sunk down, by a fine thread from the ceiling, hung oppo while in a fluid state, and formed a rough irre- site to, and within an inch of the bullet. I gular cap, lower on one side than the other, then sprinkled the heated plate with water, round the upper end of what remained, and which arose fast from it in vapour. If vapour became intimately united therewith. should be disposed to carry off the electrical,
This was all the damage that Mr. West as it does the common fire from bodies, I exsustained by a terrible stroke of lightning; a pected the plate would, by losing some of its most convincing proof of the great utility of natural quantity, become negatively electris this method of preventing its dreadful effects. ed. But I could not perceive, by any motion Surely it will now be thought as expedient in the cotton, that it was at all affected: nor to provide conductors for the lightning, as for by any separation of small cork balls sụspendthe rain.
ed from the plate, could it be observed that Mr. West was so good as to make me a the plate was in any manner electrified. present of the melted wire, which I keep as Mr. Canton here has also found, that two a great curiosity, and long for the pleasure of tea cups, set on electric stands, and filled one showing it to you. In the mean time, I beg with boiling, the other with cold water, and
equally electrified, continued equally so, not- nished. Being at Birmingham, in September, withstanding the plentiful evaporation from 1760, Mr. Bolton of that place opened a bottle the hot water. Your experiment and his that had been charged, and its long tube neck agreeing, shows another remarkable differ- hermetically sealed in January preceding. ence between electric and common fire. For On breaking off the end of the neck, and inthe latter quits most readily the body that troducing a wire into it, we found it possesscontains it, where water, or any other fluid, ed of a considerable quantity of electricity, is evaporating from the surface of that body, which was discharged by a snap and spark. and escapes with the vapour. Hence the This bottle had lain near seven months on a method, long in use in the east, of cooling li- shelf, in a closet, in contact with bodies that quors, by wrapping the bottles round with a would undoubtedly have carried off all its wet cloth, and exposing them to the wind. electricity, if it could have come readily Dr. Cullen, of Edinburgh, has given some ex- through the glass. Yet as the quantity maperiments of cooling by evaporation; and I nifested by the discharge was not apparently was present at one made by Dr. Hadley, then so great as might have been expected from a professor of chemistry at Cambridge, when, bottle of that size well charged, some doubt by repeatedly wetting the ball of a thermo- remained whether part had escaped while the meter with spirit, and quickening the evapo- neck was sealing, or had since, by degrees, ration by the blast of a bellows, the mercury, soaked through the glass. But an experiment fell from 65, the state of warmth in the com- of Mr. Canton's, in which such a bottle was mon air to 7, which is 22 degrees below kept under water a week, without having its freezing; and, accordingly, from some water electricity in the least impaired, seems to show, mixed with the spirit, or from the breath of that when the glass is cold, though extremely the assistants, or both, ice gathered in small thin, the electric fluid is well retained by it. spicula round the ball, to the thickness of near As that ingenious and accurate experimenter a quarter of an inch. To such a degree did made a discovery, like yours, of the effect of the mercury lose the fire it before contained, heat in rendering thin glass permeable by that which, as I imagine, took the opportunity of fluid, it is but doing him justice to give you escaping, in company with the evaporating his account of it, in his own words, extracted particles of the spirit, by adhering to those from his letter to me, in which he communiparticles.
cated it, dated October 31, 1760, viz. Your experiments of the Florence flask, Having procured some thin glass balls, of and boiling water, is very curious. I have about an inch and a half in diameter, with repeated it, and found it to succeed as you stems, or tubes, of eight or nine inches in describe it, in two flasks out of three. The length, I electrified them, some positively on third would not charge when filled with either the inside, and others negatively, after the hot or cold water. I repeated it, because I manner of charging the Leyden bottle, and remembered I had once attempted to make an sealed them hermetically. Soon after I apelectric bottle of a Florence flask, filled with plied the naked balls to my electrometer, and cold water, but could not charge it at all; could not discover the least sign of their bewhich I then imputed to some imperceptible ing electrical, but holding them before the fire, cracks in the small
, extremely thin bubbles, of at the distance of six or eight inches, they bewhich that glass is full, and I concluded none came strongly electrical in a very short time, of that kind would do. But you have shown and more so when they were cooling. These me my mistake. Mr. Wilson had formerly balls will, every time they are heated, give acquainted us, that red hot glass would con- the electrical fluid to, or take it from other duct electricity; but that so small a degree bodies, according to the plus or minus state of heat, as that communicated by boiling wa- of it within them. Heating them frequently, ter, would so open the pores of extremely thin I find will sensibly diminish their power; but glass, as to suffer the electric fluid freely to keeping one of them under water a week did pass, was not before known. Some experi- not appear in the least degree to impair it. ments similar to yours, have, however, been That which I kept under water, was charged made here, before the receipt of your letter, on the 22d of September last, was several times of which I shall now give you an account. heated before it was kept in water, and has
I formerly had an opinion that a Leyden been heated frequently since, and yet it still bottle, charged and then sealed hermetically, retains its virtue to a very considerable demight retain its electricity for ever; but hav- gree. The breaking two of my balls acciing afterwards some suspicion that possibly dentally gave me an opportunity of measuring that subtle fluid might, by slow imperceptible their thickness, which I found to be between degrees, soak through the glass, and in time seven and eight parts in a thousand of an inch. escape, I requested some of my friends, who “ A down feather, in a thin glass ball, herhad conveniences for doing it, to make metically sealed, will not be affected by the trial, whether after some months, the charge application of an excited tube, or the wire of of a bottle so sealed would be sensibly dimi- a charged phial, unless the ball be consider