« ZurückWeiter »
electrified body will discharge the atmosphere made of several thin sheets of clothier's pasteof that body or communicate it farthest to an- board, formed into a tube, near ten feet long other body, so the point of an unelectrified and a foot diamater. It is covered with body will draw off the electrical atmosphere Dutch embossed paper, almost totally gilt. This from an electrified body, farther than a blunter large metallic surface supports a much greater part of the same unelectrified body will do. electrical atmosphere than a rod of iron of 50 Thus, a pin held by the head, and the point times the weight would do. It is suspended presented to an electrified body, will draw off by silk lines, and when charged will strike, its atmosphere at a foot distance; where, if at near two inches distance, a pretty hard the head were presented instead of the point, stroke, so as to make ones knuckle ache. no such effect would follow. To understand Let a person standing on the floor present the this, we may consider, that if a person stand- point of a needle at 12 or more inches dising on the floor would draw off the electrical tance from it, and while the needle is so preatmosphere from an electrified body, an iron sented, the conductor cannot be charged, the crow and a blunt knitting-needle held alter- point drawing off the fire as fast as it is thrown nately in his hand, and presented for that pur- on by the electrical globe. Let it be chargpose, do not draw with different forces in pro-ed, and then present the point at the same portion to their different masses. For the man, distance, and it will suddenly be discharged. and what he holds in his hand, be it large or in the dark you may see the light on the small, are connected with the common mass point, when the experiment is made. And if of unelectrified matter; and the force with the person holding the point stands upon wax, which he draws is the same in both cases, it he will be electrified by receiving the fire at consisting in the different proportion of elec- that distance. Attempt to draw off the electricity in the electrified body, and that com- tricity with a blunt body, as a bolt of iron mon mass. But the force with which the round at the end, and smooth (a silversmith's electrified body retains its atmosphere by at- iron punch, inch thick is what I use) and tracting it, is proportioned to the surface over you must bring it within the distance of three which the particles are placed ; i. e. four inches before you can do it, and then it is done square inches of that surface retain their at- with a stroke and crack. As the pasteboard mosphere with four times the force that one tube hangs loose on silk lines, when you apsquare inch retains its atmosphere. And as proach it with the punch-iron, it likewise will in plucking the hairs from the horse's tail, a move towards the punch, being attracted degree of strength not sufficient to pull away while it is charged; but if, at the same ina handful at once, could yet easily strip it stant, a point be presented as before, it rehair by hair : so a blunt body presented cannot tires again, for the point discharges it. Take draw off a number of particles at once, but a a pair of large brass scales, of two or more pointed one, with no greater force, takes them feet beam, the cords of the scales being silk. away easily, particle by particle.
Suspend the beam by a packthread from the 18. These explanations of the power and ceiling, so that the bottom of the scales may operation of points, when they first occurred to be about a foot from the floor; the scales will me, and while they first floated in my mind, move round in a circle by the untwisting of appeared perfectly satisfactory; but now I the packthread. Set the iron punch on the have written them, and considered them more end upon the floor, in such a place as that the closely, I must own I have some doubts about scales may pass over it in making their circle ; them; yet, as I have at present nothing better then electrify one scale, by applying the wire to offer in their stead, I do not cross them out: of a charged phial to it. As they move round, for, even a bad solution read, and its faults you see that scale draw nigher to the floor, discovered, has often given rise to a good one, and dip more when it comes over the punch; in the mind of an ingenious reader. and if that be placed at a proper distance, the
19. Nor is it of much importance to us to scale will snap and discharge its fire into it. know the manner in which nature executes But if a needle be stuck on the end of the her laws; it is enough if we know the laws punch, its point upwards, the scale, instead of themselves. It is of real use to know that drawing nigh to the punch, and snapping, china left in the air unsupported will fall and discharges its fire silently through the point, break; but how it comes to fall, and why it and rises higher from the punch. Nay, even breaks, are matters of speculation. It is a if the needle be placed upon the floor near the pleasure indeed to know them, but we can punch, its point upwards, the end of the preserve our china without it.
punch, though so much higher than the needle, 20. Thus in the present case, to know this will not attract the scale and receive its fire, power of points may possibly be of some use for the needle will get it and convey it away, to mankind, though we should never be able before it comes nigh enough for the punch to to explain it
. The following experiments, act. And this is constantly observable in as well as those in my first paper, show this these experiments, that the greater quantity power. I have a large prime conductor, of electricity on the pasteboard tube, the far
ther it strikes or discharges its fire, and the handle; so the sparks, if the rod is electrified, point likewise will draw it off at a still great- will strike from the rod to the wire, and not er distance.
affect him. Now if the fire of electricity and that of 22. Before I leave this subject of lightlightning be the same, as I have endeavour- ning, I may mention some other similarities ed to show at large, in a former paper, this between the effects of that, and those of elecpasteboard tube and these scales may repre-tricity. Lightning has often been known to sent electrified clouds. If a tube of only ten strike people blind. A pigeon that we struck feet long will strike and discharge its fire on dead to appearance by the electrical shock, the punch at two or three inches distance, recovering life, drooped about the yard sevean electrified cloud of perhaps 10,000 acres ral days, eat nothing, though crumbs were may strike and discharge on the earth at a thrown to it, but declined and died. We did proportionably greater distance. The hori- not think of its being deprived of sight; but zontal motion of the scales over the floor, may afterwards a pullet, struck dead in like manrepresent the motion of the clouds over the ner, being recovered by repeatedly blowing earth; and the erect iron punch, a hill or high into its lungs, when set down on the floor, building; and then we see how electrified ran headlong against the wall, and on exclouds passing over hills or high buildings at amination appeared perfectly blind. Hence loo great a height to strike, may be attracted we concluded that the pigeon also had been lower till within their striking distance. And absolutely blinded by the shock. The biglastly, if a needle fixed on the punch with its gest animal we have yet killed, or tried to point upright, or even on the floor below the kill, with the electrical stroke, was a well punch, will draw the fire from the scale si- grown pullet. lently at a much greater than the striking dis- 23. Reading in the ingenious Dr. Miles's tance, and so prevent its descending towards account of the thunder-storm at Streatham, the punch; or if in its course it would have the effect of the lightning in stripping off all come nigh enough to strike, yet being first the paint that had covered a gilt moulding of deprived of its fire it cannot, and the punch is a pannel of wainscot, without hurting the rest thereby secured from the stroke; I say, if of the paint, I had a mind to lay a coat of paint these things are so, may not the knowledge over the filleting of gold on the cover of a of this power of points be of use to mankind, book, and try the effects of a strong electrical in preserving houses, churches, ships, &c. flash sent through that gold from a charged from the stroke of lightning, by directing us sheet of glass. But having no paint at hand, to fix on the highest parts of those edifices, I pasted a narrow strip of paper over it; and upright rods of iron made sharp as a needle, when dry, sent the flash through the gilding, and gilt to prevent rusting, and from the foot by which the paper was torn off from end to of those rods a wire down the outside of the end, with such force, that it was broke in sebuilding into the ground, or down round one veral places, and in others brought away part of the shrouds of a ship, and down her side of the grain of the Turkey-leather in which till it reaches the water? Would not these it was bound; and convinced me, that had it pointed rods probably draw the electral fire been painted, the paint would have been silently out of a cloud before it came nigh stripped off in the same manner with that on enough to strike, and thereby secure us from the wainscot at Streatham. that most sudden and terrible mischief?
24. Lightning melts metals, and I hinted in 21. To determine the question, whether the my paper on that subject, that I suspected it clouds that contain lightning are electrified to be a cold fusion ; I do not mean a fusion or not, I would propose an experiment to be by force of cold, but a fusion without heat.* tried where it may be done conveniently. On We have also melted gold, silver, and copper, the top of some high tower or steeple, place in small quantities, by the electrical Hash. a kind of centry-box (as in Fig. 9) big enough The manner is this: take leaf-gold, leaf-silto contain a man and an electrical stand. ver, or leaf-gilt copper, commonly called leafFrom the middle of the stand let an iron rod brass, or Dutch gold; cut off from the leaf rise and pass bending out of the door, and long narrow strips, the breadth of a straw. then upright 20 or 30 feet, pointed very sharp Place one of these strips between two strips at the end. If the electrical stand be kept of smooth glass that are about the width of clean and dry, a man standing on it, when your finger. If one strip of gold, the length such clouds are passing low, might be elec- of the leaf, be not long enough for the glass, trified and afford sparks, the rod drawing fire add another to the end of it, so that you may to him from a cloud. If any danger to the have a little part hanging out loose at each man should be apprehended (though I think end of the glass. Bind the pieces of glass tothere would be none) let him stand on the gether from end to end with strong silk thread; floor of his box, and now and then bring near then place it so as to be part of an electrical to the rod the loop of a wire, that has one end circuit, (the ends of gold hanging out being fastened to the leads, he holding it by a wax
* See the note in page 257.
of use to join with the other parts of the cir- | tricity, that points as they are more or less cuit) and send the flash through it, from a acute, draw on and throw off the electrical large electrified jar or sheet of glass. Then fluid with more or less power, and at greater if your strips of glass remain whole, you will or less distances, and in larger or smaller see that the gold is missing in several places, quantities in the same time we may see how and instead of a metallic stain on both the to account for the situation of the leaf of gold glasses; the stains on the upper and under suspended between two plates, the upper one glass exactly similar in the minutest stroke, continually electrified, the under one in a as may be seen by holding them to the light; person's hand standing on the floor. When the metal appeared to have been not only the upper plate is electrified, the leaf is atmelted, but even vitrified, or otherwise sotracted, and raised towards it, and would fly driven into the pores of the glass, as to be to that plate, were it not for its own points. protected by it from the action of the strong. The corner that happens to be uppermost est aqua fortis, or aqua regia. I send you en- when the leaf is rising, being a sharp point, closed two little pieces of glass with these me from the extreme thinness of the gold, draws tallic stains upon them, which cannot be re- and receives at a distance a sufficient quantity moved without taking part of the glass with of the electric fluid to give itself an electric them. Sometimes the stain spreads a little atmosphere, by which its progress to the upwider than the breadth of the leaf, and looks per plate is stopped, and it begins to be repelbrighter at the edge, as by inspecting closely led from that plate, and would be driven back you may observe in these. Sometimes the to the under plate, but that its lowest corner glass breaks to pieces; once the upper glass is likewise a point, and throws off or disbroke into a thousand pieces, looking like charges the overplus of the leaf's atmosphere, coarse salt. The pieces I send you were as fast as the upper corner draws it on. Were stained with Dutch gold. True gold makes those two points perfectly equal in acuteness, a darker stain, somewhat reddish ; silver, a the leaf would take place exactly in the middle greenish stain. We once took two pieces of space, for its weight is a trifle compared to thick looking-glass, as broad as a Gunter's the power acting on it: but it is generally scale, and six inches long; and placing leaf- nearest the unelectrified plate, because, when gold between them, put them between two the leaf is offered to the electrified plate, at a smoothly-plained pieces of wood, and fixed distance, the sharpest point is commonly first thern tight in a bookbinder's small press; yet affected and raised towards it; so that point, though they were so .closely confined, the from its greater acuteness, receiving the fluforce of the electrical shock shivered the id faster than its opposite can discharge it at glass into many pieces. The gold was melt- equal distances, it retires from the electrified ed and stained into the glass, as usual. The plate, and draws nearer to the unelectrified circumstances of the breaking of the glass dif- plate, till it comes to a distance where the fer much in making the experiment, and discharge can be exactly equal to the receipt, sometimes it does not break at all: but this the latter being lessened, and the former in. is constant, that the stains in the upper and creased; and there it remains as long as the under pieces are exact counterparts of each globe continues to supply fresh electrical other. And though I have taken up the matter. This will appear plain, when the pieces of glass between my fingers immedi- difference of acuteness in the corners is made ately after this melting, I never could perceive very great. Cut a piece of Dutch gold, the least warmth in them.
(which is fittest for these experiments on ac25. In one of my former papers, I mention- count of its great strength) into the form of ed, that gilding on a book, though at first it Fig. 10, the upper corner a right angle, the communicated the shock perfectly well, yet two next obtuse angles, and the lowest a very failed after a few experiments, which we acute one; and bring this on your plate uncould not account for. We have since found der the electrified plate, in such a manner as that one strong shock breaks the continuity that the right-angled part may be first raised of the gold in the filletting, and makes it look (which is done by covering the acute part rather like dust of gold, abundance of its parts with the hollow of your hand) and you will being broken and driven off; and it will sel- see this leaf take place much nearer to the dom conduct above one strong shock. Per- upper than the under plate; because without haps this may be the reason: when there is being nearer, it cannot receive so fast at its not a perfect continuity in the circuit, the right-angled point, as it can discharge at its fire must leap over the vacancies; there is a acute one. Turn this leaf with the acute certain distance which it is able to leap over part uppermost, and then it takes place nearaccording to its strength; if a number of small est the unelectrified plate; because, otherwise, vacancies, though each be very minute, taken it receives faster at its acute point, than it can together exceed that distance, it cannot leap discharge at its right-angled one. Thus the over them, and so the shock is prevented. difference of distance is always proportioned
26. From the before-mentioned law of elec- l to the difference of acuteness. Take care in
cutting your leaf, to leave no little ragged | makes the difference between such a bottle particles on the edges, which sometimes form and one that is sound, but this, that the fluid points where you would not have them. You can pass through the one, and not through the may make this figure so acute below, and other ?* blunt above, as to need no under plate, it dis- 29. It is true, there is an experiment that charging fast enough into the air. When it at first sight would be apt to satisfy a light is made narrower, as the figure between the observer, that the fire, thrown into the bottle pricked lines, we call it the golden fish, from by the wire, does really pass through the its manner of acting. For if you take it by glass. It is this: place the bottle on a glass the tail, and hold it at a foot or greater hori- stand, under the prime conductor, suspend a zontal distance from the prime conductor, it bullet by a chain from the prime conductor, will, when let go, fly to it with a brisk but till it comes within a quarter of an inch right wavering motion, like that of an eel through over the wire of the bottle; place your knuckle the water; it will then take place under the on the glass stand, at just the same distance prime conductor, at perhaps a quarter or half from the coating of the bottle, as the bullet is an inch distance, and keep a continual shak- from its wire. Now let the globe be turned, ing of its tail like a fish, so that it seems ani- and you see a spark strike from the bullet 10 mated. Turn its tail towards the prime con- the wire of the bottle, and the same instant ductor, and then it flies to your finger, and you see and feel an exactly equal spark strikseems to nibble it. And if you hold a plate ing from the coating on your knuckle, and so under it at six or eight inches distance, and on, spark for spark. This looks as if the whole cease turning the globe when the electrical received by the bottle was again discharged atmosphere of the conductor grows small, it from it. And yet the bottle by this means is will descend to the plate and swim back charged ! † And therefore the fire that thus again several times with the same fish-like leaves the bottle, though the same in quantis, motion, greatly to the entertainment of spec- cannot be the very same fire that entered at tators. By a little practice in blunting or the wire, for if it were, the bottle would resharpening the heads or tails of these figures, main uncharged. you may make them take place as desired, 30. If the fire that so leaves the bottle be nearer or farther froin the electrified plate. not the same that is thrown in through the
27. It is said in section 8, of this paper, wire, it must be fire that subsisted in the totthat all kinds of common matter are supposed tle (that is, in the glass of the bottle) before the not to attract the electrical Auid with equal operation began. strength ; and that those called electrics per 31. If so, there must be a great quantity in se, as glass, &c. attract and retain it strongest, glass, because a great quantity is thus 'uisand contain the greatest quantity. This lat. charged, even from very thin glass. ter position may seem a paradox to some, be- 32. That this electrical fluid or fire is ing contrary to the hitherto received opinion; strongly attracted by glass, we know from the and therefore I shall now endeavour to ex- quickness and violence with which it is resumplain it.
ed by the part that had been deprived of it, 28. In order to this, let it first be consider- when there is an opportunity. And by this, thai ed, that we cannot by any means we are yet we cannot from a mass of glass draw a quanacquainted with, force ihe electrical fluid tity of electric fire, or electrify the whole mass through glass. Î know it is commonly minus, as we can a mass of metal.
We canthought that it easily pervades glass; and the not lessen or increase its whole quantity, for experiment of a feather suspended by a thread the quantity it has it holds; and it has as in a bottle hermetically sealed, yet moved by much as it can hold. Its pores are filled with bringing a rubbed tube near the outside of the it as full as the mutual repellency of the partibottle is alleged to prove it. But, if the elec- cles will adinit; and what is already in, retrical Auid so easily pervades glass, how does fuses, or strongly repels any additional quantity. the phial become charged (as we term it) Nor have we any way of moving the electriwhen we hold it in our hands? Would not cal fluid in glass, but one; that is
, by covering the fire, thrown in by the wire, pass through part of the two surfaces of thin glass with nonto our hands, and so escape into the floor? electrics, and then throwing an additional Would not the bottle in that case be left just quantity of this fluid on one surface, which as we found it, uncharged, as we know a metal spreading in the non-electric, and being bound bottle so attempted to be charged would be? by it to that surface, acts by its repelling force Indeed, if there be the least crack, the mi- on the particles of the electrical Auid contained nutest solution of continuity in the glass, in the other surface, and drives them out of though it remains so tight that nothing else the glass into the non-electric' on that side we know of will pass, yet the extremely sub- from whence they are discharged, and then tile electric fluid flies through such a crack with the greatest freedom, and such a bottle
* See the first sixteen sections of the former paper,
called Farther Erperiments, &c. we know can never be charged: what then
See sect. 10, of Farther Esperiments, &c.
those added on the charged side can enter. The quantities of this fuid in each surface But when this is done, there is no more in the being equal, their repelling action on each glass, nor less than before, just as much hav- other is equal; and therefore those of one ing left it on one side as it received on the surface cannot drive out those of the other; other.
but, if a greater quantity is forced into one 33. I feel a want of terms here, and doubt surface than the glass would naturally draw much whether I shall be able to make this in, this increases the repelling power on that part intelligible. By the word surface, in this side, and overpowering the attraction on the case, I do not mean mere length and breadth other, drives out part of the fluid that had been without thickness; but when I speak of the imbibed by that surface, if there be any nonupper or under surface of a piece of glass, the electric ready to receive it: such there is in outer or inner surface of the phial, I mean all cases where glass is electrified to give a length, breadth, and half the thickness, and shock. The surface that has been thus empbeg the favour of being so understood. Now tied, by having its electrical fluid driven out, I suppose, that glass in its first principles, and resumes again an equal quantity with vioin the furnace, has no more of this electri- lence, as soon as the glass has an opportuni cal fluid than other common matter: that ty to discharge that over quantity more than when it is blown, as it cools, and the particles it could retain by attraction in its other surof common fire leave it, its pores become a face, by the additional repellency of which the vacuum: that the component parts of glass vacuum had been occasioned. For experiare extremely small and fine, I guess from its ments favouring (if I may not say confirming) never showing a rough face when it breaks, this hypothesis, I must, to avoid repetition, beg but always a polish ; and from the smallness leave to refer you back to what is said of the of its particles I suppose the pores between electrical phial in my former pages. them must be exceedingly small, which is 33. Let us now see how it will account for the reason that aqua fortis, nor any other several other appearances.-Glass, a body exmenstruum we have, can enter to separate tremely elastic, (and perhaps its elasticity may them and dissolve the substance; nor is any be owing in some degree to the subsisting of fluid we know of, fine enough to enter, except so great a quantity of this repelling fluid in common fire, and the electric fluid. Now the its pores) must, when rubbed, have its rubbed departing fire, leaving a vacuum, as aforesaid, surface somewhat stretched, or its solid parts between these pores, which air nor water are drawn a little farther asunder, so that the fine enough to enter and fill, the electric fluid vacancies in which the electrical fluid resides, (which is every where ready in what we call become larger, affording room for more of that the non-electrics, and in the non-electric mix- fluid, which is immediately attracted into it tures that are in the air) is attracted in ; yet from the cushion or hand rubbing, they being does not become fixed with the substance of the supplied from the common stock. But the glass, but subsists there as water in a porous instant the parts of the glass so opened and stone, retained only by the attraction of the filled, have passed the friction, they close fixed parts, itself still loose and a fluid. But again, and force the additional quantity out I suppose farther, that in the cooling of the upon the surface, where it must rest till that glass, its texture becomes closest in the mid-part comes round to the cushion again, unless dle, and forms a kind of partition, in which the some non-electric (as the prime conductor,) pores are so narrow, that the particles of the first presents to receive it.* But if the inside electrical fluid, which enter both surfaces at of the globe be lined with a non-electric, the the same time, cannot go through, or pass and additional repellency of the electrical fluid, repass from one surface to the other, and so thus collected by friction on the rubbed part mix together; yet, though the particles of of the globe's outer surface, drives an equal electric fluid, imbibed by each surface, cannot quantity out of the inner surface into that nonthemselves pass through to those of the other, electric lining, which receiving it, and carrytheir repellency can, and by this means they ing it away from the rubbed part into the act on one another. The particles of the common mass, through the axis of the globe, electric fluid have a mutual repellency, but and frame of the machine, the new collected by the power of attraction in the glass they electrical fluid can enter and remain in the are condensed or forced nearer to each other. outer surface, and none of it (or a very little) When the glass has received, and, by its at- will be received by the prime conductor. As traction, forced closer together so much of this this charged part of the globe comes round to electric Auid, as that the power of attracting * In the dark the electric fluid may be seen on the and condensing in the one, is equal to the cushion in two semi-circles or half moons, one on the power of expansion in the other, it can im- fore part, the of her on the back part of the cushions just bibe no more, and that remains its constant crescent the fire is passing out of the cushion into the whole quantity ; but each surface would re- glass; in the other it is leaving the glass, and returning ceive more, if the repellency of what is in into the back part of the cushion when the prime
conductor is applied to take it off the glass, the back the opposite surface did not resist its entrance. crescent disappears.