Mr. William Maine's Account of the Effects of the Lightning on his Rod, dated at Indian Land, in South Carolina, August 28, 1760. mischiefs done by lightning are not so fre- remained good. No other damage, as I can quent here as with us, and those who calcu- learn, was done to the house. I am told the late chances may perhaps find that not one same house had formerly been struck by lightdeath (or the destruction of one house) in aning, and much damaged, before these rods hundred thousand happens from that cause, were invented." and that therefore it is scarce worth while to be at any expense to guard against it.—But in all countries there are particular situations of buildings more exposed than others to such accidents, and there are minds so strongly impressed with the apprehension of them, as to be very unhappy every time a little thunder is within their hearing; it may therefore being of three prongs, of large brass wire tipt well to render this little piece of new knowledge as general and as well understood as possible, since to make us safe is not all its advantage, it is some to make us easy. And as the stroke it secures us from might have chanced perhaps but once in our lives, while it may relieve us a hundred times from those painful apprehensions, the latter may possibly on the whole contribute more to the happiness of mankind than the former. Your kind wishes and congratulations are very obliging. I return them cordially;-being, with great regard and esteem, B. FRANKLIN." Effects of Lightning in Carolina, Referred to in the preceding Letter-of the effects of Lightning on two of the rods commonly affixed to houses there, for securing them against Lightning. "CHARLESTON, Nov 1, 1760. Ir is some years since Mr. Raven's rod was struck by lightning. I hear an account of it was published at the time, but I cannot find it. According to the best information I can now get, he had fixed to the outside of his chimney a large iron rod, several feet in length, reaching above the chimney; and to the top of this rod the points were fixed. From the lower end of this rod, a small brass wire was continued down to the top of another iron rod driven into the earth. On the ground-floor in the chimney stood a gun, leaning against the back wall, nearly opposite to where the brass wire came down on the outside. The lightning fell upon the points, did no damage to the rod they were fixed to; but the brass wire, all down till it came opposite to the top of the gun-barrel, was destroyed. There the lightning made a hole through the wall or back of the chimney, to get to the gun-barrel,† down which it seems to have passed, as, although it did not hurt the barrel, it damaged the butt of the stock, and blew up some bricks of the hearth. The brass wire below the hole in the wall *A proof that it was not of sufficient substance to conduct with safety to itself (though with safety so far to the wall) so large a quantity of the electric fluid. † A more substantial conductor "I HAD a set of electrical points, consist with silver, and perfectly sharp, each about five in the evening, when the lightning broke weaker as the needle is shortened between the finger and thumb; and is reduced to nothing when only a short part below the point appears above the finger. Now it seems the points of Mr. Maine's rod were elevated only (a) six or seven inches above the top of the chimney; which, considering the bulk of the chimney and the house, was too small an elevation. For the great body of the matter near them would hinder their being easily brought into a negative state by the repulsive power of the electrised cloud, in which negative state it is that they attract most strongly and copi ously the electric fluid from other bodies, and convey it into the earth. (p.) What seems to me the most surprising is, that the hearth under the kettle was not hurt, yet the bottom of the kettle was drove inward, as if the lightning proceeded from under it upwards (q.) and the cover was thrown to the middle of the floor (r.) The fire dogs, an iron loggerhead, an Indian pot, an earthen cup, and a cat, were all in the chimney at the time unhurt, though a great part of the hearth was torn up (s.) My wife's sister, two children, and a negro wench, were all who happened to be in the house at the time: the first, and one child sat within five feet of the chimney; and were so stunned, that they never saw the lightning nor heard the explosion; the wench, with the other child in her (b) Nothing of the points, &c. could be arms, sitting at a greater distance, was sensi- found. This is a common effect. (See page ble of both; though every one was so stunned 297.) Where the quantity of the electric that they did not recover for some time; how- fluid passing is too great for the conductor ever it pleased God that no farther mischief through which it passes, the metal is either ensued. The kitchen, at 90 feet distance, melted, or reduced to smoke and dissipated; was full of negroes, who were all sensible of but where the conductor is sufficiently large, the shock; and some of them tell me, that they the fluid passes in it without hurting it. Thus felt the rod about a minute after, when it was these three wires were destroyed, while the so hot that they could not bear it in hand. rod to which they were fixed, being of greater substance, remained unhurt; its end only, to which they were joined, being a little melted, some of the melted part of the lower ends of those wires uniting with it, and appearing on it like solder. Remarks by Dr. Franklin. THE foregoing very sensible and distinct account may afford a good deal of instruction relating to the nature and effects of lightning, and to the construction and use of this instrument for averting the mischiefs of it. Like other new instruments, this appears to have been at first in some respects imperfect; and we find that we are, in this as in others, to expect improvement from experience chiefly: but there seems to be nothing in the account, that should discourage us in the use of it; since at the same time that its imperfections are discovered, the means of removing them are pretty easily to be learnt from the circumstances of the account itself; and its utility upon the whole is manifest. (c) (d) (e) As the several parts of the rod were connected only by the ends being bent round into hooks, the contact between hook and hook was much smaller than the rod; therefore the current through the metal being confined in those narrow passages, melted part of the metal, as appeared on examining the inside of each hook. Where metal is melted by lightning, some part of it is generally exploded; and these explosions in the joints appear to have been the cause of unhooking them; and, by that violent action, of starting also most of the staples. We learn from hence, that a rod in one continued piece is preferable to one composed of links or parts hooked together. One intention of the pointed rod, is, to prevent a stroke of lightning. (See pages 289, 296.) But to have a better chance of obtain- (f) No part of the chimney was damaged; ing this end, the points should not be too near because the lightning passed in the rod. And to the top of the chimney or highest parts of this instance agrees with others in showing, the building to which they are affixed, but that the second and principal intention of the should be extended five or six feet above it; rods is obtainable, viz. that of conducting the otherwise their operation in silently drawing lightning. In all the instances yet known of off the fire (from such fragments of cloud as the lightning's falling on any house guarded float in the air between the great body of cloud by rods, it has pitched down upon the point of and the earth) will be prevented. For the the rod, and has not fallen upon any other experiment with the lock of cotton hanging part of the house. Had the lightning fallen below the electrified prime conductor shows, on this chimney, unfurnished with a rod, it that a finger under it, being a blunt body, ex- would probably have rent it from top to bottends the cotton, drawing its lower part down-tom, as we see, by the effects of the lightning wards; when a needle, with its point present- on the points and rod, that its quantity was ed to the cotton, makes it fly up again to the very great; and we know that many chimprime conductor; and that this effect is strong- neys have been so demolished. But no pa est when as much of the needle as possible of this was damaged, only (ƒ) (g) (h) at the appears above the end of the finger; grows foundation, where it was shattered and seVOL. II.... 2 R 27 every room in it through the windows; and this I suppose to have been the case at Mr. Maine's; and that, except in and near the hearth, from the causes above-mentioned, it was not in any other part of the house; the flash meaning no more than the light of the lightning. It is for want of considering this difference, that people suppose there is a kind of lightning not attended with thunder. In fact there is probably a loud explosion_accompanying every flash of lightning, and at the same instant ;-but as sound travels slower than light, we often hear the sound some se veral bricks torn out. Here we learn the principal defect in fixing this rod. The lower joint being sunk but three feet into the earth, did not it seems go low enough to come at water, or a large body of earth so moist as to receive readily from its end the quantity it conducted. The electric fluid, therefore, thus accumulated near the lower end of the rod, quitted it at the surface of the earth, dividing in search of other passages. Part of it tore up the surface in furrows, and made holes in it: part entered the bricks of the foundation, which being near the earth are generally moist, and, in exploding that moist-conds of time after having seen the light; ure, shattered them. (See page 311.) Part went through or under the foundation, and got under the hearth, blowing up great part of the bricks (m) (s), and producing the other effects (o) (p) (q) (r). The iron dogs, loggerhead, and iron pot were not hurt, being of sufficient substance, and they probably protected the cat. The copper tea-kettle being thin suffered some damage. Perhaps, though found on a sound part of the hearth, it might at the time of the stroke have stood on the part blown up, which will account both for the bruising and melting. That it ran down the inside of the chimney (k) I apprehend must be a mistake. Had it done so, I imagine it would have brought something more than soot with it; it would probably have ripped off the pargetting, and brought down fragments of plaster and bricks. The shake, from the explosion on the rod, was sufficient to shake down a good deal of loose soot. Lightning does not usually enter houses by the doors, windows, or chimneys, as open passages, in the manner that air enters them its nature is, to be attracted by substances, that are conductors of electricity; it penetrates and passes in them, and, if they are not good conductors as are neither wood, brick, stone nor plaster, it is apt to rend them in its passage. It would not easily pass through the air from a cloud to a building were it not for the aid afforded it in its passage by intervening fragments of clouds below the main body, or by the falling rain. It is said that the house was filled with its flash (1). Expressions like this are common in accounts of the effects of lightning, from which we are apt to understand that the lightning filled the house. Our language indeed seems to want a word to express the light of lightning as distinct from the lightning itself. When a tree on a hill is struck by it, the lightning of that stroke exists only in a narrow vein between the cloud and tree, but its light fills a vast space many miles round; and people at the greatest distance from it are apt to say, "The lightning came into our rooms through our windows." As it is in itself extremely bright, it cannot, when so near as to strike a house, fail illuminating highly and as sound does not travel so far as light, we sometimes see the light at a distance too great to hear the sound. (n) The breaking some pieces of china in the bufet, may nevertheless seem to indicate that the lightning was there: but as there is no mention of its having hurt any part of the bœufet, or of the walls of the house, I should rather ascribe that effect to the concussion of the air, or shake of the house by the explosion. Thus, to me it appears, that the house and its inhabitants were saved by the rod, though the rod itself was unjointed by the stroke; and that, if it had been made of one piece, and sunk deeper in the earth, or had entered the earth at a greater distance from the foundation, the mentioned small damages (except the melting of the points) would not have happened. Dr. Heberden, London. CRAVEN-STREET, June 7, 1759. I hear that the negative electricity of one side of the tourmalin, when heated, is absolutely denied (and all that has been related of it ascribed to prejudice in favour of a system) by some ingenious gentlemen abroad, who profess to have made the experiments on the stone with care and exactness. The experiments have succeeded differently with me; yet I would not call the accuracy of these gentlemen in question. Possibly the tourmalins they have tried were not properly cut; so that the positive and negative powers were obliquely placed, or in some manner whereby their effects were confused, or the negative parts more easily supplied by the positive.— Perhaps the lapidaries who have hitherto cut these stones, had no regard to the situation of the two powers, but chose to make the faces of the stone where they could obtain the great est breadth, or some other advantage in the form. If any of these stones, in their natural state, can be procured here, I think it would be right to endeavour finding, before they are cut, the two sides that contain the opposite powers, and make the faces there. Possibly in that case, the effects might be stronger, and more distinct; for though both these stones that I have examined have evidently the two properties, yet, without the full heat given by boiling water, they are somewhat confused; the virtue seems strongest towards one end of the face; and in the middle, or near the other end, scarce discernible; and the negative, I think, always weaker than the positive. I have had the large one new cut, so as to make both sides alike, and find the change of form has made no change of power, but the properties of each side remain the same as I found them before. It is now set in a ring in such a manner as to turn on an axis, that I may conveniently, in making experiments, come at both sides of the stone. The little rim of gold it is set in, has made no alteration in its effects. The warmth of my finger, when I wear it, is sufficient to give it some degree of electricity, so that it is always ready to attract light bodies. The following experiments have satisfied me that M. Æpinus's account of the positive and negative states of the opposite sides of the heated tourmalin is well founded. I heated the large stone in boiling water. As soon as it was dry, I brought it near a very small cork ball, that was suspended by a silk thread. The ball was attracted by one face of the stone, which I call A, and then repelled. The ball in that state was also repelled by the positively charged wire of a phial, and attracted by the other side of the stone, B. The stone being heated afresh, and the side B brought near the ball, it was first attracted and presently after repelled by that side. In this second state it was repelled by the negatively charged wire of a phial. Therefore, if the principles now generally received, relating to positive and negative electricity, are true, the side A of the large stone, when the stone is heated in water, is in a positive state of electricity; and the side B, in a negative state. The same experiments being made with the small stone stuck by one edge on the end of a small glass tube, with sealing-wax, the same effects are produced. The flat side of the small stone gives the signs of positive electricity; the high side gives the signs of negative electricity. Again I suspended the small stone by a silk thread. I heated it as it hung, in boiling water. I heated the large one in boiling water. Then I brought the large stone near to the suspended small one, Which immediately turned its flat side to the side B of the large stone, and would cling to it. I turned the ring, so as to present the side A of the large stone, to the flat side of the small one. The flat side was repelled, and the small stone, turning quick, applied its high side to the side A of the large one. This was precisely what ought to happen, on the supposition that the flat side of the small stone, when heated in water, is positive, and the high side negative; the side A of the large stone positive, and the side B negative. The effect was apparently the same as would have been produced, if one magnet had been suspended by a thread, and the different poles of another brought alternately near it. I find that the face A, of the large stone, being coated with leaf-gold (attached by the white of an egg, which will bear dipping in hot water) becomes quicker and stronger in its effect on the cork ball, repelling it the instant it comes in contact; which I suppose to be occasioned by the united force of the differ ent parts of the face, collected and acting together through the metal. B. FRANKLIN. Professor Winthrop to B. Franklın. New Observation relating to Electricity in the Atmosphere. Cambridge, (Massachusetts,) Sept. 29, 1762. THERE is an observation relating to electricity in the atmosphere, which seemed new to me, though perhaps it will not to you: however, I will venture to mention it. I have some points on the top of my house, and the wire where it passes within-side the house is furnished with bells, according to your method, to give notice of the passage of the electric fluid. In summer, these bells, generally ring at the approach of a thunder-cloud; but cease soon after it begins to rain. In winter, they sometimes, though not very often, ring while it is snowing; but never, that I remember, when it rains. But what was unexpected to me was, that, though the bells had not rung while it was snowing, yet, the next day, after it had done snowing, and the weather was cleared up, while the snow was driven about by a high wind at W. or N. W. the bells rung for several hours (though with little intermissions) as briskly as ever I knew them, and I drew considerable sparks from the wire. The phenomenon I never observed but twice, viz. on the 31st of January, 1760, and the 3d of March, 1762,-I am, sir, &c. A. Small, of London, to Dr. Franklin. Flash of Lightning that struck St. Bride's Steeple. close by means of oiled paper between, or covering the joining on the canister; or if in barrels, then the barrels lined with thin sheet lead; no moisture in either of these methods could possibly enter the powder, since glass and metals are both impervious to water. By the latter of these means you see tea is brought dry and crisp from China to Europe, and thence to America, though it comes all the way by sea in the damp hold of a ship And by this method, grain, meal, &c. if well dried before it is put up, may be kept for ages sound and good. 1 HAVE just recollected that in one of our great storms of lightning, I saw an appearance, which I never observed before, nor ever heard described. I am persuaded that I saw the flash which struck St. Bride's steeple. Sitting at my window, and looking to the north, I saw what appeared to me a solid strait rod of fire, moving at a very sharp angle with the horizon. It appeared to my eye as about two inches diameter, and had nothing of the zig-zag lightning motion. I instantly told a There is another thing very proper to line person sitting with me, that some place must small barrels with; it is what they call tinbe struck at that instant. I was so much sur- foil, or leaf-tin, being tin milled between rolprised at the vivid distinct appearance of the lers till it becomes as thin as paper, and more fire, that I did not hear the clap of thunder, pliant, at the same time that its texture is exwhich stunned every one besides. Consider-tremely close. It may be applied to wood ing how low it moved, I could not have with common paste, made with boiling-water thought it had gone so far, having St. Mar- thickened with flour; and, so laid on; will tin's, the New Church, and St. Clement's steelie very close and stick well: but I should ples in its way. It struck the steeple a good way from the top, and the first impression it made in the side is in the same direction I saw it move in. It was succeeded by two flashes, almost united, moving in a pointed direction. There were two distinct houses struck in Essex-street. I should have thought the rod would have fallen in Covent-Garden, it was so low. Perhaps the appearance is frequent, though never before seen by your's, ALEXANDER SMALL. To Peter Franklin, Newport. Best Method of securing a Powder Magazine from Lightning. -You may acquaint the gentleman that desired you to inquire my opinion of the best method of securing a powder magazine from lightning, that I think they cannot do better than to erect a mast not far from it, which may reach fifteen or twenty feet above the top of it, with a thick iron rod in one piece fastened to it, pointed at the highest end, and reaching down through the earth till it comes to water. Iron is a cheap metal; but if it were dearer, as this is a public thing, the expense is insignificant; therefore I would have the rod at least an inch thick, to allow for its gradually wasting by rust; it will last as long as the mast, and may be renewed with it. The sharp point for five or six inches should be gilt. But there is another circumstance of importance to the strength, goodness, and usefulness of the powder, which does not seem to have been enough attended to: I mean the keeping it perfectly dry. For want of a method of doing this, much is spoiled in damp magazines, and much so damaged as to become of little value.-If, instead of barrels it were kept in cases of bottles well corked or in large tin canisters, with small covers shutting prefer a hard sickly varnish for that purpose, made of linseed oil much boiled. The heads might be lined separately, the tin wrapping a little round their edges. The barrel, while the lining is laid on, should have the end hoops slack, so that the staves standing at a little distance from each other, may admit the head into its groove. The tin-foil should be plyed into the groove. Then, one head being put in, and that end hooped tight, the barrel would be fit to receive the powder, and when the other head is put in and the hoops drove up, the powder would be safe from moisture This tin-foil is but about eighteen pence even if the barrel were kept under water. that I imagine a pound of it would line three sterling a pound, and is so extremely thin, or four powder-barrels.—I am, &c. B. FRANKLIN. Of Lightning; and the Methods now used in America for securing Buildings and Persons from its mischievous Effects. EXPERIMENTS made in electricity first gave philosophers a suspicion, that the matter of lightning was the same with the electric matter. Experiments afterwards made on lightning obtained from the clouds by pointed rods, received into bottles, and subjected to every trial, have since proved this suspicion to be perfectly well founded; and that whatever properties we find in electricity, are also the properties of lightning. This matter of lightning, or of electricity, is an extreme subtle fluid, penetrating other bodies, and subsisting in them, equally diffused. When by any operation of art or nature, there happens to be a greater proportion of this fluid in one body than in another, the body which has most will communicate to that which has least, till the proportion be |