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 different parts of the face, collected and acting together through the metal. B. FRANKLIN. Professor Winthrop to B. Franklin. 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. I 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 stee-lie very close and stick well: but I should ples in its way. It struck the steeple a good prefer a hard sickly varnish for that purpose, way from the top, and the first impression it made of linseed oil much boiled. The heads made in the side is in the same direction I might be lined separately, the tin wrapping a saw it move in. It was succeeded by two little round their edges. The barrel, while flashes, almost united, moving in a pointed the lining is laid on, should have the end direction. There were two distinct houses hoops slack, so that the staves standing at a struck in Essex-street. I should have thought little distance from each other, may admit the the rod would have fallen in Covent-Garden, head into its groove. The tin-foil should be it was so low. Perhaps the appearance is plyed into the groove. Then, one head being frequent, though never before seen by your's, put in, and that end hooped tight, the barrel ALEXANDER SMALL. 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. 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 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 dif fused. 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 comes equal; provided the distance between them be not too great; or, if it is too great, till there be proper conductors to convey it from one to the other. If the communication be through the air without any conductor, a bright light is seen between the bodies, and a sound is heard. In our small experiments, we call this light and sound the electric spark and snap; but in the great operations of nature, the light is what we call lightning, and the sound (produced at the same time, though generally arriving later at our ears than the light does to our eyes) is, with its echoes, called thunder. If the communication of this fluid is by a conductor, it may be without either light or sound, the subtle fluid passing in the substance of the conductor. If the conductor be good and of sufficient bigness, the fluid passes through it without hurting it. If otherwise, it is damaged or destroyed. All metals, and water, are good conductors. Other bodies may become conductors by having some quantity of water in them, as wood, and other materials used in building, but not having much water in them, they are not good conductors, and therefore are often damaged in the operation. Glass, wax, silk, wool, hair, feathers, and even wood, perfectly dry, are non-conductors: that is, they resist instead of facilitating the passage of this subtle fluid. When this fluid has an opportunity of passing through two conductors, one good and sufficient, as of metal, the other not so good, it passes in the best, and will follow it in any direction. Buildings that have their roofs covered with lead, or other metal, the spouts of metal continued from the roof into the ground to carry off the water, are never hurt by lightning, as, whenever it falls on such a building, it passes in the metals and not in the walls. When other buildings happen to be within the striking distance from such clouds, the fluid passes in the walls, whether of wood, brick, or stone, quitting the walls only when it can find better conductors near them, as metal rods, bolts, and hinges of windows or doors, gilding on wainscot or frames of pictures, the silvering on the backs of looking glasses, the wires for bells, and the bodies of animals, as containing watery fluids. And in passing through the house, it follows the direction of these conductors, taking as many in its way as can assist it in its passage, whether in a strait or crooked line, leaping from one to the other, if not far distant from each other, only rending the wall in the spaces where these partial good conductors are too distant from each other. An iron rod being placed on the outside of a building, from the highest part continued down into the moist earth, in any direction strait or crooked, following the form of the roof or parts of the building, will receive the lightning at its upper end, attracting it so as to prevent its striking any other part; and affording it a good conveyance into the earth, will prevent its damaging any part of the building. A small quantity of metal is found able to conduct a great quantity of this fluid. A wire no bigger than a goose-quill has been known to conduct (with safety to the building as far as the wire was continued) a quantity of lightning that did prodigious damage both above and below it; and probably larger rods are not necessary, though it is common in America, to make them of half an inch, some of three quarters, or an inch diameter. The distance at which a body charged with this fluid will discharge itself suddenly, striking through the air into another body that is not charged, or not so highly charged, is different according to the quantity of the fluid, the dimensions and form of the bodies themselves, and the state of the air between them. The rod may be fastened to the wall, chim-This distance, whatever it happens to be, ney, &c. with staples of iron.-The lightning between any two bodies, is called their strik-will not leave the rod (a good conductor) to ing distance, as, till they come within that distance of each other, no stroke will be made. The clouds have often more of this fluid in proportion than the earth; in which case, as soon as they come near enough (that is, within the striking distance) or meet with a conductor, the fluid quits them and strikes into the earth. A cloud fully charged with this fluid, if so high as to be beyond the striking distance from the earth, passes quietly without making noise or giving light; unless it meets with other clouds that have less. Tall trees and lofty buildings, as the towers and spires of churches, become sometimes conductors between the clouds and the earth; but not being good ones, that is, not convey ing the fluid freely, they are often damaged. pass into the wall (a bad conductor) through those staples.-It would rather, if any were in the walls, pass out of it into the rod to get more readily by that conductor into the earth. If the building be very large and extensive, two or more rods may be placed at different parts, for greater security. Small ragged parts of clouds, suspended in the air between the great body of clouds and the earth (like leaf gold in electrical experiments) often serve as partial conductors for the lightning, which proceeds from one of them to another, and by their help comes within the striking distance to the earth or a building. It therefore strikes through those conductors a building that would otherwise be out of the striking distance. quiry!" Long sharp points communicating with the in an age of so much knowledge and free inearth, and presented to such parts of clouds, drawing silently from them the fluid they are charged with, they are then attracted to the cloud, and may leave the distance so great as to be beyond the reach of striking. It is therefore that we elevate the upper end of the rod six or eight feet above the highest part of the building, tapering it gradually to a fine sharp point, which is gilt to prevent its rusting. Thus the pointed rod either prevents a stroke from the cloud, or, if a stroke is made, conducts it to the earth with safety to the building. The lower end of the rod should enter the earth so deep as to come at the moist part, perhaps two or three feet; and if bent when under the surface so as to go in a horizontal line six or eight feet from the wall, and then bent again downwards three or four feet, it will prevent damage to any of the stones of the founda tion. A person apprehensive of danger from lightning, happening during the time of thunder to be in a house not so secured, will do well to avoid sitting near the chimney, near a looking-glass, or any gilt pictures or wainscot; the safest place is the middle of the room (so it be not under a metal lustre suspended by a chain) sitting in one chair and laying the feet up in another. It is still safer to bring two or three mattrasses or beds into the middle of the room, and, folding them up double, place the chair upon them; for they not being so good conductors as the walls, the lightning will not choose an interrupted course through the air of the room and the bedding, when it can go through a continued better conductor, the wall. But where it can be had, a hammoc or swinging bed, suspended by silk cords equally distant from the walls on every side, and from the ceiling and floor above and below, affords the safest situation a person can have in any room whatever; and what indeed may be deemed quite free from danger of any stroke by lightning. Answer to the above. Ir is perhaps not so extraordinary that unlearned men, such as commonly compose· our church vestries, should not yet be acquainted with, and sensible of the benefits of metal conductors in averting the stroke of lightning, and preserving our houses from its violent effects, or that they should be still prejudiced against the use of such conductors, when we see how long even philosophers, men of extensive science and great ingenuity, can hold out against the evidence of new knowledge, that does not square with their preconceptions; and how long men can retain a practice that is conformable to their prejudices, and expect a benefit from such practice, though constant experience shows its inntility. A late piece of the Abbé Nollet, printed last year in the memoirs of the French Academy of Sciences, affords strong instances of this: for though the very relations he gives of the effects of lightning in several churches and other buildings, show clearly, that it was conducted from one part to another by wires, gildings, and other pieces of metal that were within, or connected with the building, yet in the same paper he objects to the providing metalline conductors without the building, as useless or dangerous.* He cautions people not to ring the church bells during a thunder storm, lest the lightning, in its way to the earth, should be conducted down to them by the bell ropes,† which are but bad conductors; and yet is against fixing metal rods on the outside of the steeple, which are known to be much better conductors, and which it would certainly choose to pass in rather than dry hemp. And *Notre curiosité pourroit peut-être s'applaudir des nerre, et sur la mecanisme de ses principaux effets, recherches qu'elle nous a fait faire sur la nature du tonmais ce n'est point ce qu'il y a de plus important; il vaudroit bien mieux que nous puissions trouver quel que moyen de nous en garantir; on y a pensé ; on s'est même flatté d'avoir fait cette grande de couverte; mais malheureusement douze années d'épreuves et un peu de reflexion, nous apprennent qu'il ne faut pas compter sur les promesses qu'on nous a faites Je l'ai dit, il y a long temps, et avec regret, toutes ces pointes de fer qu'on dresse en l'air, soit comme electroscopes, soit comme préservatifs, sont plus propre à nous attirer le feu du tonnerre qu'à nous en préserver;et je persiste à dire que le projet d' puiser une nuce orageuse du feu dont elle est charge, n'est pas celui d'un phy sicien Memoire sur les Effets du Tonnerre. † Les cloches, en virtu de leur benediction, doivent écarter les orages et nous preserver des coups de foudre; mais l'église permet à la prudence humaine le choix des momens ou il convient d'user de ce préservatif. Je ne sais si le son, considere physiquement, est capable ou non de faire crever une nuée et de causer Pepanchement de son feu vers les objets terrestres, mais il est cer tain et prouvé par l'expérience, que la tonnerre peut tomber sur un clocher, soit que l'on y sonne point; et si cela arrive dans le premier cas, les sonneurs sont en grand danger, parcequ'ils tiennent des cordes par lesquelles la commotion de la foudre peut se communiquer jusq'à eux: il est donc plus sage de laisser les cioches en re pos quand l'orage est arrivé au-dessus de l'église.—Ibid. hand, and the other a little elevated above the level, a constant succession of large bubbles proceeds from the end in the hand to the other end, making an appearance that puzzled me much, till I found that the space not filled with water was also free from air, and either filled with a subtle invisible vapour continually rising from the water, and extremely rarefiable by the least heat at one end, and condensable again by the least coolness at the other; or it is the very fluid of fire itself, which parting from the hand pervades the glass, and by its expansive force depresses the water till it can pass between it and the glass, and escape to the other end, where it gets through the glass again into the air. I am rather inclined to the first opinion, but doubtful between the two. An ingenious artist here, Mr. Nairne, mathematical instrument-maker, has made a number of them from mine, and improved them, for his are much more sensible than those I brought from Germany.-I bored a very small hole through the wainscot in the seat of my window, through which a little cold air constantly entered, while the air in the room was kept warmer by fires daily made in it, being winter time. I placed one of his glasses, with the elevated end against this hole; and the bubbles from the other end, which was in a warmer situation, were continually passing day and night, to the no small surprise of even philosophical spectators. Each bubble discharged is larger than that from which it proceeds, and yet that is not diminished; and by adding itself to the bubble at the other end, that bubble is not increased, which though for a thousand years past bells have been solemnly consecrated by the Romish church, in expectation that the sound of such blessed bells would drive away those storms and secure our buildings from the stroke of lightning; and during so long a period, it has not been found by experience, that places within the reach of such blessed sound, are safer than others where it is never heard; but that on the contrary, the lightning seems to strike steeples of choice, and that at the very time the bells are ringing; yet still they continue to bless the new bells, and jangle the old ones whenever it thunders.-One would think it was now time to try some other trick;and ours is recommended (whatever this able philosopher may have been told to the contrary) by more than twelve years experience, wherein, among the great number of houses furnished with iron rods in North America, not one so guarded has been materially hurt with lightning, and several have been evidently preserved by their means; while a number of houses, churches, barns, ships, &c. in different places, unprovided with rods, have been struck and greatly damaged, demolished or burnt. Probably the vestries of our English churches are not generally well acquainted with these facts; otherwise, since as good protestants they have no faith in the blessing of bells, they would be less excusable in not providing this other security for their respective churches, and for the good people that may happen to be assembled in them during a tempest, especially as those buildings, from their greater height, are more exposed to the stroke of lightning than our common dwell-seems very paradoxical. When the balls at each ings. I have nothing new in the philosophical way to communicate to you, except what follows. When I was last year in Germany, I met with a singular kind of glass, being a tube about eight inches long, half an inch in diameter, with a hollow ball of near an inch in diameter at one end, and one of an inch and half at the other, hermetically scaled, and half filled with water.-If one end is held in the * Suivant le rituel de Paris, lorsqu'on benit des cloches, on recite les oraisons suivantes: Benedic, Domine..... quotiescumque sonuerit, procul recedat virtus insidiantium, umbra phantasmatis, incursio turbinum, percussio fulminum, læsio tonitruum, calamitas tempestatum, omnisque spiritus procellarum,&c. Deus, qui per beatum Moisen, &c. procul pel lentur insidia inimici, fragor grandinum, procella tur. binum impetus tempestatum, iemperentur infesta toni trua, &c Omnipotens sempiterne Deus, &c....... ut ante soni tum ejus fugentur ignita jacula inimici, percussio fulminum, impetus lapidum, læsic tempestatum, &c. En 171. M. Deslandes fit savoir à l'Academie Royale des sciences, que la nuit du 14 ou 15 d'Avril de la meme ar e, le tonnerre étoit tombe sur vingtquatre eglises, dequis Landernau jusqu'à Saint Pol-de-Leon en Bretagne; que ces églises étoient précisément celles ou l'on sonnoit, et que la foudre avoit épargne celles o l'on ne sonnoit pas: que dans celle de Gonisnon, qui fut entierement ruinée, le tonnerre tau deux per gonnes de quatre qui sonnoient, &c.--Hist. de l'Ac. R. des. Sci. 1719. end are made large, and the connecting tube very small and bent at right angles, so that the balls, instead of being at the ends, are brought on the side of the tube, and the tube is held so as that the balls are above it, the water will be depressed in that which is held in the hand, and rise in the other as a jet or fountain; when it is all in the other, it begins to boil, as it were, by the vapour passing up through it; and the instant it begins to boil, a sudden coldness is felt in the ball held; a curious experiment, this, first observed and shown me by Mr. Nairne. There is something in it similar to the old observation, I think mentioned by Aristotle, that the bottom of a boiling pot is not warm; and perhaps it may help to explain that fact;-if indeed it be a fact, -When the water stands at an equal height in both these balls, and all at rest; if you wet one of the balls by means of a feather dipt in spirit, though that spirit is of the same temperament as to heat and cold with the water in the glasses, yet the cold occasioned by the evaporation of the spirit from the wetted ball will so condense the vapour over the water contained in that ball, as that the water of the other ball will be pressed up into it, followed |