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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 stee-lie 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.

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 dif

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 me-fused. thod 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

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 équal; 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.

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. -This distance, whatever it happens to be, between any two bodies, is called their striking 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.

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 rod may be fastened to the wall, chimney, &c. with staples of iron.-The lightning will not leave the rod (a good conductor) to 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 sus pended 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.

Paris, Sept. 1767.

B. FRANKLIN.

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Answer to the above.

- IT 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 inutility. 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 nèrre, et sur la mécanisme 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 quelque moyen de nous en garantir; on y a pensê; on s'est mème flatté d'avoir fait cette grande découverte; mais malheureusement douze années d'épreuves et un peu de réflexion, 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'épuiser une nuée orageuse du feu dont elle est chargée, n'est pas celui d'un physicien-Memoire sur les Effets du Tonnerre.

† Les cloches, en virtu de leur bénédiction, doivent mais l'église permet à la prudence humaine le choix des écarter les orages et nous preserver des coups de foudre; momens où il convient d'user de ce préservatif. Je ne sais si le son, considéré physiquement, est capable ou non de faire créver une nuée et de causer l'épanchement de son feu vers les objets terrestres, mais il est certain et prouvé par l'expérience, que la tonnèrre 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 cloches en re

pos quand l'orage est arrivé au-dessus de l'église.—Ibid.

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 dwellings.

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 halfat the other, hermetically sealed, and half filled with water.-If one end is held in the * Suivant le rituel de Paris, lorsqu'on bénit des

cloches, on recite les oraisons suivantes :

Benedic, Domine..... quotiescumque sonuerit, procul recedat virtus insidiantium, umbra phantasmatis, incursio turbinum, percussio fulminum, lesio tonitruum, calamitas tempestatum, omnisque spiritus procellarum,&c. Deus, qui per beatum Moisen, &c. procul pel lentur insidie inimici, fragor grandinum, procella turbinum, impetus tempestatum, temperentur infesta toni

trua, &c.

Omnipotens sempiterne Deus, &c.

ut ante soni

tum ejus effugentur ignita jaculu inimici, percussio ful

minum, impetus lapidum, læsic tempestatum, &c.

† En 1718. M. Deslandes fit savoir à l'Academie

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 seems very paradoxical. When the balls at each 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 temRoyale des sciences, que la nuit du 14 ou 15 d'Avril de la méme année, le tonnerre étoit tombé sur vingtquatre perament as to heat and cold with the water églises, dequis Landernau jusqu'à Saint Pol-de-Leon in the glasses, yet the cold occasioned by the en Bretagne; que ces églises étoient précisément celles où l'on sonnoit, et que la foudre avoit épargné celles evaporation of the spirit from the wetted ball ou l'on ne sonnoit pas: que dans celle de Gouisnon, will so condense the vapour over the water qui fut entiérement ruinée, le tonnerre tau deux per-contained in that ball, as that the water of the sonnes de quatre qui sonnoient, &c.--Hist. de l'Ac. Rother ball will be pressed up into it, followed

des. Sci. 1719.

above it. From the foot of this rod, a wire (the thickness of a goose-quill) came through a covered glass tube in the roof, and down through the well of the staircase; the lower end connected with the iron spear of a pump. On the staircase opposite to my chamber door, the wire was divided; the ends separat

by a succession of bubbles, till the spirit is all dried away. Perhaps the observations on these little instruments may suggest and be applied to some beneficial uses. It has been thought, that water reduced to vapour by heat was rarefied only fourteen thousand times, and on this principle our engines for raising water by fire are said to be constructed about six inches, a little bell on each end; ed: but if the vapour so much rarefied from water, is capable of being itself still farther rarefied to a boundless degree by the application of heat to the vessels or parts of vessels containing the vapour (as at first it is applied to those containing the water) perhaps a much greater power may be obtained, with little additional expense. Possibly too, the power of easily moving water from one end to the other of a moveable beam (suspended in the middle like a scale-beam) by a small degree of heat, may be applied advantageously to some other mechanical purposes, B. FRANKLIN.

and between the bells a little brass ball suspended by a silk thread, to play between and strike the bells when clouds passed with electricity in them. After having frequently drawn sparks and charged bottles from the bell of the upper wire, I was one night awaked by loud cracks on the staircase. Starting up and opening the door, I perceived that the brass ball instead of vibrating as usual between the bells, was repelled and kept at a distance from both; while the fire passed sometimes in very large quick cracks from bell to bell; and sometimes in a continued dense white stream, seemingly as large as my finger, whereby the whole staircase was enlighted as with sunshine, so that one Experiments, Observations, and Facts, tendmight see to pick up a pin.* And from the ing to support the Opinion of the utility but conceive that a number of such conducapparent quantity thus discharged, I cannot of long pointed Rods, for securing Build-tors must considerably lessen that of any apings from Damage by Strokes of Lightning. Read at the committee appointed to consider the erection of conductors to secure the magazines at Purfleet, Aug. 27,

1772.

EXPERIMENT I.

THE prime conductor of an electric machine, A, B (See the plate) being supported about 10 inches and a half above the table by a wax-stand, and under it erected a pointed wire 7 inches and a half high, and one fifth of an inch thick, and tapering to a sharp point, and communicating with the table; when the point (being uppermost) is covered by the end of a finger, the conductor may be full charged, and the electrometer, c, (Mr. Henley's) will rise to the height indicating a full charge: but the moment the point is uncovered, the ball of the electrometer drops, showing the prime conductor to be instantly discharged and nearly emptied of its electricity. Turn the wire its blunt end upwards (which represents an unpointed bar) and no such effect follows, the electrometer remaining at its usual height when the prime conductor is charged.

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proaching cloud, before it comes so near as to deliver its contents in a general stroke:—an effect not to be expected from bars unpointed.; if the above experiment with the blunt end of the wire is deemed pertinent to the case.

EXPERIMENT II.

The pointed wire under the prime conductor continuing of the same height, pinch it between the thumb and finger near the top, so as just to conceal the point; then turning the globe, the electrometer will rise and mark the full charge. Slip the fingers down so as to discover about half an inch of the wire, then another half inch, and then another; at every one of these motions discovering more and more of the pointed wire; you will see the electrometer fall quick and proportionably, stopping when you stop. If you slip down the whole distance at once, the ball falls instantly down to the stem.

OBSERVATION.

From this experiment it seems that a greater effect in drawing off the lightning

* Mr. de Romas saw still greater quantities of lightning brought down by the wire of his kite. He had explosions from it, the noise of which greatly resembled that of thunder, and were heard (from without) into the heart of the city, notwithstanding the various had the shape of a spindle eight inches long and five lines in diameter. Yet from the time of explosion to the end of the experiment, no lightning was seen above, nor any thunder heard. At another time the streams thick and ten feet long."-See Dr. Priestley's History of fire issuing from it were observed to be an inch of Electricity, pages 134-136, first edition. at Purfleet.

noises there. The fire seen at the instant of the explosion

Twelve were proposed on and near the magazines

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