the probability of those rods preventing a stroke or explosion, which is only a part of the use I proposed for them; and the other part, their conducting a stroke, which they may happen not to prevent, seems to be totally forgotten, though of equal importance and advantage. I thank you for communicating M. de Buffon's relation of the effect of lightning at Dijon, on the 7th of June last. In return, give me leave to relate an instance I lately saw of the same kind. Being in the town of Newbury, in New England, in November last, I was shown the effect of lightning on their church, which had been struck a few months before. The steeple was a square tower of wood reaching seventy feet up from the ground to the place where the bell hung, over which rose a taper spire, of wood likewise, reaching seventy feet higher, to the vane of the weathercock. Near the bell was fixed an iron hammer to strike the hours: and from the tail of the hammer a wire went down through a small gimlet-hole in the floor that the bell stood upon, and through a second floor in like manner; then horizontally under and near the plastered ceiling of that second floor, till it came near a plastered wall; then down by the side of that wall to a clock, which stood about twenty feet below the bell. The wire was not bigger than a common knitting-needle. The spire was split all to pieces by the lightning, and the parts flung in all directions over the square in which the church stood, so that nothing remained above the bell. 1. That lightning, in its passage through a building, will leave wood to pass as far as it can in metal, and not enter the wood again till the conductor of metal ceases. And the same I have observed in other in stances, as to walls of brick or stone. 2. The quantity of lightning that passed through this steeple must have been very great, by its effects on the lofty spire above the bell, and on the square tower all below the end of the clock pendulum. 3. Great as this quantity was, it was conducted by a small wire and a clock pendulum, without the least damage to the building so far as they extended. 4. The pendulum rod being of a sufficient thickness, conducted the lightning without damage to itself; but the small wire was utterly destroyed. 5. Though the small wire was itself destroyed, yet it had conducted the lightning with safety to the building. 6. And from the whole it seems probable, that if even such a small wire had been extended from the spindle of the vane to the earth, before the storm, no damage would have been done to the steeple by that stroke of lightning, though the wire itself had been destroyed. To Peter Collinson. PHILADELPHIA, Nov. 23, 1753. DEAR FRIEND,-In my last, via Virginia, I promised to send you per next ship, a small philosophical packet: but now having got the materials (old letters and rough drafts) before me, I fear you will find it a great one. Nevértheless, as I am like to have a few days' leisure before this ship sails, which I may not have again in a long time, I shall transcribe the whole, and send it; for you will be under no necessity of reading it all at once, but may take it a little at a time, now and then of a winter evening. When you happen to have nothing else to do (if that ever happens) it may afford you some amusement.* B. FRANKLIN. The lightning passed between the hammer and the clock in the above mentioned wire, without hurting either of the floors, or having any effect upon them (except making the gimlet-holes, through which the wire passed, a little bigger,) and without hurting the plastered wall, or any part of the building, so far as the aforesaid wire and the pendulum wire of the clock extended; which latter wire was about the thickness of a goose-quill. From the end of the pendulum, down quite to the ground, the building was exceedingly rent and damaged, and some stones in the foundation-wall torn out, and thrown to the distance of twenty or thirty feet. No part of the afore mentioned long small wire, between the clock and the hammer, could be found, except about two inches that hung to the tail of the hammer, and about as much that was fastened to the clock; the rest being exploded, and its particles dissipated in smoke and air, as gunpowder is by common fire, and had only left a black smutty track on the plastering, three or four inches broad, darkest in the middle, and fainter towards the edges, all along the ceiling, under which it passed, and down the As some of these papers are upon subjects not immewall. These were the effects and appear-diately connected with electricity, we have taken such ances; on which I would only make the few papers from the order in which they were placed by Mr. Collinson, and transferred them to other parts of this following remarks, viz. edition. VOL. II.... 2P * These letters and papers are a philosophical corres pondence between Dr. Franklin and some of his American friends. Mr. Collinson communicated them to the Royal Society, where they were read at different meetings during the year 1756. But Dr. Franklin having particularly requested that they might not be printed, at that time an intention of revising them, and pursuing some of the inquiries farther; but finding that he was not likely to have sufficient leisure, he was at length induced, imperfect as they were, to permit their publication, as some of the hints they contain might possibly be useful to others in their philosophical re none of them were inserted in the transactions. He had searches. Note in Mr. Collinson's edition. Extract of a letter from Mr. Bowdoin of The column, being thus acted upon, be Boston to Benjamin Franklin, concerning the crooked direction and the source of lightning, and the swiftness of the electric fire. BOSTON, Dec. 21, 1751. THE experiments Mr. K. has exhibited here, have been greatly pleasing to all sorts of people that have seen them; and I hope, by the time he returns to Philadelphia, his tour this way will turn to good account. His experiments are very curious, and I think prove most effectually your doctrine of electricity; that it is a real element, annexed to, and diffused among all bodies we are acquainted with; that it differs in nothing from lightning, the effects of both being similar, and their properties, so far as they are known, the same, &c. mag comes more dense, and, being more dense repels the spark more strongly; its repellency being in proportion to its density having acquired, by being condensed, a degree of repellency greater than its natural, it turns the spark out of its straight course; the neighbouring air, which must be less dense, and therefore has a smaller degree of repellency, giving it a more ready passage. The spark, having taken a new direction, must now act on, or most strongly repel the column of air which lies in that direction, and consequently must condense that column in the same manner as the former, when the spark must again change its course, which course will be thus repeatedly changed, till the spark reaches the body that attracted it. accumulated air within the column aforesaid, would be immediately diffused among the contiguous air, and circulate to fill the space it was driven from and consequently that the said column, on the greater density of which the phenomenon is supposed to depend, would not repel the spark more strongly than the neighbouring air. This might be an objection, if the electrical fire was as sluggish and inactive as air. Air takes a sensible time to diffuse itself If equally, as is manifest from winds which often blow for a considerable time together from the same point, and with a velocity even in the greatest storms, not exceeding, as it is said, sixty miles an hour: but the electric fire seems propagated instantaneously, taking up no perceptible time in going very great distances. It must then be an inconceivable short time in its progress from an electrified to an unelectrified body, which, in the present case, can be but a few inches apart: but this small portion of time is not sufficient for elasticity of the air to exert itself, and therefore the column aforesaid must be in a denser state than its neighbouring air. To this account one objection occurs; that The remarkable effect of lightning on as air is very fluid and elastic, and so eniron, lately discovered, in giving it the mag-deavours to diffuse itself equally, the supposed netic virtue, and the same effect produced on small needles by the electrical fire, is a further and convincing proof that they are both the same element; but, which is very unaccountable, Mr. K. tells me, it is necessary to produce this effect, that the direction of the needle and the electric fire should be north and south; from either to the other, and that just so far as they deviate therefrom, the netic power in the needle is less, till their direction being at right angles with the north and south, the effect entirely ceases. We made at Faneuil Hall, where was Mr. K.'s apparatus, several experiments, to give some small needles the magnetic virtue; previously examining, by putting them in water, on which they will be supported, whether or not they had any of that virtue; and I think we found all of them to have some small degree of it, their points turning to the north; we had nothing to do then but to invert the poles, which accordingly was done, by sending through them the charge of two large glass jars; the eye of the needle turning to the north, as the point before had done: that end of the needle which the fire is thrown upon, Mr. K. tells me always points to the north. The electrical fire passing through air has the same crooked direction as lightning.* This appearance I endeavour to account for thus: air is an electric per se, therefore there must be a mutual repulsion betwixt air and the electrical fire. A column or cylinder of air, having the diameter of its base equal to the diameter of the electrical spark, intervenes that part of the body which the spark is taken from, and of the body it aims at. The spark acts upon this column, and is acted upon by it, more strongly than any other neighbouring portion of air. *This is most easily observed in large strong sparks taken at some inches distance. About the velocity of the electric fire more is said below, which perhaps may more fully obviate this objection. But let us have recourse to experiments. Experiments will obviate all objections, or confound the hypothesis. The electric spark, if the foregoing be true, will pass through a vacuum in a right line. To try this, let a wire be fixed perpendicularly on the plate of an air pump, having a leaden ball on its upper end; let another wire, passing through the top of a receiver, have on each end a leaden ball; let the leaden balls within the receiver, when put on the air pump, be within two or three inches of each other; the receiver being exhausted, the spark given from a charged phial to the upper wire will pass through rarified air, nearly approaching to a vacuum, to the lower wire, and I suppose in a right line, or nearly so; the small portion of air remaining in the receiver, which cannot be entirely exhausted, may possibly cause it to deviate a little, but perhaps not sensibly from a right line. The spark also might be made to pass through air greatly condensed, which perhaps would give a still more crooked direction. I have not had opportunity to make any experiments of this sort, not knowing of an air-pump nearer than Cambridge, but you can easily make them. If these experiments answer, I think the crooked direction of lightning will be also accounted for. stroke, nor, which is more extraordinary, saw the light; which gave you just reason to conclude, that it was swifter than sound, than animal sensation, and even light itself. Now light (as astronomers have demonstrated) is about six minutes passing from the sun to the earth; a distance, they say, of more than eighty millions of miles. The greatest rectilinear distance within the compass of the earth is about eight thousand miles, equal to its diameter. Supposing then, that the velocity of the electric fire be the same as that of light, it will go through a space equal to the earth's diameter in about two sixtieths of the second of a minute. It seems inconceivable then, that it should be accumulated upon the sea, in its present state, which, as it is a non-electric, must give the fire an instantaneous passage to the neighbouring shores, and they convey it to the general mass of the earth. But such accumulation seems still more inconceivable when the electrical fire has but few feet depth of water to penetrate, to return to the place from whence it is supposed to be collected. With respect to your letters on electricity; your hypothesis in particular for explaining the phenomena of lightning is very ingenious. That some clouds are highly charged with electrical fire, and that their communicating it to those that have less, to mountains and other eminences, makes it visible and audible, when it is denominated lightning and thunder, is highly probable; but that the sea, which you suppose the grand source of it, can collect it, I think admits of a doubt; for though the Your thoughts upon these remarks I shall sea be composed of salt and water, an elec- receive with a great deal of pleasure. I take tric per se and non-electric, and though the notice that in the printed copies of your letters, friction of electrics per se and non-electrics, several things are wanting which are in the will collect that fire, yet it is only under cer- manuscript you sent me. I understand by tain circumstances which water will not ad- your son, that you had writ, or was writing, a mit. For it seems necessary, that the elec- paper on the effect of the electrical fire on trics per se and non-electrics rubbing one ano-loadstones, needles, &c. which I would ask ther, should be of such substances as will not adhere to, or incorporate with each other. Thus a glass or sulphur sphere turned in water, and so a friction between them, will not collect any fire; nor, I suppose, would a sphere of salt revolving in water: the water adhering to, or incorporating with those electrics per se. But granting that the friction between salt and water would collect the electrical fire; that fire, being so extremely subtle and active, would be immediately communicated, either to those lower parts of the sea from which it was drawn, and so only perform quick revolutions; or be communicated to the adjacent islands or continent, and so be diffused instantaneously through the general mass of the earth. I say instantaneously, for the greatest distances we can conceive within the limits of our globe, even that of the two most opposite points, it will take no sensible time in passing through; and therefore it seems a little difficult to conceive how there can be any accumulation of the electrical fire upon the surface of the sea, or how the vapours arising from the sea should have a greater share of that fire than other vapours. That the progress of the electrical fire is so amazingly swift, seems evident from an experiment you yourself (not out of choice) made, when two or three large glass jars were discharged through your body. You neither heard the crack, was sensible of the the favour of a copy of, as well as of any other J. Bowdoin, Boston. Observations on the subjects of the preceding letter, -Reasons for supposing the sea to be the grand source of Lightning.- Reasons for doubting this hypothesis.-Improvement in a globe for raising the Electric Fire.-Read at the Royal Society, May 27, 1756. PHILADELPHIA, Jan. 24, 1752. I AM glad to learn, by your favour of the 21st past, that Mr. Kinnersley's lectures have been acceptable to the gentlemen of Boston, and are like to prove serviceable to himself. I thank you for the countenance and encouragement you have so kindly afforded my fellow-citizen. I send you enclosed an extract of a letter containing the substance of what I observed concerning the communication of magnetism to needles by electricity. The minutes I took at the time of the experiments are mislaid. I am very little acquainted with the nature of magnetism. Dr. Gawin Knight, inventor of the steel magnets, has wrote largely on that subject, but I have not yet had leisure to peruse his writings with the attention necessary to become master of his doctrine. Your explication of the crooked direction of be repelled from the then generally electrilightning appears to me both ingenious and solid. When we can account as satisfactorily for the electrification of clouds, I think that branch of natural philosophy will be nearly complete. The air, undoubtedly, obstructs the motion of the electric fluid. Dry air prevents the dissipation of an electric atmosphere, the den ser the more, as in cold weather. I question whether such an atmosphere can be retained by a body in vacuo. A common electrical phial requires a non-electric communication from the wire to every part of the charged glass; otherwise, being dry and clean, and filled with air only, it charges slowly, and discharges gradually, by sparks, without a shock: but exhausted of air, the communication is so open and free between the inserted wire and surface of the glass, that it charges as readily, and shocks as smartly as if filled with water and I doubt not, but that in the experiment you propose, the sparks would not only be near strait in vacuo, but strike at a greater distance than in the open air, though perhaps there would not be a loud explosion. As soon as I have a little leisure, I will make the experiment, and send you the result. fied surface of the sea, and fly away with them into the air. I thought too, that possibly the great mixture of particles electric per se, in the ocean water, might, in some degree, impede the swift motion and dissipation of the electric fluid through it to the shores, &c.-But having since found, that salt in the water of an electric phial does not lessen the shock; and having endeavoured in vain to produce that luminous appearance from a mixture of salt and water agitated; and observed, that even the sea-water will not produce it after some hours standing in a bottle; I suspect it to proceed from some principle yet unknown to us (which I would gladly make some experiments to discover, if I lived near the sea) and I grow more doubtful of my former supposition, and more ready to allow weight to that objection (drawn from the activity of the electric fluid, and the readiness of water to conduct) which you have indeed stated with great strength and clearness. electric fluid, which the rising vapours might receive from the air, and retain in the clouds they form? on which I should be glad to have your sentiments. An ingenious friend of mine supposes the land-clouds more likely to be electrified than the sea-clouds. I send his letter for your perusal, which please to return me. In the mean time, before we part with this hypothesis, let us think what to substitute in its place. I have sometimes queried whether the friction of the air, an electric per se, My supposition, that the sea might possibly in violent winds, among trees, and against be the grand source of lightning, arose from the surface of the earth, might not pump up, the common observation of its luminous ap-as so many glass globes, quantities of the pearance in the night, on the least motion; an appearance never observed in fresh water. Then I knew that the electric fluid may be pumped up out of the earth, by the friction of a glass globe, on a non-electric cushion; and that notwithstanding the surprising activity and swiftness of that fluid, and the nonelectric communication between all the parts I have wrote nothing lately on electricity, of the cushion and the earth, yet quantities nor observed any thing new that is material, would be snatched up by the revolving sur- my time being much taken up with other afface of the globe, thrown on the prime con- fairs. Yesterday I discharged four jars ductor, and dissipated in air. How this was through a fine wire, tied up between two done, and why that subtle active spirit did not strips of glass: the wire was in part melted, immediately return again from the globe, into and the rest broke into small pieces from half some part or other of the cushion, and so into an inch long, to half a quarter of an inch. My the earth, was difficult to conceive; but whe-globe raises the electric fire with greater ease, ther from its being opposed by a current setting upwards to the cushion, or from whatever other cause, that it did not so return was an evident fact. Then I considered the separate particles of water as so many hard spherules, capable of touching the salt only By this post I send to ****, who is curious in points, and imagined a particle of salt could in that way, some meteorological observations therefore no more be wet by a particle of wa- and conjectures, and desire him to communiter, than a globe by a cushion; that there cate them to you, as they may afford you might therefore be such a friction between some amusement, and I know you will look these originally constituent particles of salt over them with a candid eye. By throwing and water, as in a sea of globes and cushions; our occasional thoughts on paper, we more that each particle of water on the surface readily discover the defects of our opinions, or might obtain from the common mass, some we digest them better and find new arguments particles of the universally diffused much to support them. This I sometimes practise : finer, and more subtle electric fluid, and form- but such pieces are fit only to be seen by ing to itself an atmosphere of those particles, friends. B. FRANKLIN. in much greater quantities, by the means of a wire extended from the cushion, to the iron pin of a pump handle behind my house, which communicates by the pump spear with the water in the well. four glass jars had upon a fine wire, tied be J. Bowdoin to Benjamin Franklin. Effect of Lightning on Captain Waddel's Com-tween two strips of glass, puts me in mind of a pass, and the Dutch Church at New York Read at the Royal Society, June 3, 1752. BOSTON, March 2, 1752. very similar one of lightning, that I observed at New York, October, 1750, a few days after I left Philadelphia. In company with a number of gentlemen, I went to take a view of the city from the Dutch church steeple, in which is a clock about twenty or twenty-five feet below the bell. From the clock went a wire through two floors, to the clock-hammer near the bell, the holes in the floor for the wire being perhaps about a quarter of an inch diameter. We were told, that in the spring of 1750, the lightning struck the clock hammer, and descended along the wire to the clock, melting in its way several spots of the wire, from three to nine inches long, through one third of its substance, till coming within a few feet of the lower end, it melted the wire quite through, in several places, so that it fell down in several pieces; which spots and pieces we saw. When it got to the end of the wire, it flew off to the hinge of a door, shattered the door, and dissipated. In its passage through the holes of the floors it did not do the least damage, which evidences that wire is a good conductor of lightning (as it is of electricity) provided it be substantial enough, and might, in this case, had it been continued to the earth, have conducted it without damaging the building.* I HAVE received your favour of the 24th of January past, enclosing an extract from your letter to Mr. Collinson, and ****'s letter to yourself, which I have read with a great deal of pleasure, and am much obliged to you for. Your extract confirms a correction Mr. Kinnersley made a few days ago, of a mistake I was under respecting the polarity given to needles by electrical fire," that the end which receives the fire always points north;" and “that the needle being situated east and west will not have a polar direction." You find, however, the polarity strongest when the needle is shocked lying north and south; weakest when lying east and west; which makes it probable that the communicated magnetism is less, as the needle varies from a north and south situation. As to the needle of captain Waddel's compass, if its polarity was reversed by the lightning, the effect of lightning and electricity, in regard of that, seems dissimilar; for a magnetic needle in a north and south situation (as the compass needle was) instead of having its power reversed, or even diminished, would have it confirmed or increased by the electric fire. But perYour information about your globe's raising haps the lightning communicated to some the electric fire in greater quantities, by means nails in the binnacle (where the compass is of a wire extended from the cushion to the placed) the magnetic virtue, which might dis-earth, will enable me, I hope, to remedy a turb the compass. This I have heard was the case; if so, the seeming dissimilarity vanishes: but this remarkable circumstance (if it took place). I should think would not be omitted in captain Waddel's account. I am very much pleased that the explication I sent you, of the crooked direction of lightning, meets with your approbation. As to your supposition about the source of lightning, the luminous appearance of the sea in the night, and the similitude between the friction of the particles of salt and water, as you considered them in their original separate state, and the friction of the globe and cushion, very naturally led you to the ocean, as the grand source of lightning: but the activity of lightning, or the electric element, and the fitness of water to conduct it, together with the experiments you mention of salt and water, seem to make against it, and to prepare the way for some other hypothesis. Accordingly you propose a new one, which is very curious, and not so liable, I think, to objections as the former. But there is not, as yet, I believe, a sufficient variety of experiments to establish any theory, though this seems the most hopeful of any I have heard of. The effect which the discharge of your lect the fire with the electrifying glass I use, great inconvenience I have been under, to colwhich is fixed in a very dry room, three stories from the ground. When you send your meteorological observations to ****, I hope I shall have the pleasure of seeing them. J. BOWDOIN. Proposal of an experiment to measure the time taken up by an Electric Spark in moving through any given space. By James Alexander, of New York.-Read at the Royal Society, Dec. 26, 1756. IF I remember right, the Royal Society made one experiment to discover the velocity *The wire mentioned in this account was replaced by a small brass chain. In the summer of 1763. the lightning again struck that steeple, and from the clockhammer near the bell, it pursued the chain as it had be fore done the wire, went off to the same hinge, and again shattered the same door. In its passage through the same holes of the same floors, it did no damage to the floors, nor to the building during the whole extent of the chain. But the chain itself was destroyed, being partly scattered about in fragments of two or three links melted and stuck together, and partly blown up or reduced to smoke, and dissipated. [See an account of the same effect of lightning on a wire at Newbury, p. 296. ] The steeple, when repaired, was guarded by an iron spindle down the outside of the building, into the earth. conductor, or rod, extending from the foot of the vane |