« AnteriorContinuar »
Your question, how I came first to think | cloud may occasion a neighbouring cloud to of proposing the experiment of drawing down draw into itself from others, an additional :he lightning, in order to ascertain its same- quantity, and, passing by it, leave it in a posiness with the electric fluid, I cannot answer tive state. How these effects may be probetter than by giving you an extract from the duced, you will easily conceive, on perusing minutes I used to keep of the experiments I and considering the experiments in the enmade, with memorandums of such as I pur- closed paper : and from them too it appears posed to make, the reasons for making them, probable, that every change from positive to and the observations that arose upon them, negative, and from negative to positive, that, from which minutes my letters were after- during a thunder-gust, we see in the corkwards drawn. By this extract you will see balls annexed to the apparatus, is not owing that the thought was not so much an out-of-to the presence of clouds in the same state, the-way one, but that it might have occur- but often to the absence of positive or negared to an electrician.
tive clouds, that, having just passed, leave the “Nov. 7, 1749. Electrical fluid agrees rod in the opposite state. with lightning in these particulars; 1. Giv The knocking down of the six men was ing light. 2. Colour of the light. 3. Crooked performed with two of my large jars not fully direction. 4. Swift motion. 5. Being, con-charged. I laid one end of my discharging ducted by metals. 6. Crack or noise in ex- rod upon the head of the first; he laid his ploding. 7. Subsisting in water or ice. 8. hand upon the head of the second ; the second Rending bodies it passes through. 9. De- his hand on the head of the third, and so to stroying animals. 10. Melting metals. 11. the last, who held, in his hand, the chain that Firing inflammable substances. 12. Sulphur- was connected with the outside of the jars. eous smell.—The electric fluid is attracted When they were thus placed, I applied the by points.—We do not know whether this other end of my rod to the prime conductor, property is in lightning.–But since they and they all dropped together. When they agree in all the particulars wherein we can got up, they all declared they had not felt already compare them, is it not probable they any stroke, and wondered how they came to agree likewise in this ? Let the experiment fall; nor did any of them either hear the be made.”
crack, or see the light of it. You suppose it I wish I could give you any satisfaction in a dangerous experiment; but I had once sufthe article of clouds. I am still at a loss fered the same myself, receiving, by accident, about the manner in which they become an equal stroke through my head, that struck charged with electricity; no hypothesis I have me down, without hurting me: and I had yet formed perfectly satisfying me. Some seen a young woman who was about to be time since, I heated very hot, à brass plate electrified through the feet (for some indispotwo feet square, and placed it on an electric sition) receive a greater charge through the stand. From the plate a wire extended ho- head, by inadvertently stooping forward to rizontally four or five feet, and, at the end of look at the placing of her feet, till her foreit, hung, by linen threads, a pair of cork balls. head (as she was very tall) came too near my I then repeatedly sprinkled water over the prime conductor: she dropped, but instantly plate, that it might be raised from it in vapour, got up again, complaining of nothing. А hoping that if the vapour either carried off person so struck, sinks down doubled, or foldthe electricity of the plate, or left behind it ed together as it were, the joints losing their that of the water, (one of which I supposed it strength and stiffness at once, so that he drops must do, if, like the clouds, it became elec- on the spot where he stood, instantly, and trised itself, either positively or negatively) I there is no previous staggering, nor does he should perceive and determine it by the sepa- ever fall lengthwise. Too great' a charge ration of the balls, and by finding whether they might, indeed, kill a man, but I have not yet were positive or negative; but no alteration seen any hurt done by it. It would certainwas made at all, nor could I perceive that the ly, as you observe, be the easiest of all deaths. steam was itself electrised, though I have The experiment you have heard so imperstill some suspicion that the steam was not fect an account of, is merely this: I electrifully examined, and I think the experiment fied a silver pint can, on an electric stand, should be repeated. Whether the first state and then lowered into it a cork ball, of about of electrised clouds is positive or negative, if an inch diameter, hanging by a silk string, I could find the cause of that, I should be at till the cork touched the bottom of the can. no loss about the other, for either is easily de- The cork was not attracted to the inside of the duced from the other, as one state is easily can as it would have been to the outside, and produced by the other. A strongly positive though it touched the bottom, yet when drawn cloud may drive out of a neighbouring cloud out, it was not found to be electrified by that much of its natural quantity of the electric touch, as it would have been by touching the fluid, and, passing by it, leave it in egative outside. The fact is singular. You require state. In the same way, a strongly negative the reason; I do not know it. Perhaps you
may discover it
, and then you will be so good we are indebted for the compass, and for specas to communicate it to me.* I find a frank tacles, nor have even paper and printing, acknowledgment of one's ignorance is not that record every thing else, been able to preonly the easiest way to get rid of a difficulty, serve with certainty the name and reputation but the likeliest way to obtain information, of their inventors. One would not, thereforc, and therefore I practise it: I think it an honest of all faculties, or qualities of the mind, wish, policy. Those who affect to be thought to for a friend, or a child, that he should have know every thing, and so undertake to explain that of invention. For his attempts to beneevery thing, often remain long ignorant of fit mankind in that way, however well imamany things that others could and would in- gined, if they do not succeed, expose him, struct them in, if they appeared less conceited. though very unjustly, to general ridicule and
The treatment your friend has met with is contempt; and, if they do succeed, to envy, so common, that no man who knows what the robbery, and abuse. B. FRANKLIN. world is, and ever has been, should expect to escape it. There are every where a number
Mons. Dalibard, Paris. of people, who being totally destitute of any inventive faculty themselves, do not readily Beccaria's work on Electricity.— Sentiments of conceive that others may possess it: they
Franklin on pointed Rods, not fully underthink of inventions as of miracles; there might
stood in Europe.-Effect of Lightning on the
Church of Newbury, in New England.-Rebe such formerly, but they are ceased. With
marks on the subject. -- Read at the Royal So these, every one who offers a new invention
ciety, Dec. 18, 1775. is deemed a pretender : he had it from some
PAILADELPHIA, June 29, 1755. other country, or from some book: a man of
You desire my opinion of Père Beccaria's their own acquaintance; one who has no Italian book.* Í have read it with much pleamore sense than themselves, could not possi- sure, and think it one of the best pieces on bly, in their opinion, have been the inventor the subject that I have seen in any language. of any thing. They are confirmed too, in Yet as to the article of water-spouts, I am not these sentiments, by frequent instances of pre- at present of his sentiments; though I must tensions to invention, which vanity is daily own with you, that he has handled it very inproducing. That vanity too, though an in- geniously. Mr. Collinson has my opinion of citement to invention, is, at the same time, whirlwinds and water-spouts at large, written the pest of inventors. Jealousy and envy de- some time since. I know not whether they ny the merit or the novelty of your invention; will be published ; if not, I will get them tranbut vanity, when the novelty and merit are scribed for your perusal. It does not appear established, claims it for its own. The smaller to me that Père Beccaria doubts of the absoyour invention is, the more mortification you lute impermeability of glass in the sense I receive in having the credit ,of it disputed meant it; for the instances he gives of holes with you by a rival, whom the jealousy and made through glass by the electric stroke are envy of others are ready to support against such as we have all experienced, and only you, at least so far as to make the point show that the electric Auid could not pass doubtful. It is not in itself of importance without making a hole. In the same manner enough for a dispute; no one would think we say, glass is impermeable to water, and your proofs and reasons worth their atten- yet a stream from å fire-engine will force tion: and yet, if you do not dispute the point, through the strongest panes of a window. As and demonstrate your right, you not only to the effect of points in drawing the electric lose the credit of being in that instance in- matter from clouds, and thereby securing genious, but you suffer the disgrace of not be buildings, &c. which, you say, he seems to ing ingenuous ; not only of being a plagiary, doubt, I must own I think he only speaks mobut of being a plagiary for trifles. Had the in- destly and judiciously. I find I have been but vention been greater it would have disgraced partly understood in that matter. I have you less; for men have not so contempti- mentioned it in several of my letters, and exble an idea of him that robs for gold on the cept once, always in the alternative, viz. that highway, as of him that can pick pockets for pointed rods erected on buildings, and comhalf-pence and farthings. Thus, through municating with the moist earth, would either envy, jealousy, and the vanity of competitors prevent a stroke, or, if not prevented, would for fame, the origin of many of the most extra- conduct it, so as that the building should sufordinary inventions, though produced within fer no damage. Yet whenever my opinion is but a few centuries past, is involved in doubt examined in Europe, nothing is considered but and uncertainty. We scarce know to whom
* This work is written conformable to Dr. Franklin's * Dr. F. afterwards thought, that, possibly, the mu theory, upon artificial and natural electricity, which tual repulsion of the inner opposite sides of the electris-compose the two parts of it. It was printed in Italian, ed might prevent the accumulating of an electric at. at Turin, in 4to. 1753; between the two parts is a letler mosphere upon them, and occasion it to stand chiefly to the Abbe Nollet, in defence of Dr. Franklin's system. on the outside. But recommended it to the farther er. | These papers will be found in a subsequent part of amination of the curious.
he probability of those rods preventing a 1. That lightning, in its passage through stroke or explosion, which is only a part of a building, will leave wood to pass as far as he use I proposed for them; and the other it can in metal, and not enter the wood again bart, their conducting a stroke, which they till the conductor of metal ceases. nay happen not to prevent, seems to be totally And the same I have observed in other inorgotten, though of equal importance and ad- stances, as to walls of brick or stone. rantage.
2. The quantity of lightning that passed I thank you for communicating M. de Buf- through this steeple must have been very on's relation of the effect of lightning at Di- great, by its effects on the lofty spire above on, on the 7th of June last. In return, give the bell, and on the square tower all below ne leave to relate an instance I lately saw of the end of the clock pendulum. he same kind. Being in the town of New 3. Great as this quantity was, it was convury, in New England, in November last, I ducted by a small wire and a clock pendulum, was shown the effect of lightning on their without the least damage to the building so :hurch, which had been struck a few months far as they extended. Jefore. The steeple was a square tower of 4. The pendulum rod being of a sufficient vood reaching seventy feet up from the ground thickness, conducted the lightning without o the place where the bell hung, over which damage to itself; but the small wire was ut'ose a taper spire, of wood likewise, reaching terly destroyed. seventy feet higher, to the vane of the weather 5. Though the small wire was itself derock. Near the bell was fixed an iron ham- stroyed, yet it had conducted the lightning ner to strike the hours: and from the tail of with safety to the building. the hammer a wire went down through a small 6. And from the whole it seems probable, gimlet-hole in the floor that the bell stood that if even such a small wire had been exipon, and through a second floor in like man- tended from the spindle of the vane to the aer; then horizontally under and near the earth, before the storm, no damage would plastered ceiling of that second floor, till it have been done to the steeple by that stroke came near a plastered wall; then down by of lightning, though the wire itself had been the side of that wall to a clock, which stood destroyed. 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
To Peter Collinson. lightning, and the parts flung in all directions over the square in which the church stood, so
PHILADELPHIA, Nov. 23, 1753. that nothing remained above the bell.
DEAR FRIEND,—In my last, via Virginia, I The lightning passed between the hammer promised to send you per next ship, a small and the clock in the above mentioned wire, philosophical packet : but now having got the without hurting either of the floors, or having materials (old letters and rough drafts) before any effect upon them (except making the me, I fear you will find it a great oné. Negimlet-holes, through which the wire passed, vertheless, as I am like to have a few days' a little bigger,) and without hurting the plas- leisure before this ship sails, which I may not tered wall, or any part of the building, so far have again in a long time, I shall transcribe as the aforesaid wire and the pendulum wire the whole, and send it; for you will be under of the clock extended; which latter wire was no necessity of reading it all at once, but may about the thickness of a goose-quill. From take it a little at a time, now and then of a the end of the pendulum, down quite to the winter evening. When you happen to have ground, the building was exceedingly rent nothing else to do (if that ever happens) it and damaged, and some stones in the founda
you some amusement.* tion-wall torn out, and thrown to the distance
B. FRANKLIN. of twenty or thirty feet. No part of the afore mentioned long small wire, between the clock
* These letters and papers are a philosophical corres. and the hammer, could be found, except about pondence between Dr. Franklin and some of his Ameri. two inches that hung to the tail of the ham- can friends. Mr. Collinson communicated them to the
Royal Society, where they were read at different meet. mer, and about as much that was fastened to ings during the year 1756. But Dr. Franklin having the clock; the rest being exploded, and its particularly requested that they might not be printed, particles dissipated in smoke and air, as gun- at that time an intention of revising them, and pursu. powder is by common fire, and had only left ing some of the inquiries farther; but
finding that he a black smutty track on the plastering, three was not likely to have sufficient leisure, he was at or four inches broad, darkest in the middle, publication, as some of the hints they contain might and fainter towards the edges, all along the possibly be useful to others in their philosophical re. ceiling, under which it passed, and down the searches. Note in Mr. Collinson's edition.
† As some of these papers are upon subjects not imme. wall. 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.
VOL. II.. 2P
Extract of a letter from Mr. Bowdoin of The column, being thus acted upon, be
Boston to Benjamin Franklin, concerning comes more dense, and, being more dense rethe crooked direction and the source of pels the spark more strongly ; its repellency lightning, and the swiftness of the electric being in proportion to its density: having acfire.
quired, by being condensed, a degree of re
Boston, Dec. 21, 1751. pellency greater than its natural, it turns the The experiments Mr. K. has exhibited spark out of its straight course; the neighhere, have been greatly pleasing to all sorts bouring air, which must be less dense, and of people that have seen them; and I hope, therefore has a smaller degree of repellency, by the time he returns to Philadelphia, his giving it a more ready passage. tour this way will turn to good account. His
The spark, having taken a new direction, experiments are very curious, and I think must now act on, or most strongly repel the prove most effectually your doctrine of elec- column of air which lies in that direction, and tricity; that it is a real element, annexed to, consequently must condense that column in and diffused among all bodies we are acquaint- the same manner as the former, when the ed with; that it differs in nothing from light- spark must again change its course, which ning, the effects of both being similar, and course will be thus repeatedly changed, till their properties, so far as they are known, the the spark reaches the body that attracted it
To this account one objection occurs; that The remarkable effect of lightning on as air is very fluid and elastic, and so en iron, lately discovered, in giving it the mag-deavours to diffuse itself equally, the supposed netic virtue, and the same effect produced on accumulated air within the column aforesaid, small needles by the electrical fire, is a further would be immediately diffused among the conand convincing proof that they are both the tiguous air, and circulate to fill the space it same element; but, which is very unaccounta- was driven from : and consequently that the ble, Mr. K. tells me, it is necessary to pro- said column, on the greater density of which duce this effect, that the direction of the the phenomenon is supposed to depend, would needle and the electric fire should be north not repel the spark more strongly than the and south; from either to the other, and that neighbouring air. just so far as they deviate therefrom, the
This might be an objection, if the electrical netic power in the needle is less, till their di- fire was as sluggish and inactive as air. Air rection being at right angles with the north takes a sensible time to diffuse itself equally, and south, the effect entirely ceases.
We as is manifest from winds which often blow made at Faneuil Hall, where was Mr. K.'s ap
for a considerable time together from the same paratus, several experiments, to give some point, and with a velocity even in the greatest small needles the magnetic virtue ; previously storms, not exceeding, as it is said, sixty miles examining, by putting them in water, on
an hour: but the electric fire seems propagated which they will be supported, whether or not instantaneously, taking up no perceptible time they had any of that virtue ; and I think we
in going very great distances. It must then found all of them to have some small degree be an inconceivable short time in its progress of it, their points turning to the north; we
from an electrified to an unelectrified body, had nothing to do then but to invert the poles, which, in the present case, can be but a few which accordingly was done, by sending inches apart: but this small portion of time through them the charge of two large glass is not sufficient for elasticity of the air to exert jars; the eye of the needle turning to the itself
, and therefore the column aforesaid must north, as the point before had done: that end be in a denser state than its neighbouring air
. of the needle which the fire is thrown upon,
About the velocity of the electric fire more Mr. K. tells me always points to the north. is said below, which perhaps may more fully
The electrical fire passing through air has obviate this objection. But let us have re the same crooked direction as lightning.* course to experiments. Experiments will obThis appearance I endeavour to account for viate all objections, or confound the hypothethus: air is an electric per se, therefore there sis. The electric spark, if the foregoing be must be a mutual repulsion betwixt air and true, will pass through a vacuum in a right the electrical fire. A column or cylinder of line. To try this, let a wire be fixed perair, having the diameter of its base equal to pendicularly on the plate of an air pump the diameter of the electrical spark, inter- having a leaden ball on its upper end ; let venes that part of the body which the spark another wire, passing through the top of a reis taken from, and of the body it aims at.
The ceiver, have on each end a leaden ball; let spark acts upon this column, and is acted the leaden balls within the receiver, when upon by it, more strongly than any other put on the air pump, be within two or three neighbouring portion of air.
inches of each other; the receiver being ex
hausted, the spark given from a charged phial * This is most easily observed in large strong sparks | air, nearly approaching to a vacuum, to the
to the upper wire will pass through rarified
taken at some inches distance.
lower wire, and I suppose in a right line, or stroke, nor, which is more extraordinary, saw nearly so ; the small portion of air remaining the light; which gave you just reason to conin the receiver, which cannot be entirely ex- clude, that it was swifter than sound, than hausted, may possibly cause it to deviate a animal sensation, and even light itself. Now little, but perhaps not sensibly from a right light (as astronomers have demonstrated) is line. The spark also might be made to pass about six minutes passing from the sun to the through air greatly condensed, which per- earth; a distance, they say, of more than haps would give a still more crooked direc- eighty millions of miles. The greatest rection. I have not had opportunity to make any tilinear distance within the compass of the experiments of this sort, not knowing of an earth is about eight thousand miles, equal to air-pump nearer than Cambridge, but you can its diameter. Supposing then, that the velocity easily make them. If these experiments an- of the electric fire be the same as that of light, swer, I think the crooked direction of light, it will go through a space equal to the earth's ning will be also accounted for.
diameter in about two sixtieths of the second of With respect to your letters on electricity; a minute. It seems inconceivable then, that your hypothesis in particular for explaining it should be accumulated upon the sea, in its the phenomena of lightning is very ingenious. present state, which, as it is a non-electric, That some clouds are highly charged with must give the fire an instantaneous passage electrical fire, and that their communicating to the neighbouriug shores, and they convey it to those that have less, to mountains and it to the general mass of the earth. But such other eminences, makes it visible and audible, accumulation seems still more inconceivable when it is denominated lightning and thunder, when the electrical fire has but few feet depth is highly probable; but that the sea, which of water to penetrate, to return to the place you suppose the grand source of it, can collect from whence it is supposed to be collected. it, I think adınits 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 the favour of a copy of, as well as of any other adhere to, or incorporate with each other. papers on electricity, written since I had the Thus a glass or sulphur sphere turned in wa- manuscript, for which I repeat my obligations ter, and so a friction between them, will not to you.
J. BOWDOIN. collect any fire; nor, I suppose, would a sphere of salt revolving in water : the water adhering to, or incorporating with those elec
J. Bowdoin, Boston. trics per se.
But granting that the friction Observations on the subjects of the preceding letter, between salt and water would collect the
-Reasons for supposing the sca to be the grand electrical fire; that fire, being so extremely source of Lightning.-- Reasons for doubting subtle and active, would be immediately com this hypothesis.- Improvement in a globe for municated, either to those lower parts of the raising the Electric Fire.-Read at the Royal sea from which it was drawn, and so only per
Society, May 27, 1756. form quick revolutions; or be communicated
PHILADELPHIA, Jan. 24, 1752. to the adjacent islands or continent, and so be I am glad to learn, by your favour of the 21st diffused instantaneously through the general past, that Mr. Kinnersley's lectures have been mass of the earth. I say instantaneously, for acceptable to the gentlemen of Boston, and the greatest distances we can conceive within are like to prove serviceable to himself. the limits of our globe, even that of the two I thank you for the countenance and encoumost opposite points, it will take no sensible ragement you have so kindly afforded my feltime in passing through; and therefore it low-citizen. seems a little difficult to conceive how there I send you enclosed an extract of a letter can be any accumulation of the electrical fire containing the substance of what I observed upon the surface of the sea, or how the va- concerning the communication of magnetism
pours arising from the sea should have a to needles by electricity: The minutes I took § greater share of that fire than other vapours. at the time of the experiments are mislaid. I
That the progress of the electrical fire is am very little acquainted with the nature of so amazingly swift, seems evident from an magnetism. Dr. Gawin Knight, inventor of experiment you yourself (not out of choice) the steel magnets, has wrote largely on that made, when two or three large glass jars subject, but I have not yet had leisure to pewere discharged through your body. You ruse his writings with the attention necessaneither heard the crack, was sensible of the ry to become master of his doctrine.