Benjamin Franklin Papers

The Kite Experiment, 19 October 1752

The Kite Experiment

I. Printed in The Pennsylvania Gazette, October 19, 1752; also copy: The Royal Society. II. Printed in Joseph Priestley, The History and Present State of Electricity, with Original Experiments (London, 1767), pp. 179–81.

Franklin was the first scientist to propose that the identity of lightning and electricity could be proved experimentally, but he was not the first to suggest that identity, nor even the first to perform the experiment.4 For many years pioneer electricians had noted the similarity between electrical discharges and lightning, and in 1746 John Freke in England and Johann Heinrich Winkler in Germany separately advanced the idea of identity and suggested theories to account for it. Franklin’s later adversary the Abbé Nollet wrote to the same effect in 1748.5 Franklin and his Philadelphia collaborators, working independently, also observed the similarities, and in his letter of April 29, 1749, to John Mitchell on thundergusts he took as the basis for his entire discussion the hypothesis that clouds are electrically charged.6 In the “minutes” he kept of his experiments he listed under the date of November 7, 1749, twelve particulars in which “electrical fluid agrees with lightning,” and noted further that “the electrical fluid is attracted by points,” but that it was not yet known whether this property was also in lightning. “But since they agree in all other particulars wherein we can already compare them, is it not probable they agree likewise in this? Let the experiment be made.”7

However obvious the suggestion of such an experiment may now seem, no one had made it before. Herein lies Franklin’s principal claim to priority in this great discovery. A test of lightning required the prior discoveries embodied in the “doctrine of points,” of which he was the undisputed author, and the knowledge he had gained of the role of grounding in electrical experiments. It was the pointed metal rod, with its peculiar effectiveness in electrical discharge, which both led to the suggestion and facilitated the experiment.

In the following March Franklin, writing to Collinson, suggested that pointed rods, instead of the usual round balls of wood or metal, be placed on the tops of weathervanes and masts, and that they would draw the electrical fire “out of a cloud silently,” thereby preserving buildings and ships from being struck by lightning.8 He repeated the suggestion in July 1750 in his “Opinions and Conjectures,” with the important addition that a wire be run down from the rod to the ground or water, and he then proposed the “sentry-box” experiment. This was the first public suggestion of an experiment to prove the identity of lightning and electricity.9

According to Joseph Priestley, who almost certainly received his information directly from Franklin about fifteen years later, he did not perform the experiment himself at once because he believed a tower or spire would be needed to reach high enough to attract the electrical charge from a thunder cloud, and there was no structure in Philadelphia he deemed adequate for the purpose. Presumably he was waiting until Christ Church steeple, then in the early discussion stage, should be erected.1 English scientists, who could have read Franklin’s proposal when it was published in Experiments and Observations in April 1751, apparently failed to recognize its significance. But about a year later, in the spring of 1752, when a translation had been published in Paris, the French reaction was very different. Delor, “master of experimental philosophy,” repeated most of Franklin’s experiments before the King, and then in May Dalibard, Franklin’s translator, and Delor each set up apparatus which performed successfully the “Philadelphia experiment” of drawing electricity from a thunder cloud.2 Word of these achievements awoke the English electricians, and during the summer of 1752 the experiment was repeated several times in England as well as in France and Germany.3

At some time during 1751 or 1752 Franklin got the idea that he could send his conductor high enough by means of a kite, and that if it were flown during a thunder shower, the wet string might serve to bring the electrical charge down within reach. When the idea first came to him and just when he carried it out cannot be established with absolute certainty. Priestley wrote that the famous experiment with kite and key took place during June 1752, and the present editors believe there is no good reason to doubt the correctness of this date. If so, then Franklin performed his experiment before he learned of what Dalibard and Delor had done in France.

Almost never during these years did Franklin report a particular electrical experiment until some time had elapsed and this affair seems to have been no exception. Word of Dalibard’s and Delor’s successes reached Philadelphia toward the end of August and the Pennsylvania Gazette of August 27 carried a short account reprinted from the May issue of the London Magazine. During September Franklin erected a lightning rod on his own house, ingeniously equipping it with bells that would ring when the wire became charged and thus notify him when the atmosphere above the house was electrified.4 Then at last, on October 19, he printed in the Gazette a brief statement about the kite experiment with instructions for repeating it. The text of this statement, transmitted to Collinson, was read to the Royal Society on December 21. Neither in this paper nor at any later time did Franklin—or Priestley on his behalf—ever claim priority in carrying out the experiment he had been the first to propose.5

The same October 19 issue of the Gazette also announced that Poor Richard for 1753 was then “In the Press, and speedily will be published”; in that almanac Franklin printed for the first time precise instructions for the erection of lightning rods for the protection of buildings.6 The sequence of events in this somewhat complicated chain may be clarified by the following chronology:

April 29: Franklin to Mitchell on thundergusts, discusses the electrical charge in clouds.
November 7: Franklin’s “Minutes” list points of similarity of lightning and electricity and call for experiment to prove their identity.
[March 2]: Franklin to Collinson suggests protection of buildings and ships by pointed rods.
July 29: “Opinions and Conjectures” repeats substance of next above with proposal for grounding of rods; suggests “sentry-box” experiment; further discusses similarity of lightning and electricity.
April: Experiments and Observations published in London, containing above documents of April 29, 1749, and July 29, 1750.
June 6: Watson reviews Franklin’s treatise before Royal Society but ignores suggestions for lightning rods and “sentry-box” experiment.
February: Experiments and Observations translated and published in Paris.
May 10: Dalibard’s assistant successfully carries out Franklin’s proposed experiment at Marly, France.
May 18: Delor repeats the experiment in Paris. Other repetitions during following summer in France.
May 20 and 26: French reports on Dalibard and Delor experiments sent to England.
[June]: Gentleman’s Magazine and London Magazine issues for May both print translations of the French reports.
June: According to Priestley, Franklin performs the kite experiment in Philadelphia.
July–August: Canton, Wilson, and Bevis separately repeat the French experiments in England.
August 27: Pennsylvania Gazette reprints the French report of May 26 from London Magazine.
September: Franklin erects a lightning rod with bell attachment on his house.
October 19: Pennsylvania Gazette prints Franklin’s statement of the kite experiment and states that Poor Richard (containing lightning-rod instructions) is now in press.
December 21: Franklin’s statement of kite experiment read to Royal Society.

Unfortunately, Franklin’s statement of the kite experiment has not been found in his own handwriting. Two text versions survive: that printed in the Pennsylvania Gazette of October 19, 1752, reprinted below; and a copy in the hand of Peter Collinson, now in the Royal Society.7 Aside from unimportant variations in paragraphing, spelling, capitalization, and punctuation, the Collinson copy differs from the Gazette version in several respects: (1) It is headed “From Benn: Franklin Esqr To P Collinson” and is dated “Philadelphia Octo: 1: 1752.” (2) At the end, following the words “compleatly demonstrated,” Collinson skipped the equivalent of about three lines, then added in two lines: “See his Kite Experiment” and “to be printed with the rest.” These lines were later struck out. (3) In the intervening space and running on to the right of the two canceled lines appears the following insertion not in Collinson’s hand, but in one which is strikingly like that of William Watson: “I was pleased to hear of the Success of my experiments in France, and that they there begin to Erect points on their buildings. Wee had before placed them upon our Academy and Statehouse Spires.” (4) The paper is endorsed in the hand of a Royal Society clerk: “Letter of Benjamin Franklin Esq to Mr. Peter Collinson F.R.S. concerning an Electrical Kite. Read at R.S. 21 Decemb. 1752. Ph. Trans. XLVII. p. 565.”

These text differences present several puzzles. The heading and date (item 1) have led several writers8 to believe that the text which follows is an extract of a letter from Franklin to Collinson of October 1, written more than two weeks before the statement was printed in the Gazette. In that case the Gazette text would be an extract from this earlier letter to Collinson. This is possible, but it leaves unexplained Franklin’s undated letter to Collinson, assigned below (p. 376) to the latter part of October, in which he wrote that he was sending, among other items, “my kite experiment in the Pennsylvania Gazette.” If what he had printed in the Gazette was indeed a passage from a letter already sent to Collinson, there would seem to have been no need to send him another copy of it. Conceivably, Collinson’s pen slipped when he wrote “Octo: 1,” as it occasionally did in referring to other Franklin letters, and he should have written “19,” “21,” or “31,” in which case he might have been copying the Gazette statement enclosed in Franklin’s later letter. Subsequent correspondence between the two men does not clarify the point.

The canceled addendum at the bottom (item 2) seems to have been intended as an instruction to a printer. Possibly Collinson first meant this paper for the printer of the 1753 Supplement of Experiments and Observations, and then decided to submit this copy to the Royal Society instead. But the question remains unexplained why he should have written “See his Kite Experiment,” when this document itself is the kite experiment, and is the only account of it we have in Franklin’s own words. The endorsement (item 4) presents no problem. The fact that the paper is lodged in the Royal Society makes it clear that this endorsement was added later for filing purposes after it had been printed in the Philosophical Transactions.

This leaves for consideration item 3, the short paragraph added to Collinson’s paper which mentions the French experiments and the erection of “points” in France and Philadelphia. The facts that it is written in a different hand from Collinson’s and that it is clearly an addition have not been considered by previous commentators. The paragraph has been taken as evidence that lightning rods were erected on the Academy building and the State House (Independence Hall) before October 1, 1752. The words are doubtless Franklin’s, though they have not been traced with certainty to any surviving document of his. If they were in fact part of a letter of October 1 to Collinson which also contained the original text of the statement on the kite experiment, then they must have been added to Collinson’s copy by someone else, probably Watson, who saw the original letter and thought this passage more important than Collinson had done. Or the paragraph may have been part of the later undated letter, probably of late October (the full text of which may not have been printed in the 1753 Supplement), with which Franklin enclosed the item on the kite experiment from the Gazette. Whatever the source, the paragraph must have been written by about November 1, 1752, in order for it to be read to the Royal Society as part of the report on the kite experiment on December 21 and printed as such in the Philosophical Transactions.9 The probable date for the erection of the two Philadelphia lightning rods is not materially affected in any case. The problem of the source of this added paragraph is not resolved by any printed version of Franklin’s account. The Philosophical Transactions printed the text from Collinson’s copy. The Gentleman’s Magazine and London Magazine and the 1753 Supplement to Experiments and Observations also printed the report, but all three followed the dating and text of the Gazette version, not the Collinson copy.1

It will be noticed that Franklin’s paper is not really an account of the kite experiment, but rather a brief statement that the experiment had taken place, followed by instructions as to how it could be successfully repeated. Franklin never, so far as is known, wrote out a narrative of his experience. The most detailed account that has survived is that which Joseph Priestley inserted in 1767 in his History of Electricity. There is every reason to believe that he learned the details directly from Franklin, who was in London at the time Priestley wrote the book. Franklin encouraged him to undertake the work and Priestley acknowledged in his preface the information Watson, Franklin, and Canton had supplied him. The account of the kite experiment, as Priestley wrote it about fifteen years after the event, may err in some details through faulty memory on Franklin’s part or misunderstanding on the Englishman’s, but it is probably correct in all major respects. In any case, since it is the nearest thing we have to a contemporary, first-hand account of one of the most famous episodes in Franklin’s career, it is reprinted here directly following Franklin’s statement.

I. Franklin’s Statement

Philadelphia, October 19

As frequent Mention is made in the News Papers from Europe, of the Success of the Philadelphia Experiment for drawing the Electric Fire from Clouds by Means of pointed Rods of Iron erected on high Buildings, &c. it may be agreeable to the Curious to be inform’d, that the same Experiment has succeeded in Philadelphia, tho’ made in a different and more easy Manner, which any one may try, as follows.2

Make a small Cross of two light Strips of Cedar, the Arms so long as to reach to the four Corners of a large thin Silk Handkerchief when extended; tie the Corners of the Handkerchief to the Extremities of the Cross, so you have the Body of a Kite; which being properly accommodated with a Tail, Loop and String, will rise in the Air, like those made of Paper; but this being of Silk is fitter to bear the Wet and Wind of a Thunder Gust without tearing. To the Top of the upright Stick of the Cross is to be fixed a very sharp pointed Wire, rising a Foot or more above the Wood. To the End of the Twine, next the Hand, is to be tied a silk Ribbon, and where the Twine and the silk join, a Key may be fastened. This Kite is to be raised when a Thunder Gust appears to be coming on, and the Person who holds the String must stand within a Door, or Window, or under some Cover, so that the Silk Ribbon may not be wet; and Care must be taken that the Twine does not touch the Frame of the Door or Window. As soon as any of the Thunder Clouds come over the Kite, the pointed Wire will draw the Electric Fire from them, and the Kite, with all the Twine, will be electrified, and the loose Filaments of the Twine will stand out every Way, and be attracted by an approaching Finger. And when the Rain has wet the Kite and Twine, so that it can conduct the Electric Fire freely, you will find it stream out plentifully from the Key on the Approach of your Knuckle. At this Key the Phial may be charg’d; and from Electric Fire thus obtain’d, Spirits may be kindled, and all the other Electric Experiments be perform’d, which are usually done by the Help of a rubbed Glass Globe or Tube; and thereby the Sameness of the Electric Matter with that of Lightning compleatly demonstrated.

II. Priestley’s Account

To demonstrate, in the completest manner possible, the sameness of the electric fluid with the matter of lightning, Dr. Franklin, astonishing as it must have appeared, contrived actually to bring lightning from the heavens, by means of an electrical kite, which he raised when a storm of thunder was perceived to be coming on. This kite had a pointed wire fixed upon it, by which it drew the lightning from the clouds. This lightning descended by the hempen string, and was received by a key tied to the extremity of it; that part of the string which was held in the hand being of silk, that the electric virtue might stop when it came to the key. He found that the string would conduct electricity even when nearly dry, but that when it was wet, it would conduct it quite freely; so that it would stream out plentifully from the key, at the approach of a person’s finger.3

At this key he charged phials, and from electric fire thus obtained, he kindled spirits, and performed all other electrical experiments which are usually exhibited by an excited globe or tube.

As every circumstance relating to so capital a discovery as this (the greatest, perhaps, that has been made in the whole compass of philosophy, since the time of Sir Isaac Newton) cannot but give pleasure to all my readers, I shall endeavour to gratify them with the communication of a few particulars which I have from the best authority.

The Doctor, after having published his method of verifying his hypothesis concerning the sameness of electricity with the matter of lightning, was waiting for the erection of a spire in Philadelphia to carry his views into execution; not imagining that a pointed rod, of a moderate height, could answer the purpose; when it occurred to him, that, by means of a common kite, he could have a readier and better access to the regions of thunder than by any spire whatever. Preparing, therefore, a large silk handkerchief, and two cross sticks, of a proper length, on which to extend it; he took the opportunity of the first approaching thunder storm to take a walk into a field, in which there was a shed convenient for his purpose. But dreading the ridicule which too commonly attends unsuccessful attempts in science, he communicated his intended experiment to no body but his son, who assisted him in raising the kite.4

The kite being raised, a considerable time elapsed before there was any appearance of its being electrified. One very promising cloud had passed over it without any effect; when, at length, just as he was beginning to despair of his contrivance, he observed some loose threads of the hempen string to stand erect, and to avoid one another, just as if they had been suspended on a common conductor. Struck with this promising appearance, he immediately presented his knucle to the key, and (let the reader judge of the exquisite pleasure he must have felt at that moment) the discovery was complete. He perceived a very evident electric spark. Others succeeded, even before the string was wet, so as to put the matter past all dispute, and when the rain had wet the string, he collected electric fire very copiously. This happened in June 1752, a month after the electricians in France had verified the same theory, but before he heard of any thing they had done.

[Note numbering follows the Franklin Papers source.]

4The best discussion of this entire topic is I. Bernard Cohen, “The Two Hundredth Anniversary of Benjamin Franklin’s Two Lightning Experiments and the Introduction of the Lightning Rod,” APS Proc, XCVI (1952), 331–66. The present editors are in full agreement with Cohen’s conclusions except, as this headnote will show, those derived specifically from consideration of the Collinson copy of BF’s statement on the kite experiment.

5Cohen, BF’s Experiments, pp. 104–9, discusses the matter with citations and quotations from various writers.

6See above, III, 365–76.

7Quoted by BF in his letter to John Lining, March 18, 1755, Exper. and Obser. 1769, p. 323. The originals of BF’s minutes have not survived.

8See above, III, 472–3

9See above, pp. 19–20.

1See above, p. 116.

2See above, pp. 302–10, 315–17.

3See below, 390–2.

4BF to Collinson, September 1753.

5Writing in 1788 in his autobiography, BF mentions the Dalibard and Delor successes with the “Philadelphia experiments” and then adds simply and with disappointing brevity: “I will not swell this Narrative with an Account of that capital Experiment, nor of the infinite Pleasure I receiv’d in the Success of a similar one I made soon after with a Kite at Philadelphia, as both are to be found in the Histories of Electricity.” Par. Text edit., p. 386.

6See below, p. 408.

7The Collinson copy is reproduced in facsimile in APS Proc., XCVI, pp. 334–5.

8Notably Cohen in the works cited in the first two footnotes to this headnote, and Carl Van Doren in Franklin, p. 169, and Autobiographical Writings, p. 76.

9The paragraph could be from some now missing letter of later date than about Nov. 1, 1752, only in the unlikely circumstance that it was added to the Collinson copy between the reading of the paper on December 21 and the transmission of this number of Phil. Trans. to the printer sometime in 1753.

1Gent. Mag., XXII (1752), 560–1; London Mag., XXI (1752), 607–8; Supplemental Experiments and Observations on Electricity, Part II (London, 1753), pp. 106–8. Gent. Mag. and the 1753 Supplement both add the initials “B.F.” at the end; London Mag. omits the first paragraph and begins “Make a small cross, …” but otherwise follows the Gazette version.

2In 1760 and later printed editions: “which is as follows:”

3At this point Priestley inserted a footnote reference to Exper. and Obser., p. 106, where BF’s statement is printed.

4At this time William Franklin was at least 21 years old (see above, III, 474), not the child shown in the well-known Currier and Ives print depicting the scene. There are a number of other errors in the picture.

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