Priestley’s account of Franklin’s historic kite flight (1767)

Now that I’ve spent a post defending the possibility that Benjamin Franklin could have performed, and likely did perform, his experiment demonstrating the sameness of electricity and lightning, it occurs to me that I haven’t shared in detail the most complete account of that historic experiment, published by Joseph Priestley in 1767, some 13 years after the event.

Joseph Priestley (1733-1804) was an English theologian, clergyman and natural philosopher who is credited with a number of discoveries, including the invention of soda water and the official discovery of oxygen (though the Swede Carl Wilhelm Scheele in fact discovered it earlier, Priestley was the first to publish).  When he became a fellow of the Royal Society in 1766, he decided to publish an account of the history of electricity along with descriptions of the state of the art research of the time.  He actually had a chance to meet and speak with Benjamin Franklin in person during a visit of the latter to London, and got many details about Franklin’s own electrical researches.

The result is the only historical account of the famous June 1752 kite-flying experiment (aside from Franklin’s own short and technical letter to Peter Collinson, which I have discussed previously).  The account of Priestley follows.

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 firing, and was received by a key tied to the extremity of it; that part of the string which was held in his 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.

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 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.

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 lose 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 wetted 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 had heard of any thing that they had done.

Priestley’s book (the 3rd edition, at least, which I drew the quotes from) can be read in its entirety on Google books; I may return and speak more of it in a future post, after I’ve digested more of it…

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4 Responses to Priestley’s account of Franklin’s historic kite flight (1767)

  1. Paul says:

    thankf, in any cafe, Prieftly’s book if a great read! :)

  2. Simplicio says:

    I wonder how dangerous the experiment really was. I wouldn’t think that a short length of silk would offer much protection from the kite being hit by lightening, since replacing a hundred feet of air with wet twine would give a shorter route to ground even if there were a few feet of silk at the end. Especially as the description in the letter to Collinson, it sounds like the length of silk was relatively short and that Franklin was holding it in his hands instead of just tying it off to something less prone to death by electrocution then himself.

    In any case, interesting reading. Thanks

  3. Pingback: On Giants Shoulders #54: A Sleigh Load of History « Contagions

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