From William Henly
ALS: American Philosophical Society
This letter poses a remarkable problem of dating, and we cannot solve it. Henly’s date is all too clear, and could not have been a slip: April 18 was a Sunday in 1773. Yet he makes a number of references that seem inapplicable to that year, and are definitely applicable to 1774. They were all related to the continuing controversy with Benjamin Wilson over lightning rods. Franklin had withdrawn from the fray in late 1772, and Henly had taken his place as chief protagonist.4 Developments thereafter are the background of the dating problem.
In March, 1773, Wilson published his Observations upon Lightning, which was an outgrowth of the arguments the year before about pointed versus blunt rods.5 He subsequently developed his idea that the quantity of charge in a cloud could not be known, and might well be greater than any rods could conduct in safety to the ground. To test this possibility he suggested constructing a giant metal ring, sharpened on the upper edge, and placing it horizontally on top of St. Paul’s, to see whether it would not draw more electricity from a thunderhead than any one dreamed the cloud could hold. He challenged whoever was skeptical-meaning Franklin-to try the experiment on a smaller scale: “I would ask the philosopher, whether he would chuse to put a crown of this kind upon his own head, and venture to walk or ride with it on, over Salisbury-plain, in the midst of a very violent thunderstorm; notwithstanding there should drag behind him a communication of metal from the crown itself to the earth, during the whole of his journey.” Wilson, as far as we know, first publicized his idea and made this jibe at Franklin, without naming him, in a paper that he says he read before the Royal Society on February 24, 1774, and that he published unaltered as a pamphlet the following May.6 On May 5 Henly responded, again before the Royal Society, to the wild idea of the ring by pointing out that a similar one existed, and had for more than a century without incident, on top of the Monument to the Great Fire.7 When he subsequently obtained and read Wilson’s pamphlet, he contented himself with scathing marginalia; the public controversy ended there.
This background suggests why the present letter is puzzling. In it Henly speaks of a paper read before the Royal Society the previous evening, April 17 (when the Society’s records do not show any meeting), and virtually says that the paper was Wilson’s and contained the jibe at Franklin. Wilson himself refers only to the later paper of February, 1774, which became his second pamphlet. Among Henly’s marginalia in that pamphlet is one, on the taunt to Franklin, that is similar to what he says here.8 The letter, in short, could not have been written when it was: it refers to Wilson’s argument before the Royal Society and contains some of Henly’s response; yet the paper was not presented until more than ten months later, according to its author, and Henly’s response, in his paper and his marginalia, was later still. We have two alternative explanations, both implausible. One is that the final phase of the controversy that became public in the spring of 1774 was in rehearsal a year earlier. The other is that Henly dated his letter in the grip of some aberration.
Sunday Evening Apl 18. 1773
I am much pleased that I went to the Society last [night?] I am now sensible what the crown is, which Mr. [Wilson?] informed me he had prepared for you. As you [are to?] wear it on horseback on Salisbury plain, and a [chain?] is to hang dangling from behind; when you next experiment permit me to request the honour of [being] your trainbearer. I think it will add a little [to the] state with which you’l take your ride. B[ut for?] the greater pomp I could wish to recommend a person to precede you on foot, equip’d as follows. He should have a cap of metal, furnished with a pair of ears of a very considerable length standing upright, and terminated by large round balls; which besides making a handsome appearance upon the cap, would (as I learn from a curious paper read last night,) make so great a resistance to a stroke of lightning, as effectually to preserve the head (suppose Mr. W-s) within it from harm. On second thoughts I believe it will be scarce worth our while to take this trouble, for I recollect a building called the monument whose head is adorned with much such a kind of hoop as my friend W-has proposed, and the hoop is surrounded by 1000 points to represent flames of fire. The Iron twist rail (which is carried to the bottom,) may very well serve to represent your dangling chain: but this building which hath stood very near a century, happens never to have been struck by lightning at all; I think therefore we may as well content [us;] were I to conclude by inference from the experiments [I] have already made; it would be thus. Supposing such a force used as would strike the Knob in contact with the coatings at 4½ Inches from the insulated body. In that case I suspect that the point could not be struck at more than 2 Inches, for I cannot help thinking that the point lessens the force of explosion as the distance increases to a certain quantity,9 and after that hath no more influence than Knobs.1 I should imagine this experiment (which I own to me, seems demonstration,) must convince every one who repeats it (except those who are determined not to be convinced,) of the preference due to pointed Conductors, rather than those terminated by a Knob.
I beg your indulgence in the liberty I now take, and that you would believe me to be with real regard Dear Sir your obliged and obedient Servant
Addressed: To / Dr. Franklin / Craven-street / Strand
4. In February, 1773, BF, Priestley, Price, Walsh, and others, perhaps in recognition of Henly’s new role, nominated him for the Royal Society; and he was elected on May 20. Above, VIII, 359; Royal Society archives.
5. See above, XIX, 260–2, 424–9, and the note on BF’s marginalia in Wilson’s pamphlet, after March 21, 1773.
6. The Royal Society has no record of the February paper. Wilson mentioned it by date, and made his jibe at BF, in Further Observations upon Lightning … (London, 1774), pp. iii, 15.
7. “An Account of Some New Experiments in Electricity …,” Phil. Trans., LXIV (1774), 413–14. The Monument, designed by Christopher Wren and built in 1671–77, is crowned by an urn of metal flames surrounded by an iron framework or ring; in the interior of the building is a spiral staircase. Henry B. Wheatley, London Past and Present … (3 vols., London, 1891), II, 557–9. The stair rail is of iron and connected with the ring, Henly makes clear, and would serve as a conductor.
8. “Quere, would not a cap of metal, with a pair of long ears, suit some electricians as well?” The comment is on p. 15 of Henly’s copy of Further Observations, Yale University Library.
9. [Henly’s note:] length, or distance.
1. [Henly’s note:] With respect to Inviting or Attracting the Electricity, and this distance I believe is not v[ery gre]at.