Benjamin Franklin Papers

From Benjamin Franklin to Horace-Bénédict de Saussure, 8 October 1772

To Horace-Bénédict de Saussure9

ALS: Bibliothèque de Genève; draft: American Philosophical Society

London, Oct. 8. 1772


I was not in England when your Favour of Oct. 28. 71. arrived in London, and it was not till many Months after its Date that I receiv’d it. In the meantime, the Philosophical Transactions of our Royal Society were published, containing the Letter of the Dean and Chapter of St. Paul’s, and the Report of the Committee appointed by the Society to consider of the Means of Securing that Edifice from Lightning,1 which I thought would fully answer the End of your Letter, by authenticating the Fact in a fuller Manner than anything from me could do, as I knew the Transactions go to your Country. This, with a Multiplicity of Business that press’d upon me at my Return, together with a blameable2 Backwardness in Writing that grows upon me with Years, occasion’d me to postpone answering from time to time, till I am now asham’d you should know I am alive. But, they say, it is never too late to mend, and I will endeavour to mend this Fault if you are, as I hope you are, good enough to forgive me.

Pointed Conductors to secure Buildings from Lightning have now been in use near 20 Years in America, and are there become so common, that Numbers of them appear on private Houses in every Street of the principal Towns, besides those on Churches, Publick Buildings, Magazines of Powder, and Gentlemens Seats in the Country. Thunder Storms are much more frequent there than in Europe, and hitherto there has been no Instance of a House so guarded being damaged by Lightning: for wherever it has broke over any of them, the Point has always receiv’d it, and the Conductor has convey’d it safely into the Earth, of which we have now five authentic Instances. Here in England the Practice has made a slower Progress, Damage by Lightning being less frequent, and People of course less apprehensive of Danger from it; yet besides St. Paul’s Church, St. James’s Church, the Queen’s Palace, and Blenheim House,3 a number of private Gentlemen’s Seats round the Town are now provided with Conductors; and the Ships bound to the East and West Indies and the Coast of Guinea begin to supply themselves with Chains for that purpose made by Mr. Nairne,4 especially since the Return of Messrs. Bankes and Solander, who relate that their Ship was, as they think, saved by one of those Chains from Damage, when a Dutch Ship lying near them in the Road of Batavia was almost demolished by the Lightning.5

Of late too, the Board of Ordnance here have applied to the Royal Society for their Advice how to secure the great Magazines of Gun powder at Purfleet from Lightning; the Society appointed a Committee to visit the Magazines and report their Opinion thereupon, which is done, advising the Securing them by Conductors; and you will see the Report in the next Vol. of Transactions,6 wherein the manner of doing it is directed. But as that Volume will not be published till next Summer, I will send you immediately a Copy of the Report if you desire it. On this Occasion I was induc’d, by a difference of Opinion in one of the Committee, to make some Experiments which I communicated to them in Writing, to show more clearly the Effect of pointed Rods, and the Advantage of making them extend as high as possible above the highest Part of the Building. Inclos’d I send a Copy of it.7

I hope you have removed the Prejudices of your Fellow-Citizens relating to your Conductor, and that you have long since compleated it,8 so as to make the Experiments with it that you had in View. I wish to hear how it succeeded with you.

I am much oblig’d by the curious Experiments of which you gave me an Account. I suspect that the Light remaining on the Card, is common Light, which had been imbibed by it, and was conceal’d in it till driven out by the electric Fluid.9 Accept my best Thanks, and believe me, with sincere Esteem and Respect, Sir, Your most obedient humble Servant

B Franklin

[Note numbering follows the Franklin Papers source.]

9The letter is among the papers of de Saussure (1740–99), the celebrated Swiss physician, geologist, electrical experimenter, and mountaineer, who in 1772 was a founder of the Genevan Société pour l’avancement des arts. He had visited England in 1768 and been elected an F.R.S.; BF doubtless became acquainted with him at that time, but this is the first extant communication between them. For de Saussure’s career see Douglas W. Freshfield, The Life of Horace Benedict de Saussure (London, 1920).

1See above, XVI, 146–51.

2“Inexcusable” in the draft.

3St. James’s, Piccadilly, was the work of Christopher Wren and the Queen’s House at Greenwich of Inigo Jones; Blenheim House was presumably Blenheim Palace, Vanbrugh’s vast pile in Oxfordshire.

4The instrument-maker, for whom see above, X, 171 n; he has appeared frequently in recent volumes. For an example of a chain conductor see above, XVII, 49–52.

5For the voyage of the Endeavour see above, XVIII, 214. The episode at Batavia is described in John C. Beaglehole, ed., The Journals of Captain James Cook on His Voyages of Discovery (3 vols. in 4, Cambridge, 1955–67), I, 433.

6It is printed above, Aug. 21.

7See the headnote on BF’s experiments above, under Aug. 18.

8De Saussure had erected a lightning rod, said to have been a hundred feet high, above his home in Geneva; his neighbors were so disturbed that he published a pamphlet to reassure them, Exposition abrégée de l’utilité des conducteurs électriques (Geneva, 1771). See Freshfield, op. cit., p. 130. Here and in the final paragraph BF is replying to the letter, now lost, of a year earlier.

9De Saussure’s letter must have contained an account of experiments, presumably his own, with some luminescent substance. Whatever the experimenter’s purpose, the result apparently revealed a phenomenon now known as electroluminescence: a body stimulated by an electric charge emits previously absorbed light. Controlled scientific exploration of this phenomenon did not occur until the nineteenth century; see E. Newton Harvey, A History of Luminescence from the Earliest Times until 1900 (Philadelphia, 1957), pp. 396–8, 404. BF’s brief reference is tantalizing because it is his earliest comment, as far as we know, on the absorption and re-emission of light, a subject to which he did not return until 1784: Smyth, Writings, IX, 227–30. But he had long been interested in the nature of light, and had suggested years earlier a wave theory that conflicted with the prevailing Newtonian view of moving corpuscles. See above, III, 128–9; IV, 299–300; I. Bernard Cohen, Franklin and Newton … (Philadelphia, 1956), pp. 320–3.

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