Benjamin Franklin Papers

To Benjamin Franklin from Isaac Winn, [before 1 February 1770]

From Isaac Winn8

ALS: the Royal Society

[Before February 1, 17701]


Tis a common and I am afraid just complaint, that Seamen are exceedingly backward in availing themselves of the discoveries which Men of Science have made, and the directions which they have given for their benefit and safety. Notwithstanding the pains several eminent Philosophers have taken, to bring Conductors into general use, as well in Ships as houses, ’tis too true that very few Vessells are furnish’d with them, tho’ scarce a year passes that does not afford us Instances, (some of them terrible ones) of Ships being struck by Lightning. For my part I am never without a Conductor in my Ship. I have had them of various constructions: that which I now use is a Chain of copper wire as described in the annex’d plate: that such a Chain, so disposed may conduct the lightning, and prevent a Stroke that might destroy a Ship, has often been demonstrated: but a circumstance that occurred in my last Voyage may perhaps have greater weight with some Seamen than all the reasoning of the Electricians: If it should be a means of perswading them to make use of Conductors my Intention will be answer’d. In April last, as we approached the Coast of America we met with strong Southwesterly Gales: they had continued several days, when exceeding dark heavy clouds arose in the opposite quarter, forced against the wind that blew with us till they had cover’d all the North Eastern half of the Hemisphere; the Struggle then between

the two winds was very extraordinary, sometimes one prevailing, sometimes the other. I was apprehensive we should have much Lightning, and got my Conductor in order; when in hauling up the Main Sail the sheet Block struck violently against the back stays, to which the Chain was fasten’d (EE in fig: I)2 and, as I found afterwards, broke the latter which occasion’d the Phenomenon I am going to describe. It was near midnight and very dark, when I first observed a pale bluish light a few feet above the quarter rail; at first I thought it proceeded from the light in the Binnacle, but finding that it frequently dissapear’d and return’d again precisely in the same place, and that it sometimes emitted Sparks not unlike those of a small Squib, I began to suspect that it proceeded from the Conductor. To be certain, I order’d all the lights to be put out below, and that no ray of Light might issue from the Binnacle I cover’d it entirely with my Cloak. I was presently confirmed in my conjecture, that the light and Sparks which I had observed, proceeded from the Chain; for, placing myself near it during the Space of two hours and a half, I saw it, frequently emit continued Streams of Rays or Sparks (See fig: 4) sometimes single drops as it were slowly succeeding to each other, and sometimes only a pale feeble light. On examining next morning I found the Chain broken at B, half the eye of each Link being quite gone, and the points of the remaining halves about three fourths of an Inch asunder: luckily the Chain was fasten’d to a small rope (fig: 2) above and below the Eye of each link which prevented that part of the Chain below B from falling into the water, or of being separated from the part above B beyond the striking or attracting distance. I am with the greatest respect Sir Your Obliged Humble Servant

I. L. Winn

References to the Plate

AAA The Conductor, a Chain of Copper Wire of the thickness of the Barrel of a small quill, the uppermost and lowest links of which terminate in fine points
B. Fig. 1. The broken Links, in passing between which the lightning became visible.
C An Eye in the uppermost link, to which the pendant halliards are fastened.
D Fig. 3 The pendant halliards which pass over a sheave in the truck on the top gallant mast head, and are fastened to the eye at C, and hoists up the chain, till the point of the uppermost link is a foot or two above the truck
E E The maintop mast backstay to which the chain is stopped to prevent its swinging about.
B. Fig. 4. Appearance of the lightning passing between the broken limbs.

Endorsed: Capt. Winn’s Acct. of the Appearance of Lightning in his Conductor. Received Feb. 1, 1770. March 2 A Letter to Dr. Benjamin Franklin giving an account of the appearance of lightning on a conductor fixed from the summit of the mainmast of a ship Down to the water by Capn. I. L. Winn.

[Note numbering follows the Franklin Papers source.]

8A merchant captain, master of the Dutchess of Gordon. See N.- Y. Gaz. (Gaine), May 8, 15, 29, 1769.

1The letter cannot be accurately dated. The voyage to which it refers began in the Downs on March 7 and ended at New York on April 24, 1769. Ibid., May 1, 1769; Pa. Gaz., May 18, 1769. Winn returned to England, and crossed again later in the year: he left for New York in the early autumn, arrived there in November, and cleared again for London before the month was out. PMHB, LX (1936), 472; N.- Y. Gaz. (Gaine), Nov. 20, 1769; N.- Y. Jour., Nov. 30, 1769. He might have written the account at sea during this second voyage, from which he would have returned to England in ample time to deliver his letter to BF on Feb. 1, 1770, for transmission to the Royal Society. It was read there on March 29 and published (with Winn’s initials incorrectly given as J. L.) in Phil. Trans., LX (1770), 188–91; a few words lost in the MS have been silently restored from the printed text. BF’s interest in apparently similar phenomena went back for twenty years. See above, III, 473; IV, 143.]

2The drawing that accompanied the original has been lost, although Winn’s references to it at the end of the letter survived. Our illustration is reproduced from a broadside in the Yale University Library and contains, it will be noted, two lines of reference that Winn must have added later.

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