The Papers of Joseph Henry


My Dear friend

A Committee of the Am— Philosophical Society has been appointed to enquire in to the circumstances of the destruction of the Thomas P. Cope—a packet of this port destroyed by lightning at sea,[2] having no conductor up at the time, the captain fearing to use one—apprehending that it might attract the stroke.[3] We have to enquire into the expediency of conductors their proper form &c As chairman of the Committee (Patterson[4] Peale[5] and myself) I hope to have your advice on the whole subject—and specially as respects
the lateral discharge—if danger is to be apprehended therefrom.[6] What is your opinion of Snow Harris' plan? do you think the enormous[A] sise of the copper plat[e] on the lower mast necessary?[7] What do you think of the plan used in the French ships (iron or copper wire ropes as backstays[)?][8] I have the report and documents from t[he] British Admiralty.[9] Will you if perfec[tly] convenient ascertain from our Navy Department if they have any facts from our navy officers, or others, shewing the utility or otherwise of conductors—if any ship with a good conductor has ever been injured or saved by the conductors[10]—pray excuse my lame hand and believe me as ever

Your friend>

Geo. W. Smith
No 3 Dugan's Row Spruce Street Philada

P.S. I rejoice—but with fear and trembling at your appointment—but I regard you as Daniel in the den of lions to say nothing of meaner beasts.
Prof. Henry
Henry Papers, Smithsonian Archives. First page torn on right edge. In original, illustration is in left margin.
    [1] A Princeton graduate (1822) and now a Philadelphia merchant. Henry Papers, 5:303.
    [2] Lightning struck the mainmast of the packet ship Thomas P. Cope on November 29, 1846, setting afire her cargo of hemp and tallow. On January 1, 1847, the American Philosophical Society appointed a committee to investigate the circumstances of the accident. Eliza Cope Harrison, ed., Philadelphia Merchant: The Diary of Thomas P. Cope, 1800–1851 (South Bend, Indiana, 1978), pp. 518–519; APS Proceedings, 1843–1847, 4:300–301.
    [3] The Cope, like most merchant ships, carried a removable conductor. Typically, these consisted of an iron or copper chain hung from the mainmast, with the lower end in the sea. William Snow Harris, On the Nature of Thunderstorms; and On the Means of Protecting Buildings and Shipping against the Destructive Effects of Lightning (London, 1843), pp. 130–140; A. M. Griffiths et al., “[Abridged] Report of the Committee Appointed by the Admiralty to Examine the Plans of Lightning Conductors, of W. Snow Harris, Esq. F.R.S. and Others,” Annals of Electricity, Magnetism, and Chemistry, 1840, 5:1–20, especially pp. 4–6.
    [4] Robert Maskell Patterson, director of the United States Mint and a trustee of the University of Pennsylvania. Henry Papers, 2:413n.
    [5] Franklin Peale, chief coiner of the United States Mint. Henry Papers, 4:177.
[6] Opinions differed as to whether lateral discharges posed a danger to ships fitted with lightning conductors. Some authorities believed that flying sparks could ignite a ship's cargo or, on naval vessels, a powder magazine. Others disagreed, however, stating that little danger existed if the conductors used were of sufficient capacity and continuous throughout their length. Such differing views about lateral discharges were part of a broader ongoing debate about the reality of the phenomenon. Griffiths, pp. 7–10, 19–20; Henry Papers, 3:53n–54n; 4:263; and 5:439n–440n.
Convinced that the threat posed by lateral discharges was real, Henry urged caution in the arrangement and use of lightning conductors on ships. As he observed in 1859, “It is true, the quantity which tends to fly off laterally from the rod is small, yet we have shown by direct experiment that it is sufficient even when produced by the electricity of a small machine, to set fire to combustible materials; and therefore it cannot be entirely free from danger in a ship, loaded for example with cotton. [“Atmospheric Electricity,” Part V of “Meteorology in Its Connection with Agriculture,” Report of the Commissioner of Patents for 1859: Agriculture (Washington, 1860), p. 482.]”
[7] The plan devised by William Snow Harris, a Plymouth physician and author of several papers on electricity, was intended to afford ships permanent lightning protection. His conductor was a band of copper plates. Each link in the band consisted of two plates riveted together, each “about four feet long, from six inches to one and a half broad; the thickness of the under layer being one eighth, and of the upper layer one sixteenth, of an inch.” The band was nailed in place in a continuous line along the ship's projecting points and beneath the lower decks, terminating in the hull. In 1839, a British Admiralty committee stated that smaller plates could be used without detriment. Griffiths, pp. 5, 6–15, 16–17; Encyclopaedia Britannica, 8th ed., s.v. “Electricity,” p. 610 (quotation); Henry Papers, 3:173n.
We have not found any comment by Henry on the size of Harris's plates. In 1859, he termed the plan an “admirable arrangement” whose only drawback was that it conducted lightning through the hull. “Atmospheric Electricity,” p. 482; see also Henry Papers, 3:514–515; 4:263n.
    [8] French naval vessels carried removable conductors made of copper or iron wire rope, which, when installed, ran from the mainmast, down the backstays, and into the water. Such conductors had limited utility, since their capacity was insufficient and they were lost altogether if the mast fell during a storm. Griffiths, pp. 4–6; Harris, pp. 134–136.
    [9] A. M. Griffiths et al., Copy of the Report and Evidence from the Commission Appointed to Inquire into the Plan of William Snow Harris, Esq. F.R.S. Relating to the Protection of Ships from the Effects of Lightning, United Kingdom, Parliament, January 18–August 11, 1840, House of Commons Sessional Papers, No. 63, pp. 1–96. The report contained letters, descriptions of Harris's and other plans, and accounts of ships struck by lightning.
[10] We do not know if Henry contacted the Navy Department regarding the information which the APS committee desired.
The committee never presented a report; its final disposition is not known.
    [A] Altered from i