The phenomenon of lightning, with its accompanying fire which sometimes brings destruction and death in its wake, has always strongly impressed itself upon the imagination of observers who have tried to find explanations for it. From ancient times, the wrath of the gods has often been evoked. “When in the 17th century, the healthy light of philosophy cleared away the thick shadows in which minds had for so long lost their way, men, less credulous and a little more observant, dared contemplate this fearful meteor more closely.” One generally attributes to Benjamin Franklin (1706-1790), American politician, Minister Plenipotentiary of the United States to France, and President of Pennsylvania between 1785 and 1788, the discovery of the equivalence between lightning and electricity, and the invention of the lightning conductor. Franklin was not a physicist, but he put forward a certain number of hypotheses, wishing that they would be verified by scientists. So he thought that lightning preferred to strike raised and pointed objects, such as high mountains, trees, towers, belfries, ships’ masts, etc. In the same way, according to him, all pointed conductors were more accessible to electricity than flat surfaces. He therefore suggested that lightning always follows the best conductor within its reach. He noted other similarities between lightning and electricity: the setting alight of combustible materials, melting of metals…So when Franklin advanced his ideas and, as a result, thought of the lightning conductor, he had not carried out any experiment to verify the presence of electricity in the atmosphere. He simply contented himself by suggesting it to physicists in order to verify his theories. He suggested, for example, the placing on a hut of a pointed iron bar fixed to a stool.
(Image: The Astrolabe and the Boussole at Anchor in Maui, from Voyage de La Pérouse autour du Monde (1798 edition; State Library of NSW).
During this experiment, carried out at Marly, on 10 May 1752 in the presence of Louis XV, the presence of electricity in the atmosphere was recognised for the first time, which validated Benjamin Franklin’s hunches. In September 1752, pushing the research further in order to ‘draw’ electricity from storm clouds that the pointed tips could not reach, Franklin sent up a kite which conducted electricity along a rope in order to reduce the power of the storm. In France, the physicist Romas de Nérac had already thought of using a kite for the same purpose, as acknowledged by the Académie des Sciences.
Thus, as it happens, Louis Figuier, in his work “Les merveilles de la science” [“The Marvels of Science”], published in 1867, noted that: “Science and a particular period in history give rise to the various components of great discoveries; there arises, at that time, a moment when the same idea presents itself simultaneously to a great number of minds, because it is the outcome of many fully developed works. One attributes, sometimes to Wall, sometime to Franklin, sometimes to Abbé Nollet, the glory of having been the first to demonstrate the physical similarity between lightning and electricity. The merit of this thought is not due to any one of these scientists; it was the expression, and the result, of the sum total of the work of the physicists of the last century.”
In October 1784, in France, M. Alphonsus Le Roy presented to the Académie des Sciences a “Mémoire sur la nécessité et les moyens d’armer les vaisseaux de conducteurs ou de paratonnerres… ” [“Memorandum on the necessity and ways of fitting vessels with conductors or lightning rods…”].
Le Roy recalled that a “vessel appears more exposed to be struck by lightning than the majority of buildings ashore” for “the mast of a 200-gun vessel rises 180 feet (58 m) above the water, a height that surpasses that of a great number of buildings. Moreover, “it is most often isolated from any other object…” There are numerous examples of ships having suffered the effects of lightning. He quoted, as an example, the accident suffered by a Dutch ship in the roadstead at Batavia where “lightning set fire to the main topsail from which the fire spread first to the whole rigging, then to the masts and set the vessel ablaze.” Incidentally, Le Roy is astonished that after the discovery of the lightning conductor, people waited such a long time to fit vessels in our country with it.
Le Roy then set out his recommendations for the installation of a lightning conductor on a ship.
First of all, one must “determine the direction that the lightning conductor chain must take from the main mast into the sea…” It is then necessary that “the lightning conductor, by following this direction, fulfils its object and not interfere with the ship’s handling…” and finally, one has to decide “the manner in which the lower end reaches the sea…”
Le Roy suggested having the lightning conductor chain pass along a backstay of one of the masts. A backstay is a long rope which, from the top of the topmast, comes down to the side of the vessel in order to assist the shrouds to brace the mast. Later on, he offered his views on the construction of the chain in which each link would be made of copper and connected to the next one by a ring. Finally he specified how the lightning conductor would make contact with the sea when the vessel bottom is sheathed with copper or not. The essential being to ”have the lower ends of the chain contact the sea water directly or via transmission strips so that the lightning reaches the sea by a continuation of the metallic material.”
Le Roy then noted that on large vessels it would be necessary to have several lightning conductors: one on the main mast and another on the mizzen mast.
All visitors to the Lapérouse Museum [in Albi] can see a fragment of the lightning conductor chain found at Vanikoro at the site of the wreck of the Lapérouse expedition. In a passage in “Voyage autour du monde” [“Voyage around the world”], Lapérouse points out that only the Boussole was fitted with a lightning conductor. In fact, on 25 October 1885 [sic], approaching Brazil, Lapérouse wrote: “We were struck by a most violent storm. At 8 o’clock in the evening, we were in the centre of a circle of fire; lightning bolts came from all points of the horizon; St Elmo’s fire landed on the tip of the lightning conductor, but this phenomenon was not peculiar to us; the Astrolabe, which did not have a lightning conductor, also had St Elmo’s fire on the top of its mast.” One can therefore think that Le Roy’s report before the Académie des Sciences in 1784 had been taken into consideration, the Boussole having been equipped with the device recommended in this report.
The British Navy had become aware, several years earlier, of the importance of the lightning conductor. Thus Captain Cook recounts, during the course of one of his voyages around the world, that during a terrible storm his ship had avoided the fate of a Dutch vessel thanks to an “electric chain that we had fixed to the top of our ships and which carried the lightning over the side.”
Improvements in the device occurred, notably in England. Thus, in 1830, “30 ships of the British Navy were fitted with Mr Harris’s lightning conductors, that is, masts made conductors by means of metal cladding. The ships had been selected among those stationed in the most diverse regions, in the Mediterranean, at the Cape of Good Hope, in the East Indies, in North and South America, etc. They were, for several years, exposed to the most terrible storms, and, although struck by lightning on several occasions from 1830 to 1842, did not suffer any significant damage.”
Finishing his Memorandum, Le Roy adds that: “Anyone knowing the history of the Navy will readily admit that the majority of machines and instruments in which it takes great pride…were at the beginning a long way from perfection…and that if good minds had not surmounted the obstacles that absurd prejudices put in their way, the Navy would be still in the imperfect state it was in our fathers’ times.”
Thanks to Messrs Bruno Orsel and Claude Millé for the Memorandum of M. Le Roy.
by Henri Colombié Trans. William Land, with the kind permission of the Editor of the Journal de bord, No74, Winter 2017
 Les merveilles de la Science, Louis Figuier, 1867.
 Mémoire sur la nécessité et les moyens d’armer les vaisseaux de conducteurs ou paratonnerres…par M. Le Roy (SHD Vincennes-MS 78 Br T.III)
 Le Roy, op.cit.
 Voyage autour du monde, chapter 1
 Figuier, op.cit.