The two brief notes below appear insignificant, but they belong to a scientific correspondence that continued intermittently for at least a year, and that chronicled a major advance in the knowledge of animal electricity. The writer, John Walsh (1726–95), was a man who developed his experimental bent late in life. He was the cousin both of Lord Clive and of Nevil Maskelyne, the Astronomer Royal, and moved as he grew older from the world of India to that of science. After serving to good purpose as Clive’s secretary in Bengal, Walsh returned home in 1759 with a considerable fortune; in 1761 Worcester returned him to the House of Commons, and continued to do so for almost two decades.6 But his heart was not in politics. By 1770 he had enough scientific reputation to be elected to the Royal Society, and two years later he was absorbed—for reasons that are as obscure as they are intriguing—with the subject of research that made his name. This was the torpedo fish.7

The significance of the research lies in a particular gift of the fish. Torpedo marmorata, a sea ray that frequents European coastal waters, is like other members of its family capable of producing at will strong electric shocks from organs on each side of its head.8 This phenomenon, long attributed to evil spirits, first attracted serious scientific attention in the seventeenth century. A Tuscan physician, Stefano Lorenzini, whose writings were the subject of Walsh’s second note below, concluded that the numbing shocks are due to minute particles that pass from the strange organs of the fish into its victim’s body. René-Antoine Ferchault de Réaumur (1683–1757), the physicist and naturalist, subsequently amended this hypothesis by substituting for particles the extremely rapid, if equally supposititious, motion of the muscles that compose the fish’s organs.9 Neither theory explained why a fisherman, holding a wet pole or other conductor that came into contact with the torpedo’s body, was as effectively numbed as if he had touched it.

The burgeoning of electrical investigation in the mid-eighteenth century brought with it speculation that the shocks from some fish were akin to the discharge from a Leyden jar. Edward Bancroft, the subject of Walsh’s first note, carried out a number of experiments with the torpor-inducing or “torporific” eel of Dutch Guiana, and demonstrated that its shocks were indeed electrical. The same had to be true of the torpedo, he argued, unless its physiology was markedly different from the eel’s.1 This was the challenge that Walsh took up. By early 1772 he had met Franklin,2 who was interested in the problem to the point of borrowing from him Lorenzini’s book. In June, Walsh left for France, the supposed northern limit of the torpedo’s range, to search for specimens. He found them off La Rochelle, and proved beyond question that the fish generated an electric charge; its muscles, he concluded, functioned like a Leyden jar. His findings were embodied in a letter to Franklin in 1773 and published in the Royal Society’s Transactions, and furthered the growing European and American interest in animal electricity.3 The significance of the torpedo was recognized, and the physiology of its peculiar organs was exposed.4 Only one mystery remained for later scientists to investigate—how the fish could renew its charges—and this investigation eventually played a part in the discovery of current electricity.

These two notes are impossible to date. Both were written before Walsh’s journey to France, and probably not on the eve of departure, because he was still gathering information to prepare himself for his research. Just when he left England is not known, but it must have been early in June; his letter of the 21st, below, suggests that by then he had been in Paris for some weeks. Hence we can only assign the notes to the period before the journey.