(b. Gloucester, England, 30 November 1711; d. Pennepack, Pennsylvania, March 1778)
Kinnersley intended to follow the career of his father, an English Baptist minister who settled near Philadelphia in 1714. But his period of probation coincided with that evangelical rush known as the Great Awakening, which offended his rationalistic sensibilities; and in 1740, after preaching in his minister’s absence against “whining, roaring Harangues, big with affected Nonsense,” he found himself temporarily outside his communion. Although the squabble was composed and he ordained (1743), he never received a pulpit; his religious career effectively ended in 1747 with the last of his published polemics against the elders of his church.
At just this time Franklin, who had printed some of Kinnersley’s tracts, began to study electricity. The unoccupied minister, “being honoured with Mr. Franklin’s intimacy,” became his principal collaborator. A flair for striking demonstrations and a ministerial facility of speech fitted Kinnersley for public lecturing; and, with Franklin’s help and encouragement, he successfully toured the colonies from 1749 to 1753, spreading the Philadelphia system and the truth about lightning. In 1753, again with Franklin’s help, he became professor of English and rhetoric at the Philadelphia Academy (forerunner of the University of Pennsylvania), a position he retained until 1772.
Kinnersley did his best work in electricity away from Franklin. For example, in 1752 while on a lecture tour in Boston, he rediscovered the two electricities of Dufay and forced upon Franklin the problem of deciding which was truly positive. Kinnersley raised another fundamental point in 1761. Orthodox Franklinian theory ascribed the mutual repulsion between positively charged bodies to their “atmospheres” of springy electrical matter. The reciprocal recession of negatively charged bodies therefore became a problem of principle, since they lacked by definition the necessary repulsive mechanism. Kinnersley suggested that no electrical repulsion existed; the air, he said, draws apart objects similarly charged via the usual attraction between neutral and electrified bodies. Although Franklin rejected the idea, it had important adherents, such as Beccaria (who had proposed it in his Lettere al Beccari [Turin, 1758]) and Volta. It was one of several eighteenth-century theories that avoided macroscopic actions at a distance by overtaxing the air with chores later entrusted to the electromagnetic ether. Kinnersley’s best-known contribution is the so-called electrical air thermometer, a device for estimating the increase in pressure caused by the passage of a spark through a confined volume of air. It is representative of the plight of colonial American philosophers that here again he was anticipated by Beccaria.
Kinnersley’s important paper of 1761, which includes a description of his thermometer and the theory of repulsion, appeared as “New Experiments in Electricity,” in Philosophical Transactions,53 (1763), 84-97. Franklin printed it, as well as the letter of 1752 regarding the two electricities, in later editions of his Experiments and Observations on Electricity; see 1. B. Cohen, Benjamin Franklin’s Experiments (Cambridge, Mass., 1941), 250-252, 348-358; the text of a hitherto unpublished lecture on electricity that Kinnersley wrote out in 1752 is on pp. 409-421. A full bibliography appears in J. A. L. Lemay, Ebenezer Kinnersley, Franklin’s Friend (Philadelphia, 1964), 123-124. On Kinnersley’s life see Lemay; The Papers of Benjamin Franklin, L. W. Labaree et al., eds. (New Haven, Conn., 1959); and Cohen, op. cit., 401-408. On his work see Lemay, “Franklin and Kinnersley,” in Isis,52 (1961), 575-581; M. Gliozzi, “Giambatista Beccaria nella storia dell’elettricitâ,” in Archeion, 17 (1935), 15-47; and I. B. Cohen, Franklin and Newton (Philadelphia, 1956), 492-494, 531-534.
John L. Heilbron