For Stukeley and for Stephen Hales: consult “General Biographical Dictionary,” Alex. Chalmers, London, 1814, Vol. XVII. pp. 41–43.
References.—Priestley, “History of Electricity,” Part I. period x. s. 12; Phil. Trans., abridged by John Martyn, Part II. of Vol. X. pp. 406–526, 535, 540, 541, 551; Vol. XLIV-XLV, p. 409; Appendix to the Phil. Trans. for 1750, Vol. XLVI; Hale, “Statical Essays,” II. p. 291; Thomson, “Hist. Roy. Soc.,” 1812, p. 197.
A.D. 1749.—Jallabert (Jean Louis), Professor of Philosophy and Mathematics at Geneva, is the author of “Expériences sur l’électricité, avec quelques conjectures sur la cause de ses effets,” of which a smaller edition had appeared at Geneva in 1748.
He confirms the result obtained by Dr. Watson (A.D. 1745) that the electric fluid takes the shortest course by passing through the substance of a conducting wire instead of along its surface. By making his Leyden experiments with a jar in which the water is frozen, he shows that ice is a conductor of electricity. He improves upon Nollet’s experiments, and demonstrates conclusively that plants which are electrified grow faster and have finer stems, etc., than those not electrified. He is the first to observe that a body pointed at one end and round at the other produces different appearances upon the same body, according as the pointed or the rounded end is presented to it. The Dantzig Memoirs, Vol. II. p. 378, tell us that Carolus Augustus Van Bergen, Professor of Medicine at Frankfort on Oder, had previously noticed, “as a small step toward discovering the effect of pointed bodies,” that sparks taken from a polished body are stronger than those from a rough one. With the latter he found it difficult to fire spirits, but he could easily do it with a polished conductor.
M. Jallabert is also known to have effected some medical cures through the agency of the electric fluid, as related in the “Expériences” above alluded to.
References.—“Biog. Univ.,” Vol. XX. p. 535; Bertholon, “Elec. du Corps Humain,” 1786, Vol. I. pp. 260, 292, 299, 334, 413, and Vol. II. p. 291; Beccaria, “Dell’ Elettricismo Naturale,” etc., p. 125; “Journal des Sçavans,” Vol. CXLIX. for 1749, pp. 1–18, 441–461; “Medical Electricity,” by Dr. H. Lewis Jones, Philad. 1904, p. 2.
A.D. 1749.—Mines are fired by electricity (S. P. Thompson, lecture delivered October 7, 1882, at the University College, Bristol).
A.D. 1749.—Through the important work entitled “Traité sur l’Electricité,” Louis Elisabeth de la Vergne Tressan secures, a year later, admission to both the French Académie des Sciences and the English Royal Society. During 1786, three years after his death, the above-named work was merged into a publication in two volumes under the title of “Essai sur le fluide électrique considéré comme agent universel.”
References.—“Biographie Générale,” Vol. XLV. pp. 623–626; Larousse, “Dictionnaire Universel,” Vol. XV. p. 474.
A.D. 1749.—Duhamel (Henri Louis, du Monceau) (1700–1782), member of the French Royal Academy of Sciences, develops, in conjunction with M. Antheaulme, the method introduced by Gowin Knight (A.D. 1746) for making artificial magnets, which latter process was found to be defective when applied to very large bars. To Le Maire, however, is due (Mem. de l’Acad. de Paris, 1745 and 1750), the notable improvement which consists in magnetizing at the same time two steel bars of any shape by placing them parallel to each other and connecting their extremities, with pieces of soft iron placed at right angles, in order to form a closed rectangular parallelogram. Two strong magnets, or two bunches of small magnetic bars, with their similar poles together, are then applied to the centre of one of the bars to be magnetized and are drawn away from each other, practically as in Dr. Knight’s method, while being held at an inclination of about forty-five degrees. The operation is repeated upon the other bar and continued alternately until sufficient magnetism is imparted to both, it being borne in mind that before the treatment is given to the second bar the poles must in each instance be reversed, i. e. the pole which was to the right hand should be turned to the left. The entire operation is to be repeated upon the reverse side of both bars.