References.—Latin poem entitled “Mariani Parthenii Electricorum,” in six books, Roma, 1767, lib. i. p. 34 (describing the telegrafo elettrico scintillante); also Saturday Review, August 21, 1858, p. 190, and Cornhill Magazine for 1860, Vol. II. p. 66.
A.D. 1767.—Priestley (Joseph), the earliest historian of electrical science, publishes, by advice of Benjamin Franklin, the first edition of his great work, “The History and Present State of Electricity,” of which there were four other separate enlarged issues, in 1769, 1775, 1775 and 1794. During the year 1766 he had been given the degree of Doctor of Laws by the Edinburgh University and he had also, at the instance of Franklin, Watson and others, been made a member of the English Royal Society, which, a few years later, bestowed upon him the Copley medal.
Speaking of the above-named work, Dr. Lardner says (“Lectures, 1859, Vol. I. p. 136): “This philosopher did not contribute materially to the advancement of the science by the development of any new facts; but in his ‘History of Electricity’ he collected and arranged much useful information respecting the progress of the science.” Nevertheless, to him is due the first employment of the conductor supported by an insulating pillar, as described by Noad, who gives an account of Priestley’s electrical machine at Chap. IV of his “Manual”; and he is also the first to investigate upon an extensive scale the chemical effects of ordinary electricity. The observations of M. Warltire, a lecturer on natural philosophy, and Priestley’s own experiments in this line, made by passing the electric spark through water tinged blue by litmus, also through olive oil, turpentine, etc., as well as his researches more particularly upon the gases and upon the influence of the electric fluid in expanding solid bodies, are detailed at the “Electricity” chapter of the “Encycl. Brit.”
At pp. 660–665 of the fourth edition of his “History,” Priestley describes the experiments he made to illustrate what he called the lateral force of electrical explosions; that is, the tendency of the fluid to diverge, as is the case with lightning when any material obstruction lies in its path.
Perhaps the most important of all Dr. Priestley’s electrical discoveries (Thomson, “Hist. Roy. Soc.,” p. 445) was that charcoal is a conductor of electricity, and so good a conductor that it vies even with the metals themselves. When the conducting power of charcoal was tried by succeeding electricians, it was found to vary in the most unaccountable manner, sometimes scarcely conducting at all, sometimes imperfectly and sometimes remarkably well; a diversity naturally indicating some difference in the nature of the different specimens of English charcoal (Priestley’s “History,” etc., Part VIII. s. 3). Charcoal being examined by Mr. Kinnersley (at A.D. 1761), was also by him observed to vary in its conducting power. Oak, beech and maple charcoal he found to conduct satisfactorily; the charcoal from the pine would not conduct at all, while a line drawn upon paper by a heavy black lead pencil conducted pretty well (Phil. Trans., 1773, Vol. LXIII. p. 38).
References.—Priestley’s letter to Dr. Franklin (Phil. Trans., Vol. LXII. p. 360) concerning William Henley’s new electrometer and experiments; likewise the Phil. Trans., Vol. LVIII. p. 68; Vol. LIX. pp. 57, 63; Vol. LX. p. 192; Vol. LXII. p. 359; and the abridgments by Hutton, Vol. XII. pp. 510, 600, 603; Vol. XIII. p. 36; “Trans. of the Amer. Phil. Soc.,” O. S., Vol. VI. part i. p. 190, containing proceedings of the Society on the death of Joseph Priestley; Wilkinson’s “Elements of Galvanism,” etc., London, 1804, Vol. II. pp. 74–80; Noad’s Lectures, No. 4, Knight’s edition, pp. 182, 183; “Library of Useful Knowledge,” London, 1829, Chap. “Electricity,” pp. 41 and 45; “Library of Literary Criticism,” C. W. Moulton, Buffalo, 1901–1902, Vol. IV. pp. 444–456; “Essays, Reviews and Addresses” by James Martineau, London, 1890, Vol. I. pp. 1–42; “Mém. de l’Institut” (Histoire), Tome VI. 1806, p. 29 for Elogium; “Essays in Historical Chemistry,” T. E. Thorpe, London, 1894, pp. 28, 110; “Science and Education,” by Thos. Henry Huxley, New York, 1894, pp. 1–37; “Scientific Correspondence of Jos. Priestley,” by H. C. Bolton, New York, 1902; Dr. Thos. H. Huxley, “Science Culture,” 1882, p. 102; Warltire, in Muirhead’s translation of Arago’s “Eloge de James Watt,” pp. 99, 100; also the appendix to the last-named work, p. 157 and note.
A.D. 1767.—Lane (Thomas—Timothy), a medical practitioner of London, introduces his discharging electrometer, which is now to be found described and illustrated in nearly all works on electricity.
It consists of a bent glass arm, one end of which is attached to a socket in the wire of the Leyden jar, while the other end holds a horizontal sliding brass rod, or spring tube, which bears a ball at each extremity. The rod is usually divided into inches and tenths, indicating the force of the discharge which takes place when the knob of the jar is placed in contact with the prime conductor of an electrical machine, and the charge is strong enough to leap from one to the other. In Mr. Lane’s experiments the shocks were twice as frequent when the interval between the balls was one twenty-fourth of an inch as when twice as much: from which he concluded that the quantity of electricity required for a discharge is in exact proportion to the distance between the surfaces of the balls.
A combination of the Lane and other electrometers was made by Mr. Cuthbertson, as shown at p. 528, Vol. II of Nicholson’s Journal of Natural Philosophy, and at p. 451, Vol. LVII of the Philosophical Transactions.
References.—Phil. Trans. for 1805; Hutton’s abridgments, Vol. XII; p. 475; Cavallo, “Elements ... Phil.” 1825, Vol. II. p 197; Harris, “Electricity,” p. 103; Monthly Magazine, December 1805, and Tilloch’s Philosophical Magazine, Vol. XXIII. p. 253.