And sharp conductors change for blunt,
The nation’s out of joint:
Franklin a wiser course pursues,
And all your thunder useless views,
By keeping to the point.”
Thomson informs us (“Hist. Roy. Soc.” pp. 446–447) that the Board of Ordnance having consulted the Royal Society about the best mode of securing the powder magazine, at Purfleet, from the effects of lightning, the Society appointed Mr. Cavendish, Dr. Watson, Dr. Franklin, Mr. Robertson and Mr. Wilson a committee to examine the building and report upon it. These gentlemen went accordingly, and the first four recommended the erecting of pointed conductors in particular parts of the building, as a means which they thought would afford complete security. Mr. Wilson dissented from the other gentlemen, being of the opinion that the conductors ought not to be pointed but blunt, because pointed conductors solicit and draw down the lightning which might otherwise pass by. He published a long paper on the subject, assigning a great variety of reasons for his preference (Philosophical Transactions, Vol. LXIII. p. 49). It was this dissent of Mr. Wilson which produced between the electricians of the Royal Society a controversy respecting the comparative merits of pointed and blunt conductors, which continued a number of years, and a variety of papers in support of which made their appearance in the Philosophical Transactions. The controversy, in fact, engaged almost the exclusive attention of the writers on electricity for several successive volumes of that work.
References.—William Henley, “Experiments ... pointed and blunted rods ...” in Phil. Trans, for 1774, p. 133; P. D. Viegeron, “Mémoire sur la force des pointes ...”; Edward Nairne, “Experiments ... advantage of elevated pointed conductors,” in Phil. Trans. for 1778, p. 823; Lord Mahon, “Principles ... superior advantages of high and pointed conductors,” London, 1779; Hale’s “Franklin in France,” 1880, Part I. p. 91, and Part II. pp. 254–256, 279, for some of his other correspondence with Dr. Ingen-housz; likewise Part II., pp. ix, 273, 441–451, regarding the first publication of copies of letters written by Franklin to Sir Joseph Banks, which “for some curious reason,” Mr. Hale remarks, were not publicly read and were never included in the Philosophical Transactions, as Franklin intended they should be. Consult also Thomas Hopkinson on “The Effects of Points,” etc., in Franklin’s “New Experiments,” etc., London, 1754; Tilloch’s Philosophical Magazine for 1820; Hutton’s abridgments, Vol. XIII. p. 382; “Memoir of Sir J. Pringle” in Weld’s “Hist. of Roy. Soc.,” Vol. II. pp. 58–67, 102; Jared Sparks’ edition of Franklin’s “Works,” and Sir John Pringle’s discourse delivered at the Anniversary Meeting of the Royal Society, Nov. 30, 1774, a translation of the last named appearing at p. 15, Vol. XV of the “Scelta d’ Opuscoli.” J. Clerk Maxwell, “Electrical Researches of the Hon. Henry Cavendish,” 1879, pp. 52–54.
A.D. 1778.—Martin (Benjamin), English artist and mathematician, who had already written an “Essay on Electricity” and a prominent supplement thereto (1746–1748), publishes an enlarged edition in three volumes of his “Philosophia Britannica,” originally produced in 1759. At Vol. I. p. 47 of the last-named work, he states that his experiments indicate a magnetic force inversely as the square roots of the cubes of the distances. Noad, treating of the laws of magnetic force, says (“Electricity” p. 579) that Martin and Tobias Mayer both came to the conclusion that the true law of the magnetic force is identical with that of gravitation, and that, in the previous experiments of Hauksbee and others, proper allowance had not been made for the disturbing changes in the magnetic forces so inseparable from the nature of the experiments.
His first Lecture explains all the phenomena of electricity and magnetism, the appendix thereto detailing numerous experiments of Mr. John Canton, and giving many additional facts concerning the manufacture of artificial magnets. From his preface the following extracts will, doubtless, prove interesting: “We are arrived at great dexterity since Sir Isaac Newton’s time; for we can now almost prove the existence of this aether by the phenomena of electricity; and then we find it very easy to prove that electricity is nothing but this very aether condensed and made to shine. But I believe, when we inquire into the nature and properties of this aether and electricity, we shall find them so very different and dissimilar, that we cannot easily conceive how they should thus mutually prove each other.... I see no cause to believe that the matter of electricity is anything like the idea we ought to have of the spiritus subtilissimus of Sir Isaac.... The smell also of electrical fire is so very much like that of phosphorus, that we may be easily induced to believe a great part of the composition of both is the same.”
References.—“Encycl. Britan.,” 1857, Vol. XIV. p. 320; Antoine Rivoire (Rivière), “Traité sur les aimants ...” Paris, 1752; Nicolaus von Fuss, “Observations ... aimants ...” Petersburg, 1778; Le Noble, “Aimants artificiels ...” Paris, 1772, and “Rapport ... aimants,” 1783 (Mém. de Paris); Wens, “Act. Hill,” Vol. II. p. 264; C. G. Sjoestén (Gilbert, Annalen der Physik, Vol. XVII. p. 325); Rozier, IX. p. 454.