In the twenty-third proposition of the second book, fifth section, Newton says: “The virtue of the magnet is contracted by the interposition of an iron plate and is almost terminated at it, for bodies further off are not so much attracted by the magnet as by the iron plate.” And in Book III. prop. vi. he thus expresses himself: “The magnetic attraction is not as the matter attracted; some bodies are attracted more by the magnet, others less; most bodies not at all. The power of magnetism in one and the same body may be increased and diminished, and is sometimes far stronger for the quantity of matter than the power of gravity; and in receding from the magnet decreases, not in the duplicate, but almost in the triplicate proportion of the distance, as nearly as I could judge from some rude observations.”
Newton is said to have carried in his ring a magnet weighing but three grains, which could raise 746 grains, or nearly 250 times its own weight. This magnet naturally excited much admiration, but is greatly surpassed in power by that formerly belonging to Sir John Leslie, and now in the Physical Collection at Edinburgh, weighing three and one-half grains, and having a carrying power of 1560 grains.
References.—Brewster’s “Life of Sir I. Newton,” pp. 307, 308; “Dict. of Nat. Biog.,” Vol. XL. pp. 370–393; Ch. W. Moulton, “Library of Literary Criticism,” Vol. II. pp. 710–726; “Bibl. Britan.” (Authors), Robt. Watt, Edinburgh, 1824, Vol. II., p. 701; Harris, “Magnetism,” Vol. III. p. 11; Ninth “Britannica,” Vol. XV. p. 274; Whewell, “Hist. of the Ind. Sciences,” 1858, Vol. I. pp. 385–488; the interesting note at foot of p. 683 of the Fourth Dissertation in the “Encyclopædia Britannica”; “Muspratt’s Chemistry,” Vol. II. p. 255; the English “Chemical News” for November 1867, and January 1868, reproducing Sir David Brewster’s letters to the London “Athenæum” and London “Times,” likewise Dr. Crompton’s paper read before the Manchester Literary and Philosophical Society in October 1866; Phil. Trans., Vol. LXIV. Part I for 1774, p. 153: “Remarks of John Winthrop upon ... Castillione’s Life of Sir Isaac Newton”; Dr. Geo. Miller, “Hist. Phil. Ill.,” London, 1849, Vol. III. pp. 414–415; “Newton, sa vie et ses œuvres” in “Cosmos,” September 27, 1890 to December 13, 1890; “Journal des Savants” for April, May and June 1832; for April 1846, March, April, May, June, July and August 1852, October, November 1855; Houzeau et Lancaster, “Bibl. Gén.,” Vol. II, 1882, pp. 213–214, 1586; “Hist. de la Philosophie,” par Chas. de Rémusat, Paris, 1878, Vol. II. chap. xii. pp. 202–222.
A.D. 1676.—Haward, master of several sailing vessels, and a man of good credit (Phil. Trans., Vol. XI. No. 127, p. 647, of July 18, 1676), states that “being on board of the ship Albemarle, July 24, 1641 ... in latitude of Bermuda ... after a terrible clap of thunder ... it was found that the compass card was turned around, the N. and S. points having changed positions and, though Mr. Grofton brought with his finger the flower-de-lys to point directly N., it would immediately, as soon as at liberty, return to this new unusual posture, and upon examination he found every compass (three) in the ship of the same humour; which ... he could impute to nothing else but the operation of the lightning or thunder mentioned.” The above is also alluded to at p. 33 of Vol. III. of Boyle’s “Phil. Works,” London, 1738, with this addition: “One of the compasses, pointing West, was brought to New England, where, the glass being broke and the air gaining entrance, it lost its virtue. But one of the others is in that country possess’d by Mr. Encrease Mather, the North point of the needle remaining South to this day.”
A.D. 1677.—At p. 14 of an exceedingly curious publication entitled “A Rich Cabinet with a Variety of Inventions,” etc., written by J. W. (i. e. John White, of London), who calls himself “a lover of artificial conclusions,” will be found an article on “Divers rare, conceited motions performed by a magnet or loadstone.”
A.D. 1678.—Redi (Francesco), well-known Italian scientist, physician to the Grand Duke Ferdinand II, publishes his “Experimenta circa res diversas Naturales,” wherein he is first to communicate the fact that the shock of the raia torpedo can be transmitted to the fisherman through the line and rod connecting him with the fish.
References.—Leithead, “Electricity,” Chap. XII; the Firenze, 1671 ed. of Redi’s “Esperienze,” etc., pp. 47–54; Phil. Trans. for 1673, Vol. VIII. p. 6003; Sci. Am. Supp., No. 457, pp. 7300–7302; Matteucci, “Recherches,” 1837 and 1867; Eschinardi (F. della Compagnia di Gesü), “Lettera al S. Francesco Redi,” Roma, 1681, wherein are detailed many curious experiments, including some treating of the magnetic needle by which agency are foretold sudden attacks of earthquakes, etc. etc.
A.D. 1679.—Maxwell (William)—Guillelmo Maxvello—native of Scotland, author of “Medicina Magnetica,” offers to prove to various medical faculties that, with certain magnetic means at his disposal, he could cure any of the diseases abandoned by them as incurable (Blavatsky, “Isis,” Vol. I. p. 215).
Reference.—J. H. Van Swinden, “Recueil de Mémoires,” etc., La Haye, 1784, Vol. II. p. 367.
A.D. 1683.—Arrais (Edoardo Madeira), who had been physician to—João—John IV, the first Portuguese king of the house of Braganza, is the author of this much-delayed edition of a book entitled “Arbor Vitæ, or a physical account of the Tree of Life in the Garden of Eden.” It treats of occult qualities under the headings of “Doubts,” of which latter there are eight separate ones which constitute as many different chapters, from which the following extracts will prove interesting: