=A.D. 1706.=--Hartsoeker (Nicolas), Dutch natural philosopher, friend of Christian Huyghens, while Professor of Mathematics at Düsseldorf, writes his “Conjectures Physiques,” four editions of which were published during the three years 1708, 1710 and 1712. The Tenth Discourse of the Second Book (pp. 140–182) treats of the nature and properties of the loadstone and gives numerous observations concerning magnetical phenomena, which are well illustrated. He says that many ordinary stones have become magnetic after being long exposed to the air, in consequence of iron penetrating them. He believes that the native loadstone is made up of ordinary stone and of iron containing many small bodies through which run magnetic channels; that the latter are held together so strongly as to be disintegrated with difficulty, and that they are filled with a subtile matter which circulates incessantly through and around them. The First Discourse of the Fourth Book treats of Meteors, and at pp. 91–99 of his “Eclaircissements, ...” published in 1710 he gives further reports of his curious observations on magnetic phenomena. REFERENCES.--“Journal des Sçavans,” Vol. XXIV for 1696, pp. 649–656. For particulars of the very celebrated natural philosopher, Christian Huyghens--Hugenius van Zuglichen (1629–1695) above alluded to, consult: the “Vita Hugenii,” prefixed to his “Opera Varia,” published by Van ’Sgravesande in 1724; “Meyer’s Konversations-Lexikon,” Leipzig und Wien, 1895, Vol. IX. pp. 93–94, also the biography, embracing a detailed list of his geometrical, mechanical, astronomical and optical works at pp. 536–538 of the “English Cyclopædia”; Vol. II. of Houzeau et Lancaster, “Bibliog. Générale,” p. 169; “Le Journal des Savants” for May 1834, April 1846, July 1888, April 1896, Feb. 1898, Oct. 1899; “Histoire des Sciences Math. et Phys.,” Maximilien Marie, Paris, 1888, Vol. V. pp. 15–140; “Hist. et Mém. de l’Acad. Roy. des Sc.,” Vol. I. p. 307; Hartsoeker’s biography at pp. 307–308 of the “Engl. Cycl.,” Vol. III, 1867.[49] =A.D. 1707.=--J. G. S. (not, as many suppose, Jean George Sulzer) publishes “Curious Speculations during Sleepless Nights” 8vo, Chemnitz, wherein appears the first account of the development, by heat, of electricity in the _tourmaline_, which latter, it is therein stated, was first brought from Ceylon by the Dutch in 1703. Another report of the above appears in the _Mémoires de l’Académie des Sciences_ of Paris for 1717. REFERENCE.--Beckmann, Bohn, 1846, Vol. I. pp. 86–98. =A.D. 1708.=--Wall (Dr. William), a prominent English divine, communicates to the Royal Society (_Phil. Trans._, Vol. XXVI. No. 314, p. 69) the result of his experiments, showing him to have been the first to establish a resemblance of electricity to thunder and lightning.