A.D. 1787.—Brard (Cyprien Prosper), French mineralogist, first observes that some crystals of axinite (consisting mainly of silica, alumina, lime and peroxide of iron) become electric by heat.
References.—Gmelin, article “Electricity,” etc., Vol. I. p. 319; Larousse, “Dict. Univ.,” Vol. II. p. 1205; Thomas, “Dict. of Biog.,” Vol. I. p. 429; “Enc. Brit.,” 8th ed., Vol. VIII. p. 530; Brard, “Manuel du Minéralogiste,” etc., Bordeaux Academy of Sciences Report for 1829, p. 39, and for 1838, p. 84—the latter containing M. Hatchett’s observations on one of M. Brard’s meteorolites.
A.D. 1787.—Haüy (Le Père René Just), native of Picardie and member of the Académie Royale des Sciences, publishes an abridgment of the doctrines of Æpinus (at A.D. 1759) under the title of “Exposition raisonnée de la Théorie de l’Électricité et du Magnétisme.” He was doubtless the first to observe that in all minerals the pyro-electric state has an important connection with the want of symmetry of the crystals, and no proof of the extent to which he directed his investigations in that line can more readily be had than by consulting general “Encyclopædia” articles relative to the pyro-electricity of boracite (borate of magnesia), of prehnite (silica, alumina and lime), of mesotype (hydrated silicate of alumina and of lime or of soda), of sphene (silica, titanic acid and lime), calamine (silicate of zinc) and of Siberian topaz.
At pp. 480, 481 of his “Outline of the Sciences,” etc., London, 1830, Dr. Thomas Thomson states:
“There is a hill of sulphate of lime, called Kalkberg, situated near Lunebourg, in the duchy of Brunswick, in which small cubic crystals are found. These cubes are white, have a specific gravity of 2·566, and are composed of two atoms of boracic acid combined with one atom of magnesia. They are distinguished among mineralogists by the name of boracite. If we examine the cubic crystals of boracite, we shall find that only four of the solid angles are complete, constituting alternate angles placed at the extremity of two opposite diagonals at the upper and lower surface of the cube. The other four solid angles are replaced by small equilateral triangles. When the boracite is heated all the perfect solid angles become charged with negative electricity, while all the angles replaced by equilateral triangles become charged with positive electricity. So that the boracite has eight poles: four positive and four negative. Those are obviously the extremities of four diagonals connecting the solid angles with each other. One extremity of each of these diagonals is charged with positive and the other extremity with negative electricity. In general, the electricity of boracite is not so strong as that of the tourmaline.” This curious law of the excitability of the boracite and of its eight poles was discovered by Haüy in 1791 (Haüy’s “Minéralogie,” 260, second edition).
Axinite, mesotype, and the silicate of zinc are also minerals which become electric when heated, and which, like the tourmaline, exhibit two opposite poles, the one positive, the other negative. It is not every crystal of axinite and mesotype which possesses this property, but such only as are unsymmetrical, that is to say, such as have extremities of different shapes. No doubt this remark applies also to the silicate of zinc; though as the crystals of that mineral are usually acicular it is not so easy to determine by observation the degree of symmetry which they may possess.
The topaz, prehnite, and the titaniferous mineral called sphene are also capable of being excited by heat, and have two opposite poles like those already mentioned.
Haüy also made the most extensive and accurate observations known upon the development of electricity in minerals by friction. Detailed lists of the different classes of minerals, as well as the conclusions arrived at through various experiments, are given in the “Encyclopedia Britannica,” Vol. VIII, 1855, pp. 538, 539, while at pp. 529 and 558 of the same work are to be found accounts of his observations on the electricity of the tourmaline, as well as a description of the different electroscopes employed in his many experiments.
References.—Priestley, “History of Electricity,” 1767, pp. 314–326; Gmelin’s “Chemistry,” Vol. I. p. 319; Noad, “Manual,” pp. 27–31; also article “Electricity” in “Library Useful Knowledge,” pp. 3, 54, 56; M. Lister, “Collection Académique,” Tome VI; “Société Philomathique,” An. V. p. 34; An. XII. p. 191; “Mém. du Museum d’Hist. Nat.,” Vol. III; “Mém. de l’lnstitut,” An. IV. tome i., “Sciences Math. et Phys.” p. 49; “Mém. de l’Académie,” 1785, Mem. p. 206; Philosophical Magazine, Vols. XX. p. 120; XXXVIII. p. 81; Thomas Thomson, “Hist. of the Roy. Soc.,” London, 1812, pp. 180, etc.; Young’s “Lectures,” London, 1807, Vol. II; Haüy, “Traité Élémentaire de Physique,” Chap VII, “Magnetism”; Experiments of J. L. Treméry (author of “Observations sur les Aimants Elliptiques,” recorded in Journal des Mines, Vol. VI for 1797, also in Jour. de Phys., Vols. XLVIII and LIV) and of M. De Nelis, some of whose observations are given in the Phil. Mag., Vol. XLVIII. p. 127, and in the Jour. de Phys., Vols. LXI. p. 45; LXII. p. 150; LXIII. p. 147; LXIV. p. 130; LXVI. pp. 336, 456, as shown and illustrated at pp. 153–162 of Delaunay’s “Manuel,” etc., of 1809; “Séances de l’Acad. de Bordeaux” for 1835, giving M. Vallot’s report on the difference existing between the chalcedony and the tourmaline. Regarding the latter, consult S. Rinmann (“K. Schwed. Akad. Abh.,” XXVIII. pp. 46, 114); C. Rammelsberg, “Die Zuzam ... und Feldspaths”; Mr. Magellan’s edition of Cronstedt’s Mineralogy for Steigliz’s tourmaline; Cesare G. Pozzi, on the tourmaline; H. Von Meyer (“Archiv. ... Ges. Natural,” XIV. 3, p. 342); M. Lechman (Berlin Academy Reports); Carl Von Linné (Linnæus), “Flora Zeylanica,” Stockholm, 1747; M. Leymerie (Toulouse Acad. Reports); Brewster, “Journal” I. p. 208; J. K. Wilcke (“Vetensk. Akad. Handl.,” 1766 and 1768); Jos. Muller, “Schreiben ... Tourmaline,” Wien, 1773; F. J. Muller von Reichenstein, “Nachr. ... an Born,” Wien, 1778; H. B. de Saussure (“Jour. de Paris”), 1784; Louis Delaunay’s letter on the tourmaline, 1782; D. G. Fischer’s works, published at Mosk, 1813, 1818; J. D. Forbes (“Edin. Trans.,” Vol. XIII), 1834.
A.D. 1787.—Charles (Jacques Alexandre César), a singularly able French physicist and experimentalist, who became the Secretary of the Académie des Sciences, relates many of his electrical experiments in the thirtieth volume of the Journal de Physique.