It is said by Humboldt (“Cosmos,” 1849, Vol. II. p. 718, note) that this observation, the first of the kind, was made on the tower of the church of the Augustines at Mantua (Mantova) and that Grimaldi and Gassendi were acquainted with similar instances (instancing the cross of the church of St. Jean, at Aix, in Provence), in geographical latitudes where the inclination of the magnetic needle is very considerable. Some writers give Gassendi’s observation as occurring during 1632 (see Rohaulti, “Physica,” 1718, Par. III. cap. 8, p. 399; or, Rohault’s “System of Nat. Phil.,” 1728, p. 176). “As the iron cross of an hundred weight upon the Church of St. John in Ariminum, or that load-stoned iron of Cæsar Moderatus, set down by Aldrovandus” (Sir Thomas Browne, “Pseudodoxia Epidemica,” 1658, p. 66). Consult “Lettera dell’Eccel. Cavallara.,” Mantova, 1586, for a detailed account of this discovery, made January 6, of the last-named year. The iron rod supported a brick ornament in the form of an acorn, and stood on a pyramid at the summit of the belfry of the church of St. Augustine (Cabæus, “Philos. Magn.,” p. 62; “Ulysses Aldrovandi, Patr. Bonon ... Barthol. Ambros ...” Lib. i, cap. 6, p. 134). For the account given by Aldrovandi of the Arimini observation and for references to Browne’s “Pseudodoxia Epidemica,” as well as to Boyle’s “Experiments,” see p. 53 of the valuable “Notes on the ‘De Magnete’ of Dr. William Gilbert,” by Silvanus P. Thompson, attached to the English translation of the original 1600 edition, which was so attractively produced by the Gilbert Club during the year 1900. Dr. Thompson further gives, at the page following (54), additional references to examples of iron acquiring strong permanent magnetism from the earth. REFERENCES.--Biography of Sarpi in the “Encycl. Brit.,” ninth edition, Vol. XXI. pp. 311–313; F. Micanzio, “Vita de F. P. Sarpi,” Verona, 1750; Rev. Alex. Robertson, “Fra Paolo Sarpi--the greatest of the Venetians,” 1894; Hallam, “Intro. to Lit.,” 1839, Vol. II. p. 464; U. Aldrovandi, “Musæum Metallicum,” 1648, p. 134; Tiraboschi, “Storia della Lettera,” Modena, 1794, Vol. VI. part ii. p. 506; Sarpi’s Complete Works, first published at Helmstat, 1750; Fabroni, “Vitæ Italorum,” Pisa, 1798; Giovini, “Vita,” Brussels, 1836; “Engl. Cycl.,” Biography, Vol. IV. pp. 695–697; Larousse, “Dict. Univ.” Vol. XIV. pp. 230–231; “History of the reign of Charles the Fifth,” by Wm. Robertson and Wm. H. Prescott, Philadelphia, 1883, Vol. III. p. 68; “Dict. Hist. de la Médecine,” N. F. J. Eloy, Mons, 1778, Vol. IV. pp. 180–181; “The Atlantic Monthly,” New York, January and February, 1904, wherein the author, Andrew D. White, ranks Sarpi with Machiavelli and Galileo; Libri, “Hist. des Sc. Mathém.” Paris, 1838, Vol. IV. p. 214, note.