A.D. 1530–1542.—Guillen (Felipe), an ingenious apothecary of Seville, and Alonzo de Santa Cruz (who was one of the instructors of mathematics to young Charles V, King of Spain and Emperor of Germany, and the Cosmografo Mayor of the Royal Department of Charts at Seville), construct variation charts and variation compasses by which solar altitudes can be taken.
References.—Humboldt, “Cosmos,” 1849, Vol. II. p. 658, and 1859, Vol. V. p. 56; L. A. Bauer, “U. S. Magn. Tables,” 1902, p. 26.
Although based upon very imperfect observations, the magnetic charts thus devised by Alonzo de Santa Cruz antedate by more than one hundred and fifty years the work of Dr. Halley (at A.D. 1683).
A.D. 1544.—Hartmann (Georg) a vicar of the church of Saint Sebaldus, at Nuremberg, writes March 4, to the Duke Albrecht of Prussia, a letter which was brought to light by Moser and which reads as follows: “Besides, I find also this in the magnet, that it not only turns from the north and deflects to the east about nine degrees, more or less, as I have reported, but it points downward. This may be proved as follows: I make a needle a finger long, which stands horizontally on a pointed pivot, so that it nowhere inclines toward the earth, but stands horizontal on both sides; but, as soon as I stroke one of the ends (with the loadstone) it matters not which end it be, then the needle no longer stands horizontal, but points downward (fällt unter sich) some nine degrees, more or less. The reason why this happens I was not able to indicate to his Royal Majesty.” The above seems to establish the fact that Hartmann first observed the dip of the magnetic needle independently of Robert Norman.
Gilbert refers (“De Magnete,” Book I. chap. i.) to Fortunius Affaitatus—Affaydatus—an Italian physicist who, says he, has some rather silly philosophizing about the attraction of iron and of its turning to the poles, thus alluding to the latter’s small work called “Physicæ (et) ac astronomiæ (astronomicæ) considerationes,” which appeared at Venice in 1549. Nevertheless, it is a question whether Affaitatus was not actually the first to publish the declination of the magnetic needle. (“Biogr. Gén.,” Vol. I. p. 346; Mazzuchelli, “Scrittori d’Italia”; Bertelli, “Mem. sopra P. Peregrino,” p. 115; Adelung, Supplément à Jocher, “Allgem. Gelehrten-Lexicon”; Johann Lamont, “Handbuch des Magnetismus,” Leipzig, 1867, p. 425; J. C. Poggendorff, “Biogr.-Lit. Handwörterbuch,” Leipzig, 1863, Vol. I. p. 15; Michaud, “Biogr. Univ. Anc. et Mod.,” Vol. I. p. 208, Paris, 1843; Brunet, “Manuel,” Paris, 1860; “Biog. Cremonese de Lancetti”; M. le Dr. Hœfer, “Biog. Gen.,” Paris, 1852, Vol. I. p. 346.)
References.—Dove, “Repertorium der Physik,” Vol. II, 1838, pp. 129–130; Poggendorff, “Geschichte der Physik,” 1879, p. 273; L. Hulsius, “Descriptio et usus,” Nürnberg, 1597; “Ency. Brit.,” 1883, Vol. XV. p. 221; P. Volpicelli, “Intorno alle prime ... magnete” (Atti dell Acad. Pont. de Nuov. Lincei, XIX. pp. 205, 210).
A.D. 1555.—Olaus Magnus, a native of Sweden and Archbishop of Upsala (where he died during 1568) issued in Rome his great work “Historia de Gentibus Septentrionalibus,” which, for a long time, remained the chief authority on Swedish matters. In this book, Gilbert says (“De Magnete,” lib. i. cap. 1) allusion is made to a certain magnetic island and to mountains in the north possessing such power of attraction that ships have to be constructed with wooden pegs so that as they sail by the magnetic cliffs there be no iron nails to draw out.
To this, reference is made by Thos. Browne (“Pseud. Epidem.,” 1658, Book II. p. 78) as follows: “Of rocks magnetical, there are likewise two relations; for some are delivered to be in the Indies and some in the extremity of the North and about the very pole. The Northern account is commonly ascribed unto Olaus Magnus, Archbishop of Upsala, who, out of his predecessors—Joannes, Saxo and others—compiled a history of some Northern Nations; but this assertion we have not discovered in that work of his which commonly passeth among us; and should believe his geography herein no more than that in the first line of his book, where he affirmeth that Biarmia (which is not 70 degrees in latitude) hath the pole for its zenith, and equinoctial for the horizon.”
In a Spanish book entitled “The Naval Theatre,” by Don Francisco de Seylas and Louera, we find two causes assigned for the variation of the declination; one is “the several mines of loadstones found in the several parts of the earth ...” the other being that “there is no doubt but large rocks of loadstones may affect the needles when near them ...” (“Philos. History ... Roy. Acad. Sc. at Paris,” London, 1742, Vol. II. pp. 279–280).
References.—Claudus Ptolemæus, “Geographia,” lib. vii. cap. 2 (and others named by Bertelli Barnabita at foot of p. 21 of his “Pietro Peregrino de Maricourt,” Roma, 1868, viz. Klaproth, “Lettre sur la Boussole,” Paris, 1834, p. 116; Thos. H. Martin, “Observ. et Théor. des anciens,” Rome, 1865, p. 304; Steinschneider, “Intorno. alla calamita,” Roma, 1868); also Albertus Magnus, Lugduni, 1651; Mr. (Thomas) Blundeville, “His Exercises”; Fracastorio, in the seventh chapter of his “De Sympathia et Antipathia”; F. Maurolycus, “Opuscula,” 1575, p. 122a; Lipenius, “Navigatio Salomonis Ophiritica”; Paulus Merula, “Cosmographia Generalis,” Leyden, 1605; Toussaincte de Bessard, “Dialogue de la Longitude,” Rouen, 1574; U. Aldrovandi, “Musæum Metallicum,” 1648, pp. 554, 563, wherein he alludes to the magnetic mountains spoken of by Sir John Mandeville; Ninth “Encycl. Brit.,” Vol. XVII. p. 752; also the entry at A.D. 1265–1321.