XIV. The declination of the magnet calculated upon the foregoing principles;
XV. On the causes of the magnetic declination;
XVI. Calculation of the declination of the magnet for the year 1722, at London.
References.—Béraud, “Dissertation,” etc., Bordeaux, 1748; also Priestley, 1775, p. 191; “Biographie Universelle,” Vol. III. p. 687; “Biog. Génér.,” Vol. XLIV. pp. 690–703; Daillant de la Touche, “Abrégé des ouvrages de Swedenborg,” 1788; J. Clowes, “Letters on the writings of Swedenborg,” 1799; “Svenskt Biografiskt Handlexikon,” Herm. Hofberg, Stockholm, pp. 368–369; “Swedenborg and the Nebular Hypothesis,” Magnus Nyrén, astronomer at Observatory of Pulkowa, Russia, translated from the “Viertel jahrschrift der Astronomischen Gesellschaft,” Leipzig, 1879, p. 81, by Rev. Frank Sewall.
A.D. 1735–1746.—Ulloa (Don Antonio de), Spanish mathematician, who left Cadiz May 26, 1735, for South America, whither he was sent with Condamine and other French Academicians, as well as with Spanish scientists, to measure a degree of the meridian, returned to Madrid July 25, 1746, and shortly after gave an account of his experiences during an absence of eleven years and two months.
In his “Voyage Historique de l’Amérique Méridionale,” Amsterdam and Leipzig, 1752, he speaks (Vol. I. pp. 14–18 and Vol. II. pp. 30–31, 92–94, 113, 123, 128) of the defective magnetic needles given him as well as of the means of correcting them, and he details at great length the variations of the needle observed during the voyage. He also alludes to the variation charts of Dr. Halley and to the alterations therein made by advice of William Mountaine and Jacob Dooson—James Dodson—of London, as well as to the methods of ascertaining the variation of the magnetic needle pointed out both by Manuel de Figueyredo, at Chaps. IX-X of his “Hidrographie ou Examen des Pilotes,” printed at Lisbon in 1608, and by Don Lazare de Flores at Chap. I, part ii. of his “Art de Naviguer,” printed in 1672. The latter, he says, asserts, in Chap. IX, that the Portuguese find his method so reliable that they embody it in all the instructions given for the navigation of their vessels.
At pp. 66, 67, Chap. X of vol. ii. Ulloa makes the earliest recorded reference to the aurora australis, as follows: “At half-past ten in the evening, and as we stood about two leagues from the island of Tierra de Juan Fernandez, we observed upon the summit of a neighbouring mountain a very brilliant and extraordinary light.... I saw it very distinctly from its inception, and I noticed that it was very small at first, and gradually extended until it looked like a large, lighted torch. This lasted three or four minutes, when the light began to diminish as gradually as it had grown, and finally disappeared.”
Incidentally, it may be stated here that the very learned Dr. John Dalton reported having seen the aurora australis in England, and to have besides observed the aurora borealis as far as 45° latitude south (see accounts in Philosophical Transactions, Philosophical Magazine, Manchester Transactions and Nicholson’s Journal), while Humboldt remarks (“Cosmos,” 1849, Vol. I. p. 192, note) that in south polar bands, composed of very delicate clouds, observed by Arago, at Paris, on the 23rd of June, 1844, dark rays shot upward from an arch running east and west, and that he had already made mention of black rays resembling dark smoke, as occurring in brilliant nocturnal northern lights.
References to the aurora australis are made by the naturalist John Reinhold Forster, in the article on “Aurora Borealis” of the “Encycl. Britannica.”
For Mountaine and Dodson, consult the Phil. Trans., Vol. XLVIII. p. 875; Vol. L. p. 329, also Hutton’s abridgments, Vol. XI. p. 149.