One of his biographers, Professor Chrystal says: “Scarcely had the news of Oersted’s discovery reached France, when a French philosopher, Ampère, set to work to develop the important consequences which it involved. Physicists had long been looking for the connection between magnetism and electricity, and had, perhaps, inclined to the view that electricity was somehow to be explained as a magnetic phenomenon. It was, in fact, under the influence of such ideas, that Oersted was led to his discovery. Ampère showed that the explanation was to be found in an opposite direction. He discovered the ponderomotive action of one electric current on another, and, by a series of well-chosen experiments, he established the elementary laws of electro-dynamic action, starting from which, by a brilliant train of mathematical analysis, he not only evolved the complete explanation of all the electro-magnetic phenomena observed before him, but predicted many hitherto unknown. The results of his researches may be summarized in the statement that an electric current, in a linear circuit of any form, is equivalent in its action, whether on magnets or other circuits, to a magnetic shell bounded by the circuit, whose strength at every point is constant and proportional to the strength of the current. By his beautiful theory of molecular currents, he gave a theoretical explanation of that connection between electricity and magnetism which had been the dream of previous investigators. If we except the discovery of the laws of the induction of electric currents, made about ten years later by Faraday, no advance in the science of electricity can compare for completeness and brilliancy with the work of Ampère. Our admiration is equally great, whether we contemplate the clearness and power of his mathematical investigations, the aptness and skill of his experiments, or the wonderful rapidity with which he elucidated his discovery when he had once found the clew.”

“Oersted,” remarks M. Babinet, “was the Christopher Columbus of magnetism; Ampère became its Pizarro and its Fernand Cortez.”

Of Ampère’s astatic needles, a description, taken from one of his memoirs (Ann. de Ch. et de Ph., Vol. XVIII. p. 320), appears at pp. 280–281 of Fahie’s “History” (Knight’s “Mech. Dict.,” 1874, Vol. I. p. 171, and Vol. II. p. 1181). For this greatly perfected form of galvanometer the credit has erroneously been given to Prof. Cumming, who first suggested the idea of neutralizing the directive force of the needle arising from the earth’s magnetism, which he did by placing a magnetized needle immediately beneath the movable or index needle. Fahie adds, in a footnote: “In Prof. Cumming’s paper ‘On the Connection of Galvanism and Magnetism,’ read before the Cambridge Philosophical Society, April 2, 1821, he described a near approach to the astatic needle. In order to neutralize the terrestrial magnetism he placed a small magnetized needle under the galvanometer needle” (Trans. Cam. Phil. Soc., Vol. I. p. 279). The credit of Ampère’s discovery is sometimes given to Nobili, as in Noad’s “Manual of Electricity,” London, 1859, p. 327; also Roget’s “Electro-Magnetism” in “Library of Useful Knowledge,” London, 1832, p. 42.

As has been already shown (Laplace, A.D. 1820), the first proposal to apply Oersted’s discovery to telegraphic purposes by substituting the deflection of the magnetic needle through electric currents for the divergence of the pith balls of the electroscope, was made by Ampère, in his Memoir of Oct. 2, 1820, which appears in the Comptes Rendus, and at p. 72, Vol. XV of the Annales de Chimie et de Physique. His plan, remarks Sabine, was, however, doomed to the same fate as that of Sömmering, of never coming into practice, and for the same reasons, principally the number of line wires. Had Ampère combined his system, or rather the one of Laplace, with that which Schweigger proposed of reducing Sömmering’s telegraph to two wires, or with any other using a code of signals, the problem of the electric telegraph would have been solved from the year 1820. Ampère makes no mention of surrounding the needles with coils of wire, as is so frequently stated by writers on the telegraph. Indeed he could not then have even heard of the galvanometer; for, although Schweigger’s paper on the subject was read at Halle on the 16th of September 1820, it was not published until the November following.

M. Jean Jacques Antoine Ampère (1800–1864), son of André Marie Ampère, was an accomplished scholar who succeeded François Andrieux as professor at the Collège de France and became a member of the French Academy in 1847.

References.—For accounts of Ampère’s rotary magnet, electro-dynamic cylinders, revolving battery, and of his electripeter employed to alter rapidly the direction of the electric current in voltaic batteries, consult pp. 639, 640, 643, Vol. VIII of the eighth “Britannica.” Fahie, “Hist. of El. Tel.,” p. 303. See “Catal. Sci. Papers Roy. Soc.,” Vol. I. pp. 58, 61; Messrs. Sainte-Beuve et Littré’s account of his life and labours in the Revue des Deux Mondes for Feb. 15, 1837; “Notice sur M. Ampère,” par M. E. Littré, Paris, 1843; Arago’s “Eulogy on Ampère,” translated, at pp. 111–171 of the “Report of the Smithsonian Institution” for 1872. Consult also “Report Smiths. Instit.” for 1857, pp. 100–107; Ampère’s biography in the Sci. Am. Suppl., No. 674, p. 10760; also Ampère’s “Journal et Correspondance,” Poggendorff, Vol. I. pp. 39, 40; Address of His Royal Highness the Duke of Sussex to the Eng. Roy. Soc., 1836; Barlow on “Magnetic Attractions”: Comptes Rendus for 1838, Vol. VII. p. 81; Bibl. Univ., XX; Phil. Mag., Vols. LVI. p. 308; LVII. pp. 40–47, “On the Electro-Magnetic Experiments of Oersted and Ampère,” by Mr. Hatchett, and pp. 47–49; Ann. de Phys. de Bruxelles, Vol. VII; Ann. de Ch. et de Phys., XXIX; Du Moncel, Vol. III. p. 7; “Acad. de Paris,” Sept. 12, 1825; La Lum. Elect. for Oct. 31, 1891, p. 202; Roch, in “Zeitschr. f. Mathém.” 1859, p. 295; Roget on Ampère’s theory of Mag.; K. W. Knochenhauer, Pogg. Annal., XXXIV. p. 481; J. Marsh, “On a Particular Construction of M. Ampère’s Rotating Cylinder,” Phil. Mag., LIX. p. 433, 1822; Henn, “De Amperi principiis ...”; “Memorial of Joseph Henry,” 1880, pp. 59, 81; “Lib. of Use. Know.” (El. Mag.), pp. 24, 28, 83–92; Harris, “Rud. Elec.,” pp. 170, 171, and “Rud. Mag.,” p. 130; Noad, “Manual,” pp. 661–662, 861–864; “Encycl. Metrop.” (El. Mag.), Vol. IV. pp. 5–8; Highton, “Elec. Teleg.,” p. 39; Gmelin’s “Chemistry,” Vol. I. p. 317; Mrs. Somerville, “Conn. Phys. Sci.,” 1846, pp. 320, 321; Dr. Lardner, “Lectures,” Vol. II. p. 125; J. F. W. Herschel, “Prelim. Dis. Nat. Phil.,” 1855, p. 243; Whewell, “Hist. Induc. Sc.,” 1859, Vol. II. pp. 242, 246, 619; “Ann. of Sc. Disc.” for 1850, p. 129, and for 1865, p. 125; “Smithsonian Report” for 1878, p. 273; Sturgeon, “Sci. Researches,” Bury, 1850, pp. 12, 16, 29; Jour. Frankl. Inst. for 1851, Vol. XXII. p. 59; Turnbull, “El. Mag. Tel.,” 1853, pp. 55 and 221; (Vail’s “History,” pp. 133, 134; Prof. Henry’s Evid., 85a, record; Doct. Channing’s Ev., 47a, record; Hibbard, Ev., 31a. ...) See also Humboldt’s “Cosmos,” articles “Aurora Borealis,” “Volcanoes,” “Earthquakes”; Ampère et Babinet, “Exposé des Nouv. Déc. ... de Oersted, Arago, Ampère, Davy, Biot, Erman, Schweigger, De la Rive,” etc., Paris, 1822, translated into German “Darstellung der neuen ... dem Französischen,” Leipzig, 1822, and alluded to in Lumière Electrique for July 18, 1891, pp. 148, 149; Hachette et Ampère, “Sur les Expériences de Oersted et Ampère”: Journal de Physique for September 1820. Annales de Chimie for 1825; “Journal des Savants,” for June 1872; “Dict. Génér. de Biogr. et d’Histoire,” Paris, 2e ed., pp. 85–86; “Collection de Mémoires relatifs à la Physique,” Paris 1885, 1887, Vols. II and III passim, as per indexes; “Amer. Journ. of Psychology,” Vol. IV. pp. 6–7.

For William Ritchie (1790–1837), the author of an able paper, “On electro-magnetism, and Ampère’s proposal of telegraphic communication by means of this power,” consult Phil. Trans. for 1833, p. 313; “Abstracts of Papers ... Roy. Soc.,” Vol. II. pp. 350, 382; Phil. Mag. or Annals, Vol. VII, 1830, p. 212; Phil. Mag. and Journal of Science, Vol. III, 1833, pp. 37, 122, 124, 145.

For Leopoldo Nobili (1784–1835), frequently mentioned above, consult “Bibl. Univ.,” Bruxelles, 1834 (Sc. et Arts), Tome LVI. pp. 82–89, 150–168; “Edin. Trans.” Vol. XII and Phil. Mag. Vol. XI, 1832, p. 359, for the account of experiments made by James David Forbes, similar to those of Nobili, wherein an electric spark was elicited from a natural magnet. For J. D. Forbes, see also Phil. Mag., 1832, Vol. XI. p. 359. For Nobili and Antinori, consult Phil. Mag., Vol. XI, 1832, pp. 401, 466; “Bibl. Britan.,” Vol. XXV, 1824, N.S. p. 38; Vol. XXIX, 1825, N.S. p. 119. For Antinori and Marchese Cosimo Ridolfi, consult “Bibl. Britan.” Vol. XVI, N.S., 1821, pp. 72–75, 101–118.

For Prof. James Cumming (1777–1861), also frequently named in above article, consult Phil. Mag., Vol. LX, 1822, p. 253; “Bibl. Britan.,” Vol. XXV, N.S., 1824, p. 104, for experiments of Cumming, Trail and Marsh; the investigations in the same line of Mr. Thos. Stuart being especially reported on in “Bibl. Britan.,” Vol. XXVII, N.S., 1824, pp. 199–206; “Dict. of Nat. Biog.,” Vol XIII. p. 296; “Edin. Phil. Journal,” 1824, Vol. X. p. 185; “Cat. Sc. Papers Roy. Soc.,” Vol. I. pp. 58–61; Vol. VI. p. 565; Vol. VII. p. 29; “Bibl. Britan.,” Vol. XVI, N.S. p. 309; Vol. XVII, N.S. p. 16; Vol. XIX. p. 244; Vol. XX. pp. 173, 258; Vol. XXIV. p. 109.

For Le Chevalier Julius Konrad von Yelin (1771–1826), consult “Bibl. Britan.,” Vol. XXIII, N.S., 1823, p. 38; Vol. XXIV, N.S., 1823, p. 253, and, especially, the important tract on the discovery of thermo-magnetism at p. 31 of his “Die Akademie der Wissenschaften und ihre Gegner,” Munich, 1822.