In his treatment of the theories of magnetism, Brewster alludes again to the masterly investigations of Poisson, who, says he, appears to have been “the first to conceive the idea of absolute magnetic measurement.” In a short but luminous article at the end of the “Connaissance des Temps” for 1828, he describes the method for obtaining the value of H[** symbol] in absolute measure. His first and second “Mémoire sur la Théorie du Magnétisme” appeared during 1824–1825, at pp. 247, 488, Vol. V of the Transactions of the Paris Royal Academy, and were closely followed (Vol. VI. p. 441) by his Memoir on the theory of Magnetism in motion. Translations of these will be found at pp. 336–358, 373, Vol. I and pp. 328–330, Vol. V of the Edin. Jour. of Sci. and at pp. 334, 335 of John Farrar’s “Elem. of Elect. Magn. and Electro-Mag.,” all published during the year 1826.
Poisson’s theoretical prediction of magne-crystallic action is thus alluded to by Dr. John Tyndall in his “Researches on Diamagnetism,” etc., London, 1870, pp. 13 and 66, 67:
“In March 1851, Professor William Thomson (Lord Kelvin) drew attention to an exceedingly remarkable instance of theoretic foresight on the part of Poisson, with reference to the possibility of magne-crystallic action.
“Poisson,” says Sir William, “in his mathematical theory of magnetic induction founded on the hypothesis of magnetic fluids (moving within the infinitely small magnetic elements), of which he assumes magnetizable matter to be constituted, does not overlook the possibility of those magnetic elements being non-spherical and symmetrically arranged in crystalline matter, and he remarks that a finite spherical portion of such a substance would, when in the neighbourhood of a magnet, act differently according to the different positions into which it might be turned with its centre tube fixed. But (such a circumstance not having yet been observed), he excludes the consideration of the structure which would lead to it from his researches, and confines himself in his theory of magnetic induction to the case of matter consisting either of spherical magnetic elements or of non-symmetrically disposed elements of any forms. Now, however, when a recent discovery of Plucker’s has established the very circumstance, the observation of which was wanting to induce Poisson to enter upon a full treatment of the subject, the importance of working out a magnetical theory of magnetic induction is obvious.
“Sir William Thomson then proceeds to make the necessary ‘extension of Poisson’s Mathematical Theory of Magnetic Induction,’ and he publishes a striking quotation from the ‘Mémoires de l’Institut,’ 1821–1822, Paris, 1826.”
References.—Biography in “English Encycl.,” Vol. IV. p. 899; Phil. Mag. for 1851; Roy. Soc. Catal. of Sci. Papers, Vol. IV. pp. 964–969; G. M. Racagni, “Sopra una Memoria ...” 1839; Johnson’s “Encycl.,” 1878, Vol. III. p. 227; eighth “Britannica,” Vol. XV. p. 98; ninth “Britannica,” Vol. XV. pp. 241, 249; Ann. de Chimie for Feb. 1824; “Le Globe,” No. 87; Harris, “Magnetism,” p. 131; Whewell, “Hist. of the Inductive Sciences,” 1859, Vol. II. pp. 43, 208, 209, 222, 223; Sir William Thomson’s works, 1872; Thomas Thomson, “An Outline,” etc., 1830, p. 351; Mém. de l’Acad. des Sci. for 1824–1826, 1838; Soc. Philom. for 1803, 1824–1826; Humboldt’s “Cosmos,” London, 1849, Vol. I. pp. 104, 105, 130, 165–169; N. Bowditch, “Of a mistake which exists in the calculation of M. Poisson relative to the distribution of the electric matter upon the surfaces of two globes, in Vol. XII of the “Mém. ... Sc. Math. ... de France”; Mem. Amer. Acad., O.S., Vol. IV. part i. p. 307; Houzeau et Lancaster, “Bibl. Gén.,” Vol. II. p. 228. Mention is made of Poisson’s principal writings, in Vol. XI. pp. 179–191 of M. Max Marie’s “Hist. des Sciences Mathém.,” Paris, 1888, but the complete list will be found in Vol. II of the works of Arago.
A.D. 1811.—Schweigger (Johann Salomo Christoph), a chemist of Halle (1779–1857), inserts at p. 240, Vol. II of his Journal für die Chemie und Physik, the memoir of Sömmering, relative to his electro-chemical telegraph, as well as an appendix thereto, wherein he points out the difficulties likely to attend the employment of so many different wires. He suggests the use of but two wires, and of two piles of unequal power. With these, all desired characters could be transmitted, through a preconcerted code regarding the meaning of such letters and figures as would be represented by the weaker or the stronger pile, in conjunction with the duration of the gas evolutions or the space of time separating them. He also suggested, for an alarum, the use of a pistol, by connecting a battery to the pile, in lieu of liberating an alarm by means of accumulated gas as Sömmering had done.
Two months after Oersted’s great discovery, which was announced in July 1820, Schweigger read at Halle (September 16, 1820) and communicated to the German Literary Gazette (No. 296 for November 1820), a paper relative to an important improvement made in his galvano magnetic indicator. The latter, which had been described at pp. 206–208 of Gehlen’s (1808) Journal für Chemie, was merely an electroscope, employed to indicate the attraction and repulsion of ordinary frictional electricity in lieu of a Coulomb balance, the improved apparatus being the result of his discovery that, by coiling an insulated wire several times around a magnetic needle, the deflecting power of the voltaic current increases with the number of turns (Kuhn, “Ang. Elek.-Lehre,” p. 514).
Alluding to Schweigger’s multiplier, the Abbé Moigno says:
“A conducting wire twisted upon itself and forming one hundred turns will, when traversed by the same current, produce an effect one hundred times greater than a wire with a single turn: provided always that the electric fluid pass through circumvolutions of the wire without passing laterally from one contour to another” (Cornhill Magazine, Vol. II for 1860, pp. 61, 64).