Neglected Experiment of Ampere. 539 



the announcement was premature. Similar conclusions were 

 arrived at by Pohl*. 



A year or two later, when Arago's rotations were attract- 

 ing the attention of experimenters, Becquerel f investigated 

 the supposed magnetism of bodies by taking small pieces of 

 them, which he hung within a multiplier-coil of wire in place 

 of the usual magnetic needle, and then turning on a current 

 observed whether they moved or not. He found signs of 

 magnetic action in needles made of peroxide of iron, copper, 

 wood, and even shellac. After narrating his own experi- 

 ments, he alluded to the Geneva experiment of Ampere, on 

 p. 272, in the following terms : — 



" II resulterait de cette experience, vu Paction semblable 

 exercee par les deux poles de Faimant en fer a cheval sur 

 une meme portion du circuit, que l'influence du courant 

 electrique aurait developpe dans la lame un autre courant 

 electrique, tel qu'on en observe dans un fil metallique qui 

 communique avec les deux poles d'une pile voltaique ; mais 

 M. Ampere s'est assure depuis qu'il n'en est pas ainsi." 

 What steps Ampere had in the meantime taken to assure 

 himself that induction currents did not exist, Becquerel did 

 not state, however. 



In 1831 came Faraday's discoveries of the induction of 

 currents by magnets, of the induction of currents by other 

 currents, and of the cause of Arago's rotations. A group of 

 notes | on these discoveries is to be found in December 1831 

 in the Annates de Chimie. It is curious to note the change 

 of views. Becquerel and Ampere's communication to the 

 Academy of January 23, 1832, appears along with abstracts 

 of Faraday's work, and with an account of the experiments of 

 Nobili and Antinori. There is an epitome of facts observed 

 by Becquerel, and another of things to be looked for, by 

 Ampere. This is followed by the following : — " Experiences 

 sur les Gourans electriques produits par l'influence d'un autre 

 Courant," par M. Ampere. This article gives a third version 

 of the Geneva experiments. 



" Pendant mon sejour a Geneve au mois de septembre 

 1822, M. Auguste de la Rive voulut bien m' aider dans des 

 experiences que je desirais de faire sur la production d'un 

 courant electrique par l'influence d'un autre courant. . . . 



* Oken's Isis, 1822, pt. iv. p. 407. Also see remarks signed "P" at 

 the end of an article by Savary in Pogg. Ann. viii. p. 368 (1826). 



t Ann. Chim. Phys, xxv. p. 269. 



% Ann. Chim. Phys. xlviii. 1831, pp. 405-428; see also Pogg. Ann. 

 xxiv. 1832, p. 612, and particularly p. 614. 



