Mémoire présenté á l'Académie Royale des Sciences, le 2 octobre 1820, où se trouve compris le résumé de ce qui avait été lu á la même Académie les 18 et 25 septembre 1820, sur les effets des courans électriques. [AND] Suite du Mémoire sur l'Action mutuelle entre deux courans électriques, entre un courant électrique et un aimant ou le globe terrestre, et deux animans.

Ampère first heard of Ørsted's discovery of electromagnetism on the 4th of September when Arago announced Ørsted's results to the Paris Academy of Sciences. In Ørsted's experiment a current-carrying wire is held over, and under, a compass needle - the result being that the needle is positioned at 45 degrees in respect to the wire. Ampére immediately saw that this result made no physical sense and realized that the true nature of the effect could not be observed until the force of terrestrial magnetism was somehow neutralized; what Ørsted had observed and reported on was the resultant of the force from the wire and that from the earth's magnetic field. Ampère discovered that the compass needle sets at 90 degrees to the current-carrying wire when the effect of terrestial magnetism is eliminated. He also observed that current-carrying wires which are formed as spirals act as permanent magnets, and this lead him to his theory that electricity in motion produces magnetism and that permanent magnets must contain electrical currents. And thus Ampère laid the foundation of the new field of electrodynamics.

Ampère announced his theory and experimental results, for the first time, in a series of memoires read before the Paris Academy of Sciences in September and October 1820. These memoires were first published in the September and October issues of Arago's 'Annales de Chimie et de Physique' (the offered items). In November Ampère had a seperate printing of his findings published under the title 'Mémoires sur I'action mutuelle de deux courans électriques, sur celle qui existe entre un courant électrique et un aimant ou le globe terrestre, et celle de deux aimans I'un sur I'autre.' (Dibner 62, Norman 43). On the title-page of this publication it is stated 'Extrait des Annales de Chimie et de Physique' and therefore this publication is often identified as an offprint of the two offered papers (see the Norman sales catalogue for an example). This is, however untrue, since it contains considerable changes and additions in comparison with text of the journal issues (see Williams: What were Ampère's Earliest Discoveries in Electrodynamics? ISIS, volume 74, p.492).

Honeyman 82, Barchas 51, Wheeler 762.