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Ampere and Arago on electromagnetism. French physicists Andre-Marie Ampere (1775-1836, left) and Francois Arago (1786-1853, right) studying electromagnetism. Arago is holding two conducting keys near to a compass needle and observing the deflection caused. This experiment, performed at the Academie des Sciences in 1820, was a repeat of the experiment done by the Danish physicist Hans Christian Oersted earlier that year. It led Ampere to conclude that magnetism was electricity in motion. As part of his report, Ampere detailed the forces between two parallel conducting wires. This SI unit of electrical current, named the Ampere in his honour, is based on these forces. This illustration is from 'Physique Populaire' (Emile Desbeaux, 1891).
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