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What did French Physicist Francois Arago discover today in 1820?

September 25th

Page500_218_7September 25, 1820 — French Physicist Francois Arago (Feb. 26, 1786, Estagel, Roussillon, France—died Oct. 2, 1853, Paris) discovered the principle of the production of magnetism by rotation of a nonmagnetic conductor. He also devised an experiment that proved the wave theory of lightand engaged with others in research that led to the discovery of the laws of light polarization.

Educated in Perpignan and at the École Polytechnique in Paris, at 23, he succeeded Gaspard Monge in the chair of analytic geometry. Subsequently he was director of the Paris Observatory and permanent secretary of the Academy of Sciences. And, he was active as a republican in French politics. As minister of war and marine in the provisional government formed after the Revolution of 1848, he introduced many reforms.

In 1820, Arago elaborated on the work of H.C. Ørsted of Denmark, showing that the passage of an electric current through a cylindrical spiral of copper wire caused it to attract iron filings as if it were a magnet and that the filings fell off when the current ceased. In 1824 he demonstrated that a rotating copper disk produced rotation in a magnetic needle suspended above it. Michael Faradaylater proved these to be induction phenomena.

Words of Wisdom

In the experimental sciences, the epochs of the most brilliant progress are almost always separated by long intervals of almost absolute repose.

— French Physicist Francois Arago

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