French physicist and astronomer who made major contributions to the early study of electromagnetism.
In 1820 he found that iron enclosed in a wire coil could be magnetized by the passage of an electric current.
In 1824, he was the first to observe the ability of a floating copper disc to deflect a magnetic needle, the phenomenon of magnetic rotation. From 1815, Arago worked with French physicist Augustin Fresnelon the polarization of light and was able to elucidate the fundamental laws governing it. Together they established the wave theory of light. Arago was born near Perpignan, studied at the Ecole Polytechnique in Paris, and was appointed to the Bureau of Longitudes.
He was professor of analytical geometry at the Ecole Polytechnique 1809-30, when he became permanent secretary to the Academy of Sciences, director of the Paris Observatory, and deputy for Pyrénées Orientales until 1852.
Arago's political affiliation was with the extreme left, and the revolution of 1848 saw him elected to a ministerial position in the provisional government. It was under his administration that slavery was abolished in the French colonies.
Arago also investigated the compressibility, density, diffraction, and dispersion of gases; the speed of sound, which he found to be 331.2 m/1,087 ft per second; lightning, of which he found four different types; and heat.
His studies in astronomy included investigations of the solar corona and chromosphere, measurements of the diameters of the planets, and a theory that light interference is responsible for the twinkling of stars.