Scientist and Politician François Arago

Francois Arago

Francois Arago

On February 26, 1786, French mathematician, physicist, and astronomer François Arago was born. Arago discovered the chromosphere of the sun, and made accurate estimates of the diameters of the planets. Arago entered politics in 1848 as Minister of War and Marine and was responsible for abolishing slavery in the French colonies.

Dominique-françois-jean Arago was born in Estagel, Roussillon. His father was the small town’s mayor and his family was involved in politics with mainly leftist republican views and military connections. He was educated at the Municipal College of Perpignan where he became interested in mathematics. Later, he was admitted to the École Polytechnique in Paris. There, he he succeeded Gaspard Monge in the chair of analytic geometry at the age of only 23. Subsequently, Arago also was director of the Paris Observatory and permanent secretary of the Academy of Sciences. He was also 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.

Around 1820, Arago demonstrated 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. This work is based on the scientific research by H.C. Ørsted of Denmark. Shortly after, Aragon managed to show that a rotating copper disk produced rotation in a magnetic needle suspended above it. It was later Michael Faraday who proved these to be induction phenomena.

François Arago is known to have been a great supporter of A.-J. Fresnel’s wave theory of light. The theory states that light should be retarded as it passes from a rarer to a denser medium. Laplace, Biot, and Poisson however favorited the emission theory, which means that light should rather be accelerated. Before Arago’s death, the retardation of light in denser media was demonstrated by Fizeau and Léon Foucault, who used Arago’s method with improvements in detail.

In the field of astronomy, Arago took part in the dispute between Le Verrier, who was his protégé, and the English astronomer John C. Adams over priority in discovering the planet Neptune and over the naming of the planet. In 1845, Arago suggested that Le Verrier investigate anomalies in the motion of Uranus. When the investigation resulted in Le Verrier’s discovery of Neptune, Arago proposed that the newly found planet be named for Le Verrier.

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