François Arago - SpeedyLook encyclopedia

Biography

It makes its studies with the Polytechnic school (X1803 Promotion), in Paris. At the end of its studies, it is sent in Spain to finish the statement of the Méridien of Paris. Taken in the war in Spain, it is made prisoner, escapes several times, and returns to Paris as hero three years later. This glory enables him to be elected member of the Academy of Science at only twenty-three years and named professor of analytical Geometry and Géodésie at the Polytechnic school (1809-1830), succeeding Monge. It installs its apartments with the center even of the Observatoire of Paris, from which he was director and who will be used to him as hearth until his death. It was named inspector of the royal body of the genius in 1822.

The experiment of Arago (1810), and its work in optics

The first work of physics of Arago relates to the Optique. It makes in 1810 an important experiment (which it will consign in writing only thirty years later) : it was a question of measuring speed of light coming from stars, by comparing the value the morning with 6:00 and the evening with 18:00. Being given that one does not observe stars during the day, Arago made its experiment at these hours. With 6:00, when one observes a star with the zenith, the Earth approaches some, one should measure C + V, where V is the number of revolutions of the Earth around the Sun; to 18:00, for another star with the zenith, the Earth moves away from there, one should measure C - V. But the experiment is negative, one measures C in both cases: one cannot highlight by a terrestrial experiment the earthmoving around the Sun. This experiment will open the way with the theory of relativity.

Arago, initially follower of the corpuscular theory of the light, is convinced by the undulatory theory of his/her colleague Fresnel, whom it will help to make his experiments at the Observatory or to have his results to the Academy of Science. With Biot, it determines the Index of refraction of the Air and others Gaz.

Other work

In 1825, it is charged with Dulong to determine the tension of the vapor of Eau to pressures exceeding 30 atm. Its other studies are devoted to astronomy, the Magnétisme and the polarization of the Lumière. It determines, for example, the Diamètre of the Planet S and explained inter alia the scintillation stars using the phenomenon of the Interférence S.

Touch with all, it mixes with the experiments with measurement with the Speed of sound and studies the tanks under pressure. It makes dig the first well in Paris, in current the fifteenth district. It inspires with Foucault his experiment of the revolving mirrors, which will make it possible to measure the Speed of light with precision. It promotes the Photographie then incipient by supporting the Daguerréotype developed by Daguerre. Director of the Observatory, secretary of the Academy of Science, he is a speaker frightening, able to demolish the most brilliant contradictors. He is also a large pedagog and a scientific popularizer with the noble direction of the term. In order to make known work of the Academy of Science, it creates into 1835 the Comptes-rendus of the Academy of Science , which always exists: before Arago, there was no written transcription of the meetings of the Academy. It directs also a public course of popular astronomy which désemplit not. One comes from the four corners of France to hear it.

Political career

Arago also played a great political role. It was during the Monarchie of July one of the figures of the Republican party. After the revolution of 1848, he was Minister for the War and the Navy in the provisional government of the Second Republic, set up by Lamartine then president of the Executive commission, assuming in fact lasting one month and half a load close to that of Head of the State. He contributed for this reason to the Abolition of slavery in the French colonies. He refuses thereafter préter with Louis-Napoleon Bonaparte the oath of fidelity required of the civils servant and prefers to resign of his station at the Office of Longitudes. The Prince-President refuses his resignation. After the Coup d'etat of 1852 which leads to the creation of the Second Empire, it resigns of its functions. Napoleon III asks so that it not be worried. Patient, suffering of Diabetes and various affections, Arago dies the following year.

The Royal Society decrees the to him Médaille Copley in 1825, then the Médaille Rumford in 1850.

Homages

Its name is registered on the lathe Eiffel.
the “Homage to Arago”, a Parisian monument.
the asteroid 1005 Arago was named in its honor.

External bond

François Arago (Format Flash)
refractive Power and dispersion of the liquids
the bulletin of the Company of the friends of the Library of Polytechnic devoted to Arago (May 1989)

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