François Jean Dominique Arago

François Jean Dominique Arago (February 26, 1786-October 2, 1853) was a mathematician born at Estagel[?] in the Pyrenees. He was educated at the Polytechnic school, Paris, but apparently found the professors there remarkably incapable of imparting their knowledge or maintaining discipline.

In 1804, Arago was made secretary to the observatory at Paris, and from 1806 to 1809 he was engaged in measuring a meridian arc in order to determine the exact length of a metre. He was then appointed to a leading post in the observatory, given a residence there, and made a professor at the Polytechnic school, where he enjoyed a marked success as a lecturer. He subsequently gave popular lectures on astronomy, which were both lucid and accurate - a combination of qualities which was rarer then than now. He reorganized the national observatory, the management of which has long been inefficient, but in doing this his lack of tact and courtesy raised many unnecessary difficulties. He remained to the end a consistent republican, and after the coup d'état of 1852, though half blind and dying, he resigned his post as astronomer rather than take the oath of allegiance. It is to the credit of Napoleon III that he gave directions that the old man should be in no way disturbed, and should be left free to say and do what he liked.

Arago's earliest physical researches were on the pressure of steam at different temperatures, and the velocity of sound, 1818 to 1822. His magnetic observations mostly took place from 1823 to 1826. He discovered what has been called rotatory magnetism[?], and the fact that most bodies could be magnetized; these discoveries were completed and explained by Faraday[?]. He warmly supported Fresnel[?]'s optical theories, and the two philosophers conducted together those experiments on the polarization of light which led to the inference that the vibrations of the luminiferous ether[?] were transverse to the direction of motion, and that polarization consisted in a resolution of rectilinear motion into components at right angles to each other. The subsequent invention of the polariscope[?] and discovery of rotatory polarization[?] are due to Arago. The general idea of the experimental determination of the velocity of light in the manner subsequently effected by Fizeau[?] and Foucault was suggested by him in 1838, but his failing eyesight prevented his arranging the details or making the experiments. He died in Paris in 1853.

It will be noticed that some of the last members of the French school were alive at a comparatively recent date, but nearly all their mathematical work was done before the year 1830. They are the direct successors of the French writers who flourished at the beginning of the nineteenth century, and seem to have been out of touch with the great German mathematicians of the early part of it, on whose researches much of the best work of that century is based; they are thus placed here, though their writings are in some cases of a later date than those of Gauss, Abel and Jacobi.

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The text of an earlier version of this article was taken from the public domain resource A Short Account of the History of Mathematics by W. W. Rouse Ball (4th Edition, 1908)