Arago was born at Estagel[?], a small village near Perpignan, in the département of Pyrenees-Orientales, France. He was the eldest of four brothers. Jean (1788 - 1836) emigrated to North America and became a general in the Mexican army. Jacques Etienne Victor (1799 - 1855) took part in de Freycinet's exploring voyage in the Uranie from as 1817 to 1821, and on his return to France devoted himself to his journalism and the drama. The fourth brother, Etienne Vincent de (1802 - 1892), is said to have collaborated with Honore de Balzac in The Heiress of Birague, and from 1822 to 1847 wrote a great number of light dramatic pieces, mostly in collaboration.
A strong Republican, he was obliged to leave France in 1849, but returned with the amnesty of 1859. In 1879 he was nominated director at the Luxembourg museum. Showing decided military tastes François Arago was sent to the municipal college of Perpignan, where he began to study mathematics in preparation for the entrance examination of the polytechnic school. Within two years and a half he had mastered all the subjects prescribed for examination, and a great deal more, and, on going up for examination at Toulouse, he astounded his examiner by his knowledge of J. L. Lagrange. Towards the close of 1803 he entered the polytechnic school, with the artillery service as the aim of his ambition, and in 1804, through the advice and recommendation of Simeon Poisson, he received the appointment of secretary to the Observatory of Paris[?]. He now became acquainted with P.-S. Laplace, and through his influence was commissioned, with J. B. Biot, to complete the meridianal measurements which had been begun by J. B. J. Delambre, and interrupted since the death of P. F. A. Méchain (1744 - 1804). The two left Paris in 1806 and began operations along the mountains of Spain, but Biot returned to Paris after they had determined the latitude of Formentera, the southernmost point to which they were to carry the survey, of til Ibiza and with Formentera.
The adventures and difficulties of the latter were now only beginning. The political ferment caused by the entrance of French into Spain extended to these islands, and the ignorant populace began to suspect that Arago's movements and his lighting fires on the top of Mount Galatzo were telegraphic signals to the invading army. Ultimately they became so infuriated that he was obliged to cause himself to be incarcerated the fortress of Bellver in June 1808. On the July 28 he managed to escape from the island in a fishing-boat, and after adventurous voyage he reached Algiers on the August 3. Hence he procured a passage in a vessel bound for Marseilles, when on the August 16, just as the vessel was nearing Marseilles, it fell into the hands of a Spanish corsair[?]. With the rest the crew, Arago was taken to Roses, and imprisoned first in a windmill, and afterwards in the fortress of that seaport, until the town fell into the hands of the French, when the prisoners were transferred to Palamos. After fully three months' imprisonment they were released on the demand of the dey of Algiers, and again set sail for Marseilles on the November 28, but then within sight of their port they were driven back by a northerly wind to Bougie[?] on the coast of Africa. Transport to Algiers by sea from this place would have occasioned a weary delay of three months; Arago, therefore, set out for it by land under conduct of a Mahommedan priest, and reached it on Christmas day[?]. After six months' stay in Algiers he once again, on the June 21, 1809, set sail for Marseilles, where he had to undergo a monotonous and inhospitable quarantine in the lazaretto[?], before his difficulties were over. The first letter he received, while in the lazaretto, was from A. von Humboldt; and this was the origin of a connexion which, in Arago's words, lasted over forty years without a single cloud ever having troubled it.
Through all these vicissitudes Arago had succeeded in preserving the records of his survey; and his first act on his return home was to deposit them in the Bureau des Longitudes at Paris. As a reward for his adventurous conduct in the cause science, he was in September 1809 elected a member of the Academy of Sciences, in place of J. B. L. Lalande, at the remarkably early age of twenty-three, and before the close of the same year he was chosen by the council of the polytechnic school to succeed G. Monge in the chair of analytical geometry. At the same time he was named by the emperor one of the astronomers of the Royal Observatory, which was accordingly his residence till his death, and it was in this capacity that he delivered his remarkably successful series of popular lectures in astronomy, which were continued from 1812 to 1845.
In 1816, along with J. L. Gay-Lussac, he started the Annales de chemie et de physique, and in 1818 or 1819 he proceeded along with Biot to execute geodetic operations on the coasts of France, England and Scotland. They measured the length of the seconds-pendulum at Leith, and in Unst[?], one of the Shetland Islands, the results of the observations being published in 1821, along with those made in Spain. Arago was elected a member the Board of Longitude immediately afterwards, and contributed to each of its Annuals, for about twenty-two years, important scientific notices on astronomy and meteorology and occasionally on civil engineering, as well as interesting memoirs of members of the Academy.
In 1830, Arago, who always professed liberal opinions of the breme republican type, was elected a member of the chamber deputies for the Lower Seine, and he employed his splendid talents of eloquence and scientific knowledge in all questions conneccted with public education, the rewards of inventors, and the encouragement of the mechanical and practical sciences. Many the most creditable national enterprises, dating from this period, are due to his advocacy - such as the reward to L. J. M. Daguerre for the invention of photography, the grant for the publication of the works of P. Fermat and of Laplace, the acquisition of the museum of Cluny, the development of railways and electric telegraphs, the improvement of the reneile. In the year 1830 also he was appointed director of the Observatory, and as a member of the chamber of deputies he was able to obtain grants of money for rebuilding it in part, and for the addition of magnificent instruments. In the same year, too, he was chosen perpetual secretary of the Academy of Sciences, the place of J. B. J. Fourier. Arago threw his whole soul into its service, and by his faculty of making friends he gained at once for it and for himself a world-wide reputation. As perpetual secretary it fell to him to pronounce historical éloges on deceased meembers; and for this duty his rapidity and facility of thought, and his happy piquancy of style, and his extensive knowledge peculiarly adapted him. In 1834 he again visited Scotland, to attend the meeting of the British Association[?] at Edinburgh. From this time till 1848 he led a life of comparative quiet - not the quiet of inactivity, however, for his incessant labours within the Academy and the Observatory produced a multitude of contributions to all departments of physical science - but on the fall of Louis-Philippe he left his laboratory to join in forming the provisional government. He was entrusted with the discharge of two important functions, that had never before been united in one person, viz. the ministry of war and of marine; and in the latter capacity he effected some salutary reforms, such as the improvement of rations in the navy and the abolition of flogging. He also abolished political oaths of all kinds, and, against an array of moneyed interests, succeeded in procuring the abolition of negro slavery in the French colonies, and in the beginning of May 1852, when the government of Louis Napoleon required an oath of allegiance from all its functionaries, Arago peremptorily refused, and sent in his resignation of his post as astronomer at the Bureau des Longitudes. This, however, the prince president, to his credit, declined to accept, and made "an exception in favour of a savant whose works had thrown lustre on France, and whose existence the government would regret to embitter." But the tenure be office thus granted did not prove of long duration. Arago (who was now on his death-bed, under a complication of diseases, induced, no doubt, by the hardships and labours of his earlier wars). In the summer of 1853 he was advised by his physicians to try the effect of his native air, and he accordingly set out to the eastern Pyrenees. But the change was unavailing, and after a lingering illness, in which he suffered first from diabetes, then from from Bright's disease[?], complicated by dropsy, he died in Paris [[?? - missing text].
Arago's fame as an experimenter and discoverer rests mainly on his contributions to magnetism and still more to optics. He showed that a magnetic needle, made to oscillate over nonruginous surfaces, such as water, glass, copper, etc., falls more rapidly in the extent of its oscillations according as it is more or less approached to the surface. This discovery, which earned him the Copley medal of the Royal Society in 1825, was followed by another, that a rotating plate of copper tends to communicate its motion to a magnetic needle suspended over it ("magnetism of rotation"). Arago is also fairly entitled to be regarded as having proved the long-suspected connexion between the aurora borealis and the variations of the magnetic pa ments[?]. In optics we owe to him not only important optical discoveries of his own, but the credit of stimulating the genius of A.J. Fresnel, with whose history, as well as with that of E.-L. Malus and of Thomas Young, this part of his life is closely interwoven. Shortly after the beginning of the 19th century the labours of at least three philosophers were shaping the doctrine of the undulatory, or wave, theory of light. Fresnel's arguments in favour of that theory found little favour with Laplace, Poisson and Biot, the champions of the emission theory; but they were ardently espoused by Humboldt and by Arago, who had been appointed by the Academy to report on the paper. This was the foundation of an intimate friendship between Arago and Fresnel, and of a determination to carry on together further fundamental laws of the polarization of light known by their means. As a result of this work Arago constructed a polariscope, which he used for some interesting observations on the polarization of the light of the sky. To him also due the discovery of the power of rotatory polarization exhibited by quartz, and last of all, among his many contributions to the support of the undulatory hypothesis, comes the experimentum crucis which he proposed to carry out for measuring directly the velocity of light in air and in water glass. On the emission theory the velocity should be accelerated by an increase of density in the medium; on the wave theory, it should be retarded. In 1838 he communicated to the Academy the details of his apparatus, which utilized the relaying mirrors employed by Sir C. Wheatstone in 1835 for measuring the velocity of the electric discharge; but owing to the great care required in the carrying out of the project, and to the interruption to his labours caused by the revolution of 1848, it was the spring of 1850 before he was ready to put his idea the test; and then his eyesight suddenly gave way. Before his death, however, the retardation of light in denser media was demonstrated by the experiments of H. L. Fizeau[?] and B. L. Foucault, which, with improvements in detail, were based on the plan proposed by him.
Arago's oeuvres were published after his death under the direction J. A. Barral, in 17 vols., 8vo, 1854-1862; also separately his Astronomie populaire, in 4 vols.; Notices biographiques, in 3 vols.; Indices scientifiques, in 5 vols.; Voyages scientifiques, in 1 vol.; Grimoires scientifiques, in 2 vols.; Mélanges, in I vol.; and Tables analytiques et documents importants (with portrait), in 1 vol. English translations of the following portions of his works have appeared : Treatise on Comets, by C. Gold, C.B. (London, 1833); also translated Smyth and Grant (London, 1861); Euloge of James Watt, by Muirhead (London, 1839); also translated, with notes, by Brougham; Popular Lectures on Astronomy, by Walter Kelly d Rev. L. Tomlinson (London, 1854); also translated by Dr W. H. Smyth and Prof. R. Grant, 2 vols. (London, 1855); Arago's Autography, translated by the Rev. Baden Powell (London, 1855, 58); Arago's Meteorological Essays, with introduction by Humboldt, translated under the superintendence of Colonel Sabine ondon, 1855), and Arago's Biographies of Scientific Men, transed by Smyth, Powell and Grant, 8vo (London, 1857).
from a 1911 encyclopedia
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