François Arago
gigatos | June 11, 2022
Summary
François Jean Dominique Arago (26 February 1786 – 2 October 1853) was a French mathematician, physicist, astronomer and politician.
Aragon was born in Estagel, a small village near Perpignan in the Eastern Pyrenees-Orientales department of France. He had three younger brothers and sisters: Jean (1788-1836) emigrated to America and became a general in the Mexican army. Jacques Arago (1799 – 1855) took part in Louis de Fresquinet”s voyage of discovery on the ship ”Ourania” from 1817 to 1821 and, on his return to France, devoted himself to journalism and the theatre. The fourth brother, Étienne Vincent (1802 – 1892), is said to have collaborated with Balzac on the play “The Heiress of Birague” and from 1822 to 1847 he wrote many light plays, mostly in collaboration with others.
François Aragon showed an obvious military aptitude and was sent to the primary school in Perpignan, where he began to study mathematics in preparation for the entrance exams to the polytechnic school. In two and a half years he had mastered all the examination material and more, and in taking the examination at Toulouse he astonished his examiner with his knowledge of Lagrange.
At the end of 1803 Aragon enrolled at the École Polytechnique, in Paris, but was disappointed by the teachers” lack of contagiousness and the students” lack of discipline. Artillery was his ambition, but in 1804, on the advice and recommendations of Simeon Poisson, he was appointed secretary at the Paris Observatory. There he met Pierre Simon Laplace, who commissioned him, together with Jean-Baptiste Beaux, to complete the meridian measurements begun with Delambre and discontinued after the death of Pierre Mesain in 1804. Aragon and Beau left Paris in 1806 and began measurements in the mountains of Spain. Biot returned after some time, but Aragon continued until 1808, in an attempt to accurately measure the length of a meridian arc to define the exact length of the metre as 1
The political upheaval that followed the French invasion of Spain reached the Balearic Islands and the local population suspected the Aragonese actions there, such as the firing on the top of Mount Galatzo, as actions for the French army. Arago surrendered and was imprisoned in the fortress of Belver in June 1808. On 28 July he escaped from the island in a fishing boat and after an adventurous journey he arrived in Algiers on 3 August. From there he boarded a ship for Marseilles, but on 16 August, as they approached their destination, they fell into the hands of Spanish pirates. Along with the other passengers, Arago was taken to Roses and held first in a windmill and then in a fortress until the town was captured by the French, when the prisoners were taken to Palamos.
After three months of further captivity, Aragon and the others were released at the request of the Dean of Algiers, and again set sail for Marseilles on 28 November, but while in sight of its port they were swept behind strong north winds at Bougie on the African coast. Transport to Algiers by sea from this place would be delayed for three months. Arago therefore set out by land, led by an imam, and arrived in Algiers on Christmas Day. After another six months there, he entered a ship which sailed on June 21, 1809, and this time reached Marseilles, where, however, he had to endure a tedious and inhospitable stay in quarantine before his sufferings were finally over. There he received his first letter in almost a year: it was from Alexander von Humboldt and marked the beginning of a liaison that, in Aragon”s words, lasted over 40 years without a cloud ever casting a shadow.
Aragon had managed to preserve the results of his measurements, and his first job after returning home was to file them with the Bureau des Longitudes in Paris. As a reward for his adventures in the name of Science, he was elected a member of the French Academy of Sciences at the unusually young age of 23. Before he closed in 1809, he had been chosen by the council of the Faculty of Engineering to succeed Gaspar Monge in the chair of Analytical Geometry. At the same time he was appointed by the Emperor as one of the astronomers of the “Royal Observatory,” which became his residence until his death, and in this capacity he gave the very successful series of popular Astronomy lectures for the general public, which lasted from 1812 to 1845.
In 1816, together with Ge-Lussac, he began the publication of the Annales de chemie et de physique, and in 1818 or 1819 he and Bjoe proceeded with new geodesic studies, this time on the coasts of France, England and Scotland. They measured the length of a pendulum second at Leith, Scotland, and in the Shetland Islands. The results of the surveys were published in 1821, along with those of Spain. Soon afterwards, Aragon was elected a member of the Bureau des Longitudes and contributed to each of its annual reports for the next 22 years or so important notes on Astronomy, Meteorology and once on Civil Engineering.
Aragon”s first investigations in pure physics were on the pressure of steam at different temperatures, and on the speed of sound (1818 to 1822). His research on magnetism took place mainly between 1823 and 1826. He discovered so-called rotational magnetism, and the fact that most bodies can be magnetized. These discoveries were complemented and interpreted by Michael Faraday.
Aragon fervently supported the optics theories of Jean-Augustin Fresnel, helping to confirm the wave theory of light by observing the phenomenon now known as the “Aragon Spot”. Together the two sages conducted experiments on the polarization of light, which led to the demonstration that the oscillations of the propagating medium of the oscillations (then believed to be the “ether”) were perpendicular to the direction of propagation of the waves, and that polarization constituted the resolution of vertical motion into components perpendicular to each other. The later invention of the polariscope and the discovery of rotational polarization were due to Aragon. He invented the first polarizing filter in 1812.
The general idea of experimentally determining the speed of light in the way later used by Ipolit Fizzot and Leon Foucault was proposed by Aragon in 1838, but his impaired vision prevented him from arranging the details or carrying out the experiments himself.
Arago”s reputation as an experimenter and discoverer is mainly due to his contributions to optics and magnetism. He showed that a magnetic needle set to oscillate over surfaces e.g. water, glass, copper, etc. media, exhibits a stronger damping of its oscillations in proportion to its distance from the surface. This discovery, which earned him the Royal Society”s Copley Medal in 1825, was followed by another, that a rotating copper plate tends to entrain in its motion a magnetic needle suspended above it (”magnetism of rotation”). Arago was also one of the first to demonstrate the long-suspected relationship between the aurora borealis and variations in geomagnetic field parameters.
In optics, Aragon not only made important revelations himself, but is credited with stimulating the genius of Jean-Augustin Fresnel, with whose story, as with those of Etienne-Louis Malus and Thomas Young, these investigations are closely linked.
In 1830 Arago, who had always held liberal views, was elected a member of the group of delegates of the Eastern Pyrenees district and used his eloquence and scientific knowledge on all matters relating to public education, the rewards of inventors and the encouragement of engineering and practical sciences. Many of the most positive national actions of this era were due to his support – such as rewarding Louis-Jacques Daguerre for the invention of photography, financing the publication of the works of Fermat and Laplace, acquiring the Clini museum, and developing the railways and the electric telegraph.
In 1830 Aragon was also appointed director of the Paris Observatory, and as a lay representative he was able to secure funding for its partial reconstruction, as well as for the addition of magnificent instruments. In the same year he was made secretary for life of the Academy of Sciences, in place of Fourier. Arago devoted himself wholeheartedly to the service of the Academy, and by his ability to win friends he at once won for it and for himself universal esteem.
In 1834 he visited Scotland again to attend the meeting of the British Association for the Advancement of Science in Edinburgh. From then until 1848 he lived relatively quietly, continuing to work at the Academy and the observatory, but with the fall of Louis-Philippe of France he left his laboratory to join the Provisional Government of France (24 February 1848). He was entrusted with two important responsibilities that had never before been given to the same person, namely the Ministry of the Navy and Colonies (24 February – 11 May 1848) and the Ministry of War (5 April – 11 May 1848). In the former, Aragon improved rations in the navy and abolished flogging. He also abolished political oaths of all kinds and, against many economic interests, succeeded in bringing about the abolition of black slavery in the French colonies.
On 10 May 1848 Aragon was elected a member of the Committee of Executive Power, a governing body of the French Republic. The following day he became President of this Commission, and in this capacity served as temporary head of government until June 24, 1848, when the collective resignation of the Commission was submitted to the National Constituent Assembly.
Arago remained true to his democratic ideals until the end of his life. After the coup of 1852, although he suffered first from diabetes and then from Bright”s disease complicated by dropsy, he resigned his position as an astronomer at the Bureau des Longitudes in early May to avoid being forced to take the oath of allegiance demanded by the new government. Napoleon III instructed that the now elderly Aragon should not be harassed in any way and that he should be free to say and do as he pleased. The leader refused to accept Aragon”s resignation, making “an exception for the sake of a wise man whose works had added glory to France and whose existence the government would have regretted to embitter.”
In the summer of 1853 Aragon took the advice of his doctors to try the effect of the air of his native city and set out for the Eastern Pyrenees, but this proved ineffective and he died in Paris. His tomb is in the famous cemetery of Per Lachaise in Paris.
Arago”s “complete” works were published after his death under the supervision of J. A. Barral, in 17 volumes, from 1854 to 1862. Also, separately, his Astronomie populaire (4 volumes) and:
Some of his individual works, which have also been translated into English, are:
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