Background

Arago was born on February 26, 1786 at Estagel, a small village of 3, 000 near Perpignan, in the département of Pyrénées-Orientales, France. Arago was the eldest son of Marie Roig and François Bonaventure Arago, a modest landowner of Catalonian origin who became mayor of Estagel in 1789. The family moved to Perpignan in 1795, when Arago’s father was named cashier at the mint.

Education

Showing decided military tastes Francois 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. He prepared for admission to the École Polytechnique by mastering the works of Euler, Lagrange, and Laplace, and passed the entrance examination with great distinction in 1803.

Career

After two years at the head of his class in the École Polytechnique, Arago was named secretary of the Bureau des Longitudes and sent to Spain with Biot on a geodetic expedition. After being held prisoner in Spain and Algeria, he returned in June 1809 to France, where he was welcomed into the Société d’Arcueil.

He was elected to the Institut de France as an astronomer on 18 September 1809 and in that year also succeeded Monge as professor of descriptive geometry at the École Polytechnique, where he taught a variety of subjects until his resignation in 1830. At the request of the Bureau des Longitudes, which placed the Paris Observatory under his direction, Arago also taught astronomy to the general public at the observatory from 1813 to 1846. He was the main contributor to the Annuaire du Bureau des Longitudes for more than forty years and coeditor, with Gay-Lussac, of the Annales de chimie et physique from 1816 to 1840. He was a member of most of the important scientific societies, receiving the Royal Society’s Copley Medal in 1825 and being elected perpetual secretary of the Académie des Sciences, replacing Fourier, on 7 June 1830.

Arago’s most important original work in science was carried out before 1830, for his younger brothers, particularly Étienne, drew him into politics following the July Revolution of 1830. He was repeatedly elected deputy for his native department (Pyrénées-Orientales) and for Paris between 1830 and 1852, and sat on the left in the Chamber of Deputies, delivering influential speeches on educational reform, freedom of the press, and the application of scientific knowledge to technological progress, particularly concerning canals, steam engines, railroads, the electric telegraph, and photography. He also was twice named president of the Paris Municipal Council. The peak of Arago’s political career came after the February Revolution of 1848, when he was made a member of the provisional government and was named, successively, minister of the navy and the army and president of the Executive Committee. Arago’s effective political career ended following his loss of control over the revolutionaries during the June days of 1848.

It was this series of disparate experiments that caused Fresnel to write to Arago in 1815 to announce his theory of stellar aberration and the explanation of diffraction phenomena by undulatory principles. Although Fresnel’s “discoveries” had retraced the work of Bradley and Thomas Young, Arago urged him to pursue his investigations and agreed to collaborate with the young engineer. Together they published a series of papers advocating the undulatory theory of light, answering one by one the criticisms of the partisans of emission theory, especially Arago’s colleagues and former friends, Laplace and Biot. In this collaborative enterprise Fresnel supplied the crucial mathematical analyses and the seminal concept of transverse waves, while Arago contributed his encyclopedic command of the current literature in optics, his critical powers, and a significant number of experimental insights and actual experiments.

Above all, Arago functioned as a catalytic agent and public defender of the new theory, and eventually as its major historian. In 1824 he wrote an important article on polarization, translated by Young for the Encyclopaedia Britannica, and later wrote detailed and moving biographical notices of Fresnel (1830), Young (1832), and Malus (1853), sprinkled with personal anecdotes of great significance. It was Arago who, in 1838, borrowing and amplifying the idea and apparatus from Wheatstone’s experiments for measuring the speed of electricity, suggested the “crucial experiment” to decide between the corpuscular and undulatory theories of light by comparing the speed of light in water and in air. The experiment, which vindicated the undulatory position, was carried out by Foucault in 1850 and announced to the Academy in Arago’s presence.

Arago was also concerned with optical instruments that proved useful for a variety of purposes, in physics and meteorology as well as in astronomy, for which they were mainly devised. In 1811 he invented the polariscope to determine the degree of polarization of light rays by passing them successively through a mica or rock-crystal polarizer and an Iceland spar analyzer. With the addition of a series of properly graduated plates that could be inclined at will with reference to the incident ray, Arago transformed his polariscope into a polarimeter, which he used to verify one of the few mathematically expressed laws he discovered: the cosine-squared law for calculating the intensity of the ordinary ray in double refraction. In 1833 he derived from it the ratio of the amount of polarized light to neutral light. With the polarimeter, he was able to differentiate between light emanating from solid and liquid surfaces, polarized by reflection and from incandescent gases, and to determine that the edge of the sun is gaseous. The polarimeter also suggested to him ways to determine polarization of the corona during total eclipses, to determine that rays from the sun’s halo are refracted but not reflected, to observe the nature of a comet’s tail, and to calculate the height of isolated clouds.

In 1815 Arago built a primitive cyanometer to measure the degree of blueness of the atmosphere, which was later adapted for use in hydrographical determinations of the depth of the sea. In 1833 he proposed a photometer to measure comparative intensities of stellar light; his student Paul Ernest Laugier later employed it. The workings of all these instruments, based upon polarization phenomena, were expounded with great clarity and enthusiasm in Arago’s public lectures at the observatory, published posthumously as Astronomie populaire.

As a young astronomer and member of the Bureau des Longitudes, Arago made numerous observations and important theoretical proposals. Among them were the explanation of the scintillation of stars by the use of interference phenomena and the realization of the asymmetry of the layers of atmosphere with reference to the observer. In his later years he made some important remarks on solar appendages noticed during the 1842 eclipse, which he observed with Laugier and Mauvais. But it was even more by the stimulus he gave younger astronomers—including Paul Laugier, Félix Mauvais, Jean Goujon, Jules Jamin, Hervé Faye, and Charles Mathieu—that Arago made his reputation as an astronomer. It also was Arago who urged Leverrier, his successor as director of the observatory, to take up Bouvard’s work on the tables of Uranus. These investigations eventually led to the prediction of the existence and position of Neptune. Arago was also attentive to instrument makers, being responsible for promoting the precision work of Henri Gambey and Louis Bréguet. He was proud that during his tenure at the observatory most of its late eighteenth-century, English-made instruments were gradually replaced by better, French apparatus.

In 1820 Arago interrupted his optical work to play a significant role in the elaboration of electrodynamic and electromagnetic theories. Invited to the La Rive laboratory in Geneva to witness the verification of Oersted’s experiments linking electricity to magnetism, he immediately acquired a passionate interest in the subject, displaying what Humboldt characterized as “the intolerance of a new convert.” Arago repeated the Geneva experiments at the Paris Academy on 11 September 1820, thereby inspiring Ampère to elaborate his electrodynamic theory of electricity and magnetism. Although the two scientists did not write joint papers, they were in constant and friendly communication, often working in each other’s laboratories. Just as Arago had been the champion of Fresnel’s theories in 1815, so now did he propagandize Ampère’s new theory and vehemently support his novel views. Because of his loyalty to Ampère, Arago was never fully able to appreciate or accept the rival theory of Faraday.

Arago also made several important contributions to electromagnetism on his own. On 20 September 1820 he announced the discovery of the temporary magnetization of soft iron by an electric current, which suggested to Ampère a theory about the nature of magnetic “currents” and provided the technological key to the electric telegraph. Ampère calculated that the magnetic power could be multiplied by twisting the current-carrying wire into a helix, and with Arago he carried out the first experiments on primitive solenoids. In his historical articles Arago was always careful to credit Ampère with the major share of this discovery, which ultimately depended upon Ampère’s mathematical theory.

After a delay of several years, during which he worked on the speed of sound and the crystalline nature of ice, and wrote up his observations on the chemical and thermal effects of light, Arago recognized the importance of his original observation at Greenwich. He announced that the rotation of nonmagnetic metallic substances (especially copper) created a magnetic effect on a magnetized needle. Known as Arago’s “disc” or “wheel,” it was the discovery of this effect that won him the Copley Medal in 1825. John Herschel and Babbage attempted to explain the phenomenon on the basis of Ampère’s theory, but it was Faraday who in 1831 explained it by his theory of induction. By this time Arago had abandoned electrical research and had turned to other, more eclectic concerns.

In 1824 Arago was a member of an academic commission to study steam pressure, with the aim of reducing the dangers of explosion in steam engines. He and Dulong prepared elaborate apparatus for measuring pressure under high temperatures, verifying Boyle’s law for values up to 24 atmospheres. In 1839 Arago took a personal interest in announcing and popularizing the inventions of Niepce and Daguerre, who were awarded government pensions as a result of Arago’s recognition of their inventions’ potential significance.

In his last years, while his sight was failing him, Arago continued to discharge his duties as perpetual secretary of the Academy by summarizing the achievements of other scientists and by suggesting new experiments that he himself could not carry out. Surrounded by a group of devoted younger scientists who wrote, observed, and experimented for him, Arago never lost his mental energies and his ability to stimulate his colleagues and excite the public about the progress of science.

On 22 August 1853 Arago attended the Academy of Sciences for the final time then, despite his health problems, he set out on the difficult journey to his family in the Roussillon region. After giving them advice on a wide range of matters he returned to Paris where he died shortly after. He was buried in the Père Lachaise cemetery in Paris.

Achievements

• 

  Arago made a series of valuable contributions throughout his career as a scientist and astronomer achieving a high grade of reputation within the scientific community. The results of Arago`s independent investigations by passing beams of polarized light through a variety of gaseous and crystalline substances at various degrees of incidence to study the light’s properties, which suggested the usefulness of the undulatory theory, included the discovery of chromatic polarization by the use of thin mica plates (1811), rediscovered independently by Brewster; the elaboration of the conditions necessary to produce Newton’s rings (1811); and the observation of special cases of rotary polarization (1812), which were shortly thereafter made a general law of optics by Biot.
  
  Since Arago had a great interest in optical instruments that would prove useful for a variety of purposes, in physics and meteorology as well as in astronomy, for which they were mainly devised, he invented the polariscope in 1811 in order to determine the degree of polarization of light rays by passing them successively through a mica or rock-crystal polarizer and an Iceland spar analyzer. Arago later transformed his polariscope into a polarimeter, which he used to verify one of the few mathematically expressed laws he discovered: the cosine-squared law for calculating the intensity of the ordinary ray in double refraction. He also perfected an ocular micrometer for measuring small angles, which was erroneously attributed to William Pearson.
  
  As an astronomer and member of the Bureau des Longitudes, Arago made numerous observations and important theoretical proposals. Among them were the explanation of the scintillation of stars by the use of interference phenomena and the realization of the asymmetry of the layers of atmosphere with reference to the observer. His investigations also eventually led to the prediction of the existence and position of Neptune.
  
  As minister he signed decrees outlawing corporal punishment and improving the rations of sailors on the high seas, and abolishing slavery in the French colonies.
  
  Arago`s probably most valuable contribution was made on the subject of electromagnetism. On 20 September 1820 he announced the discovery of the temporary magnetization of soft iron by an electric current, which suggested to Ampère a theory about the nature of magnetic “currents” and provided the technological key to the electric telegraph. He announced that the rotation of nonmagnetic metallic substances (especially copper) created a magnetic effect on a magnetized needle. Known as Arago’s “disc” or “wheel,” it was the discovery of this effect that won him the Copley Medal in 1825. He was also awarded the Rumford Medal in 1850. Craters on both the Moon and Mars have been named after him, as has a ring of Neptune. The Academy of Sciences inaugurated the Arago Medal in 1893.
  
  The study association for Applied Physics at the University of Twente was named after Arago. His name is one of the 72 names inscribed on the Eiffel Tower.

Works

More photos

• book

  • Oeuvres complètes : ASTRONOMIE POPULAIRE
  • histoire de ma jeunesse
  • Gaspard Monge
  • Biographies of Distinguished Scientific Men First Series
  • Francois Arago
  • Histoire ma jeunesse: annoté
  • Biografie di Galileo
  • Carnot

Politics

Arago`s politics were those of a constitutional liberal, passionately concerned with social reform (he helped found La réforme in 1843), freedom of association, and education of the lower classes. He was, however, violently opposed to mob rule and to the socialistic programs espoused by Louis Blanqui, Alexandre Ledru-Rollin, and Louis Blanc. Arago’s effective political career ended following his loss of control over the revolutionaries during the June days of 1848.

Views

Arago’s scientific life was dominated by a persistent interest in physical phenomena related to electricity, magnetism, and, above all, to light. His earliest investigations with Biot in 1805 and 1806 continued the work of Borda on the factors affecting the refraction of light passing through the atmosphere of the earth. They helped to verify the formulas given in Laplace’s Mécanique céleste, which were based on the assumption that the atmosphere is composed of concentric rings of a mixture of oxygen and nitrogen, with density as a function of altitude. Biot and Arago showed experimentally that temperature and pressure were significant variables, whereas humidity and the traces of carbon dioxide in the atmosphere could be disregarded. But when Arago extended his investigations to refraction in liquids and solids—with Petit in 1813 and Fresnel in 1815—he recognized the failure of the current theory of emission and particulate attraction to account for the empirical formulas he derived. After his return from the geodetic expedition to extend meridian triangulations from Barcelona to the Balearic Islands, Arago became a vocal critic of the Newtonian emission theory and, by 1816, an ardent supporter of the undulatory theory.

The original source of Arago’s interest was Thomas Young’s classic paper of 1801 on the color of thin glass plates and the discovery of polarization by Malus in 1808.

Quotations: "Connaître, découvrir, communiquer—telle est, au fond, notre honorable destinée. To get to know, to discover, to publish—this is the destiny of a scientist."

"I was often humiliated to see men disputing for a piece of bread, just as animals might have done. My feelings on this subject have very much altered since I have been personally exposed to the tortures of hunger. I have discovered, in fact, that a man, whatever may have been his origin, his education, and his habits, is governed, under certain circumstances, much more by his stomach than by his intelligence and his heart."

"A time will come when the science of destruction shall bend before the arts of peace; when the genius which multiplies our powers, which creates new products, which diffuses comfort and happiness among the great mass of the people, shall occupy in the general estimation of mankind that rank which reason and common sense now assign to it."

"Euler calculated without effort, just as men breathe, as eagles sustain themselves in the air."

"The ancients had a taste, let us say rather a passion, for the marvellous, which caused grouping together the lofty deeds of a great number of heroes, whose names they have not even deigned to preserve, and investing the single personage of Hercules with them. In our own time the public delight in blending fable with history. In every career of life, in the pursuit of science especially, they enjoy a pleasure in creating Herculeses."

"Such is the privilege of genius; it perceives, it seizes relations where vulgar eyes see only isolated facts."

"Let us award a just, a brilliant homage to those rare men whom nature has endowed with the precious privilege of arranging a thousand isolated facts, of making seductive theories spring from them; but let us not forget to state, that the scythe of the reaper had cut the stalks before one had thought of uniting them into sheaves!"

"On certain occasions, the eyes of the mind can supply the want of the most powerful telescopes, and lead to astronomical discoveries of the highest importance."

"The calculus of probabilities, when confined within just limits, ought to interest, in an equal degree, the mathematician, the experimentalist, and the statesman."

Membership

Arago was a member of most of the important scientific societies, such as the Royal Society of London.

Personality

Arago was at once volatile and warm-hearted in his personal relations. He either forged strong bonds with fellow scientists or engaged in sharp polemics that often were provoked by priority controversies. Among his closest friends were Alexander von Humboldt, with whom he shared a room in Paris from 1809 to 1811, Gay-Lussac, and Malus; and among his relatives, the physicist Alexis Petit and the astronomer Claude L. Mathieu. He had a stormy relationship with Biot, Thomas Young, and Brewster, but it did not blind him to their scientific merits.

In both his writings and his public appearances, Arago conveyed a contagious sense of excitement that won him a large following. His personal style, which spilled over into his work habits, was that of a romantic— restless, inquisitive, volatile, and constantly bubbling with enthusiasm and optimism.

Physical Characteristics: In his later years Arago gradually lost his eyesight, went blind, and was reduced to dictating to his students.

Quotes from others about the person

• Bertrand, in his obituary of Arago, wrote:
  
  "Arago smiled at the beautiful experiment [of Fizeau and Foucault] which, with its well deserved praise, brought back pleasant memories of his own glory days when he beat Laplace, Poisson, and Biot, to gain his place in the Academy of Sciences."

Connections

Arago married Lucie Carrier-Bescombes in 1811; one of their sons, Alfred Arago (1816-92), became an Inspector of Fine Arts, another son Emmanuel Arago served with his father on the National Assembly for many years.

Father:

François Bonaventure Arago 1754–1814

Mother:

Marie Arago 1755–1845

Wife:

Lucie Carrier-Besombes

Son:

Gabriel Arago

Son:

Emmanuel Arago

Son:

Alfred Arago

Brother:

Jacques Étienne Victor Arago 1799–1855

French writer, artist, and explorer, author of a Voyage Round the World.

Brother:

Etienne Arago

collaborator:

Augustin-Jean Fresnel

In their collaborative enterprise Fresnel supplied the crucial mathematical analyses and the seminal concept of transverse waves, while Arago contributed his encyclopedic command of the current literature in optics, his critical powers, and a significant number of experimental insights and actual experiments.

collaborator:

Alexander von Humboldt

They were investigating the same subject that dealt with the electromagnetism. In 1822, while he and Humboldt were measuring the magnetic intensity of a hill at Greenwich, Arago casually noticed the dampening effect that metallic substances had on the oscillations of the compass needle.

Through his long-standing friendship with Humboldt, Arago was led to write popular articles on meteorology and physical geography, which ranged from discussions of the temperature of the earth, the seas, and the atmosphere to earthquakes and magnetic variations on the earth. He was particularly influential in propagating Humboldt’s concept of isothermal lines and in setting down the purposes of and data required from scientific expeditions.

associate:

Thomas Young

associate:

Jean Foucault

French physicist best known for his demonstration of the Foucault pendulum, a device demonstrating the effect of the Earth's rotation. He made an early measurement of the speed of light, discovered eddy currents, and is credited with naming the gyroscope.

Friend:

Simeon Poisson

Poisson would frequently visit Arago in his apartment in the evenings and the two would discuss politics and mathematics. Although, as we have said, the two were not like student and teacher, nevertheless Poisson did influence his younger friend very considerably. Despite being taught by some of the leading mathematicians in the world, Arago did not find their abilities to teach come anywhere close to their abilities for research. In 1805 Poisson was able to offer Arago a task of far more importance than one would have expected a young student to be asked to undertake. He asked Arago to help in measuring the meridian.

References

• François Arago: A 19th Century French Humanist and Pioneer in Astrophysics
• Les Arago: Francois et les autres
• Dictionary of Scientific Biography