François Arago François Jean Dominique Arago ( ) , known simply as François Arago ( ; Catalan : " Francesc Aragó " , ) ( 1786 – 1853 ) , was a French mathematician , physicist , astronomer , freemason , carbonari and politician . Early life and work . Arago was born at Estagel , a small village of 3000 near Perpignan , in the " " of Pyrénées - Orientales , France , where his father held the position of Treasurer of the Mint . Arago was the eldest of four brothers . Jean ( 1788 – 1836 ) emigrated to North America and became a general in the Mexican army . Jacques Étienne Victor ( 1799 – 1855 ) took part in Louis de Freycinet ' s exploring voyage in the " Uranie " from 1817 to 1821 , and on his return to France devoted himself to his journalism and the drama . The fourth brother , Étienne Vincent de ( 1802 – 1892 ) , is said to have collaborated with Honoré de Balzac in " The Heiress of Birague " , and from 1822 to 1847 wrote a great number of light dramatic pieces , mostly in collaboration . 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 École Polytechnique . 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 Arago entered the École Polytechnique , Paris , but apparently found the professors there incapable of imparting knowledge or maintaining discipline . The artillery service was his ambition , and in 1804 , through the advice and recommendation of Siméon Poisson , he received the appointment of secretary to the Paris Observatory . He now became acquainted with Pierre - Simon Laplace , and through his influence was commissioned , with Jean - Baptiste Biot , to complete the meridian arc measurements which had been begun by J . B . J . Delambre , and interrupted since the death of P . F . A . Méchain in 1804 . Arago and Biot left Paris in 1806 and began operations along the mountains of Spain . Biot returned to Paris after they had determined the latitude of Formentera , the southernmost point to which they were to carry the survey . Arago continued the work until 1809 , his purpose being to measure a meridian arc in order to determine the exact length of a metre . After Biot ' s departure , the political ferment caused by the entrance of the French into Spain extended to the Balearic Islands , and the population suspected Arago ' s movements and his lighting of fires on the top of Mount Galatzó ( Catalan : Mola de l ' Esclop ) as the activities of a spy for the invading army . Their reaction was such that he was obliged to give himself up for imprisonment in the fortress of Bellver in June 1808 . On 28 July he escaped from the island in a fishing - boat , and after an adventurous voyage he reached Algiers on 3 August . From there he obtained a passage in a vessel bound for Marseille , but on 16 August , just as the vessel was nearing Marseille , 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 a fortress , until the town fell into the hands of the French , when the prisoners were transferred to Palamos . After three months ' imprisonment , Arago and the others were released on the demand of the dey of Algiers , and again set sail for Marseille on 28 November , 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 over land , guided by a Muslim priest , and reached it on Christmas Day . After six months in Algiers he once again , on 21 June 1809 , set sail for Marseille , 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 Alexander von Humboldt ; and this was the origin of a connection which , in Arago ' s words , lasted over forty years without a single cloud ever having troubled it . Scientific studies . 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 of science , he was elected a member of the French Academy of Sciences , at the remarkably early age of twenty - three , and before the close of 1809 he was chosen by the council of the École Polytechnique to succeed Gaspard 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 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 , Scotland , and in the Shetland Islands , the results of the observations being published in 1821 , along with those made in Spain . Arago was elected a member of the Bureau des Longitudes 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 . Arago ' s earliest physical researches were on the pressure of steam at different temperatures , and the velocity of sound , 1818 to 1822 . His magnet ic observations mostly took place from 1823 to 1826 . He discovered rotatory magnetism , what has been called Arago ' s rotations , and the fact that most bodies could be magnetized ; these discoveries were completed and explained by Michael Faraday . Arago warmly supported Augustin - Jean Fresnel ' s optical theories , helping to confirm Fresnel ' s wave theory of light by observing what is now known as the spot of Arago . The two philosophers conducted together those experiments on the polarization of light which led to the inference that the vibration s of the luminiferous ether were transverse to the direction of motion , and that polarization consisted of a resolution of rectilinear propagation into components at right angles to each other . The subsequent invention of the polariscope and discovery of Rotary polarization are due to Arago . He invented the first polarization filter in 1812 . The general idea of the experimental determination of the velocity of light in the manner subsequently effected by Hippolyte Fizeau and Léon Foucault was suggested by Arago in 1838 , but his failing eyesight prevented his arranging the details or making the experiments . Arago ' s fame as an experimenter and discoverer rests mainly on his contributions to magnetism in the co - discovery with Léon Foucault of eddy current s , and still more to optics . He showed that a magnetic needle , made to oscillate over nonferrous 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 , which he called " magnetism of rotation " but is now known as eddy current . 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 elements . In 1828 , he was elected a foreign member of the Royal Swedish Academy of Sciences . In optics , Arago not only made important optical discoveries on his own , but is credited with stimulating the genius of Jean - Augustin Fresnel , with whose history , as well as that of Étienne - Louis Malus and 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 is due the discovery of the power of rotatory polarization exhibited by quartz . Among Arago ' s 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 and 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 Charles 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 to 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 . Politics and legacy . In 1830 , Arago , who always professed liberal opinions of the republican type , was elected a member of the chamber of deputies for the Pyrénées - Orientales " département " , and he employed his talents of eloquence and scientific knowledge in all questions connected with public education , the rewards of inventors , and the encouragement of the mechanical and practical sciences . Many of the most creditable national enterprises , dating from this period , are due to his advocacy – such as the reward to Louis - Jacques Daguerre for the invention of photography , the grant for the publication of the works of Fermat and Laplace , the acquisition of the museum of Cluny , the development of railways and electric telegraphs , the improvement of the reneile . In 1830 , Arago also 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 himself into its service , and by his faculty of making friends he gained at once for it and for himself a worldwide reputation . As perpetual secretary it was his duty to pronounce historical eulogies on deceased members ; and for this duty his rapidity and facility of thought , and his happy piquancy of style , and his extensive knowledge peculiarly adapted him . He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1832 . In 1834 , Arago 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 – although he continued to work within the Academy and the Observatory to produce a multitude of contributions to all departments of physical science – but on the fall of Louis - Philippe he left his laboratory to join the Provisional Government ( 24 February 1848 ) . He was entrusted with two important functions , that had never before been given to one person , viz . the ministry of marine and colonies ( 24 February 1848 – 11 May 1848 ) and ministry of war ( 5 April 1848 – 11 May 1848 ) ; in the former capacity he improved rations in the navy and abolished flogging . He also abolished political oaths of all kinds and , against an array of moneyed interests , succeeded in procuring the abolition of slavery in the French colonies . On 10 May 1848 , Arago was elected a member of the Executive Power Commission , a governing body of the French Republic . He was made President of the Executive Power Commission ( 11 May 1848 ) and served in this capacity as provisional head of state until 24 June 1848 , when collective resignation of the Commission was submitted to the National Constituent Assembly . At 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 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 . " Cape Gregory ( the best known cape and , debatably , the furthest point west in Coos County , Oregon , USA , was named by Captain Cook in 1788 after the saint of the day ; it was renamed Cape Arago after the great François Arago . Last years . Arago remained a consistent republican to the end , and after the coup d ' état of 1852 , though suffering first from diabetes , then from Bright ' s disease , complicated by dropsy , he resigned his post as astronomer rather than take the oath of allegiance . Napoleon III gave directions that the old man should be in no way disturbed , and should be left free to say and do what he liked . In the summer of 1853 Arago was advised by his physicians to try the effect of his native air , and he accordingly set out to the eastern Pyrenees , but it was ineffective and he died in Paris . His grave is at the famous Père Lachaise Cemetery in Paris . Craters on Mars and the Moon , and a ring of Neptune , are named after Arago , as well as the study association for Applied Physics at the University of Twente . His name is one of the 72 names inscribed on the Eiffel Tower . Publications . Arago ' s works 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 Arago ' s works have appeared :