ARAGO, FrançoisJean Dominique, one of the most popular physicists belonging to the first half of the present century, was born on the 26th February 1786, at Estagel, a small village near Perpignan, in the department of the Eastern Pyrenees. His father was a licentiate in law, and, being appointed treasurer of the mint for the department, τemoved with his family to Perpignan about the beginning of the century. Arago has left an autobiographical sketch, drawn with great vivacity, though touched occasionally with somewhat high colouring; and to this we are indebted for the incidents of the earlier portion of his life. From boyhood he had decided military tastes, inspired by constant contact with troops at his native village, which was a halting station for soldiers on their way to Perpignan, or to the army of the Pyrenees. François was sent as an outdoor pupil to the municipal college of Perpignan, and began to study mathematics with an eye to the entrance examination to the Polytechnic school. Here he was soon beyond the depth of his master’s knowledge; but, with that undaunted spirit which carried him through many hardships and difficulties in after life, he sent to Paris for the works of Legendre, Lacroix, and Garnier, and studied them assiduously in private. Within two years and a half he had mastered all the subjects prescribed for examination, and a great deal more; he had read Euler’s Introduction à l ’ Analyse Infinitesimale, Lagrange’s Théorie des Fonctions Analytiques and Mécanique Analytique, and Laplace’s Mécanique Céleste. He does not indeed pretend to have understood at the time all he read in these works, but he had been early encouraged by D’Alembert’s maxim, “Go on, and the light will come to you,” and he had carried it into practice. On going up for examination at Toulouse he completely astounded his examiner, Μ. Monge, by his knowledge of Lagrange, and received the highest commendation from him. Towards the close of 1803 he entered the Polytechnic school, with the artillery service as the aim of his ambition. We have in the autobiography many amusing instances of the inefficiency of some of the Polytechnic professors at that time, of the peculiarly French familiarity existing between professors and pupils, as well as of the political passions absurdly allowed to distract the school. In 1804, through the advice and recommendation of Poisson, with whom he had become very intimate, Arago received the appointment of secretary to the Observatory of Paris, a valuable post for a young man of science, as it brought him in contact with the most eminent philosophers of the day. He now became acquainted with Laplace, and he had as fellow-worker in the laboratory the celebrated Biot. Through the influence of Laplace with the Government, Arago and Biot were commissioned to complete the meridional measurements which had been begun by Delambre, and interrupted since the death of Méchain in 1804. The object of this survey was to determine, with as great nicety as possible, the ten-millionth part of a quadrant of the meridian through Paris, which had been agreed upon by the National Convention as the standard unit of length, and named the mètre. To measure an actual quadrant from the north pole was, of course, an impossibility; but the plan adopted was to measure the arc of the meridian from Dunkirk to Barcelona, and from their know n difference of latitude to deduce the length of the quadrant. For this purpose they left Paris in 1806, to commence operations among the mountains of Spain—operations attended with the greatest personal privation, fatigue, and danger. Biot returned to Paris after they had determined the latitude of Formentera, the southernmost point to which they were to carry the survey, leaving Arago to make the geodetical connection of Majorca with Ivica and with Formentera.
The adventures and difficulties of the latter were now only beginning. The political ferment caused by the entrance of the French into Spain extended to these islands, and the ignorant populace began to suspect that Arago’s movements and his blazing fires on the top of Mount Galatzo were telegraphic signals to the invading army. They became ultimately so infuriated that he was obliged to cause himself to be incarcerated in the fortress of Belver in June 1808. On the 28th July he managed to escape from the island in a fishing boat, and after an adventurous voyage he reached Algiers on the 3d August. Under the disguise of a strolling merchant he procured a passage in a vessel bound for Marseilles. A journey, however, of eleven months was before him ere he was destined to reach that port, for the vessel fell into the hands of a Spanish corsair on the 16th August, just as it was nearing Marseilles. With the rest of the crew, Arago was taken to Rosas, 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 28th Nov., but when within sight of their port they were driven back by a southerly wind to Bougia on the coast of Africa. Transport to Algiers by sea from this place would have occasioned a weary stay of three months; and with his usual courage, Arago set out for it by land under conduct of a Mahometan priest, reaching it on Christmas day, after encountering many perils from lions, and having uncomfortable squabbles with natives on the way. A six months’ stay in Algiers gave him opportunity to note the manners and habits of the people, of which he gives some amusing and graphic accounts. Once again, 21st June 1809, he set sail for his native land; and, as by some strange perversity of fortune, he had to undergo a monotonous and inhospitable quarantine in the Lazaretto at Marseilles before his difficulties were over. The first letter he received, while in the Lazaretto, was from Humboldt at Paris, sympathising with him, and congratulating him on the termination of his laborious and perilous enterprise; 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.”
Through all the vicissitudes of this long campaign 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 de Longitude at Paris. As a reward for his adventurous conduct in the cause of science, he was shortly afterwards (17th Sept. 1809) voted a member of the Academy of Sciences, in room of the deceased Lalande, at the remarkably early age of twenty-three, being, to the vexation of Laplace, elected by a large majority of votes over his friend Poisson. Before the close of the same year (1809) Arago was chosen by the council of the Polytechnic school to succeed Μ. Monge in the chair of analytical geometry; and about 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. He was also made one of the examiners in connection with the École d ’ Application for engineers and artillery at Metz. In all these situations he rapidly attained very great popularity, gaining the esteem of his pupils by the charming clearness of his style in lecturing and the personal interest he showed in their progress.
In 1816, along with Gay-Lussac, Arago commenced a monthly journal of science, the Annales de Chimie et de Physique, which soon acquired that high scientific reputation which it has always maintained. In the same year the two philosophers visited England, and made the personal acquaintance of some of the most eminent men of that country, meeting among others Dr Thomas Young, a memoir of whom was afterwards written by Arago. In 1818 or 1819, Arago proceeded along with Biot to execute, on the coasts of France, England, and Scotland, the geodetic operations which the Board of Longitude had directed. They also measured the length of the seconds’ pendulum at Leith, and in Unst, one of the Shetland isles; the results of the observations being published in 1821, along with those made in Spain. He was elected a member of the Board of Longitude immediately afterwards, and proved a valuable addition to the society, contributing to each of its Annuals, for about twenty-two years, most important scientific notices on astronomy and meteorology, and occasionally on civil engineering, as well as interesting memoirs of members of the Academy.
After his appointment to the Observatory, Arago had commenced, at the request of the Board of Longitude, a series of popular lectures on astronomy, which were continued from 1812 to 1845. His success as a lecturer was almost unparalleled, and can only be compared to that of Faraday. All ranks flocked to hear him, fascinated by his graceful eloquence and his crystalline clearness of explanation. He used to remark, what many lecturers often forget, that “clearness is politeness in public speakers.” His manner in lecturing is said to have been to fix his eye on some one of his audience, whose intellect had apparently the minimum of development, and to keep it fixed till the face should brighten up with intelligence.
When Buonaparte’s hopes of empire in Europe had begun to wane, and he was turning to America as a land of refuge, where he might still have scope for his ambition, he suggested to Μ. Monge that, with a scientific guide, he should explore the new continent from Canada to Cape Horn, study the great physical wonders of that territory, and leave behind him works and discoveries worthy of himself. Monge named Arago as the proper associate and assistant in the enterprise, and had even negotiated with Napoleon for a handsome allowance to be granted to Arago, and for a fund to be devoted to the purchase of a complete set of astronomical and physical instruments. But Arago would not for a moment entertain the proposal. He pointed the emperor to the march of the English and Prussian armies on his capital as a matter demanding more pressing consideration, and declined to leave the Old World to study science in the New, “when France might perhaps lose its independence and disappear from the map of Europe.” Subsequent events prevented a renewal of Napoleon’s scientific negotiations and projects.
After the Restoration Arago took no very prominent part in the politics of the day, though he at all times maintained with boldness and ardour liberal opinione of the extreme republican type. By the revolution of 1830, however, he was summoned from the studies of the observatory and the laboratory to the field of political strife in the Chamber of Deputies, and in the Municipal Council of Paris. Elected a member of the Chamber of Deputies for the Lower Seine, he employed his splendid gifts 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 the advocacy of Arago—such as the reward to Daguerre for his wonderful invention of photography, the grant for the publication of the works of Fermat and Laplace, the acquisition of the museum of Cluny (one of the sights of Paris), the development of railroads and electric telegraphs, the improvement of the navigation of the Seine, and the boring of the Artesian wells at Grenelle.
The year 1830 was a remarkable epoch in his life on account of several other offices to which he was appointed. He now received the chief direction of the Observatory, and from his position in the Chamber of Deputies he obtained grants of money for the rebuilding of part of the Observatory and for the addition of magnificent instruments, which raised it to be a model, in place of a public disgrace, as it had been before. In the same year, too, his zeal in the cause of science was rewarded with the highest honour any philosopher might aspire to—the perpetual secretaryship of the Academy of Sciences, in room of the distinguished Fourier. On the 7th June (1830) he was elected by 39 out of 44 votes. This appointment inspired new life into the Academy. Arago threw his whole soul into its service, and by his pleasing faculty of securing friendship and lifelong attachments, he gained at once for himself and for the Academy a world-wide reputation. As perpetual secretary it fell to him to pronounce historical éloges on the decease of resident or foreign members of the Academy; and for this duty his rapidity and facility of thought, his happy piquancy of style, and his extensive knowledge peculiarly adapted him. Some of his éloges are masterpieces of elegant biography. When Μ. Flourens pronounced Arago’s own funeral eulogy, he said, “In the eulogies of the eloquent secretary are found all the qualities of his spirit, d’une verve brillante, de la vigueur, de l ’ elan, un certain charme de bonhomie.”— (Comptes Rendus de l ’ Academie, t. xxxvii. p. 513.)
In 1834 Arago visited England for the second time, to attend the third meeting of the British Association, held that year in Edinburgh. From this time till the stirring events of 1848, Arago 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, which make him one of the most voluminous of authors in this subject. But the change came. Louis Philippe, having failed to satisfy the extreme republican party, and to grant them those social advantages that they imagined a republic alone could yield, was swept from his throne, and Arago left his laboratory to join in forming an extempore government. His popularity was so great that he was entrusted with the discharge of two most important functions, that had never before been united in one person, viz., the Ministry of War and of Marine. Energetically and faithfully the philosopher of forty years’ standing applied himself to his new duties; and however ignominious may have been the ultimate failure of the Provisional Government, there can be little question that Arago struggled honestly in the cause of social liberty and improvement. While Minister of Marine he effected some salutary reforms, such as the improvement of rations in the navy and the abolition of flogging; he abolished political oaths of all kinds, and, against an array of monied interests, he succeeded in procuring the abolition of negro slavery in the colonies.
During the insurrection of June, Arago’s courage was conspicuously! displayed in his entreaties to the mob to stop their murderous outrages. For the first time in his life Arago failed, and he himself narrowly escaped with his life. With his mental and physical energies shattered by fatigue and disappointment, he terminated here his active political career, though he continued to the last to take an interest in the affairs of his country, and to watch for the dawn of a brighter future. Failing eye and trembling hand could now be of little use in the service of science; but warned by the disease (diabetes) that had attacked him, he determined to occupy his few remaining years in preparing for the press some MSS. of original researches which his political duties had prevented his communicating to the Institute.
In the beginning of May 1852 proclamation was made that the oath of allegiance to the Government of Louis Napoleon would be required from all its functionaries, including the Board of Longitude. Arago peremptorily refused, choosing to sacrifice his office and home of nearly half a century rather than violate the dictates of his conscience, which he would be doing if he complied, seeing that, as a member of the Provisional Government of 1848, he contributed to the abolition of all political oaths. In a letter to the Minister of Public Instruction, he intimated his resignation of his post as astronomer at the Bureau de Longitude, at the same time stating the services he had rendered to his country in the cause of science, and the grief which this separation from the scene of his labours of so many years would impose. To the credit of the Prince President, he respected the sentiments so boldly declared by the halfblind old philosopher, and made “an exception in favour of a savant whose works had thrown lustre on France, and whose existence his Government would regret to embitter.”
The tenure of office thus granted did not prove of long duration. Arago was now on his death-bed, under a complication of diseases, induced, no doubt, by the hardships and labours of his earlier years. In the summer of 1853 he was advised by his physicians to try the effect of his native air, and he accordingly set out for the Eastern Pyrenees, accompanied by his affectionate niece, Madame Langier. But the change was unavailing, and he returned to Paris to die. After a lingering illness, in which he suffered first from diabetes, then from Bright’s disease, and lastly from dropsy, he breathed his last on the 2d Oct. 1853, at the age of 67. The day before his death he had been visited by Lord Brougham, his old and intimate friend, and the interview had excited him much. Μ. Biot also had an interview with him only three hours before his death. Arago said to his veteran colleague and collabor ateτιr, "I intend to resign my situation of perpetual secretary to the Academy, since I can no longer discharge its duties.” Biot’s reply must have smoothed the pillow of the dying savant, “If you do, we will all come to you in a body to bring it back to you, and reproach you for your ingratitude.” A public funeral was, with good taste, decreed to Arago by the emperor, notwithstanding his refused allegiance to the Imperial Government, and it took place on the 5th Oct. with all the pomp and parade of an Imperial act. A beautiful and eloquent eulogy was pronounced over his tomb by the distinguished Μ. Flourens, who succeeded him as perpetual secretary of the Academy, while Μ. Barral performed the duty entrusted to him by the young philosophers of the public schools of the metropolis of giving utterance to their last adieu.
Thus closed perhaps the most singular career in the annals of science. Of Arago’s moral character it is difficult to form a true estimate, extolled as it is on the one side by his countrymen, and too severely criticised as it often is on the other side by British writers. Allowance must be made for the Spanish blood that flowed in his veins. The ardour of his temperament, his quick and far darting intellect, the powerful love of country which his youthful vicissitudes had only intensified, all combined to produce a consciousness of power, which, in the Academy of Sciences or in the management of the Observatory, might stamp his bearing as dictatorial, and which, in questions of national priority of invention, might render his judgment partial. With the imperiousness, perhaps, of a powerful intellect, Arago was free from that selfishness that has so often been exhibited by men who have enjoyed such high offices of trust during times of national disorder. He cared for money only as it supplied the wants of his experimental researches and the means of educating his family; he lived a simple and a frugal life; his income never exceeded £500 a year; and, refusing to accept any reward for his four months’ services as Minister of Marine, he sacrificed fortune for the sake of his country and of science.
From he personal history of Arago we turn to his literary and scientific labours and discoveries. It has been already shown that, as editor of the Annuaire or Almanac of the Board of Longitude, he commenced, in 1822, a series of regular contributions of scientific articles to that Annual, remarkable for their lucidity of style, united with mathematical accuracy of detail; that, as perpetual secretary of the Academy of Sciences, his éloges alone would have secured him lasting reputation; and that, as director of the Observatory, he rapidly restored its efficiency and completely remodelled it. He has, indeed, been often accused of doing little or nothing for the practical advancement of astronomy; and of shrinking from the steady and regular drudgery of observation as too tame to be congenial to his versatile mind. To reproach a man who has done much, because he has not done more, or because he has not followed in the beaten track, is, to say the least, far from generous criticism. His applications of physics to astronomical research—such as to his photometric measurements of lunar and stellar brightness, of the polar snows of Mars, and of . the belts of Jupiter and Saturn, to the structure of the sun as revealed by his spots, to the effect of atmospheric refraction on astronomical observations, to irradiation and variable stars—are surely in themselves not despicable contributions to the science. But apart altogether from his labours in the Observatory, he has rendered vastly greater service to astronomy by Ins popular expositions of it than hundreds of the most assiduous observers put together. Few have had, in such a degree as he, the gift of reducing the abstract conceptions of pure science to the level of the popular apprehension without descending to the puerile and frivolous.
In 1820, when the subject of steam boilers was attracting attention, Arago was employed by Government to execute, along with Dulong, a series of experiments on the elastic force of steam at different temperatures. This difficult and most hazardous task, where they were exposed to the bursting of a boiler at any moment, they accomplished with the greatest ability and coolness. Of these experiments, as well as of others,—on the density of air, on the velocity of sound, on the pressure of gases being proportional to their density, <fcc.,—there will be found elaborate memoirs in the Comptes Rendus of the Academy, and in the Annales de Chimie et de Physique.
It is, however, on his contributions to Magnetism and Optics that Arago’s fame as an experimenter and discoverer rests. By employing the method of oscillating needles, he established the universal influence of magnetism on all substances, though it was left to Faraday to make the grander generalisations of diamagnetism. Arago found that a magnetic needle, made to oscillate over non-ferru-ginous surfaces, such as water, glass, copper, &c., falls more rapidly in the extent of its oscillations according as it is more or less approached to the surface. Over ice, for example, an oscillation of 53° on each side of the magnetic meridian, fell to 43° after 60 oscillations at a distance of 52 j millimetres from the ice; while, at a distance of 7 mm., it fell by the same amount after 26 oscillations. Over glass there was a fall from 90° to 41° in 221 oscillations, at a distance of 4Ό1 mm., and in 122 oscillations at a distance of *91 mm. For this discovery Arago was awarded the Copley medal‘by the Royal Society of London in 1825; and he has the honour of being the first foreigner to whom this distinction was accorded. This discovery was followed by another. It occurred to him to try, conversely, the effect of oscillating or rotating a plate of non-ferruginous metal near a magnetic needle at rest. He caused a plate of pure copper to revolve by clock-work, which was also of copper, under a magnetic needle within a glass-receiver, and with a sheet of paper between the needle and the revolving plate to prevent air currents. Gradually the needle was drawn from the magnetic meridian, till finally, on a very rapid rotation of the plate, it fairly swung round and continued in constant rotation. An account of these experiments he read before the Academy of Sciences, on the 7th March 1825, and they were exhibited in London in the following April by Gay-Lussac, exciting universal interest among the philosophers of this and other countries. This phenomenon of rotatory magnetism, as it is termed, is indissolubly linked with the name of Arago; but it was reserved for the genius of Faraday to offer the true explanation of it, after it had long occupied the attention of Herschel, Babbage, Barlow, Nobili, and other distinguished men, as well as of its discoverer.
Arago is also fairly entitled to be regarded as having proved the long suspected connection between the aurora borealis and the variations of the magnetic elements. He established, too, the fact of an hourly variation of these, traceable, no doubt, to the influence of the sun as an enormous magnet at a distance. It is worth mentioning that Arago was the first to employ the galvanic current for the permanent magnetisation of steel, though in the field of electro-magnetism his discoveries and researches as a whole are not to be compared with those of the profounder Ampère.
It is, however, his investigations in Optics that form the most marked feature and the crowning glory of Arago’s scientific career. We owe to him not only important optical discoveries of his own, but the credit of stimulating the genius of Fresnel, with whose history, as well as with that of Malus and of Young, this part of his life is closely interwoven. Shortly after the beginning of the present century the labours of the three philosophers last named were shaping the modern doctrine of the undu latory theory of light. Malus had made in 1808 his discovery of the polarisation of light by reflection, identifying it with the effects of double refraction; Young had devised his beautiful theory of interferences; and Fresnel had been simultaneously conducting elegant experiments in the very same field as the English philosopher. It was the communication to the French Academy of Sciences of a paper on this subject by Fresnel that led to his intimacy with Arago. Fresnel’s arguments in favour of the undu-latory doctrine 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 researches in this subject. These investigations were rewarded by a remarkable discovery, in 1811, the very year that Malus terminated his career so auspiciously begun. After Huyghens’s time, when Iceland spar and rock crystal were alone supposed to have the property of double refraction, mineralogists had suspected the same property to exist in a number of other crystals, though it was often almost impossible to determine its existence. But Arago discovered that a plate of any doubly refracting crystal, such as selenite or mica, when interposed between two similar polarising prisms or piles of glass plates, displays splendid tints, varying in colour with the thickness of the plate and with its inclination to the transmitted beam, and varying in intensity as the plate of mica or selenite is turned round in its own plane. By this simple means double refraction may be detected in the smallest plate of a crystal. The explanation of this remarkable phenomenon was a difficult problem, and for some time perplexed both English and Continental investigators. Dr Young, in 1814, ascribed the cause generally to interference; but Arago saw that this explanation was incomplete. The clue to it was, however, found in the law, established by the joint labours of Arago and Fresnel, that two polarised rays cannot interfere unless polarised in the same or parallel planes. This involved the idea of transverse vibrations of the ether across the direction of propagation, an idea which at first seemed a stumbling-block to the theory of undulations, and which Fresnel and Arago did not venture for some time to embrace. Once expressed, however, this theory of transverse vibrations reduced the whole phenomena of polarisation to a simple mechanical effect, a resolution of rectilinear motion into two rectangular components; and so far from upsetting the wave theory, it has by its very simplicity and comprehensiveness but helped to establish it on a sure foundation.
Arago applied his discovery to the construction of a polariscope, for estimating the feeblest amount of polarisation; and lie used this instrument for some very interesting experiments on the polarisation of the light of the sky (which is sunlight polarised by reflection from the atmosphere), and on that of different incandescent and reflecting surfaces. He also found that the moon and the tails of comets send light to the eye which is slightly polarised, thus betraying its borrowed origin. But that of the sun, being absolutely neutral, is only comparable (according to Arago) to the light arising from incandescent vapours, thus distinguishing the sun from a solid or liquid globe.
We cannot do more than allude to Arago’s other optical papers and experiments. He was, probably, the only Frenchman of his time who was well acquainted with Young’s discoveries. The explanation by the doctrine of interference of the colours of Newton’s rings received an important confirmation from an experiment of Arago’s, which proved them to arise from the mixture of the pencils of light reflected at the two neighbouring surfaces. He pressed a lens of glass against a plate of metal, in which case the central spot is white or black when light polarised perpendicularly to the plane of incidence is reflected at an angle greater or less than the polarising angle for glass; and the rings vanish altogether at the polarising angle — results which Airy subsequently proved conformable to the undulatory theory.
To Arago is also due the discovery of the power of rotatory polarisation exhibited by quartz. He found that a beam of polarised light transmitted along the axis of a crystal of quartz becomes depolarised, and produces colours varying with the thickness of the crystal. If the polarised light be homogeneous, and the analysing plate be placed athwart this polarised beam so as to reflect none of it, the interposing of a quartz crystal will turn round the polarised beam in its passage, so that when it falls on the analysing plate it is no longer athwart it, and the light is partly reflected. The researches in this field were taken up by Biot, Fresnel, Herschel, Seebeck, Airy, and others; and the phenomenon was first explained by Airy to be due to the fact that along the axis of a quartz crystal the beam consists of two circularly polarised portions, while in other directions it consists of two elliptically polarised portions. In some substances the rotation is to the right hand, and in others to the left.
Last of all, among the many contributions of Arago to the support of the undulatory hypothesis, comes the experimentum crucis which he proposed to carry out for comparing directly the velocity of light in air and in water or 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. Wheatstone’s experiment, in 1835, of measuring the velocity of the electric discharge had suggested the idea to Arago; and in 1838 he communicated to the Academy the details of his apparatus. Owing to the great care required in the carrying out of the project, and to the interruptions to his labours by the events of the revolution, it was the spring of 1850 before he was ready to put his idea to the test. But, as fate would have it, just at that time his eye-sight suddenly gave way. With a melancholy resignation he consoled himseif with having merely laid down the problem and having indicated the means of its solution, and with the hope that other experimenters would follow in his steps and add a new proof in favour of the undulatory system. Arago lived to see his wishes realised in the beautiful experiments of Fizeau and Foucault, which, with improvements of detail in the apparatus, were based on the plan proposed by him. These, as all the scientific world knows, confirmed the deductions from the wave theory, and established the retardation of the velocity of light in denser media. With this ended those brilliant labours which have in no small degree contributed to render the arguments in favour of the undulatory doctrine all but unanswerable,
Arago’s Oeuvres were published after his death under the direction of Μ. J. A. Barral, in 17 vols., 8vo, 1854 to 1862; also separately his Astronomie populaire, in 4 vols.; Notices biographiques, in 3 vols.; Notices scientifiques, in 5 vols.; Voyages scientifiques, 1 vol.; Mémoires scientifiques, in 2 vols.; Mélanges (Miscellanies), in 1 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 by Smyth and Grant, London, 1861; Hist, éloge of James Watt, by James Muirhead, London, 1839; also translated, with notes, by Lord Brougham; Popular Lectures on Astronomy, by Walter Kelly and Rev. L. Tomlinson, London, 1854; also translated by Dr W. H. Smyth and Prof. R. Grant, 2 vols., London, 1855; Arago's Autobiography, translated by the Rev. Baden Powell, London, 1855, 1858; Arago’s Meteorological Essays, with introduction by Humboldt, translated under the superintendence of Colonel Sabine, London, 1855; and Arago's Biographies of Scientific Men, translated by Smyth, Powell, and Grant, 8vo, London, 1857.
