Beyond the introduction of the spider line it is unnecessary to mention the various steps by which the Gascoigne micrometer assumed the modern forms now in use, or to describe in detail the suggestions of Hooke, 4 Wren, Smeaton, Cassini, Bradley, Maskelyne, Herschel, Arago, Pearson, Bessel, Struve, Dawes, &c., or the successive productions of the great artists Ramsden, Troughton, Fraunhofer, Ertel, Simms, Cooke, Grubb, Clarke and Repsold.
Arago, with whom he had already carried out investigations on the refractive properties of different gases, in the measurement of an arc of the meridian in Spain, and in subsequent years he was engaged in various other geodetic determinations.
Arago 8 succeeded in magnetizing a piece of iron by the electric current, and in 1825 W.
By a decree of the president he was made a senator of France in 1852, and on the death of Arago (1853) he was chosen perpetual secretary of the Academy of Sciences.
The Exposition du Systeme du monde (Paris, 1796) has been styled by Arago "the Mecanique celeste disembarrassed of its analytical paraphernalia."
Arago, Annuaire du Bureau des Long.
Arago, the index, u for air at t° C. and at atmospheric pressure is given by 00029 iu 1-1 + 0037t.
Reference may also be made to Arago, "Joseph Fourier," in the Smithsonian Report (1871).
Arago made many measures of the diameters of the planets with such a micrometer.
This may be done by the method suggested by Arago in 1828, introduced by Aime in 1841 and again suggested by Glaisher in 1858, of sealing up the whole instrument in a glass tube exhausted of air; or, less effectively, by surrounding the bulb alone with a strong outer sheath of glass.
In 1837 Arago pronounced his eloge before the Academie des Sciences.
Tissot, Memoires historiques et militaires sur Carnot (Paris, 1824); Arago, Biographic de Carnot (Paris, 1850); Hippolyte Carnot, Memoires sur Carnot (Paris, 1863); C. Remond, Notice biographique sur le grand Carnot (Dijon 1880); A.
Arago, Connaissance des temps, 1825).
Notices of his life are contained in the Eloges by Merard de Saint Just, Delisle de Salles, Lalande and Lacretelle; in a memoir by Arago, read the 26th of February 1844 before the Academie des Sciences, and published in Notices biographiques, t.
Arago and A.
Arago, Ouvres (1855); and Silvestre, Notice sur J.
Arago (Ouvres, t.
This remarkable debut excited much attention, and, on the recommendation of Francois Arago, he took in hand the theory of Mercury, producing, in 1843, vastly improved tables of that planet.
Recalled once more, by the summons of Arago, to planetary studies, he was this time invited to turn his attention to Uranus.
After the coup d'Nat of 1851 he became a senator and inspector-general of superior instruction, sat upon the commission for the reform of the Ecole Polytechnique (1854), and, on the 30th of January 1854, succeeded Arago as director of the Paris observatory.
Arago, who, while his "revocation" was being plotted by the council of ministers, procured him an invitation to dine at the Palais Royale, where he was openly and effusively received by the citizen king, who "remembered" him.
Many of them were published in the Annales de chimie, which after it changed its title to Annales de chimie et physique he edited, with Arago, up to nearly the end of his life; but some are to be found in the Memoires d'Arcueil and the Comptes rendus, and in the Recherches physiques et chimiques, published with Thenard in 1811.
In 1830 he published a research, undertaken with Arago for the academy of sciences, on the elastic force of steam at high temperatures.
In 1820 Arago (Ann.
The study of the relation between the magnet and the circuit conveying an electric current then led Arago to the discovery of the " magnetism of rotation."
DOMINIQUE FRANCCOIS JEAN ARAGO (1786-1853), French physicist, was born on the 26th of February 1786, at Estagel, a small village near Perpignan, in the department of the eastern Pyrenees.
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.
The two left Paris in 1806 and began operations among 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, leaving Arago to make the geodetical connexion of Majorca with Ivica and with Formentera.
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.
Transport to Algiers by sea from this place would have occasioned a weary stay of three months; Arago, therefore, set out for it by land under conduct of a Mahommedan priest, and reached it on Christmas day.
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.
Arago was elected a member of 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 extreme republican type, was elected a member of the chamber of deputies for the Lower Seine, and 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.
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.
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.
Arago was now on his death-bed, under a complication of diseases, induced, no doubt, by the hardships and labours of his earlier years.
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.
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.
Arago had previously done on a smaller scale), where he made magnetic observations, and from this same observatory he sent telegraphic signals to the neighbouring town, thus showing the practicability of an electromagnetic telegraph.
Arago he studied the laws.
"All the compliments," he says, "that I have received from Arago, Laplace and Biot never gave me so much pleasure as the discovery of a theoretic truth, or the confirmation of a calculation by experiment."
Xxxix.; Arago, Ouvres completes, t.
Arago, received by general consent the neutral name of Neptune.
Arago showed that at all angles of incidence the reflected and refracted streams contain equal quantities of polarized light.
Arago, 'who summed up the results of a searching series of experiments in the following laws of the interference of polarized light: (r) Under the same conditions in which two streams of common light interfere, two streams polarized at right angles are without mutual influence.
Arago in 1811 found that in the case of white light and with moderately thin plates the transmitted light is no longer white but coloured, a variation of brightness but not of tint being produced when the polarizer and analyser being crossed are rotated together, while the rotation of the analyser alone produces a change of colour, which passes through white into the complementary tint.
This explanation is incomplete, as it leaves out of account the action of the polarizer and analyser, and it was with the purpose of removing this defect that Fresnel and Arago undertook the investigations mentioned above and thus supplied what was wanting in Young's explanation.
Arago pointed out, by supposing that in passing through the plate the plane of polarization of each monochromatic constituent is rotated by an amount dependent upon the frequency - an explanation that may be at once verified either by using monochromatic light or by analysing the light with a spectroscope, the spectrum in the latter case being traversed by one or more dark bands, according to the thickness of the plate, that pass along the spectrum from end to end as the analyser is rotated.
Returning to Paris in 1838, he refused a proffered chair at the College de France, but in 1848, the oath having been suspended, he resumed his post at the Ecole Polytechnique, and when the oath was reinstituted after the coup d'etat of 1851, Cauchy and Arago were exempted from it.