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SIMEON DENIS POISSON (1781-1840)

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Originally appearing in Volume V21, Page 897 of the 1911 Encyclopedia Britannica.
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SIMEON See also:DENIS See also:POISSON (1781-1840)  , See also:French mathematician, was See also:born at See also:Pithiviers in the See also:department of Loiret, on the 21st of See also:June 1781 . His See also:father, See also:Simeon See also:Poisson, served as a See also:common soldier in the Hanoverian See also:wars; but, disgusted by the See also:ill-treatment he received from his patrician See also:officers, he deserted . About the See also:time of the See also:birth of his son, Simeon See also:Denis, he occupied a small administrative See also:post at Pithiviers, and seems to have been at the See also:head of the See also:local See also:government of the See also:place during the revolutionary See also:period . Poisson was first sent to an See also:uncle, a surgeon at See also:Fontainebleau, and began to take lessons in bleeding and blistering, but made little progress . Having given promise of mathematical See also:talent he was sent to the Ecole Centrale of Fontainebleau, and was fortunate in having a See also:kind and sympathetic teacher, M . Billy, who, when he speedily found that his See also:pupil was becoming his See also:master, devoted himself to the study of higher See also:mathematics in See also:order to follow and appreciate him, and predicted his future fame by the punning See also:quotation from See also:Lafontaine': " See also:Petit Poisson deviendra See also:grand Pourvu que Dieu lui prete See also:vie." In 1798 he entered the )r tole Polytechnique at See also:Paris as first in his See also:year, and immediately began to attract the See also:notice of the professors of the school, who See also:left him See also:free to follow the studies of his predilection . In "Soo, less than two years after his entry, he published two See also:memoirs, one on E . Bezout's method of elimination, the other on the number of integrals of an See also:equation of finite See also:differences . The latter of these memoirs was examined by S . F . See also:Lacroix and A . M .

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Legendre, who recommended that it should be published in the Recueil See also:des savants etrangers, an unparalleled See also:honour for a youth of eighteen . This success at once procured for Poisson an entry into scientific circles . J . L . See also:Lagrange, whose lectures on the theory of functions he attended at the )tole Polytechnique, See also:early recognized his talent, and became his friend; while P . S . See also:Laplace, in whose footsteps Poisson followed, regarded him almost as his son . The See also:rest of his career, till his See also:death on the 25th of See also:April r84o, was almost entirely occupied in the See also:composition and publication of his many See also:works, and in discharging the duties of the numerous educational offices to which he was successively appointed . Immediately after See also:finishing his course at the Ecole Polytechnique he was appointed repetiteur there, an See also:office which he See also:bad discharged as an See also:amateur while still a pupil in the school; for it had been the See also:custom of his comrades often to resort to his See also:room after an unusually difficult lecture to hear him repeat and explain it . He was made professeur suppleant in 18o2, and full See also:professor in See also:succession to J . See also:Fourier in 18o6 . In 18o8 he became astronomer to the See also:Bureau des Longitudes; and when the Faculte des Sciences was instituted in a809 he was appointed professeur de in mecanique rationelle .

He further became member of the See also:

Institute in 1812, examiner at the military school at St Cyr in 1815, leaving examiner at the )/tole Polytechnique in 1816, councillor of the university in 182o, and geometer to the Bureau des Longitudes in succession to P . S . Laplace in 1827 . His father, whose early experiences led him to hate aristocrats, bred him in the stern creed of the first See also:republic . Throughout the See also:empire Poisson faithfully adhered to the See also:family principles, and refused to See also:worship See also:Napoleon . When the Bourbons were restored, his hatred against Napoleon led him to become a Legitimist—a conclusion which says more for the simplicity of his See also:character than for the strength or See also:logic of his See also:political creed . He was faithful to the Bourbons during the See also:Hundred Days; in fact, was t This prediction is sometimes attributed to Laplace.with difficulty dissuaded from volunteering to fight in their cause . After the second restoration his fidelity was recognized by his See also:elevation to the dignity of See also:baron in 1825; but he never either took out his diploma or used the See also:title . The revolution of See also:July 183o threatened him with the loss of all his honours; but this disgrace to the government of See also:Louis Philippe was adroitly averted by F . See also:Arago, who, while his " revocation " was being plotted by the See also:council of ministers, procured him an invitation to dine at the Palais Royale, where he was openly and effusively received by the See also:citizen See also:king, who " remembered" him . After this, of course, his degradation was impossible, and seven years later he was made a peer of See also:France, not for political reasons, but as a representative of French See also:science . As a teacher of mathematics Poisson is said to have been more than ordinarily successful, as might have been expected from his early promise as a repetiteur at the Ecole Polytechnique .

As a scientific worker his activity has rarely if ever been equalled . Notwithstanding his many See also:

official duties, he found time to publish more than three hundred works, several of them extensive See also:treatises, and many of them memoirs dealing with the most abstruse branches of pure and applied mathematics . There are two remarks of his, or perhaps two versions of the same remark, that explain how he accomplished so much: one, " La vie n'est bonne qu'a deux choses—a faire des mathematiques et a See also:les professeur; " the other, " La vie c'est le travail." A See also:list of Poisson's works, See also:drawn up by himself, is given at the end of Arago's See also:biography . A lengthened See also:analysis of them would be out of place here, and all that is possible is a brief mention of the more important . There are few branches of mathematics to which he did not contribute something, but it was in the application of mathematics to See also:physical subjects that his greatest services to science were performed . Perhaps the most See also:original, and certainly the most permanent in their See also:influence, were his memoirs on the theory of See also:electricity and See also:magnetism, which virtually created a new See also:branch of mathematical physics . Next (perhaps in the See also:opinion of some first) in importance stand the memoirs on See also:celestial See also:mechanics, in which he proved himself a worthy successor to P . S . Laplace . The most important of these are his memoirs " Sur les inegalites seculaires des moyens mouvements des planetes," " Sur la variation des constantes arbitraires daps les questions de mecanique," both published in the See also:Journal of the hcole Polytechnique (18o9) ; " Sur la See also:libration de la tune," in Connaiss. d. temps (1821), &c . ; and " Sur la mouvement de la terre autour de son centre de gravite," in Mem. d. l'acad . (1827), &c .

Phoenix-squares

In the first of these memoirs Poisson discusses the famous question of the stability of the planetary orbits, which had already been settled by Lagrange to the first degree of approximation for the disturbing forces . Poisson showed that the result could be extended to a second approximation, and thus made an important advance in the planetary theory . The memoir is remarkable inasmuch as it roused Lagrange, after an See also:

interval of inactivity, to compose in his old See also:age one of the greatest of his memoirs, viz. that Sur la theorie des See also:variations des elements des planetes, et en particulier des variations des grands axes de leurs orbites . So highly did he think of Poisson's memoir that he made a copy of it with his own See also:hand, which was found among his papers after his death . Poisson made important contributions to the theory of attraction . His well-known correction of Laplace's partial See also:differential equation for the potential was first published In the Bulletin de in societe philomatique (1813) . His two most important memoirs on the subject are " Sur ?'attraction des spheroides " (Connaiss. d. temps, 1829), and " Sur ?'attraction d'un ellipsoide homogene " (Mem. d. l'acad., 1835) . In concluding our selection from his physical memoirs we may mention his memoir on the theory of waves (Mem. d. l'acad., 1825) . In pure mathematics, his most important works were his See also:series of memoirs on definite integrals, and his discussion of Fourier's series, which paved the way for the classical researches of L . Dirichlet and B . See also:Riemann on the same subject; these are to be found in the Journal of the ?cote Polytechnique from 1813 to 1823, and in the Memoirs de l'academie for 1823 . In addition we may also mention his See also:essay on the calculus of variations (Mem. d. l'acad., 1833), and his memoirs on the See also:probability of the mean results of observations (Connaiss. d. temps, 1827, &e.) .

Besides his many memoirs Poisson published a number of treatises, most of which were intended to See also:

form See also:part of a See also:great See also:work on mathematical physics, which he did not live to See also:complete . Among these may be mentioned his Traite de mecanique (2 vols . 8vo, 1811 and 1833), which was See also:long a See also:standard work; Theorie nouvelle de l'See also:action cappillaire (4to, 1831) ; Theorie mathematique de la chaleur (4to, 1835) Supplement to the same (4to, 1837) ; Recherches sur la probabilite des jugements en matibres criminelles, &c . (4to,1837), all published at Paris . See F . Arago, Biographie de Poisson, read before the Academie des Sciences on the 16th of See also:December 1850 . See also:Poitou, and now the See also:chief See also:town of the department of See also:Vienne, 61 m . S.S.W. of See also:Tours on the railway to See also:Bordeaux . Pop . (1906), town, 31,532; See also:commune, 39,302 . See also:Poitiers is situated at the junction of the Boivre with the Clain (a tributary of the See also:Loire by the Vienne), and occupies the slopes and See also:summit of a See also:plateau which rises 130 ft. above the level of the streams by which it is surrounded on three sides . The town is picturesque; and its streets are interesting for their remains of See also:ancient See also:architecture, especially of the Romanesque period, and the memories of great See also:historical events .

Blossac See also:

park, named after the See also:intendant of the " generality " of Poitiers (1751-1786), and situated on the See also:south See also:side of the town, and the botanical See also:garden on the See also:north-See also:east, are the two See also:principal promenades . Till 1857 Poitiers contained the ruins of a See also:Roman See also:amphitheatre more extensive than that of See also:Nimes; remains of Roman See also:baths, constructed in the 1st and demolished in the 3rd See also:century, were laid See also:bare in 1877; and in 1879 a See also:burial-place and the tombs of a number of See also:Christian martyrs were discovered on the heights to the south-east—the names of some of the Christians being preserved in paintings and See also:inscriptions . Not far from these tombs is a huge dolmen (the " See also:Pierre See also:Levee "), 22 ft. long, 16 ft. broad and 6 or 7 ft. high, around which used to be held the great See also:fair of St See also:Luke . The See also:cathedral of St See also:Peter, begun in 1162 by See also:Henry II. of See also:England and Eleanor of See also:Guienne on the ruins of a Roman See also:basilica, and well advanced by the end of the 12th century, is a See also:building in the Romanesque and Early See also:Gothic See also:style, the latter predominating . It consists of three naves almost equal in height and width, both of which decrease towards the See also:west, thus enhancing the See also:perspective . Its length is 308 ft., and the See also:keystone of the central vaulted roof is 89 ft. above the See also:pavement . There is no See also:apse, and the exterior generally has a heavy See also:appearance . The principal front, the width of which is excessive in See also:pro-portion to its height, has unfinished side-towers 105 and See also:Ito ft. in height, begun in the 13th century . Most of the windows of the See also:choir and the transepts preserve their stained See also:glass of the 12th and 13th centuries; the end window, which is certainly the first in the order of time, contains the figures of Henry II. and Eleanor . The choir stalls, carved between 1235 and 1257, are among the See also:oldest in France . The See also:church of St See also:Jean near the cathedral is the most ancient Christian See also:monument in the See also:country . Built as a See also:baptistery in the first See also:half of the 4th century, it was enlarged in the 7th century, since when it has suffered little structural alteration .

It contains frescoes of the 12th century and a collection of tombs of the Merovingian period . The church of St Hilaire was erected at the See also:

close of the 4th century over the See also:tomb of the celebrated See also:bishop . At first an See also:oratory, it was rebuilt on a larger See also:scale by See also:Clovis, and after-wards became, in the loth, nth and 12th centuries, a sumptuous collegiate church, of which the See also:nave was flanked by triple aisles and surmounted by six cupolas . Great damage was done to it in the Wars of See also:Religion and the French Revolution, and the See also:facade was entirely rebuilt in the 19th century . The See also:confessional or oratory under the choir contains the See also:relics of St Hilary and a Christian See also:sarcophagus of the 4th century . The church of St Radegonde, a ,great resort of pilgrims, commemorates the See also:consort of See also:Clotaire (d . 587), and preserves in its See also:crypt the tomb of Radegonde, who founded at Poitiers the See also:abbey of the See also:Holy See also:Cross, and two others reputed to be those of St See also:Agnes and St Disciola . The choir and See also:tower above the entrance are of the 11th century, while the nave (See also:late 12th century) is in the Angevin style . In a See also:recess in the nave known as the Chapelle du Pas de Dieu, there is a footprint which tradition asserts to be that of See also:Christ, who appeared in a See also:vision to St Radegonde . Notre-See also:Dame la Grande, which See also:dates from the close of the i ith century, and represents a collegiate church of one or two hundred years older, has a sculptured Romanesque facade rivalled in richness only by that of St Pierre of See also:Angouleme .

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