Né à Lusigny en 1816, fils d'un géomètre Jacques Delaunay. Mort noyé à Cherbourg le 5 août 1872.
Après avoir achevé de brillantes études au collège de Troyes, il intégra en major l'école polytechnique d'où il sortit le premier en 1836. Il fut nommé ingénieur des mines, professeur à la faculté des sciences membre de l'Institut, directeur de l'Observatoire de Paris. Son oeuvre "Théorie du mouvement de la lune" eut un grand retentissement dans toute l'Europe. Lors d'une visite de la digue de Cherbourg, son embarcadation chavira et il se noya. Son corps fut transporté à Ramerupt où sa famille vivait après l'année 1818.
Bigraphie publiée dans "Histoire de département de l'Aube" par C. Dodey, inspecteur primaire, officier d'Académie chez Gustave Guérin Paris 1891.
Une biographie plus complète est due à deux auteurs anglais.
Charles Delaunay came from a family of modest
means. His father was Jacques Hubert Delaunay, a surveyor, and his
mother was Catherine Choiselat, the daughter of a farmer. Charles was
very close to his mother as a young child and remained so throughout his
life. In 1818, when Charles was two years old, his father acquired the
office of a bailiff in Ramerupt, which is about 20 km north east of
Troyes. When he was still young Charles was sent to Troyes to live with
one of his uncles who was a manual worker. He attended secondary school
in Troyes and showed great promise both at school, where he excelled in
mathematics, and with his hobby of making mechanical devices. He went to
Paris in 1833 and in the following year he entered the École
Polytechnique, being ranked second from all the students entering in
that year. When Delaunay graduated in 1836 he was ranked first among all
students across all academic disciplines.
Mme la Marquise de Laplace donated a new annual prize, the Laplace
Prize, to be given to the student who was ranked top in his year at the
École Polytechnique. Delaunay had graduated before the prize was
instituted but Mme de Laplace requested that he become the first
recipient of the prize which consisted of the complete works of Laplace. It turned out to be a decision which changed the course of Delaunay's career, for reading Laplace's
great works gave him a passion for celestial mechanics and he decided
that he would make a career in that subject. Mme la Marquise de Laplace
was delighted with the first winner of the prize and she called him "her
eldest son". Arago suggested to Delaunay that he come to the Paris Observatory and train to become an astronomer but Savary advised against this course of action. Delaunay then entered the École des Mines and trained as an engineer.
For his doctoral dissertation Delaunay undertook research on the
calculus of variations and was awarded his doctorate for his thesis De la distinction des maxima et des minima dans les questions qui dépendent de la méthode des variations in 1841. He published his first paper on astronomy submitting Note sur la précession des équinoxes to the Academy of Sciences in the same year. Biot
chose him, later in 1841, to substitute for him at the Sorbonne in
giving the course in physical astronomy. On the one hand Delaunay gained
excellent experience teaching at the Sorbonne, but he was still
enrolled as a student at the École des Mines and he had to take an extra
year to complete his studies there as a consequence. He completed his
studies and qualified as an engineer in 1843.
Delaunay published further papers on astronomy, publishing several
papers on perturbations of Uranus in 1842 and 1843 and after this his
first work on the theory of tides. He was already working on his lunar
theory by this time and published Mémoire sur une Méthode nouvelle pour la détermination du mouvement de la Lune
in 1846. This paper contains what today is known as 'Delaunay's
method' although several of his later papers contain generalisations of
the method as it first appeared here. Among his other works were Cours élémentaire de mécanique (1850) and Traité de mécanique rationnelle (1856), and Cours élémentaire d'astronomie
(1853). We should also note that when observations of the Moon's orbit
showed that it was deviating from its theoretical path, Delaunay
correctly suggested in 1865 that this could be due to the rotational
period of the earth slowing due to tidal friction. He pubilished his
theory in Ralentissement de la rotation de la terre (1866). We mention also his report on the progress of astronomy Rapport sur les progrès de l'astronomie (1867).
From 1845 to 1850 he taught courses at the École des Mines; these were
descriptive geometry, stereotomy, mechanical drawing, analytical
mechanics, and elementary physics. He suffered a great tragedy in 1849
when his young wife died and it was largely due to Liouville's
efforts to support him at this time that he was able to continue with
his academic work. He taught mechanics at the École Polytechnique from
1850 being named Professor of Mechanics there in 1851. He also held a
chair of mechanics at the Sorbonne from 1850. In 1855 Delaunay was
elected to the Astronomy Section of the Academy of Sciences.
He continued his association with the École des mines, being named
Engineer in Chief in 1858, then being raised to Engineer First Class in
1867. He published, in 1860 and 1867, two volumes on lunar theory La Théorie du mouvement de la lune which contained the results of twenty years work. Of course the theory of the moon is an important case of the three body problem. Delaunay found the longitude, latitude and parallax
of the Moon as infinite series. These gave results correct to 1 second
of arc but were not too practical as the series converged slowly.
However this work was important in that it contained the beginnings of functional analysis. From 1862 he was a member of the Bureau des Longitudes.
We should mention the rivalry between Delaunay and Le Verrier. This evolved into a full scale argument and around 1860 it was most certainly a very public argument. We should remark that Le Verrier was a difficult man and fell out with many of his colleagues. Le Verrier
was the Director of the Paris Observatory and by 1869 he had become
very unpopular with his colleagues at the Observatory following his
drive for efficiency. Attempts were being made to have him removed which
were eventually successful. He was dismissed from his post as Director
and in March 1870 Delaunay was appointed to the post to succeed his
rival. However Delaunay's appointment came only weeks before France
declared war on Prussia.
The popularity of Napoleon III, the French emperor, had declined and he
decided that a war with Prussia might change his political fortunes. His
advisers had told him that the French Army could defeat Prussia with
ease, so the plan looked like a winner. Bismarck, the Prussian
chancellor, saw a war with France as an opportunity to unite the South
German states so he too saw the political advantage of war. With both
sides actively seeking a war, the Franco-Prussian War became inevitable.
On 14 July 1870, Bismarck sent a telegram aimed at infuriating the
French government. He succeeded, for on the 19 July France declared war
on Prussia. The German offensive met with only an ineffective French
reply. In August, the German army trapped part of the French army in
Metz and they surrendered on 1 September. On 19 September the German
army began to blockade Paris which surrendered on 28 January 1871. This
was a time of extreme difficulty for Delaunay who succeeded against all
the odds to save the Paris Observatory. The French government was
threatened by an uprising in Paris in March 1871, in which radicals
established their own short-lived government, the Paris Commune. The
Commune was suppressed after two months of bitter fighting during which
time Delaunay had an equally difficult task keeping the Observatory safe
from the riots and fighting in the city. He largely succeeded but the
Observatory did sustain some damage.
In 1872 Delaunay and three companions drowned in a boating accident when
the boat they were in capsized following a gust of wind.
1 commentaire:
Quelle fin bête !Mais quel destin!
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