1911 Encyclopædia Britannica/Tisserand, François Félix

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TISSERAND, FRANÇOIS FELIX (1845–1896), French astronomer, was born at Nuits-Saint-Georges, Cote-d'Or, on the 13th of January 1845. In 1863 he entered the École Normale Supérieure, and on leaving he went for a month as professor at the lycée at Metz. Le Verrier offered him a post in the Paris Observatory, which he accordingly entered as astronomer adjoint in September 1866. In 1868 he took his doctor's degree with a brilliant thesis on Delaunay's Method, which he showed to be of much wider scope than had been contemplated by its inventor. Shortly afterwards he went out to Malacca to observe the famous solar eclipse of the 18th of August 1868. In 1873 he was appointed director of the observatory at Toulouse, whence he published his Recueil d'exercises sur le calcul infinitésimal, and in 1874 became corresponding member of the Académie des Sciences. He took part in the French expeditions of 1874 to Japan, and in 1882 to Martinique to observe the transits of Venus. In 1878 he was elected a member of the Académie des Sciences in succession to Le Verrier, and became a member of the Bureau des Longitudes. In the same year he was appointed professeur suppléant to Liouville, and in 1883 he succeeded Puiseux in the chair of celestial mechanics at the Sorbonne. Tisserand always found time to continue his important researches in mathematical astronomy, and the pages of the Comples rendus bear witness to his surprising activity. His writings relate to almost every branch of celestial mechanics, and are always distinguished by rigour and simplicity in the solution of the most difficult problems. He treated in a masterly manner (Bulletin astronomique, 1889) the theory of the capture of comets by the larger planets, and in this connexion published his valuable Criterion for establishing the identity of a periodic comet, whatever may have been the perturbations brought about in its orbit, between successive appearances, by the action of a planet. His principal work, Traité de mécanique céleste, is the noblest and most lasting monument to his memory, and is worthy to stand beside the Mécaniqne céleste of his fellow-Countryman, Laplace. In this treatise, published in four quarto volumes, the last of which appeared only a few months before his death, he fused into one harmonious whole the researches of Laplace and those of other workers in the same field since his time. It furnishes a faithful and complete résumé of the state of knowledge in that department of astronomy at the end, as Laplace's great work did for the beginning, of the 19th century. In 1892 he succeeded Mouchez as director of the Paris Observatory, and as president of the committee of the photographic chart of the heavens he contributed largely to the success of that great project. Under his direction the revision of Lalande's catalogue was brought almost to completion, and four volumes of the Annales de l'Observatoire de Paris exhibit the progress made in this important undertaking. He was also editor of the Bulletin astronomique from the beginning, and contributed many important articles to its pages. He died suddenly, in the fullness of his power, of congestion of the brain, on the 20th of October 1896. (A. A. R.)