TISSERAND, FRANcOIS FELIX ( 1845 96) . A French astronomer, born at Nuits-Saint Georges, Ctite-d'Or. In 1863 he entered the Ecole Normale Superieure. In 1806 he became pro fessor in the lycee at Metz, where he only re mained one month, being called by Leverrier to the Paris Observatory as adjunct astronomer. He received his doctor's degree in 1868, presenting a very remarkable thesis on the method of Delammy, which lie showed to he applicable to the calculation of the inequalities of all the planets and thus of a wider application than had been supposed by the inventor. In 1873 he became director of the observatory at Toulouse and professor of astronomy in the Faculty of Sciences in the university. In 187S he succeeded Leverrier as member of the Academy of Sciences and became member of the Bureau des Longi tudes. In the same year he was appointed pro fessor of rational mechanics at the Sorbonne, which he later exchanged for the chair of celestial mechanics. In 1892 he succeeded Mouchez as Erector of the Paris Observatory.
13esides the generalization of the method of Delaunay which he continued till his death, he made observations for the determination of planetary orbits, on the ring of ,Saturn, on the perturbations of Pallas, the origin of eomets and their ea pture by the larger planets, and gave also a valuable criterion for identifying a pe riodic comet. He also observed the shifting of
the orbital plane of Neptune's satellite as a re sult of Neptune's ellipsoidal shape. In conse quence of this shifting of orbit, the retrograde motion of the pole of the satellite completes a cycle in 500 years. His principal work, Traits: de mecanique celeste (1889.96), gives a complete aceount of the state of knowledge of that branch of astronomy up to the time of his death. Since 1884 he edited the Bulletin astronomique. His other writings include: Rccucil d'exereises sat le calcul infinitesimal (1876; 2d ed. 1S96). Con sult Poinear, "La vie et les travaux de serand." in Rcrue generale des sciences for 1896.