Fabry, Louis

(b. Marseilles, France, 20 April 1862; d. Les Lecques, near Toulon, France, 26 January 1939)

astronomy, applied celestial mechanics.

Fabry, the older brother of the physicist Charles Fabry, was admitted to the École Polytechnique in 1880. He obtained his licence èes sciences at the Faculté de Marseille in 1883 and the following year was accepted in the school of practical astronomy recently created at the Observatoire de Paris. During his course of study, while prating on the équatorial coudé that had just been placed in use, he had the extraordinary luck of discovering a comet.

The origin of these heavenly bodies was then much discussed—the existence of comets with hyperbolic orbits made it possible to hold the opinion that they originiated outside of the solar system. Fabry, in his doctoral thesis in 1893, proved by statistical methods that this hypothesis was not compatible with the distribution presented by the elements of the orbits. He established in particular that the distribution of motions does not yield the dissymmetry that the motion of the sun would introduce if the comets came from infinity.

The subject, however, was not exhausted. Why, in fact, are certain orbits hyperbolic? To solve this problem, the Académie des Sciences posed it as a competition. The prize was shared by Fabry and one of his colleagues, Gaston Fayet; both showed that the orbits known as hyperbolic had become so by the action of planetary perturbations— all of them were originally elliptical.

The observation of the minor planets and the elaboration of rapid methods for identifying them and for calculating and improving their ephemerides constitute, along with his researches on the comets, the essential portion of Fabry’ work. He was of that generation of astronomers who strove to cultivate observations for the use of their successors; he lived in a period in which new technology served observation, while the means of calculation were practically nonexistent.

Fabry was named in 1886 to the Observatoire de Nice and then in 1890 to that of Marseilles, where he remained until his retirement in 1925. He was elected a corresponding member of the Académie des Sciences in 1919.

BIBLIOGRAPHY

I. Orginal Works. Fabry’s principle works on comets are “Décourverte d’une comète à l— Observatiore de Paris,” in Competes rends hebdomadaires des séances de l—Académie des Sciences101 (1885), 1121–1125; “Sur le calcul du grand axe des orbits cométaires” in Bulletin astronomique11 (1894), 485–488; “Études sur la probabilité des comètes hyperboliques et l’origine des comèts,” his doctoral thesis of 1893, in Annals de Faculté des Sciences de Marseilles4 (1895), 1–214; and “Sur la véritable valeur du grand axe d’ une orbite cométare” in Comptes rends hebdomadaries des séances de l’Académie des Sciences138 (1904), 335–337.

His writings on the minor planets are “Tables numėriques destinées à faciliter le calcul des éphémérides” in Bulletin astronomique, 2 (1885), 453–463; “Procédé abrégé pour rectifier les éphémérides,” ibid., 20 (1903), 243–250; “L’identification des petites planètes,” ibid., 30 (1913), 49–64; “Sur la rectification des orbites des planétes,” ibid., 31 (1914), 68–79; “Sur l’emploi des latitudes géocentriques or faciliter l’identification des petités planètes,” in Comptes rendus hebdomadaires des séances de l’Académie des Sciences, 172 (1921), 27–31; and “Nouvelles formules pour le calcul de la ligne de recherche,” ibid., 173 (1921), 92–894.

His observations, as well as the numerous orbits of minor plantes that he determined, were generally published in Bulletin astronomique, beginning in 1885. His seismological writings appeared in Comptes rendus hebdomadaires des śances de l’Academe des sciénces, 149–152 (1909–1911).

II. Secondary Literature. On Fabry’s life and work see G. Fayet, “Notice nécrologique sur L. Fabry,” in comptes rendus hebdomadaires des seances de l’Academie sciences, 208 (1939), 545–547.

Jacques R. LÉvy