Rayet, Georges Antoine Pons
RAYET, GEORGES ANTOINE PONS
(b. Bordeaux, France, 12 December 1839; d. Floirac, near Bordeaux, 14 June 1906)
Rayet’s family belonged to the Bordeaux upper middle class. His father, a magistrate removed from office in 1830 because of his Legitimist views, worked in the wine industry in Bordeaux and then, beginning in 1853, in Paris. It was not until the latter year that Rayet went to school, but his studies did not suffer from this delay: he was admitted to the École Normale Supérieure in 1859 and graduated agrégé in physics three years later. After teaching for a year at the lycée in Orléans, he obtained a post as physicist, in the weather forecasting service newly created by Le Verrier, at the Paris observatory.
In addition to his regular work Rayet engaged in astronomical studies, participating in the research of Charles Wolf, an astronomer at the observatory. Their first joint success came in 1865, when they photographed the penumbra of the moon during an eclipse. In the meantime they had improved spectroscopic techniques and had sought to obtain the spectra of bright comets. A nova appeared on 4 May 1866. Observing it on 20 May, when its brilliance was considerably diminished, Rayet and Wolf detected bright bands in the spectrum, a phenomenon that had never been noticed in star spectra. The bands were the result of a phase that can occur in the evolution of a nova after the explosion and is now known as the Wolf-Rayet stage.
The two astronomers next attempted to determine, through systematic investigation, whether permanently bright stars exhibit the same phenomenon, and in 1867 they discovered three such stars in the constellation Cygnus. “Wolf-Rayet stars,” the spectra of which contain broad, intense emission lines, are rare—barely more than 100 are known. They are very hot stars the mechanism of which has not yet been explained. The expansion of the shell is not sufficient to account for the width of the lines, and there is a great disparity between the energy produced in the interior and the radiated energy. These stars permit the study of interstellar matter, the lines of which stand out against the bright background of the broad emission lines of the stars.
In 1868 Rayet participated in the mission sent by the Paris observatory to the Malay Peninsula to observe a solar eclipse; he was responsible for the spectroscopic work. His observations on the solar prominences provided valuable information, and in conjunction with other observations made during the same eclipse, notably those of J. Janssen, they contributed to the establishment of the first precise data on the sun. Rayet then concentrated on spectroscopic observations of the solar atmosphere and of solar prominences. He identified the brilliant lines of their spectrum with the spectral lines of the elements and developed a theory of the physical constitution of the sun that, at least in its descriptive portion, contains material found in modern theories. This work formed the basis of his doctoral dissertation, which he defended in 1871.
Rayet had no serious disagreement with Le Verrier until the latter entrusted him with running the meteorological service in 1873. Within less than a year Rayet’s opposition to the practical organization of the forecasting of storms—which he had good reason for judging to be premature—led to his dismissal. Rayet then became lecturer in physics at the Faculty of Sciences of Marseilles and in 1876 was appointed professor of astronomy at Bordeaux.
In 1871 the French government proposed to construct several new observatories. Rayet organized a collective survey of the history and equipment of the principal observatories in the world. With collaborators, he wrote three of the five volumes of the study. Rayet took a great interest in the history of science and wrote short, authoritative studies on Greek sundials (1875) and the history of astronomical photography (1887).
Along with his appointment to Bordeaux, Rayet was also designated director of the observatory to be built at Floirac in 1878. He held the post from 1879 and equipped the observatory with the most modern astrometric instruments. Rayet was one of the first supporters of the Carte international photographique du ciel. In 1900 he made an important contribution to the problem of the reduction of photographic plates. Rayet had the satisfaction of being able to publish, a year before his death, the first volume of the Catalogue photographique of the Bordeaux observatory.
Rayet became a corresponding member of the Académie des Sciences in 1892 and of the Bureau des Longitudes in 1904. He had a sophisticated conception of scientific research and appreciated the advantages of teamwork. He worked thus himself but gave his subordinates great freedom to take initiatives. He died from the effects of a serious lung disease that troubled him during his last years. Possessed of a great firmness of character, Rayet, despite the state of his health, took part in the expedition to Spain to observe the eclipse of August 1905.
I. Original Works. Rayet’s most notable early works are a note on the spectroscopic observation of the nova of 1866, inserted in U. J. J. Le Verrier, “Note sur deux étoiles …,” in Comptes rendus ,… de l’Académie des Sciences, 62 (1866), 1108–1109, written then with C. Wolf; the announcement of the discovery of the Wolf-Rayet stars, in “Spectroscopic stellaire,” ibid.,65 (1867), 292–296, written with C Wolf; and “Sur les raies brillantes du spectre de l’atmosphére solaire et sur la constitution physique du soleil,” in Annales de chimie et de physique, 4th ser., 24 (1871), 5–80.
Rayet’s meteorological observations and astronomical observations (spectroscopy, astrometry, eclipses) are contained in about thirty notes in the Comptes rendus … de l’Académie des sciences between 1866 and 1905. Rayet presented an important analysis of the evolution of the magnetic declination and inclination at Paris between 1667 and 1872 in “Recherches sur les observations magnétiques …,” in Annales de l’Observatoire de Paris. Mémoires, 13 (1876), A*l-A*140. On photographic astrometry, see “Instructions pour la réduction des clichés photographiques …,” in Annales de l’Observatoire’de Bordeaux, 9 (1900), I 87; and Catalogue photographique du del, Observatoire de Bordeaux, I (Paris, 1905).
Rayet created the Annales de observatoire de Bordeaux in 1885 and edited the first 12 vols.; his studies on the observatory’s longitude, on its latitude, and on practical astronomy are contained, respectively, in vols. 1, 2 , and 3 ; his climatological studies, in vols. 6 and 10 ; and vol. 13 contains a posthumous article on the eclipse of 1905.
His works on the history of science are “Cadrans solaires coniques,” in Annales de chimie et de physique, 5th ser., 6 (1875), 52–85; L’astronomic et les observatoires. I, Angleterre, and II, Écosse, Irlande et colonies anglaises, written with C. André (Paris, 1874); and V, Italic (Paris, 1878); “Notice historique sur la fondation de l’Observatoire de Bordeaux,” in Annates de l’Observatoire de Bordeaux, 1 (1885), 1–62; and “Histoire de la photographic astronomique,” ibid, 3 (1889), 41–99, previously pub, in 5 pts, in Bulletin astronomique, 4 (1887), 165–176, 262–272, 307–320, 344–360, 449–456.
II. Secondary Literature. A biography and a list of Rayet’s publications are given by E. Stephan in Annates de l’Observatoire de Bordeaux, 13 (1907), A1-A31; it is followed by “Discours prononcés aux obséques,” B1-B31. See also “Obséques de M. Rayet,” in Bulletin astronomique, 23 (1906), 273–285; E. Esclangon, “Nécrologie,” in Astronomische Nachrichten, 172 (1906), 111; and W. E. P., “Obituary,” in Nature, 74 (1906), 382.
Jacques R. LÉvy