Claude, François Auguste

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Claude, François Auguste

(b. Strasbourg, France, 30 December 1858; d. Paris, France, 15 July 1938),


Although Alsace had been annexed by Germany in 1871, Claude chose French citizenship as soon as he came of age; he immigrated to France and there served in the army. After being released from his military duties, he left his profession of industrial designer, at which he had worked for six years and went to the Bureau des Longitudes on his own initiative.

His entire career was spent at the observatory of the Bureau des Longitudes in the Parc de Montsouris in Paris: he became assistant calculator in 1884, chief calculator in 1898, assistant director in 1910, and director in 1929, which post he held until his death. Four times he was awarded a prize by the Academie des Sciences; nevertheless, since he held no university degrees, he was only an associate member of the Bureau des Longitudes (1906).

He was a gracious and reserved man, who devoted himself in a generous way to improving the techniques used in operations for which the Bureau des Longitudes had responsibility: telephonic and radio-telegraphic transmissions of signals and observations of the passage and altitude of stars. His main contribution was the invention of the prismatic astrolabe (1899).

This instrument is made up of a horizontal telescope with an equilateral prism mounted in front of it. The light rays given off by a star reach the prism, in part directly and in part indirectly by reflection from a basin of mercury, thus providing two images to the telescope. These images coincide at the moment when the altitude of the star reaches 60. Observation of the passage of several stars allows one to determine the geographical coordinates of a certain place.

The first results, published in 1900, led the hydrographer L. Driencourt to collaborate with Claude in the perfection of this instrument and to adapt it to the needs of geodetic engineers. In 1938 A. Danjon built a high-precision instrument called the impersonal astrolabe on the same principle, and it has become one of today’s most important instruments of fundamental astronomy, facilitating the study of the earth’s movement around its center of gravity and the determination of the coordinates of fundamental stars.


I. Original Works. Claude’s most important publications concerning the astrolabe are “Sur l’emploi d’unprisme a reflexion dans les lunettes,” in Bulletin astronomique, 17 (1900), 19–29; “La methode des hauteurs egales en astronomie de position,” in Revue generale des sciences pures et appliquees, 16 (1905), 972–983, written with L. Driencourt; “L’instrument des hauteurs egales ou astrolabe a prisme,” ibid., pp. 1071–1083, with L. Driencourt; and Description et esage de I’ astrolabe a prisme (Paris, 1910), with L. Driencourt.

His principal contributions to the Comptes rendus hebdomadaires des seances de l’Academie des sciences are “Description d’un niveau autocollimateur,” 143 (1906), 394–397, with L. Driencourt; “Comparaisons telephoniques et radiotelegraphiques de signaux…,”150 (1910), 306–309; 151 (1910), 935–938; 152 (1911), 1152–1155, written with L. Driencourt and G. Ferrié, “Lorthostatgmescope, ou instrument pour observer le passage par le zenith de deux etoiles,” 155 (1912), 574–577, with L. Driencourt; “L’astrolabe a prisme type SOM,” 171 (1920), 847–849, with L. Driencourt.

II. Secondary Literature. A historical study of instruments of the astrolabe type was made by E. Chandon and A. Gougenheim, Les instruments pour l’observation des hauteurs egales en astronomie (Paris, 1935). An interesting letter from L. Driencourt to A. Danjon is reproduced by the latter in Bulletin astronomique, 18 (1955) 254–255.

Jacques LÉvy

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Claude, François Auguste

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