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Roche, Édouard Albert

ROCHE, ÉDOUARD ALBERT

(b. Montpellier, France, 17 October 1820; d. Montpellier, 18 April 1883)

celestial mechanics, geophysics, meteorology.

Roche spent nearly his whole life in his native city. Several members of his family had been professors at the University of Montpellier, where he earned his doctuer ès sciences in 1844. While in Paris for three years in order to increase his knowledge of analysis and celestial mechanics, he engaged in scientific discussions with Cauchy and Le Verrier. Arago, who had taken notice of Roche’s observations of the solar eclipse of 1842, welcomed him at the Paris observatory as an independent student. In 1849 Roche was appointed chargé de cours at the Faculté des Sciences of Montpellier, and in 1852 he was named professor of pure mathematics. He was elected a corresponding member of the Académie des Sciences in December 1873. Roche had suffered from delicate health since his youth, and, exhausted by work, he was obliged to take a leave of absence from Montpellier in 1881. Eighteen months later he died of an inflammation of the lungs.

Roche’s investigations concerned primarily the internal structure and form of the free surface of celestial bodies, a subject he had treated in his doctoral dissertation. The law of the differential variation of terrestrial density, which he proposed in 1848, is still used. Roche studied the equilibrium figures of a rotating fluid mass subjected, in addition to internal forces, to an external attractive force or to a central attractive force: Roche’s limit, the maximum value that the distance of a satellite imposes on its diameter (stated in 1849), is an essential criterion in cosmogony. He also considered the form of cometary envelopes and analyzed the effect of a repulsive force originating in the sun. The shape of comets was thus correctly explained in 1859, before the physical discovery of radiation pressure.

The elements permitting the study of two fundamental problems were now conjoined. In 1873 Roche undertook a critical examination of Laplace’s cosmogonic hypothesis, which had never been the subject of thorough mathematical study. Roche provided important additions to it in order to render it coherent. In 1881 he analyzed hypotheses concerning the structure of the earth and was led to propose and study the first “earth model” with a solid nucleus.

Roche investigated various areas of pure matheatics and eteorology, and his generalization of Taylor’s formula has become classical. He also definitively solved the historic problem of solar obfuscations (temporary diminutions in the solar radiation) by showing that each of the cases cited was the result of an eclipse or of a local atmospheric phenomenon.

BIBLIOGRAPHY

1. Original Works. Almost all of Roche’s work is contained in thirty articles in Mémoires de l’Académie des sciences et lettres de Montpellier. Section des sciencescited henceforth as Mémoires--from 1848 to 1882.

On fluid masses in rotation, see Mémoires, 1 (1849), 243–262; 1 (1850), 333–348; and 2 (1851), 21–32. On the atmospheres of the planets and the shape of comets, see Mémoires, 2 (1854), 399–439; Annales de l’Obsercatoire de Paris, 5 (1859), 353–393; Mémoires, 4 (1860), 427–478; and 5 (1862), 263–302. On the interior of the earth and gravity, see Mémoires, 1 (1848), 117–128; 2 (1853), 251–264; 3 (1855), 107–124; and especially 10 (1881), 221–266. Laplace’s cosmogonic hypothesis is analyzed in “Essai sur la constitution et l’origine du systeme solaire,” in Mémoires, 8 (1873), 235–327. On Taylor’s formula, see Mémoires, 4 (1858), 125–130; and 5 (1864), 419–430; and Journal de mathématiques purrs et appliquées, 2nd ser., 9 (1864), 129–134. On solar obfuscations, see Mémoires, 6 (1868), 385–469. Two other articles on meteorology, published in vols. 10 (1882) and 2nd ser., 2 (1898), of the mémoires, established the invariableness of Montpellier’s climate since the eighteenth century.

II. Secondary Literature. There are reports on Roche’s work in Comptes rendus… de l’Académie des sciences: on comets (by J. Babinet) in 51 (1860), 417–419; on the origin of the solar system (by H. Faye) in 77 (1873), 957–962; and on his work as a whole (by F. Tisserand) in 96 (1883), 1171–1179, H. Poincarc analyzed the Laplace-Roche cosmogonic hypothesis in Lecons sur les hypotheses cosmogoniques (Paris, 1911), 15–68. In his Traité de mécanique céleste, 4 vols. (Paris, 1889–1896), F. Tisserand set forth Roche’s results on the shapes of fluid masses and on the interior of the earth (II, 110–116, 237–244) as well as on comets (IV, 245–257).

The speeches delivered at Roche’s funeral appeared in Mémoires, 10 (1883). See also J. Boussinesq, “Notice sur la vie et Ies travaux de M. Roche,” in Mémoires de la Société des sciences, de l’agriculture et des arts de Lille, 4th ser.,14 (1883), 17–35; and “Professor A. Roche,” in Nature, 28 (1883), 11–12; and Comptes rendus… de l’Académie des sciences, 96 (1883), 1171–1179.

Jacques R. LÉvy

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