PéROT, JEAN-BAPTISTE GASPARD GUSTAV ALFRED

(b. Metz, France, 3 November 1863; d. Paris, France, 28 November 1925)

physics.

Alfred Pérot’s most important work involved experiments in optical interferometry and in electricity. He was ingenious with apparatus and as a teacher emphasized the importance of direct contact with experimentation.

Pérot studied at the lycée in Nancy and then at the Ecole Polytechnique in Paris. In 1884 he returned to Nancy and worked under Blondlot in the physics laboratory of the university. In 1888 he received the docteur ès sciences for measurements of the specific volumes of saturated vapors and for determining the mechanical equivalent of heat. (Pérot’s result for the mechanical equivalent was good, but the work was interesting mainly because of the indirect method that Pérot used, which was based on the equation of Clapeyron.)

In 1888 Pérot joined the University of Marseilles as maitre de conferences and became much involved in problems of electricit. He studied dielectric properties and electromagnetic waves, and he was considered an expert on topics relating to the emerging electrical industry. (In 1894 a special chair in industrial electricity was created for him at the university.) He collaborated with Charles Fabry (1894–1901) in developing and using a new method of optical interferometry. In 1901 Pérot accepted an invitation to be the first director of the laboratoire d’essais of the Conservatoire des Arts et Metiers-a difficult administrative task. In 1908 he returned to research at the Meudon Observatory and to teaching at the École Polytecnique. He studied propertiers of the solar atmosphere (using the interference he had developed earlier) and problems associated with the triodeo and with telegraphy.

The initial inspiration for developing interferometry came when Fabry was asked to help in measuring the distance between metallic surfaces about a micron apart. Fabry thought using interference between the two surfaces, and he and Pérot began to study the very fine fringes produced by reflections between silvered films. This work led to development of the “Fabry-Perot interferometer”. According to Fabry, he and Pérot complemented each other nicely in this work; Fabry was more theoretically inclined, while Perot imagined the actual mechanical arrangements that would make the techniques succeed. Fabryu, Perot, and Mace de Lepinay(who already in 1885 used optical methods to determine thicknesses) used the new interferometer to determine the mass of a cubici centimeter as a spectyroscopic analyzer and measured the wavelengths of the black lines in the solar spectrum-thus making it possible to correct small erroros in Rowlan’s wavelengths.

Pérot’s analysis of solar spectra involved some interesting problems, since small shiftrs in wavelength are produced by a variety of causes (for example, pressure effects, convectioin currents, and the Doppler effect due to rotation). Perot was inspirede to separate some of these effects, and from 1920 to 1921 he triede to verify the gravitional red shift of Einstein’s general theory of relativbity. (Experimental verificatioin of the gravitatiional red shift is difficult, and conclusive measurements were not made until 1960; see R. H. Dicke, The Theoroetical Significance of Experiumental Relativity [New York, 1964], 25–27.)

BIBLIOGRAPHY

I. Original Works. Perot’s articloes include “Sur la mesure du volummme specifique des vapeurs saturees et la determination de l’equivalent mecanique de la chaleur,” in Journal de physique 7 (1888), 129–148; “Les applications industrielles d’electricite,” in Comptes rendus hebdomadaires des seamces de l’Academie des science4s 123 (1896), 802–805, written with C.Fabry; “Sur une nouvelle methode de spectroscopie interfernetielle,” ibid 126 (1898), 34–36, written with C.Fabry; and “Mesure de la pression de l’atmosphere solaire dans lal couche du magnesium et verification du principe de relative,” magnesium et verification du principe de relativite,” ibid 172 (1921), 578–581. More of Perot’s papers are listed in Royal; Society Catelogue of Scientific papers, 4th ser., XVII, 798, and in poggendrorff, IV, 1140–1141; V, 958–959; and VI, 1984.

II. Secondary Literature. On Pérot’s life and work see the essays by Charles Fabry in Bulletin de la Société astroinbomique de France 401 (1926), 40–43 (with the announcemnent on pp. 2–3), and in Astrophysical Journal. 64 (1926), 209–214, which includes information about the initiali development of the silver-film interferometer. See also the biblioigraphy to the article on C. Fabry.

Sigalia Dostrovsky