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Mascart, Éleuth

MASCART, ÉLEUTHèRE ÉLIE NICOLAS

(b. Quarouble, France, 20 February 1837; d. Paris, France, 26 August 1908)

physics.

The son of a teacher, Mascart received his secondary education at the collége in Valenciennes, after which he became maître répétiteur at the lycées in Lille (1856–1857) and Douai (1857–1858). His thorough mathematical preparation at Douai enabled him in 1858 to enter the école Normale Supérieure in Paris. Three years later he became agrégé-preéparateur at the École Normale, and in July 1864 he received his doctorate. Shortly thereafter he married a Mlle Briot.

After teaching physics at the lycée in Metz (1864–1866) and publishing his first book, éléments de mécanique (Paris, 1866; 9th ed., 1910), his former professor of physics, Verdet, helped him secure a post in Paris at the Collège Chaptal. He soon transferred, first to the Lycée Napoléon and then to the Lycée de Versailles. In December 1868 he left secondary education for good to become Régnault’s assistant at the Collège de France. In May 1872, his scientific career having been interrupted by the Franco-Prussian War, he succeeded Régnault as professor of physics, a chair that he held for the rest of his life. In 1878 he was also chosen to be the first director of the Bureau Central Météorologique. In December 1884 he was elected to J. C. Jamin’s place in the French Academy of Sciences; he served as permanent secretary and, in 1904, president.

Masart’s scientific career was marked not by great discoveries but by a steady stream of first-rate experimental and theoretical work in optics, electricity, magnetism, and meteorology. The first problem he attacked—the subject of his thesis—was a systematic and precise spectroscopic exploration (using photographic detection techniques) of the ultraviolet region of the solar spectrum, in which he greatly increased the number of lines of known wavelength. At the same time he accurately determined the relative wavelengths of the principal emission lines of ten selected metals and argued that all of his data agreed well with a modified version of Cauchy’s dispersion formula. A more detailed extension of these experiments, which Fizeau termed the “most thorough and most satisfying” work since Fraunhofer’s, won for Mascart the 1866 Prix Bordin.

During the course of this work and in the years immediately following it, Mascart made several individually significant observations, including the existence of triplets in the spectrum of magnesium. Undoubtedly the most valuable aspect of this period was the thorough preparation in experimental optics that it gave him. When the Academy in 1870 proposed for the Grand Prix des Sciences Mathématiques the experimental determination of the modifications that light experiences in its mode of propagation and its properties as a result of the movement of the source and observer, Mascart was ready to compete for it. Several years of painstaking researches followed, at the end of which Mascart found himself forced to the purely negative conclusion that refraction and diffraction experiments, independent of whether terrestrial sources or sunlight is used, are incapable of detecting the motion of the earth through the ether. Double refraction and other optical experiments yielded the same negative result. While contemporary interpretations of these experiments had to be modified later in the light of special relativity theory, the great importance of Mascart’s work was recognized by the Academy when it awarded Mascart the Grand Prix in 1874.

Optical researches of various kinds—experiments in physiological optics, determinations of the indices of refraction and dispersive powers of numerous gases, studies on metallic reflection and color, theoretical work on the rainbow and on the formation of interference fringes under various conditions—continued to occupy much of Mascart’s time both before and after 1874, especially until the publication of his well-known three-volume Traité d’optique (Paris, 1889–1893). Concurrently, however, his interests were extending into the fields of electricity and magnetism. He studied, for example, electrical machines (1873) and the efficiencies of various motors (1877–1878), the propagation of electricity in conductors (1878), the theory of induced currents (1880, 1883), the interaction of two electrified spheres (1884), diamagnetism (1886), means for determining the positions of the poles of a bar magnet (1887), and the propagation of electromagnetic waves (1893–1894). Perhaps Mascart’s most important and precise work involved the determination of the electrochemical equivalent of silver (1884) and, with F. de Nerville and R. Benoit, the absolute value of the ohm (1884–1885). Once again he incorporated his researches into textbooks: first into his two-volume Traité d’électricité statique (Paris, 1876) and then into his two-volume Leçons sur I’électricité et le magnétisme, written with J. Joubert (Paris, 1882–1886; English trans. by E. Atkinson, A Treatise on Electricity and Magnetism [London, 1883–1888]; 2nd French ed., 1896–1897), which was the first French textbook that attempted to treat synthetically the work of Maxwell, Kelvin, and Helmholtz. Since it concentrated on applications as well as on theory, it became a standard work for engineers as well as for physicists.

Mascart’s third major area of scientific activity was meteorology, which made greater demands on his time after he became director of the Bureau Central Météorologique (1878). In succeeding years he traveled widely as a member of an international committee charged with defining pressing meteorological questions and organizing international meteorological conferences. He also helped organize an international scientific polar expedition, as well as a French expedition to Cape Horn. The major goal of the latter was to map the magnetic field of the earth, a subject to which he repeatedly returned throughout the 1880’s and 1890’s and on which he published an extensive textbook, Traité de magnétisme terrestre (Paris, 1900). Concurrently, he carried out studies on atmospheric electricity (1878–1882), on the amount of carbonic acid in the air (1882), on the terrestrial variations of gravitational attraction (1882–1883) and its possible diurnal variation (1893), on the theory of cyclone formation (1887–1888), and on the mass of the atmosphere (1892).

Beginning in the late 1870’s Mascart played an increasingly prominent role in national and international scientific organizations and events. Indeed, a substantial portion of his own researches stemmed directly from issues raised at the congresses he attended or presided over. Thus, for example, at the 1881 Exposition Internationale d’Électricité in Paris, it became clear that one of the most important tasks confronting physicists was to originate a universal and coherent system of electrical units. The agreement finally reached on the definitions of the volt and the ohm prompted Mascart to carry out his determinations of the electrochemical equivalent of silver and of the absolute value of the ohm (final agreement was reached in Chicago in 1893). At a number of later congresses of electricians and meteorologists, Mascart played leading organizational and official roles. As president of the general assembly of the Société Internationale des Électriciens held in Paris in May 1887, he was instrumental in creating the Laboratoire Central d’électricité and the École Supérieure d’Électricité. He was repeatedly called upon to serve as a consultant to the French government on matters relating to national defense, public electrical and lighting facilities, and public instruction. Only in the last year of his life did he also consent to advise two private industries. His general prestige is reflected in his election in 1892 as a foreign member of the Royal Society and in his election in 1900 as vice-president of the Institution of Electrical Engineers, the first time this post was ever held by a non-British citizen.

Of medium height and of great physical stamina, Mascart was a leader who could readily get to the essence of arguments and quietly persuade others of a course of action in which he believed. An experimental physicist with a thorough command of mathematics, he could easily step outside of his laboratory and point the way to practical results in technology or policy making. He was a grand officier of the Légion d’Honneur, an honor—one of his many—that he valued very highly. He died after a serious operation, at the age of seventy-one.

BIBLIOGRAPHY

I. Original Works. Mascart’s most important papers are “Recherches sur le spectre solaire Ultra-violet et sur la détermination des longueurs d’onde,” in Annales scientifiques de I’école normale supérieure, 1 (1864), 219–262, his doctoral thesis, also published separately (Paris, 1864); “Recherches sur la détermination des longueurs d’one,” ibid., 4 (1867), 7–37, the 1866 Prix Bordin memoir; “Sur les modifications qu’éprouve la lumière par suite du mouvement de la source lumineuse et du movement de I’observateur,” ibid., 2nd ser., 1 (1872), 157–214; 3 (1874), 363–420, the 1874 Grand Prix memoir; “Sur I’équivalent électrochimique de I’argent,” in Journal de physique theéorique et appliquée, 2nd ser., 3 (1884), 283–286; and “Détermination de I’ohm et de sa valeur en colonne mercurielle,” in Annales de chimie et de physique, 4the ser., 6 (1885), 5–86, written with F. de Nerville and R. Benoit. An interesting review article of Mascart’s is “The Age of Electricity,” in Report of the Board of Regents of the Smithsonian Institution (1894), 153–172. His many textbooks —he was one of the most prolific textbook writers of all time—are cited above.

II. Secondary Literature. See Paul Janet, “La vie et les oeuvres de E. Mascart,” in Revue générale des sciences pures et appliquées, 20 (1909), 574–593; the obituary notices in Nature, 78 (1908), 446–448; and Journal de physique théorique et appliquée, 4th ser., 7 (1908), 745; and the portrait in Edward D. Adams, Niagara Power, I (Niagara Falls, N.Y., 1927), 191.

Roger H. Stuewer

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