Babinet, Jacques

(b. Lusignan, France, 5 March 1794; d. Paris, France, 21 October 1872)

physics, meteorology

Jacques Babinet was a French physicist who did important work in the theory of diffraction, meteorological optics, and optical instrumentation. His parents-Jean Babinet, the mayor of Lusignan, and Marie-Anne Félicité Bonneau du Chesne, daughter of a lieutenant-general—hoped that he would become a magistrate and gave him a strong literary education. Jacques preferred science, however, and entered the École Polytechnique in 1812. After graduation he held professorships at Fontenay-le-Comte and Poitiers. In 1820 he became professor of physics at the Collège Louis-le-Grand in Paris. Babinet was elected a member of the physics section of the Académie des Sciences in 1840 and a year later he was appointed librarian at the Bureau of Longitudes. He married Adelaide Laugier, by whom he had two sons.

An early proponent of the wave theory of light which had recently been perfected by Fresnel and Young, Babinet devoted much of his research to extending its applications. His first published paper on optics. “Sur les couleurs des réseaux,” dealt with Fraunhofer’s discovery that white light viewed through a wire grating produces a series of continuous spectra. Babinet derived the formula that relates the deviation of rays of a given color to the ratio of their wavelength divided by the sum of the diameter of the wires plus the distance between any two wires. He also showed that diffraction experiments could yield an improved measure of wavelengths and presented a table of new values.

Babinet realized that the grating was only one of a number of means of producing diffraction effects, so he extended his theoretical work to include other systems. The result was a concept known today as Babinet’s principle: “If parallel rays fall normally on a diffraction system formed from a large number of openings... the diffraction phenomena will remain identically the same if the transparent parts become opaque, and reciprocally.”

This theoretical work was accompanied by experimental investigations of several unexplained optical phenomena in mineralogy and meteorology. Here Babinet showed his talent as an inventor. Finding Malus’ goniometer (a device for measuring angles of refraction) too cumbersome for his experiment on minerals, he constructed a portable one, which was considerably easier to use and was capable of making measurements that previously required separate instruments. To aid in his study of polarization he invented the Babinet compensator, which could produce or analyze arbitrarily polarized light.

Babinet’s interests in physics transcended laboratory work and included all phenomena in nature. Thus, the study of meteorology, particularly meteorological optics, occupied much of his career. He began his work in this field with an investigation of interference phenomena produced in the atmosphere: rainbows and “coronas,” or colored rings surrounding the sun or moon under certain weather conditions. Later work included modifications of the theory of atmospheric refraction and a study of polarization of skylight, especially the mysterious existence of neutral or unpolarized points in the sky.

While engaged in this original research, Babinet also achieved considerable fame as a popularizer of science, explaining natural phenomena to the layman in public courses and in articles in popular journals. In these exercises, whose subjects ranged over geology, mineralogy, astronomy, and meteorology, Babinet exhibited his rare ability to reduce complex phenomena to an easily comprehensible level.

BIBLIOGRAPHY

I. Original Works. Among Babinet’s works are “Sur les couleurs des réseaux,” in Annales de chimie, 60 (1829), 166–176; “Mémoires d’optique météorologique,” in Académie des Sciences, Comptes rendus, 4 (1837), 638–648; “Sur les caractéres optiques des minéraux,” ibid., 758–766; “Sur la réfraction terrestre,” ibid., 52 (1861), 394–395, 417–425, 529–535. A study of polarization of skylight, especially the mysterious existence of neutral or unpolarized points in the sky, may be found in Académic des Sciences, Comptes rendus, 11 (1840), 618–620; 20 (1845), 801–804; 23 (1846), 233–235. Many of Babinet’s treatises on science for the layman were collected in a volume entitled Études et expériences sur les sciences d’observation (Paris, 1855).

II.Secondary Literature. Biographical material on Babinet is found in the following sources: Revue des cours scientifiques de la France et de l’étranger, 3 (1872), 409–410; L. Figuier, L’année scientifique, 16 (1872), 533; the speech by Becquerel at Babinet’s funeral; E. Beauchat-Filleau, Dictionnnaire historique et généalogique de Poitou, 2nd ed., I (Poitiers, 1891), 120, especially for family background. A complete bibliography of Babinet’s original papers is given in the Royal Society Catalogue of Scientific Papers, I, 134–136 and VII, 72. Other publications are listed in J.C. Poggendorff’s Biographisch-literarisches Handwörterbuch..., I (Leipzig, 1863; repr. Amsterdam, 1965), 82.

Eugene Frankel