Born Lusignan, (Vienne), France, 5 March 1794
Died Paris, France, 21 October 1872
Jacques Babinet’s major work was devoted to the diffraction of light. He used diffraction to measure wavelengths more accurately than before, and did theoretical work on general diffraction systems. He was the son of Jean Babinet, mayor of Lusignan, and Marie-Anne Félicité Bonneau du Chesne, daughter of a lieutenant general. He married Adelaide Laugier; they had two sons.
Babinet began his studies at the Lycée Napoléon, then at the École Polytechnique, where he later became an examiner. He left the École Polytechnique in 1812 to enter the Military School at Metz. For some time he was attached to the Fifth Regiment of Artillery, but at the Restoration he left the army and took up teaching. He was professor of mathematics at Fontenay-le-Comte, then professor of physics at Poitiers and, from 1820, at the Lycée Saint-Louis, Paris. From 1825 to 1828 Babinet delivered a course of lectures on meteorology. In 1838 he succeeded Félix Savary at the Collège de France. Two years later, Babinet was elected to the Académie des sciences as a member of the General Physics Section.
Babinet’s major scientific contribution was in optics, although his contributions to science include the other branches of physics and mechanics. Babinet’s theorem states that there is an approximate equivalence between the diffraction pattern of a large system and that of the complementary system, which is opaque where the original system is transparent and vice versa. He showed an interest in the optical properties of minerals, developing new instruments for the measurement of angles and polarizations, especially Babinet’s compensator, a double quartz wedge used in the study of elliptically polarized light. He was the first to suggest (1829) that the wavelength of a given spectral line could be used as a fundamental standard of length, an idea eventually used in metrology in 1960. He constructed a portable goniometer, improving upon E. L. Malus’ device.
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 the 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. He also constructed a hygrometer. In mechanics, he improved the valves of the air pump, attaining a very high vacuum.
Babinet also achieved considerable fame as a popularizer of science, explaining natural phenomena to lay audiences in public courses and in articles in popular journals. Speaking about geology, mineralogy, astronomy, and meteorology, Babinet exhibited his rare ability to reduce complex phenomena to an easily comprehensible level.