Babinet , Jacques

(1794–1872) French physicist

Babinet, who was born in Lusignan, France, studied in Paris at the Ecole Polytechnique and from 1820 he was a professor at the Collège Louis le Grand. He was elected to the Académie des Sciences in 1840.

His 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. TheBabinet 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.

Furthermore he showed an interest in the optical properties of minerals, developing new instruments for the measurement of angles and polarizations. He also studied meteorological phenomena, especially those of an optical nature, investigating rainbows and the polarization of skylight. Babinet was the first to suggest (1829) that the wavelength of a given spectral line could be used as a fundamental standard of length. The idea was adopted in 1960, when the meter was defined as 165076373 wavelengths of the radiation emitted by an atom of krypton–86 in a specified transition. (This definition was changed in 1983 to the distance traveled by light in a certain fraction of a second.)