Éleuthère Élie Nicolas Mascart (20.02.1837-26.08.1908) was a French physicist and a member of the Paris Academy of Sciences (1884), and in 1904 its president. He was born in Quarouble. He graduated from the École Normale (1864). In 1868 he began to work at the Collège de France as assistant to H. Regnault, after whom he held (from 1878) the chair.
His work was in the field of electricity, optics and magnetism. He studied electrical machines, induction currents, the propagation of electromagnetic waves and the distribution of electricity in conductors, and he determined the electrochemical equivalent of silver. He studied the ultraviolet region of the solar spectrum, was the first to begin the study of the ultraviolet spectra of various elements using a diffraction grating, and obtained photographs of them. He developed a theory of the concave diffraction grating (1883). He determined precise wavelengths in the spectra of some metals and discovered the triplets in the spectrum of magnesium. He gave the values of the refractive indices of many gases, and he studied reflection from metals and colours. His work also concerned physiological optics and meteorology.
A corresponding member of the St Petersburg Academy of Sciences (1891) and a Fellow of the Royal Society (1892). A prize of the Paris Academy of Sciences (1874).