Marie Alfred Cornu (6.03.1841-12.04.1902) was a French physicist and a member of the Paris Academy of Sciences (1878), and its president in 1896. He was born in Orléans. He studied at the École Polytechnique and the École des Mines in Paris. From 1864 he taught at the École Polytechnique (professor from 1867).
His research was in the fields of optics, crystal physics, spectroscopy and acoustics. He studied the distribution of light intensity in diffraction (the Cornu spiral) and the ultraviolet spectra of various elements, and he improved Fizeau's method of determining the speed of light (1874). He measured the density of the Earth (1873) and determined the gravitational constant. In 1898 he detected the anomalous Zeeman effect.
A foreign member of the St Petersburg Academy of Sciences (1888). The B. Rumford Medal (1878).