Sydney Chapman (1888-1970), English astronomer and geophysicist. Over the course of his career Chapman held positions at universities all over the world, including in Britain, Germany, America, Mexico and Turkey. He served as president of the Royal Astronomical Society in London and the London Mathematical Society, and published over 450 papers. His work on geomagnetism, the kinetics of gases and applied mathematics became essential reading for students of astronomy and geophysics. He was awarded the Gold Medal of the Royal Astronomical Society in 1949 and the Copley Medal of the Royal Society in 1964.