Applied mathematician and geophysicist, born in Eccles, Lancashire, NW England, UK. He studied engineering at Manchester, and mathematics at Cambridge, and was professor at Manchester (1919--24), Imperial College, London (1924--46), and Oxford (1946--53). From 1954 he worked at the High Altitude Observatory at Boulder, CO, and the Geophysical Institute in Alaska. He made a major contribution to the kinetic theory of gases, and developed the theory of thermal diffusion. He also developed theories on geomagnetism, atmospheric tides, and geomagnetic storms.