John Sealy Townsend
Sir John Sealy Edward Townsend, FRS (7 June 1868 – 16 February 1957) was an Irish-British mathematical physicist who conducted various studies concerning the electrical conduction of gases (concerning the kinetics of electrons and ions) and directly measured the electrical charge. He was a Wykeham Professor of physics at Oxford University. The phenomenon of the electron avalanche was discovered by him, and is known as the Townsend discharge. Career John Townsend was born at Galway in County Galway, Ireland, son of Edward Townsend, a Professor of Civil Engineering at Queen's College Galway and Judith Townsend. In 1885, he entered Trinity College Dublin, was elected a Scholar of the College in 1888, and came top of the class in mathematics with a BA in 1890. He became a Clerk Maxwell Scholar and entered Trinity College, Cambridge, where he became a research student at the same time as Ernest Rutherford. At the Cavendish laboratory, he studied under J. J. Thomson. He developed the "Townsend's collision theory". Townsend supplied important work to the electrical conductivity of gases ("Townsend discharge" circa 1897). This work determined the elementary electrical charge with the droplet method. This method was improved later by Robert Andrews Millikan. In 1900,