John Sealy Edward Townsend (7.06.1868 — 16.02.1957) — an English physicist, Fellow of the Royal Society (1903). He graduated from the University of Dublin (1890). In 1896 — 1900 he worked at the University of Cambridge, and in 1901—41 —at Oxford.
His work was chiefly on electric discharges in gases. He studied the passage of current through a gas. In 1897 — 98 he made the first direct measurement of the charge carried by a gas ion. In 1900 he developed the theory of the passage of an electric current through a gas (the Townsend theory) and calculated the diffusion coefficients of charged particles. He studied the mobility of electrons in various gases.