Townsend, John Sealy Edward
The Irishman Sir John Sealy Edward Townsend (1868 - 1957), son to a civil engineer, was a physicist.
He discovered the ionisation of molecules in gases by ion impact and the dependence of the mean free path of an electron on its energy.
He lent his name to the townsend, the unit of reduced electric field, i.e. the ratio of electric field and concentration of neutral particles.
See also
Last modified:10 January 2026 2.24 p.m.