An article based on two papers: Paper 4214S, entitled‘Thevacuum switch. Part 1: Properties of the vacuum arc’, and Paper42J5S, entitled‘The vacuum switch. Part 2: Extinction of an a.c.vacuum arc’, which will be published in the Proceedings. Thepapers will be read at a meeting of the Science and GeneralDivision on the 18th March 1963 at Savoy Place.