Henderson, John Tasker

John Tasker Henderson, radio-physicist (b at Montréal 9 Dec 1905; d at Perth, Ont 2 Jan 1983). Educated at McGill and London, Henderson joined the NATIONAL RESEARCH COUNCIL (1933) in charge of its radio section, where he worked on "atmospherics" (later discovered to be the effect of the ionosphere on radio signals) and built the Cathode Ray Direction Finder invented by A.G.L. MCNAUGHTON and W.A. STEEL. In 1939 he was secretly informed about British advances in RADAR and, in the next few months, Henderson laid the foundations for radar research and manufacture in Canada. He returned to the NRC after RCAF and diplomatic service 1942-47 and became head of its electricity section, which built several cesium atomic clocks (accepted in 1968 as the international timekeeping standard).