John Frank Allen. 6 May 1908—22 April 2001

John Frank (Jack) Allen was a Canadian-born pioneer of low temperature physics. With his graduate student, Don Misener, he discovered the phenomenon of superfluidity on passing HeII through very narrow glass capillaries. Simultaneously, and independently, the phenomenon was discovered by Piotr Kapitza FRS in the Soviet Union. Jack's most famous discovery in 1938 was the fountain effect in liquid HeII, a further manifestation of the role of superfluidity at very low temperatures. The Nobel Prize for the discovery of superfluidity was awarded to Kapitza in 1978. Jack invented the O-ring as a reliable vacuum seal and, in 1947, followed this by the indium-ring cryogenic seal. In 1958, with John Bardeen (ForMemRS 1973) and Jan de Boer, he initiated a project that saved three million cubic feet of helium gas from being lost to the world. After running the Mond Laboratory in the Cavendish Laboratory from the late 1930s, in 1947 he was appointed professor of natural philosophy at St Andrews University, where he led the construction of a new physics building and built up an internationally respected department. He campaigned for student representation, and was well known for his physics demonstrations. In later life, he carried out a programme to erect plaques to Nevil Maskelyne FRS, who measured the gravitational constant G , and to celebrate the achievements of St Andrews luminaries.