John Frank Allen (born 6.05.1908) was an experimental physicist. He graduated from the universities of Manitoba (1928) and Toronto (1930). In 1930-33 he worked at the National Research Council in Ottawa, in 1935—44 at the Mond Laboratory (Cambridge, England), and in 1934—47 he was a lecturer at the University of Cambridge. In 1947 —78 he was professor at the University of St Andrews (Scotland).
His research concerned low-temperature physics (the superfluidity of helium, superconductivity). He measured the surface tension of liquid helium, its viscosity and its thermal conductivity (1938). Measuring the viscosity of liquid helium II by the method of flow through capillaries, he found, together with A. Misener, anomalies in the behaviour of the viscosity — an extremely low limiting viscosity when helium II flows through narrow capillaries and slits. The same phenomenon was observed independently in the same year by P. L. Kapitza, who gave it the name “superfluidity”. Studying the thermal conductivity of liquid helium, he confirmed its anomalously high value, which had been established by W. and A. Keesom at the Leiden cryogenic laboratory, and he also found that the flow of heat through liquid helium II is not proportional to the temperature difference. The smaller the temperature difference, the greater the thermal conductivity of helium II became, reaching values millions of times greater than the corresponding quantity for helium I. To explain the peculiarities of the thermal conductivity of liquid helium he introduced (together with A. Misener) the concept of the wall layer. In 1938, with H. Jones, he discovered the fountain effect in liquid helium II, later called the thermomechanical effect.
A Fellow of the Royal Society (1949) and of the Royal Society of Edinburgh.