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Royal Society Discussion on Supraconductivity


    IN opening the Royal Society discussion on Supraconductivity, Prof. J. C. McLennan referred first to new methods of helium liquefaction which have recently been developed. In Prof. F. Simon's method, high pressure helium gas is cooled to liquid hydrogen temperatures and then allowed to expand through a valve, a small quantity of liquid helium being produced which is quite adequate for many types of experiments. A second method, developed by Prof. P. Kapitza at Cambridge, applies to helium the method first used by Claude for the liquefaction of air, part of the gas doing external work in an expansion engine and so cooling the remainder below the inversion temperature of the Joule-Thomson effect, whence it can be liquefied by expansion.

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