F. LONDON1 has recently proposed a new conception of helium II, according to which this liquid can be regarded as a degenerate Bose-Einstein gas, that is, as a system in which one fraction of the substance—say, n atoms per cm.3—is distributed over the excited states in a way determined by the temperature, while the rest—n0–n atoms per cm.3—is 'condensed' in the lowest energy level. If T0 denotes the temperature of degeneracy, the ratio n/n0 is given by
For an ideal Bose-Einstein gas, according to London, s = 3/2, but for the real fluid one should rather insert s = 5 in order to fit Keesom's specific heat measurements.