1. J. Wilks, The Properties of Liquid and Solid Helium, Clarendon Press, Oxford (1967), p. 36; also
2. J. Donnelly, Experimental Superfluidity, University of Chicago Press, Chicago (1967), p. 32.
3. J. Wilks, op. cit., p. 388; or K. R. Atkins, Liquid Helium, Cambridge University Press, Cambridge (1959), p. 159.
4. J. Wilks, op. cit., p. 56.