1. See, for example, Atkins, K. R., “Liquid Helium” (Cambridge University Press, 1959).
2. Eselson, B. N., and Laserev, B. G., J. Exp. Theor. Phys. (U.S.S.R.), 23, 552 (1952).
3. Snyder, H. A., and Donnelly, R. J., Phys. Fluids, 2, 408 (1959).
4. Feynman, R. P., Prog. Low Temp. Phys., 1, 17 (1955).