1. F. London,Superfluids (Wiley, New York), Vol. 1, p. 78.
2. J. Williams,Superconductivity and Its Applications (Pion, London), p. 46.
3. N. Brickman,Phys. Rev. 184, 460 (1969).
4. B. Cabrera, to be published.
5. M. Tinkham,Introduction to Superconductivity (McGraw-Hill, 1975), Chapter 2.