Published online by Cambridge University Press: 31 May 2012
Supported in part by Penrose Fund Grants No. 1931 (1955) and No. 2640 (7959) both from the American Philosophical Society, Philadelphia, Pa., and by G-13012 (1960) from the National Science Foundation, Washington, D,C. The writer expresses his sincere thanks for this financial assistance.
1 Supported in part by Penrose Fund Grants No. 1931 (1955) and No. 2640 (7959) both from the American Philosophical Society, Philadelphia, Pa., and by G-13012 (1960) from the National Science Foundation, Washington, D,C. The writer expresses his sincere thanks for this financial assistance.