1. Allen, C. W.: 1963,Astrophysical Quantities, 2nd ed., Athlone Press, London, p. 42.
2. Cilli�, G.: 1932,Monthly Notices Roy. Astron. Soc. 92, 820.
3. Feautrier, P.: 1968, inProc. 3rd Harvard-Smithsonian Conf. Stellar Atmospheres, 1968 (in press).
4. Fleck, J. A. Jr.: 1963,Methods in Computational Physics,I, Academic Press, New York, p. 43.
5. Griem, H. R.: 1960,Astrophys. J. 132, 883.