1. Acton, L. W.: 1968, Astrophys. J. 152, 305.
2. Arnoldy, R. L., Kane, S. R., and Winckler, J. R.: 1968, Solar Phys. 2, 171.
3. Bohr, N.: 1915, Phil. Mag. 30, 571.
4. Bruzek, A.: 1967, in Solar Physics (ed. by Xanthakis), Interscience.
5. Cheng, C. C.: 1970, preprint, Goddard Space Flight Center, Greenbelt, Maryland.