1. Bartoe, J.-D. F., Brueckner, G. E., Purcell, J. D., and Tousey, R.: 1974, Proceedings of the Society Photo-Opt. Instr. Eng. 44, 153.
2. Brueckner, G. E.: 1975a, IAU Symp. 68, 135.
3. Brueckner, G. E.: 1975b, Trans. Royal Soc. London, Series A (in press).
4. Brueckner, G. E.: 1974, IAU Symp. 57, 333.
5. Parker, E. N.: 1963, Astrophys. J. Suppl. 8, 177.