1. Arnoldy, R. L., Kane S. R., and Winckler, J. R.: 1968, in K. O. Kiepenheuer (ed.), ?Structure and Development of Solar Active Regions?, IAU Symp. 35, 490.
2. Castelli, J. P. and Guidice, D. A.: 1972, Air Force Cambridge Research Laboratory Report AFCRL- 72-0049.
3. Culhane, J.L. and Phillips, K.: 1970, Solar Phys. 11, 117.
4. de Jager, C.: 1967, Solar Phys. 2, 347.
5. Drake, J. F.: 1971, Solar Phys. 16, 152.