1. Athay, R. G. (ed.): 1974, ?Chromospheric Fine Structure?, IAU Symp. 56, 6.
2. Athay, R. G.: 1976, The Solar Chromosphere and Corona: Quiet Sun, D. Reidel Publ. Co., Dordrecht, Holland, p. 53.
3. Chapman, G. A. and Sheeley, N. R.: 1968, in K. O. Kiepenheuer (ed.), ?Structure and Development of Solar Active Regions?, IAU Symp. 35, 161.
4. Dunn, R. B.: 1971, NBS Special Publication No. 353 (Menzel Symposium), p. 71.
5. Feldman, U., Doschek, G. A., and Mariska, J. T.: 1979, Astrophys. J. 229, 369.