1. Athay, R. G.: 1970, Solar Phys. 12, 175.
2. Beckers, J. M.: 1963, Astrophys. J. 138, 648.
3. Beckers, J. M.: 1964, A Study of the Fine Structures in the Solar Chromosphere. (Thesis. AFCRL-Environmental Research Paper No. 49).
4. Beckers, J. M.: 1968, Solar Phys. 3, 367.
5. Bray, R. J.: 1969, Solar Phys. 10, 63.