1. Allen, C. W.: 1973,Astrophysics Quantities, 3rd ed., Athlone Press, London.
2. Altschuler, M. D. and Newkirk, G.: 1969,Solar Phys. 9, 131.
3. Apostolov, E.: 1988,Bull. Astron. Inst. Czech. 39, 243.
4. Billings, D. E.: 1966,A guide to the Solar Corona, Academic Press, New York.
5. Broussard, R. M., Sheeley, N. R., Jr., Tousey, R., and Underwood, J. H.: 1978,Solar Phys. 56, 161.