1. Alfvén, H. and Fälthammar, C.-G.: 1963,Cosmical Electrodynamics, Clarendon, Oxford.
2. Allen, C. W.: 1973,Astrophysical Quantities, University of London, Athlone Press, London.
3. Athay, R. G.: 1985,Solar Phys. 100, 257.
4. Beckers, J. M.: 1977, in A. Bruzek and C. J. Durrant (eds.),Illustrated Glossary for Solar and Solar-Terrestrial Physics, D. Reidel Publ. Co., Dordrecht, Holland.
5. Koutchmy, S. and Lorrain, P.: 1992, Poster paper presented at SUMER/CDS Meeting, Orsay, September 20, 1992.