1. Alfv�n, H. and Falthammar, C.-G.: 1963,Cosmical Electrodynamics, Oxford University Press, London, 2nd ed., 228 pp.
2. Arp, H.: 1966,Atlas of Peculiar Galaxies, Calif. Inst. of Tech., Pasadena, Calif. 91109, USA, xix pp., 338 plates.
3. Arp, H. and Madore, B. F.: 1975,Observatory 95, 212?214.
4. Blandford, R. D.: 1973,Astron. Astrophys. 26, 161?170.
5. Burdidge, G.: 1962, pp. 291?303, in L. Woltjer (ed.),Interstellar Matter in Galaxies, W. A. Benjamin Inc., London, 320 pp.