1. Alfvén, H.: Stockh. Obs. Ann. 14(2–3) (1942)
2. Alfvén, H.: Cosmical Electrodynamics, pp. 82–84. Clarendon, Oxford (1950)
3. Alfvén, H.: Cosmic Plasma, pp. 91–92. Reidel, Dordrecht (1981)
4. Alfvén, H., Fälthammar, C.-G.: Cosmical Electrodynamics, 2nd edn., pp. 100–104. Clarendon, Oxford (1963)
5. Babcock, H.W.: Astrophys. J. 133, 572 (1961)