1. Allen, C. W.: 1963, Astrophysical Quantities, 2nd ed., The Athlone Press, London, p. 174 or p. 164.
2. Bray, R. J. and Loughhead, R. E.: 1965a, Sunspots, John Wiley & Sons, New York, p. 261.
3. Bray, R. J. and Loughhead, R. E.: 1965b, loc. cit. Sunspots, John Wiley & Sons, New York, p. 258.
4. Carrington, R. C.: 1859, Monthly Notices Roy. Astron. Soc. 20, 13.
5. Cowling, T. G.: 1957, Magnetohydrodynamics, Interscience Publishers, New York, p. 107.