1. Baker, K. D.: 1968, Ann. Geophys
24, 285.
2. Belon, A. E., Romick, G. J., and Rees, M. H.: 1966, Planetary Space Sci. 14, 597.
3. Bunn, F. E.: 1970, M. A. Thesis, York University, Toronto.
4. Bunn, F. E., Miller, J. R., and Shepherd, G. G.: 1971, to be published.
5. Currie, B. W.: 1934, Terr. Mag
39, 293.