1. See, for example, Chapman, S., Nature, 161, 462 (1948).
2. Koenigsberger, J. G., Gerl. Beitr. Geophys., 35, 51, 204 (1932); 36, 47 (1933); Terr. Mag., 43, 119, 299 (1938).
3. Nagata, T., Bull. Earthq. Res. Inst., 19, 49 (1941); 20, 192 (1942); 21, 1 (1943); Nature, 165, 245 (1950).
4. Thellier, É., Ann. Inst. Phys. Globe, 16, 157 (1938); J. Phys. et le Rad., 12, 205 (1951).
5. Roquet, J., C.R. Acad. Sci., Paris, 229, 1135 (1949); 230, 282 (1950). Roquet, J., and Thellier, É., C.R. Acad. Sci., Paris, 230, 1939 (1950).