1. Meinel, A. B., Science, 112, 590 (1950).
2. Mitra, S. N., and Mazumdar, S. C., “Effect of Solar Activity on Ionosphere and Earth's Magnetic Field”, Indian Science Congress, January 1951.
3. See Chapman and Bartels, “Geomagnetism”, p. 818 (Oxford, 1940).
4. Chapman, S., J. Geophys. Res., 55, 361 (1950).
5. Pierce, J. A., Proc. Inst. Radio Eng., 36, 8 (1948).