1. Chapman, S...Phil. Trans. Roy. Soc., 1919,218A, 1.
2. —— and Bartels, J...Geomagnetism, Clarendon Press, Oxford 1940.
3. ----- .. “Compendium of meteotology,”Amer. Met. Soc., 1951, p. 510.
4. Martyn, D. F...Proc. Roy. Soc., 1947,190A, 273.
5. Rastogi, R. G...J. Res. (N.B.S.), 1962,66D, 601.