1. Chapman , S. J. Bartels Geomagnetism 1 Clarendon Oxford 1940
2. The absolute geomagnetic field of the equatorial ring current;Forbush;Carnegie Inst. Washington Yearb. 1965,1966
3. Sugiura , M. D. J. Poros Hourly values of equatorial Dst for the years 1957 to 1970 1971
4. Sugiura , M. D. J. Poros Dst for 1971 and 1972 Greenbelt, Md. 1973
5. Description of the earth's main magnetic field and its secular change, 1905-1945;Vestine;Carnegie Inst. Washington Publ.,1947