1. Chapman, S., and J. Bartels: Geomagnetism, 2 vols. Oxford: Clarendon Press 1940. Reprinted in 1951. This is a monumental book in the field of geomagnetism. A complete list of papers published before 1939 is given in the bibliography of this book.
2. Nagata, T., and S. Kokubun: A particular geomagnetic daily variation (Sp
q) in the polar regions on geomagnetically quiet days. Nature 195, 555–557 (1962).
3. Nagata, T., and S. Kokubun: An additional geomagnetic daily variation field (SP-field) in the polar region on geomagnetically quiet day. Rep. Ionos. Space Res. Japan 16, 256–274 (1962).
4. Vestine, E. H., L. Laporte, I. Lange, and W. E. Scott: The geomagnetic field, its description and analysis. Carnegie Inst. Washington Publ. 580 (1947).
5. Hasegawa, M.: Provisional report of the statistical study on the diurnal variations of terrestrial magnetism in the north polar regions. Trans. Washington Meeting 1939, IATME Bull. No. 10, 311–318 (1940).