抄録
The geomagnetic field is analyzed by spherical harmonics. Series representations in spherical harmonics of geomagnetic field charts are compared for truncation of the series at terms of degree 6, 8, 10, and 12. Scalings are at a uniformly spaced latitude-longitude grid from both U.S. and U.S.S.R. isomagnetic charts for 1955.0. Some minor but undesirable effects are mentioned that arise because of the uniform angular spacing of data points scaled from charts. The variation of the earth's magnetic moment and the location of the dipole axis since 1835 is described and discussed. It is shown that spherical harmonic coefficients of secular change for 1912.5, 1922.5, 1932.5, and 1942.5 seem roughly compatible with those of Nagata and Oguti for 1958.5, even though earlier data analyzed were defective in Antarctica; evidently the precision of determination of the coefficients of secular change is not high. Finally, an extrapolation of the geomagnetic field into the earth's interior is described.
