Old records of magnetic measurements and archeomagnetic data at various places were collected to examine whether the westward drift has been a persisting feature of the earth's magnetic field and to investigate the extent to which drifting of the field has contributed to the observed secular variation.It turned out that main features of the secular variation such as maxima and minima of magnetic declination and inclination; were very likely to have drifted westwards with a velocity of about 0.36/year over several hundred years.Comparison of the observed time variation with the spatial distribution of the present geomagnetic field suggests that the westward drift of the non-dipole field is responsible for producing a large part of the secular variation, even for such long period as 1000 years.

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Spherical harmonic analyses were made of the annual mean values of the geomagnetic components at 34 observatories for the period from 1940 to 1973. Annual values of the Gauss coefficients were separated into parts of external and internal origin. The external part of the first-degree component is parallel to the internal dipole and changes with solar activity. The maximum change from peak to trough amounts to 47 nanoteslas during this period. During one solar cycle, two peaks appear in the variation of this component. The first peak corresponds to the period of the maximum solar activity, the second at the declining stage of the cycle.Examination of the time variations of the first-degree components was extended to an analysis for 1900 to 1973 based on annual means from 21 observatories. Although its amplitude is small, the internal part changes with a three-year time lag behind the external field change. After Fourier analyses of the time series of both the internal and external components, their ratio was computed for the 10-year-period band. The modulus of the internal/external ratio (i/e) was obtained to be 0.32 and the phase angle (internal-external) to be 1050.