Fourier analyses were made of the geomagnetic horizontal annual means from 20 observatories and the vertical component annual means from 17 observatories from 1900 to 1972 for most of the observatories. Curves synthesized from the Fourier coefficients for periods from approximately 4 to 13 yr have patterns easily explained in terms of a westward-flowing ring current that generally increases as the sunspot numbers increase but lags behind the sunspot numbers by a year or two. External spherical harmonic coefficients should be included in models of the earth's magnetic field. By using the horizontal component curves, synthesized as described above for seven selected observatories and the vertical component curves for six selected observatories, values of both internal and external first-order zonal spherical harmonic coefficients were determined for a 22-yr span. The amplitude and phase of the ratio of these coefficients are consistent with an earth having a conductivity of 33 mhos/m from the center of the earth to a radius of 0.9 RE surrounded by a nonconducting shell to the surface.