It is assumed that magnetic dipoles are useful as a first approximation to the electrical currents in the core that produce the earth's main magnetic field. For simplicity the model is restricted to a central dipole and several additional radial dipoles at equal distances from the center of the earth. A least-squares method is used to adjust the amplitude, latitude, and longitude of each dipole for a best fit to the observed field components on the earth's surface. In the first of four studies the observed field was the field of the United States 1945 world charts. Originally 11 dipoles, 10 of them at the core-mantle interface at 0.54 earth radii, were used. Progressively better fits were obtained as the dipoles were placed deeper, and two of the dipoles were eliminated at greater depths. The 29-parameter, 9-dipole model, with the radial dipoles at 0.28 earth radii, produced nearly as good a fit to the 1945 field as Vestine's 48 spherical harmonic coefficients. Models were also fitted to the United States 1955 world chart field, to the British Admiralty 1955 world chart field, and to the field synthesized from the Finch-Leaton spherical harmonic coefficients for 1955. The last model produced the best fit. In all cases the radial dipoles are surprisingly deep and the central dipole is considerably stronger than the centered dipole given by the first three spherical harmonic coefficients. The great depth of the radial dipoles is qualitatively explained by a shielding effect from currents in the mantle and core. The spherical harmonic coefficients from the analyses of Vestine and of Finch and Leaton are compared with the spherical harmonic coefficients computed from the dipole parameters.