Abstract. For many purposes a sphere or an ellipsoid of revolution approximate the figure of the Earth fairly well. However, the Earth's topography causes effects that continuously stimulate a considerable research effort. In contrast to the concept of the so-called shrinking parameter in the classical treatment of the effect, successive approximations are applied within a weak formulation of the respective boundary-value problem in this paper. In this connection functional-analytic estimates are investigated so as to clarify the convergence of the iteration process. In particular the ellipticity of a bilinear form associated with the problem under consideration is discussed for the solution domain of an ellipsoidal boundary. The apparatus of ellipsoidal harmonics is substantially used for this purpose. Quantitative estimates for the respective parameters were derived, when the potential is assumed to follow a finite degree model.