Steady state axisymmetrical convection experiments in shells with external to internal radii ratios equal to those of the whole or the lower mantle of the Earth are performed using a finite difference method. The fluid is incompressible and can have either a constant or a temperature dependent viscosity. The Rayleigh number is less than 11 times the critical number, and the Prandtl number is infinite. A transition from a 3 or 4 cell to a 2 cell steady state structure with polar rising current is observed to occur systematically for a Rayleigh number about 7 to 8 times the critical number. In spite of the low Rayleigh number used, the structure we obtain is compatible with the strong axisymmetrical degree two pattern of the geoid anomalies or the seismic velocity anomalies.