A model of the compression of the Hermaean magnetosphere by the solar wind is presented. The model considers the consequences of the finite electrical conductivity of the planetary interior on the magneto-pause standoff distance under varying solar wind conditions. Although for average conditions the standoff distance is almost identical to that obtained for a point dipole source embedded in an insulating interior, for periods of above-average solar wind dynamic pressure the compression of the planetary field between the magnetopause and the conducting interior will increase the standoff distance. From these considerations the solar wind would be expected to impact the dayside surface directly only a very small fraction of the time. Magnetic reconnection may erode the dayside magnetosphere and increase the rate of direct impact upon the surface. However, this effect is not included in the model calculations.