In the Spanish second edition of "Electricity and Magnetism", Berkeley Physics Course, volume II, page 27, Purcell states that a cube with a perfectly constant density does not attract external bodies as if its mass was concentrated in its geometrical center. However he does not say how does such a cube attract other bodies... The only thing my intuition tells me is that if I am in front of a cube in such a way that I'm closer to a vertex than any other, I will be more attracted by the vertex than any other part of the cube. However I'm not sure it implies that I'm not attracted by the center of mass of the cube. The comment from Purcell blows up my intuition. Can you help me to understand, please?