 7. How, if at all, does the Earth's surface gravity vary with latitude, and how, if at all, does the Earth's figure differ from a sphere? Newton's answer changes from the first to the second to the third edition, but in all cases vagaries in the cited data raise the question of what the actual variations are. Also, because his idealized theoretical calculation assumes uniform density, his answer raises the questions whether the density of the Earth is uniform and whether the true figure of the Earth and variation of surface gravity can be reconciled with non-uniformities in density.