On Aristotelian physics, I was wondering about the last line of this Proposition: To set out the sides of the five figures and compare them with one another . Here Euclid proves that if a dodecahedron and an icosahedron are inscribed in the same sphere, then side of the icosahedron is greater than the side of the dodecahedron. One might think (because I did) that the icosahedron , having twenty faces, would have a greater volume than the dodecahedron inscribed in the same sphere, because the dodecahedron has only twelve faces and so should be a poorer approximation to a sphere as a result, but this intuition is false. One similarly might expect the sides of the icosahedron to be shorter than those of the dodecahedron for similar reasons, but neither is that true. However, the dodecahedron and icosahedron are dual each to the other, meaning that they each have the same number of edges, and if you swap faces with vertices you get the dual polyhedron. In both figures, opposite edges are ...