Any cone is a third part of the cylinder with the same base and equal height.
Let a cone have the same base, namely the circle ABCD , with a cylinder and equal height. I say that the cone is a third part of the cylinder, that is, that the cylinder is triple the cone. For if the cylinder is not triple the cone, then the cylinder will be either greater than triple or less than triple the cone. First let it be greater than triple. Inscribe the square ABCD in the circle ABCD .