Pappus of Alexandria
On the Equilibrium of Planes () is a treatise by Archimedes in two volumes. The first book establishes the law of the lever, and locates the centre of gravity of the triangle and the trapezoid. According to Pappus of Alexandria, Archimedes' work on levers caused him to remark: "Give me a place to stand on, and I will move the Earth." (). The second book, which contains ten propositions, examines the centres of gravity of parabolic segments.