Book I

is the principle of the lever. This was known to Plato and Aristotle, but they had no real proof. The Aristotelian _Mechanics_ merely 'refers' the lever 'to the circle', asserting that the force which acts at the greater distance from the fulcrum moves the system more easily because it describes a greater circle. Archimedes also finds the centre of gravity of a parallelogram, a triangle, a trapezium and finally (in