The many momentous events of Newton’s academic life culminated in his great work Philosophiae Naturalis Principia Mathematica published in London in 1687. This treatise, which systematizes the mechanics of the universe, is without doubt the greatest work of scientific genius that the world has yet seen. The Principia begins with the solid foundation on which the three books rest. Newton begins by defining the concepts of mass, motion (momentum), and three types of forces: inertial, impressed and centripetal. He also gives his definitions of absolute time, space, and motion, offering evidence for the existence of absolute space and motion in his famous "bucket experiment". These absolute concepts provoked great criticism from philosophers Leibnitz, Berkeley, and others, including Ernst Mach centuries later. The three Laws of Motion are proposed, with consequences derived from them. The remainder of The Principia continues in rigorously logical Euclidean fashion in the form of propositions, lemmas, corollaries and scholia. Book One, Of The Motion of Bodies, applies the laws of motion to the behavior of bodies in various orbits. Book Two continues with the motion of resisted bodies in fluids, and with the behavior of fluids themselves. From the density of air, he calculated the speed of sound waves.