'The Mathematical Principles of Natural Philosophy', or 'The Principia' as it came to be commonly known, begins with the solid foundation on which the three books rest. Newton begins by defining the concepts of mass, motion , and three types of force.  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. 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. In the Third Book, The System of the World, Newton applies the Law of Universal Gravitation to the motion of planets, moons and comets within the Solar System. He explains a diversity of phenomena from this unifying concept, including the behavior of Earth's tides, the precession of the equinoxes, and the irregularities in the moon's orbit. The Principia brought Newton fame, publicity (whether he wanted them or not!), and financial security. It established him, at the age of 45, as one of the greatest scientists in history. 