The Scientific Revolution e picture of the natural world that the scientic revolution shattered was a strange and complicated one. Its astronomy derived from Claudius Ptolemy, who lived in Alexandria in the second century c.e. Ptolemy taught that the earth was motionless at the center of the universe, that around it were ten concentric crystalline spheres carrying the planets and the stars, and that beyond the tenth sphere lay the high heavens. Angels kept the spheres in motion, and all bodies moved in perfect circles at uniform speeds. To make this picture t the observed motion of the stars and planets, Ptolemy invented a complicated system of epicycles, eccentrics, and equants. Medieval people took their physics from Aristotle, who taught that heavy objects fall to the Earth more swily than light ones, that a uniform force applied to an object will move it at a constant speed, and that an object will immediately stop if the force acting on it ceases. In Aristotelian physics an arrow should drop to the ground the minute it leaves the bowstring. e chemistry of the age was based on the writings of the Greek

philosopher Empedocles, who taught that matter consisted of four elements-re, air, water, and earth. Later writers argued that the planets and stars were made up of a h element (or quintessence), an ethereal substance that grew more pure as one traveled away from the Earth.