In antiquity, prior to the third century B.C., physics had been a branch of philosophy. It was made a separate, experimental science by Archimedes of Syracuse, who lived between 287 and 212 B.C.. He not only discovered the law of floating objects, or specific gravity, but also formulated with scientific exactness the principles of the lever, the pulley, and the screw. Among his memorable inventions were the compound pulley and the screw propeller for ships. Although he has been considered the greatest technical genius of antiquity, in fact he preferred to devote himself to pure scientific research. Tradition relates that he discovered “Archimedes’ principle,” that is, specific gravity, while pondering possible theories in his bath; when he reached his stunning insight, he dashed out naked into the street crying “Eureka!” (“I have found it!”).