"In 1851 a young French physicist erected a giant pendulum in the heart of Paris and showed astonished spectators that the Earth was turning beneath their feet. Pendulum mania swept the learned and everyday worlds and Leon Foucault's name became synonymous with his famous pendulum. The demonstration continues to captivate a century and a half later." The history and interpretation of the pendulum experiment are described in terms suitable for the general reader in this abundantly illustrated biography of Foucault. His contributions to science went well beyond the pendulum, however: most notably to the gyroscope, to decisive laboratory measurements of the speed of light, and to the invention of the telescope in its modern form. Foucault was a talented early photographer. Gifted with his hands, he valued precision and loved clockwork. He worked in optics and electricity. Though steadfast in friendship, he could be stubborn and blunt. His collaboration with Hippolyte Fizeau ended in rift while the frankness of the newspaper articles that he wrote provoked hostilities that hindered his acceptance by academic peers. Telescope making and dreams of wealth from an industrial governor were curtailed by an agonizing early death. The blend of pure and applied in Foucault's work and the ordeals he suffered make him an intriguing case study as one of the last amateur scientists at a time when science was becoming institutionalized. The book assumes some familiarity with sample scientific terms, but no detailed knowledge of physics is required.