Jean Bernard Léon Foucault was a French physicist born on September 18, 1819. He is best known for his demonstration of the Foucault pendulum, which provided evidence of the Earth's rotation. This simple yet effective experiment showcased how a pendulum's plane of swing shifts over time, illustrating the rotation of the planet beneath it. In addition to his work on the pendulum, Foucault made significant contributions to the field of optics and the study of gyroscopes. He also invented the Foucault knife-edge test, a method for testing the quality of mirrors in telescopes. His work laid important foundations for modern physics and astronomy.