Illustration of French physicist Jean Bernard Leon Foucault (1819-1868). Foucault is best known for his demonstration of the Foucault pendulum, a device demonstrating the effect of the Earth's rotation. Foucault's studies in experimental physics included the measurement of the velocity of light and proving its wave nature, the invention of the gyroscope (1857), the demonstration of the diurnal motion of the Earth with Foucault's Pendulum (1851), the improvement of the mirrors of reflecting telescopes (1862), and the Foucault polarising prism. He was awarded the Copley Medal of the Royal Society. Image published in 1859.