Love words? Sign up for our Word of the Day!
French physicist who determined that light travels more slowly in water than in air, confirming predictions made by the wave theory of light. In 1850 Foucault also measured the absolute velocity of light. In 1851, by using a type of pendulum that is now named after him, Foucault demonstrated the rotation of the Earth, and in 1852 perfected a gyroscope for the same purpose.