1862 Leon Foucault

Another French physicist, Leon Foucault, used a similar method to Fizeau. He shone a light to a rotating mirror, then it bounced back to a remote fixed mirror and then back to the first rotating mirror. But because the first mirror was rotating, the light from the rotating mirror finally bounced back at an angle slightly different from the angle it initially hit the mirror with. By measuring this angle, it was possible to measure the speed of the light. Foucault continually increased the accuracy of this method over the years. His final measurement in 1862 determined that light traveled at 299,796 Km/s.

Speed of Light Historical Measurements