In 1848, Hippolyte Fizeau determined the speed of light using two fixed mirrors about 8 km apart, one partially obscured by a rotating cogwheel with over 100 teeth rotating a few hundred times a second.
In 1848, Hippolyte Fizeau determined the speed of light between an intense light source and a mirror about 8 km distant. The light source was interrupted by a rotating cogwheel with over 100 notches rotating hundreds of times a second.