Fizeau Method

One of the first truly relativistic experiments, intended to measure the speed of light. Light is passed through a spinning cogwheel driven by running water, is reflected off a distant mirror, and then passed back through the spinning cogwheel. When the rate of running water (and thus the spinning of the cogwheel) is synchronized so that the returning pulses are eclipsed, c can be calculated.

See also: Velocity of Light in Vacuo.