Fizeau method (A. Fizeau, 1851):
One of the first really relativistic experiments intended to calculate the speed of light. Light is flow through a spinning cogwheel driven through running water, is reflected off a distant mirror, and passed back then through the spinning cogwheel. While the rate of running water (and therefore the spinning of the cogwheel) is synchronized so that the returning pulses are eclipsed, c may be calculated.