Fizeau method (A. Fizeau, 1851): One of the primary truthfully relativistic experiments intended to compute the speed of light. Light is passed via a spinning cog-wheel driven by running water, is reflected off a far-away mirror, and then passed back via the spinning cog-wheel. Whenever the rate of running water (and therefore the spinning of the cog-wheel) is synchronized and hence the returning pulses are eclipsed, c can be computed.