From the Mont Valérien, Suresse, the French physicist Fizeau projected a lightbeam towards a mirror at Montmartre. Interposed in the path was a rapidly spinning cogweel with 720 precisely machined teeth. The beam would be exclipsed if the spin of the wheel was going faster. From this, Fiezau could calculate the speed of light as 315 400 km/sec. This was 1849!