ABSTRACT
In 1851, Hippolyte Fizeau set up an experiment to measure the speed of light in flowing water. He used an interferometer to measure the difference in speed between light propagating in and against the direction of water flowing through a glass pipe with velocity. The sketch on the left shows the principle of Michelson’s interferometer. The light from the source partially passes the semi-transparent mirror onto the movable mirror where it is reflected. On its way back it is again reflected towards the observer. The other part of the source light is reflected into the right arm of the interferometer, where it meets the fixed mirror and passes back towards the observer. A magnetic torque also exists when treating the problem relativistically. However, a second force is to be taken into account, which has no effect in the non-relativistic limit.
