Reinterpretation of Fizeau’s Experiment with Moving Medium in Accord with the Sagnac Effect Due to Earth’s Rotation

The famous Fizeau’s interferometry experiment with flowing water is commonly cited as a demonstration of the velocity transformation in the special relativity. In this investigation, by taking into account the modification of the propagation velocity due to the motion of dielectric medium and the modification of the propagation length due to the Sagnac effect, an entirely different interpretation of this experiment is presented. Physically, the influence of the medium velocity on the phase velocity is associated with an effect of the polarization current. Both the medium velocity and the Sagnac effect depend on earth’s rotation, while its influence on the phase difference in Fizeau’s experiment cancels out substantially.