For thermal neutrons we have measured the Fizeau effect to 1.5% accuracy. The quoted accuracy was achieved by use of a newly designed neutron interferometer. Four fast-moving samples, all parts of a single, four-winged, aluminum, rotating propeller, could be made to engage simultaneously in the interfering beams. Our experiment complements and exceeds two recent Fizeau experiments, one of which was performed with cold neutrons and much lower accuracy and the other with a moving medium inside stationary boundaries resulting in a null Fizeau effect.

• Received 18 November 1985

DOI:https://doi.org/10.1103/PhysRevLett.56.2441