July 19, 2018
In 1851 H. Fizeau carried out an experiment to measure relative speed of light in moving water . He found that the result is in agreement with the prediction of Fresnel who assumed that the luminiferous ether within material bodies consists of two parts, free ether in the empty space - i.e. between subatomic particles - with lower density and ether bound to subatomic particles – including the particles itself - with higher density. Index of refraction was defined as square of the ether density, so Fresnel predicted that the drag correction factor should be x=1-ρe/ρm=1-1/n². Later repetitions of the experiment  confirmed the measurements of Fizeau.