Aberration of light in a moving medium

Abstract

The transverse 'Fresnel ether drag' experienced when light passes through a refracting medium moving at right angles to the original direction of the light, and confirmed indirectly by Airy's water- filled telescope experiment, has been observed directly. A change in rotation speed from 600 to 1800 rpm of a glass disc, of 19.1 mm thickness and refractive index 1.51, produced a transverse displacement of about 1.5*10-6 mm in a light beam passing twice through the disc at a radius of 110 mm from the axis of rotation. This agrees with the Fresnel formula to within the 10% accuracy of the experiment.