Experiments of Rayleigh and Brace

They were some of the first optical experiments measuring the relative motion of Earth and the luminiferous aether which were sufficiently precise to detect magnitudes of second order to v/c.

Lord Rayleigh (1902) interpreted this contraction as a mechanical compression which should lead to optical anisotropy of materials, so the different refraction indices would cause birefringence.

Depending on the direction relative to Earth's motion, the expected retardation due to birefringence was of order 10−8, which was well within the accuracy of the experiment.

Rayleigh repeated the experiments with layers of glass plates (although with a diminished precision by a factor of 100), and again obtained a negative result.

Sun light was directed into the water through a system of lenses, mirrors and reflexion prisms, and was reflected 7 times so that it traversed 28.5 m. In this way, a retardation of order 7.8×10−13 was observable.