Experiments of Rayleigh and Brace
The experiments of Rayleigh and Brace (1902, 1904) were aimed to show whether length contraction leads to birefringence or not. 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. The results were negative, which was of great importance for the development of the Lorentz transformation and consequently of the theory of relativity. See also Tests of special relativity.
To explain the negative outcome of the Michelson–Morley experiment, George FitzGerald (1889) and Hendrik Lorentz (1892) introduced the contraction hypothesis, according to which a body is contracted during its motion through the stationary aether.
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. To measure this effect, he installed a tube of 76 cm length upon a rotatable table. The tube was closed by glass at its ends, and was filled with carbon bisulphide or water, and the liquid was between two nicol prisms. Through the liquid, light (produced by an electric lamp and more importantly by limelight) was sent to and fro. The experiment was sufficiently precise to measure retardations of of a half wavelength, i.e. of the order 1.2×10−10. 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. Therefore, it was, besides the Michelson-Morley experiment and the Trouton–Noble experiment, one of the few experiments by which magnitudes of second order in v/c could be detected. However, the result was completely negative. 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.
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