Page:BraceRefraction1904.djvu/1

 THE FitzGerald-Lorentz "Contraction" Hypothesis to explain the negative results of the Michelson-Morley experiment of interference between two rays, at right angles and parallel to the earth's motion, has been tested by Rayleigh in his experiments on the double refraction of liquids and of glass. He assumes the contraction to be $$\left(10^{-4}\right)^{2}$$, and also the excess of the index above unity to be proportional to the density. The first assumption is apparently in error by a half and should be 0.5 &times; 10-8. The second assumption does not seem to be entirely valid for glass, at least, when compared with the double refraction produced by a given strain. The first correction reduces his margin down to 50 times for a liquid and 1.5 times for glass. The second will reduce the margin to considerably less than unity for glass, which would thus leave us only the observations on liquids upon which to base our conclusion.

While the method of Rayleigh cannot be regarded by any means as a conclusive test of the hypothesis, it is the only experimental one attempted and can be extended so as to give a safe margin for a solid like glass.

This suggestion of the "contraction" hypothesis by Lorentz, from considerations in regard to intermolecular forces analogous to the interaction, through the mediation ''Phil. Mag.'' S. 6. Vol. 7. No. 40. April 1904.