Page:Eddington A. Space Time and Gravitation. 1920.djvu/227

Rh An attempt was made by Stokes to reconcile mathematically a convection of aether by the earth with the accurately verified facts of astronomical aberration; but his theory cannot be regarded as tenable. Lodge investigated experimentally the question whether smaller bodies carried the aether with them in their motion, and showed that the aether between two whirling steel discs was undisturbed.

The controversy, stagnant versus convected aether, had now reached an intensely interesting stage. In 1895, Lorentz discussed the problem from the point of view of the electrical theory of light and matter. By his famous transformation of the electromagnetic equations, he cleared up the difficulties associated with the first-order effects, showing that they could all be reconciled with a stagnant aether. In 1900, Larmor carried the theory as far as second-order effects, and obtained an exact theoretical foundation for FitzGerald's hypothesis of contraction, which had been suggested in 1892 as an explanation of the Michelson-Morley experiment. The theory of a stagnant aether was thus reconciled with all observational results; and hence forward it held the field.

Further second-order experiments were performed by Rayleigh and Brace on double refraction (1902, 1904), Trouton and Noble on a torsional effect on a charged condenser (1903), and Trouton and Rankine on electric conductivity (1908). All showed that the earth s motion has no effect on the phenomena. On the theoretical side, Lorentz (1902) showed that the indifference of the equations of the electromagnetic field to any velocity of the axes of reference, which he had previously established to the first order, and Larmor to the second order, was exact to all orders. He was not, however, able to establish with the same exactness a corresponding transformation for bodies containing electrons.

Both Larmor and Lorentz had introduced a "local time" for the moving system. It was clear that for many phenomena this local time would replace the "real" time; but it was not suggested that the observer in the moving system would be deceived into thinking that it was the real time. Einstein, in 1905 founded the modern principle of relativity by postulating that this local time was the time for the moving observer; no