Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/438

 A sequel to the experiment of Michelson and Morley was performed in 1897, when Michelson attempted to determine by experiment whether the relative motion of earth and aether varies with the vertical height above the terrestrial surface. No result, however, could be obtained to indicate that the velocity of light depends on the distance from the centre of the earth; and Michelson concluded that if there were no choice but between the theories of Fresnel and Stokes, it would be necessary to adopt the latter, and to suppose that the earth's influence on the aether to many thousand kilometres above its surface. By this time, however, as will subsequently appear, a different explanation was at hand.

Meanwhile the perplexity of the subject was increased by experimental results which pointed in the opposite direction to that of Michelson. In 1892 Sir Oliver Lodge observed the interference between the two portions of a bifurcated beam of light, which were made to travel in opposite directions round a closed path in the space between two rapidly rotating steel disks. The observations showed that the velocity of light is not affected by the motion of adjacent matter to the extent of (1/200)th part of the velocity of the matter. Continuing his investigations, Lodge strongly magnetized the moving matter (iron in this experiment), so that the light was propagated across a moving magnetic field; and electrified it so that the path of the beams lay in a moving electrostatic field; but in no case was the velocity of the light appreciably affected.

We must now trace the steps by which theoretical physicists not only arrived at a solution of the apparent contradictions furnished by experiments with moving bodies, but so extended the domain of electrical science that it became necessary to enlarge the boundaries of space and time to contain it.

The first memoir in which the new conceptions were unfolded) was published by H. A. Lorentz in 1892. The