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Rh greatest axes of the ellipsoidal electrons of the equivalent system at rest. Otherwise the effect would be masked in using natural light, since, with this type of interferometer, the above components may be as low as 25 per cent, of the total interfering light, as Mills has shown.

The remaining second order tests first proposed by FitzGerald and developed and carried out by Trouton, by examining the couple on a suspended condenser, gave negative results. This is completely explained on the assumption of a shrinkage.

Direct experiments on the entrainment of the aether have also given negative results. Thus Lodge sent two interfering rays in opposite directions several times around a rectangle between two rotating steel disks, without being able to detect any displacement of the interference-bands. He estimates that if the disks had communicated one eight-hundredth part of their velocity to the aether, he would have been able to detect it.

Zehnder, using a different method, attempted to detect any dragging of the aether by a metal plug moving within a cylinder whose ends were circuited together by parallel branching tubes through which two interfering rays could be sent in opposite directions. I£ the aether had moved entirely with the plug, the effect would have been a thousand times larger than this sensibility. Fizeau's well-known experiment on the entrainment of the aether, repeated by Michelson and Morley, showed no effect after allowing for the reaction of the moving water itself upon the interfering waves. Had the aether been carried along completely, the displacement would have been nearly two and a half bands, instead of approximately the single band actually observed, due to the reaction of the water alone. We may conclude from these experiments that the aether was not entrained in any way in the experiments of Morley and Miller, and that their results are therefore valid, although performed within an enclosure.

Nordmeyer, carrying out the experiment first proposed by Fizeau on the change in intensity of a radiant due to the earth's motion, found that this variation could not have been