However, the change in this displacement caused by the variation of the propagation times — we want to call it Maxwell's displacement for sake of brevity — was found, and thus Michelson thought that he is allowed to conclude that the aether wouldn't remain at rest when the Earth is moving, a conclusion however, whose correctness was soon questioned. By inadvertence, Michelson has estimated the change of the phase differences as expected by the theory, to double of the correct value; if we correct this error, we arrive at displacements, which just could be hidden by the observational errors.
Together with Morley, Michelson has started again the investigation,[1] where (to increase the sensitivity) he let reflect every light beam by some mirrors back and forth. This artifice gave the same advantage, as if the arms of the earlier apparatus would have been considerably extended. The mirror was carried by a heavy stone plate, that floated on mercury and thus was easily rotatable. Altogether, every beam had to traverse a path of 22 meters, and by Fresnel's theory, when passing from one main-position to the other, a displacement of 0,4 of the fringe-distance was to be expected. Nevertheless, during the rotation only displacements of at most 0,02 of the fringe-distance were obtained; they probably might stem from observational errors.
Now, is it allowed to assume on the basis of this result, that the aether shares the motion of Earth, and thus Stokes' aberration theory is the correct one? The difficulties, with which this theory is confronted when explaining aberration, seem too great to me as for having that opinion, so I rather should try to remove the contradiction between Fresnel's theory and Michelson's result. Indeed
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