0,000064. The change of rotation caused by that, could not have been overlooked by Mascart, and thus his negative result can only by explained by the assumption, that, in the formula for , k has a value comparable with , and the opposite sign of j.
Now, whether (for quartz and other bodies) the two terms containing will mutually be cancelled, or whether an observable influence of Earth's motion remains finally, has to be decided by additional investigations.
The interference experiment of Michelson.
§ 89. As it was first noticed by Maxwell, and which follows from a very simple calculation, the time required by a light ray to travel forth and back between two points A and B must change, as soon as these points are subject to a common displacement, without dragging the aether. Although the variation is a magnitude of second order, it is nevertheless big enough that it can be demonstrated by means of a sensitive interference method.
The experiment was executed by Michelson in the year 1881.[1] His apparatus, a kind of interference-refractor, had two equally long, horizontal, mutually perpendicular arms P and Q, and from the two mutually interfering light beams, one went forth and back along arm P and the other one along arm Q. The whole instrument, including the light source and the observation device, could be rotated around a vertical axis, and especially the two locations come into consideration, at which arm P or arm Q had (so far as possible) the direction of Earth's motion. Now, during the rotation from one "main-position" into the other, a displacement of the interference fringes was expected on the basis of Fresnel's theory.
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