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 The difference between the observed and the average values was added to the observed values in order to determine the deviation at either side of the average. It was observed that they generally represent a very minute fraction of the width of the fringe; the greatest deviation did not exceed 1/13 of a fringe.

A difficulty, impossible to avoid, furnished the explanation for these differences. The maximum displacement takes place during a very short time, and, consequently, the observation must be done rapidly. If it were possible to maintain a constant flow speed of the water for a longer time, the measurements would be more precise. But this has not been possible without introducing considerable changes in the apparatus. Such changes would have retarded this experiment to a time of the year when experiments requiring the use of sunlight become almost impossible to perform.

I want now to compare the value found for the displacement of the fringes to that which would be the result of each of the hypotheses in question.

To start with, it suffices that the motion of the water displaces the fringes in any amount to exclude the supposition that the ether is completely free and independent of the motion of the body.

It is also necessary to calculate what the displacement of the fringes would be assuming that the ether is attached to the molecules of the body so that they would share in each other's motion.

The speed of light in water, when this liquid is in motion, will be for both rays,

$v'+u$ and $v'-u$