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 This number is actually in relation to velocity in a vacuum. In order to relate it to air, it should be divided by the refraction index of this medium. But, this index is so close to unity that for the sake of simplification, it is possible to ignore the transformation while introducing an error no greater than unity in the last figure.

The value for the fringe displacement, as a function of the width of a fringe, is obtained by dividing the above quantity by the value of a wavelength. As a matter of fact, for a difference in speed of 1, 2, 3, m wavelengths, the fringe system is displaced by 1, 2, 3, m fringes.

The wavelength for ray E is $$\lambda$$ = 0.000526. These are the rays that seem to maintain the greatest intensity, since the light must travel through a rather considerable thickness of water.

Finally the fringe displacement is found,

$\frac{\Delta}{\lambda}=0,4597$

If there were agreement with the hypothesis in question, the ether would be placed in motion at a speed equal to that of the water, which, in the preceding experiment would have caused a displacement of 0.46 fringes.

But, the average of the observations has been only 0.23, and observation of the individual values higher than the average shows that none of them approaches the number 0.46. I should also add that this number should be still greater because of a small error in the evaluation of the speed of water. The source of this error is known, as will be seen later, but it has not been possible to correct the error exactly.

It is evident that this hypothesis is not in agreement with the experiment.

On the other hand, we shall see that the third hypothesis put forward by Fresnel, leads to a displacement value very close to the observational result.