is the velocity of light in resting water. Or, the motion of the water has no influence at all on the ether which transmits light and which permeates the water. In this case the velocity of light is
in both limbs. According, as the one or the other of these two assumptions is valid, the interference fringes would have to become displaced or remain at rest when the direction of the current is reversed. The experiment decided in favour of neither of these possibilities. The interference fringes did, indeed, become shifted, not to the expected amount, however, but only to an amount that would result if the ether assumes the velocity
in water, and not the full value
. This value of the convection of the ether is called Fresnel's convection coefficient. Yet this term is capable of being misunderstood inasmuch as in the electrodynamics developed by Lorentz, the result of Fizeau's experiment speaks in favour of an ether that is absolutely at rest, and the so-called convection coefficient is only a consequence of the structure of matter, in particular of the interaction between electrons and matter, a question into which we cannot enter here. At any rate, at the time preceding the Michelson-Morley experiment aberration, as well as Fizeau's experiment, appeared to speak in favour of an ether that was absolutely at rest.
Now, the Michelson-Morley experiment was to establish the existence of the current of ether (ether "wind") through which the earth continually moves, since the ether is supposed not to participate in the motion of the earth. The scheme of the experiment is as on [p. 74].
A ray of light, starting out from
