For the ray
the length of an undulation is
, and the rays about it appear to preserve the greatest intensity after the light has traversed a rather considerable thickness of water. Selecting this ray, then, we find for the displacement the value
Had, therefore, the æther participated fully in the motion of the water, in accordance with the hypothesis under consideration, a displacement of
of a band would have been observed in the foregoing experiments. But the mean of our observations gave only
