. Since the mutual position of the mirror was not known to me, I was unable to calculate the influence of this error, and it was only possible to estimate it only superficially, by making an appropriate assumption on that location, and by applying the usual formulas for the metal reflection. In this way, the calculation, however, led to a difference in the analyzer positions with respect to the two locations of the system, but it was clearly smaller than the differences observed by Fizeau. It should be noted, incidentally, that by one of the experimental series, the heliostat mirror was replaced by a totally reflecting prism and that this seems to have been without influence on the results.
Everything taken together, the question is forced upon us, whether it might be possible to adapt the theory to observations, without ceasing to explain the other phenomena discussed in this work. I haven't succeeded in this, and I must therefore leave the whole question open, in the hope that others might overcome the difficulties that still exist.
That the improvement of the theory will not be so easy, and that the phenomena in the experiments of Fizeau in any case did not happen in the way, as they were interpreted by him in his introductory observations, this is what I finally want to show.
It will suffice to consider for this purpose, a single glass plate. If we decompose the velocity of translation in two component that are perpendicular to the plate, or parallel, then, if we neglect magnitudes of second order, the effects of those components remain side by side. The problem can thus be reduced to two simpler cases. It is now possible, without making special assumptions about the nature of light oscillations, that a translation perpendicular to the plate, can not have the expected influence of Fizeau; we will derive some general considerations. As for the other direction of translation, we can not speak so determined; it can only be shown, that the
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