is the index of refraction of the liquid. On the other hand, owing to
the smallness of
image017
as compared with 1, we can replace (B) in the first place by
image018
or to the same order of approximation by
image019
which agrees with Fizeau s result.
Nevertheless we must now draw attention to the fact that a theory of
this phenomenon was given by H. A. Lorentz long before the statement of
the theory of relativity. This theory was of a purely electrodynamical
nature, and was obtained by the use of particular hypotheses as to the
electromagnetic structure of matter. This circumstance, however, does
not in the least diminish the conclusiveness of the experiment as a
crucial test in favour of the theory of relativity, for the
electrodynamics of Maxwell-Lorentz, on which the original theory was
based, in no way opposes the theory of relativity. Rather has the
latter been developed trom electrodynamics as an astoundingly simple
combination and generalisation of the hypotheses, formerly independent
of each other, on which electrodynamics was built.
XIV.
31