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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.