It is clear that we have the problem of Section 6 again before us. The tube plays
the part of the railway embankment or of the co-ordinate system K, the liquid
plays the part of the carriage or of the co-ordinate system K1, and finally, the
light plays the part of the
Figure 03: file fig03.gif
man walking along the carriage, or of the moving point in the present section. If
we denote the velocity of the light relative to the tube by W, then this is given by
the equation (A) or (B), according as the Galilei transformation or the Lorentz
transformation corresponds to the facts. Experiment * decides in favour of
equation (B) derived from the theory of relativity, and the agreement is, indeed,
very exact. According to recent and most excellent measurements by Zeeman,
the influence of the velocity of flow v on the propagation of light is represented
by formula (B) to within one per cent.
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.
Notes
*) Fizeau found eq. 10 , where eq. 11
is the index of refraction of the liquid. On the other hand, owing to the smallness
of eq. 12 as compared with I,
we can replace (B) in the first place by eq. 13 , or to the same order of
approximation by