D O C . 3 1 I D E A S A N D M E T H O D S 1 1 5
i.e., the movement of a non-light-refracting fluid has no influence upon the propa-
gation velocity of the light penetrating it.
This result forced the conception that the light ether does not partake at all in the
movement of matter and that the influence of moving matter upon light, as given in
(2), is not to be explained by a movement of the light ether but rather in another
more indirect manner. This other explanation was later given by H. A. Lorentz in a
very complete and satisfying manner by maintaining the hypothesis of a fixed—or
as one can also say—light ether at
In passing, we mention that the fact of the aberration of light (discovered by
Bradley in 1727) could only be satisfactorily explained if one assumed that the
ether at the surface of the earth does not partake in the movement of the earth
around the
3. The Lorentz Theory
The theory of the light ether at rest became completely successful by the pioneering
research of H. A. Lorentz
who simplified and deepened the Maxwellian
theory and simultaneously brought it into agreement with all electromagnetic and
optical results known at that time. His theory rests on the following basis:
a. In matter, too, only the ether (but not matter) is the base of the electromagnetic
b. Matter is electromagnetically effective only as the carrier of electric masses
that are movable, together with it (when matter moves) and relative to it (when
there is electric current, a changing electric polarization, a magnetization).
c. The Maxwellian equations for vacuum are valid everywhere (also inside mat-
ter) in a coordinate system relative to which the light ether is at rest.
Between Maxwell’s and Lorentz’s time, a slow and important change in funda-
mental concepts of theoretical physics took place that we cannot ignore. Maxwell
himself still clung to the conception that all physical events have to be interpreted
in terms of mechanics. But his efforts, and those of other important theoreticians,
to devise a mechanical model of electromagnetic phenomena in the ether did not
meet with success. Poincaré pointed out that even if the construction of such a pic-
ture were accomplished, it would not be a decisive success because such a picture
would only be one in an infinite number of possible ones which, in principle, would
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