1 1 6 D O C . 3 1 I D E A S A N D M E T H O D S
be equally
justified.[10]
Gradually, one got used to viewing electromagnetic fields
as ultimate physical realities that do not require a reduction to mechanical ele-
ments. Today the mechanical interpretation of the electromagnetic field appears su-
perfluous to the expert, because, under the impression of many failures, we became
used to resignation in this respect, and furthermore, because in the latest state of
theoretical development we have abandoned the opinion that mechanical processes
are simpler or better known and can conceptually be grasped more easily than
physical process of another kind.—
The 〈Lorentz〉 ether consequently has lost during this period something of its
corporeality. While it was an elastic solid body in the past, it now was only a carrier
of electromagnetic fields. One can say of the ether: its only mechanical property
was its immovability.
I do not want to go into the details of the important confirmations of Lorentz’s
theory except to note that even today there is no other theory of electromagnetic
processes comparable to it as far as truth content and internal consistency are con-
cerned.
4. 〈The Principle of Special Relativity〉 The Ether Wind
One fatal aspect, however, seemed to cling to Lorentz’s theory—namely, the light
ether at rest which, more or less, is a materialization of absolute space as Newton
introduced it. This is due to the following pressing consideration. The earth moves
on its course around the sun with a velocity of 30 km/sec. Whatever the state of mo-
tion of the sun against the ether might have been, there certainly had to be a con-
siderable velocity of the earth relative to the medium of light during part of the year.
Alternatively, this can be phrased as follows: the ether flows by with very consid-
erable speed (of at least 30 km) while we sit on this earth, and furthermore it flows
through us and through earth (ether wind). While the blowing of this wind cannot
be felt directly, it should be noticeable at least indirectly in electromagnetic and op-
tical experiments. One would expect, for example, that the speed of light in a vac-
uum in the direction of the ether wind amounts to , in the opposite direction
when v is the velocity of the earth relative to the ether. In general, one would
expect with optical and electromagnetic experiments that the orientation of the ap-
paratus relative to the direction of the ether wind should show some influence.
Naturally, the experimental confirmation of the 〈directed〉 existence of the ether
wind tempted physicists immensely. Most diverse apparatuses were investigated
whose total orientation relative to the direction of the ether wind could be changed
[p. 4]
c v +
c v –