TRANSACTIONS OF SECTION A. 433 
2, Huperiments to decide whether the Ether moves with the Earth. 
By Professor W. WIEN. 
In the theory of electro-dynamics, founded by H. A. Lorentz on the hypothesis 
of electrons, the questions as to a possible influence of the earth’s motion on optic 
and electric phenomena are of the greatest importance. A short time ago, it 
seemed dubious whether the theory was able to overcome the difficulties of the 
negative result of the well-known experiments of Michelson and Morley, Lord 
Rayleigh, Brare, Trouton, and Noble. But the recent assumption of Lorentz that 
the electrons have the form of an ellipsoid, the relation of the axes being depen- 
dent upon the velocity—-Mr. Searle has called such ellipsoids Heaviside ellipsoids 
—leads to the conclusion that all optical experiments in which a part of the 
system is made dark by interference or rotation of the plane of polarisation should 
give a negative result, One must of course make the hypothesis that all forces 
and all masses follow the general electro-magnetic laws, and that we have to 
consider only electro-magnetic phenomena. I myself! pronounced the opinion some 
years ago that it may be of the utmost consequence to found mechanics, too, on the 
general equations of the electro-magnetic field, and to define the mass as the 
M, 
electro-magnetic mass of the charged Heaviside ellipsoids, regarded as the 
constituents of all material bodies. 
Taking this point of view, it seems to me that no results could be expected 
from the experiments with the rotation of the plane of polarisation of light, from 
which the earlier theory of Lorentz led us to expect an influence of the earth’s 
motion of the first order. (nthe other hand, I found that the common theory 
of dispersion gives a positive result of the Michelson-Morley experiment if the 
rays go through water instead of air. This result cannot be annulled by the 
FitzGerald-Lorentz contraction hypothesis. But the recent theory of Lorentz 
expects a negative result in this case too, andI must confess that I have no further 
hope that we should find anything of a positive effect from those optical or elec- 
trical observations. 
But from one experiment it seems to me that, independent of all theory, a 
positive result should be expected if the ether does not move at all with the earth. 
The experiment lies exactly on the limit that by extreme accuracy could be 
observed, and I do not know whether it is possible or not with our present means 
of observation. 
If we measure the velocity of light, using Fourault’s method, but in such a 
manner that the ray of light does not go back along the same path, we should 
1 And Prof, Larmor has had the same idea. 
1904, FF 
