Motion of the Earth and the ALthcr. 815 



10 -4 . Thus the greatest effect due to the irrotational motion 

 is about 10 -4 of the Doppler effect due to the earth's daily 

 motion. This is an effect of the second order, as was to be 

 expected, and is vastly smaller than the least effect which can 

 be detected. 



The theory proposed therefore appears to offer a simple 

 explanation of all available facts, and does not seem to lead 

 to any contradictions or discrepancies. On the other hand, 

 it does not appear to be easily capable of special verification 

 or the reverse. It is necessary to suppose that the density of 

 the aether is very small because otherwise there would be 

 appreciable forces between pieces of matter of high permea- 

 bility put in the aetherial stream. This supposition, however, 

 is not one to which most physicists will be disposed to object. 



In conclusion, it may perhaps be worth while to Fay a few 

 words about the bearing of the theory proposed on the 

 so-called " principle of relativity.'" This principle is based 

 on the negative results of the experiments made to detect 

 the motion of the aether relative to the earth. The present 

 theory suggests that the negative results are due not to any 

 inherent impossibility of detecting the motion, but merely to 

 the arrangement of the experiments and character of the 

 motion. The principle of relativity with some of its conse- 

 quences, including the supposed change of length with 

 velocity and the apparent dependence of time on velocity and 

 position, appears therefore not to be necessary, at any rate 

 for the explanation of the facts on which it is based. 



It is necessary to suppose that the aether behaves like a 

 perfect incompressible fluid for irrotational motions, but has 

 nevertheless rotational elasticity which enables it to transmit 

 light-vibrations. The hydrodynamical aether doublets which, 

 aocording to the theory proposed, are present in the atom, are in 

 some ways analogous to Lord Kelvin's vortex rings, but may 

 be supposed to have a fixed size determined by the distance 

 between the source and sink. This gets rid of the difficulty in- 

 herent in the vortex-ring theory, that there is nothing in it to 

 determine the scale of linear magnitude of the atoms. Accord- 

 ing to the present theory, a piece of matter in a stream ot: 

 aether behaves like a piece of iron in a stream ot aether on the 

 theory that a magnetic field consists of an aetherial stream 

 along the lines of force. This theory of the magnetic 

 field seems, however, to require the aether to be at rest rela- 

 tively to the earth at the earth's surface, because otherwise 

 there ought to be a magnetic field corresponding to the 

 aetherial stream. If we suppose that this field is too weak to 

 be detected, then the velocity of the aether in a strong field 

 must be very large compared with the velocitv of the earth. 



