812 Prof. H. A. Wilson on the Relative 



aberration, and the negative results of the experiments on the 

 relative motion of the earth and the aether. 



According to this view a hollow space inside a piece of 

 matter will be partly screened off from a stream of aether 

 just as a space inside a piece of iron is screened off from a 

 magnetic field. I believe most of the experiments made to 

 detect effects due to aetherial motion have been carried out 

 inside buildings ; so that if any of them could have detected 

 a vertical motion, these may have failed on account of the 

 walls of the building screening off the aatherial stream. I 

 think, however, that no experiment which would have detected 

 a vertical motion has yet been attempted. 



Let us now consider Sir Oliver Lodge's experiment, which 

 showed that the aether near a rapidly rotating steel disk is 

 not carried round by the disk. Any change in the motion of 

 the aether due to setting the disk in rotation must be due to 

 free sources and sinks produced by the displacement of the 

 sources relatively to the sinks. But it is clear that this dis- 

 placement due to the rotation will take place in circles round 

 the axis of the disk, so that no free .sources or sinks will be 

 produced, and so the aether outside will be unaffected by the 

 rotation. In any case, the motion of matter through the 

 aether will only produce irrotational motion of the aether 

 outside the matter, and so will not produce any first order 

 optical effects. 



It will be convenient now to consider Fizeau's experiment 

 on the velocity of light in moving water, and the absence of 

 any effect due to the earth's motion on refraction, and other 

 optical phenomena taking place inside transparent media. If 

 Ave assume that the velocity of light relative to the aether is 

 iucreased inside matter by 1 — l//u 2 times the velocity of the 

 matter relative to the aether, which was shown to be the case 

 by Fizeau's experiment, then it is easy to show that the 

 aetherial motion due to matter according to the theory here 

 put forward will have no first order optical effects inside as 

 well as outside matter. To show this it is sufficient * to prove 

 that the change in the time taken by light to pass from one 

 point to another due to the aetherial molion is the same for all 

 paths between the two points. Let ds denote an element of 

 such a path and c the velocity of light in free aether. Then 

 the time in question when the aether is at rest is 



ds 



S, 



where fi is the refractive index of the matter at ds and v m the 



* See H. A. Lorentz, ■ Theory of Electrons," p. 181. 



