THE ETHER OF SPACE 339 



the kind would be expected on almost any theory. The 

 refractive index properties — the fiK properties — of matter must 

 be expected to travel with it. 



But as to the carrying of ether along near matter by a 

 kind of viscous or mechanical connection, experiment shows 

 that close to rapidly moving steel there is no perceptible 

 effect on the velocity of light, so that the ether appears to be 

 absolutely stationary. But then another experiment yields what 

 at first sight appears to be a precisely contrary result — namely, 

 that light takes precisely the same time to travel to and fro 

 whether its path lies across or along the direction of the earth's 

 motion. For this is just what it would do, if the ether near 

 the earth were clinging to and carried with the earth ; just what 

 it would not do, if the earth were moving through a stationary 

 medium — a medium totally unaffected by its motion. And in 

 general we may say that in all experiments no drift of stationary 

 ether past the moving earth has ever been detected ; thus 

 arises the suggestion that in the neighbourhood of the earth 

 the ether is carried along so as to be relatively stagnant with 

 reference to the earth. 



If a single effect due to the motion of the earth through 

 space could be detected, we might have some hope of de- 

 monstrating a sort of absolute motion, i.e. a motion of the 

 planet with reference to the universal and presumably stationary 

 infinite connecting medium. 



Failing that discovery, what must be our conclusion ? There 

 are some who think that this must be our conclusion : — That 

 absolute motion of this kind can never be detected, that there 

 is no sense in it, that no universal stationary medium exists, 

 that humanity can never detect anything but the effect of 

 relative motion of one piece of matter with respect to another. 

 Relative motion is familiar enough ; absolute motion— or motion 

 relative to an imaginary ether of space — is either meaningless 

 or for ever beyond us. The Principle of Relativity is dominant. 



So — though in other words — runs the argument ; and if 

 the principle of relativity is ever really established, it will 

 give a death-blow to the Ether. 



The principle of relativity has to-day attracted the favour- 

 able attention of many great minds. To the writer it appears 

 a confusing mistake and he wishes to contend against it to 

 the utmost. 



