VELOCITY THROUGH THE AETHER 31 



east from the north pole we should probably receive 

 the same mathematical answer. "Velocity through 

 aether" is as meaningless as "north-east from the north 

 pole". 



This does not mean that the aether is abolished. We 

 need an aether. The physical world is not to be analysed 

 into isolated particles of matter or electricity with 

 featureless interspace. We have to attribute as much 

 character to the interspace as to the particles, and in 

 present-day physics quite an army of symbols is required 

 to describe what is going on in the interspace. We 

 postulate aether to bear the characters of the interspace 

 as we postulate matter or electricity to bear the charac- 

 ters of the particles. Perhaps a philosopher might ques- 

 tion whether it is not possible to admit the characters 

 alone without picturing anything to support them — thus 

 doing away with aether and matter at one stroke. But 

 that is rather beside the point. 



In the last century it was widely believed that aether 

 was a kind of matter, having properties such as mass, 

 rigidity, motion, like ordinary matter. It would be 

 difficult to say when this view died out. It probably 

 lingered longer in England than on the continent, but 

 I think that even here it had ceased to be the orthodox 

 view some years before the advent of the relativity 

 theory. Logically it was abandoned by the numerous 

 nineteenth-century investigators who regarded matter 

 as vortices, knots, squirts, etc., in the aether; for clearly 

 they could not have supposed that aether consisted of 

 vortices in the aether. But it may not be safe to assume 

 that the authorities in question were logical. 



Nowadays it is agreed that aether is not a kind of 

 matter. Being non-material, its properties are sui generis. 

 We must determine them by experiment; and since we 



