48 Presidential Address 



The truth underlying this doctrine is 

 that absolute motion without reference 

 to anything is unmeaning. But the 

 narrowing down of " any thing" to mean 

 any piece of matter is illegitimate. The 

 nearest approach to absolute motion 

 that we can physically imagine is motion 

 through or with respect to the Ether of 

 Space. It is natural to assume that the 

 Ether is on the whole stationary, and to 

 use it as a standard of rest; in that sense 

 motion with reference to it may be called 

 absolute, but in no other sense. 



The Principle of Relativity claims that 

 we can never ascertain such motion: in 

 other words it practically or pragmati- 

 cally denies the existence of the Ether. 

 Every one of our scientifically observed 

 motions, it says, are of the same nature 

 as our popularly observed ones, viz., 

 motion of pieces of matter relatively to 

 each other; and that is all that we can 

 ever know. Everything goes on says 

 the Principle of Relativity as if the 

 Ether did not exist. 



Now the facts are that no motion with 



