32 RELATIVITY 



have no ground for any preconception, the experimental 

 conclusions can be accepted without surprise or mis- 

 giving. Characters such as mass and rigidity which we 

 meet with in matter will naturally be absent in aether; 

 but the aether will have new and definite characters of 

 its own. In a material ocean we can say that a particu- 

 lar particle of water which was here a few moments ago 

 is now over there; there is no corresponding assertion 

 that can be made about the aether. If you have been 

 thinking of the aether in a way which takes for granted 

 this property of permanent identification of its particles, 

 you must revise your conception in accordance with the 

 modern evidence. We cannot find our velocity through 

 the aether; we cannot say whether the aether now in this 

 room is flowing out through the north wall or the south 

 wall. The question would have a meaning for a mate- 

 rial ocean, but there is no reason to expect it to have a 

 meaning for the non-material ocean of aether. 



The aether itself is as much to the fore as ever it was, 

 in our present scheme of the world. But velocity through 

 aether has been found to resemble that elusive lady 

 Mrs. Harris; and Einstein has inspired us with the 

 daring scepticism — "I don't believe there's no sich a 

 person". 



Is the FitzGerald Contraction Real? I am often asked 

 whether the FitzGerald contraction really occurs. It 

 was introduced in the first chapter before the idea of 

 relativity was mentioned, and perhaps it is not quite 

 clear what has become of it now that the theory of 

 relativity has given us a new conception of what is going 

 on in the world. Naturally my first chapter, which 

 describes the phenomena according to the ideas of 

 classical physics in order to show the need for a new 



