io DOWNFALL OF CLASSICAL PHYSICS 



physicists on the Earth! The FitzGerald contraction 

 will be quite appreciable, and all their measures with 

 scales will be seriously wrong. What a weird system of 

 laws of Nature they will have deduced, if they have over- 

 looked this correction !" 



There is no means of deciding which is right — to 

 which of us the observed relative velocity of iooo 

 miles a second really belongs. Astronomically the gal- 

 axy of which the earth is a member does not seem to 

 be more important, more central, than the nebula. 

 The presumption that it is we who are the more nearly 

 at rest has no serious foundation; it is mere self- 

 flattery. 



"But", you will say, "surely if these appreciable 

 changes of length occurred on the earth, we should 

 detect them by our measurements." That brings me to 

 the interesting point. We could not detect them by any 

 measurement; they may occur and yet pass quite un- 

 noticed. Let me try to show how this happens. 



This room, we will say, is travelling at 161,000 miles 

 a second vertically upwards. That is my statement, and 

 it is up to you to prove it wrong. I turn my arm from 

 horizontal to vertical and it contracts to half its original 

 length. You don't believe me? Then bring a yard- 

 measure and measure it. First, horizontally, the result 

 is 30 inches; now vertically, the result is 30 half-inches. 

 You must allow for the fact that an inch-division of the 

 scale contracts to half an inch when the yard-measure 

 is turned vertically. 



"But we can see that your arm does not become 

 shorter; can we not trust our own eyes?" 



Certainly not, unless you remember that when you 

 got up this morning your retina contracted to half its 

 original width in the vertical direction; consequently it 



