132 GRAVITATION— THE LAW 



revolutionary than anything Einstein has ventured to 

 advocate. Let us take the problem of a falling stone. 

 There is a relative acceleration of 32 feet per second 

 per second — of the stone relative to ourselves or of our- 

 selves relative to the stone. Which end of the relation 

 must we choose? The one indicated by molecular bom- 

 bardment? Well, the stone is not bombarded; it is 

 falling freely in vacuo. But we are bombarded by the 

 molecules of the ground on which we stand. Therefore 

 it is we who have the acceleration; the stone has zero 

 acceleration, as the man in the lift supposed. Your sug- 

 gestion makes out the frame of the man in the lift to 

 be the only legitimate one; I only went so far as to 

 admit it to an equality with our own customary frame. 



Your suggestion would accept the testimony of the 

 drunken man who explained that u the paving-stone got 

 up and hit him" and dismiss the policeman's account of 

 the incident as "merely spinning paradoxes". What 

 really happened was that the paving-stone had been 

 pursuing the man through space with ever-increasing 

 velocity, shoving the man in front of it so that they kept 

 the same relative position. Then, through an unfor- 

 tunate wobble of the axis of the man's body, he failed 

 to increase his speed sufficiently, with the result that 

 the paving-stone overtook him and came in contact with 

 his head. That, please understand, is your suggestion; 

 or rather the suggestion which I have taken the liberty 

 of fathering on you because it is the outcome of a very 

 common feeling of objection to the relativity theory. 

 Einstein's position is that whilst this is a perfectly 

 legitimate way of looking at the incident the more usual 

 account given by the policeman is also legitimate; and 

 he endeavours like a good magistrate to reconcile them 

 both. 



