60 TIME 



to which they are referred is evidently the frame appro- 

 priate to an electron engaged in self-contemplation, viz. 

 the frame in which it is at rest But when we talk about 

 mass we refer it to the frame in which we are at rest. 

 By the geometry of the four-dimensional world we can 

 calculate the formulae for the change of reckoning of 

 mass in two different frames, which is consequential on 

 the change of reckoning of length and time; we find 

 in fact that the mass is increased in the same ratio as the 

 length is diminished (FitzGerald factor). The increase 

 of mass that we observe arises from the change of 

 reckoning between the electron's own frame and our 

 frame. 



All electrons are alike from their own point of view. 

 The apparent differences arise in fitting them into our 

 own frame of reference which is irrelevant to their 

 structure. Our reckoning of their mass is higher than 

 their own reckoning, and increases with the difference 

 between our respective frames, i.e. with the relative 

 velocity between us. 



We do not bring forward these results to demonstrate 

 or confirm the truth of the theory, but to show the use 

 of the theory. They can both be deduced from the 

 classical electromagnetic theory of Maxwell coupled (in 

 the second problem) with certain plausible assumptions 

 as to the conditions holding at the surface of an electron. 

 But to realise the advantage of the new theory we must 

 consider not what could have been but what was deduced 

 from the classical theory. The historical fact is that the 

 conclusions of the classical theory as to the first prob- 

 lem were wrong; an important compensating factor 

 escaped notice. Its conclusions as to the second problem 

 were (after some false starts) entirely correct numer- 

 ically. But since the result was deduced from the electro- 



