Albert Einstein 99 



theories, but in each case the reply given has been the 

 same: " It is impossible to explain Relativity except in 

 terms of algebra." One went on to say further: 



This doctrine has to do with the relationship between physical 

 and mathematical events and can therefore be explained only 

 in mathematical terms. It is impossible to present it in any 

 form which can be understood by those who have not a fairly 

 advanced knowledge of algebra. 



Still, Einstein's theory of space is not so difficult as 

 the idea to which mankind has been accustomed for 

 centuries — the idea that space is infinite. The human 

 mind is baffled by infinity or eternity, but it does seem 

 able to cope with Einstein's conception of curved space. 

 It is possible that before the end of the present century 

 boys and girls will understand Relativity and marvel at 

 their grandparents' inability to do so. 



Einstein's theory of Relativity, by the way, is not a 

 reversal of Sir Isaac Newton's theory of gravity unfolded 

 in his Principia Mathematica in 1687. Einstein's great 

 intellect has simply capped Newton's theory with what 

 he calls an " elliptic interval." While Newton's equa- 

 tions of motion state the true conditions of motion only 

 approximately, Einstein's, as stated in his epoch-making 

 paper of 1915, give them with absolute accuracy. Seated 

 in his study, Einstein proved that Mercury's perihelion 

 should advance forty-three seconds in one hundred years, 

 thus solving at one stroke the problem that had been 

 puzzling astronomers for so long. 



Einstein's achievement went farther still. During his 

 investigations he came to the conclusion that light -rays 

 do not travel in dead straight lines as had hitherto been 

 believed, but that they curve under the influence of a 

 ' gravitational field ' such as the sun. For the moment 

 there was no means of proving this startling statement, 

 which Einstein made with the calmness of conviction. 



