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XXXII. On the Einstein Spectral Line Effect. 



To the Editors of the Philosophical Magazine. ■ 



Gentlemen, — 



PROF. H. J. PRIESTLEY'S suggestion in the May- 

 number of the Magazine appears to possess one dis- 

 advantage. 



In using the form of the equations 



\ds / 





and r fc =h > ( iL > 



we generally compare these with the Newtonian equations 

 for elliptic motion, 



©'-•( 



d6\ 2 m 2m ,... N 



and r fa =ll > ( iv *> 



and finally identify the terms involving ds and dt. In the 

 suggested form of equations, the time unit would have to be 

 variable, in order to make the ds^ and ds# intervals agree, 

 as has been suggested. 



In the equation (i.) ds measures the proper time for the 

 particle. With a variable time unit, the identification of 

 the ds and the dt terms would not gain in clearness by the 

 new form as suggested by Prof. Priestley. 



Yours faithfully, 



D. Laugharne Thornton. 



Magdalene College, Cambridge. 

 May 25, 1921. 



