EINSTEIN'S LAW OF GRAVITATION 



(Address of the President of the American Psy- 

 sical Society, St. Louis, 1919) 



BY 



J. S. AMES 

 Professor of Physics Johns Hopkins University 



IN the treatment of Maxwell's equations of the electro- 

 magnetic field, several investigators realized the impor- 

 tance of deducing the form of the equations when applied 

 to a system moving with a uniform velocity. One object 

 of such an investigation would be to determine such a set 

 of transformation formulae as would leave the mathemati- 

 cal form of the equations unaltered. The necessary re- 

 lations between the new space-coordinates, those applying 

 to the moving system, and the original set were, of course, 

 obvious ; and elementary methods led to the deduction of 

 a new variable which should replace the time coordinate. 

 This step was taken by Lorentz and also, I believe, by 

 Larmor and by Voigt. 



Lorentz' paper on this subject appeared in the Pro- 

 ceedings of the Amsterdam Academy in 1904. In the 

 following year there was published in the Annalen der 

 Physik a paper by Einstein, written without any knowl- 

 edge of the work of Lorentz, in which he arrived at the 

 same transformation equations as did the latter, but with 

 an entirely different and fundamentally new interpreta- 

 tion. Einstein called attention in his paper to the lack of 

 definiteness in the concepts of time and space, as ordi- 



230 



