1918] on Gravitation and the Principle of Relativity -^31 



the new form of Poisson's equation V'f/) = - 47r/j '? It is found that 

 equation (6) can be transformed into a Hamiltonian form — 



6(/Hr?r) = (7) 



where dr is a four-dimensional element of volume, and H a certain 

 function of the ^'s and their derivates. 



The electromagnetic equations of Maxwell in the absence of a gravi- 

 tational field can also be expressed in a Hamiltonian form — 



S(/H'^r) = (8) 



where H' is a function of the quantities defining the electromagnetic 



field. 



' It is clear that we must form the general equations, when gravitation 



and electromagnetic forces are both present, by combining (7) and 



(8) thus— 



5(/(H + AH') dr) = (9) 



The constant X, whose value cannot be predicted a Xfyiori, indicates 

 the relation between the gravitational and electromagnetic effects caused 

 by the same mass, and corresponds to the constant of gravitation. 



The mathematical operations, omitted in this brief sketch, are long 

 and rather difficult ; but it is hoped that it maj" enable the reader to 

 gather the general nature of the argument. 



R 2 



