WEBSTER. — AN ELECTROMAGNETIC THEORY OF GRAVITATION. 575 



is the set which makes the gravitational permeability of any conductor 

 equal to that of a vacuum. And we see, furthermore, that if electro- 

 static forces are to obey the principle of relativity, and the first of these 

 assumptions is made, the second and the obedience of the force of 

 gravity to the relativity principle are necessary consequences of the 

 first. 



By comparison of the electrostatic repulsion of two electrons, whose 

 ratio of charge to inertia is 5.595 X 10"*'^, with the gravitational attrac- 

 tion between two spheres, we would find that 



G^=1.67 X 10-*-, 



if the fundamental positive charge were similar to the negative elec- 

 tron. ^^ This readily accounts for the fact that its existence has never 

 been experimentally observed. 



We may or may not, as we please, assume that this slight difference 

 between the forces is produced by the same cause which produces the 

 rest of the forces, but from the fact that it is transmitted through the 

 same ether, with the same velocity, it seems most reasonable to assume 

 that it is due to the same cause. 



Consequences of this Theory, Negative Energy. — One of the most 

 surprising facts about the electromagnetic theory of gravitation, and 

 one with most surprising consequences, is the fact that we have to 

 introduce the conception of negative energy, both potential and kinetic, 

 distributed through the space around any gravitating matter. And 

 by the term, "negative energy," we cannot mean a mere diminution 

 of the positive energy in the space, as the following considerations 

 will show. 



First let us consider the energy radiated from an accelerated mass, 

 whose inertia is balanced by the inertia of some mass at a great dis- 

 tance, so that the radiations of gravitational energy cannot interfere 

 for a considerable time. We now see that during that time the transfer 

 of energy across any element of surface dS per unit ct is 



--i^gxh-dS, 



^•^ Since the inertia of an electric charge e on a sphere of radius a is propor- 

 tional to eVa, G is different from the above value if the fundamental positive 

 charge has not the same e/o as the electron, where a in this case is a sort of 

 average radius of points in the electron or positive charge. But the fact that 

 k is the same for all kinds of matter indicates that, if there is only one kind 

 of positive electricity, with only one value of G, it must be collected in funda- 

 mental charges for all of which e/a is the same. Hence we have reason to 

 believe that all atoms of positive electricity are probably alike. 



