WEBSTER. — AN ELECTROMAGNETIC THEORY OF GRAVITATION. 581 



tive ; 1* SO that instead of being drawn towards its neighbors in space 

 by their attractions it will appear to avoid them as if it were repelled, 

 while they, being drawn towards it by its enormous attraction, will 

 pursue it as it flees from them. 



The more sluggish of them will soon be left far behind, but the 

 livelier ones, with the least inertia, will draw nearer and nearer, until 

 at last one will overtake it, hit it from behind and slow it down. By 

 this process its negative inertia will be further increased, until it has 

 collected to itself all matter with positive inertia within reach. 



This process will be repeated in many different parts of the universe 

 until at last all matter will be collected in enormous masses with 

 negative inertia. They will then act as if they all had positive inertia 

 but repelled each other, and, therefore, there will be no more collisions. 

 But their heat will be lost by radiation, with no chance to renew the 

 supply, and at last, if the present laws of nature still hold, the uni- 

 verse will be cold and dead forever. 



Are all Forces Electromagnetic? — And now that we see that the 

 reason gravitational forces obey the principle of relativity is the fact 

 that they are really electromagnetic forces, and now we know from 

 the Michelson-Morley experiment that all internal stresses in even the 

 most rigid bodies obey the same principle, we may say that we have 

 at last some evidence to show that all such stresses are of electro- 

 magnetic origin. And we may now say that the principle of relativity 

 applies to all the laws of nature because it applies to all the laws 

 of electromagnetic phenomena, and because all the laws of nature are 

 laws of electromagnetic phenomena. 



Jefferson Physical Laboratory, 

 Cambridge, Mass. 



" It might be supposed, at first sight, that just when the inertia became 

 zero in the process of losing electromagnetic energy, the mass might have 

 an infinite acceleration. But it will be noticed that the tendencies to resist 

 change of acceleration, not being in the ratio — mg/m, will not be equal and 

 opposite, so that no such effects will occur, 



