"WEBSTER. — AN ELECTROMAGNETIC THEORY OF GRAVITATION. 573 



Therefore to avoid continually increasing energy we must again have 

 the two ethers at rest relative to each other. 



Now let us consider a similar case where the centre of the line join- 

 ing them is not at rest in the ether. Here we may again introduce the 

 gravitational relativity principle and with the aid of the gravitational 

 local time and auxiliary distance units thus defined, we may solve the 

 problem exactly as we did the one above. But we now see that if the 

 velocity of mi in the new system is in the direction of the velocity of 

 the new system by the old, and if 



B/ = - B/ 



where primes denote measurement on the moving system, then, since 

 the electromagnetic units of apparent distance and local time are 

 different from the corresponding gravitational quantities, 



Pa' ^ p/, and /?/ it Bi 

 unless C — c. 



It seems strange at first sight that Theory V is not overthrown by 

 the same considerations that proved Theory III impossible even for the 

 case of a rotating body. But the arguments used in that case do not 

 apply here ; because every particle in the body is affected at every 

 instant by forces radiated from the other particles, and it is obvious 

 from qualitative considerations that they will exert a backward force on 

 the particle of the order of | P' ^ | times the total force on it, and it 

 is further evident from the fact that the radiation theorem proves that 

 there is no gain of energy that this force must exactly balance the for- 

 ward component of the non-radiational force. 



Reasons for Preference of Electromagnetic Theory. — We now see 

 that Theory V is the only theory we have examined, except the 

 practically impossible Theory I, that does not involve an extremely 

 improbable, continual increase of energy in any rotating planet, sun, 

 or nebula. With such a continual increase of energy it is doubtful 

 if the solar system could have been formed. Furthermore, Theory 

 V is the one that involves the least radiation of negative energy, 

 which we see is a destructive process, from such a system as the solar 

 system is at present. Of course, we cannot prove that the solar system 

 would yet have gone to pieces with more radiation than this, but we 

 can say that if there had been enough additional radiation of this sort 

 it would have. 



We have, however, a much more convincing argument, for if we think 

 of such laws as the law of the minimum possible loss of heat in electric 



