248 SCIENCE PROGRESS 



I wish to argue that the real fact lying at the base of the 

 explanation is the varying mass of the planet as a function 

 of its speed through the ether, and is not dependent on the 

 theory of relativity as such. I contend that this extra or 

 spurious inertia due to motion does not really appertain to 

 matter, but to the medium in which it moves, and that there- 

 fore it is extremely unlikely to be subject to gravitation. 



A sphere moving through a perfect fluid is known to have 

 its mass apparently increased by 50 per cent, of the mass of 

 fluid displaced. A cylinder still more. This apparent mass 

 is really due to a distribution of fluid pressures. Virtually 

 more matter has to be accelerated, but the effect in no way 

 alters the floating or sinking forces acting on the body. Nor 

 does it encounter any resistance such as dissipates energy. 



Extra inertia due to motion through the ether is not so 

 simple as that, it is more like an approach to the critical speed 

 (easily attained by sharp edges) at which fluid finds it difficult 

 to get out of the way ; but however it be explained in detail 

 the extra inertia is something belonging to the ether, not to 

 matter, and therefore ought not to influence the body's weight. 

 The ether must be assumed to be the vehicle of gravitation, 

 but not to be affected by it — at least not until it is constitu- 

 tionally contorted into the peculiar condition of an electron. 

 By this contortion or strain, whatever its nature, a stress 

 appears to be set up which is the gravitational field. Paren- 

 thetically one may remark that this stress thus set up is 

 no new thing, electrons cannot be manufactured ; their 

 tension simply exists, inversely as the distance, throughout 

 space. 



So I argue that in the extra inertia due to motion through 

 ether we have mass or virtual mass without weight, and 

 that an increased inertia of this kind must diminish accelera- 

 tion in much the same way as a lessening of gravitational pull 

 would diminish it. Thus the centripetal acceleration acting 

 on a planet will not only be slightly less than in Newtonian 

 theory, but will vary with its position in the orbit ; and this 

 must give rise to a definite perturbation. 



In an article in the August number of The Philosophical 

 Magazine for the present year I reckon the actual effect of 

 extra and fluctuating mass upon the orbit of a planet, and 

 show that it introduces a revolution of the orbit in its own 



