February 17, 192 1] 



NATURE 



799 



city. That is the assumption on which his whole 

 argument is based ; and, as an instinctive intuition, 

 there may be a foundation for it (see below), and 

 even for the further assumption that the funda- 

 mental absolute velocity is either equal to, or of 

 the same order as, the velocity of light. 



It must not be supposed however that the 

 Michelson-Morley experiment substantiates the 

 structure thus begun upon it. It does not 

 really prove that the velocity of light in a moving 

 medium is the same in all directions ; that is a 

 gratuitous but fundamental hypothesis, not really 

 based on any experiment — certainly not on one 

 which only deals with to-and-fro journeys over 

 matter-fixed distances. Nevertheless, whether or 

 not this foundation-stone of Relativity is well and" 

 truly laid, the structure built over it is of remark- 

 able interest ; and possibly can sustain itself by 

 its own consistency, and by its attachments to 

 other facts, even if it be admittedly arched over 

 the particular experiment on which it was origin- 

 ally supposed to be founded. 



A Few Remarks on the More General Theory of 

 Relativity. 



The consistency of all these things, including 

 the conservation of energy and momentum, with 

 simple relativity, amply accounts for the 

 enthusiasm with which brilliant mathematicians, 

 untrammelled by a sense of physical reality, have 

 absorbed and developed the idea. 



Indeed, as we know, Einstein was enticed to 

 go on and try a trartsformation to accelerated axes 

 al.so, to identify gravitation and inertia, to ally 

 both with the so-called centrifugal force, and to 

 reduce them all to a still more elaborate geometry, 

 in which the Lorentz transformation is inadequate, 

 and Kuclidean propositions are superseded. He 

 found ready to his hand a recondite scheme, pro- 

 vided for other and less worldly purposes by Gauss 

 and Kiemann ; but, to make use of it, he had to 

 introduce a fresh agnostic principle, a Principle 

 of Equivalence. He must assume that we cannot 

 discriminate between a whirling table and a gravi- 

 tational field ; that we have no criterion between a 

 falling apple and a rising Earth ; and that it is 

 only prejudice which makes us feel assured about 

 a rotating Earth, and unwilling to contemplate a 

 diurnally revolving star. Cieometrically they are 

 all the same ; and a suitable space-time system 

 can be devised, and expressed in equations, which 

 will account for, or at least express, most things 

 observed in astronomy, and some additional 

 tilings more allied with physics. 



Now we must admit that if we are permitted to 

 discard relativity as a philosophy and accept it as 

 .1 method, the form of the most striking of its 

 >'r|uations is advantageous, and represents an 

 advance in symbolism, quite apart from any un- 

 physical contributions to its origin and any lack of 

 legitimacy about its birth. For the weight of an 

 apple must be really, as it always has been hypo- 

 thetically and vaguely, attributable to a gravita- 

 tiiinally mmlificd a;ther pressing down on each 

 particle. Similarly the path of a planet from in- 

 NO. 2677, VOL. 106] 



stant to instant can be expressed more intimately 

 by a variational equation, involving always the 

 next step, than by an action-at-a-distance formula, 

 or by a merely kinematic summary which inte- 

 grates the result over an entire orbit. But this 

 powerful and ingenious method of research can 

 be interpreted, in words, so as to suggest nothing 

 more than a warping of an unreal emptiness — a 

 sort of return to Descartes' vortices without their 

 imagery, a rejection of Copernicus and Galileo 

 and Newton. 



Whereas what is really wanted for a truly 

 Natural Philosophy is a supplement to Newtonian 

 Mechanics, expressed in terms of the medium 

 which he suspected and sought after but could not 

 attain, and introducing the additional facts, chiefly 

 electrical — especially the fact of variable inertia — 

 discovered since his time. Such a philosophy 

 would insist that the specific state of the medium 

 throughout a gravitational field must be the im- 

 mediate consequence, indeed the absolute essence, 

 of the existence of each material particle ; their 

 separate potentials being combined by simple addi- 

 tion without any second-order complications. 

 Equally an electric field must be part of the actual 

 constitution of an electron, and inseparable from 

 it : though the compounding of electric fields need 

 not be so simple a matter, since charges in proxi- 

 mity do interfere with each other. 



If we could understand the structure of the 

 particle, in terms of the medium of which it is 

 composed, and if we knew the structure of the 

 rest of the medium also, so as to account for the 

 potential stress at every point — that would be a 

 splendid step, beyond anything accomplished yet. 

 But that the particle is a singularity in the 

 medium, and that its inertia and gravitational field 

 are essential to, and part of, its very existence, 

 must certainly be true ; and this is what the 

 Einstein theory, in its own peculiar geometrical 

 unphysical way, has grasped. There are not half 

 a dozen diverse but interlocked things in Nature : 

 there is one definite quiescent medium, full of ex- 

 ceedingly fine-grained turbulent energy, with con- 

 sequent properties which, when unravelled, will 

 supply the key to all the non-mental phenomena 

 occurring in it. Provided always that the locking 

 up of small regions of this turbulence, not merely 

 in the travelling form of light-waves, but in the 

 potentially stationary form of electrons, can also 

 be explained and understood. 



Relativity, as a consecutive point-to-point 

 method of arriving at results, is a first step to- 

 wards this ideal, but it is not a Newtonian step; 

 it is rather a blindfold method of investigation, 

 like Entropy and Least Action. 



The Fundamental Velocity. 

 To make a philosophic scheme of existence com- 

 plete, more than the expression of a static instant 

 is required, there must be duration likewise : the 

 universe is not merely a Being but truly a Becom- 

 ing; Time has to be associated with Space. This 

 can only l>e done by a velocity fa,ctor of some 

 kind; but to arrive at an appropriate factor, rcia- 



