192 



Suppleme7tt to ''Nature" August 4, 1923 



impact of one electron, after travelling a long way 

 and becoming greatly enfeebled, can eject another 

 electron with the same or nearly the same energy 

 as the first. Facts such as these have suggested 

 the discontinuous nature of a wave-front, and the 

 actual concrete existence of discrete tubes of force, 

 which are apparently analogous to, or suggestive 

 of, vortex filaments in the ether. Again, there is 

 the fact that the electrostatic potential energy of a 

 charge is similar to what the equivalent mass would 

 possess if it were moving with the speed of light. 

 Also, a propos of this, I understand that Sir J. J. 

 Thomson has expressed himself thus : 



" When the energy of a system passes from kinetic 

 into potential, there need be no transformation of 

 fundamental energy, but merely the flow of a mass- 

 producing material, with its intrinsic kinetic energy, 

 from one position of space to another, under the 

 guidance of the lines of electric force." 



In accordance with a few other physicists, Thomson 

 has been led to postulate a fine-grained structure for 

 the ether, which I think rotational, but which he speaks 

 of as particles. He suggests tliat mass is made 

 up of identical particles all of the same kind, very 

 small compared even with an electron, moving with 

 the velocity of light, and subject only to a deflecting 

 acceleration, not to any change of energy ; the mass 

 and energy of each particle being constant, but their 

 distribution depending on the number or concentration 

 of lines of force, each line being as it were anchored 

 normally to positive and negative electrons, but 

 capable of being thrown by motion into loops or 

 closed curves, which would then move away with 

 the velocity of light and constitute radiation. Where- 

 fore it would follow that emission of radiant energy 

 must be accompanied by a diminution in the mass 

 of the radiating body. 



The converse, therefore, that absorption of radiant 

 energy might be accompanied by an increase in mass, 

 almost naturally follows. 



My presidential address to the Physical Society of 

 London on the subject of opacity, that is, on the 

 orthodox theory of absorption generally, — electrical 

 as well as optical, — is contained in the Phil. Mag. for 

 April 1899, and also in the Society's Proceedings ; 

 in the latter place it is preceded by preliminary 

 matter not irrelevant to the present discussion. 



Mechanism of Absorption and Emission. 

 To understand the mechanics of absorption we can 

 learn from the mechanics of emission. In a wave 

 the electric and magnetic vectors are simultaneous ; 

 that is, the electric and magnetic displacements exist 

 together, superposed. At a source they are only 

 coexistent in space, not in time ; one succeeds and 

 gives rise to the other, with successive alternations. 

 A source may be at rest, and is merely an alternator : 

 a wave is necessarily in motion. The relative phases 

 of electric and magnetic oscillations in the neighbour- 

 hood of a source determine the fact and the direction 

 of motion at each locality. Combined in one phase 

 they expand or advance, combined in another phase 

 they contract or recede ; all this is known to occur 

 near the source, that is, near a Hertz vibrator. In 

 that region, within a radius of X/2y'7r, the etherial 



disturbance oscilktes to and fro ; and beyond that 

 range a portion of the energy acquires its locomotive 

 character, and sets out with the velocity of light. 



Shall not the converse take place when this sfKcd 

 of propagation is annihilated, and the ether disturbance 

 is reduced to locomotive rest, within a similar range 

 near an absorber ? In that region the simultaneous 

 electric and magnetic disturbances would be separated, 

 and converted into a stationary oscillation, by a process 

 inverse to that of radiative emission. 



Considerations of this character are indicated by 

 me more quantitatively in the Phil. Mag. for June 

 1913*. PP- 770-788, and in February 1920, p. 173 ; 

 also in April 1921, pp. 555-557, where I endeavour 

 to associate the ultimate fate of radiation with a kind 

 of Einsteinian gravitational theory. It there turn.N 

 out to be necessary to examine electrically the essential 

 nature of absorption ; and the illustration or analog) 

 with a Hertz vibrator, as either source or sink, is 

 employed. I return to the subject in June 192 1, 

 p. 943, and again in July 1921, pp. 181-183 ; though 

 in the last paper the chief point is the disintegration 

 of atoms which is to be expected at a certain calculated 

 very high temperature — such as has since been con- 

 sidered by Prof. Eddington likely to occur in the 

 interior of giant stars. 



Eddington has taught us — at any rate hypothetically 

 — that in the interior of giant stars, where the tempera- 

 ture is excessive and the radiation powerful beyond 

 easy imagination, the substance of the star is dis- 

 tended, blown out, supported, as it were, by radiation 

 bombardment, as the skin of a football, or an india- 

 rubber tyre, is distended by the molecular bombardment 

 of the air inside. He has further speculated, so I 

 understand, that the interior of these stars may 

 constitute a laboratory in which the more complex 

 atoms can be built up, — those same heavy atoms of 

 which we have now at length begun to witness the 

 breaking down, under the operations of spontaneous 

 radio-activity. There cannot be lireaking down every- 

 where : there must be building up somewhere. We 

 do not yet know what can be accomphshed under 

 conditions of extreme heat and pressure, — nor, I may 

 add, under conditions of great pressure combined 

 with extreme cold. 



It may be said : the analogy fails, since what I am 

 trying to suggest is the generation of electrons, and 

 we nowhere know of the breaking down of electrons. 

 That is true : we do not know either of their breaking 

 down or their building up. It may be that we shall 

 discover the untying of an electron first ; or it may be 

 that we shall discover a tying-up first, and the untying 

 later. Or it may be that, once tied, they are permanent. 

 Or of course it may be that they cannot be tied. But 

 these questions seem to me all open. The time for 

 discovery is not yet ; but he would be rash who would 

 say that discovery in any particular region is impossible. 

 If there are any clues, it is the privilege and indeed 

 the duty of science to follow them up. If the clues 

 are imaginar}^ and useless, then open discussion will 

 demonstrate their futility. But if we can see any 

 distance, however dimly, into the unknown, then 

 sooner or later we may be sure that pioneers will 

 explore those dim regions until they are illuminated 

 with the searchlights of systematic knowledge. 



