86 



NATURE 



[September 25, 1919 



it may be only spe^d-acceleration that is realU' effec- 

 tive, and not transverse or curvature-acceleration at 

 constant speed. For this will not perturb the lines of 

 force holding the electron to the nucleus, but will 

 leave them in a constant condition so long as the 

 orbit is circular and the speed therefore constant. 

 There is a recognised difference of the same sort in 

 connection with varying inertia ; its value is not 

 affected by transverse acceleration, with the speed left 

 constant, but it is affected by longitudinal accelera- 

 tion, which alters the speed. 



So I am in hopes that it may be found that this 

 latter or speed-acceleration is what is responsible for 

 radiation, and that mere curvature at constant speed 

 in a circular orbit need not radiate at all, provided 

 always that the superposition of an external alter- 

 nating field of the right frequency may cause absorj)- 

 tion. Manv of the difficulties connected with the 

 stabilitv of the astronomical atom would be evaded 

 if the theory of radiation could be modified in this 

 wav, and the excitation of characteristic radiation by 

 alrnost any kind of perturbation of the orbit would be 

 intelligible. 



Speculations on Radiation and Atomic Structure. 



Bohr's remarkable theory of atomic structure does 

 not pretend to be strictly dynamical ; it is partly 

 empirical, being based on the discontinuity signalised 

 by Planck's constant, but it is very brilliant, and 

 extensively justifies itself by agreement with facts. 



His expression for the frequency of radiation 

 emitted by any element is virtually, to a fair approxi- 

 mation, 



_ 27rhne * /E^ / I _J^\ 

 " K'/fi' \el \'p^ gy 



where — is Moselev's atomic number N, the number 



e 



of unbalanced charges in the nucleus or the number 

 of electrons in the atom, and where p and q are 

 integers, of which p changes from series to series, 

 while the lines in each series are given by the muta- 

 tions of q. For heavy atoms the E in the above 

 formula should be E minus a geometrical function 

 of all the other electrons inside the radiating orbit, 

 because they will affect the central attracting force. 

 In this way outstanding discrepancies may plausibly 

 be explained. But the remarkable thing is that the 

 formula gives the frequencies, not merely relatively, 

 but absolutely. For if the experimental values other- 

 wise obtained for e, m, and h are inserted, the con- 

 stant outside the brackets, called Rydberg's constant, 

 which is sfKjctroscopically determined and known to 

 be the same for all elements, comes out right. \ 

 verv notable fact ! 



The above expression for spectral lines not only 

 agrees with the Rydberg-Balmer known spectroscopic 

 series, and with the kind of formula given by many 

 pioneer workers, but has been able to predict other 

 series which have been afterwards observed. It also 

 accounts for many cxtra-lovv-frequency lines which, 

 though not obtainable in the laboratory, are observable 

 astronomically by suggesting that they come from 

 very large rrlasse's of highly rarefied gas. For under 

 such conditions the atoms would have more room 

 and could possess far outlying or ultra-Neptunian 

 electrons, and yet have total substance enough to 

 display their spectra. 



To contemplate the emission of radiation, both 

 waves and particles, we may picture one of the 

 satellite electrons in a many-orbited atom struck or 

 so thoroughly perturbed by the sudden arrival of a 

 foreign charge as to precipitate it into the next inner 

 ring, ejecting the constituent of that ring into the, 



NO. 2604, VOL. 104] 



one below, and so on, after the manner of the "jack 

 for mustard " game with a series of wooden bricks 

 set up on end. 



Wave-emission should accompany each transition. 

 The effect of precipitating the innermost electron on 

 the body of the nucleus is not clear; but a compound 

 nucleus must be a strangely interlocked conglomerate, 

 and an explosion seems not unlikely, especially if one 

 of the supposed binding negative electrons were 

 ejected. The potential gradient close to a nucleus is 

 prodigious. 



The effect of the arrival or departure of a charged 

 particle at the nucleus would be suddenly to change 

 its intrinsic attracting force; and this of itself would 

 render all the orbits elliptical for a time, with eccen- 

 tricity ^TT--, " thus exciting radiation of several fre- | 



quencies. If the radiation ceased when the eccentricity 

 was got rid of, a new circular orbit would be taken 

 up ; and thus perhaps discontinuities might be 

 accounted for in a dynamical manner. 



The effect of properly attuned X-rays or ultra- 

 violet light, if it is to be accomplished through reson- 

 ance — and it is difficult to account for its independence 

 of intensity otherwise — seems to require a fair range 

 of frequency in those rays ; for their effect on _ a 

 revolving electron would naturally be to increase its 

 angular speed and so throw it out of tune with the 

 particular disturbance to which it initially responded. 

 The sectorial area swept out would increase, the , 

 radius vector would inciease, the linear speed would I 

 therefore diminish in spite of the resonant effort to ' 

 increase it — unless, indeed, under the peculiar condi- 

 tions in an atom, there may be some compromise. 

 The alternative would be for the electron to be con- 

 strained, under conditions of stability, to maintain its 

 frequency unaltered, either proceeding in an outward 

 spiral towards a position of Planckian instability, or 

 trying still to obey the law of inverse squares by 

 increasing the eccentricity of its orbit with _ given 

 axis major until it becomes practically parabolic. 



This could represent an inversion of the process by 

 which the electron mav have been originally bound, 

 according to Bohr's theory of what happened before 

 the atom became neutral.' For it is to be presumed 

 that a positivelv charged a-particle, after ejectment, 

 neutralises itself by accretion and settles down. 



Conclusion. 



I have led vou over a great deal of territory in a 

 hurried manner, and occasionally have entered 

 on regions where the ground is not yet solid and 

 secure. Let it be granted that the chemist may 

 naturallv object to an astronomical atom and may 

 prefer a more static or geometrical structure, although . 

 such a structure would have less clear and explicable I 

 properties. The static or Boscovich atom, with purely | 

 hvpothetical interior fluctuations of force, leaves every- 



2 This can be proved as Tollows ;— 

 For a circular orbit 



rr2 = ii 

 and rl!r,2 = A2=,ir. 



When /I suddenly changes to ^ji(where * n-ay be -^') tli= velocity does 

 not instantly change, but the orbit acqu'res an a and an e, such that 



also 



This last gives 



a (r -c^^=~ or e^ = 

 r \ r a f 



And the plare where the sudden impulse occiirred, liecomei an ap^e of the 

 new orbit, because r=a(ii^). (See also Appendix I. in Proe, R.I.) 



