CONTEMPORARY ADVANCES IN PHYSICS 701 



elements in the latter theory, which indeed appears to be an alternative 

 way of thinking to reach the same conclusions as emerge from the 

 speculations of de Broglie and Schroedinger.^^ 



Nevertheless the image is still far from perfect; there is certainly 

 something still lacking, something still to be discovered and added. 

 Radiation may flow forth from the atom when two stationary states 

 coexist, but it does not flow forever; one or the other of the wave- 

 patterns must therefore die out, soon after the radiation commences; 

 yet no agency has thus far been provided to effect the extinction of 

 either. It may not be difficult to insert such an agency into the theory, 

 in the form perhaps of an interaction between the "^-waves and the 

 outflowing electromagnetic waves. It may be much more troublesome 

 to extricate ourselves from the paradox into which the identification 

 of square-of-amplitude-of-the-'^-vibration with density-of-electric- 

 charge has led us. All of the numerical agreements between this 

 theory of the hydrogen atom and the features of the hydrogen spectrum 

 are obtained by putting — e-jr for the potential-energy -function of 

 the atom- model. This is the potential-energy-function for a point- 

 nucleus and a point-electron. If we dissolve the electron, spread it 

 out like a cloud in space around the centre of the atom, how can we 

 consistently retain the potential-energy-function derived from the 

 picture of a point-charge? How is it defensible to define electric 

 charge in one way in order to lay the cornerstone of the new theory, 

 and then redefine it in a contrasting way in order to raise the super- 

 structure? 



Wave-mechanics, striking as are the pictures which it offers of 

 certain of the processes within the atom, still abounds in conceptual 

 difficulties of which the last is a fair instance; and those who share 

 the view of Lessing that it is more desirable to be approaching truth 

 perpetually than ever to attain it may still find satisfaction in physics. 

 Wave-mechanics still is tentative, not definitive; a plan of cam- 

 paign, rather than a conquest. The outcome cannot now be foreseen. 

 Yet we may reflect that twenty-five years ago it was universally sup- 

 posed that light possesses only the qualities of a wave-motion; and 

 then experiment was piled upon experiment which showed that in 

 addition it behaves in many situations as though it were a stream of 

 corpuscles. Perhaps we stand at the beginning of an equally imposing 

 series of experiments, which will show that matter with equal incon- 

 sistency partakes of the qualities of particles and of the qualities of 

 waves. 



31 Schroedinger, Ann. d. Phys., 79, pp. 734-756 (1926); C. Eckart, Phys. Rev. 

 (2), 28, pp. 711-726 (1926). 



