96 Prof. J. W. Nicbolson on Atomic Structure 



behaviour is as simple as that of the electron in a hydrogen 

 atom. The consequences of such an hypothesis in connexion 

 with spectra will appear later. At present it has only been 

 shown that it is the only hypothesis which will, on Bohr's 

 theory, allow a coplanar-ring structure of the ordinary 

 elements. 



We may notice that this hypothesis is a step towards 

 Sir J. J. Thomson's conception of tubes of force in the 

 atom. The relation between the two points of view is as 

 follows. If an electron when free has tubes of force, with 

 some material significance, radiating from it, it may when 

 bound have these tubes diverted to pass into the nucleus, 

 and all the electrons in an atom being in this connexion with 

 the nucleus, cannot exert force on each other. An accelerated 

 electron might radiate if its tubes extended to a distance, but 

 not when they all passed to the nucleus. This connexion 

 between two points of view is interesting, but may have no 

 special significance. 



Tlie Spectrum of Helium. 



On the supposition that a helium atom, when neutral, 

 contains only two electrons and a nucleus 2e, and that the 

 spectrum of the atom when one electron has disappeared is 

 that calculated by Bohr, and previously believed to be due 

 to hydrogen, we are compelled to suppose that the more 

 normal helium spectrum is produced by a neutral atom. For 

 a helium atom, on Bohr's theory and according to Sir J. J. 

 Thomson's experiments, will not take up a third electron. 

 The neutral atom must therefore possess six types of stationary 

 states, as there are six types of function to which the appli- 

 cation of the combination principle gives the helium spectrum. 

 We shall attempt to arrive at any one of the^e functions by 

 Bohr's method in the most general manner which is yet 

 consistent with the theory of the spectra of the hydrogen atom 

 and the positively charged helium atom. The best series is 

 evidently the sharp or second subordinate series of parhelium, 

 given by the very accurate Hicks' formula 



71=27174-917 - 109726-0 / fm + -861181 - '° ^ 809 J *, 



where n is the wave number. For the Rydberg constant is 

 in this case 109726*0, which is almost precisely Bohr's 

 estimate 109725 instead of the usual 109675 of hydrogen. 

 If the theory is correct, 109725 is the theoretical value for 

 elements heavier than hydrogen. We deduce that one of 

 the types of stationary states concerned in the production 



