NO. II 



STRUCTURE OF THE ATOM PARSON 



25 



§8. The Number of Magnetons in the Atom 



The following table gives a comparison of the numbers of mag- 

 netons apportioned to the atoms in the last section with the " atomic 

 numbers " of van den Broek (which are the numbers of electrons in 

 the atom, according to Bohr), and also the atomic weights of the 

 elements : 



The two sets of numbers become identical for the heavy atoms for 

 which Rutherford has calculated numbers of electrons from a-particle 

 scattering, but for the lighter elements the atomic numbers seem at 

 first to have much in their favor. First there is their close approxi- 

 mation to half the atomic weight, although this does not hold for 

 Hydrogen or the heavy atoms. Secondly, the most definite calcula- 

 tions made from experimental results, viz., those from Barkla's 

 work on the secondary Rontgen radiation (Phil. Mag., 5, 685-698, 

 1903; 21, 648-652, 191 1 ), give numbers of electrons that are about 

 half the atomic weight numbers for the lighter atoms. 



The point to be emphasized here, however, is that none of such 

 calculations have any meaning for the present theory, for the follow- 

 ing reasons : 



Rutherford's numbers, got from the phenomena of a-particle 

 scattering, assume that the total charge on the electrons is equivalent 

 to the charge on a small positive nucleus ; but for the model atoms 

 described in this paper, the nucleus, if there is any, must be neutral 

 (see the note at the end of §16) . Also the " characteristic numbers " 

 got by Moseley, which, it should be remembered, are less than the 

 atomic numbers by unity, have not been definitely correlated with 

 the numbers of electrons in the atoms except through the idea of a 

 positive nucleus. To turn to Barkla's work, the calculation of abso- 

 lute values by means of Thomson's formula requires certain assump- 

 tions. One is that the dimensions of an electron are small compared 

 with the length of a Rontgen ray pulse : this is not entirely the case 

 with magnetons. Another, that the electrons in the atom are so far 

 apart that any pulse can act on only one at a time : this can hardly be 

 true of the electrons in the inner ring (radius io -10 cm.) of the atoms 

 of Bohr's theory, which is the prominent application of the hypothesis 



