90 



Prof. J. W. Nicholson on Atomic Structure 



Table VII. gives the results of some of these experiments. 



The values of k 2 are in good agreement with the numbers 



obtained from Watson's experiments, but h x is somewhat 



larger. 



Table VII. 



Values of l\ and k 2 for air at atmospheric pressures deduced 

 from Schaffer's experiments, b being the radius of the 

 cylinder and a the radius of the wire in centimetres. 



XII. Atomic Structure and the Spectrum of Helium. By 

 J. W. Nicholson, M.A., D.Sc, Professor of Mathematics 

 in the University of London* . 



AN earlier paperf has indicated that the crucial test of 

 Bohr's theory of spectra is to be found in its appli- 

 cation to the ordinary spectrum of helium. For the theory 

 gives a precise specification of the constituents of a helium 

 atom, — a specification which is in accord with the results 

 obtained by a combination of the atomic number hypothesis 

 of Van den Broek and the experiments of Moseley, and with 

 those to which Rutherford and others have been led by some 

 other lines of study. The necessity for this accordance, 

 in fact, dictated the particular model which Bohr has 

 used. His corresponding models for lithium and the heavier 

 elements have been shown to be at fault, in that they involve 

 distributions of electrons which cannot exist by virtue of the 

 assumptions on which the theory is founded, in spite of the 

 fact that these assumptions are of a very general character. 

 The success of the theory therefore rests on its application 

 to the spectra of hydrogen and helium, — leaving out of 

 account, for the moment, the controversial question of its 

 application to X-ray spectra, which was partially dealt with 

 in the earlier paper, — in so far as that application has been 

 made. The theory must therefore stand or fall according to 



* Communicated by the Author, 

 t Phil. Mag. April* 1914. 



