506 Dr. N. Bohr on the Effect of 



For gold the number of deflexions was observed up to 

 <£ = 150°and found to be correct. Taking e as 100 times 

 the electronic charge and V=2 x 10 9 cm. per sec, this gives as 

 the closest approach of nucleus and a particle 3*5 x 10 ~ 12 cm. 

 The closest possible approach of all-is between an a, particle 

 and a hvdrogen nucleus in a straight-on collision. With 

 V = 2xl0 9 this gives a distance l-7xl0 _13 cm. If it can 

 be verified that the distribution of H particles is as predicted 

 in this paper, then we may conclude that the radii of the 

 nuclei of hydrogen and helium are certainly less than 



LIX. On the Effect of Electric and Magnetic Fields on Spectral 

 Lines. By N. Bohr, Dr.phil. Copenhagen * 



i 



an 



N a previous paper f the writer has shown that 



explanation of some-of the laws of line spectra may be 



obtained by applying Planck's theory of black radiation to 

 Rutherford's theory of the structure of atoms. In the pre- 

 sent paper these considerations will be further developed, 

 and it will be shown that it seems possible on the theory to 

 -account for some of the characteristic features of the recent 

 discovery by Stark % of the effect of an electric field on 

 spectral lines, as well as of the effect of a magnetic field 

 first discovered by Zeeman. It will also be shown that the 

 theory seems to offer an explanation of the appearance of 

 ordinary double spectral lines §. 



§ 1. The Emission of a Line Spectrum, 



The theory put forward by the writer to explain the emis- 

 sion of a line-spectrum may be summarized as follows : — 

 The principal assumption of Planck's theory is that the 



* Communicated by Sir E. Rutherford, P.E.S. 



t Phil. Mag-, vol. xxvi. pp. 1, 476, 857 (1913). 



X Siizungsb. d. Kgl. Akad. d. Wiss. Berlin, 1913, p. 932. 



§ While this paper was in course of preparation, a theoretical paper 

 dealing with the same subject was published by E. Warburg ( Verh. d. 

 deutsch. Phys. Ges. xv. p. 1259 (1913)). The later finds that the effect of 

 electric and magnetic fields to be expected on my theory of the hydrogen 

 spectrum is of the same order of magnitude as determined by experiment. 

 However, contrary to the conclusions of the present paper, Warburg 

 concludes that it does not seern possible on the theory to account in 

 detail for the experimental results. In his opinion the theory leads to 

 a broadening of the hydrogen lines in an electric field, instead of the 

 appearance of the homogeneous components observed by Stark. He also 

 calculates that the Zeeman effect should vary from line to line in a 

 manner inconsistent with experiment. 



