100 



while the continuous spectrum of hydrogen, when observed as emission spectrum 

 in stars, shows a abrupt beginning at the head of the Balmer series, the con- 

 tinuous spectrum, observed by Stark in his experiments referred to above, was 

 not sharply limited but showed a pronounced maximum in the spectral region 

 which corresponds to transitions between two states, in the first of which the velo- 

 city of the free electron relative to the nucleus, before the "collision" with the 

 latter, was of the same order of magnitude as the velocity of the positive rays by 

 means of which the spectrum was excited. 



Besides the series spectrum and the connected continuous spectrum just con- 

 sidered, there exists, as well known, another hydrogen spectrum, the socalled many- 

 line spectrum, which on account of its complex structure and its resemblance with 

 the band spectra, emitted by other elements and combinations of elements, is gener- 

 ally ascribed to the hydrogen molecule and not to the atom. This assumption would 

 also seem to present itself directly from the point of view of the quantum theory, 

 according to which the simple structure of the series spectrum is directly con- 

 nected with the simple periodic character of the motion of the particles in the 

 atom, while a spectrum of a complexity of the order exhibited by the many-line 

 spectrum must be assumed to originate from a system the motion of which does 

 not show such simple periodicity properties. The problem of the constitution of the 

 hydrogen molecule, to be expected on the quantum theory, and the possible motions 

 of the particles of this system will be treated in Part IV. In this connection we 

 shall also consider the problem of dispersion of light in hydrogen gas and the pro- 

 blem of the voltage necessary to produce the lines of the series spectrum of hydrogen 

 by an electric discharge in this gas. 



Færdig ira Trykkeriet d. 30. December 1918. 



