94 WHAT la LIFE 



complications register in the spectrum," says J. 

 Franck.^^ Irving Langmuir said that "recent work 

 on spectra has shown that a molecule cannot be 

 set in rotation without changing the configuration 

 of the electron orbits." 



It is well known that the hydrogen molecule does 

 not show as an exact duplicate of two single hydro- 

 gen atoms, but shows marked changes, in that the 

 orbital electrons belong to both nuclei in common. 



All orbital changes of the path of a planetary 

 electron are defined in terms of quantum conditions. 



The modified Bohr theory of the atom, then, 

 pictures the atom as a planetary system in which 

 the planets are negative electrons that revolve about 

 the central body, the nucleus. Max Born tersely 

 says that "the two facts of experience that served as 

 a basis for the considerations that led to the Bohr 

 theory of the atom are: (1) the stability of the 

 atoms; and (2) the validity of the classical mechanics 

 and electrodynamics for macroscopic occurrences."^^ 



In picturing the atom as a planetary system, 

 several differences are recognized. Thus, whereas 

 there is mutual attraction between the planets as 

 well as between the sun and the planets, the nega- 

 tive electrons while held in their orbits by the 



12 Zeitschrift fur Elehtrochemie und Angewandte Physikalische Chemie, Juli, 

 1925. 



" Vorlesungen iiber Atommechanik, I, 18 (1925). 



