Radiation and the Structure of the Atom. 407 



"the type (11) and the measurements of Rau mentioned below 

 indicate that the configuration of the inner electron in the 

 two corresponding systems of stationary states possesses the 

 same energy. A simple assumption is therefore that in one 

 of the two systems the orbit of the electron is circular and 

 in the other very flat. For high values of n the inner 

 electron in the two configurations will act on the outer elec- 

 tron very nearly as a ring of uniformly distributed charge 

 with the nucleus in the centre or as a line charge extending 

 from the nucleus, respectively. In both cases several 

 different types of orbit for the outer electron present them- 

 selves, for instance, circular orbits perpendicular to the axis 

 of the system or very flat orbits parallel to this axis. The 

 different configurations of the inner electrons might be 

 due to different ways of removing the electron from the 

 neutral atom : thus, if it is removed by impact perpendicular 

 to the plane of the ring, we might expect the orbit of the 

 remaining electron to be circular, if it is removed by an 

 impact in the plane of the ring we might expect the orbit to 

 be flat. Such considerations may offer a simple explanation 

 of the fact that in contrast with the helium spectrum the 

 lithium spectrum contains only one system of series of the 

 type (11). The neutral lithium atom contains three electrons, 

 and according to the configuration proposed in paper II. the 

 two electrons move in an inner ring and the other electron 

 in an outer orbit ; for such a configuration we should expect 

 that the mode of removal of the outer electron would be 

 of no influence on the configuration of the inner electrons. 

 It is unnecessary to point out the hypothetical nature of 

 these considerations, but the intention is only to show that 

 it does not seem impossible to obtain simple interpretations 

 of the spectra observed on the general principles of the 

 theory. However, in a quantitative comparison with the 

 measurements we meet with the difficulties mentioned in 

 the first section of applying assumptions analogous with 

 C and D to systems for which ordinary mechanics do not 

 lead to periodic orbits. 



The above interpretation of the formula? (11) and (12) 

 has recently obtained very strong support by Fowler's work 

 on series of enhanced lines on spark spectra *. Fowler 

 showed that the frequency of the lines in these spectra, as of 

 the lines in the ordinary spectra, can be represented by the 

 formula (11). The only difference is that the Rydberg 

 constant K in (12) is replaced by a constant 4K, It will be 

 seen that this is just what we should expect on the present 

 * Fowler, Phil. Trans. Roy. Soc. A. 214. p. 225 (1914). 



