270 Dr. Megh Nad Saha on the Problems oj 



double charge. The characteristic Rydberg number is 



4N( = — Yg — (2e) 2 \. These lines are produced at a higher 



stimulus, and generally, but not always *, lie in the ultra- 

 violet. 



(3) The atom may lose two electrons, and now a new 

 series of vibrations may begin with the new outermost 

 electron. The Rydberg number is 9N. 



The lines of any of these groups are as distinct from each 

 other as if they belong to different elements altogether. 

 According to Sommerfeld f, when an atom loses one electron, 

 its spectral properties become similar to those of the element 

 just preceding it in the Periodic Tables. Thus the system of 

 lines of C;i + are constituted in the same manner as those 

 of K ; similarly, the relation between Sr + and Kb, Ba + 

 and Cs. 



Lines of these different groups may be simultaneously 

 present, but generall} r one group gains in intensity at the 

 expense of the other. Thus in the flame Ca + lines (the H, 

 K) are very faint, the Ca-line (^-line) is very strong. Now 

 " g" begins to lose relatively in intensity as the (H, K) are 

 strengthened with rise of temperature. At the spark- 

 conditions, the most intense lines are the H, K, while the 

 "g" is almost evanescent. 



Let us now examine how the transition from the neutral 

 state to the ionized states (from Ca to Ca + ) takes place, 

 under the influence of heat alone. In Phil. Mag. Oct. 1920 

 (" Ionization in the Solar Chromosphere," called henceforth 

 paper A), it has been shown that the problem can be 

 attacked with the aid of the "New Thermodynamics 5 ' of 

 Planck and NernstJ, and the statistical equilibrium between 

 neutral atoms and ionized atoms can be calculated in terms 

 of temperature and pressure, when the energy of ionization 

 is known. The calculations for alkaline earths will be found 

 in paper A, and those for the alkalies are given in paper B §. 



According to the mechanical theory, the outermost 

 electron of the neutral atom revolves in a stable orbit when 

 the atom is not subject to any stimulus. Ionization means 

 the transference of this electron to infinity. But the process 



* For example, in case of alkaline earths. All alkaline earths are 

 distinguished by having large (2, p) terms, which causes the principal 

 lines to occur in the visible region. 



f Sommerfeld, Atombau unci Spektralanalyse, Chap. 4, § 6 and 

 Appendix. 



I Planck, Wannestrahlung. Nernst, Das Neue Warmesatz, etc. 



§ " Elements in the Sun,"' I^il. Mag. Dec. 1920. 



