onwards, owing chiefly to the rise of second ionization and the consequent formation of Ca++, which gives a spectrum in the ultra-violet and is therefore not detected in the stars.
As the temperature is further raised, the second and third ionizations set in, and presumably follow the same procedure as has been outlined for less ionized atoms. The lines of N++, C++, Si++, and Si+++ will serve as examples. The lines of the doubly ionized atoms of the metals are in general in the ultra-violet portion of the spectrum, and the corresponding elements do not therefore appear in the hotter stars, where they would otherwise be anticipated.
Qualitatively the prediction of the theory of ionization is fully satisfied. The quantitative discussion involves more rigorous treatment, and is reserved for a later chapter.
FOOTNOTES:
[355] Stewart, Phys. Rev., 22, 324, 1923.
[356] De Gramont, C. R., 171, 1106, 1920.
[357] Russell, Pop. Ast., 32, 620, 1924.
[358] A. Fowler, Report on Series in Line Spectra, 1922.
[359] R. H. Fowler, Phil. Mag., 47, 257, 1924.