The Series Spectra of Two-Valence-Electron Atoms of Phosphorus (${\mathrm{P}}_{\mathrm{IV}}$), Sulphur (${\mathrm{S}}_{\mathrm{V}}$), and Chlorine (${\mathrm{Cl}}_{\mathrm{VI}}$)

Series spectra of two-valence-electron atoms of P, S, and Cl.—In a previous ${\mathrm{Paper}}^1$, the regular and irregular x-ray doublet laws were used to predict the spectra of stripped atoms, that is, atoms having only one valence electron. The method has now been applied to the spectra of two-electron atoms, since, although these spectra consist of triplets or singlets instead of doublets, the same laws apply to them. In this way 23 lines of ${\mathrm{P}}_{\mathrm{IV}}$ have been identified, 17 lines of ${\mathrm{S}}_{\mathrm{V}}$ and 6 lines of ${\mathrm{Cl}}_{\mathrm{VI}}$. With the help of the Ritz equation, 12 term values of ${\mathrm{P}}_{\mathrm{IV}}$ and 8 of ${\mathrm{S}}_{\mathrm{V}}$ were also determined. In a table are collected all known term values for two-electron atoms of Mg, Al, Si, P and S.