The Series Spectra of the Stripped Atoms of PhosPhorus (${\mathrm{P}}_{\mathrm{V}}$), Sulphur (${\mathrm{S}}_{\mathrm{VI}}$), and Chlorine (${\mathrm{Cl}}_{\mathrm{VII}}$)

Spectra of stripped atoms, sodium to chlorine.—Grating spectrograms of order three to eight have been obtained of the hot-spark spectra of these elements, which have yielded more accurate values for the ($3p_2-3\mathrm{}{p}_1$), ($3s-3p_2$) and ($3p_1-3d$) terms of ${\mathrm{Al}}_{\mathrm{III}}$, ${\mathrm{Si}}_{\mathrm{IV}}$, ${\mathrm{P}}_{\mathrm{V}}$ and ${\mathrm{S}}_{\mathrm{VI}}$, and have enabled the identification and determination within about 5 frequency units (1) of 18 series lines of ${\mathrm{P}}_{\mathrm{V}}$, and thence of the 14 most important term values ($3s \mathrm{to} 6f^{\prime \prime }$), (2) of 11 series lines of ${\mathrm{S}}_{\mathrm{VI}}$, and 10 corresponding term values ($3s \mathrm{to} 5f^{\prime }$), and (3) of the first doublet of the principal series of ${\mathrm{Cl}}_{\mathrm{VII}}$ at 800.70 and 813.00 A. The position of this doublet was first predicted by use of the method developed in a previous ${\mathrm{paper}}^1$, based on observed regularities in these spectra. Further evidence is presented for the fact that both the regular and the irregular doublet laws of x-ray spectra, hold also throughout the field of optics. A plot of $\sqrt{\frac{\nu }{R}}$ for the stripped atom levels as a function of atomic number gives approximately straight lines (Moseley law), those for the $3s$, $3p$ and $3d$ terms and for the $4s$, $4p$, $4d$ and $4f$ terms being approximately parallel (irregular doublet law). The doublet separations $d_1{d}_2$, however, do not fit well into the relativity doublet law, the ratio of observed to theoretical values decreasing from about.8 for ${\mathrm{S}}_{\mathrm{VI}}$ to less than.2 for ${\mathrm{Si}}_{\mathrm{IV}}$, while ${\mathrm{Al}}_{\mathrm{III}}$ and ${\mathrm{Mg}}_{\mathrm{II}}$ are anomalous, $d_1$ having a greater frequency than