The spectra of two and three-valence-electron atoms, SiII, PIII, SIV, SiIII, PIV and SV

New measurements of the vacuum spark spectra of silicon, phosphorus and sulphur have been made with a vacuum spectrograph. With the aid of these data it has been possible to analyse a large number of hitherto unclassified lines. In Si III and P IV the stronger singlet lines have been classified, while in these ions and in S V a large number of lines involving terms in which both electrons are excited have been identified. In Si II, P III and S IV many of the important quartet lines have been located.