Multiplets in Two Electron Systems of the First Long Period

Wave-lengths and comparative positions of certain multiplets in the spectra of CaI, ScII, TiIII, VIV, CrV.---When an electron in a $4p$ orbit jumps to a $4s$ orbit in the presence of another valence electron in a $3d$ orbit, multiplets of the type ³D1,2,3-³P0,1,2; ³D1,2,3-³D^'1,2,3; ³D1,2,3-³F2,3,4 appear. These multiplets for CaI, ScII, TiIII have already been recognized by other investigators. The same multiplets for VIV and CrV have now been found and the wave-lengths of the lines have been measured. The progressive shift in the relative positions of these multiplets in passing from element to element has been noted. The regular and irregular doublet laws have been found to hold fairly accurately for two electron systems when one of the electrons jumps between two orbits, p and s, having the same total quantum number.