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Carroll, Smith, Rao and Narayan and Schoepfle have established terms of the one-electron configurations of Pb IV. Schoepfle, whose analysis is the most complete, has identified the 6 s , 7 s , 8 s , 6 p 7 p , 6 d , 7 d , 5 f doublets, and in addition assigned a number of terms to the many-electron configurations that have as limit the 5 d 9 6 s configuration of Pb V. The Au I iso -electronic sequence, especially the configurations involving the 5 d 9 core, has been under investigation in this laboratory for some time. The analysis of Au I and of Hg II have been published and that of Pb IV is presented here. The investigation of Tl III is practically completed and will be published soon; Bi V is partially analysed. The state of our work on Tl III and Bi V is mentioned here because certain terms of these spectra and the corresponding terms of Pb IV have been established mainly by the regularity of the Moseley curves for these terms throughout the sequence Au I to Bi V. Thus the analysis of one spectrum has been facilitated and confirmed by a knowledge of the others. It is certain that some of the terms of Pb IV would not have been found except by such a method.

The spectrum of Zn II has been extended to complete the configuration 3d94s(3D)4p′ and 3d94s(1D)4p″. The configurations 3d109f, 3d1010f, and 3d94s(3D)5s′ have been added and a number of levels of the configurations 3d94s(3D)4d′, 3d94s(1D)4d″, and 3d94s(3D)6s′ have been tentatively established. Our list of Zn II lines contains 363 classified lines.Improved wavelength measurements have necessitated a revision of our earlier report on the spectrum of Zn IV. All the energy levels have been shifted slightly with respect to the ground state doublet 3d92D. In addition, 3 of 17 even levels and 10 of 43 odd levels have been changed. The new energy-level scheme results in the classification of 329 spectral lines as compared with 200 lines in the previous report.

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