Further progress in studies of atomic structure was in tight connection with the advance to shorter wavelength in EUV region. Millikan, Sawyer, Bowen used electric discharges in vacuum to observe some emission spectral lines down to 13 nm they prescribed to stripped atoms. In 1927 Osgood and Hoag reported on grazing incidence concave grating spectrographs and photographed lines down to 4.4 nm (K α of carbon). Dauvillier used a fatty acid crystal of large crystal grating space to extend soft x-ray spectra up to 12.1 nm, and the gap was closed. In the same period Manne Siegbahn constructed a very sophisticated grazing incidence spectrograph that enabled Ericson and Edlén to obtain spectra of vacuum spark with high quality and to reliably identify lines of multiply ionized atoms up to O VI, with five stripped electrons. Grotrian developed his graphic presentation of energy structure of the atoms. Russel and Saunders proposed their coupling scheme for the spin-orbit interaction and their generally recognized notation for spectral terms.