Absolute wave-length measurements by photographic methods with plane gratings (280 and 1180 lines per mm) have been made on very soft x-ray lines of Th, Pb, Hg, Au, Ir, W and Ta. The wave-lengths range from 43.6A to 104.8A. For Hg, Au, Ir, W and Ta doublets were observed whose probable origins are transitions within the N shell, i.e., $\Delta n=0\mathrm{}$. These doublets fall on a smooth Moseley curve of small curvature.

• Received 31 May 1932

DOI:https://doi.org/10.1103/PhysRev.41.136