1. Thibaud, J.: J. de Phys. 8, 13, 447 (1937). Phys. Z. 29, 241 (1928). These papers, now of historical importance, contain a summary of methods involving the use of plane gratings.
2. Siegbahn, M.: Ergebn. exakt. Naturw. 16, 104 (1937). An excellent survey article which describes methods used in making measurements in the soft x-ray region by the use of gratings. Contains a summary of investigations in emission and absorption spectra of the light elements carried out by him and his collaborators at Upsala. Includes a fairly complete list of references to papers in the field up to 1937.
3. Edlén, B.: Nova Acta Reg. Soc. Sci. Upsaliensis 9, Nr. 6 (1934). Gives precision measurements of wavelengths in the extreme ultraviolet and includes valuable information on the isoelectronic sequences of the light atoms.
4. Sommerfeld, A., u. H. Bethe: Elektronentheorie der Metalle. In GEIGER-SCHEEL’S Handbuch der Physik, Bd. 24/2, S. 333. 1933.
5. Seitz, F.: The Modern Theory of Solids. New York: McGraw-Hill 1940.