IT is well known that the edges of X-ray absorption spectra are very often accompanied by secondary edges on the short wave-length side. For this phenomenon the following explanation has been proposed (D. Coster, Zs. f. Phys., 25, 83; 1924: A. Sommerfeld, “Atombau”, fourth German edition, p. 326 ; 1924). Whereas the main edge in the case of the K-absorption line corresponds to the transition of the K-electron just to the outside of the atom, the secondary edges should correspond to a simultaneous transition of a K-electron and an outer electron by one single absorption act.