For most of the M5 and M4 x-ray absorption edges already measured there is a discrepancy between observed and calculated values. The M1 edges occasionally have a small discrepancy while the M2 and M3 edges seldom show any. Siegbahn and Phelps have suggested that the final levels in the edge transitions are valence and low lattice levels and that the selection rule Δ1= ± 1 is usually giving the transition preference. A change in atomic spacing of a metal, such as often results from alloying it, should produce a change in the energies of its lattice levels. The gold M5 and M4 edges from gold and from a 50 atomic per cent copper gold alloy were photographed in a vacuum spectrometer. Significant shifts to higher energies in M5 of 2.5 electron volts and in M4 of 6.8 volts were found. These results show that the final levels in M absorption transitions are lattice levels, and they give credence to the assumption that there are preferred atomic to lattice level transitions
