IN a paper recently published (Z. f. Phys. 33, 601, 1925) the present authors came to the conclusion that the new line beta' constitutes with the line beta1 the ``relativity doublet''. In a letter received by the authors, Prof. Sommerfeld points out that, in his opinion, the line beta' ought to be considered as a spark line or as a line of unknown origin, since Deltalambda according to our data
... [Show full abstract] is equal to 4.3 X.U., whilst according to Allison's Deltalambda for M0 is equal to 0.56 X.U. The value given by Allison may be verified with the aid of the data for the wave-lengths Lbeta3 and Lbeta4 which are emitted, when the transition of electrons takes place between the levels M3 or M4 and the level L3, while the transition of electrons from the same levels M3 and M4 to the level K gives rise to the lines Kbeta1 and Kbeta'. Accordingly we obtain for Deltanu/R from the data for the L series for M0 the value 1.63, and from Allison's data -1.27.