Dispersion theory of X-rays

In connexion with the two interesting experimental papers by Rupp and Wierl, I should like to attempt to give a concise outline of the way in which the theoretical treatment of interference phenomena with X-rays and electrons has been developed hitherto. I particularly wish to emphasize those points which eventually led to the adoption of the Darwin-Ewald dispersion theory of X-rays, in order to draw comparisons with the present position in the realm of electrons. This will perhaps make it clear to what extent we are meantime obliged in the case of electrons to accept Bethe s dispersion theory, and which experiments seem best adapted for testing the special results of this theory. 

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