The production of characteristic Röntgen radiations

We know from the researches of Barkla and Sadler and others that many of the phenomena in connection with the emission of secondary Röntgen rays can be explained quite simply by supposing that there are two distinct ways in which matter subjected to the action of primary rays may itself become a centre of radiation:— (1) The primary rays may be scattered—an effect which is always very small. (2) The primary rays may be transformed into a type of radiation characteristic of the transforming material and re-emitted as such.