Barkla Discovers the Characteristic X Rays of the Elements.

For several decades in the nineteenth century, physicists studied cathode rays. For an even longer time, scientists had known of the existence of atoms. Nevertheless, during the last decade of the nineteenth century, scientists still had great difficulty in comprehending the physical nature of either cathode rays or atoms. Apparently, atoms of some chemical elements were heavier and others were lighter. It was not known why. The reason could have been that atoms consisted of different materials or that the heavier ones had more of the same materials. Chemical facts gave clues about the existence of atoms. Cathode rays appeared to be “tentacles” originating from the atom.