Charles Glover Barkla, 1877-1944

Abstract The name of Barkla will always be distinguished on account of his fundamental researches on Rontgen rays. In 1905 he made the discovery that scattered X-rays are polarized, but only to a certain degree. He also established the fact that each chemical element can radiate Röntgen rays having properties characteristic of that element, and in this way he anticipated the assignment to each element of an ‘atomic number’, the number being, in general, about one-half the atomic weight. For these discoveries he was admitted a Fellow of the Society in 1912, his investigations having resulted in the most important additions to our knowledge of the Röntgen rays since their discovery. Barkla consistently adopted the electromagnetic wave or pulse theory of the nature of the rays. At the end of the year 1912, von Laue put forward his theory of the diffraction of X-rays by transmission through a crystal regarded as a three-dimensional grating, thus introducing an entirely new’ method of investigation.