The Immediate Sequels to Laue’s Discovery

Abstract

In 1912 William Henry Bragg was Cavendish Professor of Physics at the University of Leeds. Born in 1862 in Wigton (Cumberland) he was Laue's senior by seventeen years. His career was unusual in that he began research only after his fortieth year, although his great mental ability appeared from his early childhood on. After studying mathematics in Cambridge, and finishing there in 1884 with high honours, he was appointed, at the age of 22, as Professor of Mathematics and Physics at the young University of Adelaide, then in its tenth year. Here, Bragg's activity and interest was directed to physics, and to the perfection of his teaching and lecturing, in which he became one of the great artists. It was here also that he set up, soon after Röntgen's discovery became known, the first X-ray tube in Adelaide. Seventeen years passed after Bragg had become the head of the physics laboratory before the spark of original research reached him,---but from there on a mighty and steady flow of scientific results emanated from him until shortly before his death. The occasion which brought this change about was the need of reviewing, for a presidential address to the Australian Association for the Advancement of Science, the recent advances in radioactivity. He was struck with the possibility that a decision between the hypotheses of J.J. Thomson and of Ph. Lenard on the constitution of the atom might be obtainable from measurements of the absorption of $α$-rays in matter. In his paper of 1904 with R. Kleeman `On the Ionization Curves of Radium' he showed that the exponential law which had been tacitly assumed for the decrease in intensity of an $α$-ray passing through matter was far from correct, and the characteristics of the range of $α$-particles were established.