A Nobel Prize-winning chemist explains the nature of radioactivity and the structure of the atom in nontechnical language in this classic scientific text, appropriate for upper-level undergraduates and graduate students. Beginning with the discovery of radioactivity, the text covers radium, the rays of radioactive substances, and radium's emanation. Additional topics include helium and radium, the theory of atomic disintegration, the origin of radium and its successive changes, radioactivity and the nature of matter, radioactivity and the evolution of the world, the thorium and actinium disintegration series, and the ultimate structure of matter. Concluding chapters examine the nuclear atom, isotopes, and x-rays. 1920 ed. 44 figures.