"Radio-Activity" by Ernest Rutherford is a scientific publication written in the early 20th century. The book provides a thorough examination of naturally radio-active substances, summarizing experimental findings and the theoretical frameworks that help explain the complex phenomena associated with radioactivity. The opening of "Radio-Activity" introduces the evolution of scientific understanding regarding radio-active materials and their properties. Rutherford reflects on past discoveries, including the works of Henri Becquerel and the early explorations of X-rays, leading to the advancement of theories on spontaneous disintegration of radioactive atoms. He emphasizes the rapid growth of knowledge in the field and outlines the significance of the disintegration theory in correlating a vast array of experimental data. This foundation sets the stage for a more detailed exploration of the ionization theory of gases, the methods of measuring radioactivity, and the ongoing developments in the study of radio-active minerals. (This is an automatically generated summary.)