Radio-Activity CAMBRIDGE PHYSICAL SERIES. GENERAL EDITORS:—F. H. NEVILLE, M.A., F.R.S. AND W. C. D. WHETHAM, M.A., F.R.S. RADIO-ACTIVITY CAMBRIDGE UNIVERSITY PRESS WAREHOUSE C. F. CLAY, MANAGER. London: FETTER LANE, E.C. Glasgow: 50, WELLINGTON STREET. ALSO London: H. K. LEWIS, 136, GOWER STREET, W.C. Leipzig: F. A. BROCKHAUS. New York: THE MACMILLAN COMPANY. Bombay and Calcutta: MACMILLAN AND CO., LTD. [_All Rights reserved._] RADIO-ACTIVITY BY E. RUTHERFORD, D.Sc., F.R.S., F.R.S.C. MACDONALD PROFESSOR OF PHYSICS, McGILL UNIVERSITY, MONTREAL SECOND EDITION CAMBRIDGE AT THE UNIVERSITY PRESS 1905 _First Edition 1904_ _Second Edition 1905_ J. J. THOMSON A TRIBUTE OF MY RESPECT AND ADMIRATION PREFACE TO THE FIRST EDITION. In this work, I have endeavoured to give a complete and connected account, from a physical standpoint, of the properties possessed by the naturally radio-active bodies. Although the subject is comparatively a new one, our knowledge of the properties of the radio-active substances has advanced with great rapidity, and there is now a very large amount of information on the subject scattered throughout the various scientific journals. The phenomena exhibited by the radio-active bodies are extremely complicated, and some form of theory is essential in order to connect in an intelligible manner the mass of experimental facts that have now been accumulated. I have found the theory that the atoms of the radio-active bodies are undergoing spontaneous disintegration extremely serviceable, not only in correlating the known phenomena, but also in suggesting new lines of research. The interpretation of the results has, to a large extent, been based on the disintegration theory, and the logical deductions to be drawn from the application of the theory to radio-active phenomena have also been considered.