 Section 1 of Radioactive Substances. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Availly in July 2010. Radioactive Substances. By Madame Sklodowska-Curie. Thesis presented to the Faculté des Sciences de Paris. Introduction. The object of the present work is the publication of researches which I have been carrying on for more than four years on radioactive bodies. I began these researches by a study of the phosphorescence of uranium discovered by Monsieur Becquerel. The results to which I was led by this work promised to afford so interesting a field that Monsieur Curie put aside the work on which he was engaged and joined me. Our object being the extraction of new radioactive substances and the further study of their properties. Since the commencement of our research we thought it well to hand over specimens of the substances discovered and prepared by ourselves to certain physicists in the first place to Monsieur Becquerel to whom is due the discovery of the uranium rays. In this way we ourselves facilitated the research by others besides ourselves on the new radioactive bodies. At the termination of our first publications Monsieur Giesel in Germany also began to prepare these substances and passed on specimens of them to several German scientists. Finally these substances were placed on sale in France and Germany and the subject growing in importance gave rise to a scientific movement such that numerous memoirs have appeared and are constantly appearing on radioactive bodies principally abroad. The results of the various French and foreign researches are necessarily confused as is the case with all new subjects in course of investigation. The aspect of the question becoming modified from day to day. From the chemical point of view however one point is definitely established that is the existence of a new element strongly radioactive that is radium. The preparation of the pure chloride of radium and the determination of the atomic weight of radium form the chief part of my own work. Whilst this work adds to the elements actually known with certainty a new element with very curious properties a new method of chemical research is at the same time established and justified. This method based on the consideration of radioactive...