A serious discussion took place between P. Curie in Paris and E. Rutherford in Montreal from 1900 until 1904 through the medium of scientific publications. P. and M. Curie had observed that radium pro- duces "induced radioactivity", whereas, at the same time, Rutherford had observed that thorium emits a kind of "emanation". P. Curie, per- forming different experiments with his collaborators, believed that ra- dioactive atoms draw from the environment the energy that they will release. Rutherford, together with F. Soddy, in a series of delicate ex- periments, discovered that radioactivity is the spontaneous transforma- tion of one radio-element into another. Finally, in March 1904, P. Curie "adopted the point of view of Mr Rutherford"