the Cause and Nature of Radioactivity. 395 



is not at all dependent on the source from which the element 

 is derived, or the process of purification to which it has been 

 subjected, provided sufficient time is allov/ed for the equi- 

 librium point to be reached. It is not possible to explain 

 the phenomena by the existence of impurities associated with 

 the radioactive elements, even if any advantage could be 

 derived from the assumption. For these impurities must 

 necessarily be present always to the same extent in different 

 specimens derived from the most widely different sources, 

 and, moreover, they must persist in unaltered amount after 

 the most refined processes of purification. This is contrary 

 to the accepted meaning of the term impurity. 



All the most prominent workers in this subject are agreed 

 in considering radioactivity an atomic phenomenon. M. and 

 Mme. Curie, the pioneers in the chemistry of the subject, 

 have recently put forward their views {Comptes Rendas, 

 cxxxiv. 1902, p. 85). They state that this idea underlies 

 their whole work from the beginning and created their 

 methods of research. M. Becquerel, the original discoverer 

 of the property for uranium, in his announcement of the 

 recovery of the activity of the same element after the active 

 constituent had been removed by chemical treatment, points 

 out the significance of the fact that uranium is giving out 

 cathode-rays. These, according to the hypothesis of Sir 

 William Crookes and Prof. J. J. Thomson, are material 

 particles of mass one thousandth of the hydrogen atom. 



Since, therefore, radioactivity is at once an atomic pheno- 

 menon and accompanied by chemical changes in which new 

 types of matter are produced, these changes must be occurring 

 within the atom, and the radioactive elements must be under- 

 going spontaneous transformation, The results that have so 

 far been obtained, which indicate that the velocity of this re- 

 action is unaffected by the conditions, makes it clear that the 

 changes in question are different in character from any that 

 have been before dealt with in chemistry. It is apparent 

 that we are dealing with phenomena outside the sphere of 

 known atomic forces. Radioactivity may therefore be con- 

 sidered as a manifestation of subatomic chemical change. 



The changes brought to knowledge by radioactivity, 

 although undeniably material and chemical in nature, are of 

 a different order of magnitude from any that have before 

 been dealt with in chemistry. The course of the production 

 of new 7 matter which can be recognized by the electrometer, 

 by means of the property of radioactivity, after the lapse of 

 a few hours or even minutes, might conceivably require 

 geological epochs to attain to quantities recognized by the 



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