580 



The Evolution of Matter 



We can now exhibit in tabular form the amazing pedigree of 

 radio-active change shown by this one family of elements. An im- 

 mediate descent is indicated by -*, while one which may either be 

 immediate or involve an intermediate step is shown by ... 

 No place is found in tliis pedigree for thorium and its derivatives. 

 They seem to form a separate and independent radio-active family. 



As soon as the transmutation theory of radio-activity was accepted, 

 it became natural to speculate about the intimate structure of the 

 radio-active atoms, and the mode in which they broke up with the 

 liberation of some of their store of internal energy. How could we 

 imagine an atomic structure which would persist unchanged for long 



