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 this 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 i| "' 

 imagine an atomic structure which would persist unchanged for long 



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1 



