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Profpssor Ernest Rutherford 



[Jan. 81, 



removed from the radio-active body and their further transformations 

 studied quite apart from the parent element. The analysis of the 

 transformation of the radium emanation has yielded results of great 

 importance and interest. After passing through three stages, radium 

 A, B, and C, of short period, a substance, radium D, of long period, 

 makes its appearance. This is transformed through two stages E and 

 F of short period into radium G, of period 140 days. Meyer and 

 Schweidler have conclusively shown that radium D is the primary 

 constituent of the radio-active substance separated by Hofmann, and 

 called bv him radio-lead. Radium G is identical with the first radio- 



o-o 



active substance separated from pitch-blende by Madame Curie, viz. 

 polonium. We are thus sure that these bodies are transformation 

 products of radium. It will be seen that I have added another pro- 

 duct of period -1-5 days between radium D and polonium. The 

 presence of such a product has been shown by Meyer and Schweidler. 

 In the case of thorium, a very long list of products is now known. 

 For several years thorium X was thought to be the first product of 

 thorium, but Hahn has recently shown that at least two other 

 products of slow transformation intervene, which he has called 

 mesothorium and radiothorium. The radiothorium emits a rays, and 



