DUAL DISINTEGRATIONS 123 



radiation of internal energy by the electrons in their 

 orbits within the atom. So far, we must admit, the 

 cause of atomic disintegration remains unknown, 

 although Lindemann (Phil. Mag., 1915, [vi.], 30, 

 560) has attempted, with some success, to frame a 

 theory to account for it. 



BRANCH SERIES. 



The development of the various radioactive 

 sequences revealed that sometimes the series 

 branches, and that in the change of one radio- 

 element sometimes two products result, in general, 

 in different amounts. Thus the uranium series at 

 one point branches into the radium and actinium 

 series, in proportion 92 to 8 out of 100 atoms dis- 

 integrating. Again, in the case of radium- C and 

 thorium- C a similar branching occurs, and here in 

 one branch an a-ray change is followed by a /3-ray 

 change, and in the other branch the sequence is 

 reversed. These cases are sufficiently explained if 

 it be supposed that two simple radioactive changes 

 are in progress in the same substance simultaneously, 

 and that each obeys the law of simple change as 

 though the other did not occur. The distribution of 

 the original substance into the two products is then 

 proportional to the relative rates of the two changes. 

 If A! and X 2 are the radioactive constants of the two 

 changes, the proportion between the two products is 

 as Xj to X 2 , and the constant of the double change 

 as a whole, \+^ 2 - For thorium- C, the ratio is as 

 65 to 35, but for radium-C 99-97 to 0-03. The first 

 is relatively easy, but the second extremely difficult 

 to follow experimentally. It is, for example, impos- 

 sible to follow further what occurs to the minor 

 branch owing to the minuteness of the quantity of 

 material, and although this has to be represented as 



