SOME ASPECTS OF THE ATOMIC THEORY 585 



entitled to be considered transmutational in character. By a 

 /3-ray change radium-D, which is the isotope of lead, passes 

 into radium-E, which is the isotope of bismuth, and so on. 

 The example serves to bring out into clearer relief the normal 

 role of the electron, which so far from being a primordial 

 constituent is a partner of the material atom, the loss or gain of 

 which is accompanied by no fundamental change of the atom. 

 But even so it seems a forced mode of expression to represent 

 even the /3-ray electron as a primordial material constituent, 

 especially as the a-particle is such a primodial material constituent 

 which does not contain a single electron. 



