RADIOACTIVE CHANGE UNIQUE 115 



of simple alternative explanation. Different investi- 

 gators have obtained entirely opposite results, and 

 there is not that consensus of evidence one finds 

 among- those who have investigated radioactive 

 change. 



In another direction there has been a tendency to 

 underrate the unique and unparalleled phenomenon 

 of radioactive change, and to connect what is entirely 

 and solely a development of the new experimental 

 science of radioactivity with the somewhat older 

 isolation of the electron and the electronic hypotheses 

 of the constitution of matter to which that discovery 

 has given rise. For example, Sir J. J. Thomson 

 in his Romanes Lecture, 1914, says: " Since the 

 electron can be got from all the chemical elements 

 we may conclude that electrons are a constituent of 

 all the atoms. We have thus made the first step 

 towards a knowledge of the structure of the atom 

 and towards the goal towards which since the time 

 of Prout many chemists have been striving, the proof 

 that the atoms of the chemical elements are all built 

 up of simpler atoms primordial atoms, as they have 

 been called." The removal of electrons from matter 

 occurs in physical, chemical, and radioactive changes 

 alike, exampled, respectively, by the electrification of 

 a glass rod by friction, the ionisation of an electrolyte 

 by solution, and by the /3-ray change of radioactive 

 substances. It is only in the latter case, however, 

 that the electron can be regarded as a primordial 

 constituent and the change as transmutational. 

 Even to-day it is in radioactive phenomena, and in 

 these alone, that the limits reached long ago in the 

 chemical analysis of matter have been overstepped 

 and the Rubicon, which a century ago Prout vaulted 

 over so lightly in imagination, has actually been 

 crossed by science. 



