22 SODDY, Evolution of Matter by Radio-active Elements^ 



Name. 



Actinium Emanation 



Thorium Emanation 



Radium " Induced Activity- 

 Matter " ( last stage ) 

 (Emanation X) 



Thorium " Excited Activity 

 Matter " (last stage) . . . 



Radium Emanation. 



Thorium X 



Polonium 



Actinium 



Radium 



Thorium 



Uranium 



}... 



Average Life, \\x 



57 seconds 

 87 seconds. 



43 minutes 



16 hours. 



5 days 8 hours. 



5 days 19 hours. 



About 16 months (?) 



? 



About 1,500 years. 



About 1,000,000,000 



years. 



All the recent advances that have been made in our 

 knowledge of the ultimate constitution of matter have a 

 common starting point. The energy associated with 

 matter under special circumstances has been the object of 

 study, rather than the matter itself by direct means. In 

 consequence, far smaller quantities than could be directly 

 perceived have been brought within the experimental range. 

 Thus in the phenomenon of a conducting gas, the ' ion ' 

 or charged atom is rendered evident by means of its 

 charge and differentiated from the rest of the gas, although 

 its quantity even under favourable conditions is probably 

 less than one-billionth part of the whole. In consequence, 

 as Professor J. J. Thomson has remarked, we know far 

 more about the ion than we do about the uncharged 

 molecule. Again, if the ion is placed under the influence 

 of sufficiently powerful electrical attraction or repulsion it 

 may acquire kinetic energy to such an extent that its 

 existence may be thereby revealed even in such minute 



