108 ROYAL SOCIETY OF CANADA 



obtained with cylinders made from différent samples of almost any 

 metal selected at random. Considering also the difference in the atomic 

 weights of tlie three substances, aluminium, zinc, and lead, and having 

 in mind that radioactivity is a property associated with atomic structure, 

 it would seem that if these metals could be obtained entirely free from 

 active impurities, and tl^o conductivity of air contained in vessels made 

 from them studied, it would be found, if the observations were carried 

 out under conditions, or in places where no ionization was possible from 

 penetrating radiations arising from external sources, to drop to a very 

 low value if it did not entirely vanish. 



Tn conclusion I desire to thank Professor McLennan, both for his 

 valuable suggestions and for his assistance at all times throughout the 

 investiration. 



