Radioactivity of Mineral Springs. 



153 



effects were obtained by keeping the tinfoil disk charged at a 



potential of about —600 volts, by means of a Zamboni pile. 

 The activity decaved with time, falling to half its value in 



Fie. 3. 





\ 





! 





c C i 



















\ 



j 



6C 



: 1 



\ 





N 









i 



i 







\ > 





40 







\1 1 





5C 











,0 



, , 1 , 

















1 



! ! i i ! i 





20 40 £C 80 .'00 120 (40 16O .'80 20 



Ti me /A' Seconds 



about eleven hours. The resulting curve is shown in fig. 4 

 (p. 154). The close agreement that exists between these 

 measurements and the values obtained by other observers for 

 thorium, seems to establish clearly the existence of this metal 

 in the sediments of a certain number of thermal springs. 



I could detect no similar effects with the other deposits, 

 which, as I have mentioned above, give rise to an emanation 

 that loses half of its activity in 3*2 days. The excited activity 

 obtained from this emanation decayed at a rate very like the 

 one of radium-excited activity, i.e. falling to half its value 

 in about half-an-hour. 



