produced by the Action of Thorium Compounds. Ill 



Fig. 7. 



100' 

 90 

 80 

 70 



60 

 50 

 40 

 30 

 20 



10 



















































































1 





































V 































T/ME //V 



Hoc//?s 









— o 



-Q 



10 



20 



30 



40 



50 



60 



70 



In a previous paper * I have shown that the radio-active 

 " emanation " from thorium compounds quickly loses its 

 radio-active power. 



The intensity in that case falls to half its value in about 

 one minute, while the intensity of the " excited " radiation 

 falls to half its value in about eleven hours, or one decays 660 

 times faster than the other. The law of falling off of intensity 

 is the same in the two cases. 



On page 166 it has been shown that the current i (for 

 a " saturating " E.M.F.) between two cylinders is given by 



•■-t?*i- 



■a)l 



S J o i _ A(i 



w T ith the same notation as before. 



The intensity I of the radiation after a time t is given by 



i — ± e , 



and the total quantity of electricity passing between the 

 cylinders during the time taken for the intensity to fall 

 to zero is given by 



Q = f idt =^°{l - e-M*-«) } p e~ Lt dt 



LA* »' 



* Phil. Mag. Jan. 1900. 

 Phil. Mag. S. 5. Vol. 49. No. 297. Feb. 1900. N 



