1K4 



PROFESSOR E. RUTHERFORD ON Till'. 



100 



80 



c 

 o 



3.40 



' 



I 

 20 



\ 



Relative 

 present 



amounts 



at 

 3. long 



of matter 



instant 

 exjposure. 



30 45 60 



Time in Minutes. 



Fig. 9. 



A.B.C. 



tfter 



75 



105 



12. Any Time of Exposure. Suppose that a body is exposed in the presence of a 

 constant supply of emanation, and that n a particles of the matter A are deposited 

 each second. After a time of exposure T, the number of particles P T of the matter A 

 present is given by 



P T = w 



At any time t, after removal of the body from the emanation, the number of 

 particles P of the matter A is given by 



P = 



Consider the number of particles n dt of the matter A deposited during the 

 interval dt. At any time t later, the number of particles <7Q of the matter B, which 

 results from the change in A, is given (see equation 4) by 



= n \ 



A., 



- ,-*') . dt . = n /(0 dt 



(10). 



After a time of exposure T, the number of particles Q T of the matter B present is 

 readily seen to be given by 



