178 



PROFESSOR R RUTHERFORD ON THE 



curve are similar in shape, and, disregarding the first 1 5 minutes after removal, the 

 activity decays at exactly the same rate in both cases. 



100 



so 



20 



ft 



Shott 



Curv j 



Expos 



ure. 



30 45 60 75 



Time in Minutes. 



Fig. 5. 



105 



120 



The curves obtained by means of the y rays are identical with those obtained for 

 the $ rays. This shows that the ft and y rays always occur together and in the 

 same proportion. 



IOO 



80 



6 

 s 40 



_c 



20 



Decay of E.;ccited Activity 



of 



Radium. 



O 20 40 60 80 IOO 120 



Time in Minutes. 

 Fig. 6. 



For increase of the time of exposure from 1 minute to 24 hours the curves obtained 

 are intermediate in shape between the two representative limiting curves, figs. 5 

 and 6. 



