SUCCESSION OF CHANGES IN RADIOACTIVE BODIES. 



179 



The results obtained by CURIE and DANNE for the decay of the excited activity oi 

 radium for different times of exposure are shown graphically in fig. 7. The ordinates 



-i 



Time in hours. 

 Fig. 7. 



represent the logarithm of the activity and the abscissae time in hours. A comparison 

 of the curves obtained by myself and those obtained by CURIE and DANNE at once 

 discloses some marked differences. 



The lowest curve for a short exposure of 20 seconds is very similar in shape to the 

 corresponding curve, fig. 4, curve B, where the activity was measured by the a. rays. 

 On the other hand, the upper curve A of fig. 7 does not show the initial drop found 

 by me (see fig. 4, curve A), where the activity is measured by the a rays. If the 

 activity is supposed to be measured by the ft rays, the upper curve A, fig. 7, is 

 .similar to that shown in fig. 6. The lower curve of fig. 7 is, however, again different 

 from the corresponding /3-ray curve shown in fig. 5. 



I think the difference between the results of CURIE and DANNE and those obtained 

 by myself lies in the fact that the former did not take into account that the shape of 

 the curves depended on whether the a or ft rays were used as a means of measure- 

 ment. CUKIK and DANNE do not state, or give any evidence to show, which of the types 

 of rays they employed for measurement, but I think there is no doubt that the lower 



2 A 2 



