Fig. 6. 
214 Profs. E. Rutherford and H. T. Barnes on the 
mined at regular intervals. The results are shown in fig. 6, 
curve B. The heating effect dropped rapidly during the first 
ten minutes after the removal of the emanation, then more 
slowly, and finally dibraenea eae according to an 
exponential law with the time, falling to half value about 
every 30 minutes. The curve of decrease of the heating 
effect to zero is about the same as the curve of decrease of 
the heating effect of the radium to a constant minimum. 
wv 
iw 
= 
ro) 
2 
= 
2) 
= 


