22 Dadouricm — Radio-activity of Underground Air. 



the product was subtracted from the former. The results 

 when plotted gave curve II of the same figure, which repre- 

 sents the rate of decay of the ground-air excited activity minus 

 the part due to thorium. A glance at figure 2 is enough to 

 show the difference both in nature and rate of decay of curves 



I and III on one hand, and the agreement between the curves 



II and III on the other. Yet it will be observed that the latter 

 are not exactly parallel ; curve II slopes at a little slower rate 

 than curve III. Hence apparently the ground-air excited 

 activity decays at a slightly slower rate than a combination of 

 radium and thorium excited activities, in the same proportion 

 as they occur in the ground-air excited activity. Bu instead 

 has observed a similar disagreement between the rates of decay 

 of the excited activity obtained from atmospheric air and a 

 combination of radium and thorium excited activities.* No 

 attempt will be made in this paper towards explaining the 

 disagreement, as the writer is at present engaged in a series of 

 experiments to that end, the results of which will appear in a 

 later number of this Journal. 



In conclusion, I wish to express my thanks to Professor H. 

 A. Bumstead for his kind interest in these experiments and 

 for his valuable suggestions. 



Sheffield Scientific School of 



Yale University, Nov., 1904. 



* Loc. cit. p. 7. 



