102 



Bumstead and Wheeler — Radio-active Gas. 



Earth-Gas. 



Interval 



in hours. a. 



19-31 0-00784 



24-32 0-00702 



43-63 0-00738 



Radium Emanation. 



Interval 





in hours. 



K. 



20-00 



0-00703 



23-31 



0-00739 



22-61 



0-00787 



65-93 



0*00745 



Av. 0-00741 ± -00016 Av. 0*00744 ± -00012 



emanation has been determined by P. Curie* and by Ruther- 

 ford and Soddyf and, when reduced to the hour as the unit of 

 time, the value obtained by Curie is 0*00724, while Rutherford 

 and Soddy obtained 0*00778. Curie's measurements were made 

 with the emanation in a sealed glass tube, and there could thus 

 have been no acceleration of the apparent rate of decay by 

 escape of the gas. The lower value obtained by us would be 

 accounted for if one-half per cent of the emanation leaked 

 from the cylinder in twenty-four hours. Such a lack of tight- 

 ness is by no means impossible. Rutherford and Soddy' s experi- 

 ments were made with emanation stored in a gas-holder and 

 drawn off from time to time for testing ; a slightly greater rate 

 of leak from their gas-holder might account for the higher 

 value of k obtained by them. 



The Rise of the Excited Activity. 



It has been observed by Rutherford that the excited activity 

 due to the radium emanation does not decay according to a 

 simple exponential law, and this we find to be the case also 

 with the excited activity due to the earth-gas. The most prac- 

 ticable method of comparing the two seems therefore to be to 

 reduce the measurements on the two gases to the same scale 

 and to plot a curve for each. Two such curves are found in 

 figs. 4 and 5. 



In the reduction to the same scale, the mean of the last four 

 observations has been taken as 100. The following tables give 

 the actual measurements and the plotting scale : 







Earth- Gas. 







Time in 



Observed 



Plotting 





Time in 



Observed 



Plotting 



minutes. 



ionization. 



Scale. 





minutes. 



ionization. 



Scale. 



3*5 



1-98 



59-3 





92-0 



3-21 



96*1 



12*0 



2-28 



68-3 





102-0 



3-08 



92-2 



20*0 



2-49 



74-6 





121-5 



3-42 



102-4 



26*4 



2-62 



78-4 





139-5 



3-35 



100*3 



330 



2-60 



77-9 





223-5 



3-36") 



100-6 "J 



42-0 



2-75 



823 





240-5 



3-36 ! 

 3-21 

 3-43 J 



100-6 ! 

 96-1 [ 



62-0 



2-86 



85-6 





273-5 



76-0 



3-05 



91-3 





284-5 



102-7 J 





* P. Curie, C. 



R. cxxxv, 



p. 857, 1902 









f Eutherford and Soddy, 



Phil. 



Mag. (6), v, 



p. 445, 1903. 





