1042 Mr. Shenstone and Prof. Schlundt on the Number 



the count was in progress. Thorium should fall to half 

 value in 60*5 minutes and radium C in 19'5 minutes. 

 Actually we obtained decay curves giving- periods of 60 to 

 61 minutes for thorium C and 19*5 to 20'2 for radium C. 



To calculate the result of a day's count, we first plotted the 

 logarithms of the 7-activities against the time. The best 

 straight line was then drawn through these points, and the 

 7-activity calculated from it for each half minute during 

 which counting was carried on. 



The number of particles counted per half minute per 

 arbitrary unit of 7-activity is then obtained by dividing the 

 total number of a's counted by the sum of all the 7~activities 

 calculated. For counts on both thorium C and radium G 

 the ratio of the numbers of a-particles emitted per ^ minute 

 for equal 7-ray activities is then obviously 



2«-narticles P ,, ~ 2 a-particles „ .. ~ 



tor thorium O -=- ^ — - — . .,. tor radium 0. 



2 7-activities 



2 7-activities 



Such a ratio is independent of the dimensions of the 

 apparatus as long as those dimensions remain unchanged 

 during all the counts. The work was divided, therefore, 

 into groups, and necessary adjustments to the apparatus 

 were made only between groups. It will be seen in the 



following table that the ratios -' vary very considerably 

 between groups, but that the ratios —— — ^ do not differ 



by more than the probable error. 



a. thorium C 





Thorium C. 



Radium C. 



ThQ 

 EaC. 



i 



Group. 



Count. 



Activities. 



Ratio. 



Count. 



Activities. 



Ratio. 



1 Ratio. 



I. 



2700 



2506 



1-08 



2953 



1993 



1-48 



, -73 



11. 



1019 



780 



1-306 



913 



545 



1-68 



•78 



in. 



3191 



2722 



117 



3515 



2285 



154 



•76 



IV. 



3105 



2231 



1-39 



3803 



2100 



1-81 



•77 



V. 



3250 



2411 



1-35 



2316 



1246 



1-86 



■73 



13265 



w . . . , aThC ' , 



Weighted mean — — —^ =0"7o. 

 aRaC 



13500 



