Radio-active Products of Short Life. 



633 



were discarded, the probable error in the mean of the various 

 decay ratios obtained from the sets of readings deciding the 

 value of the result. 



In this way the following values of X were obtained 



t. 



\t. 



X(sec) 



000726 sec. 



0-234 



323 



000843 



0-316 



375 



00169 



0-562 



332 



00260 



0-861 



332 



00405 



T56 



386 



Weighted mean \ = 347. Hence half-value period ='00200 

 sec, the error being probably not greater than 5 per cent. 



In fig. 1 the logarithm to base e of the activity ( — \t) is 

 plotted against the time if) . 



Fig. 1. 

 Oi 































\ 











J \. 



Time 



3 4 



Thousandths of a secohd 



This result is in agreement with that of Geiger* who, 

 from the behaviour of actinium emanation in an electric 

 field, deduced the existence of this new product and the 

 order of magnitude of its period. The value given by Geiger 

 as a rough estimate is, by a remarkable coincidence, identical 

 with that obtained above. 



It has been mentioned in the foregoing calculation that 

 the sensitiveness of the first box was found to be 13 per cent. 

 * PM1. Mag. vol. xxii. p. 201, July 1911. 



