Manchester Memoirs, Vol. Hi. (1908), No. 0. 3 



of a particles counted by this method is of the same order 

 as the calculated number, but special experiments are in 

 progress to determine with accuracy the value of this 

 important constant. By counting at intervals the number 

 of a particles expelled per minute, we have been able to 

 obtain the curves of decay of activity of a plate coated 

 with radium C or actinium B. 



The a particles from a constant source are shot out at 

 irregular intervals. The time interval between the 

 entrance of successive a particles has been observed over 

 a long interval, and the results show that the distribution 

 curve with time is similar in general shape to the 

 probability curve of distribution of the velocity of 

 molecules in a gas. Further observations, however, are 

 in progress to determine the distribution curve with the 

 accuracy required for comparison with the mathematical 

 theory. 



