342 H. M. Dadourian — Atmospheric Radio-activity. 



The rate of decay of Tli C lias not yet been measured 

 accurately, so far as the writer is aware. But it is stated 

 that its half -value period is only a few seconds.* If that is the 

 case \' s is large compared with A/ 2 , therefore we can simplify 

 the right-hand number of equation (13) 



N'_I' AA' 2 R 3 



N I X\R\ l } 



Substituting the values of the constants from the table on 

 p. 339 we obtain 



~ = 7-37xlCr 5 j- (15) 



I' 



Taking - 25 and 0*40 as the limiting values of -- for the air at 



JSTew Haven, we find the amount of radium emanation to be, in 

 round numbers, from 30,000 to 50,000 times as great as the 

 amount of thorium emanation. Substituting the limiting 



values of =■ obtained from data given by Blanc,f the equation 



(15) gives from 20,000 to 30,000 for the ratio of the amount of 

 radium emanation to that of thorium emanation present in the 

 atmosphere at Rome. 



New Haveii, Conn., February, 1908. 



* Halm, loc. cit. 

 fLoc. cit. 



