Products present in the Atmosphere. 323 



-deposits obtained are due to the direct disintegration of the 

 emanations in the vicinity of the wire. He finds that there 

 is 30,000 to 50,000 as much radium as thorium emanation in 

 the air of New Haven, Conn., U.S.A., and from Blanc's results 

 20,000 to 30,000 at Rome. 



We can calculate this ratio from our results as follows : — 

 When the emanation and active deposit are in equilibrium, 

 an equal number of atoms of each product break up per 

 second. Now the initial activity of the thorium deposit is 

 due to a particles from ThB and ThC. The number of 

 each breaking up per second is XN r , where N is the number 

 of atoms of emanation necessary to keep ThB and C on the 

 wire in equilibrium, and \ its radioactive constant. 



The initial ionization is then given by \N(R 1 + R 2 )??, 

 where Rx and R 2 are the ranges of the a particles from ThB 

 and ThC, and n is the number of ions produced by an a 

 particle per cm. of its path (supposed to be the same for all). 

 ■Similarly, if A/, W, R/, R/ are the corresponding values for 

 the radium products, the ionization due to the radium 

 deposit is A/N'(R/ + R 2 >. 



The ratio — ,^ T , / ,. 1 . — ^~. — has been shown to have the 

 \'Jx'(Ri + R 2 )n 



N' 

 value 1*64, which gives —=3700 on substituting the known 



values Ri = 5-0, R 2 = 8'G, R/ = 4-8, R 2 ' = 7-0, A=^ ; 



X'«- ±- 



In the same manner we find from the results given by 

 Blanc and Dadourian the ratios 2600 to 4000 at Rome, and 

 9000 to 18,000 at New Haven. We see, then, that the 

 radium and thorium emanations exist in the atmosphere in 

 about the same proportion in this country as in Rome, while 

 in America there is relatively less thorium. 



The discrepancy between these results and those of 

 Dadourian may be explained as follows : — 



In equation ([)) p. 105 of his paper he makes use of the 



formula I=»K 3 M 3 , 



where v is the number of ions produced by an a particle per 

 cm. of its path, R 3 the range of the a particle, and M 3 the 

 number of atoms of RaC present. 



This equation should read I = \ 3 rR 3 M 3 , that is the ionization 

 is proportional to A 3 M 3 the number of atoms breaking up 

 per second. If we substitute this in Dadourian's equation 

 we obtain values Corresponding to those given above. The 



