of Radioactive Products present in the Atmosphere. 833 



Since at the surface of each wire V== — 11,000 volts and 

 A 1 = 650, 7i 2 = 150 cm. and the radius of the wires = '025 cm., 

 we have 



fii = A80 and /-i 2 = 560. 



A simple consideration shows that the expression for Q 

 for each wire remains the same when there are two wires 

 placed in a vertical plane, as long as w s is greater than 



. — j cm. per second. Of course, when the potential of 



each wire is given, its charge /jl is affected by the presence 

 of the other. 



(14) We have, on the other hand, determined the magnitude 

 of the current observed in the electroscope by a method 

 devised by Eve*, using 6'4 mgs. of radium bromide, which was 

 kindly standardized for one of us by Professor Rutherford, 

 and found that the unit of the activity ice have used corre- 

 sponded to 



4-52 xlO" 13 amp. 



(15) Now, when the radioactive equilibrium is established 

 on the w T ire, the number of atoms of the radium A or that of 

 the radium C breaking up per second per centimetre w T as 



4tt/^ 



shown to be 47r/xfflA, +, provided that w*/.tt^ — 7 • 



Suppose that I cm. of the wire is introduced into the 

 electroscope in the way already described. One half of the 

 a-particles emitted from the deposit are stopped in the wire 

 itself, and only one half of the remainder are shot out into 

 the space bounded by the cage, and a fraction of the ioniza- 

 tion due to these a-particles is effective in producing a 

 current, as some of the particles travel only a fraction of 

 their range through that space. From the dimensions of the 

 cage and the range of the a-particles, we have estimated this 

 fraction to be about §, for those emitted from radium 0. 

 Assuming that this is § , for the present, the current 1 which 

 is observed in the electroscope produced by the ionization 

 due to the radium C will be 



-r-p . , 7 >eN e 



M '^a* VW*eN e ( 7 )+\ e 'i\t e V) + ?o' 



where e is the charge on an ion and R is the ratio of the 

 effective ionization to the total ionization of the a-particles, 

 and equal to l'i'5 = Toi as mentioned above. 



* Eve, Phil. Mag. Jan. 1911. 



