Emanation in the Lower Regions of the Atmosphere. 33 



from radium emanation is 1*74 xlO 5 , from Radium A 

 1-87 x 10 5 , and from Radium C 2*37 x 10 5 . The average for 

 these three products is 2'0 x 10 5 . Hence working on the same 

 lines as before we fiud that the number of ions produced 

 per sec. par cub. metre of air by the radium emanation, 

 radium A, and radium C in radioactive equilibrium with 

 105 x 10 — 12 grm. of radium is 



(105 x 10- 12 ) x 3 x (3-4 x 10 10 ) x (2-0 x 10 5 ) 



or 2-1 x 10 6 , 



or about 2 per c.c. per sec. 



When the emanation content is at its lowest value this 

 would be reduced to '7, and when at its highest value would 

 be raised to 7. 



The average emanation content at Montreal, as measured 

 by Eve, is -f^ °^ the amount in Cambridge, so that the 

 number of ions produced by the emanation at Montreal per 

 c.c. per sec. is about 1*2. 



Amount of Ionization of the Air due to the Thorium 

 Emanation present. 



W. Wilson* has shown that there is about 4000 times as 

 much radium emanation as thorium emanation in the atmo- 

 sphere near the earth's surface. The radioactive constant of 

 thorium emanation is about 5000 times greater that of 

 radium emanation, hence there are about the same number 

 of thorium emanation atoms and radium emanation breaking 

 up per second in the atmosphere near the earth, and there- 

 fore the thorium series of disintegrating products would also 

 be responsible for about 2 ions per c.c. per second. 



Therefore in free air the number of ions produced per c.c. 

 per sec. by the emanation of radium and thorium present is 

 about 4. If a vessel were slowly filled with filtered air the 

 thorium products would not enter the vessel, and therefore 

 only 2 of the number of ions produced per c.c. per sec. in a 

 closed vessel are due to emanations, and those 2 to radium 

 emanation. 



Apportionment of the ions produced in a metal vessel and in 

 free air to the ionizing agents at work. 



The number of ions produced per c.c. per second in a metal 

 vessel has rarely been reduced below 10. This number has 



* Phil. Mag. Feb. 1909. 

 Phil. Mag. Ser. 6. Vol. 20. No, 115. July 1910. D 



