Radioactivity and Ionization of the Atmospheft 



717 



is not very different for the two samples of air, but in Curve I. 

 the current reaches an approximate maximum much earlier 

 than in Curve II. This difference is probably due to the 

 presence of dust particles in the air in the latter case. Some 



Fig. 0. 



-70 



■bo 



50 



;4o 



-50 



■2c 



■ 











1 













— o 









-t> 















^ 







u . 













9 











/ 























/ 



/ 





















/ 



/ 











-SatUl 



it/ on c 



"uri/es 







/ 













-G/t 



/nc/er 









/ 













J 











/ 























I 













































I 













































k 













































h 











-ROi/ 



fl/o/tSb 



etween 



Z/ectroa 



es- 





10 Zo 30 4o 50 



of the ions in their slow passage between the cylinders give 

 up their charges to the dust nuclei. This action causes an 

 increase in the rate of combination of the ions and conse- 

 quently a larger electric field is required to produce the 

 maximum current. 



The capacity of the electrometer, cylinder, and connexions, 

 was 150 E.s. units when 1 mm. division of electrometer 

 corresponded to "00182 volt. The average value of the 

 movement of the electrometer needle was 100 divisions in 

 132 seconds for 50 volts between the cylinders. 



The current between the cylinders was thus 

 6'9 10-^E.s. units 

 or 2*3 10 — 13 amperes. 



The volume of air between the cylinders was 71200 c.c. 

 Taking the value of 6*5 10 -1(J E.s. units, found by J. J. 

 Thomson * as the charge on an ion, the number of ions 

 produced per c.c. per second is 15. 



* Phil. Mag., 1898. 



