Periodicity of the Spontaneous Ionization of Air, etc. 269 



minimum between 12 h. and 15 h. Not quite so well 

 defined but still quite obvious ore the second maximum 

 occurring between 8 h. and 11 h., and the second minimum 

 occurring between 2 h. and 6 h. The curves for lead and 

 carbon dioxide thus show a double daily period. Looking 

 now at the curves for lead and coal-gas (fig. 2), we find that 



Fio-. 2. 



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1-50 



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 /4 



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8 12 16 



f/ou/?<S OF THE DAY. 



Lead and Coal-Gas. 



20 



24- 



the scale to which they are drawn makes them appear more 

 regular, but the same features are apparent. Once more 

 each curve shows a well marked maxim am between 20 h, and 

 23 h., and a minimum between 12 h. and 16 h. Another maxi- 

 mum may be observed between 7 h. and 10 h., and a second 

 minimum between 3 h. and 6 h. From this and other similar 

 evidence it is concluded that the periodic variation of the 

 ionization in the vessel is independent of the nature of the 

 gas enclosed. 



Phil. Mag. S. 6. Vol. 13. No. 74. Feb. 1907. U 



