McClelland and Kknnedy — The Large lom in the Atmosphere. 85 



intervals. The results ave represented in the curve (fig. 10), where the 

 ordinates represent the saturation currents in arbitrary units, and the abscissae 

 represent the time measured from the first passage of the air from i? to ^ at 

 which the successive observations were made. The curve shows that large 

 ions are produced again after the air has been repeatedly freed from them, 

 though the amount produced during any interval is less than that produced 

 during the preceding interval. The air becomes less effective in producing 

 large ions according as those already produced are removed. From this it 

 would seem that the reproduction of the large ions does not depend merely 

 on the state of the air as regards such characteristics as humidity, tempera- 



























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40 

 30 

 20 

 10 



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TiirhQj Itv Mirvwtcs. 

 Fig. 10. 



ture, or pressure ; nor does it depend merely on the amount of radioactive or 

 penetrating radiation to which it is exposed. The air must contain a limited 

 quantity of something from which the large ions are produced and portion of 

 which is removed with the large ions formed from it. From these considera- 

 tions one is immediately led to examine the possibility of the large ion being- 

 formed by a nucleus suspended in the air, originally uncharged, but becoming 

 charged by attracting to it one of the small ions, of which a certain number 

 always exist in the atmosphere. The existence of such nuclei has been 

 abundantly proved by the condensation experiments of Aitken, Wilson, 

 and others. 



The truth of this conception of the large ion receives strong confirmation 



