the Radioactive Emanations by Charcoal. 

 Integrating, we get 



381 



Aw 



A, 



and substituting for n Q , 





The ionization current is proportional to the number of 

 emanation-atoms breaking up per second, which is A, times 

 the number present, L e. XP. Hence, if i is the ionization 

 current, . = KxPj 



where K is a constant ; and therefore 



Xv Xw 

 i = KKe~[l—e~T] (1) 



If we plot a curve with ionization currents as or d mates 

 and flow of air in c.c. per second as abscissa?, we can see 

 from (1) what the shape of the curve should be. 



Denoting — XV as a, and — XW as h, we have 



; = KN«f[i— ««], 



from which we can at once see that i = when q — or x> . 

 Differentiating, we get 



|?.= KN««[(a + &)*f— a], 



from which it follows that i is maximum when 



a 



9 = 



log 



■or when 



? = 



a 



a~+ 



XV 



log v 



(2) 



The ionization, then, must rise from zero to a maximum, 

 and fall off to nothing as the speed of the air-current increases 

 to infinity. 



Phil. Mag. S. 6. Vol. 17. No. 99. March 1909. 2 D 



