Radioactivity and Ionization of the Atmosphew, 719 



of two concentric cylinder- of radii b and a, is given by 



V -82 V 



X = 



log e - 



substituting values of 6 and a of cylinders in fig. 5. 



Now if X is the maximum number of ions per c.c. the 

 current i per unit length of cylinder over any ero?---ection. 

 when a small P.D. Y is applied, is given by 



i=2irr . X . e . u . X. 

 where n = sum of velocities of positive and negative ions in 

 unit field. 



Substituting the value of X 



t = 1'64 irSeuV. 



If I id the maximum current when all the ions produced 

 reach the electrodes 



I=qe?r(b s — a 2 ). 

 and 



i_l-64N. u.Y 



I" q (lr-cr) ' 



Now for a P.D. of '36 volt the current i is # 4 of it- 

 maximum value (see Table I. p. 716). 



Xow it will be shown later in the paper that the velocity of 

 the ions produced in air is about the same as that of the ion- 

 produced by Rontgen rays. The value of u (the sum of the 

 velocities of the positive and negative ions) for a gradient ot 

 1 volt per cm. is thus about 3*2 cms. per sec. 



Substituting these values, we obtain 



9 

 Taking into consideration that "4 of the ion- are removed 

 by the current before recombination, it follows that when no 

 voltage i- acting 



X 32 KQ ., 



- = T 6 = ; ^ ™ughly. 



X >w we have shown that if a has the same value as that 

 obtained for intense ionizations 



-hould equal 174, 

 9 



a value over three times as great. 



There are, however, several causes at work which tend to 

 make the observed value les^ than the theoretical. In the 



