Wheeloch — Nature of Ionization Produced hy a Rays. 247 



The explanation of the discrepancy hetween the experimental 

 curve and that given by the equation is not, tlierefore, the lack 

 of parallelism between the field and the colunms. 



This discrepancy may be due to the fact that in the theory 

 above given, it was assumed that uniform distribution of the 

 ions existed in the columns themselves, wliich is probably not 

 the case. It would be expected that the density of ions would 

 be greater along the axis of the column and would fall off with 

 the distance according to some law, which, if known, would 

 give a theoretical curve, that might more nearly and perhaps 

 exactly fit the experimental curve. 



On the other hand, it is quite possible that " initial recombi- 

 nation " (\n the sense used by Bragg) may account for part of 

 the lack of saturation, and that the final ex])lanation may 

 require both the "initial recombination" and " columnar ioni- 

 zation" hypotheses. 



V. Comparison of the curves obtained when the ions are 

 produced at different parts of the range of the a particle. 



Since the velocity of the a particle increases as the distance 

 from the source decreases, it is probable that the ejected 

 electron would be sent farther away from its parent molecule 

 when the ionizing soxirce is near the chamber than when it is 

 farther away ; that is, the greater the velocity of the ionizing 

 a particle, the greater the velocity of the ejected electron. 



If this be true, it would be expected, according to Bragg's 

 initial recombination hypothesis, that the amount of recombi- 

 nation would be greater when the ions are produced in the 

 part of the range where the velocity of the a particle is less. 



According to the hypothesis of columnar ionization, recom- 

 bination would be greatest in the part of the range where 

 the greatest ionization per column is obtained. 



The following data were obtained with the source at differ- 

 ent distances from the ionization chamber : 



Parallel Field. 



3.5cm 3. gem 1.9cm 



Volts/cm. Current % lack Current "/o lack Current % lack 



5 4-95 35-9 12-77 33-9 11-35 30-2 



10 5-37 30-5 13-67 29-25 12-35 24-1 



20 5-87 24-2 15-10 21-8 13-15 19-2 



40 6-32 18-6 15-95 17-4 13-95 14-3 



100 6-77 12-4 17-45 9-7 15-0 78 



200 7-15 7-5 18-35 5-0 15-45 5-0 



400 7-55 2-3 19-15 1-9 IG'O 1-7 



800 7-70 0-6 19-32 0-0 16-27 O-Q 



1200 7-75 0-0 .... 



For curves see fig. 7. 



