Wheeloch— Nature of Ionization Produced hy a Rays. 243 



As before, the ratio of the currents is constant, as would be 

 expected if the ions are formed in columns. 



{e) The active deposit from thorium was also used as an ion- 

 izing agent. This was obtained in the usual way by putting 

 thorium hydroxide in a closed metal dish, through the top of 

 which a small brass plug was placed. The containing vessel 

 was charged positively and a difference of potential of about 

 300 volts was maintained between the vessel and the plug. _ 



The deflections were corrected for the decay of the excited 

 activity. 



The" plug was exposed for different lengths of time and the 

 following data were obtained : 



Parallel Field. 



Active deposit S-S^" from the middle of the chamber. 



-Current- 



VoUs/cm 



5-3 



21-8 



104-8 



488-8 



1013-8 



27 hrs. 

 Exposure 



1-62 

 1-82 

 1-95 

 2-09 

 2-17 



51 hrs. 

 Exposure 



2-16 

 2-37 

 2-68 

 2-91 

 3-0 



Ratio 



of 



Currents 



1-33 

 1-3 

 1-37 

 1-39 



1-38 



The activity was tested at two different times during its 

 decay with the following """"i*-" • 



jg results 



Parallel Field. 



Active deposit 3-5*='" from the middle of the chamber. 





, Current 



V 



Eatio 





65 hrs. 



After 



of 



Volts/cm 



Exposure 



6-5 hrs. 



Currents 



5-25 



1-82 



0-94 



1-93 



21-8 



2 



1-12 



1-8 



102o 



2-28 



1-15 



1-98 



413-8 



2-39 



1-27 



1-88 



1036-0 



2-40 



1-29 



1-86 



The ratio is again constant when the field is applied parallel 

 to the path of the a particle. The above deflections are not 

 corrected for ionization due to the /3 and 7 rays of thorium B, 

 but this is so small that it will have no appreciable effect. 



Experiment, therefore, seems to justify the assumption that 

 in the case of ionization by a rays, ions are formed in col- 

 umns along the path of the a particle. These columns are 

 not broken up by the parallel field, but are when the field is 

 at right angles to the path. 



