498 Prof. McLennan and Mr. Found on Delta Radiation 



days' evacuation. With an applied potential difference of 

 80 volts and a magnetic field of 1400 gauss, however, the 

 readings obtained on the two occasions were practically the 

 same. This showed that the current carried by the alpha 

 particles and the recoil atoms remained the same for the two 

 days, but that in the interval the electronic current from the 

 zinc plate under bombardment by the alpha rays had dropped 

 from 40 x 10~ 5 e.s.u. to 18 X 10~ 5 e.s.u. 



Table TIT. 



Voltage on 



Current 



Magnetic 



Deflexion 



Current X10 5 



Polonium. 



through coils. 



field. 



per min. 



e.s.u. 



Volts. 



amps. 



gauss. 



mm. 





zero 



zero 



zero 



-10 



-29-5 



2 



, 



., 



- 6 



-17-0 



4 



j> 



',, 



11 



30 



8 



ii 



t , 



19 



56 



14 





f} 



21 



62 



20 



>» 



>> 



21 



62 



40 



» 





21-7 



64 



60 





, 



20-5 



60 



80 



>? 





21-2 



62-6 



80 



•8 



240 



195 



57 6 



80 



10 



410 



17-8 



53 



80 



17 



690 



16-5 



49 



80 



25 



905 



14-8 



44 



80 



35 



11.40 



14-5 



43 



80 



4-4 



1275 



15 



44 



80 



50 



1330 



15 



44 



80 



5-7 



1390 



15 



44 



This result made it evident that the electronic stream 

 from the zinc plate was determined to a considerable extent 

 by the amount of air occluded in its surface. For it is clear 

 that under the continuous evacuation for two days there must 

 have been a gradual diminution in the amount of air occluded 

 in the metal, and as everything else in the experiment re- 

 mained the same this diminution must have been the cause 

 of the decrease in the stream of delta radiation. 



Experiment IV. — In this experiment a freshly cleaned 

 plate of zinc was attached to the rod H at X, and the appa- 

 ratus was left full of air at atmospheric pressure for six days. 

 It was then exhausted as highly as possible with the Gaede 

 pump and the coconut charcoal surrounded with liquid air. 



Readings were first taken with positive potentials applied 

 to P up to 80 volts, and then keeping the potential of P at 



