[MCLENNAN- ON THE DELTA RAYS EMITTED BY ZINC 229 



found] 



Table III. 



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 remained 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 apparatus was left full 

 of air at atmospheric pressure for 6 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 80 volts positive 

 readings were taken with increasing magnetic fields up to 1,245 gauss. 

 These readings are given in Table IV and the curve representing them 

 is shown in Fig. 5. 



