[MCLENNAN- ON THE DELTA RAYS EMITTED BY ZINC 

 found] 



Table IL 



225 



From these it will be seen that the current gradually fell off as 

 the field was increased and ultimately reached a steady state with a 

 field of approximately 1,000 gauss. 



From the known properties of the ionisation currents of the alpha 

 rays and of recoil atoms, it is clear that a field of this intensity was not 

 sufficient to modify to any appreciable extent the current carried by 

 them to X and it follows therefore that the decrease in the current 

 observed was due to the action of the magnetic field in curling the 

 electrons emitted by the zinc plate under bombardment by the alpha 

 rays back again into that plate. This experiment, therefore, showed 

 that a field of 1,000 gauss was sufficient, when the applied potential 

 difference was 80 volts, to entirely cut off the stream of electrons. The 

 problem before us, then, was to apply the procedure just described 

 to the investigation of the intensity of the electronic stream from the 

 zinc plate X when the surface of this plate was made to undergo various 

 modifications. 



Before leaving this experiment it may be pointed out that the 

 results obtained go to show that approximately three electrons were 

 emitted by the bombarded zinc plate for every alpha particle which 

 struck it. 



From the table it will be seen that the current under the electric 

 field combined with the maximum magnetic field was approximately 

 44 x 10"^ e.s.u. This current consisted of (1) alpha particles; (2) 

 recoil atoms and (3) the ionisation current. As the gas pressure in the 



