226 THE ROYAL SOCIETY OF CANADA 



apparatus was exceedingly low the ionisation current must have been 

 negligible. Taking it to be so the current must have been carried by 

 the alpha particles and the recoil atoms. If, now, we assume that as 

 many alpha particles were shot back into the polonium plate as were 

 projected forward from it, it follows that the number of recoil atoms 

 taking part in the current was very closely equal to the number of 

 alpha particles which contributed to it. Taking the charge on the 

 alpha particle to be 2e, and that on the recoil atom to be e, we have 

 then, since the current carried by the electrons emitted by the zinc 

 plate must have been 40 x 10"^ e.s.u., the number of alpha particles 

 striking X given by 44 x 10"^ /3e. Since the number of electrons emit- 

 ted by the zinc plate was 40 x 10"^ /e it follows that 2 • 73 electrons were 

 emitted by the zinc plate per alpha particle which struck it. 



Experiment III. The next experiment which was performed 

 served to illustrate the fatigue of the delta ray effect. In this case the 

 apparatus was continuously evacuated for two days after the measure- 

 ments made in Experiments I. and II were taken. At the end of this 

 time readings were taken by applying various positive potentials up 

 to 80 volts and when this was reached the magnetic field was turned 

 on and readings were taken with fields up to 1,400 gauss. These are 

 all recorded in Table III and are shown graphically in Fig. 4 together 

 with the results of Experiments I. and II. From the results it will 

 be seen that while the maximum current under 80 volts was 84 x 

 10"^ e.s.u. at the beginning of the experiment it was only 63 x 10"^ 

 e.s.u. after two days evacuation. With an applied potential differ- 

 ence of 80 volts and a magnetic field of 1,400 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 bombard- 

 ment by the alpha rays had dropped from 40 x 10"^ e.s.u. to 18 x 10"^ 

 e.s.u. 



