IN AN KLECTRIC FIELD. HENDEKSON. 



Table I. 



129 



\'(>lts per cm. 



Percentafj;e 

 cathode activity. 



13 



92.7 



25 



93.5 



80 



94.8 



150 



94.9 



1000 



96.2 



2000 



96.4 



4000 



96.9 



12000 



97.8 



These results differ in two respects from those found 

 by Wellisch. In the first place a considerably larger fraction 

 of the total activity is found positively charged at the higher 

 voltages than the results of Wellisch indicated. Secondly, 

 there appears to be no limiting value to the percentage 

 brought to the cathode. As the potential-gradient is in- 

 creased this percentage gradually, though slowly, increases. 

 Thus, the evidence of Wellisch to the contrarj^, one seems 

 justified in concluding that all the rest-atoms could be brought 

 to the cathode in a sufficiently strong field, and hence that all 

 the rest-atoms are initially positively charged. It is further 

 to be noticed how much more difficult it is to bring over to 

 the cathode the rest-atoms of radium than those of thorium 

 under similar conditions. To obtain 97.8% of the thorium 

 rest-atoms on the cathode a potential-gradient of only 

 about 30 volts per cm. would be required, as compared 

 with a potential gradient of 12,000 volts per cm. in the case 

 of radium. The ionization between the plates was of the 

 same order of magnitude in the two cases. 



That the value previously found for the percentage 

 cathode activity' of radium was but little above that obtained 



