﻿Helium Atoms by Loic-Voltaye Electronic Bombardment. 1143 



decrease of negative current, or an increase of positive 

 current, if an (I-R) arrangement were employed. 



The cases in which evidence was obtained of the production 

 of ionization of abnormal helium atoms by bombardment 

 with electrons having about 5 volts energy are illustrated by 

 the curve given below, in which the current measured by 

 the electrometer is plotted against the energy of the electrons 

 in the bombarding stream. In obtaining the results repre- 

 sented in this curve it was arranged to have a large quantity 

 of resonance radiation coming into the main tube of the 

 apparatus from the auxiliary side tube, and in order that an 

 intense stream of electrons should bombard the abnormal 



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helium atoms formed in the main tube by this radiation, the 

 filament supplying the bombarding electrons was heated to 

 the limit of safety. Pure helium gas was constantly 

 streaming through the apparatus during the experiment at 

 an average pressure of 0*12 mm. The arrangement of 

 electric fields was that required for an (I-R) curve. The 

 curve shows that a positive current was measured which 

 began to increase when the electron energy exceeded about 

 4*5 volts. The detection of a positive current below 4*5 volts 

 is to be attributed to the ionization of 20'4 volts abnormal 

 atoms by 21 2 volts radiation. The measured current at this 

 stage couid be made positive or negative by adjustment of 

 the electric field in the V 2 space*. One of the complicating 

 factors in the investigation was the recombination which 

 occurred between the bombarding electrons and the positive 



* See Phil. Mag. vol. xlii. p. 746 (1921). 



