﻿1144 Prof. Horton and Dr. Davies : Ionization of Abnormal 



ions which were produced by the radiation, for as the energy 

 of the bombarding electrons was increased, the distance 

 through which they travelled also increased, and hence the 

 amount of recombination became greater, and fewer positive 

 ions were collected. This variation in the amount of re- 

 combination occurring tended to mask the effect of ioni- 

 zation by the bombardment of abnormal atoms, and was 

 responsible for the negative results obtained in some instances.. 

 The downward slope of the curve given in the figure, before 

 4*5 volts is reached, illustrates the reduction in the positive 

 current due to increased recombination as the energy of the 

 electrons is increased. 



Some idea of the amount of recombination occurring 

 between the bombarding stream of electrons and positive 

 ions produced by the radiation which comes from the 

 auxiliary tube, is given by the following experiment : — With 

 the electric fields arranged for an (I-R) curve, and with V 2 

 adjusted so that the measured current was of the negative 

 sign, the current measured in a certain experiment was 

 3*94 x 10~ 13 amp. when the energy of the bombarding elec- 

 trons was 3*5 volts. By means of a current sent through a 

 coil of many turns of wire wrapped round the main tube, a 

 magnetic field could be applied parallel to the axis of this tube 

 This magnetic field served to prevent the electron stream 

 emitted from the hot filament from spreading laterally by 

 concentrating it into the central part of the tube, thereby 

 diminishing the possibility of encounters between these 

 electrons and positive ions produced throughout the space by 

 the radiation. It was found that the effect of switching on 

 the magnetic field (all the electric fields remaining as before) 

 was to cause a positive current of 0*53 x 10 -13 amp. to be 

 measured instead of the negative current of 3*94 x 10~ 13 amp. 

 previously observed, the increase of positive current being 

 due to the smaller amount of recombination occurring. 



Owing to the fact that when curves such as that given 

 in the figure were obtained the filament supplying the 

 bombarding electrons was extremely hot, it was desirable to 

 complete a series of observations as quickly as possible. 

 For this reason observations were taken at rather large 

 voltage intervals, and the genuineness of the observed effects 

 was tested by taking observations at decreasing values of the 

 voltage, as well as at increasing values, to see if the curve 

 retraced it's course. The results do not make it possible to 

 decide with any great accuracy the minimum energy of the 

 bombarding electrons for which ionization is produced, but 



