﻿674 Dr. T. S. Taylor on the Number of Ions 



The polonium was then moved so as to be 1*2 centimetres 

 from the ionization-chamber, and readings were taken of the 

 deflexions of the electrometer for intervals of 5 minutes. 

 The value of this deflexion gave a measure of the ionization 

 current produced by 2' 66 centimetres of the range of the 

 alpha particle. This was proportional to the ionization that 

 is represented by the area under the ionization curve to the 

 right of the ordinate corresponding to the abscissa 1*2 in 

 fig. 2. 



The difference between the readings obtained when the 

 polonium was 0*9 centimetre and 1*2 centimetres from the 

 ionization-charnber gave a value that is proportional to the 

 ionization represented by the area of the shaded portion of 

 fig. 1. By comparing the area of this shaded portion w T ith 

 the area under the curve to the left of the abscissa 0*9, the 

 amount that should be added to the electrometer reading in 

 order to take account of the ionization produced in the first 

 0*9 centimetre of the path was obtained. This value could 

 also be obtained by comparing the area to the left of the 

 ordinate corresponding to the abscissa 09 in fig. 2 with the 

 area to the right of the same ordinate. 



The corrected reading of the electrometer, that is, the 

 reading obtained when the polonium was 2'96 centimetres from 

 the ionization-chamber plus the value corresponding to the 

 first 09 centimetre of the path obtained in the above manner, 

 gave a measure of the potential that the plate iC A" and the 

 electrometer system would have assumed had the beam of 

 particles spent their entire range in the ionization-chamber. 

 The corrected scale-readings, that would correspond to the 

 ionization that would be produced by the entire range of the 

 beam of rays used, are given in column 1, Table II. Each 

 of the values given is the mean value of several separate 

 determinations. By multiplying this corrected electrometer 

 deflexion by the value of a scale-division in electrostatic units, 

 the potential to which the plate " A " had been raised was 

 obtained. One centimetre scale-deflexion corresponded to a 

 potential of 4* 39 X 10 ~ 5 electrostatic unit. The potentials in 

 electrostatic units corresponding to the above cited corrected 

 scale-deflexions are recorded in column 2, Table II. From 

 the values of the potential and the capacity of the system, 

 the quantity of electricity that would be given to the plate 

 " A " by the total beam used was calculated. These values 

 of the charge given to the plate " A " during the time 

 of an observation (5 minutes) are recorded in column 3, 

 Table II. 



