﻿378 Mass of the a particles from Thorium. 



being left two days in position in the base of the apparatus. 

 The rays from both thorium B and C were present, but the 

 photographic effect of the former was small compared with 

 the latter, and could not be distinguished on the plate. 



The electrostatic deflexion was obtained in two distinct 

 experiments. In one case, the photographic plate was 

 3* 94 cms. above the parallel plates and the P.O. applied was 

 337 volts; in the other, the distance of the photographic 

 plate from the parallel plates was 10 cms. and the 

 voltage 423*5. The formulae employed in the calculations 

 have already been given in the accompanying paper by 

 Rutherford. 



2 



In the first experiment the value of — ■ was found to be 



e 



6-7 x 10 14 , and in the second 7*3 X 10 14 . The mean value 



^ =7-0x10". 



e ~~ 



From the magnetic experiments, 



— = 3-53 x 10°. 



e 



This gives the values 



u = 1*98 x 10 9 cms. per second. 

 e/m — 5*6 x 10 3 . 



It has been shown in a previous paper that the value of 

 e/m for the a particle from radium is 5'07 X 10 3 . Remem- 

 bering that too high a value of e/m is to be expected when 

 the electrostatic deflexion of the rays is determined from a 

 weak photograph, the agreement between the values of e/m 

 is sufficiently close to indicate that the a particle expelled 

 from thorium G has the same mass as the a particle expelled 

 from radium, and is identical with it. 



The significance of this result has been discussed in the 

 companion paper dealing with the mass of the a particle 

 expelled from radium and actinium. 



Berkeley, Cal t 

 July 30, 1906. 



