﻿the Mass of the cl particles from Thorium. 377 



is no blurring of the edges of the bands due to the rays from 

 thorium B, such as is shown in fig. 2 A. 



The observed ratio J- ='18, while the calculated ratio 



is -82. 



Values of . 



J e 



Considering the difficulty of accurately measuring up some 

 of the weak photographs obtained with the thorium rays, the 

 observed deflexions are found to agree fairly closely with 

 those calculated from the known ranges of the a particles. 

 The calculated ratios are probably more accurate than the 

 experimental values, and the former will consequently be used 



11XXL 



to determine the value of — for the rays from thorium B 



e J 



mil 



and C. The value of for the unscreened rays from 



radium C has been shown in a previous paper to be 4'0 6 X 10 5 . 



The value of for the rays from thorium B is conse- 

 quently given b e 



mu 



e 



\/wiS x4 - 06 - io5 = 3 - 52 * io! 



The corresponding value for the rays from thorium C is 

 given by 



mu 

 e 



V / Sw5 x4 ' 06 - 10 ' =i,42xlff ' 



The value of — for the a rays from thorium C after their 

 e J 



passage through the standard thickness of mica, equal to 



3*5 cms. of air, is given by 



^ = 3-53x10'. 



Electrostatic Deflexion of the a rays. 



The same apparatus was used as in the radium experiments. 

 The rays from the active wire passed through the standard 

 mica screen and the base of the vessel. Two wires were 

 used to obtain a measurable photographic effect, each wire 



