﻿a Pat tide from Radium in passing through Matter. 141 



a particles expelled from a thin film of each of the radium 

 products. The values are collected in the table given below 

 and are expressed in terms of V , the initial velocity of the 

 (x, particles expelled from radium 0. 



Product. 



Eange of 



a particles 



in air. 



Calculated 

 velocity. 



Observed 

 velocity. 



■XT 1 W« 



Value 



e 



Radium 



Emanation... 

 Radium A ... 

 Radium C ... 

 Radium F ... 



350 cms. 

 4-23 „ 



4-83 „ 

 7-06 ,. 

 3-86 „ 



•750V 

 •814 „ 

 •858 „ 

 1-000 „ 

 •787 „ 



•76 V 



•88 V 



l'OO „ 



•81 „ 



3-04x105 



3-30x10* 

 3-48x10- 

 4-06x10* 

 3-20 Xl0 5 



The ranges of the a particles from the radium products are 

 taken from the paper of Bragg and Kleeman. The range of 

 the a particles from radium F (polonium) has been found by 

 Dr. Levin in the laboratory of the writer. 



7YIV 



In the fourth column are given the values of Hp= — > 



where H is the strength of the magnetic field, p the radius of 

 curvature of the path of the rays, and e, m, v have the usual 

 signification. I have redetermined accurately the initial value 

 of Hp for the a particles expelled from radium C and found 

 the value 4*06 x 10 5 , in place of the value 3*98 x 10 5 given in 



771V 



a previous paper. The values of — have been deduced from 



the calculated velocity and the value given above. 



We shall now consider some direct experiments that have 

 been made to determine the velocity of the a particles from 

 some of the radium products in terms of V , assu ning that 

 e/m has the same value for the a particles from all products. 



Magnetic Deflexion of the a Particle from Radium itself. 



About one milligram of pure radium bromide, spread 

 uniformly in a narrow groove, served as a source of a rays. 

 The radium was heated to a sufficient temperature to drive off 

 the emanation completely. After three hours, the products 

 radium A and C have nearly disappeared, and the a. radiation 

 then mainly comes from radium itself. The magnetic de- 

 flexion of the pencil of rays was determined in the standard 

 apparatus (fig. 1), using a narrow slit. The trace of the rays 

 was first obtained without a magnetic field. The deflected 

 traces on each side of the central band were then obtained by 



