﻿374 Prof. E. Rutherford and Dr. 0. Hahn on 



Let ABC, A'B'C (PL Y. fig. 1, a) represent the deflected 

 hands due to the a rays from the wire coated with the active 

 deposit o£ thorium. Each of these deflected bands consists of 

 two distinct parts. The inside portions AB, A'B' are due to the 

 a. rays from thorium C, the outer portions BO, B'C X to the a. rays 

 from thorium B. Since the rays from the latter produce less 

 photographic effect than those from thorium C, the outer 

 bands BC, B'C are much less clearly defined than the inner 

 bands due to the rays from thorium C. Let EF (fig. 1, b) 

 represent the bands obtained under identical conditions using 

 the same wire coated with radium C. The width D of the 

 bands E, F represents the normal width of the photographic 

 trace due to a single homogeneous source of a rays. 



Let di, d 2 , d d represent twice the normal magnetic deflexions 

 of the pencil of a. rays emitted by thorium B, thorium 0, and 

 radium C respectively. The distances CC, AA', are 

 measured on the photograph in the usual way. 



Then ^ = CC'-D 



d 2 =AA' + D, 

 <7 3 =EF, 



where E and F are the centres of the radium bands. 

 Now the amount of deflexion of the pencil of a, rays is 



mu 

 inversely proportional to the value ■ — •, where m is the 



mass of the a particle, e its charge, and u its velocity. 



Knowing the value of — for the a rays from radium C 



under the conditions of the experiments, the value of 



— for the rays from thorium B and C can at once be 

 e 



determined. A number of experiments were made on the 



magnetic deflexions ot' the a rays from the active thorium 



wire when covered with different absorbing layers to cut 



down the velocity of the ex. rays, We have seen in a previous 



paper that the velocity of an ex. particle which has a range 



r cms. in air is proportional to ^/r-f-}.'25. This relation 



should hold for the ex. particles from thorium as well as from 



radium if the a particles in all cases have the same value 



of ejm. It is of interest to compare the observed deflexions 



of the a rays from thorium B and C with those to be expected 



from the known range of their a. particles in air. 



Experiment 1.— The magnetic deflexions of the a rays from 



thorium B and were first determined with an unscreened 



