﻿260 Velocity of the « Particles from Radium A. 



the same side of the centre of the plate as the first image of 

 radium A. The plate was then removed and developed, and 

 showed two pairs of lines dne respectively to the a. rays from 

 radium A and radium C. The appearance of the plate can be 

 seen from fig. 2 (PI. V.). The plates were examined by means 

 of a travelling telescope, and the distances, d A and dc< between 

 the two lines due to radium A and those due to radium C were 

 measured in the way described for determining the deflexion 

 of the recoil stream *. From these measurements the ratio 

 of the radius of curvature of the a rays from radium A to 

 that for the rays from radium C could easily be calculated. 

 The results obtained are given in Table L, in which the 

 numbers recorded for each plate represent the mean of 

 thirty observations. In each experiment the distance from 

 the wire to the slit was 3*6 cm. In the case of plate 1 

 the distance from the slit to the photographic plate was 

 3*60 cm., and for each of the other plates this distance 

 was 2"85 cm. The small variations in the deflexions on 

 plates 2, 3, and 4 were due to differences in the strengths of 

 the magnetic fields used. 



Table I. 



Plate. 



Distance in cm. 



between 



Radium A lines. 



d . 



A 



Distance in cm. 



between 

 Radium C lines. 



d 



A 



do 



•8757 



Ratio of 



radii of 



curvature . 



•8784 



i 

 j.. 



1-0548 



•9238 



2- 



•7831 



•6359 



•8759 



•8782 



3 

 3. 



•7334 



•6437 



•S776 



•8796 



4. 



•7376 



•6480 



•8782 



•8805 







Me a 



n 



•8792 





Taking the velocity of the a particles from radium C as 

 1*922 x 10 9 centimetres per second, this gives for the velocity 

 of the ec rays from radium A the value 1*690 x 10 9 centimetres 

 per second, which is in close agreement with the value 

 l*(J93xl0 9 centimetres per second calculated by Geiger's 

 formula from the known ranges of the a particles. 



* Zoc. cit. 



