378 Drs. Russ and Makower : Deflexion hy Electrostatic 



probable that this undeflected portion was deposited on the 

 strip during the exhaustion of the apparatus ; owing to the 

 large electric fields used, it was not possible to apply the 

 voltage until the evacuation was almost complete. The 

 fraction of the " recoil-atoms " deflected by the electric field 

 with different voltages between the plates can be seen from 

 Table I. 



Table I. 



Voltages between 

 plates. 



Activity on 

 cross-piece A. 



Activity on 

 cross-piece B. 







100 



08 



340 



100 



G95 



340 



100 



68-5 



1110 



100 



50 



1180 



100 



38 



Ma (j nitride of the Electric Deflexion. 



Having established that the "recoil-stream" in a high 

 vacuum is deviated by an electric field, it remained to 

 determine the magnitude of the effect, to see whether the 

 observed deflexion is in agreement with that calculated on 

 the following simple assumptions. Since radium B is formed 

 from radium after three successive stages, at each of which 

 an a particle is evolved, then since the atomic weight of 

 radium is 226 and that of helium 3'96, the atomic weight of 

 radium B should be 214 according to this view. Taking this 

 value, then, if the velocity of the a particle from radium A is 

 taken as I'll x 10 9 centimetres per second*, we obtain from 

 the equation of momentum the value 3'27 x 10 7 centimetres 

 per second for the velocity of the " recoil-atoms " of radium B. 

 Assuming, further, that the atoms of radium B on recoil each 

 carry with them 4'65 X 10" 10 electrostatic unit (the charge 

 carried by the hydrogen ion in electrolysis), it is easy to 

 calculate the radius of curvature of the particles when passing 

 through an electrostatic field applied at right angles to the 

 direction in which they are travelling. 



A number of experiments made to measure the magnitude 

 of the deflexion of the u recoil-atoms " of radium B in an 



* Rutherford, Phil. Mag. Oct. 1906. 



