184 Prof. E. Rutherford on the Magnetic and 



With a P.D. of 600 volts, a consistent difference* of 7 per 

 cent, was observed in the rate of discharge due to the a. rays 

 with the eleclric field off and on. A larger potential- 

 difference could not be used as a spark passed between the 

 plates in the presence of radium. 



The amount of deviation in this experiment was too small 

 to determine the direction of deviation by the electric field. 



Determination of the Velocity of the Rays. 



It is difficult to determine with certainty the value of the 

 curvature of the path of the rays in a given magnetic field 

 from the percentage amount of rays deviated, on account of 

 the fact that some of the rays which strike the sides of the 

 parallel plates are deviated so as to pass into the testing 

 vessel. 



Prom data obtained, however, by observing the value of 

 the magnetic field for complete deviation of the rays, it was 

 deduced that 



Hp = 390,000, 



where H = value of magnetic field, 



p s= radius of curvature of path of the rays. 

 This gives the higher limit of the value Up. 



By using the usual equations of the deviation of a moving 

 charged body it was deduced that the velocity V of the rays 

 was given by 



V==2*5 X 10 9 cms. per sec, 



and that the value — , the ratio of the charge of the carrier 



to its mass, was given by 



-=6xl0 3 . 

 rn 



These results are only rough approximations and merely 

 indicate the order of the values of these quantities, as the 

 electric deviations observed were too small for accurate 

 observations. The experiments are being continued with 

 special apparatus, and it is hoped that much larger electro- 

 static deviations will be obtained, and in consequence a more 

 accurate determination of the constants f of the rays. 



* In later experiments, which are not yet completed, I have been 

 able to deviate about 45 per cent, of the a rays in a strong electric field. 



f The a rays are complex, and probably consist of particles projected 

 with velocities lying between certain limits ; for the radiations includs 

 the a radiations from the emanation and excited activity which are dis- 

 tributed throughout the radium compound. 



