Iv] NATURE OF THE RADIATIONS 123 
to apply a stronger electric field without the passage of a spark. 
He found values of the constants given by 
Vi= Gay 10? cmss per sec: 
£ = 6-4 x 10° 
me 
These values are in very good agreement with the numbers found 
by the electric method. The rays from radium are complex, and 
probably consist of a stream of positively charged bodies projected 
at velocities lymg between certain limits. The amount of devia- 
tion of the particles in a magnetic field will thus differ according 
to the velocity of the particle. The photographic results of 
Becquerel seem to indicate that the velocity of the rays of radium 
can vary only within fairly narrow limits, sce the trajectory of 
the rays in a magnetic field is sharply marked and not nearly as 
diffuse as in similar experiments with the 8 rays. 
85. Becquerel’ has examined the amount of magnetic devia- 
tion of the a rays at different distances from the source of the rays 
in a very simple way. A narrow vertical pencil of the rays, after 
its passage through a narrow slit, fell on a photographic plate, 
which was inclined at a small angle to the vertical and had its 
lower edge perpendicular to the slit. The trajectory of the rays 
is Shown by a fine line traced on the plate. Ifa strong magnetic 
field is applied parallel to the slit, the trajectory of the rays is 
displaced to the right or left according to the direction of the 
field. If equal times of exposure are given for the magnetic field 
in the two directions, on developing the plate two fine diverging 
lines are found traced on the plate. The distance between these 
lines at any point is a measure of twice the average deviation 
at that point, corresponding to the value of the magnetic field. 
By measuring the distance between the trajectories at various 
points, Becquerel found that the radius of curvature of the path of 
the rays increased with the distance from the slit. The product 
Hp of the strength of the field and the radius of curvature of the 
path of the rays is shown in the following table. 
1 ¢. R. 136, p. 1517, 1903. 
