He found values of the constants given by
These values are in very good agreement with the numbers found by the electric method. The α rays from radium are complex, and probably consist of a stream of positively charged bodies projected at velocities lying between certain limits. The amount of deviation 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, since the trajectory of the rays in a magnetic field is sharply marked and not nearly as diffuse as in similar experiments with the β rays. The evidence, however, discussed in the following section, shows that the velocities of the α particles from a thick layer of radium vary over a considerable range.
92. Becquerel35 has examined the amount of magnetic deviation of the α 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. If a 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 Hρ of the strength of the field and the radius of curvature of the path of the rays is shown in the following table.
| Distance in mms. from the slit | H ρ |
|---|---|
| 1 | 2·91 × 10 5 |
| 3 | 2·99 „ |
| 5 | 3·06 „ |
| 7 | 3·15 „ |
| 8 | 3·27 „ |
| 9 | 3·41 „ |
The writer (loc. cit.) showed that the maximum value of Hρ for complete deviation of the α rays was 390,000. The results are thus in good agreement. Since
these results show that the values either of V or of e/m for