Page:Radio-activity.djvu/153

 of the magnetic field. Curve II, Fig. 30 is the first differential of Curve I, and the ordinates represent the relative number of β particles which are projected at each velocity.

Fig. 30.

From the data given by Kaufmann (see section 82) Paschen deduced that the group of rays examined by the former, which had velocities lying between 2·12 × 10^{10} and 2·90 × 10^{10} cms. per second, corresponded to the group of rays between the points A and B, that is, to the group of rays which were completely deflected from the lead cylinder between the magnetic fields of strengths of 1875 and 4931 units. Since radium gives off β particles which require a field of strength over 7000 units to deflect them, Paschen concluded that β particles are expelled from radium with still greater velocities than the highest recorded by Kaufmann.

Paschen considered that the small charge observed in still higher fields was mainly due to the γ rays. The effect is small and is probably not due to an actual charge carried by the γ rays but to a secondary effect produced by them. This question will be discussed in more detail in section 112.

There is a group of low velocity β particles emitted by radium (see Fig. 30) which have about the same speed as the electrons