The velocity of the β rays of radium varies between wide
limits. Taking for an average value
v_{2} = 1·5 × 10^{10},
e/m_{2} = 1·8 × 10^7,
it follows that the energy of the [Greek: alpha] particle from radium is almost 83 times the energy of the β particle. If equal numbers of [Greek: alpha] and β particles are projected per second, the total energy radiated in the form of [Greek: alpha] rays is about 83 times the amount in the form of β rays.
Evidence will be given later (section 246) to show that the number of [Greek: alpha] particles projected is probably four times the number of β particles; so that a still greater proportion of the energy is emitted in the form of [Greek: alpha] rays. These results thus lead to the conclusion that, from the point of view of the energy emitted, the [Greek: alpha] rays are far more important than the β rays. This conclusion is supported by other evidence which is discussed in chapters XII and XIII, where it will be shown that the [Greek: alpha] rays play by far the most important part in the changes occurring in radio-active bodies, and that the β rays only appear in the latter stages of the radio-active processes. From data based on the relative absorption and ionization of the β and γ rays in air, it can be shown that the γ rays carry off about the same amount of energy as the β rays. These conclusions are confirmed by direct measurement of the heating effect of radium, which is discussed in detail in chapter XII.