e / m for the α particle, if the α particle consists of any known kind of matter, this result indicates that it consists either of projected helium or hydrogen. Further evidence on this important question is given in section 260.
The α rays from all the radio-active substances and their products, such as the radio-active emanations and the matter causing excited activity, possess the same general properties and do not vary very much in penetrating power. It is thus probable that in all cases the α rays from the different radio-active substances consist of positively charged bodies projected with great velocity. Since the rays from radium are made up in part of α rays from the emanation stored in the radium, and from the excited activity which it produces, the α rays from each of these products must consist of positively charged bodies; for it has been shown that all the α rays from radium are deviated in a strong magnetic field.
The kinetic energy of each projected particle is enormous, compared with its mass. The kinetic energy of each α particle is
Taking the velocity of a rifle bullet as 105 cms. per second, it is seen that, mass for mass, the energy of motion of the α rays is 6 × 108 times as great as that of the rifle bullet. In this projection of bodies atomic in size with great velocity probably lies the principal cause of the heating effects produced by radium (chapter XII).
95. Atomic disintegration. The radio-activity of the radio-elements is an atomic and not a molecular property. The rate of emission of the radiations depends only on the amount of the element present and is independent of its combination with inactive substances. In addition, it will be shown later that the rate of emission is not affected by wide variations of temperature, or by the application of any known chemical or physical forces. Since the power of radiating is a property of the radio-atoms, and the radiations consist for the most part of positively and negatively charged masses projected with great velocity, it is necessary to suppose that the atoms of the radio-elements are undergoing disintegration, in the course of which parts of the atom escape from the atomic system. It seems very improbable that the α and β particles can suddenly acquire their enormous velocity of projection by the action of forces existing inside or outside the atom. For example, the α particle would have to