Ebook Electromagnetic Radiation and the Mechanical Reactions, Arising From It, Being an Adams Prize Essay in the University of Cambridge

Moreover it is by no means certain that all the electrons inside the atom are moving with speeds small compared with that of light; we know that B-particles are expelled from comparatively stable atoms, like that of Radium, with speeds differing from that of light by only 2 The kinetic energy of such a B-particle amounts to three millionths of an erg, which is five times the mutual electrostatic energy of two negative electrons in contact. It is not easy to imagine an arrangement of negative and positive charges in equilibrium, or in slow stationary motion, which shall be sufficiently permanent and stable to serve as a model of the Radium atom, and at the same time be capable of setting free sufficient potential energy to supply the kinetic energy of a B — particle and also overcome the attraction of the positive charges. If on the other hand we suppose the B-particle to be already moving inside the Radium atom with a speed comparable with that of light, this difficulty does not arise. A supposition of this kind no doubt has difficulties of its own, but it would be unwise to.ignore it altogether. For these reasons it is desirable, before attempting to frame any com prehensive Electron Theory of Matter, to develope the theory of moving electric charges with as few restrictions respecting their structure and motion as possible. When expressions for the electromagnetic field due to them have been obtained, the radiation from them and the mechanical reaction on them can be calculated; the former depends on the field at a great distance, the latter on that inside them. The object of this essay is to carry out these preliminary investigations, to provide, as it were, prolegomena to any future Electron Theory of Matter.