THERMIONICS.) Constitution of Atoms.—Since Faraday discovered his laws of electrolysis, which showed that atoms of electricity are asso ciated with atoms of matter, the scope of electrical science has continued to expand, until it appears that the material universe contains nothing but atoms of electricity and the electromagnetic fields excited by these atoms. The positive nuclei of atoms have masses proportional to integers, so it is natural to conclude that they are built up of atomic units. These units must be identical with the nucleus of the hydrogen atom, which is a positively charged particle carrying the ionic charge e. The hydrogen nu cleus was called a proton by Rutherford, so that we may say that matter is composed of protons and electrons. Each proton has, or is, a positive charge e, and each electron is a negative charge e. An atom of atomic weight W (0=16) contains W protons, and, when it is electrically neutral, also W electrons. If the atomic number of the atom is N, the atom has N electrons outside the nucleus, and W—N inside. The positive charge on the nucleus is therefore !W—(W—N) } e, or Ne. It is found that N is about one half of W, so that about half the electrons in an atom are inside the nucleus; e.g., for oxygen W = 16 and N=8, and for uranium W = 238 and N=92.
Rutherford and his co-workers have recently found in their re searches that swift a-rays knock protons out of some atomic nuclei. The a-ray, which is a helium nucleus for which W=4 and N=2, may enter the atomic nucleus and eject a pro ton. The atom must, in such a case, be changed into a new atom, with W increased by three. It appears therefore that atoms of greater atomic weight can be built up in this way. Radioactive processes on the other hand appear to involve the emission of a-rays by atomic nuclei, with decrease of the atomic weight. The atoms of the chemist, therefore, are really compounds of protons and electrons, so that protons and electrons are the only true ele ments. It is, however, customary and convenient to continue to speak of the chemical elements as elements, since the combination of protons and electrons in atomic nuclei is much more intimate than the combination of atoms in the molecules of compounds.
According to the recent developments of the quantum theory, it is suggested that protons and electrons consist essentially of groups of waves. Electromagnetic radiation also seems to con sist of groups of waves, the quanta of energy liv and frequency v. Moreover, the energy of an electron or a proton is also equal to h v, where v is the frequency of the waves in the particle. We seem therefore to be coming to a view of the universe, according to which there is nothing in it but groups of waves of energy liv and frequency v; but the nature of the difference between a posi tive charge and a negative charge remains obscure on such a view. The principle of the conservation of energy, on this theory, seems to mean merely that the sum of all the frequencies re mains constant, since the total energy is /hv or li v. In any case it is clear that electricity is the fundamental constituent of matter.