The most important and interesting feature of the
β
-ray disintegration is the energy distribution of the emitted electrons. It is now well established that these electrons form a continuous energy spectrum and that this fact is irreconcilable with the simultaneous validity of the conservation of energy and the principle of identity of atoms of the same species. Further, it seems highly probable, although it has not been conclusively proved, that the energy difference between the parent and product nucleus is determined by the upper energy limit of the continuous spectrum. No progress has yet been made by adopting either of the hypotheses that the conservation of energy or the principle of identity are not universally valid, although such would appear to be the natural interpretation of the experimental facts. Instead, a particle, the neutrino, has been invented which is thought to be emitted simultaneously with the
β
-particle. Whenever the
β
-particle is emitted with less than its maximum energy the neutrino carries away the remainder of the energy, allowing the total energy of disintegration in each case to be the same. Besides having no charge the neutrino is supposed to have the same spin as the electron, as this helps to conserve angular momentum in the disintegration. The detailed theory ascribes to it zero rest mass and a free path in matter so great that failure to detect any evidence of interaction between neutrino and matter is no argument against its existence. It is certainly true that if the principles of the conservation of energy and of identity be accepted as universally valid that the evidence, although circumstantial, for the existence of the neutrino is strong. Yet it must be remembered that it is precisely the validity of these principles which is in question. If clear experimental evidence for the existence of the neutrino could be obtained, then we should have conclusive proof of the validity of these principles; but until this happens the neutrino must remain purely hypothetical. It should also be emphasized that no amount of agreement between the resulting theory of
β
disintegration and experiment can help to a decision, since the properties of the neutrino are arbitrary.
DILATON DECAYS INTO UNPARTICLES AND A SINGLE PHOTON
