The success of Fermi’s theory of β decay, from its earliest prediction of the shape of the energy spectrum in β decay to its ability to incorporate the nonconservation of parity, quite naturally provided physicists with good reasons to believe in the existence of the neutrino. “Fermi’s theory is remarkable in that it accounts for all the observed properties of beta decay. It correctly predicts the dependence of the radioactive-nucleus lifetime on the energy released in the decay [FxQ is a constant]. It also predicts the correct shape of the energy spectrum of the emitted electrons. Its success was taken as convincing evidence that a neutrino is indeed created simultaneously with an electron every time a nucleus disintegrates through beta decay.” 1 “The Fermi theory was so successful in the explanation of most of the important features of beta-decay that most physicists accepted the neutrino as one of the ‘particles’ of modern physics” (Allen 1958, p. v). Frederick Reines, who believed that the neutrino could be detected and was one of the physicists who first observed the neutrino directly, remarked, “It must be recognized, however, that independent of the observation of a Tree neutrino’ interaction with matter, the theory was so attractive in its explanation of beta decay that belief in the neutrino as a ‘real’ entity was general” (Reines 1982a, pp. 238–239).