[W]e should expect an ordinary electron, with positive energy, to be a — Antimatter

"The interpretation of these tracks as due to protons, or other heavier nuclei, is ruled out on the basis of range and curvature. Protons or heavier nuclei of the observed curvatures could not have ranges as great as those observed. The specific-ionization is close to that for an electron of the same curvature, hence indicating a positively-charged particle comparable in mass and magnitude of charge with an electron."

"Dear Millikan, I have just received a letter from Rutherford which contains some of Blacketts work which may interest you and Anderson. It is that they have capitulated on the question of positive electrons and agree with Anderson that there are present in large numbers among the tertiary or quartinary (or whatever they are) ionizing particles seen in a Wilson photograph of the effects particles of positive charge and electronic mass. ...I take it that Blackett has collected so many photographs of such tracks as those earlier ones of Anderson that he can no longer resist this devastatingly interesting conclusion. Blacketts photos will come out in P.R.S. (Proceedings of the Royal Society) in March. I have a lecture to deliver."

"The wave equation... refers equally well to an electron with charge e as to one with charge -e. If one considers for definiteness the limiting case of large quantum numbers one would find that some of the solutions of the wave equation are wave packets moving in the way a particle of charge -e would move on the classical theory, while others are wave packets moving in the way a particle of charge e would move classically. ...the electron suddenly changing its charge from -e to e ...has not been observed. The true relativity wave equation should thus be such that its solutions split up into two non-combining sets, referring respectively to the charge -e and the charge e. ...The resulting theory is therefore still only an approximation, but it appears to be good enough to account for all the duplexity phenomena without arbitrary assumptions."

"The new quantum mechanics, when applied to the problem of the structure of the atom with point-charge electrons, does not give results in agreement with experiment. The discrepancies consist of "duplexity" phenomena, the observed number of stationary states for an electron in an atom being twice the number given by the theory. ...It appears that the simplest Hamiltonian for a point-charge electron satisfying the requirements of both relativity and the general transformation theory leads to an explanation of all duplexity phenomena without further assumption."

"In the course of the next few weeks other photographs were obtained which could be interpreted logically only on the positive-electron basis, and a brief report was then published with due reserve in interpretation in view of the importance and striking nature of the announcement."

"On August 2, 1932, during the course of photographing cosmic-ray tracks produced in a vertical Wilson chamber (magnetic field of 15,000 gauss) designed in the summer of 1930 by Professor R. A. Millikan and the writer, the tracks... seemed... interpretable only on the basis of the existence in this case of a particle carrying a positive charge but having a mass of the same order of magnitude as that normally possessed by a free negative electron."