  Weyl (1929c, 233) abandoned his unified field theory only with the  advent of the quantum theory of the electron. He did so because in  that theory a different kind of gauge invariance associated with  Dirac’s theory of the electron was discovered, which more adequately  accounted for the conservation of electric charge. Weyl’s  contributions to quantum mechanics, and his construction of a new  principle of gauge invariance, are discussed in   §4.5.3.[53] 