 One of the earliest and most forceful critics of Bohr’s correspondence principle was Arnold Sommerfeld (1868–1951). As Darrigol has recounted in detail, Sommerfeld was never comfortable with Bohr’s correspondence principle, and only begrudgingly admitted its fertility (Darrigol 1992, pp. 138–145). Sommerfeld preferred to view quantum theory as a self-contained set of formal rules, and wanted to derive the selection rules “by a remarkably rigorous manner of deduction, reminiscent of the incontrovertible logic of numerical calculations” (Sommerfeld [1919] 1923, pp. 265–266). In the first edition of his book Atombau und Spektrallinen (Atomic Structure and Spectral Lines) Sommerfeld disparagingly refers to Bohr’s correspondence principle as a “magic wand”: