  Probably the most dramatic historical challenge to scientific realism
concerns Arnold Sommerfeld's 1916 derivation of the fine structure energy
levels of hydrogen. Not only were his predictions good, he derived exactly the
same formula that would later drop out of Dirac's 1928 treatment, something not
possible using 1925 Schroedinger-Heisenberg quantum mechanics. And yet the most
central elements of Sommerfeld's theory were not even approximately true: his
derivation leans heavily on a classical approach to elliptical orbits,
including the necessary adjustments to these orbits demanded by relativity.
Even physicists call Sommerfeld's success a 'miracle', which rather makes a
joke of the so-called 'no miracles argument'. However, this can all be turned
around. Here I argue that the realist has a story to tell vis-a-vis the
discontinuities between the old and the new theory, leading to a realist
defence based on sufficient continuity of relevant structure.
