This paper has two goals: to use the electromagnetic world-view as a means of probing what we now know as the quantum theory, and to use the case of the quantum theory to explicate the practices of the electromagnetic program. It focuses on the work of Arnold Sommerfeld (1868––1951) as one of the leading theorists of the so-called ““older”” quantum theory. By 1911, the year he presented a paper on the ““Quantum of action”” at the Solvay Conference, Sommerfeld vocally espoused the necessity of some form of a quantum hypothesis. In his earlier lectures, however, his reservations about Max Planck's position were far more apparent. Section 1 argues that Sommerfeld's hostility towards Planck's derivation of the Black-body law, and his support for the result achieved by James Jeans and rederived using the electron theory by Lorentz, can be traced to his commitment to the programmatic aims of the electromagnetic world-view. Section 2 suggests that this conclusion has deep implications for our understanding of the ““conversion”” of several leading physicists to the quantum theory after around 1908. Section 3 traces a partial continuation of Sommerfeld's deeply held beliefs. Sommerfeld's Solvay paper is best understood as an attempt to reconcile the programmatic aims of the electromagnetic world-view with the necessity of recourse to the quantum hypothesis. No longer a universalizing vision, the attempt to prove the necessity of electromagnetic theory at all levels of explanation remained a key element of Sommerfeld's research agenda until (and even beyond) the advent of Niels Bohr's ““planetary”” model of the atom in 1913.

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