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In an undergraduate atomic physics experiment, 2.8 MeV protons are used to bombard thick elemental targets. X rays emitted from the targets are detected with a Si(Li) detector, and their energies are measured with a multichannel analyser. The Kα and Kβ x-ray energies are each plotted as functions of (Z-1)², and the Rydberg energy, Rch, is extracted from the slopes of the resulting lines. The Kα plot gives Rch = 14.099 ± 0.025 eV, while the Kβ plot gives 13.557 ± 0.027 eV. The experiment extends the Bohr Theory as discussed in class, serves to introduce PIXE as a quantitative technique for elemental analysis, gives the students experience in using modern instruments which may be used in later experiments, and experience in using uncertainty analysis to decide whether their measurements agree or disagree with other measurements or theoretical calculations. Although the experimental values differ from each other and from the accurately-known value of 13.606 eV by less than 4%, they do not agree to within the experimental uncertainties, forcing students to consider a systematic error arising from their use of the Bohr Theory to derive Moseley's Law. [ABSTRACT FROM AUTHOR]