In 1931, he co-wrote a paper on the "Relativistic Theory of the Photoelectric Effect" with his student Harvey Hall, in which, based on empirical evidence, he correctly disputed Dirac's assertion that two of the energy levels of the hydrogen atom have the same energy.
En 1931 escribiu xunto o seu estudante Harvey Hall o artigo "Relativistic Theory of the Photoelectric Effect", no que, baseándose en probas empíricas, disputou a afirmación de Dirac de que dous dos niveis de enerxía do átomo de hidróxeno teñen a mesma enerxía.