A historical and methodological analysis is given for an important stage in the development of atomic spectroscopy, which was completed by the introduction of the spectral-term concept and the formulation of the Rydberg--Ritz combination principle. J. R. Rydberg's life and scientific activity are briefly reviewed. His fundamental paper of 1890 on the laws governing atomic spectra is considered in detail. Rydberg's decisive contribution to the discovery of the basic spectroscopic laws, whose determination created the necessary prerequisites for interpreting line spectra in the context of the Bohr model, is shown. It is shown that the final step in constructing Bohr's theory, the introduction of the frequency condition, was achieved in the process of reconciling his preliminary model with the spectroscopic scheme of Balmer, Rydberg, and Ritz.