His next work was about investigating the atomic spectra, explaining why these occurred. Rydberg's research was preceded by Johann Jakob Balmer's, who presented an empirical formula for the visible spectral lines of the hydrogen atom in 1885. However, Rydberg's research led him to publish a formula in 1888 which could be used to describe the spectral lines not only for hydrogen but other elements as well. After his publication in 1890 on the subject, Rydberg returned to his fruitless research on the periodic table.