Johannes Rydberg was a Swedish chemist who classified optical spectra and developed (1890) empirical formulae for spectral lines, using a constant (1.097 × 10⁷ m^–1) now known as the Rydberg's constant (symbol R ). He also studied hydrogen line wavelengths (see hydrogen spectrum). The Rydberg atom is a highly excited hydrogen atom that exhibits chaotic behavior in a strong magnetic field.