This Demonstration shows the absorption and emission lines in the visible spectrum of the hydrogen atom, according to the model proposed by Niels Bohr in 1913. This involved electronic transitions among discrete (quantized) energy levels. The energy levels are labeled by the principal quantum number . We have analyzed the Balmer series, whose wavelengths lie in the visible region. The electron jumps corresponding to the Balmer series involve as either the initial or the final level. These hypothetical "quantum jumps" between electron orbits can be simulated in the lower right-hand panel. The observed spectrum is represented by arrows connecting energy levels, with up arrows for absorption and down arrows for emission. You can select the quantum number . The ground state is out of the energy range considered and is not seen [1].