The observation comes before the picture
A discharge tube and a spectroscope provide positions and intensities of spectral lines. They do not track an electron around a nucleus. Repeated wavelengths across preparations ask for an explanation of reproducible atomic energy differences. The regularity of hydrogen was already a constraint on a theory, rather than a discovery made by drawing quantized circles.
Bohr’s 1913 paper begins with a tension: Rutherford’s nuclear atom accounts for scattering, but ordinary electrodynamics makes an orbiting, accelerating electron radiate. Mechanical orbits alone supply neither the observed stability nor a unique atomic scale. A successful account must explain both stable atoms and their characteristic radiation. Read Part I, introduction and §1, with those two requirements in mind.
Read the evidence: N. Bohr (1913), On the Constitution of Atoms and Molecules, Part I, §§1–3
The decisive change was the rule for radiation
Bohr introduced stationary states and connected the frequency of emitted light to the difference between two state energies. The emitted frequency is not generally the electron’s mechanical orbital frequency. This breaks with the classical radiation rule precisely where the spectrum needs a new account.
In the relation below, the initial state has higher energy than the final state; the frequency is positive and the Planck constant converts it to energy. A collection of allowed energy differences can organize many lines with a common set of states. It is a stronger constraint than assigning an unrelated oscillator to every observed wavelength.
Read the evidence: N. Bohr (1913), On the Constitution of Atoms and Molecules, Part I, §§1–3
Agreement is powerful, but has a scope
Part I, §2 compares the hydrogen spectrum and discusses lines attributed to helium. The one-electron case offers a particularly sharp test because the Coulomb problem fixes the scale and pattern together. Matching a series of spectral lines supports the energy structure and transition rule; it does not independently establish that electrons trace the proposed circular paths.
The 1922 award recognizes Bohr’s investigation of atomic structure and radiation. It is not a certificate that every mechanical detail of the 1913 model survived. Modern orbital probability densities and the historical orbit picture belong to different descriptions. The existing hydrogen Lab is a place to compare states and spectra, not a reconstructed 1913 measurement.
Read the evidence: N. Bohr (1913), On the Constitution of Atoms and Molecules, Part I, §§1–3Nobel Prize in Physics 1922 — official award record
A second instrument can test the energy ledger
A spectrum samples energy released as radiation. Electron-impact measurements instead ask how much kinetic energy an atom can take from a projectile. Agreement between those methods would connect two different observables, making a purely optical explanation less sufficient. The next article follows that connection through Franck and Hertz.
When using the linked Lab, record which transition produced a line and separate its position from its displayed width or intensity. Do not infer an absolute historical intensity calibration, a multi-electron mercury spectrum, or a Lamb-shift test from a hydrogen teaching model. Those require their own apparatus assumptions and evidence.
Read the evidence: N. Bohr (1913), On the Constitution of Atoms and Molecules, Part I, §§1–3