Electron Spin Magnetic Moment in Atomic Hydrogen

The ratio of the electron-spin $g$ factor to the proton $g$ factor has been measured in atomic hydrogen by a precision microwave magnetic resonance absorption technique. The result obtained is $-\frac{g_s}{g_p}=658.2277\mathrm{}\pm 0.0002,$ where $g_p$ refers to protons in molecular hydrogen. The ratio is in good agreement with the atomic-beam result of Koenig, Prodell, and Kusch, and verifies their conclusions concerning the magnitude of the quantum electrodynamical contribution to $g_s$.