The Global Oscillation at Low Frequencies (GOLF) investigation will perform uninterrupted velocity oscillation and magnetic field measurements of the full solar disk, spatially unresolved, with extremely high sensitivity (<1 mm/s and 1 milligauss). To determine the velocity, the Doppler effect is measured by the resonant scattering technique. A resonant cell filled with sodium vapor in a strong magnetic field enables, by the Zeeman effect, the selective absorption of light in the two wings of the solar D lines. A comparison of the intensity on both sides of the line leads to an extremely sensitive determination of the velocity. This information is from the paper SOHO - An Observatory to Study the Solar Interior and the Solar Atmosphere,'' by A. I. Poland and V. Domingo (inObservatories in Earth Orbit and Beyond,'' pp. 277-284, ed. by Y. Kondo, Kluwer Academic Publishers, Dordrecht, 1990).