During almost the whole day of April 7, 1979, wave activity with frequencies between 2 and 5 mHz and amplitudes between 5 and 20 km/sec has been observed with the electron beam experiment on GEOS-2. No corresponding activity showed up in the magnetic field data. The waves observed in the dayside magnetosphere are nearly toroidal and elliptically polarized. Their polarization is left- handed in the forenoon sector and right-handed in the afternoon sector of the magnetosphere. The orientation angles of the polarization ellipses on average change sign near local noon. A comparison between the electron number density as measured on the same spacecraft and the observed wave frequencies shows that these waves are consistent with fundamental mode eigenoscillations of the magnetic field. The model according to which solar wind driven surface waves at the outer boundaries of the magnetosphere are the energy sources for this kind of pulsations is supported by the tilt of the polarization ellipses and by a switch in the sense of polarization near local noon. GEOS-2 should be located on the earthward side of the resonance in terms of this model.