[en] A new magnetic spectrometer is described it is used as part of the experimental equipment of the european satellite GEOS. The spectrometer was developed to measure distribution functions f(E, α, t) for electrons in the energy range 18 KeV < E < 250 KeV and for protons in the energy range 30 KeV < E < 3.3 MeV. Several methods are discussed to measure pitch-angular distributions. The image characteristics of the spectrometer are analysed. Further, the scattering of electrons inside the instrument, the backscattering of electrons from detectors and all relevant background problems are considered. The detectors and the electronic components of the equipment are described in detail. (KBE)