The astronomical advantages of a photoelectric grating spectrometer are outlined and the theoretical and practical design considerations are given for an instrument of this type recently constructed at the University of Manchester. It has a relative aperture of f /5 and a spectral resolving power of 20 to 25 thousand over the near ultra-violet and visible regions of the spectrum. Its angular resolution is of the order of the “seeing” disk when used with the 50-inch reflector at Asiago. Tests of the instrument are described, including its optical performance and its ability to compensate to a high degree for fluctuations in entrance slit iUuniination. A description is given of observations of the 3727 A O II radiation from the North America Nebula and luminescent radiation from the Moon. The accuracy with which this latter has been measured is considerably higher than that achieved by earlier observers and the implications of its existence are briefly discussed in the light of present day estimates of the lunar environment.