A single prism spectrometer is described which uses a photoconductive detector of short response time to display spectra in the near infra-red region at a high repetition rate on a cathode-ray tube. The performance of the instrument is briefly discussed and illustrated by photographs of typical spectra. Using a lead-telluride cell, the long wave limit is about 5.5 μ. The instrument could be made to work at longer wavelengths by using a bolometer or pneumatic detector, but at a sacrifice of speed or resolution, and in the visible and ultra-violet by using a photoemissive cell or other suitable detector.