A three-fold coincidence arrangement of two scintillation counters and an optical Cerenkov counter was used to form a cosmic-ray muon momentum selection system of 0.21 sr cm2 aperture. The variation of pressure of the nitrogen gas in the Cerenkov counter enabled the cosmic ray muon momentum spectrum at sea level to be determined by the technique of threshold discrimination. The spectrum so obtained compared favourably with that determined by magnetic spectrography. The work presented in the paper formed part of a final-year undergraduate project undertaken by the authors.