The differential and integral spectra of muons moving in the near-vertical direction have been measured at Nottingham using a solid iron magnetic spectrometer. This instrument utilised an automatic recording system for data collection which allowed the range of muon momenta covered by this investigation to extend from 4 to 3000 GeV/c, the lower limit being set by the magnet itself. The diffusion model for particle propagation through the Earth's atmosphere was used to provide the muon momentum spectrum incident upon the instrument.