The channelling of protons through a thin beryllium crystal is simulated in a computer. The angular dependence of the momentum density is computed using particle trajectory approximation and is reported as the transmission spectra. In obtaining the spectra, the energy loss suffered by protons due to electron multiple scattering is considered and the effect of thermal vibrations treated separately. The spectra obtained are characteristic of the hcp structure of Be. Positions of the major dips in the transmission spectra are found to correlate well with the directions of neighbouring strings. Variations in the angle of incidence of the beam and in its initial azimuthal angle bring about modifications in the spectra depending on the transverse kinetic energy of the incident particles and the crystalline structure of Be. Thermal vibration of the lattice does not modify the spectra appreciably.