A two beam interferometer has been constructed for use as an infrared spectrometer in the spectral region 1.0 to 8.0 microns ; the spectral analysis, which consists of a Fourier analysis of the interferogram, is carried out by a digital computer. The state of interference in the interferometer is independent of small rotations of the moving mirror and a path difference of up to one metre may be introduced. The instrument is currently being used to measure at high resolution the vibrational spectrum of gaseous hydrogen induced by a strong electric field.