Since the astronomical measurements, for solar lines by Fabry and Perot in 1902 and of radiation from the Orion Nebula by Fabry and Buisson in 1911, Fabry–Perot interferometers have been pointed towards the heavens. Indeed it is clear that a very large fraction of the total worldwide application of Fabry—Perot instruments is devoted to astronomical research and to astrophysics. In astronomy, unlike many other areas of spectroscopy, neither of the two source characteristics—the angular extent and spectral character—are within the control of the observer. One of the most outstanding aspects of the Fabry–Perot interferometer applied to astronomy is the wide variety of techniques that have been employed. Following P. Jacquinot's analysis of 1954 showing the advantage of the Fabry-Perot instrument and the further emphasis by T. Dunham, J. E. Geake et al discussed a detailed design and prototype pressure scanned instrument for use in astronomy.