ryle m smith f g elsmore b a preliminary survey of the radio stars in the northern hemisphere mnras smith f graham astronomer who joined martin ryle's radio group in he observed cygnus a using a michelson interferometer eric weisstein's world of physics at mhz he also built the long michelson interferometer at the old rifle range in cambridge in this device operated at a wavelength of meter and was operated using ryle's phase switching technique to compile the c survey in he also used the interferometer to measure the electron eric weisstein's world of physics density in the ionosphere eric weisstein's world of astronomy c f evans in his book pulsars was published sullivan p i have updated the c page accordingly