Abstract: A velocity interferometer has a continuously variable sensitivity and is particularly applicable to the study of the movement of reflecting polished surfaces or back-scattered rough surfaces. The interferometer is a Michelson interferometer with a widened field comprising in a per se known manner a light splitter and two light reflectors, one of which is associated with a medium having parallel faces. The medium is constituted by a fluid in which the associated reflector is immersed and displaceable in translation parallel to the path of the light falling on it, the other reflector also being displaceable in translation parallel to the path of the light falling thereon.