ACCELEROMETER. This instrument consists essentially of an elastic cantilever (q.v.) loaded at its free end. Accelerations perpendicular to the cantilever produce a deflection. One type consists in a semicircular glass fibre fixed at both ends, the mass centre being situated in the middle of the arc ; this instrument measures accelerations normal to the plane of the semicircle. The air-speed recording accelerometer is a combination of the fore going with a diaphragm gauge in connection with the Pitot and static tubes (see AERIAL NAVIGATION), and is used to deduce the flight-path of an aircraft.