The instrument consists of two bell-shaped members, 1 and 2, suspended from a triple-arm lever 3 which turns about fixed axis A. Members 1 and 2 are immersed in two communicating vessels holding a liquid. When the space under a bell-shaped member is connected by tube 7 to the place where the measurement is to be made, the pressure under the member displaces it. This turns lever 3 whose rotation is transmitted through tie-rod 4, connected by turning pairs B and E to lever 3 and segment gear 5, and meshing gears 5 and 5 to hand b of the instrument. Weight 8, mounted on arm a of lever 3, stabilizes the motion of this lever.
$3936$LHP,M$