The Centre of Pressure Apparatus has beendesigned to determine the static thrust exerted by a fluid on a submergedsurface and allow comparison of the measured magnitude and position of thisforce with simple theory. A fabricated quadrant is mounted on a balance arm,which pivots on knife-edges. The knife-edges coincide with the Centre of arc ofthe quadrant. Thus, of the hydrostatic forces acting on the quadrant whenimmersed, only the force on the rectangular end face gives rise to a momentabout the knife-edges. The balance arm incorporates a balance pan for theweights supplied and an adjustable counterbalance. This assembly is mounted ontop of an acrylic tank, which may be leveled by adjusting screwed feet. Anindicator attached to the side of the tank shows when the balance arm ishorizontal. Water is admitted to the top of the tank by a flexible tube and maybe drained through a cock in the side of the tank. The water level is indicatedon a scale on the side of the quadrant.