MANOMETER, for the air pump. This is a small glass tube about two or three inches high, hermetically sealed at one end, and open at the other, being divided regularly into inches and lines. It is used for ascertaining the rarefaction of the air produced by working an air pump. The tube previously filled with mercury, is placed in the receiver of an air pump. As the piston is worked, the mercury gradually sinks in the tube, and the expansion is estimated by its height; for the smaller the height at which the mercury in the tube stands above the mercury in the bason, the greater is the expansion.