A hoisting or lifting device, consisting of a screw arrangement by which a heavy weight may be lifted with small power. The hydraulic jack is the most powerful of lifting machines. In its use water is forced through a small hole into a chamber of considerable dimensions. By its aid a man may lift 10 tons I foot in a minute and a half, or 100 tons in 15 minutes. The term jack is applied to many other tools used in the arts.