Hydrostatics
a department of science which treats of the conditions of equilibrium in liquids. For a liquid to remain at rest in any vessel, first, its surface must be everywhere at right angles to the forces which act on the molecules of the liquid, and, second, every molecule of the mass of the liquid must be subject in every direction to equal and contrary pressure. If the same liquid be placed in several vessels freely communicating with each other, it will stand in them all at the same horizontal level. If two or more liquids be tal level. If two or more liquids be placed in the same vessel they will arrange themselves according to their relative densities, after which the equi- Hallam, the real creators of the science were Castellio (1577-1644), and Torri-