Meniscus, (from the Greek meniskos — crescent), the curved free surface of a liquid near the boundary where it touches a solid body (for example at the walls of a vessel). In capillary tubes the meniscus is spherical — concave if wetting takes place, and convex — if it does not. The vapour pressure above a concave surface is lower, and above a convex one higher, than above a flat liquid surface. This accounts for the drawing of liquid into capillaries, for capillary condensation and for other effects (see Capillary phenomena).