At the interface between a liquid and gas, or two immiscible liquids, a film or special layer seems to from on the liquid, apparently owing to attraction of liquid molecules below the surface. it is a simple experiment to place a small needle on a quiet water surface and observe that it is supported there by the film.
Capillary attraction is caused by surface tension and by the relative value of adhesion between liquid and solid to cohesion of the liquid. A liquid that wets the solid has a greater adhesion than cohesion. The action of surface tension in this case is to cause the liquid to rise within a small vertical tube that is partially immersed in it. For liquids that do not wet the solid, surface tension tends to depress the meniscus in a small vertical tube. When the contact angle between liquid and solid is known, the capillary rise can be computed for an assumed shape of the meniscus. Figure 1.4 shows the capillary rise for water and mercury in circular glass tubes in air.