capillary action, the process involving molecular adhesion by which the surface of a liquid in a tube is either elevated or depressed, depending on the cohesiveness of the liquid molecules. The more cohesive the molecules, the more depressed will be the surface of the liquid. Less cohesive liquid molecules will adhere to the surfaces of the tube in which they are contained and elevate the surface of the liquid. Also called capillary attraction, capillarity.
