Capillary Action, or Capillarity, is the tendency of liquids (like water) to rise or to be depressed in tubes of small diameter. Capillarity is due to the adhesion of the liquid to the sides of the tube, and to the surface tension of the liquid. A liquid that wets a capillary tube will rise. If the liquid does not wet the tube it will be depressed. The smaller the diameter of the tube, the greater the elevation or depression of the liquid. As temperature increases, the amount of elevation or depression decreases.