The water adheres to the surface of the container greater than the water molecules are attracted to each other. We do not see this downward curvature when the surface area is great, but if the liquid is confined to a small diameter tube such as a graduated cylinder, pipette, burette, or volumetric flask then the surface tension is great enough to noticeably distort the surface. In such cases when we are trying to read the liquid surface level such as measuring a liquid in a graduated cylinder, then one should make the reading at eye level and the lowest curvature of the meniscus should be read. When the adhesive forces against the walls of the container are less than the intermolecular forces, then the surface of a confined liquid will bulge upward slightly forming a convexed surface. Again, such a surface should be read at eye level and the topmost part of the surface should be read.
Surface tension helps to explain why the feathers of a duck can help the duck float on water.
R. H. Logan, Instructor of Chemistry, Dallas County Community College District, North Lake College.