A meniscus forms mainly because of adhesion and partly because of the fairly high surface tension of water, according to the U.S. Geological Survey (USGS). A meniscus can move up or down depending on whether the molecules of the liquid are attracted to themselves or to the outside material.
The USGS defines meniscus as a curve in the surface of water when the liquid touches another material. An example of this is when water sticks to the inside of a glass. Adhesion is the major reason that meniscus occurs. Water’s fairly high surface tension is also partly responsible. Water sticks because the water molecules become attracted to the molecules in the glass beaker’s wall. Because water molecules usually stick together, other water molecules cling to the molecules touching the glass when the molecules touching the glass cling to the container, thereby forming a meniscus. These molecules move up the glass as far as the cohesive forces of water allow them, until they are hindered by gravity from going farther.
A meniscus can go upward or downward, explains the USGS. What people normally see is a concave meniscus, wherein the liquid’s molecules are attracted to those of the container. It is important to read the center of the liquid in the tube to get the real volume of the liquid, notes the USGS.