Carol Burkhardt, age 13, of San Diego, California, for her question:

Is it true that water has a skin?

On a gentle summer's day, find a quiet pond and get set to watch the water ballet. The miniature cast includes an assortment of long legged insects    and they perform their antics on the shiny surface of the pond. What's more, their tiny feet stay dry. This amazing show is possible because water does have a "skin."

Striders and certain other insects live most of their lives on the surface of ponds and streams, swamps and even seas. The water's skin is strong enough to support their tiny bodies. Most of them have long spreading legs to distribute their weight and ail of them wear oily furry boots that keep them dry. In shallow water, sometimes they cast tiny shadows on the bottom. These are shadows of dimples that their bitsy feet make in the elastic skin of the water. This amazing skin is called "surface tension."

It is created by forces somewhat similar to the opposite poles of a pair of toy magnets. In magnets, of course, opposite poles attract each other and two north or two south poles repel and pull away from each other. In the water's skin, this phenomenon is reduced to the size of miniature molecules and their arrangement of infinitesimal electrons.

Each water molecule, as you know, is a bond of one atom of oxygen and two atoms of hydrogen. Most of the electrons are near the oxygen atom. This creates a negative charge to the oxygen end of the package and a positive charge to the hydrogen end. The opposite charges act somewhat like the opposite magnetic poles. This attraction tends to link groups of six to eight water molecules in chains. They are, of course, always on the move and the mutual attraction with their neighbors is exerted equally on every side    except at the surface.

There the mutual attraction is modified because the top sides of the surface molecules are exposed to the air. The mutual pushing and pulling forces are exerted horizontally among their neighbors. Twice this force is exerted by the molecules below. These vertical and horizontal forces combine to add a special quality of tension in the thin layer of surface molecules. They cling together to form an invisible, elastic skin.

The water's skin is just strong enough to provide a niche in nature for an assortment of tiny, feather weight creatures. Its surface tension also acts to squeeze the rest of the water. This pulls tiny droplets into sphere shapes. However, the stronger force of gravity tends to pull large falling raindrops into pear shapes.

The chemical attraction of water molecules also reacts with similar forces within other substances. Water is wet because its chains of molecules are attracted through the pores of certain materials. But water molecules are repelled by the opposite charges of certain oily substances. The water ballet bugs remain dry shod because the water molecules and the oil on their hairy boots repel each other.