This section is from the "The New Student's Reference Work Volume 5: How And Why Stories" by Elinor Atkinson.
Do you want to be told? It's more fun to find things out for yourself. Get the smallest glass tube that is sold in drug stores. Put one end of it into a glass full of water and see what happens. The water rises in the tube a little higher than it stands in the glass No one knows just why it does this. It is thought that the wall of a tube has an attraction for the tiny molecules of water, and pulls them up a little way. The finer the tube the higher the water is drawn up into it.
Now a hair is a very small, hollow tube. The sponge is made up of hair-like hollows that pull up or, as we say, soak up water. The Latin word for hair is capillary. So this force is called capillary attraction. Sugar, salt, starch, chalk, sponges and the hairs of animals and fibers of plants have capillary attraction. You can prove this by dipping threads, strings, pieces of cloth, the edge of a lump of sugar or salt in a liquid, and watching the water climb. It is by capillary attraction that water is pulled from the roots to the farthest leaves of tall trees. The water it not only pulled up, it is held up. If the hair tubes of a sponge or a towel are too full, some of the water falls or drips away, but most of it is held until it is evaporated into the air.