When a great scientist named Sir William Thomson was asked about the size of a molecule, he replied: "If a drop of water were magnified to the size of the earth, the molecules would each occupy spaces greater than those filled by small shot and smaller than those occupied by cricket balls." That gives us about as clear an idea as it is possible to get of the size of molecules. And yet molecules are made up of even smaller particles, called atoms. An atom is the smallest division of anything that we know about now.

A molecule of water is made up of three atoms. Evaporation of water consists of the movement of these atoms in such a way as to make the liquid water change into a gas. Freezing water into ice is caused by making the molecules, and, in turn, the atoms, stick to each other. It takes a great deal of power to separate the molecules in water, and for this reason water was long regarded as something which could not be divided up, or, in other words, a basic element, such as the oxygen in the air

Six pictures by courtesy of Gloucester (Mass.) Board of Trade..

Drawing the Net.