This chapter describes the relationship between atomic particles. Every known substance is composed of molecules which in turn are made up of atoms. Molecules are always in a state of rapid motion, but when they are densely packed together this movement is restricted and the substance formed by these molecules is stable. The simplest atom is that of hydrogen which has one proton and one electron. Electrons are arranged in layers or clouds at varying distances from the nucleus. These wandering or random electrons that move about the molecular structure of the material are what makes up electricity. Having shown that electricity is the general drift of random electrons, it follows that materials with large numbers of such electrons give rise to a greater drift than those with few random electrons. The two different types are known as conductors and insulators. There are only two types of electricity supply, namely direct current and alternating current.