The images on the cover call attention to the relationship between macro observations and the intimate structure of chemical substances and the changes, both chemical and physical, that they undergo. Fireworks: One of the ingredients is phosphorus, a molecular form of which is believed to consist of linked tetrahedra of phosphorus atoms. The chemical reaction of phosphorus with oxygen is partly responsible for the spectacular show of light. Carbon: The element is found in several forms, including the familiar diamond and another, recently discovered, sooty substance that consists of soccer-ball shaped molecules, often referred to as "buckeyballs." Diamond is not the most stable form of carbon and is created from other forms of carbon at high temperatures and pressures deep within the earth. Acetylene torch: Cutting steel is possible because of the intense heat generated by the chemical reaction of acetylene with oxygen, a reaction between molecules of C_2H_2 and O_2 to give CO_2 and H_2O. Hot air balloon: The air that helps it rise is heated by the combustion of molecules of propane, each composed of three carbon and eight hydrogen atoms. Stormy weather: The evaporation of water serves to store energy provided by the sun. Subsequent condensation of the water vapor releases this energy and is the basis of all the weather systems on our planet.