The image on the front cover depicts a carbon nanotube emerging from a glowing plasma of hydrogen and carbon, as it forms around particles of a metal catalyst. Carbon nanotubes are a recently discovered allotrope of carbon. Three other allotropes of carbon-buckyballs, graphite, and diamond-are illustrated at the left, as is the molecule methane, CH4, from which nanotubes and buckyballs can be made. The element carbon forms an amazing number of compounds...