Richard Rennie, BSc, MSc, PhD has conducted research at the Universities of Aberdeen, Oxford, Cambridge, and California, Santa Barbara. His main interest is in the theory of the structure of matter. He has written a number of articles and reviews. He has contributed to several other reference books, including the Oxford Dictionary of Chemistry. He wrote the Facts on File Dictionary of Atomic and Nuclear Physics which was published in 2003. He has taught mathematics, physics, and chemistry at various Sixth Form Colleges and is a Senior Invigilator for the University of Cambridge.Contributors:Editor of the 7th and 8th editions: Richard Rennie BSc, MSc, PhDEditor of the previous editions: John Daintith BSc, PhDAdvisers:B. S. Beckett BSc, BPhil, MA(Ed)R. A. Hands BScMichael Lewis MA Contributors:John Clark, BSCH. M. Clarke MA, MScDerek Cooper PhD, FRICJohn Cullerne DPhilD. E. Edwards BSc, MScDavid Eric Ward BSc, MSc, PhD