David E. H. Jones is a guest staff member in the chemistry department at the University of Newcastle-upon-Tyne. In 1962, he earned a Ph.D. in organic chemistry from Imperial College, London. In 1974, he was the Sir James Knott Research Fellow at Newcastle-upon-Tyne. For many years, he wrote the “Daedalus” column for Nature and, before that, New Scientist. He is perhaps best know for the modern theory of bicycle stability, his determination of arsenic in Napoleon’s wallpaper and his series of fake perpetual-motion machines—the latest of which is in the Technisches Museum, Vienna. Address: Chemistry Department, University of Newcastle upon Tyne NE1 7RU, U.K. Internet: david@davidjones.fsworld.co.uk