Book excerpt: A reissue with a foreword and supplement, of a modern classic published in 1960. The invention of the mechanical clock was one of the most important turning points in the history of science and technology. This study revealed six centuries of mechanical clockwork preceding the first mechanical escapement clocks of the West of about AD 1300. Detailed and fully illustrated accounts of elaborate Chinese clocks are accompanied by a discussion of the social context of the Chinese inventions and an assessment of their possible transmission to medieval Europe. For this revised edition, Dr Joseph Needham has contributed a new foreword on recent research and perceptions. In a supplement John H. Combridge details a modern reconstruction of Su Sung's timekeeping device, which together with textual studies modifies our understanding of this important early technology.