This is a biography of 'England's greatest medieval scientist, a man who solved major practical and theoretical problems to build an extraordinary and pioneering astronomical and astrological clock'. John North tells an extraordinary story here; Richard of Wallingford (1292-1336) was the son of a blacksmith who became Abbot of St Albans, where he invented his clock, before finally succumbing to leprosy. The story of the invention of the clock and its science, is accompanied by a fascinating discussion of early 14th-century scientific endeavour, which examines the Oxford that Richard knew from his studies there, and how science and theology merged in the minds of medieval intellectuals. John North examines Richard's career at the great abbey of St Albans as well as its people and, in particular, its mills. Half of the study, however, focuses on the clock and its principles. North looks at the history of horologia , the sources, and Richard's own manual which North identified in the Bodleian Library in the 1960s. Finally, North discusses the history of astronomy and natural philosophy, the instruments used and the enormous legacy that Richard left even though so few have heard his name today. This is an excellent book, with fine illustrations throughout.