Roger Bacon, the medieval natural philosopher who broke new ground in promoting scientific method, produced the encyclopedic Opus Majus or 'Greater Work' in the mid-thirteenth century. This 1897 publication in two volumes was the first complete edition of the work to appear in print. Written at the request of Pope Clement IV, the Opus Majus is the most significant and most influential of Bacon's works, containing his observations of the natural world and theories on knowledge acquisition. Bacon's text appears in the original Latin, and Bridges includes a substantial introduction and brief analysis of each chapter in English, as well as extensive footnotes and an analytical table to aid the reader. The book covers theology, language and mathematics, optics, experimental science, and moral philosophy. This reissue also incorporates a later supplement containing additional material and corrections.