In the course of collecting data for a general history of scientific instruments, Dr. Price came across the manuscript that forms the subject of this volume in the Library of Peterhouse, Cambridge. It attracted his attention because of its subject matter, because it was written in Middle English, and because the date 1392 frequently occurred. As Chaucer's Treatise on the Astrolabe was written in 1391 and is apparently incomplete, it seemed at first sight possible that the Peterhouse manuscript might be a missing part of Chaucer's Treatise, which at that time was the only instrument tract written in Middle English known to Dr. Price.