Geoffrey Chaucer. A Treatise on the Astrolabe. Edited by, Sigmund Eisner. (Variorum Edition of the Works of Geoffrey Chaucer, 6; The Prose Treatises, Pt. 1.) xxiv + 358 pp., frontis., figs., tables, indexes. Norman: University of Oklahoma Press, 2002. $75 (cloth).Marijane Osborn. Time and the Astrolabe in The Canterbury Tales. (Science and Culture.). 320 pp., illus., bibl., index. Norman: University of Oklahoma Press, 2002. $49.95 (cloth).