When a physicist embarks on a discussion of time, such notions as special and general relativity, ""Planck"" time, Big Bang theory, black holes, and the closed-ness or openness of the universe are bound to come up for discussion. It is to Morris' credit that by the time he deals with these 20th-century developments, he has carefully laid down a proper historical and philosophical foundation. Thus he begins with ancient concepts of time--essentially the cyclical and eternal-return ideas common to early stargazers and old religions--and the later emergence of linear historical time in the Judaeo-Christian tradition. By the Middle Ages in the West, clockmaking and craftsmanship began to take on new meaning as the clock became an important instrument for the abstract measurement of hours, not only for prayers but for delimiting the workman's day. The notion of time-flow, shored up by religion and the industrial revolution, continued to ramify in ideas of progress and evolution toward the bigger and better. Galileo helped start the ball rolling scientifically with measurements of the acceleration of gravity and formulas for velocity and distance. Newton polished off the three laws of motion and, together with Leibniz, introduced the complex idea of infinitesimals--rates of change in time and other variables--that led to the development of calculus. Morris does a splendid job of building these concepts, especially in getting at the kernel of what differential equations entail and why they are pertinent to a discussion of time. The second part of the book is less innovative, covering territory plowed by numerous cosmological speculators and popularizers (including Morris himself, and Paul Davies, John Wheeler and others). These writers all ponder grand unification theories, the first three minutes after the Big Bang, the possibilities of an inflationary universe, of parallel worlds, and various violations of symmetry. Time's arrow may be unidirectional in terms of the second law of thermodynamics (the overall increase in entropy) and in terms of psychological time. For the exceptions--electrons racing backwards, mesons behaving strangely--Morris provides as useful a guide as any, and as enjoyable.