The concision and simplicity of style characteristic of this series, are somewhat offset in this case by the difficulty of the subject--primarily the arithmetic disparities underlying the evolution of the calendar--making it suitable only for children who can follow the complex figuring. The authors describe the movements of earth and moon which form the basis for measuring days, months and years, explain how ""the parts won't fit,"" and recount the efforts of the Egyptians, the Babylonians, other ancients, and the Romans to reconcile the lunar and solar measurements. The development of the Roman calendar from the legendary first through the Julian and Gregorian calendar is presented in detail with accompanying tables; so is the basis for naming the months and the days. Instructions for making a fifty-year calendar supplement the historical coverage. This has a somewhat limited potential for self-instruction but it could be a useful supplement to a school unit.