Tony Jones has crafted an excellent history of time keeping from basic astronomy to pendulum and quartz clocks to modern atomic clocks. The problems and successes at each level are clearly explained. The text is at the early undergraduate level and is unencumbered with mathematics. Precision time has become imbedded in the activities of modern civilizations and it is interesting to see how the determination and dissemination of time has become complex as the accuracy has improved.
I think a better subtitle would have been, "The Constant Search for Time," because only a third of the book is devoted to atomic clocks. The development of increasingly stable and accurate clocks is covered in detail, thankfully without dwelling on Harrison's efforts (already well covered in other books).
As better clocks were built, measurements showed increasingly subtle causes for variations in the length of the day ranging from a non-circular orbit, to tidal effects, to crust movements, and down to atmospheric effects on the rotation rate. All these are covered in detail.
The most convenient source of time with nanosecond accuracy is now the GPS satellites. Jones describes how special and general relativity affect their timekeeping and how these effects are compensated.
He also goes into great detail about the international organizations responsible for managing UTC and the complex methods used to average the time from the primary standards and hundreds of secondary standards to produce UTC. Jones manages to do this without losing the reader's attention.
Although the book avoids any math or advanced physics, it does not condescend in any way, and is directed to the mature reader. There are explanations of cesium and rubidium frequency standards, hydrogen masers, and also the latest developments: laser cooling and cesium fountains.
It would have been nice if the author had included a bibliography, but this is compensated by providing the URLs for all the major world timekeeping organizations and also links to a number of web sites devoted to time.
