Many people in modern Westernized societies pay little heed to nature's clock. It's a 24/7 world out there, with the Internet, television, power plants, transportation industry, and even the neighborhood grocery store always open for business, and always busy, too.

But nature's clock continues to hold more sway over our lives than some may suspect. The constant beat of your mother's heart was the first sound you heard, while still in her womb. Your own heart beats about 75 times a minute. A woman's menstrual cycle is approximately the length of a lunar month. Your sleep/wake cycle runs close to (though not exactly) 24 hours long, the length of a solar day. The human body has more than 1000 known daily rhythms, according to an essay in this lavishly illustrated book, a cross-cultural exploration of time over the centuries.

The Story of Time includes more than 400 color photos of objects and images now on view at the National Maritime Museum and Royal Observatory at Greenwich, England. The exhibit, timed to coincide with the celebration of the start of the new millennium at midnight, December 31, Greenwich Mean Time, will run through September 24, 2000.

The sun is the primary timekeeper in almost every culture, almost always personified as a healer, provider, and friend, the book reports. Cultures near the equator venerated the sun as a god more than did those in the far north, where hours of daylight are fewest. The book shows day clocks, such as sundials, and night clocks that measure the transit of stars.

An Egyptian calendar of good and bad days presaged by many centuries the pseudoscience of biorhythms. Sample advice includes: "Do not work on this day...slay no oxen." Illustrations include calendars on papyrus, baked clay, painted cloth, stone, and bronze. A contemporary view of the seasons includes four prints by Jasper Johns, depicting not only the weather, but also the Four Ages of Man.

The image of Father Time came into its own in the late Middle Ages. Armed with sickle or scythe, Time became the "grim reaper," death. Large public clocks began to appear around the same time, in the second half of the fourteenth century, one of the first signs of growing urbanization. In our own time, Salvador Dali's soft and sometimes exploding watches acknowledge Einstein's theories of relativity, and the death of old notions about time and permanence.

Umberto Eco meditates on Einstein, too, as he explores views of time over time in one of 23 essays by scholars in literature, art, history, science, and other fields. St. Augustine wondered how past and future can exist if the past is no longer and the future is not yet? Our capacity to imagine, Eco notes, allows us to explore time's dimensions. Viewers have no trouble understanding films such as Back to the Future, for example, with its complex interweaving of present, future, past, and present again.

Members of traditional Inuit society practiced what contemporary sleep specialists call good sleep hygiene. They frowned on oversleeping, as a hindrance to hunting. To achieve long life, people were told to rise early, go outside, and walk three times around the house in the direction of the sun. This practice synchronizes the body's biological clock with the earth's day/night cycle.

While recognizing the value of using time productively, the Inuit have no word in their language for time. They have escaped the contemporary obsession with the notion that "time is money," at least until recently. A government worker visiting the Inuit used this phrase to extol the virtues of hard work. The translator tried to be helpful. "A watch," he said, "costs a lot!"

The many timekeepers depicted in this book undoubtedly "cost a lot." The larger cost comes if our use of them cuts us off from reliance on the rhythms in our own bodies and in the world around us.

To see a sampling of objects from the exhibit, visit the Royal Observatory's website: