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When keeping time was an art

We all know that time flies, marches on, and awaits no man, but how did it come to be measured? "The Art and Science of Finding Time," an exhibit at Harvard University's Houghton Library through Feb. 26, looks at how humans have kept track of the fourth dimension, through artifacts and books dating to the 1500s.

By the 16th century, the sundial - an ancient means of telling time - had been refined to the point that it was small, collapsible, and often made of intricately inscribed ivory. The pocket sundial shown at left was made in 1636. It is marked with regular hours, Italian hours (in which the 24-hour day began at sunset), and Babylonian hours (in which the day begins at dawn).

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This model also has a compass (to orient it correctly), a conversion chart for using it by moonlight, a chart of various latitudes for recalibrating the gnomon (the part that casts the shadow), and even a tiny weather vane (not shown).

To be accurate year-round, sundials had to be custom-made depending on the latitude at which they were used. Several old manuscripts show how this was accomplished.

Many of the finest ivory sundials are German, but the exhibit also has fine examples from China, Japan, France, Italy, and the United States. Another design on view is a hemispherical sundial also known as a Dial of Ahaz. The name refers to the Biblical story of Hezekiah (See II Kings 20) in which the shadow cast by the sun moves backward 10 steps. In the example of this type shown at right, the gnomon's shadow refracts to indicate the hour in a water-filled, gilded bowl.

This fascinating exhibit is a tribute to David Wheatland, the founder of the Harvard Collection of Scientific Instruments in Cambridge, Mass., who collected most of the objects.