These objects helped people find the time and keep track of it. The sundial, the classic time-finding instrument, reads the hour by observing changes in nature–changes, specifically, in the sun's position in the sky. Clocks are for time–keeping, a different matter altogether. They follow nothing in nature at all, but rather an abstract concept of absolute time, which flows smoothly, uniformly, mysteriously, and without reference to anything but itself.

Is time a flow or a measurement? Is it a natural process or an abstract standard? Is it embedded deeply within nature, or is it merely an invention we humans use to analyze nature?

Here you will find a few of the treasures on display in Instruments of Time, part of the Adler's Special Topics in the History of Astronomy exhibit series. This exhibit was curated by Bruce Stephenson from the Adler's History of Astronomy Department.

Grand Orrery
England, ca. 1780
Yew, brass, ivory, steel
A-61

This complicated piece of mechanical gearing combines planetary models with clock faces and calendars. Designed by James Ferguson, one of the first "popular science" writers, it looks from the side like a model of the inner planets, but when seen from above it looks more like a group of mechanical clocks and calendars. Grand orreries represent perhaps the high water mark of the "clockwork universe" concept, uniting time–within–nature and time–as–human–invention.

Heliochronometer
Stockholm, Sweden, ca. 1800
Gilt brass, silver, steel, enamel, marble
M-302

Sundials show "solar" time, which depends upon the sun's position in the sky. Solar time has two obvious drawbacks. First, you cannot see the sun when it is nighttime or cloudy. Second, the apparent motion of the sun across the sky is not constant throughout the course of the year, so solar time flows at a varying rate! People today are most familiar with "mean time," which flows uniformly and without regard to the seasons or the weather. Clocks are designed to show mean time.

This extremely accurate sundial (called a "helio-chronometer") has a special mechanism to let you find uniform or mean time from the position of the sun! You observe solar time, and adjust it to find the mean time or clock time that most of us use.

Perpetual Calendar
Germany, 17th century
Gilt, silvered brass
W-204

This perpetual calendar of gold– and silver–plated brass ties together many concepts of time. Each month is illustrated with an emblematic activity (warming hands at a fire in January, picking tulips in May, and so on).

A calendar such as this served as a kind of almanac, teaching people about the order of their world. The saints in heaven above, celestial bodies circling in the sky, and ordinary daily human activities here on earth joined in a harmonious arrangement, to reassure people that there was an underlying meaning in their lives.