Astronomical Clocks

Astronomical clocks

In Western Europe the first mechanical clocks appeared during the first half of the fourteenth century. They were driven by a weight suspended from a drum, and controlled by a heavy bar, or “foliot”. Pivoted near its centre and pushed first one way and the other by a toothed wheel. The Chinese, however, had mechanical clocks long before this time. One particularly fine example, fully documented, was the 30-foot astronomical clock tower of Su Sung, built in 1080 A.D. In this case the motive power was provided by a turning water wheel, held in check by a weighbridge and trip levers.

A clock at 576 Sherbourne street. A modern clock at 576, Sherbourne street, Toronto. Photo: Elena

Most early mechanical clocks were designed to indicate the time by a hand or hands moving over a dial. But several had elaborate dials for showing astronomical events like the age and phases of the moon, and the position of the sun. Foremost among the latter was a remarkable clock designed by Giovanni de Dondi and made in 1364. This not only showed the time of day but also, through its complex system of gear wheels, the fixed and movable feast-days and the earth-centered motions and positions of the seven wanderers (the Greec definition of the sun, moon and five naked-eye planets).

By far, the most famous astronomical clock is the one in Strasbourg Cathedral, built between 1838 and 1842. It had two predecessors, the first completed in 1354, and the second in 1574.