Public mechanical clocks

The story

How time was measured

For thousands of years time was measured by looking at the sky. The sundial showed the hours with the shadow of the Sun, but did not work at night or when it was cloudy. For the night there were the sand hourglass, the water clock and graduated candles. In monasteries, alarms and bells marked the hours of prayer: the monk in charge got up, looked at the stars or at the water running down, and rang the bell.

“Temporary hours” were also used: the day, from dawn to dusk, was divided into twelve hours equal to one another, and the night into another twelve. But since a summer day lasts much longer than a winter one, temporary hours were longer in summer and shorter in winter. A good rule for life in the fields, but not very practical for people doing business.

The machine that strikes the hour

At the end of the 1200s, perhaps in Italy or in England, someone invented the first mechanical clock. We do not know who it was: no document speaks of it clearly. It was a machine made of toothed wheels, driven by a weight hung on a rope. The weight came down slowly, turning the gears, and a mechanism called an “escapement” made it come down in regular steps, one after another. This mechanism, the first of its kind, served to regulate time.

The first clocks had neither hands nor dial: they served only to make a bell ring at regular intervals, reminding the monks to pray. The English “clock” and the French “cloche” derive from a medieval word meaning “bell”, and recall this origin. In time a dial with a hand was added, and then more hands.

The clocks of the towns

In the 1300s the Italian, Flemish and German towns competed to build a public clock on the town hall tower or the church bell tower. In Milan in 1335-1336 one was put up at the church of San Gottardo, and a chronicler wrote that it struck the twenty-four hours of the day, something that seemed extraordinary. In Padua, around 1344, one was built on the tower of the palace of the Carrara lords. Paris, Strasbourg, London and many other towns followed.

These clocks measured hours that were always equal, twenty-four in a day, in summer as in winter. Daily life changed as a result: markets opened and closed at the right hour, cloth workers in Flanders were paid by the hour, and the clock bells said when work began and when it stopped. Time, once tied to the Sun and the Church, became a good that could be counted, used and paid for.

For the people who lived around the tower, the clock was an incredible novelty: a machine that seemed to work by itself, day and night, with nobody running it. Many stopped to watch it, and in some towns the clock tower became the symbol of the commune, sometimes more important than the government palace.

Clocks and astronomy

Some clocks also showed the movements of the Sun, the Moon and the planets. Giovanni Dondi dall'Orologio, a physician and astronomer of Padua, built between 1348 and 1364 a very complicated “astrarium”, with seven dials for the seven planets then known, and wrote a book to explain how it was made. The astronomical clock of Prague, installed in 1410 on the town hall, still works today, with a procession of statues that appears every hour.

The first clocks were not very accurate: they could be wrong by a quarter of an hour or more a day, and had to be set every day by looking at the Sun. True accuracy came in 1656 with the pendulum clock, devised by the Dutchman Christiaan Huygens on the basis of Galileo's studies.