What is Time? Waterclocks

Waterclocks represented a step away from reliance on celestial bodies and are still in use today.

(This is the third post of Time and Clocks, the thread that follows Time and Calendars.)

Waterclock hieroglyphs and inset Amenhotep I

Clepsydra Amenhetep I and inset drawing, both by Borchardt

Waterclocks classically have a hole at the bottom or near the base of a vessel which starts the day full, ending it empty. As the Egyptians discovered, to be successful the angle of the side of the bowl needs to be 70º to ensure an even flow. The earliest known version was found in the tomb of the pharaoh Amenhotep, from 1500 BCE, although waterclocks have also been discovered throughout the Middle East, in India and through Europe to the ancient Britons and Picts in Ireland. Sinking bowls, a reverse form of the waterclock, where water flows into the bowl, can still be found in North Africa.

Called clepsydras or Klepsydras (‘water thief’) in Ancient Greece, small waterclocks were used to limit the time a lawyer could present his case in court (with plenty of opportunity for bribery by either side), and in the theatre they showed the duration of the performance. Archimedes, a third-century BCE Greek mathematician, made a carefully crafted waterclock for his friend Hiero, the king of Syracuse, while conducting experiments which led to the measurement of an object’s weight by displacing water, and the water screw, a method of moving water from one level to another.

The Greeks and Romans took great pride in their waterclocks, making elaborate, ornamented versions and endlessly refining the timing of the flow, trying to regulate the pressure of the water. Bells, gongs, doors with figures and astrological models were added in flamboyant displays of craftsmanship and scholarship.

Waterclocks in the Modern world

In the ninth century CE, the Islamic world had inherited much of the Mesopotamian, Greek and Egyptian learning, and continued in the tradition of making elaborate waterclocks, adding automata animals and birds which sang on the hour.

Water clock and probable hydraulic drum operating bells, from Medieval Manuscript 1250 CE, One part of an early Bible Moralisées held at the Bodleian Library

In CE 809 the Caliph of Baghdad sent such a clock to Charlemagne, the Holy Roman Emperor. The clock contained a dazzling display of devices, including a different door which opened for each hour: the appropriate number of copper balls fell out and struck a metal cylinder, marking the hour. At noon automata knights emerged to shut each door.

In Medieval Europe, in lands we now know as France, Germany and Spain waterclocks were depicted in the illuminated manuscripts decorated by learned monks.

In China, clock making developed rapidly from CE 200 to 1300: a manuscript by Su Sung describes a massive water tower of CE 1088, 9.1 m (30 ft) tall, with gongs, five doors, mannequins holding bells, other mannequins holding tablets up showing the hour, a celestial globe in the centre and the use of a device invented in CE 725 by Chang Sui, which provided a water-driven escapement. The Chinese invented the escapement device 900 years before it appeared in Europe: its purpose was to regulate the energy created by the flow of water.

Waterclocks, like sundials, had a built-in weakness: they could freeze in the cold. Alphonso X of Castile in the thirteenth century, used expensive mercury instead of water in his Klepsydra, in fact the invention and use of clocks in the Muslim era of Spain are covered in some detail at the Muslim Heritage website, see the link below.

In the next article on we take a look at other simple clocks…