How Were Water Clocks Used?
A water clock uses a flow of water to measure time. If viscosity is neglected, the physical principle required to study such clocks is the Torricelli’s law. There are two types of water clocks: inflow and outflow. In an outflow water clock, a container is filled with water, and the water is drained slowly and evenly out of the container. This container has markings that are used to show the passage of time.
As the water leaves the container, an observer can see where the water is level with the lines and tell how much time has passed. An inflow water clock works in basically the same way, except instead of flowing out of the container, the water is filling up the marked container. As the container fills, the observer can see where the water meets the lines and tell how much time has passed.
Water Clocks were among the earliest timekeepers that did not depend on the observation of celestial bodies. The oldest one was found in the tomb of an Egyptian king, buried around 1500 B.C. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and in Egypt around the 16th century B.C.
Later named Clepsydra (water thief) by the Greeks, who began using them about 325 B.C., these were stone vessels with sloping sides that dripped water at a nearly constant rate from a small hole near the bottom.
Some modern timepieces are called “water clocks” but work differently from the ancient ones. Their timekeeping is governed by a pendulum, but they use water for other purposes, such as providing the power needed to drive the clock by using a water wheel or something similar, or by having water in their displays.
Some water clock designs were developed independently and some knowledge was transferred through the spread of trade. These early water clocks were calibrated with a sundial. While never reaching a level of accuracy comparable to today’s standards of timekeeping, the water clock was the most accurate and commonly used timekeeping device for millennia, until it was replaced by more accurate pendulum clocks in 17th-century Europe.
Only a few modern water clocks exist today. In 1979, French scientist Bernard Gitton began creating his Time-Flow Clocks, which are a modern-day approach to the historical version. His unique glass tube designs can be found in over 30 locations throughout the world, including one at Europa-Center’s The Clock of Flowing Time in Berlin, Centre Commercial Milenis in Guadeloupe, the Giant Water Clock at The Children’s Museum of Indianapolis in Indianapolis, Indiana, the Abbotsford International Airport (formerly at Sevenoaks Shopping Centre) in Abbotsford, British Columbia, and the Shopping Iguatemi in São Paulo and Porto Alegre, Brazil.
Gitton’s design relies on gravity powering multiple siphons in same principle as the Pythagorean cup; for example, after the water level in the minute or hour display tubes is reached, an overflow tube starts to act as a siphon and thus empties the display tube. Actual time keeping is done by a calibrated pendulum powered by a water stream piped from the clock’s reservoir. The pendulum has a carefully constructed container attached to it; this measures the water that is then poured into the display system.
There are other modern designs of water clocks, including the Royal Gorge water clock in Colorado, the Woodgrove Mall in Nanaimo, British Columbia, and the Hornsby Water Clock in Sydney, Australia.
In the early-to-mid-14th century, large mechanical clocks began to appear in the towers of several large Italian cities. Another advance was the invention of spring-powered clocks between 1500 and 1510 by Peter Henlein, a German locksmith from Nuremberg. Replacing the heavy drive weights permitted smaller (and portable) clocks and watches.
Henlein nicknamed his clocks ‘Nuremberg Eggs.’ Although they slowed down as the main spring un-wound, they were popular among wealthy individuals due to their size, and the fact that they could be put on a shelf or table instead of hanging from the wall. They were the first portable time pieces.