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Water Clocks and Whistling Wakeups

How did the ancient Greeks measure time and drag themselves out of bed before the modern alarm clock or smart phone? With the help of Ctesibius and Plato.

Ancient Greek inventor and engineer, Ctesibius of Alexandria via Encyclopedia Brittanica

It’s early October in Melbourne, which means that daylight savings has just come into effect. As we woke last Sunday morning, we bemoaned our lost hour of sleep, yes. But we also found ourselves grateful for our trusty digital alarms for still rousing us out of bed on time!

Which gave us pause for thought. How did the ancient Greeks wake up on time before the invention of the bedside alarm clock, or the smart phones we know today? It’s easy to forget or take for granted, but the majority of us don’t go a day without relying on modern systems and instruments of time, which we owe to millennia of scientific developments by scientists and engineers throughout history.

The oldest known sundial ca. 1500 BCE found at the Valley of the King, Egypt

Ancient civilisations used the position of the sun, moon and stars in order to determine time. In the daylight, the shadow clock and sundial evolved as tools to determine the position of the sun. In the evenings, knowledgeable stargazers observed their local systems for timekeeping and navigation. As studies of astronomy evolved, instruments such as the astrolabe and early telescope were developed.

These early systems faced limitations; shadow clocks and sundials, for instance, could only be used outdoors in daylight. As civilisations continued to evolve, the need for more reliable and accurate timekeeping devices increased.

Enter the water clock. The ancient Greeks were not the first to use water clocks – a tomb inscription identifies Amenemhet, a 16th century BCE Egyptian court official as its alleged inventor – but there are two particular figures of Ancient Greece who helped refine its development and catapult it into more common use.

Reconstructed Egyptian Clepsydra, Temple of Karnak

The clepsydra, or ‘water thief’ is a bowl-like vessel with a hole at its base, which is sized to create a non-stop pressured water flow. In early versions, as the water level dropped, notches on the inside wall were revealed to indicate the passage of time according to the rate of the water's flow.

Physicist Christiaan Huygens and the pendulum clock

In the 3rd century BCE, a Greek engineer and inventor named Ctesibius improved this design so much that his version of the water clock was considered the world’s most accurate timekeeping instrument for almost 2,000 years. While others were

invented and iterated in those years, none were found to be as accurate until Dutch physicist Christiaan Huygens invented the pendulum clock in 1656, kickstarting the era of precision timekeeping.

First, Ctesibius revised the design by introducing a second vessel to catch the flowing water. On this second vessel, he added an overflow pipe which fed into yet another chamber. The water in this chamber would rise at a much more

Ctesibius' water clock reconstruction, Kotsanas Museum

precise rate, allowing time to be measured more accurately. This revision still faced some limitations, as chambers would periodically need emptying. To resolve this, he invented the world’s first siphon and added this to the system, allowing the clock to be emptied and refilled automatically.

More hurdles arose but again Ctesibius overcame them. This time, how the Greeks measured time itself began to pose a problem. Their system divided the daylight hours into twelve – meaning as days grew shorter in the winter months, the duration of their hour also became shorter, and the flow rate of the water clock would fall out of sync.

Early 19th century illustration of Ctesibius' clepsydra with water wheel and cogs

To work around this, Ctesibius took the principles of the water clock and added a waterwheel and cogs. These rotated a cylinder a small amount each day, tracing the hour lines on a pole to be nearer or farther according to the time of year. It ran seven days a week, every day of the year. It is this clock which was considered most accurate for almost two millennia and was one of the first recorded uses of oscillating devices in timekeeping.

So, what about alarms? Throughout history, a few techniques have been used to rouse people from their slumber, including personal 'knocker-uppers’ hired to come to your door, or nails inserted into candles, which when the candle had melted past the nail, would drop and 'ping' on the plate.

A model of Plato's clock at Kotsanas Museum – the vent can be seen on the second bottom chamber

But far more sophisticated, it's the famous 5th century BCE philosopher Plato who is credited with the first proper alarm clock, which he used to wake in time for his famous dawn lectures. This alarm was an evolution of Ctesibius’ simple water clock. In Plato's clock, the design of the overflow vessel – that provided the most accurate measurement – was revised to trap the air inside. As the water level increased, so too did the internal pressure. When this pressure became great enough, it would force its way out a valve fitted to its side, and whistle like a kettle to wake its owner. An effective but unfriendly wakeup!

While the world eventually moved on to mechanical and quantum clocks, there is no denying that the water clock, and its advancements by Ctesibius and Plato were instrumental to the evolution of timekeeping devices throughout history.

For a bit of fun, you might like to try building your own simple water clock with common household items. This simple activity is a great way to gain deeper understanding and for parents to explore the historical and scientific concepts behind water clocks with kids.


You'll need:

  • Plastic soft drink bottle

  • Scissors

  • Thumbtack/pin

  • Marker pen

  • Food colouring

  • Stopwatch/timer


  • Cut the plastic bottle in half as shown

  • Use the thumbtack to poke a hole through the bottle lid

  • Flip the top half to sit inside the bottom bottle half with lid pointing down

  • Add a few drops of food colouring to half a litre of water

  • Pour the water into the open top of the bottle and start the timer immediately!

  • At every minute, use the marker to indicate the water level on the bottom half

  • Once all the water has flowed to the bottom and minute marks are made, return the water to the top half and watch as your new clepsydra counts for you! Depending on the volume your bottle can hold and the size of the pinhole in the lid, every water clock will track a different amount of time.


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