A boat which is an alarm clock


The device that closes the book is also the simplest of all. In the ancient world, one of the means of measuring time was the submersible float (طرزهار). It’s a buoy with a hole so that the water penetrates and causes it to sink after a given time. This was necessary to monitor the water flow in irrigation canals or for cooking. Al-Jazari feared that the user would nap and miss the sinking of the buoy, so he added a sound effect. It made me search for materials on ancient alarm clocks, which is the subject of this post.

Boat for measuring one hour, Topkapi manuscript, 1205

How does it work?

Sinking buoys don’t require an explanation, so I gave up the traditional blue coloring of the engineering explanations. Obviously, if there is a hole in the buoy, water will penetrate it, and the buoy, or in this case, the boat will sink. The duration of the sinking was achieved by trial and error. Al-Jazari used sinking buoys in the elephant clock and elsewhere. The twist here is the sound alert. I added to al-Jazari’s drawing contours that enclose the airspace and highlights the hole in the bottom:

A drawing by al-Jazari with my additions and captions.

The sailor and boat are made of copper. And they are welded together so that a common airspace is created. At first, the boat sinks slowly, and the trapped air slowly exits under the pressure of the rising water. Due to the slowness of the process, the whistle does not make a sound. There are also five holes for a secondary air exit from the sailor’s hat, which reduce the air output through the whistle and help to silence it. The boat is full of water at the end of the hour, and a rapid sinking begins. The air quickly compresses through the whistle and makes a sound, and helps the sleepy watcher to wake up and do his job.

Early alarm clocks

The earliest alarm clock I have found is associated with Plato, the Greek philosopher. Plato would get up early. In “The Laws,” his last work, he wrote what might explain his need for an alarm clock:

” Asleep, man is useless, he may as well be dead…it a disgrace and unworthy of a gentleman…if he devotes the whole of any night to sleep.”

Plato allegedly designed his own alarm clock. I have reservations because the information comes from Athenaeus of Naucratis,  who wrote the “Deipnosophistae” some 200 years later, and there is no other evidence for this alarm clock. It’s an interesting water clock (not based on a sinking buoy), but in terms of sound play, it’s not very different from Al-Jazari. You can see a nice animation:

There is a good variety of antique alarm clocks. Ctesibius built a particularly precise water clock. We already encountered Ctesibius in a post about A Pump Powered by a Water Wheel. He was an inventor and mathematician in Alexandria, Ptolemaic Egypt, and is best known as the “father of pneumatics.” Very little is known about his life. He was probably the first director of the Museum of Alexandria. His writings have not survived, but his inventions were documented by Athenaeus, I already mentioned, Philo of Byzantium, Heron of Alexandria, and an exceptionally detailed description of the water clock appears in “De architectura, libri decem,” known today as The Ten Books on Architecture by Marcus Vitruvius, a Roman architect and engineer during the 1st century BC. I will expand on the water clock immediately, but Vitruvius also wrote:

 ” At Jaffa in Syria and among the Nomads in Arabia, are lakes of enormous size that yield very large masses of asphalt, which are carried off by the inhabitants thereabouts.”

apparently referring to the Dead Sea. The strange combination of Jaffa, Syria, and the Dead Sea sounds like a child confused by various holidays and mixes Christmas and Chanuka, but this whole Levant may seem like one geographical unit from Rome. This is a good  animation of the clock:

You can see that Ctesibius was aware of the well-known problem of water clocks, which is the variable flow rate with the vessel’s water level. You can read more here. His solution is a tank always full of water, and the excess spills out. This creates a constant flow rate in the second tank, raising the buoy with the indicator indicating the passing minutes. At the end of an hour, the siphon (an invention attributed to Ctesibius) empties the buoy tank and turns the gear counting the hours. Vitruvius writes that there was an “alarm clock system that dropped gravel stones on a gong and blew the trumpets,” but this part has no technical details, so we can only imagine how it worked. A somewhat strange story is that the clock was installed at court in Alexandria and indicated the amount of time lawyers could speak while the severity of the crime determined the amount of water. Ctesibius’ water clock was considered the most accurate until Dutch physicist Christiaan Huygens invented the pendulum clock.

There are other ancient alarm clocks, but it is amusing to know, and says quite a bit about the importance of patents, that a French inventor named Antoine Redier patented an alarm clock in 1847, more than 2,000 years after Plato, who was astonished in his grave and perhaps expected some of the royalties…


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