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  • 6/2/2025
Transcript
00:00This ancient timekeeping device was fully automatic, needed no sunlight and kept better
00:05time than anything else on earth for over 1800 years.
00:09It wasn't powered by electricity, but by flowing water and a few clever mechanics.
00:14But how exactly did it work?
00:16In this video we'll break down the inner workings behind a design that was well ahead
00:20of its time.
00:21Over 2000 years ago, the city of Alexandria stood as the world's intellectual epicenter,
00:27a hub of innovation in fields such as mathematics, astronomy and engineering, where groundbreaking
00:32ideas flourished.
00:35One of the most extraordinary inventions to emerge from this era was a clock that ran on
00:39water.
00:40An ingenious timekeeping device so precise it remained unmatched until the invention of the
00:46pendulum clock in 1656.
00:50But long before that, in 3rd century BCE, a brilliant Greek inventor named Decibius was
00:55already redefining how time could be measured.
00:58Though often forgotten by history, his work paved the way for a technical revolution, the
01:02science of timekeeping.
01:10In ancient Greek society, the ability to tell time accurately had become increasingly important.
01:16As daily life became more structured, the need for order and scheduling made accurate timekeeping
01:21being essential.
01:22For millennia, civilizations have relied on the sun's movement to track time.
01:27Sundials measure time by tracking the movement of the shadow cast by a pointer, called Gnomon,
01:33onto a reference scale.
01:35As the sun moves across the sky, the shadow changes position along marked intervals, allowing
01:40people to estimate the time based on where it lands.
01:45But sundials had a major flaw.
01:47They only worked when the sun was shining.
01:50On cloudy days, during the night, or in covered spaces, they were useless.
01:56To address these limitations, other methods of measuring time emerged as alternatives to
02:00sundials, such as early forms of water clocks, also called Clipsidrus, from the Greek meaning
02:07water thief.
02:08The simple devices appeared long before the more sophisticated design developed by Decibius,
02:14and relied on the flow of water to mark the passage of time.
02:18They were used in various ways, in courtrooms and temples to limit the length of speeches,
02:24and in public assemblies and political forums to keep debates and discussions within set timeframes.
02:31Early water clocks were simple in design.
02:33A large vessel would be filled with water.
02:35And to start the timer, a plug at the bottom was removed, letting the water flow out gradually.
02:42As the water level dropped, it passed time markings etched along the inner wall.
02:47The time could be paused by simply placing the plug back into the spout, preserving whatever
02:52water remained.
02:54Early water clocks also had their limitations.
02:57As the water level dropped, so did the pressure driving the flow.
03:01This caused the stream of water to slow down over time, meaning the passage of time wasn't
03:06constant.
03:08This inconsistency meant that hours measured later in the cycle took longer than those
03:13at the beginning.
03:14To compensate for the slowing flow as the water level dropped, the scale inside the bowl was
03:19graduated, meaning the time intervals were spaced unevenly to match the changing speed.
03:25While this helped improve accuracy, it still wasn't enough to maintain a truly constant measurement
03:30of time.
03:31Unlike modern timekeeping, where every hour is of equal length, the ancient Greeks used
03:36temporal hours, which divided the time between sunrise and sunset into 12 daytime hours.
03:43This system made sense in a world organized around daylight activities, but it also meant
03:48that the length of the hour wasn't fixed.
03:52Since the length of the day changed with the seasons, the length of each hour also changed.
03:57A daytime hour in summer was longer than a daytime hour in winter, which means that in the summer,
04:03a daytime hour could last as long as 70 minutes, while in the winter it could be as short as
04:0950 minutes.
04:11As a result, the markings inside had to be adjusted for each season to account for the changing length
04:17of daytime hours throughout the year.
04:20Early water clocks were an improvement over sundials because they could be used outdoors
04:25and indoors, at any time of day, and weren't dependent on the weather.
04:29However, they were only timers, not constant clocks, as they had to be manually refilled when
04:35they ran out of water.
04:37This meant that someone had to constantly maintain it.
04:41Tecibius was credited with the discovery of the elasticity of air, and the invention of
04:45several devices using compressed air.
04:48However, one of his most famous inventions remains the improvement of the water clock.
04:54To build a water clock that provided a consistent and reliable measure of time, Tecibius had
04:59to solve three fundamental problems, something no one before him had achieved.
05:04The first was maintaining a steady water flow to ensure consistent time measurement.
05:10The second was resetting the system automatically without manual intervention.
05:15The third was accounting for seasonal time variations, ensuring that hours remained proportional
05:21to the shifting length of days and nights.
05:25Let's first look at Tecibius' clock key components.
05:28The clock consisted of a vertical cylinder that rotated around its axis, completing one full
05:34rotation every year.
05:36The cylinder was marked with 12 vertical lines, representing the months, and 24 horizontal
05:42lines representing the hours, with the first hour at the bottom and the last hour of the
05:47day at the top.
05:49Next to the cylinder, a pointer was mounted on a rod with a cork float at the bottom.
05:54The float was placed in a long, narrow reservoir that gradually filled with water.
06:00As the water level rose, the float moved upward, causing the pointer to rise and indicate the
06:06passage of hours marked on the cylinder.
06:09In order to ensure consistent time measurement, a steady flow of water was required to fill
06:13the float reservoir.
06:16This was achieved by adding a feeding reservoir above it, which was constantly supplied with
06:21water, ensuring that water flowed into the reservoir faster than it could flow out,
06:26thereby maintaining a constant water level.
06:29Any excess water was directed to an overflow conduit.
06:33By keeping the water level constant, the pressure at the overflow spout, and thus the flow rate
06:38feeding the float reservoir remained steady.
06:42As water entered the float reservoir, the float gradually rose at a constant speed over the
06:47next 24 hours, eventually filling the reservoir.
06:51As the float reached its highest position, the system needed to reset.
06:55But how could the reservoir be drained automatically, without human intervention?
06:59To Sibius' solution, the siphon.
07:03A siphon is a device that allows liquid to flow from one reservoir to another without the
07:09need for a pump.
07:10But how did it work?
07:11The siphon was an inverted U-tube, with its input side connected to the bottom of the
07:17float reservoir, where the water level gradually rose alongside the water level in the reservoir.
07:22It was positioned so that the water level would reach the top of the inverted U-tube after
07:2724 hours.
07:28At that point, gravity caused the water to flow through the output side, creating a vacuum
07:34effect that automatically pulled water through the siphon, draining the float reservoir.
07:39The siphoning action continued until the water level dropped below the point where siphoning
07:44could no longer occur, resetting the clock for the next cycle.
07:49But there was still one last crucial problem to solve.
07:51How could the length of each hour stay proportional to the changing lengths of days and nights throughout the year?
07:58To address this, the Sibius added a water wheel, powered by the water draining from the
08:02float reservoir via the siphon.
08:05The water wheel was designed so that it would rotate one-sixth of a turn only after one of
08:10its six buckets was completely filled, at which point the water was emptied into a drainage
08:15basin.
08:17This drainage basin was also collecting excess water from the feeding reservoir.
08:22A gear was attached to the water wheel, and its rotation powered a two-stage gear mechanism.
08:28The last gear was mounted on a shaft attached to the vertical cylinder.
08:33The gear ratio was designed so that each one-sixth rotation of the water wheel turned the cylinder
08:38by one over 365 of a full rotation, allowing it to complete one full cycle in a year.
08:47Hours were engraved on the cylinder as horizontal lines, with their spacing varying by month.
08:53This design ensured that the duration of each hour adjusted throughout the year, staying
08:58proportional to the changing length of daylights across the seasons.
09:03With these innovations, the Sibius' device evolved beyond a simple clock.
09:07It became a fully automatic calendar, capable of tracking both time and the changing months
09:12of the year.
09:13And perhaps most remarkably, it was one of the earliest examples of a self-regulating system.
09:18A machine, that once set in motion, could operate continuously and accurately, needing nothing
09:24more than a steady supply of water.
09:27In a world without electricity, digital logic, or even mechanical clocks, this ancient invention
09:33laid the foundation for automation and timekeeping, as we know them today.
09:38And speaking of time, it's time to announce the winner from our last video.
09:44Congrats, and thank you for your comments.
09:47For this video's giveaway, we've created a brand new poster of the Sibius' water clock.
09:52For a chance to win one, just subscribe, like this video, and leave a comment below telling
09:57us what was the most fascinating part of the Sibius' invention for you.
10:01Lastly, a huge thank you to our Patreon and YouTube members.
10:12Your support makes all of this possible.
10:14Until next time, stay curious.