Past Masters: The Astronomical Water Clock Of Su Song

It is said that those who do not learn from the past are doomed to repeat it, but in the case of horology –especially nowadays –the past is constantly being mined enthusiastically for inspiration –sometimes with antecedents acknowledged, and credit given where it’s due, and sometimes not, with the hope that nobody will notice that the latest exotic complication was actually invented by some anonymous journeyman watchmaker at a time when indoor plumbing was an unspeakable luxury.

Mechanics, in short, have been around for some time and from the 1st century BCE’s Antikythera mechanism on down to the present day, some of the cleverest people on the planet have not only loved to make interesting machines, they’ve loved to make interesting timekeeping machines.

One such was the Han Dynasty’s Su Song.  Su Song was born in 1020 and died in 1101 and like many educated gentlemen of his time, he was a polymath whose polymathery would put to shame most polymaths of today –an accomplished poet, he was also a cartographer, art collector, astronomer, an expert on the abstruse properties of the Chinese calendar, a prize-winning scholar and a statesman as well as something of an expert on Chinese medicine.

His single greatest contribution to horology was an enormous astronomical tower clock he designed and had built in Kaifeng, which was completed in 1094.  It was a water-clock but one of enormous sophistication.  The escapement, for instance, was a unique, constant-force design in which every step was taken to ensure that the flow of water was continuous, for as Su Song wrote:

According to your servant’s opinion there have been many systems and designs for astronomical instruments during past dynasties all differing from one another in minor respects. But the principle of the use of water-power for the driving mechanism has always been the same. The heavens move without ceasing but so also does water flow (and fall). Thus if the water is made to pour with perfect evenness, then the comparison of the rotary movements (of the heavens and the machine) will show no discrepancy or contradiction; for the unresting follows the unceasing.”

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Diagram by Su Song of the escapement of his clock; image; Wikipedia

The heart of the clock was an enormous wheel, 11 feet in diameter, with 36 scoops.  Once filled, each scoop would then pivot and empty, releasing the wheel –which is, essentially, an escape wheel –allowing it to advance until locked by the next scoop.  The inflow of water came from a supply tank kept at a constant volume so that the rate of water flow would never vary (Su Song considered using mercury rather than water, to prevent the problem of the mechanism freezing in winter, but eventually decided against it.)  The escape wheel rotated in the vertical plane, and through a crown-wheel gear system, turned a group of horizontal wheels on which were platforms decorated with what in Western clockmaking would be called “jacks” –that is, figures that showed the time.  The entire, pagoda-shaped structure was topped with a spherical bronze star chart and an armillary sphere both of which were driven by the clock mechanism.

This Wonder of the World was unfortunately destroyed in 1127 by an invading Manchurian army, who disassembled the clock and brought it to Beijing (then their capital) but could not determine how to reassemble it.

Su Song’s treatise on its construction survived, however –and in 2009, on a trip to Japan as a guest of Seiko, we visited the Gishodo Suwako Watch and Clock Museum, in Suwa City, Nagano Prefecture, where to my astonishment I found, in a courtyard behind the museum, a full-sized working replica of Su Song’s clock.


The model is astonishingly detailed, complete with figurines, time-keeping wheels and a working replica of Su-Song’s hydro-mechanical escapement, as well as the astronomical sphere and the armillary sphere.






Background, the escape wheel; horizontal beam supporting crown wheel that turns the horizontal time display wheels

I have been unable to determine thus far who made the replica and who funded it, but if you happen to be in Suwa and you have the slightest interest in clocks and watches, it’s a must-see.

If you are fortunate enough to visit Suwa with Seiko, you may also be able to arrange to see one of their most interesting watchmaking facilities: the Micro-Artists Studio, where among other treasures you may be able to see under construction one of the world’s rarest chiming complications: the Credor Sonnerie Spring Drive.

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The other big attraction in Suwa is to visit the great Shinto shrine there, where once every six years the Onbashira Festival is held, as it has been for over a thousand years.



The climax of the festival is the “Ki-Otoshi” in which young men prove their bravery by riding enormous, multi-ton logs down the mountain slopes.  The logs are erected at the four corners of the shrine at the end of the ceremony and it is certainly a demonstration of bravery to ride them as they are massive and can easily maim or kill anyone unlucky enough to fall off or get in the way.

Come for the Onbashira Festival, stay for the clock.

Many thanks to Seiko USA and Seiko Japan whose generosity made the discovery of this remarkable model of Su Song’s clock possible.


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