The Seis of China

Life in Eastern Han (AD 25-250) from a fresco in Luoyang

Growing up in racist Philippines meant hearing racist jokes. One that was particularly popular dealt with a natural catastrophe. It goes like this: “Why do earthquakes occur? Because the Chinese decided to jump at the same time.”

If the Chinese really decided to do so, the earth will only be perturbed very very slightly, causing minor problems for the people nearby. But for that to even happen, careful and critical conditions must be met, like having all of the participants near each other, then they must commence with the jump and land at exactly the same time as everybody else. Difficult. Not exactly a wok in the park.

As with most racist jokes, the Chinese jump theory has nothing to do with actual science. Well, jokes don’t necessarily have to be scientific in the first place (which is why the chicken and the egg conundrum is still unresolved even if phylogeny has judged the egg to be first). But the joke is a prima facie attempt at describing two of China’s most prominent features: 1.) China is really really big and 2.) there are very very many people in China then and now.

Like the BeeGees, I started this piece with a joke. And like them I also once “fell out of bed, hurting my head”, but not because of the “things that I said”, but because of an earthquake. Natural calamities, like earthquakes, however, are nothing to joke about. People die, which usually starts the whole world crying. Especially in China, which is really really big with very very many people. Epochs injured by earthquakes have scarred China throughout its existence, so, an early Chinese scholar sat down, studied the matter with scientific seriousness, and came up with a device that can detect earthquakes. His name was Zhang Heng (張衡).

Artist sketch of Zhang Heng. Image credits: Yeuan Fang/Epoch Times

Zhang (AD 78-139) was born in the town of Xi’e (西鄂), a small principality in what is now Henan (河南) province. His privileged childhood afforded him a good family and education. Two potent ingredients that stirred in him a love for the arts in his youth. But what else was there to learn in this small town? Surely, the world out there holds knowledge far greater than what this place can offer. So at the age of 15, Zhang decided to pack his bags and set out for Luoyang (洛阳市) to pursue further studies. The journey was long, and not to mention treacherous, a deadly combination usually ending in ennui and melancholy. To combat this, Zhang decided to look around and immerse himself in the events that surrounded him. One particular sight that fascinated him was the number of people flocking a hot spring in Mount Li (驪山). The panoply of sounds and sights was captured by Zhang in verse, titled Fu on the Hot Springs (溫泉賦). Zhang invoked the natural to detail what his eyes told him: the droves of people are “clustering like schools of fish”, and in their sheer numbers they are “thronging thick as mist”. This was Zhang’s earliest attempt at poetry, his first foray into a long distinguished career as a man of letters.

Zhang enrolled in Luoyang’s Taixue (太學), or imperial academy, and established himself as a young scholar of great literary acumen. It wasn’t long until bureaucrats heard of him and sought his talents. They offered Zhang employment in various government posts, which he all denied. When he was done with his studies, Zhang went to Nanyang (南陽) in AD 100 and took up the position of master of documents under the governorship of Bao De.

It was late in life when Zhang devoted his time to mathematical and scientific research. At the age of 30, he pored over ancient Chinese astronomical and mathematical texts and made his own commentaries. He wrote a treatise on Yang Xiong’s (揚雄) text Canon of Supreme Mystery (太玄經) which was positively received by other scholars. In fact, this exposition earned him fame as a competent, if not, gifted mathematician – culminating in an invitation to work for Emperor An (漢安帝) himself in Luoyang. He accepted. An imperial carriage arrived to escort him to the capital – a symbol of authority and prestige during that time. The year was 112. Three years later he was promoted to Chief Astronomer.

While working in the emperor’s court, Zhang also busied himself with mechanical tinkering and mathematical explorations. For example, he improved an old version of the water clock. He also worked on the armillary (or celestial) sphere of an earlier Chinese scholar, and made it water powered after installing complex gears. In mathematics, he also came close to the correct value of pi, by approximating its value as 3.17 and later on 3.1466. But there was one invention of his that was really considered groundbreaking.

In 132 Zhang brought to the imperial court a strange looking object.

It looked like an urn. Or a jar. On its sides were eight dragon-heads, all facing different directions. Inside the mouths of these serpents were metal balls. Just below each dragon’s head was a toad with its mouth agape, perfectly aligned to catch the ball when it drops. Its function? To detect earthquakes. It was the world’s first seismograph (候風地動儀).

The way it worked was fairly simple. When an earthquake was detected, a dragon-head pointing to the direction of the earthquake dropped the ball in its mouth into the toad’s. In one event, a clang was heard in the courtroom. It was the sound of a metal ball rattling inside the mouth of a toad. The court officials wondered why the device recorded an earthquake when they didn’t feel anything. Chatters of doubt echoed around the chambers clamoring about the device’s actual effectiveness. But days later a squire from Longxi (陇西县)) province arrived in the capital delivering a message of destruction. There was an earthquake in Longxi a few days ago, on the very same day when a clang was heard. It was west of the capital. The same direction where Zhang’s device pointed at when it dropped the ball.

No more doubts were raised after that incident. Zhang’s seismograph worked. It solved one problem of how to send help immediately. Now, officials had a way to have themselves alerted of a tragedy and send aid as soon as possible.

Replica of Zhang Heng’s seismograph at the Chabot Space and Science Center in Oakland, California.

The actual device was lost in time. And no record of its internal workings survived. No one actually knows how it really worked. Recently, a team of scientists worked out the problem (click here to see a video explanation of how they did it and how it worked) and made a modern replica of Zhang’s seismograph. But we can never be too sure if it truly represents Zhang’s work.

The only way to find out would be to ask Zhang himself, but there’s no way to do that: even if an earthquake were to wake him up from his mortal sleep; or even if everyone, not just in China, decided to jump altogether.



Deng, Yingke. Ancient Chinese inventions. Beijing, China: China Intercontinental Press. 2005

Needham, Joseph. Science and Civilization in China (Vols. 3-4). 1st ed. Cambridge: Cambridge University Press. 1954

Owen, Stephen & Chang, Kang-i Sun, eds. The Cambridge history of Chinese literature (Vol. 1). Cambridge: Cambridge University Press. 2010

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