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Roger Weller, geology instructor

by Eder-Lyn Dayrit
Physical Geology
Spring 2012


The Dragon Jar or The Dragon Crock?

Earthquakes – or “seismic events” – are now detected via seismograph; the defining features of a seismograph include the having the capabilities to measure and record the vibrations of quakes (“Seismograph”).  However, before we managed to venture towards the invention of seismographs, seismoscopes were the devices used to determine the earth’s vibrations.  Seismoscopes are now seen as obsolete instruments that just simply indicate the occurrences of an earthquake (“Seismoscope”).

During the Eastern Han Dynasty earthquakes were disastrous and plentiful, at this time they were known to have the strength to divert the courses of rivers. The tremors of the earth were thought to be caused by angry gods punishing those on earth.  When in reality earthquakes are caused by faulting (a sudden vertical or lateral movement of rock along a surface. The thought that the cause might just be a natural disaster was simply.. unnatural.  But considerable amounts of time and many tedious experiments sparked a thought to come to mind (to the mind of Zhang Heng specifically).

An unprecedented invention created SEISMIC history in China.  As the inventor of a rotating celestial globe, odometer, and one of the four great painters of his era, Zhang Heng created the primitive 6-foot (in diameter) apparatus named “The Houfang Didong Yi” – translating to "instrument for measuring the seasonal winds and the movements of the Earth"—in 132 A.D. (

Figure  SEQ Figure \* ARABIC 1 Sismomètre

Zhang claimed his invention (the urn-like dragon jar) was able to determine the exact cardinal direction of a distant (hundreds of miles) earthquake. The jar contained a pendulum connected to eight copper rods, which connected to eight bronze dragon heads. These dragon heads each faced a distinct direction – north, south, east, west, north east, southeast, northwest, or southwest – and held bronze balls in their mouths. They surrounded the outside of the jar at equal distance to one another, and if a seismic event occurred, it could be determined in which direction the epicenter (the exact location on the Earth's surface that is directly overhead the origin of an earthquake) was located. This is because a pendulum located inside the jar would lose it balance and sway, activating levers inside to eject a single bronze ball and have it fall into a toad’s open mouth. The noisy plummet would alert of the seismic occurrence. Resulting in a dragon now empty-handed – or rather, empty mouthed – facing in the direction of the earthquake’s epicenter.

Figure  SEQ Figure \* ARABIC 2 Chang Heng's Seismoscope

The instrument’s reliability raised some eyebrows considering in February of 138 A.D it was reported to have detected an earthquake to the northwest – which pointed to the capital. No vibration was felt at the location, the lack of earth shaking caused heads to shake. This was until a messenger arrived to report an event about three-hundred miles northwest Luoyang so vicious it was causation for severe landslides. This proved the device was sensitive enough to record the earthquake (Tomczak).

There have been many skeptics in regards to this primitive seismometer. Since the seismograph works on principles of inertia, foreign seismologists argued two spheres should fall from the mouths of dragons on opposite sides of the jar (Xinhua News Agency). Global Times has quoted scientist Fang Zhouzi to have said, “I have every reason to believe that is was a story fabricated to make the device sound magical.” (Global Times).  In rebuttal to doubts, others hold that all the replicas are just reconstructed from guesses and imagination rather than from actual knowledge as to how the real device used to look like (Hui). Since the original device is lost, it is hard to determine which side is right, and which side is mistaken.

A few Western scholars even contend Zhang Heng's device was lost because it was never a reality (Xinhua News Agency).  Nevertheless, whether the accuracy of this vision was dream-like, or just a dream, in history it will always be the first.

Even though the original dragon jar did not survive in history, it has been reconstructed.  A Japanese scholar in 1875 reconstructed the seismoscope, basing his design on the description of the device in Zhangs’s biography.  And later in 1951, a Chinese museum researcher named Wang -Zhenduo redesigned the device, creating two different models. The first reconstruction contained a pendulum as the central pillar acting as the sensor, the second contained an inverted pendulum. A normal pendulum is stable when hanging downwards. While an inverted pendulum is unstable, and must constantly be balanced to stay upright.

None of the recreations could detect any tremors, proving they were not up to par with the accurateness and sensitivity of the original as described in Chinese history records. Some argued Zhang’s central pillar was a suspended pendulum, others proposed the pillar an inverted model.

            Then on June 13, 2005 modern day seismologists and archeologists announced they have successfully created a replica of Houfang Didong Yi in Zhengzhou, which is also the home of the original seismometer inventor.  According to scientists and the designers, the recreation responded to four actual earthquakes in Tangshan, Yunnan (Xinhua News Agency).

            To this day Zhang Heng is celebrated for his works.  People still highly esteem the inventor as a great scientist living more than 1,800 years ago. Commemorative activities are held to show respect for him.  Even a ring of hills on the moon was named after him (Zhang Heng and The Seismograph).  He will forever live in our history as a renowned inventor, politician, writer, mathematician, philosopher, and astronomer (to make the list short). To be brief, he was a man before his time; and he will live long after.



Works Cited

Chen-To, Wang. Cheng Heng’s Seismoscope. 2009. Photograph. Bulletin of the Seismological Society of America.

Clark, Josh.  "Top 10 Ancient Chinese Inventions"  09 March 2009.    12 April 2012.

Dewey, James. "The Early History of Seismometry (to 1900)." Earthquake Hazards Program. U.S Department of The Interior, 27 Oct. 2009. Web. 12 Apr. 2012.

Global Times. "Ancient Seismograph Debunked." 3 Dec. 2010. Web. 12 Apr. 2012.

Health Tips Reporter. "The World’s First Seismograph – The Dragon Jar." Notes of A Health Tips Reporter. 22 May 2007. Web. 12 Apr. 2012.

Hui, Feng. "Revisiting the Ancient Chinese Seismgraph." Http:// Web. 9 Apr. 2012. <>.

Michigan Technological University. "How Are Earthquakes Studied?" Michigan Technological University. Web. 12 Apr. 2012.

Museumdetoulouse. Sismomètre. 2008. Photograph. Muséum De Toulouse, Toulouse. 27 Nov. 2008. Web. 12 Apr. 2012. <>.

"seismograph." © Encyclopedia Britannica, Inc.. Encyclopedia Britannica, Inc.. 09 Apr. 2012. <>.

"seismoscope." Unabridged. Random House, Inc. 4 Apr. 2012.

Toads Frolicking with Dragons." Chinatown Online Co. Web. 12 Apr. 2012.

Tomczak, Matthias. "Chang Heng (Zhang Heng)." Science, Civilization, and Society. Web. 12 Apr. 2012.

Xinhua News Agency. "China Resurrects Worlds Earliest Seismograph." China Internet Information Center, 13 June 2005. Web. 10 Apr. 2012.

"Zhang Heng and the Seismograph." Confucius Institute Online. Confucius Institute Network, 4 Nov. 2009. Web. 10 Apr. 2012.