Zhang Heng and the World's First Seismometer

A replica of Zhang Heng's seismoscope at an exhibition in Oakland, CA in July 2004 (Shizhao/Wikimedia Commons).
Over the last century or two, science has provided us many new insights into the forces that cause earthquakes. Many new devices such as seismometers have been developed that detect earthquakes and give us detailed information about an earthquake. But did you know one of the most efficient earthquake-detection instruments was developed almost 1900 years ago in ancient China?

This device is a seismoscope known as the Houfeng Didong Yi (候风地动仪, or "instrument for measuring the seasonal winds and the movements of the Earth" in English) and was invented by the Eastern Han philosopher and court official Zhang Heng. Zhang was a multi-talented man who excelled at mechanics and mathematics and was, among other things, a poet, cartographer, literary scholar, artist, and geographer.

At that time, most Chinese believed that earthquakes were a result of divine punishment for acts committed by the current ruling dynasty, as well as an imbalance between Yin and Yang. Zhang, however, theorized that earthquakes were caused by disturbances in wind and air.

It was this theory that led to the creation of Zhang's seismoscope. The seismoscope, which was approximately 1.82 (6 ft) tall, resembled a gigantic bronze urn with eight tubes shaped as dragons' heads around the top. Surrounding the seismoscope were four bronze toads which were positioned in the four directions. Inside the casing was a pendulum, a crank and right-angle lever, and some bronze balls. In the event of an earthquake, the pendulum would swing, the crank and lever would raise one of the dragons' heads, and the balls would drop out of the mouth of the dragon into the mouth of a bronze toad. This would create a large 'clang', which served as a warning alarm, and the toad indicated the direction of the quake.

Zhang presented his seismoscope to the Han court in 132 AD. According to records from the time, the device detected an earthquake over 600 km (372 miles) away from the Han capital of Luoyang in February 138. Also, the seismoscope is said to have detected a quake in Gansu province in 143, which was not felt.

Zhang and his seismoscope were given special mention in the Book of Later Han detailing the reign of Emperor Shun.

So could Zhang Heng's seismoscope be used to detect earthquakes in 2012. Most certainly! As a matter of fact, in 2005, scientists in Zengzhou, China (which was also Zhang's hometown) managed to replicate Zhang's seismoscope and used it to detect simulated earthquakes based on waves from four different real-life earthquakes in China and Vietnam. The seismoscope detected all of them. As a matter of fact, the data gathered from the tests corresponded accurately with that gathered by modern-day seismometers!

When Zhang Heng created his seismoscope, he created a device that was very advanced for the time and would still give accurate results and warnings almost two millinea later.

For more about Zhang Heng and his seismoscope, check out the links below:
Zhang Heng Wikipedia entry
Article from Xinhua/ about the modern replica of the seismoscope


Post a Comment