Chinese seismologists and archeologists have announced that they have created a replica of Didong Yi, the world's first seismograph.

The announcement in Zhengzhou, capital of central China's Henan Province, also home to the seismograph's original inventor Zhang Heng (78-139 AD), came almost two months after the device passed relevant appraisal and examination by a scientific committee in April.

Seven scientists in seismology, archeology and mechanical engineering from Chinese Academy of Sciences, the National Museum and China Earthquake Administration confirmed that the replica was a "historic step" towards complete reconstruction.

"We believe the newly restored seismograph model is the best at present," said Academician Teng Jiwen, a research fellow at the Institute of Geology and Geophysics under the Chinese Academy of Sciences, China's top scientific research body.

"It represents our current utmost understanding of the ancient Didong instrument," said Teng, who was among the seven-member appraisal and examination panel.

According to the History of Later Han Dynasty (25-220 AD), Zhang Heng's seismograph was an urn-like instrument with a central pendulum. An earth tremor would cause the pendulum to loose balance and activate a set of levers inside. Then, one of the eight dragons placed in eight directions outside the urn would release a bronze ball held in its mouth. The ball would fall into the mouth of a toad and give off a sound in the meantime, letting people know when and in which direction an earthquake had occurred.

The Han-style wine goblet-like replica with a ridgy coping, can respond to the reproduced waves of four actual earthquake events in Tangshan, Yunnan, the Qinghai-Tibet Plateau and Vietnam, according to scientists and designers. They say the test of the model's internal mechanism with modern earthquake graphs is scientific and accurate and the shape of the replica is very close to the original one described in history books.

"What we are exhibiting is a scientific device, not a toy," said Tian Kai, deputy curator of Henan Museum, where a smaller-sized new replica is on show.

"If we put a seismograph that is unable to move or detect on exhibition," Tian said, "we will not only deceive our audience, but also show our apathy and irresponsibility towards our nation's splendid cultural legacy."

Invented by Zhang Heng in 132 AD and rejoiced in the Chinese name Houfeng Didong Yi (Instrument for inquiring into the wind and the shaking of the earth), the original of the seismograph did not survive history. It is recorded as detecting an earthquake in February in the year 138 about 600 kilometers away from Luoyang, then China's capital, according to the History of the Later Han.

The Didong Yi was first reconstructed by a Japanese scholar in 1875 based on the description about the device in Zhang's biography in the History of the Latter Han and archaeological research findings. The currently well-known model was redesigned by noted Chinese museum researcher Wang Zhenduo in 1951. None of the replicas could detect an earthquake.

"As a treasure of our Chinese nation, Didong Yi is an attractive goal for reconstruction to scientists around the globe," Teng said. "If we can't get the job done, it will be our fault."

However, there has been some scholarly disagreement about the exact scientific principles applied on the seismograph and how precisely the instrument originally worked.

Some foreign seismologists argue that if Zhang Heng's seismograph worked on principles of inertia, then two (not one) "pearls" should fall out from mouths of dragons on opposite sides of the device.

Others hold that all the replicas are just reconstructed from our guess and imagination rather than from our true knowledge as to how the real device used to look like. A few Western scholars even contend Zhang Heng's device was lost because it was never a reality.

Feng Rui, a China Seismological Networks Center research fellow who heads the restoration team, believes he and his colleagues can testify the existence of Zhang Heng's seismograph through collection of historical data and simulated analysis.

(Xinhua News Agency June 13, 2005)