"For decades, China’s middle school students were introduced to the world’s first seismograph through an image in their history textbooks: a large, bronze urn with eight dragons perched the same distance apart along the outside, each with a copper ball hanging precariously in its mouth."

"Whenever there was a tectonic tremor from a particular direction, the corresponding dragon would drop its copper ball into the gaping mouth of a frog perched below it — or so students were taught. But for a new history textbook being used in public school classrooms across the country this fall, the image of China’s iconic earthquake detector and its accompanying text were removed.... The seismograph is widely believed to have been invented by Zhang Heng, a scholar and polymath who was born in the first century A.D. during the Eastern Han Dynasty.... For decades, the popular conception of Zhang’s seismograph came from a 1951 model by the historian Wang Zhenduo, based on the description in the ancient biography. This image was added to China’s textbooks, but in most cases without a caption explaining that it was merely a scholar’s artistic interpretation. It became so commonly accepted that even U.S. President Richard Nixon was shown a seismograph model based on Wang’s during his historic visit to China in 1972. However, the 1951 model’s fame and ubiquity have worried seismologists, who aren’t convinced that the design holds scientific weight. Most notably, it failed to detect tremors that could have predicted a devastating earthquake in 1976 that killed hundreds of thousands of civilians and rescue workers."

Reports Sixth Tone.

Here's the Wikipedia article on Zhang Heng (b. 78 AD, d. 139 AD), with a long section on his seismograph:

During the Han Dynasty, many learned scholars—including Zhang Heng—believed in the "oracles of the winds". These oracles of the occult observed the direction, force, and timing of the winds, to speculate about the operation of the cosmos and to predict events on Earth.... Zhang Heng [wrote]:

The chief cause of earthquake is air, an element naturally swift and shifting from place to place. As long as it is not stirred, but lurks in a vacant space, it reposes innocently, giving no trouble to objects around it. But any cause coming upon it from without rouses it, or compresses it, and drives it into a narrow space ... and when opportunity of escape is cut off, then 'With deep murmur of the Mountain it roars around the barriers', which after long battering it dislodges and tosses on high, growing more fierce the stronger the obstacle with which it has contended.

In 132, Zhang Heng presented to the Han court what many historians consider to be his most impressive invention, the first seismoscope.... It was named "earthquake weathervane" (houfeng didongyi 候風地動儀)...  To indicate the direction of a distant earthquake, Zhang's device dropped a bronze ball from one of eight tubed projections shaped as dragon heads; the ball fell into the mouth of a corresponding metal object shaped as a toad, each representing a direction like the points on a compass rose. His device had eight mobile arms (for all eight directions) connected with cranks having catch mechanisms at the periphery....