Not exactly Caltech high-tech, but it does the job: When the earth shakes, a bar delicately balanced inside topples in the direction of the movement, causing one of eight bronze dragons to open its mouth and expel a bronze ball. The ball falls into the mouth of one of eight bronze toads in a circle around the base.
The resulting clang is the earthquake alert.
The original was in Shinxi province during the Qin Dynasty. If a strong enough temblor hit Peking, about 500 miles away, the device could detect it.
"They wouldn't know the magnitude, but they'd know approximately where (the quake) was centered," David Tsai, our guide to "The Chinese Science and Arts Expo: A 7,000 Year Odyssey," explains. Pre-seismograph, a horseman would have had to ride for days to deliver the news.
Tsai is CEO of the Downtown Asian Pacific Mart, which is presenting the expo through Jan. 31 in cooperation with Beijing's National Science And Technology Museum.
The first stop for expo visitors is a 10th-Century bronze basin. Rub the handles just so and the water ripples and splashes. A little amusement for the emperors, who'd watch as their female servants made the water dance.
Next stop: An ingenious contraption that assured the emperor's carriage wouldn't emerge topless from under a bridge. Approaching the bridge, the driver would pull in his reins, raising the head of one of the horse team. A pompon atop the horse's head was exactly the height of the carriage roof.
The best-known Chinese inventions--the firecracker, paper, the compass and the first printing device (wood blocks)--are also all here.
There's nothing musty and dusty about this exhibit. Artists and artisans are sculpting dough, making paper, at work on a two-story loom. Missing, unfortunately, are a Chinese knotter, an acupuncturist and a 13-year-old boy who is abacus master of China. All were denied exit visas.
But there's an abacus display, where Tsai engages his father, Tsai Ten Tsai, a Taiwan engineer, in a contest between abacus and calculator. Each multiplies 25 by 25. The abacus wins.
"The abacus always wins," David Tsai says, "and abacuses don't need batteries."