Thursday 1 December 2011

Earthquakes and toads...

It’s been a few months since I last posted – been busy doing talks on the Grand Canal of China and polishing off the manuscript to Chusan: the forgotten story of Britannia’s first Chinese island. Still, no excuse, but when I was lying in bed listening to the Today Programme on Radio 4 this morning and heard an item about some scientific research about toads and earthquakes it rang a bell in the Ancient China gland of my brain (a little to the left/east of my cingulate cortex, if you’re interested).
Zhang Heng's seismometer from 132AD - put that in your pipe and smoke it, The West!
Apparently researchers have found evidence of a mechanism to explain the phenomenon whereby toads flee their watery homes before an earthquake: charged particles created by rocks under tension are concentrated in surface water near the epicentre (or something), and the toads clearly find the extra charge unpleasant. I imagine it’s rather like the icky feeling you get when you lick the terminals of a PP3 battery, but over your entire body.

To get to the point, the Ancient Chinese, as with most things (electric toothbrushes and fragrance-changing air-fresheners aside) had noticed the link between toads and earthquakes and had used it in their scientific endeavours while we were still living in trees (or under the Romans to be precise).

In 132AD, so the biographies of the Book of the Eastern Han Dynasty record, the astronomer Zhang Heng invented a seismometer which could tell when an earthquake had occurred, and in which direction from the capital. It worked by means of a vertical rod which was displaced by the transverse waves from the quake, and which triggered a ball to be dislodged from one of eight dragons’ mouths. The ball then fell noisily into a receptacle below, the interesting bit being that the receptacle was of bronze cast in the shape of a toad. “When the mechanism was set off, a ball was spat out, and a toad caught it in its mouth” (机发吐丸而蟾蜍衔之 in the original classical Chinese if you’re interested). I can’t see this choice of animal being a coincidence – the Chinese were eminent nature-watchers and must have observed the flight of toads before earthquakes. Hurrah for Zhang Heng.

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