The seismograph, the instrument used to record the shaking of the earth caused by seismic waves, is actually much much older than you might imagine. The first recorded usage of such a device comes from second century China.
A mathematician called Chang Heng invented a device that he called an 'earthquake weathercock.' THe way it works is really clever. If you look at the picture at the top, you'll see a replica of the device.
Each dragon had a small bronze ball in its mouth. Whenever there was a tremor, the mouth of the dragon would open and drop the ball into the mouth of one of the frogs below. They were even able to tell where the tremor came from by seeing which dragon had dropped the ball.
Only a few years later, in 136 AD an updated version of the device was created. Instead of balls, it used liquids that measured how large the tremor was based on how much liquid was displaced.
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