History of Seismometer

220px-EastHanSeismograph.jpg history of early Seismometer
In AD 132, zhang heng of China's invented the first seismoscope which was called Houfeng Didong Yi The description we have, from the says that it was a large bronze vessel, about 2 meters in diameter;

How to use it?

 * 1) If have earthquake that you will first know it.How Does a Seismometer Work?

how that look at
it is just looks like a buck with 9 dragons head. Had below those heads. There is 8 frogs here.