<P> In AD 132 , Zhang Heng of China 's Han dynasty invented the first seismoscope ( by the definition above ) , which was called Houfeng Didong Yi ( translated as , `` instrument for measuring the seasonal winds and the movements of the Earth '' ) . The description we have , from the History of the Later Han Dynasty , says that it was a large bronze vessel , about 2 meters in diameter ; at eight points around the top were dragon 's heads holding bronze balls . When there was an earthquake , one of the mouths would open and drop its ball into a bronze toad at the base , making a sound and supposedly showing the direction of the earthquake . On at least one occasion , probably at the time of a large earthquake in Gansu in AD 143 , the seismoscope indicated an earthquake even though one was not felt . The available text says that inside the vessel was a central column that could move along eight tracks ; this is thought to refer to a pendulum , though it is not known exactly how this was linked to a mechanism that would open only one dragon 's mouth . The first earthquake recorded by this seismoscope was supposedly `` somewhere in the east . '' Days later , a rider from the east reported this earthquake . </P>
who developed the first procedure used to measure the local size of an earthquake
Zhang Heng of China 's Han dynasty