Where does the seismograph come from?

The American scientist John Winthrop (1714-1779) was one of the first to make scientific studies of earthquakes and is known as the founder of seismology. However, we cannot say that he was the inventor of the seismograph, as it is quite likely that various versions of this “machine” had already been constructed by his time. We do know that Zhang Heng invented an earthquake detector in China around A.D. 132. It consisted of a copper-domed urn with dragons’ heads — each containing a bronze ball — around the outside. Inside the dome was a pendulum that would swing when the earth shook and knock a ball from the mouth of a dragon into the mouth of a bronze toad waiting below. The ball made a loud noise and signaled the occurrence of an earthquake.