The Chinese seismograph was an instrument developed in 132 A.D. by the Chinese philosopher Chang Hêng to detect earthquakes and determine the direction from which they came. It was a brass instrument decorated with eight dragons, each holding a copper ball. On the base were eight frogs, each with their mouth open, to catch the ball when it drops.
Scientists have attempted to replicate the Chinese seismograph but don't know what was inside of Hêng's brass container. They have tried several approaches but have been unsuccessful in recreating a device that is accurate in predicting the direction of the disturbance, for which the device became famous. While records show the Chinese used the instrument for four centuries after its invention, there is no physical evidence that it ever existed. Some Chinese writers question if the machine was possible.
Historians have no record of Europeans working to develop seismographs until 1703. J. de la Haute Feuille proposed using a bowl of mercury with containers to collect spills surrounding it to determine direction. Later Europeans used a swinging pendulum attached to a pencil to record seismic activity. They connected some of these devices to a clock to move the paper and record the waves. Modern seismographs use electromagnetic sensors. The waves recorded by these sensors display on electronic screens or paper graphs.