Chang Heng's invention consisted of a large hollow ball standing on its base which was set on level ground. A heavy weight was suspended inside the shell. Around the large ball, at equal distances, were eight open-mouthed bronze dragon heads, and on the tongue of each was a small copper ball. A bronze open-mouthed toad stood beneath each dragon head. The whole instrument was so arranged that, at the slightest jarring by an earthquake wave, the suspending weight would cause one of the balls to shoot out of the dragon's mouth into the toad's mouth. Which ball shot out depended on the nearest path of the wave" (Marcus 57).
In today's modern world, technology would make Chang Heng's seismometer look crude and untrust worthy. Today's modern seismometer looks similar but more complicated because it involves photographic paper, a beam of light, a mirror, and many other things.
In 1935, Charles Richter created a scale that measured earthquakes. In February 1977, Richter's scale was slightly revised because of the fact that there are now more sophisticated ways of measurement and the scale didn't cover the higher magnitude rating.
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