《后汉书·张衡传》详细记载了张衡的这一发明:“阳嘉元年,复造候风地动仪,以精铜铸成.员径八尺,合盖隆起,形似酒尊,饰以篆文山龟鸟兽之形.中有都柱,旁行八道,施关发机.外有八龙,首衔铜丸,下有蟾蜍,张口承之.其牙机巧制,皆隐在尊中,覆盖周密无际.如有地动,尊则振,龙机发,吐丸而蟾蜍衔之,振声激扬,伺者因此觉知.虽一龙发机,而七首不 ”Han Zhang Heng Chuan,“ a detailed account of Zhang Heng’s invention: ”Yang Jia first year, rehabilitation of the wind seismograph, cast with refined copper. Bare foot diameter, combined cover uplift, shaped like wine respect, decorated with Zhuanwen mountain turtle birds and animals in the shape of all the columns, the line of eight, Shigatong machine. Outside the eight dragons, the first title of copper pill, under the toad, open mouth of its teeth clever system, are hidden in respect, cover If there is a move, respect is the vibration, the dragon machine hair, spit pill and toad title, vibrating sound, so aware of the servo .Although a dragon hair machine, and seven are not