Early in the century, a pump had come into use in which expanding steam raised a piston in a cylinder, and atmospheric pressure brought it down again when the steam condensed inside the cylinder to form a vacuum.
Early in the century,( 时间状语 ,翻译这个世纪早期) a pump had come into use 泵早被使用了 ( 是主句)in which expanding steam raised a piston in a cylinder,膨胀的气体在汽缸中上升一个活塞 and atmospheric pressure brought it down again 而且大气压又使其下降 when the steam condensed inside the cylinder to form a vacuum.当气体在气缸内压缩形成真空的时候。 ( 时间状语从句) (in which ... 定语从句,修饰pump) 本世纪世纪初期, 泵已投入使用,当气体在气缸内压缩形成真空的时候, 泵里膨胀的气体在汽缸中会上升一个活塞而且大气压又会使其下降。