It's two fans, one which he could turn from outside after he got the vacuum established, and he discovered that if he pulled all the air out of it, the one fan would no longer turn the other one, right?
两个风扇，其中一个风扇，在他抽出真空之后， 他可以在真空器外面启动， 这样他发现如果他把所有的空气都抽出来， 一个风扇就不能带动另一个了。对吧？