这是一个很简单的问题，通过观察重量是多少以及它下降了多远，来确定桨轮做了多少功。
It's a trivial matter, by looking at what is the weight and how far does it drop, to say OK, how much work is done by the paddlewheel.
只要我能够旋转照片，我就可以好好观察它然后做出一个合理的结论。
If only I could spin the photo around, then I could get a good look at it and make a sound judgement.
如果我们在一月份观察一颗恒星——那时地球在其轨道上的一个点——它的位置似乎会与六个月后它出现的位置不同。
If we look at a star in January—when Earth is at one point in its orbit—it will seem to be in a different position from where it appears six months later.
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