Those are the familiar and empirical objects that we can see, pieces of paper, bodies, pieces of chalk, bars of metal.

那就是我们能看见的,熟悉的已知的物体，纸，身体，粉笔，金属棒。

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Lastly, up here, is a picture of a much smaller device, this is actually an artificial heart valve that is made of plastics and metal and can replace the valve inside your heart.

最后,在上面这里,这张图片是一个相对较小的装置,这实际上是一个人工心脏瓣膜,由塑料和金属制成,可以取代人的心脏瓣膜

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that's one way to think about it, and there's also another way, and this is the way that your book presents it. If you, in fact, have two of the same atom right next to each other, let's say you have a crystal, or let's say you're talking about a metal, what you can do is just look at the distance between the two nuclei, and split that in 1/2, and take the atomic radius that way.

这只是一种定义的思路，另外还有其它方法，也就是你们课本上的方法，如果你，事实上，有两个相同的原子彼此靠在一起，比如说你有一个晶体，或者说你讨论的是一个金属，你所要做的就是,看看这两个原子核之间的距离，然后将距离除以二，就得到了这个原子的半径。

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