He comes into my little story here because it was he, in explaining not how planetary motion worked but how light bent through lenses, it was Kepler who coined the term focus.

我在故事中谈到开普勒，不是因为他解释了星球运行规律，而是因为他解释了光如何在透镜中发生折射。正是他首创了focus(焦点)这个词。

youdao

The jade here usually comes in a natural light green color and is semi-translucent. The best Xiu jade pieces are clear and watery in appearance without any marks.

这里的玉石通常都呈绿色的半透明状，如水滴般透明且无任何瑕疵的则是最好的岫玉。

youdao

So, now we can talk about it in different terms, Ei for example, talking about e sub i, which is the incident energy or the energy of the light that comes in, or talking about work function here, and that's just another way to say threshold energy.

现在我们可以从不同的方面,来谈论它了，举例来说，它是入射能量或者进来的光的能量,或者谈论这里的功函数，它是另一种描述临界能量的方式。

麻省理工公开课 - 化学原理课程节选