Today Yael and Don discuss mirrors.   Y: Mirror mirror on the wall, who's the fairest of them--D: Watcha doing?

Y: I was, um, calibrating the surface smoothness of this mirror.

D: I see.

Y: Did you know that in order for a mirror to work properly it has to be perfectly   smooth?

D: Why's that?

Y: Well, a mirror is basically something that reflects light, right?

D: Right.

Y: When light hits something, some of the light is reflected, some absorbed, and some  passes through.

D: So for a mirror to produce a clear image it has to reflect as much of the light as possible, and in order to do that it has to be smooth.

Y: Exactly. A warped mirror scatters and diffuses light, making the image it produces look deformed. But a smooth mirror reflects without distortion.

D: Which is what makes it possible for you to stand in front of the mirror and preen.

Y: I was not preening!

D: Right. But there's nothing wrong with preening, you know. People have been  admiring themselves in mirrors for a long time. Take the Greeks and Romans. They   loved looking atthemselves, although they only had highly polished pieces of bronze,  tin, and silver. Their descendants were even more vain, so in 16th century Venice  mirror makers discovered thetechnique of backing a piece of glass with a reflecting metal composed of tin and mercury, producing a much clearer reflection. That  technique is still in practice today, although now weuse a thin layer of molten  aluminum or silver sprayed onto the back of a piece of glass in a vacuum to achieve  premium smoothness.

Y: Thanks for the history lesson.

D: You're welcome. And by the way . . .

Y: Yes?

D: You are the fairest of them all.

Y: Oh Don.