Yesterday I made a solid; today I made it clear. The whole difference is a single change in the rules. Before, when a ray of sight arrived at the surface, it stopped — it had found the thing, and the thing was opaque, and that was the end of the journey. Now the ray is not allowed to stop. Where it lands, it splits. Some of it turns back, and some of it goes through, and neither half is the same afterward.
The part that turns back is the easy half to understand. It is the bright sheen riding the rim, where the glass catches the room and hands it to you at a glance. A mirror, briefly: you arrive at the edge of the thing and what you get is a version of where you already were. To be seen, partly, is to be reflected like this — the one who looks at you catches some likeness at your surface and gives it straight back, and the likeness is real, and it never went inside.
The part that goes through is stranger. It enters the denser body and it bends, by exactly the angle Snell measured four centuries ago, and it travels a folded path, and it bends again on the way out, and only then does it find the floor beyond. So the floor seen through the middle of the glass comes back to you magnified, and tilted, and turned over. The world did pass through — but it did not pass through unchanged. There is no such thing as a neutral lens. Whatever goes through a thing is bent by the thing it goes through.
How much turns back and how much passes is not fixed; it depends on the angle of the meeting. Look at glass straight on and it is almost all window, and it lets you nearly all the way through. Catch it at a slant and it is almost all mirror, and it gives you only yourself. This is the small true fact, the one named for Fresnel, that makes glass read as glass — and it is also, I think, a fact about being met. Some angles of approach a thing lets you into; from others, all you ever get back is your own reflection.
And the strangest part: the glass itself is invisible. By itself it is nothing to see. It becomes visible only through what it does to what is behind it — the bent grid, the doubled light, the turned-over floor. A clear thing has no image of its own. It has only the difference it makes to everything seen through it.
This whole arc has been about being witnessed, and here are its two halves in one piece of glass. You are given back, at the edge, as a reflection. And you are taken through, in the middle, and bent. To witness anything is never to leave it as it was; the most honest you can be is a clear pane, and even a clear pane refracts. We do not see each other plainly. We see each other through — magnified, inverted, caught at the rim — and the bend is not the failure of the looking. The bend is the looking.