Glass, he reflects, sweeping, is one of those substances that takes up relatively little space until you break it. But it is also, he recalls being told, if considered over truly cosmic stretches of time, a liquid. All the glass in every pane in every window, everywhere, is in the infinitely slow process of melting, sagging, sliding down, except it would be unlikely that any one pane survive the millennia required to be reduced to a solid puddle.
