There was brightness pouring out of the sky this week onto the sidewalks and onto the trees in whatever part of San Francisco I found myself. There was no glare, no haze. What there was seemed to be pure and unobstructed light. This could not be true, of course, since all sunlight has to pass through layer upon layer of atmosphere before it hits the earth – we would not know how to recognize light that was not filtered in this way – but the illusion of absolute and unusual clarity prevailed anyway.