“There is not much talk about the clouds that are visible up here. No one seems to think it remarkable that somewhere above an ocean we are flying past a vast white candy-floss island that would have made a perfect seat for an angel or even God himself in a painting by Piero della Francesca. In the cabin, no one stands up to announce with requisite emphasis that if we look out the window, we will see that we are flying over a cloud, a matter that would have detained Leonardo and Poussin, Claude and Constable.”