Wolf-Meyer refers to the practice of going to bed at around eleven o’clock at night and staying there until about seven in the morning as sleeping “in a consolidated fashion.” Nowadays, adults are expected to sleep in this manner; anything else—sleeping during the day, sleeping in bursts, waking up in the middle of the night—is taken to be unsound, even deviant.

This didn’t use to be the case. Until a century and a half or so ago, Wolf-Meyer observes, “Americans, like other people around the world, used to sleep in an unconsolidated fashion, that is, in two or more periods throughout the day.” They went to bed not long after the sun went down. Four or five hours later, they woke from their “first sleep” and rattled around—praying, chatting, smoking, or making love. (Benjamin Franklin reportedly liked to spend this time reading naked in a chair.) Eventually, they went back to bed for their “second sleep.”