A survey of the latest in sleep science (and sleep science books) by Elizabeth Kolbert in the New Yorker. This is from The Slumbering Masses, by Matthew J. Wolf-Meyer:
“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.”