The historian A. Roger Ekirch has written about the history of sleep in two important books. Among his many intriguing discoveries is this one: In medieval times people went to bed at dusk, woke for a meal around midnight, and then slept again until dawn—a ritual almost certainly lost with the advent of electricity. The when, where, and way people sleep, and what happens to them while they do, remains an under-explored avenue of historical inquiry. And what about sleep as it appears in art? In pursuit of answers, the neuroscientist Laura Bossi and the museum director Sylvie Carlier have co-curated the exhibition “The Empire of Sleep,” in which they present artworks from 1800 to 1920, along with relevant works from antiquity, the Middle Ages, and more recent decades. “Sleep is an active state,” Bossi told the Financial Times. “But the Devil is an insomniac.” —Elena Clavarino