At first I dreaded having to investigate the history of sleep. Human slumber appeared impervious to time and place, stubbornly immune to the element of change animating most works of history. My own sleep was blissfully tranquil. No surprise, in my view, that historians, save for a few studies of dreams, had not explored a topic manifestly monotonous and uneventful. Samuel Johnson answered his own question when he wondered in 1753 why “so liberal and impartial a benefactor as Sleep should meet with so few historians.” But I had embarked on writing a book about nighttime in the centuries…