Giotto, Sleeping Guards, detail from a fresco in the Cappella degli Scrovegni (1304-1306)

My friend Will sent me this fascinating article, which suggests that eight hours of sleep for most adults is not necessarily the ideal. As any parent of a small baby will tell you, we seem to be naturally inclined to sleep in four-hour chunks.

According to the article, a psychiatrist conducted an experiment where a group of people were plunged into darkness for 14 hours a day for a month. They eventually settled into a pattern of four hours of sleep, one or two hours of wakefulness, and then a second four-hour sleep.

It seems that for centuries, people used to sleep this way, and a historian found hundreds of references to this “first sleep” and “second sleep” pattern. The period between first and second sleep was a time to pray, walk around, or socialize with the throngs of people who might be sharing your bed.

By the seventeenth century, the pattern began to change, in part because cities began to use street lighting, and because coffee houses became popular  (I’ll blog about those soon—they’re fascinating).