“The impulse to stash things away,” Nick Yablon writes in Remembrance of Things Present: The Invention of the Time Capsule, “is ancient, perhaps universal.” This accounts for the cornerstone ceremonies of early republican America, or the ancient Greek and Roman practice of placing coins in sacred places, or maybe even letters, “sealed for at least a day.” But a time capsule has a specific destination in time, an opening day. For Yablon, a historian at the University of Iowa, time capsules were invented in the United States around 1876. Two were on display at the Centennial Exposition in