Senders specified each capsule’s destination by manipulating brass rings at its base electro-mechanical widgets in the tubes read those settings and routed each capsule toward its destination. Messages, sealed in fibreglass containers, rocketed at thirty feet a second among approximately a hundred and fifty stations spread over eight floors. The tubes were installed in the early nineteen-sixties, as part of an elaborate, vacuum-powered intra-office mail system. The walls of the Central Intelligence Agency’s original headquarters, in Langley, Virginia, contain more than thirty miles of four-inch steel tubing.
