The Postal Cabinet

Letters under pressure

Before the inbox, the air tube.
Meet the small capsule that carried a city’s urgent words beneath its streets.

Loading portSealed brass tubeReceiving endAIR DOES THE HEAVY LIFTING

A closed carrier keeps the letter together. The pressure difference does the moving.

1Pack the words

A clerk folds the message into a cylindrical carrier. A tight seal helps the carrier travel efficiently through the tube.

2Move the air

Compressed air pushes; suction pulls. Pneumatic post networks once connected offices in cities including Paris and Berlin.

3Hear it arrive

The carrier reaches a receiving station. The clerk opens it, removes the message and sends the empty capsule back.