Before the internet, pneumatic tubes moved messages across cities using nothing but air pressure.
In short: Long before digital email, cities relied on vast underground networks of pressurized pipes to transmit telegrams and mail. By 1886, London operated 34 miles of these tubes, moving thousands of messages daily at high speeds. Today, this same clever physics keeps hospitals and banks running behind the scenes.
The fundamental principle behind pneumatic transport is the manipulation of air pressure to create motion. The concept dates back to Hero of Alexandria, a Ptolemaic Greek mathematician who explored using pressurized gas for mechanical work. However, the first practical, large-scale implementation emerged in London during the 1850s. By 1886, the city had developed a sophisticated network spanning 34 miles, capable of transmitting 32,000 messages daily at speeds reaching 51 miles per hour. Similar infrastructure was adopted by major cities including New York, Boston, Paris, Berlin, and Vienna by the turn of the century.
A pneumatic system functions through an airtight tube equipped with sealable hatches. To send an item, it is placed inside a canister featuring flexible skirts that conform to the tube's interior. When activated, a motor at the destination end turns a fan, which vents air out of the tube. This process creates a pressure differential: the air density behind the canister is higher than the air in front, effectively pushing the canister toward its destination. Once the canister reaches the end, a trap door closes and the motor stops, equalizing the pressure.
This mechanism is analogous to drinking through a straw, where suction creates a low-pressure zone that allows higher-pressure liquid to be pushed upward. While simple systems use a single tube, complex modern networks incorporate branching paths, switches, and multiple fans. Today, these systems are primarily used for transporting medical samples in hospitals, moving materials within manufacturing plants, and handling bank transactions. Although the rise of the automobile and the impact of the world wars led to the decline of city-wide mail networks by the 1950s, computer-regulated air pressure continues to provide a reliable, safe method for moving sensitive items.
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Sources
- Summary by Intellect · source: How Do Pneumatic Tubes Work?
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