3. The Coin-Operated Dispenser: Ancient Self-Service
Insert money. Receive a measured quantity of something. That familiar transaction did not have to wait for railway platforms, soda cans, or electricity.
Among the devices described by Hero of Alexandria was a coin-operated dispenser for water used in religious rituals. A coin landed on a small pan attached to a lever. Its weight opened a valve, allowing water to flow. When the coin slipped off, the mechanism returned and the flow stopped.
The cleverness lay in making the payment itself do the mechanical work. There was no electronic sensor deciding whether a customer had paid, just gravity, balance, and a valve. Reconstructions help explain the mechanism, although they are not surviving ancient machines. Next time a modern dispenser refuses to cooperate, consider how long people have been trying to automate this very simple bargain.
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